Multifactoral immune modulation potentiates durable remission in multiple models of aggressive malignancy

Tumors typically lack canonical danger signals required to activate adaptive immunity and also frequently employ substantial immunomodulatory mechanisms that downregulate adaptive responses and contribute to escape from immune surveillance. Given the variety of mechanisms involved in shielding tumors from immune recognition, it is not surprising that single-agent immunomodulatory approaches have been largely unsuccessful in generating durable antitumor responses. Here we report a unique combination of immunomodulatory and cytostatic agents that recondition the tumor microenvironment and eliminate complex and/or poor-prognosis tumor types including the non-immunogenic 4T-1 model of TNBC, the aggressive MOC-2 model of HNSCC, and the high-risk MYCN-amplified model of neuroblastoma. A course of therapy optimized for TNBC cured a majority of tumors in both ectopic and orthotopic settings and eliminated metastatic spread in all animals tested at the highest doses. Immune responses were transferable between therapeutic donor and naïve recipient through adoptive transfer, and a sizeable abscopal effect on distant, untreated lesions could be demonstrated experimentally. Similar results were observed in HNSCC and neuroblastoma models, with characteristic remodeling of the tumor microenvironment documented in all model systems. scRNA-seq analysis implicated upregulation of innate immune responses and antigen presentation in tumor cells and the myeloid cell compartment as critical early events. This analysis also highlighted the potential importance of the autonomic nervous system in the governance of inflammatory processes. The data indicate that the targeting of multiple pathways and mechanisms of action can result in substantial synergistic antitumor effects and suggest follow-up in the neoadjuvant setting may be warranted.

Phase IIa Study of SurVaxM Plus Adjuvant Temozolomide for Newly Diagnosed Glioblastoma

PURPOSE

Despite intensive treatment with surgery, radiation therapy, temozolomide (TMZ) chemotherapy, and tumor-treating fields, mortality of newly diagnosed glioblastoma (nGBM) remains very high. SurVaxM is a peptide vaccine conjugate that has been shown to activate the immune system against its target molecule survivin, which is highly expressed by glioblastoma cells. We conducted a phase IIa, open-label, multicenter trial evaluating the safety, immunologic effects, and survival of patients with nGBM receiving SurVaxM plus adjuvant TMZ following surgery and chemoradiation (ClinicalTrials.gov identifier: NCT02455557).

METHODS

Sixty-four patients with resected nGBM were enrolled including 38 men and 26 women, in the age range of 20-82 years. Following craniotomy and fractionated radiation therapy with concurrent TMZ, patients received four doses of SurVaxM (500 μg once every 2 weeks) in Montanide ISA-51 plus sargramostim (granulocyte macrophage colony-stimulating factor) subcutaneously. Patients subsequently received adjuvant TMZ and maintenance SurVaxM concurrently until progression. Progression-free survival (PFS) and overall survival (OS) were reported. Immunologic responses to SurVaxM were assessed.

RESULTS

SurVaxM plus TMZ was well tolerated with no serious adverse events attributable to SurVaxM. Of the 63 patients who were evaluable for outcome, 60 (95.2%) remained progression-free 6 months after diagnosis (prespecified primary end point). Median PFS was 11.4 months and median OS was 25.9 months measured from first dose of SurVaxM. SurVaxM produced survivin-specific CD8+ T cells and antibody/immunoglobulin G titers. Apparent clinical benefit of SurVaxM was observed in both methylated and unmethylated patients.

CONCLUSION

SurVaxM appeared to be safe and well tolerated. The combination represents a promising therapy for nGBM. For patients with nGBM treated in this manner, PFS may be an acceptable surrogate for OS. A large randomized clinical trial of SurVaxM for nGBM is in progress.

Molecular characterization of metastatic colorectal cancer (mCRC) in patients (pts) treated with cetuximab and pembrolizumab

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Background: Anti-EGFR therapy has the potential to increase a localized anti-tumor immune response. We recently published the results of a phase Ib/II trial of the anti-EGFR antibody cetuximab in combination with the anti-PD1 antibody pembrolizumab in pts with advanced, RASwt CRC (PMID: 34645646). Despite its partial local immunologic efficacy, this combination of cetuximab and pembrolizumab was inactive. Here we present the results of comprehensive molecular characterization of pts with tumors amenable to DNA and RNA sequencing. Methods: Forty-two pts with RASwt mCRC were treated with cetuximab plus pembrolizumab. Archival or fresh tumor samples were obtained at baseline and, in select patients, on-treatment. Tumor samples underwent targeted DNA sequencing and whole transcriptome sequencing. Gene set enrichment analysis (GSEA), metabolic dysregulation assessment, and immune deconvolution were performed. Genomic data were linked to clinical outcomes. Results: Eighteen pts had tissue available for dual DNA/RNA extraction and sequencing. Of these, 10 had available matched on-treatment tumor samples. The most common mutations detected in protein coding regions were TP53 (14 pts), ERBB4 (5 pts), CDKN2A and APC (6 pts each). There were no statistically significant differences in progression-free survival (PFS) in pts with and without resistance-associated mutations (i.e., RAS, MET, ERBB4). Further, there was no significant difference associated with the consensus molecular subtype (CMS). However, when we compared patients with stable/increased tumor change percentage to those with decreased tumor change percentage, we found downstream transcriptional differences associated with altered metabolism, and in particular lipid and amino acid metabolism. Conclusions: We identified a significant number of patients with mutations predicting resistance to either or both cetuximab and pembrolizumab; however, none were associated with survival. However, we did identify metabolic pathways of interest, which may be associated with response to therapy. It is important to note, our analysis is limited by the small number of specimens (Trial registration NCT02713373). Clinical trial information: NCT02713373 .

Abstract 154: Novel AKT isoform-preferred substrates as potentially targetable drivers of metastatic prostate cancer

PI3K/AKT pathway activating mutations are the most prevalent in all of human cancers, and yet drugs that target the PI3K lipid kinase or AKT serine/threonine kinase families have performed poorly in clinical trials on solid cancers. PTEN loss, one of the most frequent mutations in prostate cancer (PC), results in AKT activation, an assumed driver of aggressive metastatic disease (mPC). The poor efficacy of PI3K/AKT inhibitors in PC likely relate to multiple PI3K and AKT isoforms which have compensatory or even oppositional roles. Whereas PI3K-p110 isoform-specific inhibitors are being used in clinical trials, no clinical AKT isoform-specific inhibitors exist. Data from our lab and others indicate that progression to aggressive mPC is dependent on AKT2-, and possibly AKT3-specific pathways. However, previous screens could not distinguish between direct vs. indirect AKT isoform-preferred substrates, and they only focused on substrates with canonical phosphorylation motifs (RxRxxS*/T*). We addressed this gap using a novel phosphoproteomics analysis that identifies direct AKT isoform substrates from PC lysates in which substrates are in endogenous protein-protein complexes. Scores of novel and previously known substrates were identified that are preferred by individual or combinations of AKT isoforms, conforming to both the canonical and four novel non-canonical motifs; >95% of these sites exist in phosphoproteome databases. By comparing data from PC cell lines isogenic for PTEN loss or expression, we identified PTEN-influenced substrate phosphorylation or AKT isoform preference. However, most of these cases did not correlate with changes in substrate abundance, suggesting novel roles for PTEN in regulating substrate modifications or cellular compartmentalization. We hypothesize that AKT2 and AKT3 substrate phosphorylation drives parameters of in vitro and in vivo mPC progression, suggesting that these AKT isoforms may be therapeutic targets if specific inhibitors can be produced. Data will be shown i) confirming AKT isoform preference of specific substrates, ii) identifying novel mechanisms by which PTEN influences substrate usage or isoform preference via altering cellular compartmentalization or post-translational modification, and iii) validating our identified non-canonical AKT isoform-specific phosphorylation sites. We also show that the phosphorylation of AKT2/3-preferred substrates drives metastatic progression in vitro and in vivo. Our data identify a much broader array of AKT isoform-specific, -preferred and -shared substrates, including those encoding previously unidentified non-canonical phosphorylation motifs. We also show novel function for PTEN, namely, to influence AKT isoform substrate usage and preference. These data will allow us to develop AKT isoform-specific inhibitors that could be used to suppress mPC progression.

Citation Format: Seamus Degan, Renae Holtz, Henry G. Withers, Jun Qu, Sailee Suryakant Rasam, Irwin H. Gelman. Novel AKT isoform-preferred substrates as potentially targetable drivers of metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 154.

Abstract 3643: The role of HBP1 in controlling breast cancer dormancy reawakening

At least 22% of breast cancer (BrCa) cases recur after 3 to 15 years, typically at metastatic sites such as the bone. Bone metastases derive from early disseminated tumor cells that become dormant because of interaction with specific cells that define the endosteal niche (EN) microenvironment. However, outside knowing that dormancy is driven by a p38MAPKhi, ERK1/2lo activation profile, our understanding of what factors regulate dormancy maintenance and reawakening is poor. We used a genomic shRNA screen to identify HBP1 as a suppressor of BrCa dormancy reawakening in a 3D-EN culture system. Our data indicate that under 3D-EN conditions, HBP1 is upregulated by p38MAPK, interacts with the metastasis suppressors, BRMS1 and BRMS1L, and with the histone modifiers, SIN3A and HDAC1-3. We hypothesize that HBP1 suppresses p38MAPK-mediated dormancy reawakening by complexing with BRMS1/BRMS1L/SIN3A to alter cell cycle gene expression through histone landscape remodeling. HBP1 suppresses the expression of cell cycle progression genes, such as MYC and CCND1, and concomitantly upregulates cyclin kinase inhibitors, p16 and p21. HBP1 RNA and protein levels are decreased in BrCa metastases relative to primary tumors, and this downregulation correlates with poorer overall survival. We are investigating whether the anti-histiminic drug, cyproheptadine, which upregulates HBP1 expression through the activation of p38MAPK, can suppress dormancy reawakening of BrCa cells in 3D-EN cultures and in in vivo models of bone dormancy using mouse mammary carcinoma D2A1 cell lines with varying abilities to form active or dormant metastatic bone colonization. Data will be shown addressing how cell-cell interactions and secretory factors between BrCa and bone EN cells facilitates dormancy signaling through a p38MAPK/HBP1/BRMS1 axis, and how drugs such as cyproheptadine agonize that pathway in order to prevent the reawakening that drives the growth of BrCa metastases in the bone, thereby increasing overall survival.

Citation Format: Irwin H. Gelman, Seamus Degan, Henry G. Withers, Subrahmanya Anirudh Kaligotla Venkata. The role of HBP1 in controlling breast cancer dormancy reawakening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3643.

Final data from the phase 2a single-arm trial of SurVaxM for newly diagnosed glioblastoma

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Background: Newly diagnosed glioblastoma (nGBM) routinely treated with surgery, radiation, and temozolomide (TMZ), still result in early progression and near-universal lethality within 5 years. Tumor associated “survivin” is expressed in >95% of nGBM and targetable by SurVaxM immunotherapy. Results from the recently completed multi-center phase 2a trial of SurVaxM in nGBM are presented. Methods: nGBM patients (pts) were enrolled at 5 trial sites. Eligibility criteria included: age ≥ 18, Karnofsky performance status ≥70, IHC confirmation of survivin expression, expression of HLA-A*02, A*03, A*11 or A*24 MHC-I alleles and residual contrast enhancement of ≤1 cm3 by MRI within 72h post-resection. Pts received standard TMZ chemoradiation followed by initiation of 4 priming doses of SurVaxM (500 mcg in emulsion with Montanide ISA 51, every 2 weeks) with 100 mcg sargramostim. Maintenance doses of SurVaxM-Montanide plus sargramostim were thereafter administered every 12 weeks. Adjuvant TMZ was administered for at least 6 cycles, after at least the first dose of SurVaxM and beginning no sooner than 28 days after completion of chemoradiation. Pts were monitored by MRI every 8 weeks, and progression was assessed using modified RANO criteria. The primary endpoint was 70% progression free survival (PFS) at 6 mos. Primary analyses of median PFS (mPFS) and median overall survival (OS) were measured from first immunization. Safety, tolerability, and immune responsiveness were also determined. Results: 63 pts with nGBM were enrolled, comprised of 38 males and 25 females with a median age of 60 years. The cohort was consistent with the 4 commonly observed primary molecular GBM subtypes (classical, mesenchymal, neural and proneural). SurVaxM was well tolerated, with no serious adverse events. A strong positive correlation, accounting for censoring, was observed between PFS and OS of all pts (r = 0.79; 95% CI (0.66,0.87)). SurVaxM was immunogenic and produced survivin-specific CD8+ T-cells and antibody (IgG) titers in both methylated and unmethylated MGMT pts and both groups showed clinical benefit. Conclusions: SurVaxM appeared to be safe and well-tolerated in pts with nGBM. SurVaxM was effective at stimulating survivin-specific immune responses and the primary endpoint was met. SurVaxM represents a promising therapy for nGBM, including for those pts with unmethylated MGMT genes. For pts treated with SurVaxM, PFS may be an acceptable surrogate for OS. Clinical trial information: NCT02455557. [Table: see text]

MUC1-C integrates type II interferon and chromatin remodeling pathways in immunosuppression of prostate cancer

The oncogenic MUC1-C protein drives dedifferentiation of castrate resistant prostate cancer (CRPC) cells in association with chromatin remodeling. The present work demonstrates that MUC1-C is necessary for expression of IFNGR1 and activation of the type II interferon-gamma (IFN-γ) pathway. We show that MUC1-C→ARID1A/BAF signaling induces IFNGR1 transcription and that MUC1-C-induced activation of the NuRD complex suppresses FBXW7 in stabilizing the IFNGR1 protein. MUC1-C and NuRD were also necessary for expression of the downstream STAT1 and IRF1 transcription factors. We further demonstrate that MUC1-C and PBRM1/PBAF are necessary for IRF1-induced expression of (i) IDO1, WARS and PTGES, which metabolically suppress the immune tumor microenvironment (TME), and (ii) the ISG15 and SERPINB9 inhibitors of T cell function. Of translational relevance, we show that MUC1 associates with expression of IFNGR1, STAT1 and IRF1, as well as the downstream IDO1, WARS, PTGES, ISG15 and SERPINB9 immunosuppressive effectors in CRPC tumors. Analyses of scRNA-seq data further demonstrate that MUC1 correlates with cancer stem cell (CSC) and IFN gene signatures across CRPC cells. Consistent with these results, MUC1 associates with immune cell-depleted "cold" CRPC TMEs. These findings demonstrate that MUC1-C integrates chronic activation of the type II IFN-γ pathway and induction of chromatin remodeling complexes in linking the CSC state with immune evasion.

Identification of Genes Regulating Breast Cancer Dormancy in 3D Bone Endosteal Niche Cultures

Tumor cell dormancy is a significant clinical problem in breast cancer. We used a three-dimensional (3D) in vitro model of the endosteal bone niche (EN), consisting of endothelial, bone marrow stromal cells, and fetal osteoblasts in a 3D collagen matrix (GELFOAM), to identify genes required for dormancy. Human triple-negative MDA-MB-231 breast cancer cells, but not the bone-tropic metastatic variant, BoM1833, established dormancy in 3D-EN cultures in a p38-MAPK-dependent manner, whereas both cell types proliferated on two-dimensional (2D) plastic or in 3D collagen alone. "Dormancy-reactivation suppressor genes" (DRSG) were identified using a genomic short hairpin RNA (shRNA) screen in MDA-MB-231 cells for gene knockdowns that induced proliferation in the 3D-EN. DRSG candidates enriched for genes controlling stem cell biology, neurogenesis, MYC targets, ribosomal structure, and translational control. Several potential DRSG were confirmed using independent shRNAs, including BHLHE41, HBP1, and WNT3. Overexpression of the WNT3/a antagonists secreted frizzled-related protein 2 or 4 (SFRP2/4) and induced MDA-MB-231 proliferation in the EN. In contrast, overexpression of SFRP3, known not to antagonize WNT3/a, did not induce proliferation. Decreased WNT3 or BHLHE41 expression was found in clinical breast cancer metastases compared with primary-site lesions, and the loss of WNT3 or BHLHE41 or gain of SFRP1, 2, and 4 in the context of TP53 loss/mutation correlated with decreased progression-free and overall survival. IMPLICATIONS: These data describe several novel, potentially targetable pathways controlling breast cancer dormancy in the EN.

Abstract LB-148: Characterization of an off-target RNAi genomic screen hit identifies GPRC6A as a novel suppressor of metastatic chemotaxis and invasiveness

Metastatic events define the lethal phenotype of prostate cancer; however, as a result of enhanced and more widespread screening, many cancers are now detected prior to the presentation of overt metastases. In these cases, there is a need to characterize the molecular and genetic profile of primary tumors to use as accurate predictors of aggressive, metastatic disease. The following study utilizes unconventional analysis of off-target data from two genome-wide RNAi screens for metastasis suppressor genes in prostate and breast cancer models to identify novel markers and potential therapeutic targets of advancing disease. One screen enriched for increased Matrigel invasiveness by human T-47D breast cancer clones whereas the other screen selected for increased macrometastasis formation in distant organs after orthotopic xenograft of human LNCaP prostate cancer clones. A particular hairpin targeting apolipoprotein L-II (APOL2) was enriched in both screens and this shRNA sequence increases LNCaP invasion and chemotaxis in transwell assays. Notably, knockdown of APOL2 by alternative RNAi sequences does not induce LNCaP invasion indicating that off-target effects of the specific shRNA (called si/shAPOL2*) are responsible for the phenotype. Microarray profiling identified 132 transcripts differentially downregulated by siAPOL2* and sequence analysis reveals similarity to a number of microRNA (miR) seed sequences, miR-8087, miR-548u, miR-4432, and miR-543. With the exception of miR-548u, transfection with the other miR mimics recapitulates the enhanced chemotactic phenotype induced by siAPOL2* in LNCaP cells. Both miR-4432 and miR-543 expression varies in a panel of prostate cancer cell lines (LNCaP, C4-2, PC3, and DU-145), whereas miR-8087 is not detected by qPCR in these cell lines and has no associated expressed sequence tags (ESTs) in the GenBank database. Amplifications of miR-4432 and miR-543 are present in large numbers of patients across multiple cancer types in The Cancer Genome Atlas (TCGA) datasets. Microarray data and qPCR validation suggests G-protein coupled receptor family C group 6 member A (GPRC6A) as a candidate off-target transcript affected by siAPOL2*. Indeed, GPRC6A was also identified independently in the LNCaP orthotopic xenograft RNAi screen, and independent siRNA-mediated knockdown of GPRC6A in LNCaP cells increases chemotaxis. Further investigation is underway to determine whether miR-4432 or miR-543 mediate their effects through the regulation of GPRC6A, presumably through 3’UTR miRNA binding sites. This study demonstrates that the analysis of off-target effects in RNAi screens is a viable method to identify functionally relevant microRNAs contributing to regulation of chemotaxis in metastatic disease.

Citation Format: Henry G. Withers, Irwin H. Gelman. Characterization of an off-target RNAi genomic screen hit identifies GPRC6A as a novel suppressor of metastatic chemotaxis and invasiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-148. doi:10.1158/1538-7445.AM2017-LB-148

Inhibition of cellular respiration by doxorubicin

Doxorubicin executes apoptosis, a process known to produce leakage of cytochrome c and opening of the mitochondrial permeability transition pores. To define the loss of mitochondrial function by apoptosis, we monitored cellular respiration during continuous exposure to doxorubicin. A phosphorescence analyzer capable of stable measurements over at least 5 h was used to measure [O(2)]. In solutions containing glucose and cells, [O(2)] declined linearly with time, showing that the kinetics of oxygen consumption was zero order. Complete inhibition of oxygen consumption by cyanide indicated that oxidations occurred in the respiratory chain. A decline in the rate of respiration was evident in Jurkat and HL-60 cells exposed to doxorubicin. The decline was abrupt, occurring after about 2 h of incubation. The inhibition was concentration-dependent and was completely blocked by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone. Respiration in resistant HL-60/MX2 cells, characterized by an altered topoisomerase II activity, was not inhibited by doxorubicin. A decline in cellular ATP was measured in Jurkat cells after 2-4 h of incubation with 20 microM doxorubicin, paralleling the decline in respiration rate. Thus, cells incubated with doxorubicin exhibit caspase-mediated inhibition of oxidative phosphorylation.