Evaluation of copanlisib in combination with eribulin in triple negative breast cancer patient-derived xenograft models

The phosphoinositide 3-kinase (PI3K) pathway regulates essential cellular functions and promotes chemotherapy resistance. Activation of PI3K pathway signaling is commonly observed in triple negative breast cancer (TNBC). However previous studies that combined PI3K pathway inhibitors with taxane regimens have yielded inconsistent results. We therefore set out to examine whether the combination of copanlisib, a clinical grade pan-PI3K inhibitor, and eribulin, an antimitotic chemotherapy approved for taxane-resistant metastatic breast cancer, improves the anti-tumor effect in TNBC. A panel of 8 TNBC patient-derived xenograft (PDX) models were tested for tumor growth response to copanlisib and eribulin, alone or in combination. Treatment induced signaling changes were examined by reverse phase protein array, immunohistochemistry, and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET). Compared to each drug alone, the combination of eribulin and copanlisib led to enhanced tumor growth inhibition, which was observed in both eribulin-sensitive and -resistant TNBC PDX models, regardless of PI3K pathway alterations or PTEN status. Copanlisib reduced PI3K signaling and enhanced eribulin induced mitotic arrest. The combination enhanced induction of apoptosis compared to each drug alone. Interestingly, eribulin upregulated PI3K pathway signaling in PDX tumors, as demonstrated by increased tracer uptake by 18F-FDG PET scan of PDX tumor and AKT phosphorylation by immunohistochemistry. These changes were inhibited by the addition of copanlisib. These data support further clinical development for the combination of copanlisib and eribulin. These data led to a phase I/II trial of copanlisib and eribulin in patients with metastatic TNBC.

Reciprocal antagonism of PIN1-APC/CCDH1 governs mitotic protein stability and cell cycle entry

Induced oncoproteins degradation provides an attractive anti-cancer modality. Activation of anaphase-promoting complex (APC/CCDH1) prevents cell-cycle entry by targeting crucial mitotic proteins for degradation. Phosphorylation of its co-activator CDH1 modulates the E3 ligase activity, but little is known about its regulation after phosphorylation and how to effectively harness APC/CCDH1 activity to treat cancer. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1)-catalyzed phosphorylation-dependent cis-trans prolyl isomerization drives tumor malignancy. However, the mechanisms controlling its protein turnover remain elusive. Through proteomic screens and structural characterizations, we identify a reciprocal antagonism of PIN1-APC/CCDH1 mediated by domain-oriented phosphorylation-dependent dual interactions as a fundamental mechanism governing mitotic protein stability and cell-cycle entry. Remarkably, combined PIN1 and cyclin-dependent protein kinases (CDKs) inhibition creates a positive feedback loop of PIN1 inhibition and APC/CCDH1 activation to irreversibly degrade PIN1 and other crucial mitotic proteins, which force permanent cell-cycle exit and trigger anti-tumor immunity, translating into synergistic efficacy against triple-negative breast cancer.

Allosteric PI3Kα Inhibition Overcomes On-target Resistance to Orthosteric Inhibitors Mediated by Secondary PIK3CA Mutations

PIK3CA mutations occur in ∼8% of cancers, including ∼40% of HR-positive breast cancers, where the PI3K-alpha (PI3Kα)-selective inhibitor alpelisib is FDA approved in combination with fulvestrant. Although prior studies have identified resistance mechanisms, such as PTEN loss, clinically acquired resistance to PI3Kα inhibitors remains poorly understood. Through serial liquid biopsies and rapid autopsies in 39 patients with advanced breast cancer developing acquired resistance to PI3Kα inhibitors, we observe that 50% of patients acquire genomic alterations within the PI3K pathway, including PTEN loss and activating AKT1 mutations. Notably, although secondary PIK3CA mutations were previously reported to increase sensitivity to PI3Kα inhibitors, we identified emergent secondary resistance mutations in PIK3CA that alter the inhibitor binding pocket. Some mutations had differential effects on PI3Kα-selective versus pan-PI3K inhibitors, but resistance induced by all mutations could be overcome by the novel allosteric pan-mutant-selective PI3Kα-inhibitor RLY-2608. Together, these findings provide insights to guide strategies to overcome resistance in PIK3CA-mutated cancers.

SIGNIFICANCE

In one of the largest patient cohorts analyzed to date, this study defines the clinical landscape of acquired resistance to PI3Kα inhibitors. Genomic alterations within the PI3K pathway represent a major mode of resistance and identify a novel class of secondary PIK3CA resistance mutations that can be overcome by an allosteric PI3Kα inhibitor. See related commentary by Gong and Vanhaesebroeck, p. 204 . See related article by Varkaris et al., p. 240 . This article is featured in Selected Articles from This Issue, p. 201.

Effect of testosterone therapy on breast tissue composition and mammographic breast density in trans masculine individuals

Objective

Determine the association between TT and breast tissue composition and breast tissue density in trans masculine individuals (TMIs).

Design

This is a cross-sectional study.

Setting

TMIs (n=444) underwent chest-contouring surgeries to treat their gender dysphoria between 2013 and 2019 at an urban medical center.

Participants

Of the 444 TMIs, 425 had pathology images analyzed by our deep-learning algorithm to extract breast tissue composition. A subset of 42/444 TMIs had mammography prior to surgery; mammography files were available for 25/42 TMIs and analyzed using a breast density software, LIBRA.

Main Outcomes and Measures

The first outcome was the association of duration of TT and breast tissue composition assessed by pathologists (categories of lobular atrophy and stromal composition) or by our algorithm (% epithelium, % fibrous stroma, and % fat). The second outcome is the association of TT and breast density as assessed by a radiologist (categorical variable) or by LIBRA (percent density, absolute dense area, and absolute non-dense area).

Results

Length of TT was associated with increasing degrees of lobular atrophy ( p <0.001) but not fibrous content ( p =0.821) when assessed by the pathologists. Every six months of TT was associated with decreased amounts of both epithelium (exp(β)=0.97, 95% CI 0.95-0.98, adj p =0.005) and stroma (exp(β)=0.99, 95% CI 0.98-1.00, adj p =0.051), but not fat (exp(β)=1.01, 95%CI 0.98-1.05, p =0.394) in fully adjusted models. There was no association between TT and radiologist's breast density assessment ( p =0.575) or LIBRA measurements ( p >0.05).

Conclusions

TT decreases breast epithelium and fibrous stroma, thus potentially reducing the breast cancer risk of TMIs. Further studies are warranted to elucidate the effect of TT on breast density and breast cancer risk.

Summary Box

Very little is known about the effect of gender-affirming testosterone therapy on cancer risks, such as breast cancer.Epidemiological studies had different conclusions about the association between testosterone and breast cancer in cisgender women (positive association) and trans masculine individuals (inverse association).More laboratory-based research are needed to understand the effect of testosterone on breast cancer risk in the understudied trans masculine population.Our study provides quantitative histological evidence to support prior epidemiological reports that testosterone may reduce breast cancer risk in trans masculine individuals.

Homologous Recombination Deficiency Landscape of Breast Cancers and Real-World Effectiveness of Poly ADP-Ribose Polymerase Inhibitors in Patients With Somatic BRCA1/2, Germline PALB2, or Homologous Recombination Deficiency Signature

PURPOSE

Poly ADP-ribose polymerase inhibitors (PARPi) are approved for patients with human epidermal growth factor receptor 2-negative metastatic breast cancer (mBC) and germline pathogenic/likely pathogenic variant (hereafter mutation) in the BRCA1/2 genes (gBRCA); however, clinical benefit has also been demonstrated in mBC with somatic BRCA1/2 mutations (sBRCA) or germline PALB2 mutations (gPALB2). This study aims to describe the genomic landscape of homologous recombination repair (HRR) gene alterations in mBC and assess PARPi treatment outcomes for patients with gBRCA compared with other HRR genes and by status of a novel homologous recombination deficiency signature (HRDsig).

METHODS

A real-world (RW) clinico-genomic database (CGDB) of comprehensive genomic profiling (CGP) linked to deidentified, electronic health record-derived clinical data was used. CGP was analyzed for HRR genes and HRDsig. The CGDB enabled cohort characterization and outcomes analyses of 177 patients exposed to PARPi. RW progression-free survival (rwPFS) and RW overall survival (rwOS) were compared.

RESULTS

Of 28,920 patients with mBC, gBRCA was detected in 3.4%, whereas the population with any BRCA alteration or gPALB2 increased to 9.5%. HRDsig+ represented 21% of patients with mBC. BRCA and gPALB2 had higher levels of biallelic loss and HRDsig+ than other HRR alterations. Outcomes on PARPi were assessed for 177 patients, and gBRCA and sBRCA/gPALB2 cohorts were similar: gBRCA versus sBRCA/gPALB2 rwPFS was 6.3 versus 5.4 months (hazard ratio [HR], 1.37 [0.77-2.43]); rwOS was 16.2 versus 21.2 months (HR, 1.45 [0.74-2.86]). Additionally, patients with HRDsig+ versus HRDsig- had longer rwPFS (6.3 v 2.8 months; HR, 0.62 [0.42-0.92]) and numerically longer rwOS (17.8 v 13.0 months; HR, 0.72 [0.46-1.14]).

CONCLUSION

Patients with sBRCA and gPALB2 derive similar benefit from PARPi as those with gBRCA alterations. In combination, HRDsig+, sBRCA, and gPALB2 represent an additional 19% of mBC that can potentially benefit from PARPi. Randomized trials exploring a more inclusive biomarker such as HRDsig are warranted.

Toker Cell Hyperplasia in the Nipple-Areolar Complex of Transmasculine Individuals

We previously reported breast histopathologic features associated with testosterone therapy in transmasculine chest-contouring surgical specimens. During that study, we observed a high frequency of intraepidermal glands in the nipple-areolar complex (NAC) formed by Toker cells. This study reports Toker cell hyperplasia (TCH)-the presence of clusters of Toker cells consisting of at least 3 contiguous cells and/or glands with lumen formation-in the transmasculine population. Increased numbers of singly dispersed Toker cells were not considered TCH. Among the 444 transmasculine individuals, 82 (18.5%) had a portion of their NAC excised and available for evaluation. We also reviewed the NACs from 55 cisgender women who were aged <50 years old and had full mastectomies. The proportion of transmasculine cases with TCH (20/82; 24.4%) was 1.7-fold higher than cisgender women (8/55; 14.5%) but did not achieve significance (P = .20). However, in cases with TCH, the rate of gland formation is 2.4-fold higher in transmasculine cases, achieving borderline significance (18/82 vs 5/55; P = .06). Among transmasculine individuals, TCH was significantly more likely to be present in those with higher body mass index (P = .03). A subset of 5 transmasculine and 5 cisgender cases were stained for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), androgen receptor (AR), cytokeratin 7, and Ki67. All 10 cases were cytokeratin 7+ and Ki67-; 9 out of 10 cases were AR+. Toker cells in transmasculine cases demonstrated variable expression of ER, PR, and HER2. For cisgender cases, Toker cells were consistently ER+, PR-, and HER2-. In conclusion, there is a higher rate of TCH in the transmasculine than cisgender population, particularly among transmasculine individuals with high body mass index and taking testosterone. To our knowledge, this is the first study to demonstrate that Toker cells are AR+. Toker cell features display variable ER, PR, and HER2 immunoreactivity. The clinical significance of TCH in the transmasculine population remains to be elucidated.

Abstract 6190: Polymerase theta inhibition activates the cGAS-STING pathway and cooperates with immune checkpoint blockade in BRCA-deficient cancers

Cancers deficient in homologous recombination (HR) repair secondary to mutations in genes such as BRCA1 or BRCA2, are dependent on alternative DNA damage response (DDR) pathways to maintain genomic integrity, rendering them susceptible to synthetic lethal targeting of these pathways. Recently, inhibitors of polymerase theta (POLθ, encoded by POLQ), the critical enzyme in microhomology-mediated end-joining (MMEJ), have been shown to be synthetic lethal with HR repair deficiency (Zhou et al. Nature Cancer 2021). Both HR and MMEJ require nucleolytic DNA end-resection to allow for DSB repair, and we have previously shown that MMEJ acts as a barrier to DNA end-resection at DSBs (Patterson-Fortin et al. Cancer Research 2022). Given the synthetic lethality between HR and MMEJ leads to unrestrained DNA end-resection generating chromosomal abnormalities and the release of nuclear DNA into the cytoplasm, we hypothesized that POLθ inhibition in HR-deficient cancers would activate the cGAS/STING innate immune response pathway and facilitate immunotherapy. To investigate the interactions of POLθ inhibition with the immune microenvironment in HR-deficient cancers, we used human cell lines and genetically modified mouse models representative of BRCA1-deficient triple-negative breast cancer (TNBC) and BRCA2-deficient pancreatic ductal adenocarcinoma (PDAC). Genetic or pharmacological inhibition of POLθ using novobiocin, a first-in-class inhibitor of the POLθ ATPase domain, induced significantly increased cytosolic dsDNA contained in micronuclei. This free DNA was sensed by the cytosolic DNA sensor cyclic GMP-AMP (cGAMP) synthetase (cGAS), increasing synthesis of cGAMP, in HR-deficient tumor cells but not in HR-proficient tumor cells. Increased cGAMP bound to and activated stimulator of interferon genes (STING), triggering phosphorylation of TBK1 and ultimately of IRF3. Activation of the cGAS/STING pathway by POLθ inhibition drove the expression of type I interferon response elements, including PD-L1. Depletion of STING by siRNA or by CRISPR abrogated this pro-inflammatory signaling and abolished the anti-tumor efficacy of novobiocin-mediated POLθ inhibition. Pharmacologic inhibition of POLθ enhanced Granzyme B+ CD8+ T-cell tumor infiltration. Importantly, antibody-mediated depletion of CD8+ T-cell severely compromised the anti-tumor efficacy of novobiocin-mediated POLθ inhibition, whereas anti-tumor activity of POLθ inhibition was augmented with the addition of either anti-PD-1 or anti-CTLA-4 antibodies. These results demonstrate that POLθ inhibition in HR-deficient cancers mediates a pro-inflammatory response in HR-deficient TNBC or PDAC tumor microenvironments, and that immune checkpoint blockade inhibition enhances the therapeutic efficacy of POLθ inhibition.

Citation Format: Jeffrey Patterson-Fortin, Heta Jadhav, Constantia Pantelidou, Tin Phan, Carter Grochala, Anita K. Mehta, Jennifer L. Guerriero, Gerburg M. Wulf, Brian M. Wolpin, Ben Z. Stanger, Andrew J. Aguirre, James M. Cleary, Alan D. D'Andrea, Geoffrey I. Shapiro. Polymerase theta inhibition activates the cGAS-STING pathway and cooperates with immune checkpoint blockade in BRCA-deficient cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6190.

Polymerase θ inhibition activates the cGAS-STING pathway and cooperates with immune checkpoint blockade in models of BRCA-deficient cancer

Recently developed inhibitors of polymerase theta (POLθ) have demonstrated synthetic lethality in BRCA-deficient tumor models. To examine the contribution of the immune microenvironment to antitumor efficacy, we characterized the effects of POLθ inhibition in immunocompetent models of BRCA1-deficient triple-negative breast cancer (TNBC) or BRCA2-deficient pancreatic ductal adenocarcinoma (PDAC). We demonstrate that genetic POLQ depletion or pharmacological POLθ inhibition induces both innate and adaptive immune responses in these models. POLθ inhibition resulted in increased micronuclei, cGAS/STING pathway activation, type I interferon gene expression, CD8⁺ T cell infiltration and activation, local paracrine activation of dendritic cells and upregulation of PD-L1 expression. Depletion of CD8⁺ T cells compromised the efficacy of POLθ inhibition, whereas antitumor effects were augmented in combination with anti-PD-1 immunotherapy. Collectively, our findings demonstrate that POLθ inhibition induces immune responses in a cGAS/STING-dependent manner and provide a rationale for combining POLθ inhibition with immune checkpoint blockade for the treatment of HR-deficient cancers.

Abstract P2-23-01: Patient-derived xenografts allow deconvolution of single agent and combination chemotherapy responses in triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) patients frequently receive combination chemotherapy treatment, but a direct comparison of response to carboplatin, docetaxel, and their combination in 50 TNBC patient-derived xenografts (PDXs) showed that combination treatment was largely ineffective at generating enhanced responses over the best single agent. This suggests de-escalation of chemotherapy may be possible if molecular mechanisms and biomarkers underlying response to individual treatments can be identified. To this end, we performed multi-omics profiling for the 50 TNBC PDXs. Methods: Orthotopic TNBC PDXs were treated with four weekly cycles of docetaxel, carboplatin, or the combination. Changes in tumor volume after 4 weeks of treatment were assessed quantitatively and by modified RECIST criteria. Genomic, transcriptomic, and mass-spectrometry-based proteomic profiling were performed on baseline tumors prior to treatments to identify associations with chemotherapy response at the gene and pathway level. ProMS was used to integrate both RNA and protein data to select a 5 RNA feature combination for optimized prediction of carboplatin response in a logistic regression model. Publicly available neoadjuvant chemotherapy clinical datasets with transcriptomic data and response information used for validation/testing included TNBC samples from: GSE18864, I-SPY2 (GSE194040), and BrighTNess (GSE164458). Results: Proteogenomic profiles revealed distinct genes associated with response to each agent and their combination, respectively, suggesting distinct molecular mechanisms underlying response to each treatment. A substantial number of genes associated with single agent and combination treatment were validated in multiple independent patient cohorts receiving platinum and taxane containing neoadjuvant therapy, confirming clinical relevance of our PDX panel. For the same treatment, different types of molecular data identified distinct sets of associated genes, providing highly complementary information. At the pathway level, RNA and protein data converged to metabolic and E2F/G2M related pathways which were upregulated in PDXs resistant or responsive to all treatment types, respectively, while variable levels of MYC-related proliferation pathways were observed across all treatments suggesting pathways that are common across and unique to different treatments. Several individual genes found to be higher in PDXs with better response to either single-agent had discriminatory power in external clinical TNBC datasets treated with similar neoadjuvant chemotherapy regimens. In addition, a logistic regression-based carboplatin response prediction model trained to select a group of 5 RNA markers (TKT, MAGI2, ATF6B, MCM7, LRP6) using both RNA and protein data performed the best in predicting response to cisplatin in a clinical TNBC dataset vs predicting response to other datasets with taxane and platinum + taxane combination containing chemotherapy regimens, demonstrating specificity of the prediction model. These results suggest potential individual biomarkers or biomarker combinations to select TNBC tumors that may respond to either single agent carboplatin, docetaxel, or their combination. PDXs refractory to all treatment arms had higher levels of proteostasis-related pathways including proteasome degradation and the unfolded protein response (UPR) related to endoplasmic reticulum stress and altered levels of chromatin regulation. Subsequent pharmacological targeting of the UPR pathway and targeting HDACs enhanced chemotherapy response. Conclusion: Proteogenomic characterization identifies molecular mechanisms and putative biomarkers for stratifying TNBC tumors for single or combination chemotherapy treatments, suggests targeted therapies to augment chemotherapy response, and provides a valuable resource for researchers and clinicians.

Citation Format: Jonathan T. Lei, Chen Huang, Ramakrishnan R. Srinivasan, Suhas Vasaikar, Lacey E. Dobrolecki, Alaina N. Lewis, Na Zhao, Jin Cao, Susan G. Hilsenbeck, C. Kent Osborne, Mothaffar Rimawi, Matthew J. Ellis, Varduhi Petrosyan, Alexander B. Saltzman, Anna Malovannaya, John D. Landua, Bo Wen, Antrix Jain, Gerburg M. Wulf, Shunqiang Li, Daniel C. Kraushaar, Tao Wang, Xi Chen, Gloria V. Echeverria, Meenakshi Anurag, Bing Zhang, Michael T. Lewis. Patient-derived xenografts allow deconvolution of single agent and combination chemotherapy responses in triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-23-01.

Reciprocal inhibition of PIN1 and APC/CCDH1 controls timely G1/S transition and creates therapeutic vulnerability

Cyclin-dependent kinases (CDKs) mediated phosphorylation inactivates the anaphase-promoting complex (APC/CCDH1), an E3 ubiquitin ligase that contains the co-activator CDH1, to promote G1/S transition. PIN1 is a phosphorylation-directed proline isomerase and a master cancer signaling regulator. However, little are known about APC/CCDH1 regulation after phosphorylation and about PIN1 ubiquitin ligases. Here we uncover a domain-oriented reciprocal inhibition that controls the timely G1/S transition: The non-phosphorylated APC/CCDH1 E3 ligase targets PIN1 for degradation in G1 phase, restraining G1/S transition; APC/CCDH1 itself, after phosphorylation by CDKs, is inactivated by PIN1-catalyzed isomerization, promoting G1/S transition. In cancer, PIN1 overexpression and APC/CCDH1 inactivation reinforce each other to promote uncontrolled proliferation and tumorigenesis. Importantly, combined PIN1- and CDK4/6-inhibition reactivates APC/CCDH1 resulting in PIN1 degradation and an insurmountable G1 arrest that translates into synergistic anti-tumor activity against triple-negative breast cancer in vivo. Reciprocal inhibition of PIN1 and APC/CCDH1 is a novel mechanism to control timely G1/S transition that can be harnessed for synergistic anti-cancer therapy.

Invasive Ductal Carcinoma of the Breast in a Transgender Man: A Case Report

There is limited literature about breast cancer in the transgender population. Very little is known about how gender-affirming hormone therapy affects their breast cancer risk. On the other end, for those diagnosed with breast cancer, there are no clinical guidelines to manage their breast cancer, specifically, how to manage their gender-affirming hormone therapy during breast cancer treatment. Here, we report a 52-year-old transman diagnosed with a grade 2 invasive ductal carcinoma (ER+/PR+/HER2-), and ductal carcinoma in situ (DCIS) of intermediate grade. We discussed his risk factors as well as treatment options.

Mutational Signature 3 Detected from Clinical Panel Sequencing is Associated with Responses to Olaparib in Breast and Ovarian Cancers

PURPOSE

The identification of patients with homologous recombination deficiency (HRD) beyond BRCA1/2 mutations is an urgent task, as they may benefit from PARP inhibitors. We have previously developed a method to detect mutational signature 3 (Sig3), termed SigMA, associated with HRD from clinical panel sequencing data, that is able to reliably detect HRD from the limited sequencing data derived from gene-focused panel sequencing.

EXPERIMENTAL DESIGN

We apply this method to patients from two independent datasets: (i) high-grade serous ovarian cancer and triple-negative breast cancer (TNBC) from a phase Ib trial of the PARP inhibitor olaparib in combination with the PI3K inhibitor buparlisib (BKM120; NCT01623349), and (ii) TNBC patients who received neoadjuvant olaparib in the phase II PETREMAC trial (NCT02624973).

RESULTS

We find that Sig3 as detected by SigMA is positively associated with improved progression-free survival and objective responses. In addition, comparison of Sig3 detection in panel and exome-sequencing data from the same patient samples demonstrated highly concordant results and superior performance in comparison with the genomic instability score.

CONCLUSIONS

Our analyses demonstrate that HRD can be detected reliably from panel-sequencing data that are obtained as part of routine clinical care, and that this approach can identify patients beyond those with germline BRCA1/2mut who might benefit from PARP inhibitors. Prospective clinical utility testing is warranted.

Phase Ib study of pembrolizumab in combination with trastuzumab emtansine for metastatic HER2-positive breast cancer

Background

Preclinical and clinical data support potential synergy between anti-HER2 therapy plus immune checkpoint blockade. The safety and tolerability of trastuzumab emtansine (T-DM1) combined with pembrolizumab is unknown.

Methods

This was a single-arm phase Ib trial (registration date January 26, 2017) of T-DM1 plus pembrolizumab in metastatic, human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Eligible patients had HER2-positive, metastatic breast cancer previously treated with taxane, trastuzumab, and pertuzumab, and were T-DM1-naïve. A dose de-escalation design was used, with a dose-finding cohort followed by an expansion cohort at the recommended phase 2 dose (RP2D), with mandatory baseline biopsies. The primary endpoint was safety and tolerability. Secondary endpoints included objective response rate (ORR) and progression-free survival (PFS). Immune biomarkers were assessed using histology, protein/RNA expression, and whole exome sequencing. Associations between immune biomarkers and treatment response, and biomarker changes before and during treatment, were explored.

Results

20 patients received protocol therapy. There were no dose-limiting toxicities. The RP2D was 3.6 mg/kg T-DM1 every 21 days plus 200 mg pembrolizumab every 21 days. 85% of patients experienced treatment-related adverse events (AEs) ≥grade 2, 20% of patients experienced grade 3 AEs, and no patients experienced grade >4 AEs. Four patients (20%) experienced pneumonitis (three grade 2 events; one grade 3 event). ORR was 20% (95% CI 5.7% to 43.7%), and median PFS was 9.6 months (95% CI 2.8 to 16.0 months). Programmed cell death ligand-1 and tumor infiltrating lymphocytes did not correlate with response in this small cohort.

Conclusions

T-DM1 plus pembrolizumab was a safe and tolerable regimen. Ongoing trials will define if there is a role for checkpoint inhibition in the management of HER2-positive metastatic breast cancer.

Trial registration number

NCT03032107.

STING agonism enhances anti-tumor immune responses and therapeutic efficacy of PARP inhibition in BRCA-associated breast cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors exert their efficacy via synthetic lethal effects and by inducing cGAS/STING-mediated immune responses. We demonstrate that compared to monotherapies, combined PARP inhibition and STING agonism results in increased STING pathway activation, greater cytotoxic T-cell recruitment and enhanced dendritic cell activation in BRCA1-deficient breast cancer models. The combination markedly improved anti-tumor efficacy in vivo, with evidence of complete tumor clearance, prolongation of survival and induction of immunologic memory.

A phase I/II trial evaluating the safety and efficacy of eribulin in combination with copanlisib in patients with metastatic triple-negative breast cancer (TNBC)

TPS1128

Background: Metastatic (met) TNBC remains a clinical challenge with limited treatment options and inevitable chemoresistance. Aberrant PI3K pathway signaling is frequently observed in TNBC. Increasing evidence shows PI3K pathway activation maintains the stemness and chemoresistance of BC stem cells (CSCs), and PI3K inhibition sensitizes CSCs to chemotherapy (chemo). Eribulin (E), a non-taxane microtubule dynamics inhibitor, showed survival benefit in met HER2 negative BC. Preclinically, E impacts tumor vascular remodeling, inhibits epithelial-to-mesenchymal transition and metastasis – key mechanisms implicated in PI3K inhibition resistance. Copanlisib (C), a potent pan-class I PI3K inhibitor ( i), improved anti-tumor effect in E-sensitive and resistant TNBC patient-derived xenograft models, irrespective of PIK3CA/PTEN mutation (mut) status, when combined with E. This phase I/II study is aimed to determine the safety and efficacy of E+C in pts with met TNBC. Methods: This trial includes a phase I portion with the primary objective to determine the dose limiting toxicity (DLT) and recommended phase 2 dose (RP2D) of E+C, followed by a phase II randomized portion of E+C (at RP2D) versus ( vs) E with the primary objective of progression-free survival (PFS). Key secondary objectives include objective response rate (ORR) and clinical benefit rate (CBR) [phase I]; and ORR and CBR, by arm and by PIK3CA/PTEN mut status and assessment of treatment induced target engagement [phase II]. Key exploratory objectives include analysis of genomic, proteomic and metabolomic changes as potential response biomarkers in tumor tissue and blood. Key eligibility criteria include pts with: met TNBC who progressed on ≤5 chemo lines, including anthracycline/taxane (unless contraindicated), ECOG 0-1, adequate organ function and known archival tumor PIK3CA/PTEN mut status. Key exclusions: prior E or PI3K/mTOR/AKT i, grade ≥2 neuropathy, tumor AKT mut, congenital QT prolongation, and uncontrolled diabetes or hypertension. Phase I portion will follow a 3+3 design for E+C dose escalation to enroll 18 max pts, starting at E 1.1 mg/m2 IV and C 45 mg IV on days (D) 1/8 of 21-D cycle (C) (to E 1.4 mg/m2 and C 60 mg max). RP2D will be defined as the highest dose level at which at most 1 of 6 pts experience DLT during C1. 88 pts will be randomized (1:1) in the phase II portion to E+C vs E (1.4 mg/m2 D 1/8), stratified by PTEN/PIK3CA mut status. Response assessment by Response Evaluation Criteria in solid tumors (RECIST) v1.1 will occur every 9 weeks (+/-7 D). Tumor biopsy is required at baseline and C2D1-2, and optional at progression. A sample size of 88 achieves 80% power to detect PFS difference of median PFS 6.95 vs 4 months (corresponding to a hazard ratio of 0.5755) between the 2 arms, based on 1-sided two-sample log rank test at 0.1 α level. The phase I study is actively enrolling pts. Clinical trial information: NCT04345913.

Phase 1b Clinical Trial with Alpelisib plus Olaparib for Patients with Advanced Triple-Negative Breast Cancer

PURPOSE

We had previously reported on the safety and the recommended phase 2 dose (RP2D) of olaparib in combination with the PI3Kα-specific inhibitor alpelisib in patients with high-grade serous ovarian cancer as studied in a phase 1b trial (NCT01623349). Here we report on the breast cancer cohort from that study.

EXPERIMENTAL DESIGN

Eligible patients had recurrent triple-negative breast cancer (TNBC), or recurrent breast cancer of any subtype with a germline BRCA mutation and were enrolled to a dose escalation or expansion cohort. After definition of the RP2D, secondary end points included safety and objective response rate (ORR). Exploratory analyses were performed using circulating free DNA (cfDNA).

RESULTS

17 patients with TNBC were enrolled with a median of 3 prior lines of chemotherapy. The most common treatment-related grade 3-4 adverse events were hyperglycemia (18%) and rash (12%). The ORR was 18% (23% for patients treated at the RP2D) and 59% had disease control. The median duration of response was 7.4 months. Analysis of cfDNA tumor fractions (TFx) revealed that patients with TFx<15% after completion of the first cycle had a longer progression-free survival compared to those with TFx>15% (6.0 months vs 0.9 months, p=0.0001).

CONCLUSIONS

Alpelisib in combination with olaparib is tolerable in patients with pre-treated TNBC, with evidence of activity in non-BRCA carriers. CfDNA provided important prognostic information. Results highlight potential synergistic use of a PI3Ki to sensitize HR-proficient (BRCA wild-type) TNBC to PARPi and suggest the potential to expand the use of PARPi beyond BRCA-mutant tumors.

WWP1 inactivation enhances efficacy of PI3K inhibitors while suppressing their toxicities in breast cancer models

Activation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway is a pervasive event in tumorigenesis due to PI3K mutation and dysfunction of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Pharmacological inhibition of PI3K has resulted in variable clinical outcomes, however, raising questions regarding the possible mechanisms of unresponsiveness and resistance to treatment. WWP1 is an oncogenic HECT-type ubiquitin E3 ligase frequently amplified and mutated in multiple cancers, as well as in the germ lines of patients predisposed to cancer, and was recently found to activate PI3K signaling through PTEN inactivation. Here, we demonstrate that PTEN dissociated from the plasma membrane upon treatment with PI3K inhibitors through WWP1 activation, whereas WWP1 genetic or pharmacological inhibition restored PTEN membrane localization, synergizing with PI3K inhibitors to suppress tumor growth both in vitro and in vivo. Furthermore, we demonstrate that WWP1 inhibition attenuated hyperglycemia and the consequent insulin feedback, which is a major tumor-promoting side effect of PI3K inhibitors. Mechanistically, we found that AMPKα2 was ubiquitinated and, in turn, inhibited in its activatory phosphorylation by WWP1, whereas WWP1 inhibition facilitated AMPKα2 activity in the muscle to compensate for the reduction in glucose uptake observed upon PI3K inhibition. Thus, our identification of the cell-autonomous and systemic roles of WWP1 inhibition expands the therapeutic potential of PI3K inhibitors and reveals new avenues of combination cancer therapy.

Targeting Pin1 renders pancreatic cancer eradicable by synergizing with immunochemotherapy

Pancreatic ductal adenocarcinoma (PDAC) is characterized by notorious resistance to current therapies attributed to inherent tumor heterogeneity and highly desmoplastic and immunosuppressive tumor microenvironment (TME). Unique proline isomerase Pin1 regulates multiple cancer pathways, but its role in the TME and cancer immunotherapy is unknown. Here, we find that Pin1 is overexpressed both in cancer cells and cancer-associated fibroblasts (CAFs) and correlates with poor survival in PDAC patients. Targeting Pin1 using clinically available drugs induces complete elimination or sustained remissions of aggressive PDAC by synergizing with anti-PD-1 and gemcitabine in diverse model systems. Mechanistically, Pin1 drives the desmoplastic and immunosuppressive TME by acting on CAFs and induces lysosomal degradation of the PD-1 ligand PD-L1 and the gemcitabine transporter ENT1 in cancer cells, besides activating multiple cancer pathways. Thus, Pin1 inhibition simultaneously blocks multiple cancer pathways, disrupts the desmoplastic and immunosuppressive TME, and upregulates PD-L1 and ENT1, rendering PDAC eradicable by immunochemotherapy.

Visualizing the effects of lactate dehydrogenase (LDH) inhibition and LDH-A genetic ablation in breast and lung cancer with hyperpolarized pyruvate NMR

In many tumors, cancer cells take up large quantities of glucose and metabolize it into lactate, even in the presence of sufficient oxygen to support oxidative metabolism. It has been hypothesized that this malignant metabolic phenotype supports cancer growth and metastasis, and that reversal of this so-called "Warburg effect" may selectively harm cancer cells. Conversion of glucose to lactate can be reduced by ablation or inhibition of lactate dehydrogenase (LDH), the enzyme responsible for conversion of pyruvate to lactate at the endpoint of glycolysis. Recently developed inhibitors of LDH provide new opportunities to investigate the role of this metabolic pathway in cancer. Here we show that magnetic resonance spectroscopic imaging of hyperpolarized pyruvate and its metabolites in models of breast and lung cancer reveal that inhibition of LDH was readily visualized through reduction in label exchange between pyruvate and lactate, while genetic ablation of the LDH-A isoform alone had smaller effects. During the acute phase of LDH inhibition in breast cancer, no discernible bicarbonate signal was observed and small signals from alanine were unchanged.

Abstract 156: Mutational signature 3 predicts responses to olaparib plus buparlisib in triple-negative breast cancer and high-grade serous ovarian cancer

Background: Poly (ADP-ribose) polymerase (PARP) inhibitors target cancers with homologous recombination deficiency (HRD). Preclinical data showed PI3K inhibitors impair homologous recombination (HR) pathways; exposure may sensitize HR-proficient cancers to PARP inhibition. Single-base substitution mutational signature 3 (Sig3) is strongly associated with HRD. We report correlative analysis of Sig3 as predictor of response from a Phase Ib trial of the PARP inhibitor olaparib in combination with the PI3K inhibitor buparlisib (BKM120) in patients (pts) with advanced high-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC).

Methods The parent trial (NCT01623349) is a multicenter phase 1b trial of escalating doses of olaparib and buparlisib. Eligible pts enrolled in the trial carried a diagnosis of advanced TNBC, HGSOC, or recurrent breast cancer of any histology with a germline BRCA1 or BRCA2 (BRCA1/2) mutation. Archival tumor tissue was available from 39 pts, and was analyzed by panel sequencing and whole-exome sequencing (WES). A score for the Sig3 was calculated from panel sequencing data and WES using SigMA. Genomic Instability Score (GIS) based on copy-number variation (CNV) were also calculated from WES data using scarHRD. Survival analyses and Cox regression were performed.Results: Our cohort comprised 39 pts (28 pts with HGSOC and 11 pts with TNBC). The median age was 58 years (range 34 - 78). Pts with Sig3+ tumors had a progression-free survival (PFS) of 7.7 months vs 5.6 months for those with Sig3- tumors (log-rank test; p = 0.036). CNV+ group did not differ significantly from CNV- group (log-rank test; p = 0.18). Even though Sig3 identified the majority of cancers with BRCA1/2 mutations (18/24), the PFS for pts with BRCA1/2 mutations was not statistically different from those with BRCA wild type tumors (log-rank test; p = 0.15). In our Cox regression model, Sig3+ had a significant positive impact on PFS (HR 0.27, CI 0.092 - 0.77, p = 0.015) while GIS did not (HR 0.41, CI 0.13 - 1.3, p = 0.14). We tested the influence of copy number alterations of genes associated with PARPi resistance on PFS, and identified ATR amplification as a feature of PARPi resistance (HR 4.48, p = 0.002).Conclusions: Within a trial that combined the PARP inhibitor olaparib and the PI3K inhibitor BKM120 in advanced ovarian and breast cancer, Sig3 positivity from panel sequencing data was associated with longer PFS while the CNV-based HRD prediction score (i.e. GIS) from WES was not. SigMA identified Sig3 from readily-available clinical sequencing as a candidate biomarker to refine patient selection for therapy with PARP inhibitors. Mutational signatures may improve HRD identification compared to a selection solely based on the mutation status of BRCA1/2 genes. Clinical utility should be explored in the setting of a confirmatory clinical trial.

Citation Format: Felipe Batalini, Doga Gulhan, Victor Mao, Madeline Polak, Eric P. Winer, Erica L. Mayer, Ursula A. Matulonis, Panagiotis A. Konstantinopoulos, Peter Park, Gerburg M. Wulf. Mutational signature 3 predicts responses to olaparib plus buparlisib in triple-negative breast cancer and high-grade serous ovarian 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 156.

Analysis of real-world (RW) data for metastatic breast cancer (mBC) patients (pts) with somatic BRCA1/2 (sBRCA) or other homologous recombination (HR)-pathway gene mutations (muts) treated with PARP inhibitors (PARPi)

10512

Background: PARPi are approved for treatment of pts w/ HER2-negative mBC and germline BRCA1/2 (g BRCA) pathogenic or likely pathogenic variants (muts); however, clinical benefit has also been demonstrated in mBC pts w/ sBRCA or other HR-pathway gene muts. Using a RW Clinico-Genomic Database (CGDB), we assessed outcomes for pts w/ gBRCA muts compared to pts w/ either s BRCA or other HR-pathway muts treated w/ PARPi. Methods: 6,329 mBC pts from ̃280 US cancer clinics were included in the Flatiron Health (FH) -Foundation Medicine (FM) CGDB, which includes comprehensive genomic profiling (CGP) linked to de-identified, electronic health record (EHR)-derived clinical data. Eligible pts had mBC, received care in the FH network from 1/1/2011-9/1/2020, and had tissue CGP by FM. Pts classified as gBRCA: positive germline result in EHR and BRCA mut predicted germline per FM’s somatic, germline, zygosity algorithm (SGZ) (Sun et al PMID 29415044). Non-g BRCA: negative germline results in EHR and a somatic BRCA (s BRCA) mut per SGZ or BRCA wild-type w/ another HR mut per CGP result. Pts w/o a documented gBRCA result in EHR, unknown FM BRCA SGZ result, or conflicting results were excluded. RW overall survival (rwOS) and RW progression-free survival (rwPFS) from start of PARPi for pts w/ gBRCA and non- gBRCA mBC were compared using Kaplan-Meier analysis and Cox regression adjusted for mBC line number, prior platinum, age at PARPi initiation, race, and receptor status. Results: Among pts who received PARPi in the mBC setting, 44 had gBRCA and 18 had non -gBRCA: 9 s BRCA (5 BRCA1, 4 BRCA2), 4 PALB2, 2 ATM, and 1 each of ATM+CDK12, BARD1+FANCF+RAD54L, and CHEK2. Of HR muts 76% were confirmed biallelic: 33/44 gBRCA (11 unknown), 8/9 sBRCA, 3/4 PALB2, and 3/5 other (1 unknown). Neither median rwPFS nor rwOS from start of PARPi were significantly different between the non-g BRCA and g BRCA cohorts (rwPFS: 7.0 [4.6-11.3] vs 5.5 [4.3-7.2] months (mos), aHR: 1.19 [0.57 – 2.43]; rwOS: 15.0 [7.95-16.3] vs 11.5 [9.46-NA] mos, aHR: 0.85 [0.36-1.98]). For 9 pts w/ sBRCA mut, median rwPFS was 7.1 mos (range 1.4-12.4) and all pts had progressed by data cut off. Conclusions: Despite small pt numbers and limitations from RW data, our results suggest that pts w/ biallelic non-g BRCA mBC may derive similar benefit from PARPi when tumor CGP detects a s BRCA mut or germline or somatic mut in other HR-pathway genes. These findings are consistent w/ the results from TBCRC-048 (Tung et al PMID 33119476) and support further randomized trials exploring the efficacy of PARPi in this population.[Table: see text]

Phase II Single-Arm Study to Assess Trastuzumab and Vinorelbine in Advanced Breast Cancer Patients With HER2-Negative Tumors and HER2-Positive Circulating Tumor Cells

PURPOSE

Human epidermal growth factor receptor 2 (HER2)-directed treatments improve outcomes for patients with HER2-positive metastatic breast cancer (MBC). Current identification of patients with HER2-positive disease relies on tumor tissue testing, which can be inaccurate because of tumor heterogeneity or tumor evolution. Circulating tumor cells (CTCs) are often present in patients with cancer. We hypothesized that HER2 assessment of CTCs in patients with HER2-negative breast cancer could identify a subset of patients with HER2-positive CTCs who could benefit from HER2-directed treatments.

METHODS

This was a single-arm, two-stage, phase II trial. Patients with HER2-negative progressive MBC with HER2-positive CTC (defined as HER2/CEP17 ratio ≥ 2.0 by fluorescence in situ hybridization), ≥ 1 prior chemotherapy regimen for MBC, and no prior vinorelbine received trastuzumab in combination with vinorelbine on days 1, 8, and 15 of a 21-day cycle. The primary end point was objective response rate.

RESULTS

From January 2013 to June 2014, we prospectively screened CTCs from patients with HER2-negative MBC. CTCs were detected in 201 of 311 patients (65%). The median number of CTCs was 10 (interquartile range, 3-57). Sixty-nine of 311 patients (22%) had HER2+ CTCs, with a median of three HER2+ CTCs (range 1-21). Twenty patients with HER2+ CTCs were treated on study. At data cutoff (January 13, 2017), no patients remained on study therapy. The objective response rate was 5% (95% CI, 0.1 to 24.9), with one of 20 patients experiencing a partial response. The clinical benefit rate was 20.0% (1 partial response and 3 stable diseases > 24 weeks, 95% CI, 5.7% to 43.7%). The median progression-free survival was 2.7 months.

CONCLUSION

CTC analysis of patients with HER2-negative MBC identifies a subset with HER2-amplified CTCs. However, clinical activity of an HER2-directed regimen in this population was low. The functional significance of HER2-positive CTCs remains uncertain.

Blockade of 6-phosphogluconate dehydrogenase generates CD8+ effector T cells with enhanced anti-tumor function

Although T cell expansion depends on glycolysis, T effector cell differentiation requires signaling via the production of reactive oxygen species (ROS). Because the pentose phosphate pathway (PPP) regulates ROS by generating nicotinamide adenine dinucleotide phosphate (NADPH), we examined how PPP blockade affects T cell differentiation and function. Here, we show that genetic ablation or pharmacologic inhibition of the PPP enzyme 6-phosphogluconate dehydrogenase (6PGD) in the oxidative PPP results in the generation of superior CD8+ T effector cells. These cells have gene signatures and immunogenic markers of effector phenotype and show potent anti-tumor functions both in vitro and in vivo. In these cells, metabolic reprogramming occurs along with increased mitochondrial ROS and activated antioxidation machinery to balance ROS production against oxidative damage. Our findings reveal a role of 6PGD as a checkpoint for T cell effector differentiation/survival and evidence for 6PGD as an attractive metabolic target to improve tumor immunotherapy.

Testosterone therapy and breast histopathological features in transgender individuals

Testosterone therapy (TT) is administered to enhance masculinization in transgender individuals. The long-term effect of exogenous testosterone on breast tissues remains unclear. Our study evaluated the modulation of breast morphology by TT in transgender individuals with special attention to duration of TT. We reviewed 447 breast surgical specimens from gender affirming chest-contouring surgery, and compared histopathological findings including degree of lobular atrophy, and atypical and non-atypical proliferations between subjects who did (n = 367) and did not (n = 79) receive TT. TT for one patient was unknown. TT for >12 months was associated with seven histopathological features. Longer duration of TT was significantly associated with higher degrees of lobular atrophy (p < 0.001). This relationship remained significant after accounting for age at surgery, ethnicity, body mass index, and presurgical oophorectomy (adjusted p < 0.001). Four types of lesions were more likely to be absent in breast tissues exposed to longer durations of TT: cysts (median = 16.2 months; p < 0.01; adjusted p = 0.01), fibroadenoma (median = 14.8 months; p = 0.02; adjusted p = 0.07), pseudoangiomatous stromal hyperplasia (median = 17.0 months; p < 0.001; adjusted p < 0.001), and papillomas (median = 14.7 months; p = 0.04; adjusted p = 0.20). Columnar cell change and mild inflammation were also less likely to occur in subjects receiving TT (p < 0.05), but were not linked to the duration of TT. Atypia and ductal carcinoma in situ were detected in 11 subjects (2.5%) all of whom received TT ranging from 10.1 to 64.1 months. The incidental findings of high-risk lesions and carcinoma as well as the risk of cancer in residual breast tissue after chest-contouring surgery warrant the consideration of culturally sensitive routine breast cancer screening protocols for transgender men and masculine-centered gender nonconforming individuals. Long-term follow-up studies and molecular investigations are needed to understand the breast cancer risk of transgender individuals who receive TT.

Not Black or White but Shades of Gray: Homologous Recombination Deficiency as a Continuous Variable Modulated by RNF168

In this issue of Cancer Research, the study by Krais and colleagues underscores that DNA damage repair by homologous recombination (HR) is not an all-or-nothing phenomenon, but that HR competency comes on a spectrum, ranging from complete deficiency to proficiency. Residual low-level HR in BRCA1-mutant cancer cells turns out to be critically important for their survival and is afforded by low levels of Histone 2A (H2A) ubiquitination resulting from lowered RNF168 levels. The findings raise the possibility that, if ubiquitination of H2A could be enforced by inhibition of deubiquitinases, residual HR in BRCA1mt cells might be extinguished. Extinction of residual HR might improve the therapeutic efficacy of the emerging inhibitors of DNA damage repair. The development of methods to measure HR directly and quantitatively is crucial to develop this field.See related article by Krais et al., p. 2848.

TBCRC 048: Phase II Study of Olaparib for Metastatic Breast Cancer and Mutations in Homologous Recombination-Related Genes

PURPOSE

Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi), is approved for the treatment of human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC) in germline (g)BRCA1/2 mutation carriers. Olaparib Expanded, an investigator-initiated, phase II study, assessed olaparib response in patients with MBC with somatic (s)BRCA1/2 mutations or g/s mutations in homologous recombination (HR)-related genes other than BRCA1/2.

METHODS

Eligible patients had MBC with measurable disease and germline mutations in non-BRCA1/2 HR-related genes (cohort 1) or somatic mutations in these genes or BRCA1/2 (cohort 2). Prior PARPi, platinum-refractory disease, or progression on more than two chemotherapy regimens (metastatic setting) was not allowed. Patients received olaparib 300 mg orally twice a day until progression. A single-arm, two-stage design was used. The primary endpoint was objective response rate (ORR); the null hypothesis (≤ 5% ORR) would be rejected within each cohort if there were four or more responses in 27 patients. Secondary endpoints included clinical benefit rate and progression-free survival (PFS).

RESULTS

Fifty-four patients enrolled. Seventy-six percent had estrogen receptor-positive HER2-negative disease. Eighty-seven percent had mutations in PALB2, sBRCA1/2, ATM, or CHEK2. In cohort 1, ORR was 33% (90% CI, 19% to 51%) and in cohort 2, 31% (90% CI, 15% to 49%). Confirmed responses were seen only with gPALB2 (ORR, 82%) and sBRCA1/2 (ORR, 50%) mutations. Median PFS was 13.3 months (90% CI, 12 months to not available/computable [NA]) for gPALB2 and 6.3 months (90% CI, 4.4 months to NA) for sBRCA1/2 mutation carriers. No responses were observed with ATM or CHEK2 mutations alone.

CONCLUSION

PARP inhibition is an effective treatment for patients with MBC and gPALB2 or sBRCA1/2 mutations, significantly expanding the population of patients with breast cancer likely to benefit from PARPi beyond gBRCA1/2 mutation carriers. These results emphasize the value of molecular characterization for treatment decisions in MBC.

The INPP4B Tumor Suppressor Modulates EGFR Trafficking and Promotes Triple-Negative Breast Cancer

Inactivation of the tumor suppressor lipid phosphatase INPP4B is common in triple-negative breast cancer (TNBC). We generated a genetically engineered TNBC mouse model deficient in INPP4B. We found a dose-dependent increase in tumor incidence in INPP4B homozygous and heterozygous knockout mice compared with wild-type (WT), supporting a role for INPP4B as a tumor suppressor in TNBC. Tumors derived from INPP4B knockout mice are enriched for AKT and MEK gene signatures. Consequently, mice with INPP4B deficiency are more sensitive to PI3K or MEK inhibitors compared with WT mice. Mechanistically, we found that INPP4B deficiency increases PI(3,4)P₂ levels in endocytic vesicles but not at the plasma membrane. Moreover, INPP4B loss delays degradation of EGFR and MET, while promoting recycling of receptor tyrosine kinases (RTK), thus enhancing the duration and amplitude of signaling output upon growth factor stimulation. Therefore, INPP4B inactivation in TNBC promotes tumorigenesis by modulating RTK recycling and signaling duration. SIGNIFICANCE: Inactivation of the lipid phosphatase INPP4B is frequent in TNBC. Using a genetically engineered mouse model, we show that INPP4B functions as a tumor suppressor in TNBC. INPP4B regulates RTK trafficking and degradation, such that loss of INPP4B prolongs both PI3K and ERK activation.This article is highlighted in the In This Issue feature, p. 1079.

Trial in progress: A phase II open-label, randomized study of PARP inhibition (olaparib) either alone or in combination with anti-PD-L1 therapy (atezolizumab) in homologous DNA repair (HDR) deficient, locally advanced or metastatic non-HER2-positive breast cancer

TPS1102

Background: While immunostimulatory therapies have shown great success, a major challenge remains identification of mechanisms to effectively treat the majority of patients with so-called "non-inflamed" tumors lacking marked lymphocyte infiltration and PD-L1 expression. The DNA repair proficiency of a tumor may impact its potential for immune recognition and sensitivity to immune checkpoint blockade. Preclinically, PARP inhibition in HDR-deficient tumors has been shown to trigger antitumor immunity through a STING-dependent antitumor immune response. Effects of PARP inhibitors were augmented when combined with PD-1 blockade. We hypothesize that enhanced DNA damage and cell death induced by PARP inhibition in tumors with homology directed repair (HDR) deficiency will enhance adaptive anti-tumor immune responses and increase sensitivity to PD-1 axis blockers. Methods: This is a randomized, open-label phase II clinical trial exploring the PARP inhibitor olaparib either alone or in combination with the anti-PD-L1 human monoclonal antibody atezolizumab in BRCA1/2 mutated locally advanced or metastatic non-HER2-positive breast cancer. HDR deficiency is defined as the presence of deleterious BRCA 1/2 mutations. Randomization occurs in a 1:1 fashion to two arms: (1) olaparib 300 mg PO bid continuously in 21-day cycles or (2) olaparib 300 mg PO bid continuously in combination with atezolizumab 1200 IV every 3 weeks in 21-day cycles. Patients undergo baseline evaluations and pre-treatment biopsy within 2 weeks of starting therapy. Repeat biopsies are required at the time of first tumor assessment scan (6 weeks from the start of treatment) and in the event of disease progression. Correlative studies, including detailed analysis of the genomic profile and tumor immune contexture, will be performed at each biopsy time point. The primary objective is to compare progression free survival between the study arms. If progression occurs on the olaparib monotherapy arm, cross-over to the combination arm is allowed. This study began enrolling in August 2018; 47 of the planned 72 patients have been registered. Clinical trial information: NCT02849496 .

TBCRC 048: A phase II study of olaparib monotherapy in metastatic breast cancer patients with germline or somatic mutations in DNA damage response (DDR) pathway genes (Olaparib Expanded)

1002

Background: Olaparib, a PARP inhibitor, is approved for HER2-negative MBC in g BRCA1/2 mutation carriers. Olaparib Expanded, an investigator-initiated study, assessed the response to olaparib in MBC patients with sBRCA1/2 mutations or g/s mutations in DDR-pathway genes other than BRCA1/2. Methods: Eligibility included: MBC with measurable disease; progression on < 2 metastatic chemotherapy regimens. Prior PARP inhibitor or progression on platinum was not allowed. Cohort 1 included patients with germline mutations in non- BRCA1/2 DDR-pathway genes. In Cohort 2 were those with somatic mutations in these genes or BRCA1/2; germline testing was required only to exclude a gBRCA mutation if a s BRCA mutation was present. Patients received olaparib 300 mg bid until progression or unacceptable toxicity. For each cohort, a single-arm Simon two-stage design was used with 13 then 14 patients in the 1st and 2nd stages, respectively. The null hypothesis within each cohort [≤ 5% objective response rate (ORR)] would be rejected if > 4 responses were seen at the end of stage 2. Secondary endpoints include clinical benefit rate, progression-free survival, and duration of response. Results: 54 patients enrolled from March 2018 to Jan 2020; 1 ineligible s BRCA2 was excluded. Median age was 59 yrs (range: 30-87). 40 patients had ER+ HER2-, 3 HER2+, and 10 TNBC. 87% had a mutation in PALB2, s BRCA1/2, ATM or CHEK2. ORR was 29.6% (8/27, 90%-CI: 15.6%-47.1%) in Cohort 1 and 38.5% (10/26, 90%-CI: 22.5%-56.4%) in Cohort 2. Responses were gene specific (Table): g PALB2 and s BRCA mutations predicted response; no responses were seen with only a CHEK2 or ATM mutation. To date, responses as long as 16.4 months have been observed. Responses were seen in all subtypes: 5/10 TNBC, 1/3 HER2+, 12/40 ER+ HER2-. 11 responses occurred after prior CDK4/6 inhibitor. In June 2020, final data for confirmed ORR and secondary endpoints will be reported. Conclusion: In this proof-of-principle study, single-agent olaparib successfully met its primary endpoint in both cohorts. Activity was seen largely in patients with MBC and s BRCA1/2 or g PALB2 mutations but not with ATM or CHEK2 mutations. Clinical trial information: NCT03344965 . [Table: see text]

A phase Ib study of pembrolizumab (pembro) plus trastuzumab emtansine (T-DM1) for metastatic HER2+ breast cancer (MBC)

1046

Background: Preclinical evidence suggests treatment (tx) with T-DM1 plus an anti-PD1 antibody triggers antitumor immunity. We conducted a phase 1 trial to determine the safety and explore the efficacy of T-DM1 plus pembro. Methods: Eligible patients (pts) had MBC previously treated with trastuzumab (H) and taxane (T), were T-DM1-naïve, and received >1 prior line of tx for MBC or developed recurrence within 6 months (mo) of adjuvant tx. A dose de-escalation (esc) design was used with 6 pts in the dose-finding cohort, followed by an expansion (exp) cohort at the recommended phase 2 dose (RP2D), with mandatory baseline biopsies (bx). The primary endpoint was safety and tolerability. Secondary endpoints included objective response rate (ORR), progression-free survival (PFS), and clinical benefit rate (CBR: complete response + partial response + stable disease >24 weeks). Associations between immune biomarkers and tx response were explored. Results: 20 pts started protocol tx (6 in dose de-esc cohort; 14 in exp cohort). Median follow-up was 23.5 mo. Pts had median age 54 yrs and median 1 line of prior MBC tx (range 0-2); 100% had received prior T, H, and pertuzumab. There were no dose-limiting toxicities in the dose de-esc cohort; thus full doses of T-DM1 (3.6 mg/kg q21 days) and pembro (200 mg q21 days) were the RP2D. 85% of pts experienced tx-related adverse events (AEs) > grade (gr) 1; 20% of pts experienced gr3 AEs. There were no gr>4 AEs. Gr3 AEs were fatigue; AST increase; ALT increase; pneumonia; pneumonitis; oral mucositis; and vomiting, each in 1 pt. 17 pts had baseline bx; 6 pts had repeat bx after 1 tx cycle. Efficacy results, overall and by PD-L1 Combined Positive Score (CPS; 22C3 staining) and tumor-infiltrating lymphocyte (TIL) status, are shown in the table. Tumors’ antigen presentation will be explored through HLA/dendritic cell marker staining and immune signatures by RNA sequencing. Conclusions: T-DM1 plus pembro was safe and tolerable. The regimen demonstrated clinical activity. Further exploration of immune-related predictive biomarkers is warranted. Clinical trial information: NCT03032107 . [Table: see text]

Inactivation of the Prolyl Isomerase Pin1 Sensitizes BRCA1-Proficient Breast Cancer to PARP Inhibition

PARP inhibitor monotherapies are effective to treat patients with breast, ovary, prostate, and pancreatic cancer with BRCA1 mutations, but not to the much more frequent BRCA wild-type cancers. Searching for strategies that would extend the use of PARP inhibitors to BRCA1-proficient tumors, we found that the stability of BRCA1 protein following ionizing radiation (IR) is maintained by postphosphorylational prolyl-isomerization adjacent to Ser1191 of BRCA1, catalyzed by prolyl-isomerase Pin1. Extinction of Pin1 decreased homologous recombination (HR) to the level of BRCA1-deficient cells. Pin1 stabilizes BRCA1 by preventing ubiquitination of Lys1037 of BRCA1. Loss of Pin1, or introduction of a BRCA1-mutant refractory to Pin1 binding, decreased the ability of BRCA1 to localize to repair foci and augmented IR-induced DNA damage. In vitro growth of HR-proficient breast, prostate, and pancreatic cancer cells were modestly repressed by olaparib or Pin1 inhibition using all-trans retinoic acid (ATRA), while combination treatment resulted in near-complete block of cell proliferation. In MDA-MB-231 xenografts and triple-negative breast cancer patient-derived xenografts, either loss of Pin1 or ATRA treatment reduced BRCA1 expression and sensitized breast tumors to olaparib. Together, our study reveals that Pin1 inhibition, with clinical widely used ATRA, acts as an effective HR disrupter that sensitizes BRCA1-proficient tumors to PARP inhibition. SIGNIFICANCE: PARP inhibitors have been limited to treat homologous recombination-deficient tumors. All-trans retinoic acid, by inhibiting Pin1 and destabilizing BRCA1, extends benefit of PARP inhibitors to patients with homologous recombination-proficient tumors.See related commentary by Cai, p. 2977.

An immune-centric exploration of BRCA1 and BRCA2 germline mutation related breast and ovarian cancers

Background

BRCA1/2 germline mutation related cancers are candidates for new immune therapeutic interventions. This study was a hypothesis generating exploration of genomic data collected at diagnosis for 19 patients. The prominent tumor mutation burden (TMB) in hereditary breast and ovarian cancers in this cohort was not correlated with high global immune activity in their microenvironments. More information is needed about the relationship between genomic instability, phenotypes and immune microenvironments of these hereditary tumors in order to find appropriate markers of immune activity and the most effective anticancer immune strategies.

Methods

Mining and statistical analyses of the original DNA and RNA sequencing data and The Cancer Genome Atlas data were performed. To interpret the data, we have used published literature and web available resources such as Gene Ontology, The Cancer immunome Atlas and the Cancer Research Institute iAtlas.

Results

We found that BRCA1/2 germline related breast and ovarian cancers do not represent a unique phenotypic identity, but they express a range of phenotypes similar to sporadic cancers. All breast and ovarian BRCA1/2 related tumors are characterized by high homologous recombination deficiency (HRD) and low aneuploidy. Interestingly, all sporadic high grade serous ovarian cancers (HGSOC) and most of the subtypes of triple negative breast cancers (TNBC) also express a high degree of HRD.

Conclusions

TMB is not associated with the magnitude of the immune response in hereditary BRCA1/2 related breast and ovarian cancers or in sporadic TNBC and sporadic HGSOC. Hereditary tumors express phenotypes as heterogenous as sporadic tumors with various degree of “BRCAness” and various characteristics of the immune microenvironments. The subtyping criteria developed for sporadic tumors can be applied for the classification of hereditary tumors and possibly also characterization of their immune microenvironment. A high HRD score may be a good candidate biomarker for response to platinum, and potentially PARP-inhibition.

Trial registration

Phase I Study of the Oral PI3kinase Inhibitor BKM120 or BYL719 and the Oral PARP Inhibitor Olaparib in Patients With Recurrent TNBC or HGSOC (NCT01623349), first posted on June 20, 2012. The design and the outcome of the clinical trial is not in the scope of this study.

Destruction of a Microtubule-Bound MYC Reservoir during Mitosis Contributes to Vincristine's Anticancer Activity

Tightly regulated activity of the transcription factor MYC is essential for orderly cell proliferation. Upon deregulation, MYC elicits and promotes cancer progression. Proteasomal degradation is an essential element of MYC regulation, initiated by phosphorylation at Serine62 (Ser62) of the MB1 region. Here, we found that Ser62 phosphorylation peaks in mitosis, but that a fraction of nonphosphorylated MYC binds to the microtubules of the mitotic spindle. Consequently, the microtubule-destabilizing drug vincristine decreases wild-type MYC stability, whereas phosphorylation-deficient MYC is more stable, contributing to vincristine resistance and induction of polyploidy. PI3K inhibition attenuates postmitotic MYC formation and augments the cytotoxic effect of vincristine. IMPLICATIONS: The spindle's function as a docking site for MYC during mitosis may constitute a window of specific vulnerability to be exploited for cancer treatment.

Abstract A105: PARP inhibition modulates the infiltration, phenotype, and function of tumor-associated macrophages (TAMs) in BRCA-associated breast cancer and can be augmented by harnessing the antitumor potential of TAMs

Patients with BRCA-associated triple-negative breast cancer (TNBC) have few effective treatment options. PARP inhibitors are promising, and we recently showed they induce an influx of white blood cells, including CD8+ T cells and macrophages into the tumor. The influx of CD8+ cells, mediated by activation of the STING pathway in tumor cells, contributes substantially to efficacy of PARP inhibition in mice. Strikingly, in these studies the greatest infiltration of immune cells into the tumor was macrophages. Given that objective responses to PARP inhibition have been observed in clinical trials but the benefits are transitory, we hypothesized that this was due to a suppressive tumor microenvironment, driven by tumor macrophages. To better understand the molecular basis of resistance to PARP inhibitors, we used high-dimensional single-cell immune profiling on human TNBC. We observed a ≥10-fold increase in TAMs in BRCA-associated TNBC compared to BRCA-wild-type TNBC. Using a preclinical model of BRCA1-deficient triple-negative breast cancer, we found that PARP inhibitors not only further increased TAM abundance but also induced functional and phenotypic changes associated with STING pathway activation, antigen presentation, and chemokine and cytokine signaling. PARP inhibitors increased the frequency of TAMs expressing costimulatory molecules CD80 and CD86 as well as the activation and maturation marker CD40, which are indicative of an antitumor phenotype. We also identified a novel negative feedback mechanism that limits the functionality of the anti-tumor TAMs and is consistent with induction of an immune-suppressive macrophage population. Utilizing transcriptomic, proteomic, and metabolic profiling of ex vivo cultured human myeloid cells, we identified multiple biologic processes associated with PARP inhibition, showing that these drugs directly affect macrophage states and phenotypes. Remarkably, in the preclinical BRCA1-deficient TNBC model, the novel combination of PARP inhibition with macrophage modulation significantly extended remissions obtained with PARP inhibitor therapy only, and this advantage persisted when treatment was discontinued, suggestive of a durable reprogramming of the tumor microenvironment. Moreover, CD8+ cells were required for the extension of PARP inhibitor-induced remissions, suggesting that targeting macrophages lifted the constraints imposed by protumor macrophages on CD8+ T cell-mediated tumor cell killing. We identify mechanisms related to macrophage and T-cell activation that increase PFS and provide evidence that TAMs may serve as targets for new therapeutic interventions designed to overcome PARP inhibitor resistance in BRCA-associated TNBC.

Citation Format: Anita K. Mehta, Emily M. Cheney, Jessica A. Castrillon, Jia-Ren Lin, Mateus de Oliveira Taveira, Christina A. Hartl, Nathan T. Johnson, William M. Oldham, Marian Kalocsay, Sarah A. Boswell, Olmo Sonzogni, Constantia Pantelidou, Brett P. Gross, Shawn Johnson, Deborah A. Dillon, Sandro Santagata, Judy E. Garber, Nadine Tung, Elizabeth A. Mittendorf, Gerburg M. Wulf, Geoffrey I. Shapiro, Peter K. Sorger, Jennifer L. Guerriero. PARP inhibition modulates the infiltration, phenotype, and function of tumor-associated macrophages (TAMs) in BRCA-associated breast cancer and can be augmented by harnessing the antitumor potential of TAMs [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A105.

Abstract P5-04-01: PARP inhibition modulates the infiltration, phenotype and function of tumor-associated macrophages (TAMs) in BRCA-associated breast cancer and can be augmented by harnessing the anti-tumor potential of TAMs

Patients with BRCA-associated triple negative breast cancer (TNBC) have few effective treatment options. PARP inhibitors are promising, and we recently showed they induce an influx of white blood cells, including CD8+ T-cells and macrophages into the tumor. The influx of CD8+ cells, mediated by activation of the STING pathway in tumor cells, contributes substantially to efficacy of PARP inhibition in mice. Strikingly, in these studies, the greatest infiltration of immune cells into the tumor was macrophages. Given objective responses to PARP inhibition have been observed in clinical trials but the benefits are transitory, we hypothesized that this was presumably due to a suppressive tumor microenvironment, driven by tumor macrophages. To better understand the molecular basis of resistance to PARP inhibitors, we used high dimensional single-cell immune profiling on human TNBC. We observed a ≥10-fold increase in TAMs in BRCA-associated TNBC compared to BRCA-wildtype TNBC. Using a pre-clinical model of BRCA1-deficient triple-negative breast cancer, we found that PARP inhibitors not only further increased TAM abundance but also induced functional and phenotypic changes associated with STING pathway activation, antigen presentation, and chemokine and cytokine signaling. PARP inhibitors increased the frequency of TAMs expressing co-stimulatory molecules CD80 and CD86 as well as the activation and maturation marker CD40, which are indicative of an anti-tumor phenotype. We also identified a novel negative feedback mechanism which limits the functionality of the anti-tumor TAMs, and is consistent with induction of an immune suppressive macrophage population. Utilizing transcriptomic, proteomic and metabolic profiling of ex vivo cultured human myeloid cells, we identified multiple biological processes associate with PARP inhibition, showing that these drugs directly affect macrophage states and phenotypes. Remarkably, in the pre-clinical BRCA1-deficient TNBC model, the novel combination of PARP inhibition with macrophage modulation significantly extended remissions obtained with PARP inhibitor therapy only, and this advantage persisted when treatment was discontinued, suggestive of a durable reprogramming of the tumor microenvironment. Moreover, CD8+ cells were required for the extension of PARP inhibitor-induced remissions, suggesting that targeting macrophages lifted the constraints imposed by pro-tumor macrophages on CD8+ T cell-mediated tumor cell killing. We identify mechanisms related to macrophage and T-cell activation that increase PFS and provide evidence that TAMs may serve as targets for new therapeutic interventions designed to overcome PARP inhibitor resistance in BRCA-associated TNBC.

Citation Format: Jennifer L Guerriero, Anita K Mehta, Emily M Cheney, Jessica A. Castrillon, Jia-Ren Lin, Mateus de Oliveira Taveira, Olmo Sonzogni, Constantia Pantelidou, Christina A Hartl, William M Oldham, Nathan T Johnson, Sarah A Boswell, Marian Kalocsay, Matthew J Berberich, Sholin Mei, Dan Wang, Shawn Johnson, Brett Gross, Deborah A Dillon, Mikel Lipschitz, Evisa Gjini, Scott Rodig, Sandro Santagata, Judy E Garber, Nadine Tung, Peter Sorger, Geoffrey I Shapiro, Gerburg M Wulf, Elizabeth A Mittendorf. PARP inhibition modulates the infiltration, phenotype and function of tumor-associated macrophages (TAMs) in BRCA-associated breast cancer and can be augmented by harnessing the anti-tumor potential of TAMs [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-04-01.

Transcriptome analysis reveals overlap in fusion genes in a phase I clinical cohort of TNBC and HGSOC patients treated with buparlisib and olaparib

PURPOSE

Fusion genes can be therapeutically relevant if they result in constitutive activation of oncogenes or repression of tumor suppressors. However, the prevalence and role of fusion genes in female cancers remain largely unexplored. Here, we investigate the fusion gene landscape in triple-negative breast cancer (TNBC) and high-grade serous ovarian cancer (HGSOC), two subtypes of female cancers with high molecular similarity but limited treatment options at present.

METHODS

RNA-seq was utilized to identify fusion genes in a cohort of 18 TNBC and HGSOC patients treated with the PI3K inhibitor buparlisib and the PARP inhibitor olaparib in a phase I clinical trial (NCT01623349). Differential gene expression analysis was performed to assess the function of fusion genes in silico. Finally, these findings were correlated with the reported clinical outcomes.

RESULTS

A total of 156 fusion genes was detected, whereof 44/156 (28%) events occurred in more than one patient. Low recurrence across samples indicated that the majority of fusion genes were private passenger events. The long non-coding RNA MALAT1 was involved in 97/156 (62%) fusion genes, followed in prevalence by MUC16, FOXP1, WWOX and XIST. Gene expression of FOXP1 was significantly elevated in patients with vs. without FOXP1 fusion (P= 0.02). From a clinical perspective, FOXP1 fusions were associated with a favorable overall survival.

CONCLUSIONS

In summary, this study provides the first characterization of fusion genes in a cohort of TNBC and HGSOC patients. An improved mechanistic understanding of fusion genes will support the future identification of innovative therapeutic approaches for these challenging diseases.

Establishing a Cohort of Transgender Men and Gender Nonconforming Individuals to Understand the Molecular Impact of Testosterone on Breast Physiology

Purpose: To characterize a cohort of transgender men and masculine-centered gender nonconforming individuals who underwent gender-affirming chest-contouring surgeries at our institution between 2013 and 2018.

Methods: Demographics, medical history, and breast histopathological assessment for 340 patients were retrieved from medical records.

Results: Most of our patients were white, non-Hispanic (75.0%), were taking testosterone (83.2%), and opted for chest-contouring surgery after 12–14 months of testosterone therapy. Ten patients were parous (2.9%). Seventy-nine (23.2%) and 27 (7.9%) patients had a family history of breast cancer or ovarian cancer, respectively. One transgender man was incidentally diagnosed with ductal carcinoma in situ at chest-contouring surgery.

Conclusion: Future studies on this cohort will provide valuable insights about the impact of testosterone on breast physiology.

Chromosome 12p Amplification in Triple-Negative/BRCA1-Mutated Breast Cancer Associates with Emergence of Docetaxel Resistance and Carboplatin Sensitivity

Taxanes are the mainstay of treatment in triple-negative breast cancer (TNBC), with de novo and acquired resistance limiting patient's survival. To investigate the genetic basis of docetaxel resistance in TNBC, exome sequencing was performed on matched TNBC patient-derived xenografts (PDX) sensitive to docetaxel and their counterparts that developed resistance in vivo upon continuous drug exposure. Most mutations, small insertions/deletions, and copy number alterations detected in the initial TNBC human metastatic samples were maintained after serial passages in mice and emergence of resistance. We identified a chromosomal amplification of chr12p in a human BRCA1-mutated metastatic sample and the derived chemoresistant PDX, but not in the matched docetaxel-sensitive PDX tumor. Chr12p amplification was validated in a second pair of docetaxel-sensitive/resistant BRCA1-mutated PDXs and after short-term docetaxel treatment in several TNBC/BRCA1-mutated PDXs and cell lines, as well as during metastatic recurrence in a patient with BRCA1-mutated breast cancer who had progressed on docetaxel treatment. Analysis of clinical data indicates an association between chr12p amplification and patients with TNBC/basal-like breast cancer, a BRCA1 mutational signature, and poor survival after chemotherapy. Detection of chr12p amplification in a cohort of TNBC PDX models was associated with an improved response to carboplatin. Our findings reveal tumor clonal dynamics during chemotherapy treatments and suggest that a preexisting population harboring chr12p amplification is associated with the emergence of docetaxel resistance and carboplatin responsiveness in TNBC/BRCA1-mutated tumors. SIGNIFICANCE: Chr12p copy number gains indicate rapid emergence of resistance to docetaxel and increased sensitivity to carboplatin, therefore sequential docetaxel/carboplatin treatment could improve survival in TNBC/BRCA1 patients. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/16/4258/F1.large.jpg.

Open-label Clinical Trial of Niraparib Combined With Pembrolizumab for Treatment of Advanced or Metastatic Triple-Negative Breast Cancer

Importance

Poly(adenosine diphosphate-ribose) polymerase inhibitor and anti-programmed death receptor-1 inhibitor monotherapy have shown limited clinical activity in patients with advanced triple-negative breast cancer (TNBC).

Objective

To evaluate the clinical activity (primary) and safety (secondary) of combination treatment with niraparib and pembrolizumab in patients with advanced or metastatic TNBC.

Design, Setting, and Participants

This open-label, single-arm, phase 2 study enrolled 55 eligible patients with advanced or metastatic TNBC irrespective of BRCA mutation status or programmed death-ligand 1 (PD-L1) expression at 34 US sites. Data were collected from January 3, 2017, through October 29, 2018, and analyzed from October 29, 2018, through February 27, 2019.

Interventions

Patients were administered 200 mg of oral niraparib once daily in combination with 200 mg of intravenous pembrolizumab on day 1 of each 21-day cycle.

Main Outcomes and Measures

The primary end point was objective response rate (ORR) per the Response Evaluation Criteria in Solid Tumors, version 1.1. Secondary end points were safety, disease control rate (DCR; complete response plus partial response plus stable disease), duration of response (DOR), progression-free survival (PFS), and overall survival.

Results

Within the full study population of 55 women (median age, 54 years [range, 32-90 years]), 5 patients had confirmed complete responses, 5 had confirmed partial responses, 13 had stable disease, and 24 had progressive disease. In the efficacy-evaluable population (n = 47), ORR included 10 patients (21%; 90% CI, 12%-33%) and DCR included 23 (49%; 90% CI, 36%-62%). Median DOR was not reached at the time of the data cutoff, with 7 patients still receiving treatment at the time of analysis. In 15 evaluable patients with tumor BRCA mutations, ORR included 7 patients(47%; 90% CI, 24%-70%), DCR included 12 (80%; 90% CI, 56%-94%), and median PFS was 8.3 months (95% CI, 2.1 months to not estimable). In 27 evaluable patients with BRCA wild-type tumors, ORR included 3 patients (11%; 90% CI, 3%-26%), DCR included 9 (33%; 90% CI, 19%-51%), and median PFS was 2.1 months (95% CI, 1.4-2.5 months). The most common treatment-related adverse events of grade 3 or higher were anemia (10 [18%]), thrombocytopenia (8 [15%]), and fatigue (4 [7%]). Immune-related adverse events were reported in 8 patients (15%) and were grade 3 in 2 patients (4%); no new safety signals were detected.

Conclusions and Relevance

Combination niraparib plus pembrolizumab provides promising antitumor activity in patients with advanced or metastatic TNBC, with numerically higher response rates in those with tumor BRCA mutations. The combination therapy was safe with a tolerable safety profile, warranting further investigation.

Trial Registration

ClinicalTrials.gov identifier: NCT02657889.

Efficient Human Cytomegalovirus Replication in Primary Endothelial Cells Is SOCS3 Dependent

BACKGROUND

In immunocompromised patients, human cytomegalovirus (HCMV) infection is a major cause of morbidity and mortality. Suppressor of cytokine signaling (SOCS) proteins are very potent negative regulators of the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways. We hypothesized that HCMV exploits SOCS1 and/or SOCS3 to its advantage.

METHODS

All experiments were carried out with primary human lung-derived microvascular endothelial cells (HMVEC). SOCS1 and SOCS3 were silenced by transfecting the cells with siRNA. HCMV was propagated and titered on human lung-derived fibroblasts MRC5. Real-time PCR and Western blot were used to detect mRNA and protein levels, respectively.

RESULTS

The data presented show that an efficient replication of HCMV in HMVEC is dependent on SOCS3 protein. Time course analysis revealed an increase in SOCS3 protein levels in infected cells. Silencing of SOCS3 (siSOCS3) resulted in inhibition of viral immediate early, early, and late antigen production. Consistently, HCMV titers produced by siSOCS3 cultures were significantly decreased when compared to control transfected cultures (siCNTRs). STAT1 and STAT2 phosphorylation was increased in siSOCS3-infected cells when compared to siCNTR-treated cells.

CONCLUSION

These findings indicate the implication of SOCS3 in the mechanism of HCMV-mediated control of cellular immune responses.

Phase II trial of AKT inhibitor MK-2206 in patients with advanced breast cancer who have tumors with PIK3CA or AKT mutations, and/or PTEN loss/PTEN mutation

BACKGROUND

The PI3K/AKT pathway is activated through PIK3CA or AKT1 mutations and PTEN loss in breast cancer. We conducted a phase II trial with an allosteric AKT inhibitor MK-2206 in patients with advanced breast cancer who had tumors with PIK3CA/AKT1 mutations and/or PTEN loss/mutation.

METHODS

The primary endpoint was objective response rate (ORR). Secondary endpoints were 6-month progression-free survival (6 m PFS), predictive and pharmacodynamic markers, safety, and tolerability. Patients had pre-treatment and on-treatment biopsies as well as collection of peripheral blood mononuclear cells (PBMC) and platelet-rich plasma (PRP). Next-generation sequencing, immunohistochemistry, and reverse phase protein arrays (RPPA) were performed.

RESULTS

Twenty-seven patients received MK-2206. Eighteen patients were enrolled into the PIK3CA/AKT1 mutation arm (cohort A): 13 had PIK3CA mutations, four had AKT1 mutations, and one had a PIK3CA mutation as well as PTEN loss. ORR and 6 m PFS were both 5.6% (1/18), with one patient with HR+ breast cancer and a PIK3CA E542K mutation experiencing a partial response (on treatment for 36 weeks). Nine patients were enrolled on the PTEN loss/mutation arm (cohort B). ORR was 0% and 6 m PFS was 11% (1/9), observed in a patient with triple-negative breast cancer and PTEN loss. The study was stopped early due to futility. The most common adverse events were fatigue (48%) and rash (44%). On pre-treatment biopsy, PIK3CA and AKT1 mutation status was concordant with archival tissue testing. However, two patients with PTEN loss based on archival testing had PTEN expression on the pre-treatment biopsy. MK-2206 treatment was associated with a significant decline in pAKT S473 and pAKT T308 and PI3K activation score in PBMC and PRPs, but not in tumor biopsies. By IHC, there was no significant decrease in median pAKT S473 or Ki-67 staining, but a drop was observed in both responders.

CONCLUSIONS

MK-2206 monotherapy had limited clinical activity in advanced breast cancer patients selected for PIK3CA/AKT1 or PTEN mutations or PTEN loss. This may, in part, be due to inadequate target inhibition at tolerable doses in heavily pre-treated patients with pathway activation, as well as tumor heterogeneity and evolution in markers such as PTEN conferring challenges in patient selection.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01277757 . Registered 13 January 2011.

Abstract 4490: PARP inhibitor efficacy depends on CD8+ T-cell recruitment via the STING pathway in BRCA-deficient models of triple-negative breast cancer

Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-deficient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8+ T cell infiltration and activation in vivo, and that depletion of CD8+ T cells severely compromises anti-tumor efficacy. Olaparib-induced T cell recruitment is mediated through activation of the STING/TBK1/IRF3 pathway in tumor and dendritic cells and is more pronounced in HR-deficient compared to HR-proficient TNBC cells. CRISPR-knockout of STING in cancer cells prevents type I IFN production and is sufficient to abolish PARP inhibitor-induced T cell infiltration in vivo. These findings elucidate a novel mechanism of action of PARP inhibitors and provide mechanistic rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC.

Citation Format: Constantia Pantelidou, Olmo Sonzogni, Mateus De Oliveira Taveira, Anita K. Mehta, Dan Wang, Aditi Kothari, Michelle K. Li, Tanvi H. Visal, Jennifer L. Guerriero, Gerburg M. Wulf, Geoffrey I. Shapiro. PARP inhibitor efficacy depends on CD8+ T-cell recruitment via the STING pathway in BRCA-deficient models of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4490.

Randomized phase II study of eribulin mesylate (E) with or without pembrolizumab (P) for hormone receptor-positive (HR+) metastatic breast cancer (MBC)

1004

Background: Studies of checkpoint inhibitor monotherapy show only modest activity in HR+ MBC. We report data from the first randomized study comparing E plus P versus E alone in HR+/HER2- MBC. Methods: Eligible patients (pts) had HR+/HER2- MBC, ≥2 lines of hormonal therapies and 0-2 lines of chemotherapy for MBC. Pts were randomized 1:1 to E 1.4mg/m2 intravenously (IV) on d1 and d8 with P 200 mg/m2 IV on d1 of a 21-day cycle (Arm A) or E alone (Arm B). At time of progression, pts in arm B could crossover and receive P alone. Primary endpoint was progression-free survival (PFS). Key secondary endpoints were: objective response rate (ORR) and overall survival (OS). Exploratory analyses assessed the association between PFS and PD-L1 status, tumor-infiltrating lymphocytes (TILs), neutrophil-lymphocyte ratio (NLR), tumor mutation burden (TMB), and genomic alterations by next generation sequencing on archival tissue. Results: 88 pts initiated protocol therapy; the median age was 58, median prior lines of chemotherapy 1, prior lines of hormonal therapy 2. Median follow-up was 6.3 months. Median PFS and ORR were not different between Arms A and B (PFS 4.1 vs 4.2 months p = 0.38; ORR 25% and 34% respectively (p = 0.49). 14 patients initiated crossover treatment with pembrolizumab; 1 patient experienced a PR (ORR 7%). All-cause AEs occurred in 100% of pts (G3-4, 54.6%) including 2 treatment related deaths on Arm A, both from known AEs attributed to both drugs. PD-L1 assay was performed in 65 pts: 24 (36.9%) had PD-L1 positive ( > 1% with 22C3, centrally tested) tumors. PD-L1 status, TILs, NLR, TMB, and genomic alterations were not associated with PFS (Table). Updated data, including OS and genomic results, will be presented. Conclusions: Among pts with HR+/HER2- MBC, the combination of E and P was not associated with longer PFS than E alone in the ITT or PD-L1+ population, though the PD-L1+ subgroup had very limited power to assess P benefit. Clinical trial information: NCT03051659. [Table: see text]

PARP Inhibitor Efficacy Depends on CD8+ T-cell Recruitment via Intratumoral STING Pathway Activation in BRCA-Deficient Models of Triple-Negative Breast Cancer

Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-deficient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8⁺ T-cell infiltration and activation in vivo, and that CD8⁺ T-cell depletion severely compromises antitumor efficacy. Olaparib-induced T-cell recruitment is mediated through activation of the cGAS/STING pathway in tumor cells with paracrine activation of dendritic cells and is more pronounced in HR-deficient compared with HR-proficient TNBC cells and in vivo models. CRISPR-mediated knockout of STING in cancer cells prevents proinflammatory signaling and is sufficient to abolish olaparib-induced T-cell infiltration in vivo. These findings elucidate an additional mechanism of action of PARP inhibitors and provide a rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC. SIGNIFICANCE: This work demonstrates cross-talk between PARP inhibition and the tumor microenvironment related to STING/TBK1/IRF3 pathway activation in cancer cells that governs CD8⁺ T-cell recruitment and antitumor efficacy. The data provide insight into the mechanism of action of PARP inhibitors in BRCA-associated breast cancer.This article is highlighted in the In This Issue feature, p. 681.

Olaparib and α-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial

BACKGROUND

Based on preclinical work, we found that combination of poly (ADP-ribose) polymerase (PARP) inhibitors with drugs that inhibit the homologous recombination repair (HRR) pathway (such as PI3K inhibitors) might sensitise HRR-proficient epithelial ovarian cancers to PARP inhibitors. We aimed to assess the safety and identify the recommended phase 2 dose of the PARP inhibitor olaparib in combination with the PI3K inhibitor alpelisib in patients with epithelial ovarian cancer and in patients with breast cancer.

METHODS

In this multicentre, open-label, phase 1b trial following a 3 + 3 dose-escalation design, we recruited patients aged 18 years or older with the following key eligibility criteria: confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of high-grade serous histology; confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of any histology with known germline BRCA mutations; confirmed diagnosis of recurrent breast cancer of triple-negative histology; or confirmed diagnosis of recurrent breast cancer of any histology with known germline BRCA mutations. Additional patients with epithelial ovarian cancer were enrolled in a dose-expansion cohort. Four dose levels were planned: the starting dose level of alpelisib 250 mg once a day plus olaparib 100 mg twice a day (dose level 0); alpelisib 250 mg once a day plus olaparib 200 mg twice a day (dose level 1); alpelisib 300 mg once a day plus olaparib 200 mg twice a day (dose level 2); and alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Both drugs were administered orally, in tablet formulation. The primary objective was to identify the maximum tolerated dose and the recommended phase 2 dose of the combination of alpelisib and olaparib for patients with epithelial ovarian cancer and patients with breast cancer. Analyses included all patients who received at least one dose of the study drugs. The trial is active, but closed to enrolment; follow-up for patients who completed treatment is ongoing. This trial is registered with ClinicalTrials.gov, number NCT01623349.

FINDINGS

Between Oct 3, 2014, and Dec 21, 2016, we enrolled 34 patients (28 in the dose-escalation cohort and six in the dose-expansion cohort); two in the dose-escalation cohort were ineligible at the day of scheduled study initiation. Maximum tolerated dose and recommended phase 2 dose were identified as alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Considering all dose levels, the most common treatment-related grade 3-4 adverse events were hyperglycaemia (five [16%] of 32 patients), nausea (three [9%]), and increased alanine aminotransferase concentrations (three [9%]). No treatment-related deaths occurred. Dose-limiting toxic effects included hyperglycaemia and fever with decreased neutrophil count. Of the 28 patients with epithelial ovarian cancer, ten (36%) achieved a partial response and 14 (50%) had stable disease according to Response Evaluation Criteria in Solid Tumors 1.1.

INTERPRETATION

Combining alpelisib and olaparib is feasible with no unexpected toxic effects. The observed activity provides preliminary clinical evidence of synergism between olaparib and alpelisib, particularly in epithelial ovarian cancer, and warrants further investigation.

FUNDING

Ovarian Cancer Dream Team (Stand Up To Cancer, Ovarian Cancer Research Alliance, National Ovarian Cancer Coalition), Breast Cancer Research Foundation, Novartis.