Capivasertib in combination with enzalutamide for metastatic castration resistant prostate cancer after docetaxel and abiraterone: Results from the randomized phase II RE-AKT trial

BACKGROUND

PTEN loss and aberrations in PI3K/AKT signaling kinases associate with poorer response to abiraterone acetate (AA) in metastatic castration-resistant prostate cancer (mCRPC). In this study, we assessed antitumor activity of the AKT inhibitor capivasertib combined with enzalutamide in mCRPC with prior progression on AA and docetaxel.

METHODS

This double-blind, placebo-controlled, randomized phase 2 trial, recruited men ≥ 18 years with progressing mCRPC and performance status 0-2 from 15 UK centers. Randomized participants (1:1) received enzalutamide (160 mg orally, once daily) with capivasertib (400 mg)/ placebo orally, twice daily on an intermittent (4 days on, 3 days off) schedule. Primary endpoint was composite response rate (RR): RECIST 1.1 objective response, ≥ 50 % PSA decrease from baseline, or circulating tumor cell count conversion (from ≥ 5 at baseline to < 5 cells/7.5 mL). Subgroup analyses by PTENIHC status were pre-planned.

RESULTS

Overall, 100 participants were randomized (50:50); 95 were evaluable for primary endpoint (47:48); median follow-up was 43 months. RR were 9/47 (19.1 %) enzalutamide/capivasertib and 9/48 (18.8 %) enzalutamide/placebo (absolute difference 0.4 % 90 %CI -12.8 to 13.6, p = 0.58), with similar results in the PTENIHC loss subgroup. Irrespective of treatment, OS was significantly worse for PTENIHC loss (10.1 months [95 %CI: 4.6-13.9] vs 14.8 months [95 %CI: 10.8-18]; p = 0.02). Most common treatment-emergent grade ≥ 3 adverse events for the combination were diarrhea (13 % vs 2 %) and fatigue (10 % vs 6 %).

CONCLUSIONS

Combined capivasertib/enzalutamide was well tolerated but didn't significantly improve outcomes from abiraterone pre-treated mCRPC.

CB307: A Dual Targeting Costimulatory Humabody VH Therapeutic for Treating PSMA-Positive Tumors

PURPOSE

CD137 is a T- and NK-cell costimulatory receptor involved in consolidating immunologic responses. The potent CD137 agonist urelumab has shown clinical promise as a cancer immunotherapeutic but development has been hampered by on-target off-tumor toxicities. A CD137 agonist targeted to the prostate-specific membrane antigen (PSMA), frequently and highly expressed on castration-resistant metastatic prostate cancer (mCRPC) tumor cells, could bring effective immunotherapy to this immunologically challenging to address disease.

EXPERIMENTAL DESIGN

We designed and manufactured CB307, a novel half-life extended bispecific costimulatory Humabody VH therapeutic to elicit CD137 agonism exclusively in a PSMA-high tumor microenvironment (TME). The functional activity of CB307 was assessed in cell-based assays and in syngeneic mouse antitumor pharmacology studies. Nonclinical toxicology and toxicokinetic properties of CB307 were assessed in a good laboratory practice (GLP) compliant study in cynomolgus macaques.

RESULTS

CB307 provides effective CD137 agonism in a PSMA-dependent manner, with antitumor activity both in vitro and in vivo, and additional activity when combined with checkpoint inhibitors. A validated novel PSMA/CD137 IHC assay demonstrated a higher prevalence of CD137-positive cells in the PSMA-expressing human mCRPC TME with respect to primary lesions. CB307 did not show substantial toxicity in nonhuman primates and exhibited a plasma half-life supporting weekly clinical administration.

CONCLUSIONS

CB307 is a first-in-class immunotherapeutic that triggers potent PSMA-dependent T-cell activation, thereby alleviating toxicologic concerns against unrestricted CD137 agonism.

Thio-2 inhibits key signaling pathways required for the development and progression of castration resistant prostate cancer

Therapies that abrogate persistent androgen receptor (AR) signaling in castration resistant prostate cancer (CRPC) remain an unmet clinical need. The N-terminal domain (NTD) of the AR that drives transcriptional activity in CRPC remains a challenging therapeutic target. Herein we demonstrate that BAG-1 mRNA is highly expressed and associates with signaling pathways, including AR signaling, that are implicated in the development and progression of CRPC. In addition, interrogation of geometric and physiochemical properties of the BAG domain of BAG-1 isoforms identifies it to be a tractable but challenging drug target. Furthermore, through BAG-1 isoform mouse knockout studies we confirm that BAG-1 isoforms regulate hormone physiology and that therapies targeting the BAG domain will be associated with limited 'on-target' toxicity. Importantly, the postulated inhibitor of BAG-1 isoforms, Thio-2, suppressed AR signaling and other important pathways implicated in the development and progression of CRPC to reduce the growth of treatment resistant prostate cancer cell lines and patient derived models. However, the mechanism by which Thio-2 elicits the observed phenotype needs further elucidation since the genomic abrogation of BAG-1 isoforms was unable to recapitulate the Thio-2 mediated phenotype. Overall, these data support the interrogation of related compounds with improved drug-like properties as a novel therapeutic approach in CRPC, and further highlight the clinical potential of treatments that block persistent AR signaling which are currently undergoing clinical evaluation in CRPC.

Olaparib and Ceralasertib (AZD6738) in Patients with Triple-Negative Advanced Breast Cancer: Results from Cohort E of the plasmaMATCH Trial (CRUK/15/010)

PURPOSE

Approximately 10% to 15% of triple-negative breast cancers (TNBC) have deleterious mutations in BRCA1 and BRCA2 and may benefit from PARP inhibitor treatment. PARP inhibitors may also increase exogenous replication stress and thereby increase sensitivity to inhibitors of ataxia telangiectasia and Rad3-related (ATR) protein. This phase II study examined the activity of the combination of PARP inhibitor, olaparib, and ATR inhibitor, ceralasertib (AZD6738), in patients with advanced TNBC.

PATIENTS AND METHODS

Patients with TNBC on most recent biopsy who had received 1 or 2 lines of chemotherapy for advanced disease or had relapsed within 12 months of (neo)adjuvant chemotherapy were eligible. Treatment was olaparib 300 mg twice a day continuously and celarasertib 160 mg on days 1-7 on a 28-day cycle until disease progression. The primary endpoint was confirmed objective response rate (ORR). Tissue and plasma biomarker analyses were preplanned to identify predictors of response.

RESULTS

70 evaluable patients were enrolled. Germline BRCA1/2 mutations were present in 10 (14%) patients and 3 (4%) patients had somatic BRCA mutations. The confirmed ORR was 12/70; 17.1% (95% confidence interval, 10.4-25.5). Responses were observed in patients without germline or somatic BRCA1/2 mutations, including patients with mutations in other homologous recombination repair genes and tumors with functional homologous recombination deficiency by RAD51 foci.

CONCLUSIONS

The response rate to olaparib and ceralasertib did not meet prespecified criteria for activity in the overall evaluable population, but responses were observed in patients who would not be expected to respond to olaparib monotherapy.

Development and Validation of a New BAG-1L-Specific Antibody to Quantify BAG-1L Protein Expression in Advanced Prostate Cancer

BCL-2-associated athanogene-1L (BAG-1L) is a critical co-regulator that binds to and enhances the transactivation function of the androgen receptor, leading to prostate cancer development and progression. Studies investigating the clinical importance of BAG-1L protein expression in advanced prostate cancer have been limited by the paucity of antibodies that specifically recognize the long isoform. In this study, we developed and validated a new BAG-1L-specific antibody using multiple orthogonal methods across several cell lines with and without genomic manipulation of BAG-1L and all BAG-1 isoforms. Following this, we performed exploratory immunohistochemistry to determine BAG-1L protein expression in normal human, matched castration-sensitive prostate cancer (CSPC) and castration-resistant prostate cancer (CRPC), unmatched primary and metastatic CRPC, and early breast cancer tissues. We demonstrated higher BAG-1L protein expression in CRPC metastases than in unmatched, untreated, castration-sensitive prostatectomies from men who remained recurrence-free for 5 years. In contrast, BAG-1L protein expression did not change between matched, same patient, CSPC and CRPC biopsies, suggesting that BAG-1L protein expression may be associated with more aggressive biology and the development of castration resistance. Finally, in a cohort of patients who universally developed CRPC, there was no association between BAG-1L protein expression at diagnosis and time to CRPC or overall survival, and no association between BAG-1L protein expression at CRPC biopsy and clinical outcome from androgen receptor targeting therapies or docetaxel chemotherapy. The limitations of this study include the requirement to validate the reproducibility of the assay developed, the potential influence of pre-analytical factors, timing of CRPC biopsies, relatively small patient numbers, and heterogenous therapies on BAG-1L protein expression, and the clinical outcome analyses performed. We describe a new BAG-1L-specific antibody that the research community can further develop to elucidate the biological and clinical significance of BAG-1L protein expression in malignant and nonmalignant diseases.

Targeting myeloid chemotaxis to reverse prostate cancer therapy resistance

Inflammation is a hallmark of cancer1. In patients with cancer, peripheral blood myeloid expansion, indicated by a high neutrophil-to-lymphocyte ratio, associates with shorter survival and treatment resistance across malignancies and therapeutic modalities2-5. Whether myeloid inflammation drives progression of prostate cancer in humans remain unclear. Here we show that inhibition of myeloid chemotaxis can reduce tumour-elicited myeloid inflammation and reverse therapy resistance in a subset of patients with metastatic castration-resistant prostate cancer (CRPC). We show that a higher blood neutrophil-to-lymphocyte ratio reflects tumour myeloid infiltration and tumour expression of senescence-associated mRNA species, including those that encode myeloid-chemoattracting CXCR2 ligands. To determine whether myeloid cells fuel resistance to androgen receptor signalling inhibitors, and whether inhibiting CXCR2 to block myeloid chemotaxis reverses this, we conducted an investigator-initiated, proof-of-concept clinical trial of a CXCR2 inhibitor (AZD5069) plus enzalutamide in patients with metastatic CRPC that is resistant to androgen receptor signalling inhibitors. This combination was well tolerated without dose-limiting toxicity and it decreased circulating neutrophil levels, reduced intratumour CD11b+HLA-DRloCD15+CD14- myeloid cell infiltration and imparted durable clinical benefit with biochemical and radiological responses in a subset of patients with metastatic CRPC. This study provides clinical evidence that senescence-associated myeloid inflammation can fuel metastatic CRPC progression and resistance to androgen receptor blockade. Targeting myeloid chemotaxis merits broader evaluation in other cancers.

Unbiased differential proteomic profiling between cancer-associated fibroblasts and cancer cell lines

Cancer-associated fibroblasts (CAFs) are a key component of tumors. We aimed to profile the proteome of cancer cell lines representing three common cancer types (lung, colorectal and pancreatic) and a representative CAF cell line from each tumor type to gain insight into CAF function and novel CAF biomarkers. We used isobaric labeling, liquid chromatography and mass spectrometry to evaluate the proteome of 9 cancer and 3 CAF cell lines. Of the 9460 proteins evaluated, functional enrichment analysis revealed an upregulation of N-glycan biosynthesis and extracellular matrix proteins in CAFs. 85 proteins had 16-fold higher expression in CAFs compared to cancer cells, including previously known CAF markers like fibroblast activation protein (FAP). Novel overexpressed CAF biomarkers included heat shock protein β-6 (HSPB6/HSP20) and cyclooxygenase 1 (PTGS1/COX1). SiRNA knockdown of the genes encoding these proteins did not reduce contractility in lung CAFs, suggesting they were not crucial to this function. Immunohistochemical analysis of 30 tumor samples (10 lung, 10 colorectal and 10 pancreatic) showed restricted HSPB6 and PTGS1 expression in the stroma. Therefore, we describe an unbiased differential proteome analysis of CAFs compared to cancer cells, which revealed higher expression of HSPB6 and PTGS1 in CAFs. Data are available via ProteomeXchange (PXD040360). SIGNIFICANCE: Cancer-associated fibroblasts (CAFs) are highly abundant stromal cells present in tumors. CAFs are known to influence tumor progression and drug resistance. Characterizing the proteome of CAFs could give potential insights into new stromal drug targets and biomarkers. Mass spectrometry-based analysis comparing proteomic profiles of CAFs and cancers characterized 9460 proteins of which 85 proteins had 16-fold higher expression in CAFs compared to cancer cells. Further interrogation of this rich resource could provide insight into the function of CAFs and could reveal putative stromal targets. We describe for the first time that heat shock protein β-6 (HSPB6/HSP20) and cyclooxygenase 1 (PTGS1/COX1) are overexpressed in CAFs compared to cancer cells.

Germline ATM Mutations Detected by Somatic DNA Sequencing in Lethal Prostate Cancer

Background

Germline mutations in the ataxia telangiectasia mutated (ATM) gene occur in 0.5-1% of the overall population and are associated with tumour predisposition. The clinical and pathological features of ATM-mutated prostate cancer (PC) are poorly defined but have been associated with lethal PC.

Objective

To report on the clinical characteristics including family history and clinical outcomes of a cohort of patients with advanced metastatic castration-resistant PC (CRPC) who were found to have germline ATM mutations after mutation detection by initial tumour DNA sequencing.

Design setting and participants

We acquired germline ATM mutation data by saliva next-generation sequencing from patients with ATM mutations in PC biopsies sequenced between January 2014 and January 2022. Demographics, family history, and clinical data were collected retrospectively.

Outcome measurements and statistical analysis

Outcome endpoints were based on overall survival (OS) and time from diagnosis to CRPC. Data were analysed using R version 3.6.2 (R Foundation for Statistical Computing, Vienna, Austria).

Results and limitations

Overall, seven patients (n = 7/1217; 0.6%) had germline ATM mutations detected, with five of them having a family history of malignancies, including breast, prostate, pancreas, and gastric cancer; leukaemia; and lymphoma. Two patients had concomitant somatic mutations in tumour biopsies in genes other than ATM, while two patients were found to carry more than one ATM pathogenic mutation. Five tumours in germline ATM variant carriers had loss of ATM by immunohistochemistry. The median OS from diagnosis was 7.1 yr (range 2.9-14 yr) and the median OS from CRPC was 5.3 yr (range 2.2-7.3 yr). When comparing these data with PC patients sequenced by The Cancer Genome Atlas, we found that the spatial localisation of mutations was similar, with distribution of alterations occurring on similar positions in the ATM gene. Interestingly, these include a mutation within the FRAP-ATM-TRRAP (FAT) domain, suggesting that this represents a mutational hotspot for ATM.

Conclusions

Germline ATM mutations are rare in patients with lethal PC but occur at mutational hotspots; further research is warranted to better characterise the family histories of these men and PC clinical course.

Patient summary

In this report, we studied the clinical and pathological features of advanced prostate cancers associated with germline mutations in the ATM gene. We found that most patients had a strong family history of cancer and that this mutation might predict the course of these prostate cancers, as well as response to specific treatments.

Apolipoprotein E induces pathogenic senescent-like myeloid cells in prostate cancer

Tumor cells promote the recruitment of immunosuppressive neutrophils, a subset of myeloid cells driving immune suppression, tumor proliferation, and treatment resistance. Physiologically, neutrophils are known to have a short half-life. Here, we report the identification of a subset of neutrophils that have upregulated expression of cellular senescence markers and persist in the tumor microenvironment. Senescent-like neutrophils express the triggering receptor expressed on myeloid cells 2 (TREM2) and are more immunosuppressive and tumor-promoting than canonical immunosuppressive neutrophils. Genetic and pharmacological elimination of senescent-like neutrophils decreases tumor progression in different mouse models of prostate cancer. Mechanistically, we have found that apolipoprotein E (APOE) secreted by prostate tumor cells binds TREM2 on neutrophils, promoting their senescence. APOE and TREM2 expression increases in prostate cancers and correlates with poor prognosis. Collectively, these results reveal an alternative mechanism of tumor immune evasion and support the development of immune senolytics targeting senescent-like neutrophils for cancer therapy.

B7-H3 as a Therapeutic Target in Advanced Prostate Cancer

BACKGROUND

B7-H3 is a cell surface immunomodulatory glycoprotein overexpressed in prostate cancers (PCs). Understanding its longitudinal expression at emergence of castration resistance and association with tumour genomics are critical to the development of and patient selection for B7-H3 targeted therapies.

OBJECTIVE

To characterise B7-H3 expression in same-patient hormone-sensitive (HSPC) and castration-resistant (CRPC) PC biopsies, associating this with PC genomics, and to evaluate the antitumour activity of an anti-B7-H3 antibody-drug conjugate (ADC) in human CRPC in vitro and in vivo.

DESIGN, SETTING, AND PARTICIPANTS

We performed immunohistochemistry and next-generation sequencing on a cohort of 98 clinically annotated CRPC biopsies, including 72 patients who also had HSPC biopsies for analyses. We analysed two CRPC transcriptome and exome datasets, and PC scRNASeq datasets. PC organoids (patient-derived xenograft [PDX]-derived organoids [PDX-Os]) were derived from PDXs generated from human CRPC biopsies.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We evaluated B7-H3 mRNA expression in relation to a panel of 770 immune-related genes, compared B7-H3 protein expression between same-patient HSPC and CRPC biopsies, determined associations with PC genomic alterations, and evaluated the antitumour activity of DS-7300a, a topoisomerase-1 inhibitor payload anti-B7-H3 ADC, in human PC cell lines, organoids (PDX-Os), and xenografts (PDXs) of different histologies, B7-H3 expressions, and genomics.

RESULTS AND LIMITATIONS

B7-H3 was among the most highly expressed immunomodulatory genes in CRPCs. Most CRPCs (93%) expressed B7-H3, and in patients who developed CRPC, B7-H3 expression was frequently expressed at the time of HSPC diagnosis (97%). Conversion from B7-H3 positive to negative, or vice versa, during progression from HSPC to CRPC was uncommon. CRPC with neuroendocrine features were more likely to be B7-H3 negative (28%) than adenocarcinomas. B7-H3 is overexpressed in tumours with defective DNA repair gene (ATM and BRCA2) alterations and is associated with ERG expression, androgen receptor (AR) expression, and AR activity signature. DS7300a had antitumour activity against B7-H3 expressing human PC models including cell lines, PDX-Os, and PDXs of adenocarcinoma and neuroendocrine histology.

CONCLUSIONS

The frequent overexpression of B7-H3 in CRPC compared with normal tissue and other B7 family members implicates it as a highly relevant therapeutic target in these diseases. Mechanisms driving differences in B7-H3 expression across genomic subsets warrant investigation for understanding the role of B7-H3 in cancer growth and for the clinical development of B7-H3 targeted therapies.

PATIENT SUMMARY

B7-H3, a protein expressed on the surface of the most lethal prostate cancers, in particular those with specific mutations, can be targeted using drugs that bind B7-H3. These findings are relevant for the development of such drugs and for deciding which patients to treat with these new drugs.

Immune Biomarkers in Metastatic Castration-resistant Prostate Cancer

BACKGROUND

Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease in which molecular stratification is needed to improve clinical outcomes. The identification of predictive biomarkers can have a major impact on the care of these patients, but the availability of metastatic tissue samples for research in this setting is limited.

OBJECTIVE

To study the prevalence of immune biomarkers of potential clinical utility to immunotherapy in mCRPC and to determine their association with overall survival (OS).

DESIGN, SETTING, AND PARTICIPANTS

From 100 patients, mCRPC biopsies were assayed by whole exome sequencing, targeted next-generation sequencing, RNA sequencing, tumor mutational burden, T-cell-inflamed gene expression profile (TcellinfGEP) score (Nanostring), and immunohistochemistry for programmed cell death 1 ligand 1 (PD-L1), ataxia-telangiectasia mutated (ATM), phosphatase and tensin homolog (PTEN), SRY homology box 2 (SOX2), and the presence of neuroendocrine features.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The phi coefficient determined correlations between biomarkers of interest. OS was assessed using Kaplan-Meier curves and adjusted hazard ratios (aHRs) from Cox regression.

RESULTS AND LIMITATIONS

PD-L1 and SOX2 protein expression was detected by immunohistochemistry (combined positive score ≥1 and >5% cells, respectively) in 24 (33%) and 27 (27%) mCRPC biopsies, respectively; 23 (26%) mCRPC biopsies had high TcellinfGEP scores (>-0.318). PD-L1 protein expression and TcellinfGEP scores were positively correlated (phi 0.63 [0.45; 0.76]). PD-L1 protein expression (aHR: 1.90 [1.05; 3.45]), high TcellinfGEP score (aHR: 1.86 [1.04; 3.31]), and SOX2 expression (aHR: 2.09 [1.20; 3.64]) were associated with worse OS.

CONCLUSIONS

PD-L1, TcellinfGEP score, and SOX2 are prognostic of outcome from the mCRPC setting. If validated, predictive biomarker studies incorporating survival endpoints need to take these findings into consideration.

PATIENT SUMMARY

This study presents an analysis of immune biomarkers in biopsies from patients with metastatic prostate cancer. We describe tumor alterations that predict prognosis that can impact future studies.

SMG8/SMG9 Heterodimer Loss Modulates SMG1 Kinase to Drive ATR Inhibitor Resistance

Gastric cancer represents the third leading cause of global cancer mortality and an area of unmet clinical need. Drugs that target the DNA damage response, including ATR inhibitors (ATRi), have been proposed as novel targeted agents in gastric cancer. Here, we sought to evaluate the efficacy of ATRi in preclinical models of gastric cancer and to understand how ATRi resistance might emerge as a means to identify predictors of ATRi response. A positive selection genome-wide CRISPR-Cas9 screen identified candidate regulators of ATRi resistance in gastric cancer. Loss-of-function mutations in either SMG8 or SMG9 caused ATRi resistance by an SMG1-mediated mechanism. Although ATRi still impaired ATR/CHK1 signaling in SMG8/9-defective cells, other characteristic responses to ATRi exposure were not seen, such as changes in ATM/CHK2, γH2AX, phospho-RPA, or 53BP1 status or changes in the proportions of cells in S- or G2-M-phases of the cell cycle. Transcription/replication conflicts (TRC) elicited by ATRi exposure are a likely cause of ATRi sensitivity, and SMG8/9-defective cells exhibited a reduced level of ATRi-induced TRCs, which could contribute to ATRi resistance. These observations suggest ATRi elicits antitumor efficacy in gastric cancer but that drug resistance could emerge via alterations in the SMG8/9/1 pathway.

SIGNIFICANCE

These findings reveal how cancer cells acquire resistance to ATRi and identify pathways that could be targeted to enhance the overall effectiveness of these inhibitors.

A Phase I Trial of CT900, a Novel α-Folate Receptor-Mediated Thymidylate Synthase Inhibitor, in Patients with Solid Tumors with Expansion Cohorts in Patients with High-Grade Serous Ovarian Cancer

PURPOSE

CT900 is a novel small molecule thymidylate synthase inhibitor that binds to α-folate receptor (α-FR) and thus is selectively taken up by α-FR-overexpressing tumors.

PATIENTS AND METHODS

A 3+3 dose escalation design was used. During dose escalation, CT900 doses of 1-6 mg/m2 weekly and 2-12 mg/m2 every 2 weeks (q2Wk) intravenously were evaluated. Patients with high-grade serous ovarian cancer were enrolled in the expansion cohorts.

RESULTS

109 patients were enrolled: 42 patients in the dose escalation and 67 patients in the expansion cohorts. At the dose/schedule of 12 mg/m2/q2Wk (with and without dexamethasone, n = 40), the most common treatment-related adverse events were fatigue, nausea, diarrhea, cough, anemia, and pneumonitis, which were predominantly grade 1 and grade 2. Levels of CT900 more than 600 nmol/L needed for growth inhibition in preclinical models were achieved for >65 hours at a dose of 12 mg/m2. In the expansion cohorts, the overall response rate (ORR), was 14/64 (21.9%). Thirty-eight response-evaluable patients in the expansion cohorts receiving 12 mg/m2/q2Wk had tumor evaluable for quantification of α-FR. Patients with high or medium expression had an objective response rate of 9/25 (36%) compared with 1/13 (7.7%) in patients with negative/very low or low expression of α-FR.

CONCLUSIONS

The dose of 12 mg/m2/q2Wk was declared the recommended phase II dose/schedule. At this dose/schedule, CT900 exhibited an acceptable side effect profile with clinical benefit in patients with high/medium α-FR expression and warrants further investigation.

Assessment of Androgen Receptor Splice Variant-7 as a Biomarker of Clinical Response in Castration-Sensitive Prostate Cancer

PURPOSE

Therapies targeting the androgen receptor (AR) have improved the outcome for patients with castration-sensitive prostate cancer (CSPC). Expression of the constitutively active AR splice variant-7 (AR-V7) has shown clinical utility as a predictive biomarker of AR-targeted therapy resistance in castration-resistant prostate cancer (CRPC), but its importance in CSPC remains understudied.

EXPERIMENTAL DESIGN

We assessed different approaches to quantify AR-V7 mRNA and protein in prostate cancer cell lines, patient-derived xenograft (PDX) models, publicly available cohorts, and independent institutional clinical cohorts, to identify reliable approaches for detecting AR-V7 mRNA and protein and its association with clinical outcome.

RESULTS

In CSPC and CRPC cohorts, AR-V7 mRNA was much less abundant when detected using reads across splice boundaries than when considering isoform-specific exonic reads. The RM7 AR-V7 antibody had increased sensitivity and specificity for AR-V7 protein detection by immunohistochemistry (IHC) in CRPC cohorts but rarely identified AR-V7 protein reactivity in CSPC cohorts, when compared with the EPR15656 AR-V7 antibody. Using multiple CRPC PDX models, we demonstrated that AR-V7 expression was exquisitely sensitive to hormonal manipulation. In CSPC institutional cohorts, AR-V7 protein quantification by either assay was associated neither with time to development of castration resistance nor with overall survival, and intense neoadjuvant androgen-deprivation therapy did not lead to significant AR-V7 mRNA or staining following treatment. Neither pre- nor posttreatment AR-V7 levels were associated with volumes of residual disease after therapy.

CONCLUSIONS

This study demonstrates that further analytical validation and clinical qualification are required before AR-V7 can be considered for clinical use in CSPC as a predictive biomarker.

Prostate-Specific Membrane Antigen Expression and Response to DNA Damaging Agents in Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) targeting therapies such as Lutetium-177 (177Lu)-PSMA-617 are affecting outcomes from metastatic castration-resistant prostate cancer (mCRPC). However, a significant subset of patients have prostate cancer cells lacking PSMA expression, raising concerns about treatment resistance attributable at least in part to heterogeneous PSMA expression. We have previously demonstrated an association between high PSMA expression and DNA damage repair defects in mCRPC biopsies and therefore hypothesized that DNA damage upregulates PSMA expression.

EXPERIMENTAL DESIGN

To test this relationship between PSMA and DNA damage we conducted a screen of 147 anticancer agents (NCI/NIH FDA-approved anticancer "Oncology Set") and treated tumor cells with repeated ionizing irradiation.

RESULTS

The topoisomerase-2 inhibitors, daunorubicin and mitoxantrone, were identified from the screen to upregulate PSMA protein expression in castration-resistant LNCaP95 cells; this result was validated in vitro in LNCaP, LNCaP95, and 22Rv1 cell lines and in vivo using an mCRPC patient-derived xenograft model CP286 identified to have heterogeneous PSMA expression. As double-strand DNA break induction by topoisomerase-2 inhibitors upregulated PSMA, we next studied the impact of ionizing radiation on PSMA expression; this also upregulated PSMA protein expression in a dose-dependent fashion.

CONCLUSIONS

The results presented herein are the first, to our knowledge, to demonstrate that PSMA is upregulated in response to double-strand DNA damage by anticancer treatment. These data support the study of rational combinations that maximize the antitumor activity of PSMA-targeted therapeutic strategies by upregulating PSMA.

Abstract 3415: The neutrophil-to-lymphocyte ratio (NLR) reflects intratumor myeloid derived suppressor cell (MDSC) infiltration in metastatic castration-resistant prostate cancers (mCRPC)

Background: High neutrophil-to-lymphocyte ratio (NLR) associates with worse overall survival (OS) from prostate cancer (PC) and low response rates to abiraterone and taxane chemotherapy and may reflect systemic inflammatory changes. A direct link between high NLR and intratumoral myeloid infiltration has not been demonstrated to date. We evaluated the relationship between NLR and intratumor immune cell densities in mCRPC biopsies.

Design: mCRPC biopsies from 71 patients treated at The Institute of Cancer Research/Royal Marsden Hospital (ICR/RMH, UK) were stained by immunofluorescence for CD11b, CD15, and DAPI and by immunohistochemistry for CD3 to algorithmically quantify PMN-MDSC and T cell densities in the tumor and stromal compartments. NLR (neutrophil count divided by lymphocyte count), ALP, LDH, and albumin were obtained from blood collected contemporaneous with mCRPC biopsies. Clinical data were retrospectively collected. Negative binomial regression determined the association between leucocyte densities and log-transformed NLR. Modified Poisson regression estimated the risk ratio (RR) for the presence of PMN-MDSCs in relation to higher NLR (&gt;3). OS was analysed using Cox regression and Kaplan-Meier. RNAseq data from Stand Up 2 Cancer/Prostate Cancer Foundation (SU2C/PCF, n=159) and RMH cohorts (n=98) were analysed by Spearman’s correlation.

Results: NLR positively associated with the density of PMN-MDSCs infiltrating the tumor (p=0.0004) and stromal (p=0.0007) compartments of mCRPC biopsies as determined by Halo࣪ computational modelling. Tumors with high NLR were more likely to be infiltrated by PMN-MDSCs (RR: 1.41; 95% confidence interval [CI]: 1.04-1.92; p=0.03). NLR independently associated with worse OS from the time of mCRPC biopsy after adjusting for LDH, ALP, metastasis at the time of diagnosis, and albumin (HR: 1.71; 95% CI: 1.20-2.46). Patients with low NLR and an absence of tumor-infiltrating PMN-MDSC had longer OS than those with a high NLR, tumor-infiltrating PMN-MDSCs or a combination of both (p=0.015). Whilst there was no association between NLR or PMN-MDSC density and CD3 T cell density, RNAseq analyses of two independent CRPC cohorts showed that MDSC signatures strongly and positively associated with signatures of T cell terminal exhaustion (SU2C/PCF: rs=0.74; p&lt;1x10-6; RMH: rs=0.64; p&lt;1x10-6) providing credence for the impact of MDSCs on T effector function.

Conclusion: Peripheral blood NLR was positively correlated with prostate tumor-infiltrating PMN-MDSC density supporting the interaction between the circulating myeloid compartment and intratumoral myeloid infiltration in patients with advanced PC.

Citation Format: Christina Guo, Jan Rekowski, Mateus Crespo, Bora Gurel, Wei Yuan, Adam Sharp, Rafael Grochot, Khobe Chandran, Semini Sumanasuriya, Ana Ferreira, Andrea Alimonti, Johann S. de Bono. The neutrophil-to-lymphocyte ratio (NLR) reflects intratumor myeloid derived suppressor cell (MDSC) infiltration in metastatic castration-resistant prostate cancers (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3415.

Abstract 2807: HER3 is an actionable target in advanced prostate cancer

Background: ERBB signaling is implicated in castration resistant prostate cancer (CRPC), but so far clinical trials of ERBB targeting drugs failed to demonstrate antitumor activity. We elected to re-investigate ERBB receptors in endocrine treatment-resistant lethal PC, hypothesizing that targeting ERBB receptors merits further evaluation in metastatic CRPC (mCRPC).

Design: We analyzed matching, same-patient, formalin-fixed paraffin-embedded (FFPE) treatment-naïve, castration-sensitive PC (CSPC) samples (n=88), and mCRPC biopsies (n=51), from patients treated at The Royal Marsden Hospital, UK. Samples were stained for HER2 and HER3 protein, by immunohistochemistry (IHC), data was generated through digital image analysis and results were analyzed against clinical characteristics and outcome data. Moreover, we treated HER3 high (CP50) and low (CP142) expressing patient derived xenograft (PDX) models with anti-HER3 antibody-drug conjugate (HER3-ADC) U3-1402 (10mg/Kg), IgG-ADC (MAAA-9289, 10mg/Kg), anti-HER3 antibody Patritumab (U3-1287, 10mg/Kg) and 10mM acetate buffer-5% sorbitol-pH 5.5 as vehicle control, in vitro and in vivo. In vitro cell growth inhibitory activity was monitored for 7-days with endpoint assay luminescence. In vivo efficacy was evaluated comparing tumor volumes, measured every 2-3 days. Statistical significance was analyzed using ANOVA with Dunnett’s multiple comparisons correction test.

Results: Membranous HER2 (mHER2) and HER3 (mHER3) proteins were detectable in both CSPC and mCRPC biopsies, with HER3 being highly expressed in many tumors. The median optical density (OD) for mHER3 expression at diagnosis was 2958.0; PC with high mHER3 expression (&gt; median OD; n=44) had a significantly shorter median time to CRPC (20.3 vs 14.2 months; p=0.016) and worse overall survival (OS) (79.0 vs 48.8 months; p=0.04) compared to CSPC with low mHER3 (≤ median; n=44). mHER2 staining did not associate with outcome. U3-1402 demonstrated in vivo potent and sustained antitumor activity in CP50, without inducing any body weight loss or apparent toxicity. Additionally, no tumor regrowth was observed up to 60-days following the end of dosing. This anti-HER3-ADC had minimal antitumor activity in CP142, highlighting the relevance of high HER3 expression as a functional therapeutic target.

Conclusion: HER3 is commonly expressed in advanced PC and has clinical relevance in this setting. Our data indicate that HER3 is a valid target for clinical trials for men suffering from high HER3 expressing advanced PC.

Citation Format: Susana Miranda, Veronica Gil, Ruth Riisnaes, Bora Gurel, Mariantonietta D’Ambrosio, Alessandro Vasciaveo, Mateus Crespo, Ana Ferreira, Daniela Brina, Martina Troiani, Adam Sharp, Beshara Sheehan, Rossitza Christova, George Seed, Ines Figueiredo, Maryou Lambros, David Dolling, Jan Rekowski, Abdullah Alajati, Matthew Clarke, Rita Pereira, Penny Flohr, Gemma Fowler, Gunther Boysen, Semini Sumanasuriya, Diletta Bianchini, Pasquale Rescigno, Caterina Aversa, Nina Tunariu, Christina Guo, Alec Paschalis, Claudia Bertan, Lorenzo Buroni, Jian Ning, Suzanne Carreira, Paul Workman, Amanda Swain, Andrea Califano, Michael M. Shen, Andrea Alimonti, Antje Neeb, SU2C/PCF International Prostate Cancer Dream Team, Jonathan Welti, Wei Yuan, Johann de Bono. HER3 is an actionable target in advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2807.

Abstract 2898: HPN424, a Tri-specific T-cell Activating Construct, induces T cell-mediated cytotoxicity against human metastatic castration-resistant prostate cancers (mCRPC)

Background: Advanced prostate cancers (PC) are largely insensitive to existing immunotherapies. T-cell-engaging antibodies, linking tumor cells to T cells, are being developed to treat malignancies. HPN424 is a Tri-specific T-cell Activating Construct (TriTAC), binding PSMA, CD3ε, and albumin to improve drug half-life. We evaluated the activity of HPN424 to induce T-cell-mediated cytotoxicity against organoids generated from patient-derived xenograft (PDX-Os) established from human mCRPC biopsies.

Design: PDX-Os from three models were evaluated; their membranous PSMA immunohistochemical expression was quantified using H-scores (HS). PDX-Os were co-cultured with: i) healthy donor allogeneic T cells, ii) healthy donor allogeneic T cells combined with HPN424 (1pM, 10pM or 100pM), or iii) healthy donor allogeneic T cells combined with PL711, a non-targeting TriTAC control (1pM, 10pM, 100 pM). Cytotoxicity was determined by LDH release and visualisation of T cell/PDO co-localisation and PDO disruption using confocal microscopy. Early and mid-late T cell activation was determined by FACS for CD69 and CD25 expression, respectively. Cytolytic (CTL) and CD4 T cell cytokine release (IFNγ, TNF∝, IL-1β/2/4/6/8/10) was evaluated using the AlphaLISA kit (MSD). FACS studies were performed after 48- and 72-hours, while microscopy, LDH and cytokine assays were performed after 24, 48, and 72-hours, of co-culture respectively.

Results: In the highest PSMA-expressing PDX-Os (CP50c, HS: 225; CP142c, HS: 165), co-culture of resting healthy donor T cells with CRPC PDX-Os led to dose-dependent increases in LDH release at 48-hours (p&lt;0.0001) and 72-hours (p&lt;0.0001), in the presence of HPN424 but not PL711. Correspondingly, in these models, confocal microscopy showed T cells co-localising with and disrupting the PDX-Os by 24-hours across all 3 HPN424 concentrations tested. HPN424 induced T-cell expression of CD25 and CD69 within 48-hours of co-culture across all 3 concentrations in both models. When compared with PL711, HPN424 induced dose-dependent upregulation of IFNγ, IL-1β, IL-2, IL-4, IL-10, and TNF∝ in the PSMA-high PDX-Os, CP50c and CP142c (all p&lt;0.0001), indicating T cell activation and induction of CTL and Th1/Th2/Treg cytokines by HPN424. Interestingly, in co-cultures of T cells and CP89c PDX-Os, which have lower PSMA expression (HS of 25), HPN424 did not significantly increase LDH release when compared with PL711; in this model CD25/CD69 induction and the upregulation of IFNγ, IL-1β/2, and TNF∝ was only observed at the highest concentration of HPN424 (100pM).

Conclusions: HPN424, a PSMA-targeting TriTAC antibody construct, induced T cell activation and elicited T-cell mediated cytotoxicity against PSMA expressing mCRPC PDX-Os. Our data support further evaluation of this agent in advanced PC with membranous PSMA expression.

Citation Format: Veronica Gil, Christina Guo, George Seed, Antje Neeb, Lorenzo Buroni, Bora Gurel, Ines Figueiredo, Golzar Hemmati, Wade Aaron, Johann S. de Bono. HPN424, a Tri-specific T-cell Activating Construct, induces T cell-mediated cytotoxicity against human metastatic castration-resistant prostate cancers (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2898.

Results from plasmaMATCH trial cohort E: A phase II trial of olaparib and ceralasertib in patients with triple-negative advanced breast cancer (CRUK/15/010)

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Background: The plasmaMATCH trial was an open label platform trial, consisting of circulating tumour DNA (ctDNA) testing in ̃1000 patients with advanced breast cancer (ABC) linked to parallel treatment cohorts with therapies matched to mutations identified in ctDNA. Cohorts A-D have already reported (Turner N et al, Lancet Oncol 2020). Cohort E recruited patients with triple negative breast cancer (TNBC) without a targetable mutation identified at ctDNA screening, treating with olaparib (PARP inhibitor) plus ceralasertib (ATR inhibitor). Methods: Patients with TNBC who had received 1 or 2 lines of chemotherapy for advanced disease or relapsed within 12 months of (neo)adjuvant chemotherapy were eligible. Treatment was olaparib 300mg b.i.d continuously and ceralasertib 160mg qd on days 1–7 on a 28 day cycle, until disease progression. The primary endpoint was confirmed objective response rate by RECIST v1.1. Secondary endpoints included clinical benefit rate, progression-free survival (PFS) and safety. Biomarker analysis included response according to BRCA and somatic DNA repair gene status and ATM loss. Using a two-stage design with a target response rate of 25%, unacceptable response rate of 10%, alpha=2% and power=90%, ≥13 responses out of 69 evaluable stage 2 patients were required to infer efficacy (5/37 stage 1). Results: Between 17/09/18 and 5/10/20 75 patients enrolled in Cohort E of whom 70 were evaluable for response. The median age was 55.6 years. 42 (56%) patients had 1 and 13 (17.3%) had 2 prior line(s) of chemotherapy for metastatic disease. Efficacy is shown in Table. The most common grade ≥3 adverse events were: hypertension 12 (17%) and anaemia 9 (13%). Dose reductions and interruptions occurred in 19 (26.4%) and 34 (47.2%) patients respectively. Conclusions: The response rate to olaparib and ceralasertib did not meet pre-specified criteria for efficacy in the overall evaluable population. Responses were observed in patients without germline or somatic BRCA1/2 mutations. Translational analyses are underway to identify potential biomarkers of response in this population and will be presented at the meeting. Clinical trial information: ISRCTN16945804. [Table: see text]

Phase 1, dose-escalation study of guadecitabine (SGI-110) in combination with pembrolizumab in patients with solid tumors

Background

Data suggest that immunomodulation induced by DNA hypomethylating agents can sensitize tumors to immune checkpoint inhibitors. We conducted a phase 1 dose-escalation trial (NCT02998567) of guadecitabine and pembrolizumab in patients with advanced solid tumors. We hypothesized that guadecitabine will overcome pembrolizumab resistance.

Methods

Patients received guadecitabine (45 mg/m² or 30 mg/m², administered subcutaneously on days 1–4), with pembrolizumab (200 mg administered intravenously starting from cycle 2 onwards) every 3 weeks. Primary endpoints were safety, tolerability and maximum tolerated dose; secondary and exploratory endpoints included objective response rate (ORR), changes in methylome, transcriptome, immune contextures in pre-treatment and on-treatment tumor biopsies.

Results

Between January 2017 and January 2020, 34 patients were enrolled. The recommended phase II dose was guadecitabine 30 mg/m², days 1–4, and pembrolizumab 200 mg on day 1 every 3 weeks. Two dose-limiting toxicities (neutropenia, febrile neutropenia) were reported at guadecitabine 45 mg/m² with none reported at guadecitabine 30 mg/m². The most common treatment-related adverse events (TRAEs) were neutropenia (58.8%), fatigue (17.6%), febrile neutropenia (11.8%) and nausea (11.8%). Common, grade 3+ TRAEs were neutropaenia (38.2%) and febrile neutropaenia (11.8%). There were no treatment-related deaths. Overall, 30 patients were evaluable for antitumor activity; ORR was 7% with 37% achieving disease control (progression-free survival) for ≥24 weeks. Of 12 evaluable patients with non-small cell lung cancer, 10 had been previously treated with immune checkpoint inhibitors with 5 (42%) having disease control ≥24 weeks (clinical benefit). Reduction in LINE-1 DNA methylation following treatment in blood (peripheral blood mononuclear cells) and tissue samples was demonstrated and methylation at transcriptional start site and 5’ untranslated region gene regions showed enriched negative correlation with gene expression. Increases in intra-tumoural effector T-cells were seen in some responding patients. Patients having clinical benefit had high baseline inflammatory signature on RNAseq analyses.

Conclusions

Guadecitabine in combination with pembrolizumab is tolerable with biological and anticancer activity. Reversal of previous resistance to immune checkpoint inhibitors is demonstrated.

A non-coding RNA balancing act: miR-346-induced DNA damage is limited by the long non-coding RNA NORAD in prostate cancer

BACKGROUND

miR-346 was identified as an activator of Androgen Receptor (AR) signalling that associates with DNA damage response (DDR)-linked transcripts in prostate cancer (PC). We sought to delineate the impact of miR-346 on DNA damage, and its potential as a therapeutic agent.

METHODS

RNA-IP, RNA-seq, RNA-ISH, DNA fibre assays, in vivo xenograft studies and bioinformatics approaches were used alongside a novel method for amplification-free, single nucleotide-resolution genome-wide mapping of DNA breaks (INDUCE-seq).

RESULTS

miR-346 induces rapid and extensive DNA damage in PC cells - the first report of microRNA-induced DNA damage. Mechanistically, this is achieved through transcriptional hyperactivation, R-loop formation and replication stress, leading to checkpoint activation and cell cycle arrest. miR-346 also interacts with genome-protective lncRNA NORAD to disrupt its interaction with PUM2, leading to PUM2 stabilisation and its increased turnover of DNA damage response (DDR) transcripts. Confirming clinical relevance, NORAD expression and activity strongly correlate with poor PC clinical outcomes and increased DDR in biopsy RNA-seq studies. In contrast, miR-346 is associated with improved PC survival. INDUCE-seq reveals that miR-346-induced DSBs occur preferentially at binding sites of the most highly-transcriptionally active transcription factors in PC cells, including c-Myc, FOXA1, HOXB13, NKX3.1, and importantly, AR, resulting in target transcript downregulation. Further, RNA-seq reveals widespread miR-346 and shNORAD dysregulation of DNA damage, replication and cell cycle processes. NORAD drives target-directed miR decay (TDMD) of miR-346 as a novel genome protection mechanism: NORAD silencing increases mature miR-346 levels by several thousand-fold, and WT but not TDMD-mutant NORAD rescues miR-346-induced DNA damage. Importantly, miR-346 sensitises PC cells to DNA-damaging drugs including PARP inhibitor and chemotherapy, and induces tumour regression as a monotherapy in vivo, indicating that targeting miR-346:NORAD balance is a valid therapeutic strategy.

CONCLUSIONS

A balancing act between miR-346 and NORAD regulates DNA damage and repair in PC. miR-346 may be particularly effective as a therapeutic in the context of decreased NORAD observed in advanced PC, and in transcriptionally-hyperactive cancer cells.

Association of Serum Carotenoids and Retinoids with Intraprostatic Inflammation in Men without Prostate Cancer or Clinical Indication for Biopsy in the Placebo Arm of the Prostate Cancer Prevention Trial

Non-supplemental carotenoids and retinol may potentiate antioxidant and anti-inflammatory mechanisms. Chronic intraprostatic inflammation is linked to prostate carcinogenesis. We investigated the association of circulating carotenoids and retinol with intraprostatic inflammation in benign tissue. We included 235 men from the Prostate Cancer Prevention Trial placebo arm who had a negative end-of-study biopsy, most (92.8%) done without clinical indication. α-carotene, β-carotene, β-cryptoxanthin, lycopene, and retinol were assessed by high-performance liquid chromatography using pooled year 1 and 4 serum. Presence and extent of intraprostatic inflammation in benign tissue was assessed in 3 (of 6-10) biopsy cores. Logistic (any core with inflammation vs none) and polytomous logistic (some or all cores with inflammation vs none) regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) of intraprostatic inflammation by concentration tertile adjusting for age, race, prostate cancer family history, and serum cholesterol. None of the carotenoids or retinol was associated with intraprostatic inflammation, except β-cryptoxanthin, which appeared to be positively associated with any core with inflammation [vs none, T2: OR (95% CI) = 2.67 (1.19, 5.99); T3: 1.80 (0.84, 3.82), P-trend = 0.12]. These findings suggest that common circulating carotenoids and retinol are not useful dietary intervention targets for preventing prostate cancer via modulating intraprostatic inflammation.

HER3 Is an Actionable Target in Advanced Prostate Cancer

It has been recognized for decades that ERBB signaling is important in prostate cancer, but targeting ERBB receptors as a therapeutic strategy for prostate cancer has been ineffective clinically. However, we show here that membranous HER3 protein is commonly highly expressed in lethal prostate cancer, associating with reduced time to castration resistance (CR) and survival. Multiplex immunofluorescence indicated that the HER3 ligand NRG1 is detectable primarily in tumor-infiltrating myelomonocytic cells in human prostate cancer; this observation was confirmed using single-cell RNA sequencing of human prostate cancer biopsies and murine transgenic prostate cancer models. In castration-resistant prostate cancer (CRPC) patient-derived xenograft organoids with high HER3 expression as well as mouse prostate cancer organoids, recombinant NRG1 enhanced proliferation and survival. Supernatant from murine bone marrow-derived macrophages and myeloid-derived suppressor cells promoted murine prostate cancer organoid growth in vitro, which could be reversed by a neutralizing anti-NRG1 antibody and ERBB inhibition. Targeting HER3, especially with the HER3-directed antibody-drug conjugate U3-1402, exhibited antitumor activity against HER3-expressing prostate cancer. Overall, these data indicate that HER3 is commonly overexpressed in lethal prostate cancer and can be activated by NRG1 secreted by myelomonocytic cells in the tumor microenvironment, supporting HER3-targeted therapeutic strategies for treating HER3-expressing advanced CRPC. SIGNIFICANCE: HER3 is an actionable target in prostate cancer, especially with anti-HER3 immunoconjugates, and targeting HER3 warrants clinical evaluation in prospective trials.

Biomarkers Associating with PARP Inhibitor Benefit in Prostate Cancer in the TOPARP-B Trial

PARP inhibitors are approved for treating advanced prostate cancers (APC) with various defective DNA repair genes; however, further studies to clinically qualify predictive biomarkers are warranted. Herein we analyzed TOPARP-B phase II clinical trial samples, evaluating whole-exome and low-pass whole-genome sequencing and IHC and IF assays evaluating ATM and RAD51 foci (testing homologous recombination repair function). BRCA1/2 germline and somatic pathogenic mutations associated with similar benefit from olaparib; greater benefit was observed with homozygous BRCA2 deletion. Biallelic, but not monoallelic, PALB2 deleterious alterations were associated with clinical benefit. In the ATM cohort, loss of ATM protein by IHC was associated with a better outcome. RAD51 foci loss identified tumors with biallelic BRCA and PALB2 alterations while most ATM- and CDK12-altered APCs had higher RAD51 foci levels. Overall, APCs with homozygous BRCA2 deletion are exceptional responders; PALB2 biallelic loss and loss of ATM IHC expression associated with clinical benefit. SIGNIFICANCE: Not all APCs with DNA repair defects derive similar benefit from PARP inhibition. Most benefit was seen among patients with BRCA2 homozygous deletions, biallelic loss of PALB2, and loss of ATM protein. Loss of RAD51 foci, evaluating homologous recombination repair function, was found primarily in tumors with biallelic BRCA1/2 and PALB2 alterations.This article is highlighted in the In This Issue feature, p. 2659.

Preliminary evidence of antitumour activity of Ipatasertib (Ipat) and Atezolizumab (ATZ) in glioblastoma patients (pts) with PTEN loss from the Phase 1 Ice-CAP trial (NCT03673787)

Aims

Despite improved understanding of effector T-cell trafficking into the central nervous system, initial trials with anti-PD1/PD-L1 immune checkpoint inhibitors (ICIs) have failed to meet their primary endpoints. PTEN loss of function is frequent in GBM and has been correlated with not only poor overall prognosis, but also impaired antitumour responses, including reduced T cell infiltration into tumour and reduced efficacy of ICIs.

Ipatasertib is a novel, potent, selective, small-molecule inhibitor of Akt. We have shown that Ipatasertib efficiently depletes FOXP3+ regulatory T cells from the tumour microenvironment (TME) resulting in increased infiltration of effector T cells in solid tumours (Lopez 2020, AACR).

We hypothesize that the use of AKT inhibition in PTEN glioblastomas may deplete the TME of suppressive immune cells, and render malignant brain tumours more responsive to ICIs. We present updated data for the combination of Ipat+ATZ in patients with glioblastoma.

Method

Patients with relapsed WHO grade IV GBM with stable neurological symptoms ≥5 days prior to enrolment, requiring &lt;3mg Dexamethasone were recruited into two cohorts of this early phase, open-label, single-centre trial studying the combination of Ipatasertib (Ipat) and Atezolizumab (ATZ): a dose finding cohort (A2; n=9) and an expansion cohort (B3; n=7, recruitment ongoing).

The Ice-CAP A2 cohort assessed safety, pharmacodynamic, and preliminary clinical activity of Ipat (200mg or 400mg OD) + ATZ (1200mg Q3W) in pts with potentially resectable relapsed WHO Grade IV GBM. Pts had a 14-21-day run-in phase of Ipat then surgical tumour resection. Combination Ipat+ATZ commenced post surgery. Patients who declined surgery or who were deemed high risk for surgery proceeded directly to combination.

Patients in the expansion cohort B3 commenced directly on Ipat+ATZ at the RP2D of 400mg Ipat with ATZ.

Results

16 evaluable recurrent GBM pts were enrolled across two cohorts. Median age 56 yrs (25-71 yrs). Median ECOG PS 1. Median lines of prior therapy 1 (range 1-4). 10 pts had PTEN loss by IHC (H&lt;30) and/or PTEN mutations on next generation sequencing.

No DLTs, treatment-related (TR) serious adverse events (AEs), or immune-related AEs were observed. Most common TR AEs were G1 diarrhoea (44%), mucositis (17%), rash (28%).

Clinical benefit rate (CR, PR and SD&gt; 6 cycles) at clinical cutoff date (23/02/21) in patients with PTEN aberration was 30% (3/10). A 58-year-old man with PTEN loss had MRI at Cycle 5 showing worsening enhancement suggestive of disease progression. Resection of the lesion showed intense lymphocyte infiltration and pathological CR. He is currently on Cycle 22 with no evidence of disease. Two other patients with PTEN loss with radiological stable disease per RANO criteria remain well on study for &gt;6 cycles.

Conclusion

Combination Ipat+ATZ appears safe and tolerable in GBM pts, with 400mg Ipatasertib OD + 1200mg ATZ Q3W declared as RP2D. Early efficacy signals were detected with PTEN loss being a promising predictive biomarker for response to combination. An expansion cohort enriched with pts with PTEN loss is ongoing.

Abstract LB035: B7-H3 as a therapeutic target in prostate cancer

Background: Advanced prostate cancer (PC) is invariably fatal and largely insensitive to established immune checkpoint inhibition (ICI). The immune checkpoint, PD-L1 (B7-H1; CD274), is infrequently overexpressed in PC; whilst other B7 family immunomodulatory glycoprotein, B7-H3 (CD276), is overexpressed in many PCs. B7-H3 targeted immunoconjugates are in clinical development. We therefore studied the longitudinal expression of B7-H3 in PC and its associations with advanced PC immunogenomics.

Design: We analysed matching, same-patient, formalin-fixed paraffin-embedded (FFPE) metastatic castration resistant PC (mCRPC) (n=98), and treatment-naïve, castration-sensitive PC (CSPC) biopsies (n=43) from patients treated at The Royal Marsden Hospital (UK). Biopsies were analysed by: targeted next-generation sequencing (NGS) for deleterious DNA repair gene alterations; immunohistochemistry (IHC) for ATM, PTEN, B7-H3 and mismatch repair (MMR) proteins using validated antibodies; and multi-color immunofluorescence (IF) assays for T cell surface markers to determine the density of tumour infiltrating T lymphocyte (TIL) subsets. Wilcoxon signed-rank test and Mann-Whitney U test compared B7-H3 expression across matched and unmatched subsets, respectively. Spearman correlation determined associations between continuous variables.

Results: Most CRPC and CSPC biopsies had both membranous B7-H3 (mB7-H3) expression (134/141, 95.0%) and cytoplasmic B7-H3 expression (137/141, 97.2%). Analysis of the 43 matched samples sets showed that there was no significant change in mB7-H3 expression as tumours progressed from CSPC to CRPC (median Histoscore [HS] [range]: 130 [5-300] for CSPC vs. 130 [5-290] for CRPC; p=0.6). There was significant interpatient and intratumor heterogeneity in mB7-H3 expression, but a subset of tumour biopsies had very high mB7-H3 expression (HS ≥200: 28/98 [28.6%] CRPC; 14/43 [32.6%] CSPC). mB7-H3 expression strongly associated with the presence of deleterious alterations of genes involved in homologous recombination (HR) repair (p&lt;0.0001), including BRCA2 mutations and homozygous deletions (p=0.0003) as well as ATM loss (p=0.001). mB7-H3 expression did not associate with defective MMR. Interestingly, mB7-H3 expression inversely associated with the density of intra-tumor CD3+ TILs (median: 104.6 TILs/mm2 in B7-H3 low tumors (HS &lt; median) vs. 39.2 TILs/mm2 in B7-H3 high tumours (HS ≥ median), p=0.004) but did not associate with stromal TIL density (p=0.4).

Conclusion: mB7-H3 is highly expressed in advanced PC, with higher expression associating with BRCA2 and ATM loss of function alterations and low intratumor TILs. B7-H3 may be an actionable target for treating this disease subset.

Citation Format: Christina Guo, Ines Figueiredo, Bora Gurel, Matues Crespo, Jan Rekowski, Suzanne Carreira, Antje Neeb, Adam Sharp, Maria D. Fenor de la Maza, Pasquale Rescigno, Khobe Chandran, Ana Ferreira, Ruth Riisnaes, Susana Miranda, Rita Pereira, Veronica Gil, George Seed, Claudia Bertan, Chloe Baker, Wei Yuan, Johann S. de Bono. B7-H3 as a therapeutic target in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB035.

Abstract 2797: Changes in the phenotype of macrophages and CD8+ T Cells in the perivascular niche of prostate tumours following androgen deprivation

Men with intermediate/high-risk, localized prostate cancer usually receive neoadjuvant androgen deprivation therapy (ADT). Although this markedly reduces tumor burden, it may not be curative and over time cancer cells develop resistance to ADT causing the tumor to regrow and spreads to other sites like the bones. Tumors are then termed ‘castration resistant' (CR) and require more aggressive forms of treatment like radical prostatectomy (RP) and chemotherapy. These can have unpleasant side effects so preventing the development of castration resistance and subsequent tumor regrowth/metastasis, would be highly beneficial for patients. A distinct subset of perivascular (PV) tumor-associated macrophages (TAMs) expressing the cell-surface receptor, MRC1, has been shown to be proangiogenic, immunosuppressive and to stimulate tumor regrowth after chemotherapy, irradiation or vascular targeting drugs. In the current study, we have examined the density and phenotype of TAMs in PV vs non-PV areas of localized, human prostate tumors and orthotopic mouse (Myc-CaP) tumors following neoadjuvant ADT or castration respectively. In human tumors, MRC1+ TAMs accumulated at highest density around stromal blood vessels, and were abundant in these sites following ADT. In mice, castration markedly reduced primary tumor growth and changed the distribution and phenotype of TAMs and cytotoxic CD8+ T lymphocytes (CTLs) just prior to the development of CR. In PV areas of tumors in sham-castrated (i.e. control) mice there were significantly more TAMs expressing MRC1 and the broad-spectrum negative checkpoint regulator, VISTA than in non-PV areas. This was accompanied by the preferential accumulation of CTLs around blood vessels (contrasting with the even distribution of CD4+ (helper) cells and CD4+FOXP3+ Tregs across PV and non-PV areas). Following castration, the PV density of MRC1+ and VISTA+ TAMs was markedly increased, along with that of CTLs expressing the cytotoxic protease, granzyme B - a marker of active CTLs. Although these cells may cross the vasculature into tumors in an active state, passing through a PV niche enriched in VISTA+ TAMs would likely suppress their cytotoxic function before they progressed into the tumor mass. An interesting picture is, therefore, emerging of tumor-promoting TAMs accumulating around blood vessels after various forms of treatment, where they regulate a number of important events including the extravasation and function of various immune effectors.

Citation Format: Haider Al-janabi, Xuan Pu, Munitta Muthana, Ning Wang, Mateus Crespo, Bora Gurel, Johann De Bono, Janet E. Brown, Claire E. Lewis. Changes in the phenotype of macrophages and CD8+ T Cells in the perivascular niche of prostate tumours following androgen deprivation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2797.

Abstract CT120: Results of the glioblastoma multiforme (GBM) cohort of phase 1 trial Ice-CAP (NCT03673787): Preliminary evidence of antitumour activity of Ipatasertib (Ipa) and Atezolizumab (A) in patients (pts) with PTEN loss

Background: Hyperactivation of the PI3K/AKT pathway correlates with impaired antitumour response, including reduced T cell infiltration into tumour and reduced efficacy of immune checkpoint inhibitors (ICIs). PTEN loss of function, often observed in GBM, may contribute to refractoriness of ICIs in this disease. Methods: The Ice-CAP A2 cohort assessed safety, pharmacodynamic, and preliminary clinical activity of Ipa (200mg or 400mg OD) + A (1200mg Q3W) in pts with potentially resectable relapsed WHO Grade IV GBM. Key inclusion criteria were stable neurological symptoms ≥5 days prior to enrolment, steroid requirement &lt;3mg Dexamethasone. Pts had a 14-21-day run-in phase of Ipa then surgical tumour resection. Combination Ipa+A commenced post surgery. Dose-limiting toxicity (DLT) period included run-in phase to Cycle 1 completion (≤11 wks). Results: 10 evaluable pts were enrolled (3 had Ipa at 200mg, 7 at 400mg); median age 58 (range 25-70y), ECOG score 1; median duration of treatment 8 wks. 2 remain on treatment. No DLTs, treatment-related (TR) serious adverse events (AEs), or immune-related AEs were observed. Most common TR AEs were G1 diarrhoea (60%), mucositis (30%), rash (20%). 7 pts had PTEN loss and/or PTEN mutations. Clinical benefit rate in pts with PTEN aberration was 2/7 (29%): 1 pCR and 1 SD &gt;12wks, both on 400mg Ipa. A 58-year-old man with PTEN loss had MRI at Cycle 5 showing worsening enhancement suggestive of disease progression. Resection of the lesion showed intense lymphocyte infiltration and pathological CR. He is currently on Cycle 18 with no evidence of disease.

Conclusion: Combination Ipa+A appears safe and tolerable in GBM pts, with 400mg Ipa OD + 1200mg A Q3W declared as RP2D. PTEN loss may be a promising predictive biomarker for response to combination. An expansion cohort enriched with pts with PTEN loss is ongoing. Cytokine and FACS data will be presented at AACR

Table 1.Clinical Benefit Rate of glioblastoma patients stratified according to PTEN aberrationsPTEN statusnBest responseClinical Benefit RatePTEN loss on IHC (H&lt;30)51 pCRa2/7 (29%)1 SD &gt;12 wks, ongoingb3 PDPTEN aberration on NGS but PTEN protein expression pending11 PDcPTEN loss of heterozygozity on PCR11 PDWild type PTEN on NGS or IHC (H≥30)33 PDLegend: IHC = immunohistochemistry; NGS = next generation sequencing; PCR = polymerase chain reaction;pCR = pathologic complete response; SD = stable disease; PD = progressive diseaseaExceptional responder with PTEN H=5 on IHC and splice site 75_79+2delGACCTGT on NGSb PTENY68*; c PTENQ298*

Citation Format: Crescens Tiu, Andrea Biondo, Liam C. Welsh, Timothy L. Jones, Anna Zachariou, Toby Prout, Alison J. Turner, Robert Daly, Igor Vivanco, Christina Yap, Ben Jenkins, Mateus Crespo, Ruth Riisnaes, Suzanne Carreira, Bora Gurel, Nina Tunariu, Anna Minchom, Udai Banerji, Johann S. de Bono, Juanita S. Lopez. Results of the glioblastoma multiforme (GBM) cohort of phase 1 trial Ice-CAP (NCT03673787): Preliminary evidence of antitumour activity of Ipatasertib (Ipa) and Atezolizumab (A) in patients (pts) with PTEN loss [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT120.

Abstract CT161: A homologous recombination repair (HRR) functional assay to stratify patients with metastatic prostate cancer for PARP inhibitor treatment in the TOPARP-B clinical trial

Background: PARP inhibitors (PARPi) are approved for the treatment of metastatic prostate cancer (mPC) associated to various DNA damage repair (DDR) gene mutations; but clinical benefit differs among patients. Biomarkers of homologous recombination repair (HRR) deficiency may help refine patient stratification for a more precise therapy selection. We report an exploratory analysis from the TOPARP-B phase II clinical trial of olaparib in mPC (NCT01682772), investigating the predictive value of an HRR function assay detecting RAD51 foci by immunofluorescence in tumor biopsies. Design: We analyzed formalin-fixed paraffin-embedded (FFPE) primary or metastatic biopsies from mPC patients treated with olaparib in the clinical trial. We evaluated baseline HRR function based on detection of RAD51 and γH2AX foci in geminin-positive tumor cells by immunofluorescence (IF). All samples were scored by two trained readers blinded to genomic and clinical data. Samples were considered HRR deficient (HRD) when RAD51 scores were low, pre-defined as &lt;10% tumor cells presenting ≥5 RAD51 foci/cell. The association of the RAD51 score, response to olaparib and survival (radiographic progression-free survival, rPFS, and overall survival, OS) was analyzed by Chi-Square and log-rank tests. Results: RAD51 and γH2AX were successfully scored in 52 cases, in the same biopsies previously used for NGS in the clinical trial. All tumors showed abundant DNA damage (γH2AX scores &gt;40%). The intra-class correlation score (ICC) between the two blinded readers was 0.88. Overall, 22 of 52 (42%) cases were considered as HRD based on low RAD51 scores. Response rate (based on the composite RECIST/PSA/CTC trial criteria) was 15/22 (68%) vs 7/30 (23%) for patients with low vs high RAD51 scores (p=0.001). Patients with low RAD51 scores also had longer rPFS (median 9.3 vs 2.9 months p=0.002) and overall survival (median 17.4 vs 9.5 months, p=0.05) from initiation of olaparib. All 16/16 cases with BRCA1/2 alterations were identified as RAD51 low. For patients with PALB2 mutations, 2/2 patients with biallelic loss showed RAD51 low scores and responded to olaparib, whereas 2/2 patients with monoallelic PALB2 mutations showed RAD51 high scores and did not respond to olaparib. Mutations in ATM and CDK12 did not associate with low RAD51. Indeed, 10/11 ATM-mutated and 8/10 CDK12-mutated tumors presented high RAD51 scores; RECIST/PSA responses were observed in two patients with ATM mutations and high RAD51 scores. Conclusion: A RAD51-based IF assay performed on FFPE biopsies can detect prostate cancers with deficient HRR function, including BRCA1/2 and biallelic PALB2 mutated cases, and may be useful for patient stratification for PARP inhibitor treatment in prostate cancer. Further validation of the assay in larger cohorts is warranted.

Citation Format: Sara Arce-Gallego, Alba Llop-Guevara, Suzanne Carreira, Nuria Porta, Roberta Fasani, Diletta Bianchini, George Seed, Pasquale Rescigno, Alec Paschalis, Claudia Bertan, Chloe Baker, Jane Goodall, Susana Miranda, Ruth Riisnaes, Ines Figueiredo, Ana Ferreira, Rita Pereira, Bora Gurel, Daniel Nava Rodrigues, Wei Yuan, Jan Rekowski, Emma Hall, Violeta Serra, Johann S. de Bono, Joaquin Mateo. A homologous recombination repair (HRR) functional assay to stratify patients with metastatic prostate cancer for PARP inhibitor treatment in the TOPARP-B clinical trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT161.

Abstract 2362: Long non-coding RNA NORAD interaction with miR-346 impacts DNA damage response and anti-tumor immunity in prostate cancer

NORAD (NOn-Coding RNA Activated by DNA Damage) is a highly-abundant, evolutionarily-conserved lncRNA. It maintains mitosis, DNA damage repair (DDR), and chromosomal integrity through PUM1/2 sequestration (PUM1/2 activity increases turnover of DDR factors), and through formation of a TOPO2-containing complex critical for genome integrity. We show that NORAD activity is regulated by microRNA-346 (miR-346), which disrupts NORAD:PUM2, interaction, leading to PUM2 destabilization and derepression of PUM1/2 DDR targets in prostate cancer (PCa) cells. RNA-seq reveals widespread miR-346 dysregulation of DNA damage, DNA replication and cell cycle transcripts. A novel method for high resolution, amplification-free genome-wide mapping of double strand DNA breaks (DSBs) (INDUCE-seq) reveals miR-346 induces DSBs specifically at transcription start sites characterized by phospho-PolII/CTCF/ZFX binding - a phenomenon not previously described for any microRNA. Mechanistically, DSBs result from miR-346 activation of transcription, R-loop formation and replicative catastrophe. This results in rapid dose-dependent induction of DNA damage, leading to checkpoint activation and cytosolic DNA accumulation, rescuable by NORAD. This cytosolic DNA activates cytokine-inducing cGAS-STING/RIG-1 innate immune pathways. Indeed, RNA-seq analysis reveals the top NORAD-enriched pathway as interferon signaling, while cytokine arrays reveal secretion of pro-Treg, MDSC and TAM factors by NORAD-overexpressing cells. NORAD inversely correlates with tumor immune response in gene expression data sets, and expression-based immune infiltration scoring predicts increased M2 macrophages, and reduced NK, CD8+ve, Th1 and cytotoxic T cells in NORAD-high vs NORAD-low PCa, indicating an ‘immune-cold' microenvironment. Excitingly, NORAD silencing results in several thousand-fold increase in mature miR-346 without affecting pri-miR levels, supporting NORAD's ability to drive target-directed microRNA decay (TDMD) of miR-346 as a critical novel genome protection mechanism. However, miR-346-induced DNA damage is in part NORAD-independent, since miR-346 induces DSBs within 1h, and in contrast to most miRs is predominantly chromatin-bound (NORAD is cytoplasmic). Critically, miR-346 sensitizes PCa cells to DNA-damaging chemotherapy and PARP inhibition. MiR-346 expression is associated with improved PCa survival, and reduced in high vs low Gleason grade PCa. Notably, NORAD strongly correlates with DDR signatures in early-stage, but not advanced metastatic PCa. Despite its DDR-promoting activity, and in contrast to miR-346, it is associated with worse survival across multiple patient cohorts. In conclusion, these data demonstrate that the NORAD:miR-346 interaction determines DNA damage response and innate immune pathway activity to regulate tumor immune response in PCa.

Citation Format: Claire Fletcher, Lin Deng, Folake Orafidiya, Wei Yuan, Ines Figueiredo, Bora Gurel, Damien Leach, Fadi Issa, Antje Neeb, Denisa Bogdan, Felix Dobbs, Yiannis Philippou, Emma A. Murphy, Shuang G. Zhao, Joanna Hester, Richard J. Bryant, Simon H. Reed, Karen E. Knudsen, Ian G. Mills, Johann de Bono, Charlotte L. Bevan. Long non-coding RNA NORAD interaction with miR-346 impacts DNA damage response and anti-tumor immunity in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2362.

HER3 expression and MEK activation in non-small-cell lung carcinoma

Aim:

We explore HER3 expression in lung adenocarcinoma (adeno-NSCLC) and identify potential mechanisms of HER3 expression.

Materials & methods:

Tumor samples from 45 patients with adeno-NSCLC were analyzed. HER3 and HER2 expression were identified using immunohistochemistry and bioinformatic interrogation of The Cancer Genome Atlas (TCGA).

Results:

HER3 was highly expressed in 42.2% of cases. ERBB3 copy number did not account for HER3 overexpression. Bioinformatic analysis of TCGA demonstrated that MEK activity score (a surrogate of functional signaling) did not correlate with HER3 ligands. ERBB3 RNA expression levels were significantly correlated with MEK activity after adjusting for EGFR expression.

Conclusion:

HER3 expression is common and is a potential therapeutic target by virtue of frequent overexpression and functional downstream signaling.

HER3 expression is common in adeno-NSCLC and is a potential therapeutic target by virtue of frequent overexpression and functional downstream signaling.

CD38 in Advanced Prostate Cancers

Background

CD38, a druggable ectoenzyme, is involved in the generation of adenosine, which is implicated in tumour immune evasion. Its expression and role in prostate tumour-infiltrating immune cells (TIICs) have not been elucidated.

Objective

To characterise CD38 expression on prostate cancer (PC) epithelial cells and TIICs, and to associate this expression with clinical outcomes.

Design, setting, and participants

RNAseq from 159 patients with metastatic castration-resistant prostate cancer (mCRPC) in the International Stand Up To Cancer/Prostate Cancer Foundation (SU2C/PCF) cohort and 171 mCRPC samples taken from 63 patients in the Fred Hutchinson Cancer Research Centre cohort were analysed. CD38 expression was immunohistochemically scored by a validated assay on 51 castration-resistant PC (CRPC) and matching, same-patient castration-sensitive PC (CSPC) biopsies obtained between 2016 and 2018, and was associated with retrospectively collected clinical data.

Outcome measurements and statistical analysis

mCRPC transcriptomes were analysed for associations between CD38 expression and gene expression signatures. Multiplex immunofluorescence determined CD38 expression in PC biopsies. Differences in CD38⁺ TIIC densities between CSPC and CRPC biopsies were analysed using a negative binomial mixed model. Differences in the proportions of CD38⁺ epithelial cells between non-matched benign prostatic epithelium and PC were compared using Fisher’s exact test. Differences in the proportions of biopsies containing CD38⁺ tumour epithelial cells between matched CSPC and CRPC biopsies were compared by McNemar’s test. Univariable and multivariable survival analyses were performed using Cox regression models.

Results and limitations

CD38 mRNA expression in mCRPC was most significantly associated with upregulated immune signalling pathways. CD38 mRNA expression was associated with interleukin (IL)-12, IL-23, and IL-27 signalling signatures as well as immunosuppressive adenosine signalling and T cell exhaustion signatures. CD38 protein was frequently expressed on phenotypically diverse TIICs including B cells and myeloid cells, but largely absent from tumour epithelial cells. CD38⁺ TIIC density increased with progression to CRPC and was independently associated with worse overall survival. Future studies are required to dissect TIIC CD38 function.

Conclusions

CD38⁺ prostate TIICs associate with worse survival and immunosuppressive mechanisms. The role of CD38 in PC progression warrants investigation as insights into its functions may provide rationale for CD38 targeting in lethal PC.

Patient summary

CD38 is expressed on the surface of white blood cells surrounding PC cells. These cells may impact PC growth and treatment resistance. Patients with PC with more CD38-expressing white blood cells are more likely to die earlier.

Putative biomarkers of response to anti-PD-1 therapy in metastatic castration-resistant prostate cancer (mCRPC)

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Background: Metastatic castration resistant prostate cancer (mCRPC) is a heterogeneous disease in which molecular stratification is needed to improve clinical outcomes. Targeting programmed cell death protein 1 (PD-1) elicits durable antitumor responses in multiple cancer types. Putative biomarkers predictive of response to anti-PD-1 therapies include programmed death-ligand-1 (PD-L1), tumour mutational burden (TMB), T cell-inflamed 18-gene expression profile (GEP), and DNA repair defects. Objective: To study potential biomarkers of response in mCRPC to anti-PD-1 therapy (PD-L1, GEP, mismatch repair (MMR) protein), other biomarkers of interest including BRCA2, PALB2, CDK12, PTEN, TP53, SOX2, and to determine association with clinical outcomes. Methods: The study population included 100 men with mCRPC treated at the Royal Marsden Hospital with available fresh mCRPC biopsy tissue. All men had received at least one line of therapy with a next generation hormonal agent and one line of taxane-based chemotherapy. Clinical characteristics and outcomes were extracted from medical records. mCRPC biopsies were assayed by whole exome sequencing (WES), targeted next generation sequencing (NGS), RNA sequencing (RNAseq), GEP score (Nanostring), PD-L1 immunohistochemistry (IHC; DAKO 22C3 assay), SOX2 IHC, ATM IHC. Correlations among these biomarkers and clinical outcomes were assessed. Results: The median age of patients was 68.0 years; 46/84 (54.8%) had de novo metastatic disease at diagnosis and 24/100 (24.0%) patients had visceral disease. Median follow-up from mCRPC biopsy was 56.2 months. The prevalence of loss of protein expression by IHC and/or pathogenic mutation by NGS of MMR was 7/100 (7%). Loss of PTEN and ATM by IHC was 29/100 (29%) and 13/100 (13%) respectively. SOX2 expression (defined as expression in >5% of cells) was 27/100 (27%). The prevalence of TP53 mutation was 25/100 (25%); deleterious alterations of BRCA2 was 9/100 (9%), CDK12 3/100 (3%) and PALB2 1/100 (1%). PDL1 and GEP results were available for 70 and 93 samples respectively. PD-L1 was expressed (combined positive score ≥1) in 24 (33%) mCRPC biopsies; 23 (26%) had high GEP scores (> -0.318). PD-L1 and GEP expression were positively correlated (Phi 0.63). No other biomarkers showed strong correlations. Of 5 samples with MMR loss for which PD-L1 was available, 1 (20%) had PD-L1 ≥1; one of the CDK12 samples had PD-L1 ≥1 (33%). 0/6 BRCA2 mutated biopsies expressed PD-L1 (0%). Based on univariate analysis, PD-L1 expression [HR: 1.75 (1.00;3.06), p=0.045], high GEP score [HR: 2.00 (1.18;3.39), p=0.0083] and SOX2 expression [HR: 1.81 (1.12;2.94), p=0.015] were associated with worse overall survival (OS). No other biomarkers associated with OS. Conclusions: PD-L1 IHC expression was detected in 33% of mCRPC patients and associated with high GEP score. Higher PD-L1, GEP, and SOX2 expression were associated with poor prognosis.

Genetic manipulation of LKB1 elicits lethal metastatic prostate cancer

Gene dosage is a key defining factor to understand cancer pathogenesis and progression, which requires the development of experimental models that aid better deconstruction of the disease. Here, we model an aggressive form of prostate cancer and show the unconventional association of LKB1 dosage to prostate tumorigenesis. Whereas loss of Lkb1 alone in the murine prostate epithelium was inconsequential for tumorigenesis, its combination with an oncogenic insult, illustrated by Pten heterozygosity, elicited lethal metastatic prostate cancer. Despite the low frequency of LKB1 deletion in patients, this event was significantly enriched in lung metastasis. Modeling the role of LKB1 in cellular systems revealed that the residual activity retained in a reported kinase-dead form, LKB1^K78I, was sufficient to hamper tumor aggressiveness and metastatic dissemination. Our data suggest that prostate cells can function normally with low activity of LKB1, whereas its complete absence influences prostate cancer pathogenesis and dissemination.

JMJD6 Is a Druggable Oxygenase That Regulates AR-V7 Expression in Prostate Cancer

Endocrine resistance (EnR) in advanced prostate cancer is fatal. EnR can be mediated by androgen receptor (AR) splice variants, with AR splice variant 7 (AR-V7) arguably the most clinically important variant. In this study, we determined proteins key to generating AR-V7, validated our findings using clinical samples, and studied splicing regulatory mechanisms in prostate cancer models. Triangulation studies identified JMJD6 as a key regulator of AR-V7, as evidenced by its upregulation with in vitro EnR, its downregulation alongside AR-V7 by bromodomain inhibition, and its identification as a top hit of a targeted siRNA screen of spliceosome-related genes. JMJD6 protein levels increased (P < 0.001) with castration resistance and were associated with higher AR-V7 levels and shorter survival (P = 0.048). JMJD6 knockdown reduced prostate cancer cell growth, AR-V7 levels, and recruitment of U2AF65 to AR pre-mRNA. Mutagenesis studies suggested that JMJD6 activity is key to the generation of AR-V7, with the catalytic machinery residing within a druggable pocket. Taken together, these data highlight the relationship between JMJD6 and AR-V7 in advanced prostate cancer and support further evaluation of JMJD6 as a therapeutic target in this disease. SIGNIFICANCE: This study identifies JMJD6 as being critical for the generation of AR-V7 in prostate cancer, where it may serve as a tractable target for therapeutic intervention.

Emergence of Enzalutamide Resistance in Prostate Cancer is Associated with BCL-2 and IKKB Dependencies

PURPOSE

Although enzalutamide (ENZ) has been widely used to treat de novo or castration-resistant metastatic prostate cancer, resistance develops and disease progression is ultimately inevitable. There are currently no approved targeted drugs to specifically delay or overcome ENZ resistance.

EXPERIMENTAL DESIGN

We selected several ENZ-resistant cell lines that replicated clinical characteristics of the majority of patients with ENZ-resistant disease. A high-throughput pharmacologic screen was utilized to identify compounds with greater cytotoxic effect for ENZ-resistant cell lines, compared with parental ENZ-sensitive cells. We validated the potential hits in vitro and in vivo, and used knockdown and overexpression assays to study the dependencies in ENZ-resistant prostate cancer.

RESULTS

ABT199 (BCL-2 inhibitor) and IMD0354 (IKKB inhibitor) were identified as potent and selective inhibitors of cell viability in ENZ-resistant cell lines in vitro and in vivo which were further validated using loss-of-function assays of BCL-2 and IKKB. Notably, we observed that overexpression of BCL-2 and IKKB in ENZ-sensitive cell lines was sufficient for the emergence of ENZ resistance. In addition, we confirmed that BCL-2 or IKKB inhibitors suppressed the development of ENZ resistance in xenografts. However, validation of both BCL-2 and IKKB in matched castration-sensitive/resistant clinical samples showed that, concurrent with the development of ENZ/abiraterone resistance in patients, only the protein levels of IKKB were increased.

CONCLUSIONS

Our findings identify BCL-2 and IKKB dependencies in clinically relevant ENZ-resistant prostate cancer cells in vitro and in vivo, but indicate that IKKB upregulation appears to have greater relevance to the progression of human castrate-resistant prostate cancer.

Abstract PO003: CD38 in the advanced prostate cancer

Background: CD38, an ecto-enzyme involved in adenosine synthesis, is implicated in tumor immune evasion. Its expression and role in the prostate tumor microenvironment (TME) has not been fully elucidated. Main objectives: To determine whether CD38 is associated with prostate cancer (PC) immune evasion, to characterize CD38 expression on PC epithelial cells and tumor infiltrating immune cells (TIICs) as tumors progress from castration-sensitive PC (CSPC) to metastatic castration-resistant PC (mCRPC), and to determine the association between CD38+ TIICs and survival.

Methods: Data from 159 mCRPC transcriptomes from the Stand Up To Cancer/Prostate Cancer Foundation cohort were analyzed for associations between CD38 and 200 cell signaling pathways, an adenosine signature and T cell exhaustion signatures. CD38 protein expression on tumor epithelial cells and TIICs was scored using validated immunohistochemistry (IHC) assays on 51 treatment-naïve CSPC biopsies and matching, same-patient mCRPC biopsies obtained between 2016-2018 from men treated at The Royal Marsden Hospital. To characterize CD38+ TIICs, CD38 co-expression with immune cell surface markers for T cells (CD3), B cells (CD19, CD20, CD138, CD79a), and myeloid cells (CD11b, CD15, CD33) was determined by dual-color IHC or multiplex immunofluorescence. The change in CD38+ TIICs density from CSPC to mCRCP was assessed by negative binomial regression and the associations between CD38+ TIIC density and survival were studied using Kaplan-Meier methods, Cox regression and the log-rank test.

Results: Unbiased transcriptome analyses showed that CD38 mRNA expression in mCRPC was associated with upregulated immune signaling pathways, with the ten pathways showing the strongest evidence of association (all P &lt; 1 × 10^-10) with CD38 mRNA expression all being immunomodulatory. CD38 expression was associated with IL-23 signaling (P &lt; 1 × 10^-10), a myeloid suppressor cell-derived mediator of endocrine resistance, as well as immunosuppressive adenosine signaling (P &lt; 1 × 10^-8) and T cell exhaustion signatures (P &lt; 1 × 10^-10). CD38 protein was largely absent from tumor epithelial cells (7.7%). CD38 was expressed by phenotypically diverse TIICs. CD38+ TIICs co-expressed myeloid cell surface markers (CD33, CD15), B cell surface markers (CD19, CD20, CD79a, CD138), and the T cell surface marker (CD3). CD38+ TIIC density increased as tumors progressed from CSPC to CRPC (negative binomial regression, P = 0.03). CSPC and CRPC with higher CD38+ TIIC density (dichotomized based on the median; &gt; 1.5 cells/mm^2) were associated with shorter overall survival from the time of PC diagnosis (hazard ratio [HR]: 1.89; 95% CI: 1.02-3.50) and the time of mCRPC biopsy (HR: 2.14; 95% CI: 1.15-4.00), respectively.

Conclusion: CD38 is expressed by diverse TIICs in the prostate TME and was associated with potential mechanisms of immune evasion. CD38 expression may serve as a potential prognostic biomarker and therapeutic target in PC aimed at overcoming PC immunoresistance.

Citation Format: Christina Guo, Mateus Crespo, Bora Gurel, David Dolling, Jan Rekowski, Adam Sharp, Antonella Petremolo, Semini Sumanasuriya, Daniel N. Rodrigues, Ana Ferreira, Rita Pereira, Ines Figueiredo, Niven Mehra, Maryou B.K. Lambros, Antje Neeb, Veronica Gil, Leon Terstappen, Andrea Alimonti, Charles G. Drake, Wei Yuan, Johann S. de Bono. CD38 in the advanced prostate cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO003.

Advanced Prostate Cancer with ATM Loss: PARP and ATR Inhibitors

BACKGROUND

Deleterious ATM alterations are found in metastatic prostate cancer (PC); PARP inhibition has antitumour activity against this subset, but only some ATM loss PCs respond.

OBJECTIVE

To characterise ATM-deficient lethal PC and to study synthetic lethal therapeutic strategies for this subset.

DESIGN, SETTING, AND PARTICIPANTS

We studied advanced PC biopsies using validated immunohistochemical (IHC) and next-generation sequencing (NGS) assays. In vitro cell line models modified using CRISPR-Cas9 to impair ATM function were generated and used in drug-sensitivity and functional assays, with validation in a patient-derived model.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

ATM expression by IHC was correlated with clinical outcome using Kaplan-Meier curves and log-rank test; sensitivity to different drug combinations was assessed in the preclinical models.

RESULTS AND LIMITATIONS

Overall, we detected ATM IHC loss in 68/631 (11%) PC patients in at least one biopsy, with synchronous and metachronous intrapatient heterogeneity; 46/71 (65%) biopsies with ATM loss had ATM mutations or deletions by NGS. ATM IHC loss was not associated with worse outcome from advanced disease, but ATM loss was associated with increased genomic instability (NtAI:number of subchromosomal regions with allelic imbalance extending to the telomere, p = 0.005; large-scale transitions, p = 0.05). In vitro, ATM loss PC models were sensitive to ATR inhibition, but had variable sensitivity to PARP inhibition; superior antitumour activity was seen with combined PARP and ATR inhibition in these models.

CONCLUSIONS

ATM loss in PC is not always detected by targeted NGS, associates with genomic instability, and is most sensitive to combined ATR and PARP inhibition.

PATIENT SUMMARY

Of aggressive prostate cancers, 10% lose the DNA repair gene ATM; this loss may identify a distinct prostate cancer subtype that is most sensitive to the combination of oral drugs targeting PARP and ATR.

Characterizing CDK12-Mutated Prostate Cancers

PURPOSE

Cyclin-dependent kinase 12 (CDK12) aberrations have been reported as a biomarker of response to immunotherapy for metastatic castration-resistant prostate cancer (mCRPC). Herein, we characterize CDK12-mutated mCRPC, presenting clinical, genomic, and tumor-infiltrating lymphocyte (TIL) data.

EXPERIMENTAL DESIGN

Patients with mCRPC consented to the molecular analyses of diagnostic and mCRPC biopsies. Genomic analyses involved targeted next-generation (MiSeq; Illumina) and exome sequencing (NovaSeq; Illumina). TILs were assessed by validated immunocytochemistry coupled with deep learning-based artificial intelligence analyses including multiplex immunofluorescence assays for CD4, CD8, and FOXP3 evaluating TIL subsets. The control group comprised a randomly selected mCRPC cohort with sequencing and clinical data available.

RESULTS

Biopsies from 913 patients underwent targeted sequencing between February 2015 and October 2019. Forty-three patients (4.7%) had tumors with CDK12 alterations. CDK12-altered cancers had distinctive features, with some revealing high chromosomal break numbers in exome sequencing. Biallelic CDK12-aberrant mCRPCs had shorter overall survival from diagnosis than controls [5.1 years (95% confidence interval (CI), 4.0-7.9) vs. 6.4 years (95% CI, 5.7-7.8); hazard ratio (HR), 1.65 (95% CI, 1.07-2.53); P = 0.02]. Median intratumoral CD3+ cell density was higher in CDK12 cancers, although this was not statistically significant (203.7 vs. 86.7 cells/mm2; P = 0.07). This infiltrate primarily comprised of CD4+FOXP3- cells (50.5 vs. 6.2 cells/mm2; P < 0.0001), where high counts tended to be associated with worse survival from diagnosis (HR, 1.64; 95% CI, 0.95-2.84; P = 0.077) in the overall population.

CONCLUSIONS

CDK12-altered mCRPCs have worse prognosis, with these tumors surprisingly being primarily enriched for CD4+FOXP3- cells that seem to associate with worse outcome and may be immunosuppressive.See related commentary by Lotan and Antonarakis, p. 380.

Targeting the p300/CBP Axis in Lethal Prostate Cancer

Resistance to androgen receptor (AR) blockade in castration-resistant prostate cancer (CRPC) is associated with sustained AR signaling, including through alternative splicing of AR (AR-SV). Inhibitors of transcriptional coactivators that regulate AR activity, including the paralog histone acetyltransferase proteins p300 and CBP, are attractive therapeutic targets for lethal prostate cancer. Herein, we validate targeting p300/CBP as a therapeutic strategy for lethal prostate cancer and describe CCS1477, a novel small-molecule inhibitor of the p300/CBP conserved bromodomain. We show that CCS1477 inhibits cell proliferation in prostate cancer cell lines and decreases AR- and C-MYC-regulated gene expression. In AR-SV-driven models, CCS1477 has antitumor activity, regulating AR and C-MYC signaling. Early clinical studies suggest that CCS1477 modulates KLK3 blood levels and regulates CRPC biopsy biomarker expression. Overall, CCS1477 shows promise for the treatment of patients with advanced prostate cancer. SIGNIFICANCE: Treating CRPC remains challenging due to persistent AR signaling. Inhibiting transcriptional AR coactivators is an attractive therapeutic strategy. CCS1477, an inhibitor of p300/CBP, inhibits growth and AR activity in CRPC models, and can affect metastatic CRPC target expression in serial clinical biopsies.See related commentary by Rasool et al., p. 1011.This article is highlighted in the In This Issue feature, p. 995.

Research Related Tumour Biopsies in Early-Phase Trials with Simultaneous Molecular Characterisation - a Single Unit Experience

Early-phase cancer clinical trials are becoming increasingly accessible for patients with advanced cancer who have exhausted standard treatment options and later phase trial options. Many of these trials mandate research tissue biopsies. Research biopsies have been perceived as ethically fraught due to the perception of potential coercion of vulnerable human subjects. We performed an audit of two years of practice to assess the safety of ultrasound (US)-guided research biopsies, and to look at the yield of a simultaneous tumour next-generation sequencing (NGS) and immunohistochemistry (IHC) molecular characterisation programme. We show that in our institution, US-guided research biopsies were safe, produced adequate tumour content and in a selected subset who underwent in-house NGS sequencing, showed a high rate of actionable mutations with 30% having a Tier 1 variant. Nevertheless, these research biopsies may only provide direct benefit for a minority of patients and we conclude with a reflection on the importance of obtaining truly informed consent.

Abstract LB-075: CDK12-mutated lethal prostate cancers: How hot are these tumors

Background: Genomic analyses describing the molecular landscape of primary prostate cancer (PCa) and metastatic castration-resistant prostate cancer (mCRPC) have identified recurrent CDK12 alterations in 2-4% of primary PCa and 4-11% of mCRPC. These aberrations, as well as high lymphocyte tumor infiltration, could be clinically relevant as putative biomarkers of response to immunotherapies. However, there are few studies looking into whether CDK12 biallelic mutant cases are immune ‘hot'. Here, we describe a cohort of patients with CDK12 aberration and studied the tumor infiltration of those cancers.

Methods: Patients with mCRPC and available diagnostic archival and/or CRPC tumor samples were evaluated. Mutation analysis involved custom designed targeted sequencing on MiSeq sequencer. Loss of heterozygosity (LOH) was assessed for the CDK12 cases from exome sequencing using ASCAT, which include single copy lost or copy neutral LOH. Tumor infiltrating lymphocytes were assessed initially with CD3 IHC, using a deep learning-based AI analysis approach. We then subtyped the TILs using a multiplex IF approach, classifying lymphocytes using CD4, CD8 and FOXP3 positivity.

Results: Overall 913 samples (between Feb/15 and Oct/19) were sequenced by targeted NGS, 42 patients presented with pathogenic alterations in CDK12 (4.6%), 27 had bi-allelic alterations, 14 mono-allelic, 1 likely biallelic. In these cases, we identified 39 frameshift alterations, 10 missense mutations mainly involving the kinase domain; with 5 having concomitant LOH. One case showed deep deletion of CDK12 and five presented with additional aberrations in other DNA repair related genes. CDK12 biallelic alterations were present in all 3 cases with both diagnostic and matched mCRPC samples available. We studied T cell infiltration in 100 (23 CDK12 biallelic alterations, 7 monoallelic, 70 controls) samples selected from within the initial targeted NGS cohort. Median intratumoral CD3+ cell density was significantly higher in CDK12 biallelic loss samples compared to matched controls in diagnostic biopsies (271.4 vs 104.683 cells/mm2, p=0.026). A similar trend was seen in mCRPC samples (142.130 vs 51.75 cells/mm2, p=0.36). Intratumoral CD4+ cell infiltration was again significantly higher in CDK12 biallelic loss samples compared to controls (98.864 vs 6.188 cells/mm2, p=0.014).

Conclusions: In our analysis we show that a proportion of mCRPC patients harbor defects in CDK12, these are often alterations involving both alleles, likely present from the time of diagnosis. A majority of these CDK12 altered cancers has high CD3 infiltration compared to controls. We envision that these CDK12 aberrant ‘hot' tumors could represent a subset of mCRPC likely to respond to immune-checkpoint inhibition.

Citation Format: Bora Gurel, Pasquale Rescigno, Wei Yuan, Rita Pereira, Mateus Crespo, Mattia Rediti, Ines Figueiredo, Maialen Barrero, Diletta Bianchini, Maria D. Fenor de la Maza, Khobe Chandran, Juliet Carmichael, Alec Paschalis, Adam Sharp, George Seed, Ruth Riisnaes, Claudia Bertan, Suzanne Carreira, Johann S. De Bono. CDK12-mutated lethal prostate cancers: How hot are these tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-075.

Abstract CT129: HyPeR: A phase 1, dose escalation and expansion trial of guadecitabine (SGI-110), a second-generation hypomethylating agent in combination with pembrolizumab (MK3475) in patients with refractory solid tumors

Background: Methylation is reported to support cancer immune tolerance. We conducted a phase 1 dose-escalation trial [NCT02998567] of combination guadecitabine (G; DNA hypomethylating agent) and pembrolizumab (P) in patients (pts) with advanced cancers. We hypothesized that G can normalize the expression of epigenetically suppressed immune genes, increase interferon producing tumor-infiltrating lymphocytes (TILs), and enhance the anticancer activity of P. Methods: In dose escalation (Es), pts received G (45 mg/m2 or 30 mg/m2, administered SC on days 1-4) with P (200 mg, administered IV starting from cycle 2 onwards) as outpatient Q3W; in expansion (Ex), the RP2D of G (30 mg/m2) with P (200 mg) Q3W was administered. Pre-treatment and on-treatment tumor biopsies were evaluated for PD-L1 expression, tumor infiltrating lymphocytes, gene expression by RNAseq and methylome studies. Longitudinal analyses of peripheral blood CD3, CD4 and CD8 lymphocytes by flow cytometry were performed. Results: Overall, 34 pts (Es, n = 14; Ex, n = 20) were evaluable for safety. The most common treatment-related adverse events (TRAEs) were neutropenia (n = 21), fatigue (n = 6) and thrombocytopenia (n = 3), diarrhea (n = 2). G3+ TRAEs were neutropenia (n = 14), febrile neutropenia (n = 4), raised ALP (n = 1), raised AST (n=1), colitis (n = 1), diarrhoea (n = 1) and lung infection (n = 1). Two DLTs (neutropenia, febrile neutropenia) were reported at G 45mg/m2 with none reported at G 30mg/m2. There were no treatment-related deaths. In total, 28 pts (Es, n = 12; Ex, n = 16) were evaluable for antitumor activity studies (≥2 scans); ORR (CR+PR) and DCR (CR+PR+SD) were 3% and 57%; 10/15 pts with non-small cell lung cancer (13 pts resistant/refractory to PD-1/PD-L1 targeting agents) were evaluable, with a DCR of 80% and 5 pts having DCR &gt; 6 months with 8 pts remaining on study treatment. Overall, 25 paired biopsies were obtained. Using LINE1 sequences to study global methylation, both tumor biopsies and peripheral blood showed reduced methylation post-G treatment. Preliminary data on tumor-infiltrating lymphocytes assessed by multicolor immunofluorescence in 9 paired biopsies showed a numerical increase in median values of T-helper (CD4+FOXP3-) (10.20 to 19.70, p = 0.5469), T-regulatory (CD4+FOXP3+) (5.1 to 6.7, p=0.8438), and T-cytotoxic (CD8+) cell densities (2.7 to 7.4, p=0.6523) . Comparing with matched pre-treatment, on treatment tumor had numerical increases in interferon alpha and gamma response pathway activation in serial biopsy RNAseq analyses but did not reach significance. Conclusions: G plus P resulted in no unexpected toxicities with evidence suggestive of biological and anti-cancer activity.

Citation Format: Dionysis Papadatos-Pastos, Abhijit Pal, Melek Akay, Malaka Ameratunga, Sanjena Mithra, Joo-Ern Ang, Sofia Levva, Reece Caldwell, Ruth Riisnaes, Mateus Crespo, Wei Yuan, George Seed, Bora Gurel, Ines Figueiredo, Rita Pereira, Susana Miranda, Anna Ferreira, Suzanne Carreira, Claudia Bertan, Chloe Baker, Ricardo Morilla, Robert Brown, Nahal Masrour, Toby Prout, Anna Zachariou, Alison Turner, Mona Parmar, Mark Van de Velde, Ben Jenkins, Christina Yap, Nina Tunariu, Udai Banerji, Juanita Lopez, Anna Minchom, Johann De Bono. HyPeR: A phase 1, dose escalation and expansion trial of guadecitabine (SGI-110), a second-generation hypomethylating agent in combination with pembrolizumab (MK3475) in patients with refractory solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT129.

Abstract CT140: Proof-of-concept evidence of immune modulation by blockade of the phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathway in the phase I dose escalation study of Ipatasertib (Ipa) in combination with atezolizumab (A) in patients (pts) with advanced solid tumors (Ice-CAP)

Background: Hyperactivation of the PI3K/AKT pathway correlates with impaired anti-tumor responses, including reduced T cell infiltration into tumor, and reduced efficacy of immune checkpoint inhibitors. Blockade of this pathway synergizes with PD-L1/PD-1 axis blockade preclinically.

Methods: This Phase I clinical trial (NCT03673787) assessed the safety, pharmacodynamic, and preliminary clinical activity of Ipa (200mg or 400mg OD) given in combination with A 1200mg q3 wk in refractory pts. Serial paired blood and tumor samples were analysed to interrogate the effect of Ipa on the tumor micro-environment and host immune system prior to the addition of the immune check point inhibitor, A.

Results: 18 adult pts were treated in dose escalation. Median age 49 yrs. All pts had ECOG PS 0-1 and median 7 prior therapies. Most common TRAEs (&gt;15%) were mild Gr1-2 diarrhea (56%), rash (50%), fatigue (33%), nausea (33%), raised ALT/AST (33%), headache (28%) and arthralgia (22%). 1 pt had G2 systemic immune activation; 2 pts had G3 rash, both rapidly reversible. 1 DLT of G3 raised ALT seen at 200mg (1 DLT/9 evaluable pts) but none at 400mg (0 DLT/6). Of 14 RECIST evaluable patients, there were 2 confirmed PRs, and 5 SD (clinical benefit rate 50%). Reductions of CD4+FOXP3+ Tregs in tumor microenvironment were seen after 2wks of single agent Ipa, regardless of PIK3/AKT somatic mutation status (Table 1). Responding pts had a &gt;400% median increase in intra-tumoral CD8+ Teff cell infiltration, effectively switching from a desert phenotype to an inflamed phenotype. Paired changes in FACS, transcriptome and cytokine will also be presented.Conclusions: The RP2D of Ipa 400mg OD combination with A was well tolerated with early efficacy signals. Further biomarker work is ongoing and will be evaluated in expansion cohorts.

Table 1:Changes in immune cell populations as assessed by multicolour Immunofluorescence in paired biopsies of breast/gynae patients, % change in cell number/mm2 from baseline (median [min,max$])&Post 2 weeks single agent Ipatasertib(n=9)Post 1 cycle of combination Ipatasertib and Atezolizumab(n=7)CD4+FOXP3+Tregs cellsCD 8+ Teff cellsCD4+FOXP3+Tregs cellsCD 8+ Teff cellsIntra-tumourstromaIntra-tumourstromaIntra-tumourstromaIntra-tumourstromaAll patients-23.9*[-89.7, BL0]-30.0*[-91.6, BL0]-37.7*[-84.4, -24.5]-28.4[-92.4, 259.8]335.9[-44.0,BL0]45.4[-51.0, BL0]59.6[-60.6,493.3]64.7[-51.7,293.3]Stratified by somatic PI3K/AKT/PTEN mutational statusPathogenic mutations (mt)11.1[-82.2, BL0]#-10.7[-91.6, BL0]Φnsnsnsns-30.5[-60.6,-0.5]11.3[-51.7,50.0]Wildtype (wt)-63.1[-89.7,19.0]#-47.5[-77.0,11.1]Φnsnsnsns426.5[59.6,493.3]126.7[79.4,293.3]Stratified by responseResponders (PR + SD&gt;4 cycles). 1 ER+ HER2+ breast cancer (wt), 1 ER+ HER2- breast cancer (wt)459.9[426.5,493.3]@103.1[79.4,126.7]Non-responders (PD at 4 cycles) 1 cervical cancer, 4 ER+ breast cancer-0.5[-60.6, 59.6]@30.6[-51.7,293.3]*significant change (p≤0.05; Wilcoxon sign-rank test) from baseline, $maximum values denoted by BL0indicate that the baseline value was zero, and so percentage change from baseline is not defined. For the analysis, the baseline value has been replaced by a nominal value of 0.1 so that a large percentage increase is associated with these cases. Note that these large percentage increases do not affect the non-parametric statistical tests used.#no significant difference in distribution of reduction in intra-tumoural CD4+ FOXP3+Tregsbetween pts with pathogenic mutations in PI3K/AKT and those without (p=0.30; Wilcoxon rank-sum test)Φno significant difference in distribution of reduction in stromal CD4+FOXP3+Tregsbetween pts with pathogenic mutations in PI3K/AKT and those without (p=0.44; Wilcoxon rank-sum test) @ difference between responders and non-responders p=0.083; Wilcoxon rank-sum test)mt pathogenic mutations in PI3K/AKT and PTEN as per COSMIC database present in tumour or PTEN loss by IHC. wt no pathogenic mutations in PI3K/AKT and PTEN as per COSMIC database detected in tumour and intact PTEN expression by IHC. &exploratory analyses with no adjustment for multiple testing

Citation Format: Juanita S. Lopez, Andrea Biondo, Crescens Tiu, Mariana Scaranti, Malaka Ameratunga, Anna Zachariou, Alison Turner, Nina Tunariu, Toby Prout, Mona Parmar, Hannah Badham, Karen Swales, Wei Yuan, Ricardo Morilla, Mateus Crespo, Rob Daly, Ines Figueiredo, Bora Gurel, Rita Pereira, Ruth Riisnaes, Igor Vivanco, Anna Minchom, Ben Jenkins, Christina Yap, Udai Banerji, Johann De Bono. Proof-of-concept evidence of immune modulation by blockade of the phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathway in the phase I dose escalation study of Ipatasertib (Ipa) in combination with atezolizumab (A) in patients (pts) with advanced solid tumors (Ice-CAP) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT140.

Prostate carcinogenesis: inflammatory storms

Prostate cancer is a major cause of cancer morbidity and mortality. Intra-prostatic inflammation is a risk factor for prostate carcinogenesis, with diet, chemical injury and an altered microbiome being causally implicated. Intra-prostatic inflammatory cell recruitment and expansion can ultimately promote DNA double-strand breaks and androgen receptor activation in prostate epithelial cells. The activation of the senescence-associated secretory phenotype fuels further 'inflammatory storms', with free radicals leading to further DNA damage. This drives the overexpression of DNA repair and tumour suppressor genes, rendering these genes susceptible to mutagenic insults, with carcinogenesis accelerated by germline DNA repair gene defects. We provide updates on recent advances in elucidating prostate carcinogenesis and explore novel therapeutic and prevention strategies harnessing these discoveries.

The association between serum sex steroid hormone concentrations and intraprostatic inflammation in men without prostate cancer and irrespective of clinical indication for biopsy in the placebo arm of the Prostate Cancer Prevention Trial

BACKGROUND

Intraprostatic inflammation is an emerging prostate cancer risk factor. Estrogens are pro-inflammatory while androgens are anti-inflammatory. Thus, we investigated whether serum sex steroid hormone concentrations are associated with intraprostatic inflammation to inform mechanistic links among hormones, inflammation, and prostate cancer.

METHODS

We conducted a cross-sectional study among 247 men in the placebo arm of the Prostate Cancer Prevention Trial who had a negative end-of-study biopsy, most (92.7%) performed without clinical indication per trial protocol. Serum estradiol, estrone, and testosterone were previously measured by immunoassay in pooled baseline and Year 3 serum. Free estradiol and free testosterone were calculated. Inflammation was visually assessed (median of three prostate biopsy cores per man). Polytomous or logistic regression was used to estimate the odds ratio (OR) and 95% confidence interval (CI) of some or all cores inflamed (both vs none) or any core inflamed (vs none) by hormone tertile, adjusting for age, race, and family history. We evaluated effect modification by waist circumference and body mass index (BMI).

RESULTS

In all, 51.4% had some and 26.3% had all cores inflamed. Free (P-trend = .11) but not total estradiol was suggestively inversely associated with all cores inflamed. In men with waist circumference greater than or equal to 102 cm (P-trend = .021) and BMI ≥ 27.09 kg/m² (P-trend = .0037) free estradiol was inversely associated with any core inflamed. Estrone was inversely associated with all cores inflamed (T3: OR = 0.36, 95% CI 0.14-0.95, P-trend = .036). Total (T3: OR = 1.91, 95% CI 0.91-4.02, P-trend = .11) and free (T3: OR = 2.19, 95% CI 1.01-4.74, P-trend = .05) testosterone were positively associated with any core inflamed, especially free testosterone in men with waist circumference less than 102 cm (T3: OR = 3.51, 95% CI 1.03-12.11, P-trend = .05).

CONCLUSIONS

In this first study in men without prostate cancer and irrespective of clinical indication for biopsy, contrary to the hypothesis, circulating estrogens appeared to be inversely associated, especially in heavy men, whereas androgens appeared to be positively associated with intraprostatic inflammation.