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Background: Polycomb repressive complex 2 (PRC2) tri-methylates histone H3 at lysine 27 (H3K27me3) leading to transcriptionally silenced genes. ORIC-944 is a potent, highly selective allosteric small molecule inhibitor of PRC2’s embryonic ectoderm development (EED) subunit that is undergoing clinical development as an orally bioavailable monotherapy in patients with metastatic prostate cancer. We previously reported strong tumor growth inhibition with ORIC-944 in enzalutamide-resistant 22Rv1 prostate cancer xenografts. Here, to devise and implement a biomarker strategy aimed at ORIC-944 dose selection in the ongoing phase 1 study (NCT05413421), we undertook preclinical pharmacology studies and assay development. Methods: Naïve and 22Rv1-tumor bearing male mice were treated with vehicle, 10, 30 or 100 mg/kg ORIC-944 PO for up to 37 days. H3K27me3 was evaluated in dorsal skin (epidermal layer) and peripheral monocytes by IHC and an alphaLISA test, respectively. Since dying tumor cells release nucleosomes to circulation, cell-free (cf)-nucleosomal H3K27me3 levels normalized to cf-H3.1 were also assessed in plasma using a proprietary magnetic bead-based sandwich immunoassay. Tumors were profiled by RNA-sequencing and H3K27me3 chromatin immunoprecipitation sequencing. Results: In the epidermal skin layer, H3K27me3 was present in vehicle-treated naïve animals but strongly depleted in ORIC-944-treated mice in a dose-dependent manner. Likewise in monocytes, H3K27me3 was reduced to undetectable levels in 100 mg/kg ORIC-944-treated mice. In plasma, normalized cf-nucleosomal H3K27me3 levels significantly decreased in response to ORIC-944 in a dose- and time-dependent manner, selectively in 22Rv1-tumor bearing mice compared to non-tumor bearing mice. Putative PRC2 target genes were identified in 22Rv1 xenografts by focusing on those genes with H3K27me3 binding in the promoter, whose expression was de-repressed by ORIC-944 in a time-dependent manner and then re-expressed after dose suspension. In the ongoing phase 1 study, H3K27me3 levels are being evaluated in the stratum spinosum of skin and in blood-derived monocytes using a proprietary IHC assay and alphaLISA test, respectively. Modulation in the expression of the putative PRC2 target genes is being assessed in blood-derived peripheral blood mononuclear cells by RNA-sequencing. Conclusion: This comprehensive biomarker strategy enables us to establish target engagement and capture exposure-dependent pharmacodynamics in the ongoing phase 1 study evaluating ORIC-944 as a best-in-class PRC2 inhibitor for the treatment of patients with advanced prostate cancer. Citation Format: Anneleen Daemen, Natalie Yuen, Aleksandr Pankov, Eric A. Ariazi, Subhash D. Katewa, Frank L. Duong, Amber Wang, Shravani Barkund, Shelly Kaushik, Jessica D. Sun, Lori S. Friedman, Melissa R. Junttila. Biomarker strategy for a phase 1 study of ORIC-944, a potent and selective allosteric PRC2 inhibitor, in patients with metastatic prostate cancer [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 2791.

Background The ability to detect tumor-specific biomarkers in real-time using optical imaging plays a critical role in preclinical studies aimed at evaluating drug safety and treatment response. In this study, we engineered an imaging platform capable of targeting different tumor biomarkers using a multi-colored library of nanoprobes. These probes contain rare-earth elements that emit light in the short-wave infrared (SWIR) wavelength region (900–1700 nm), which exhibits reduced absorption and scattering compared to visible and NIR, and are rendered biocompatible by encapsulation in human serum albumin. The spectrally distinct emissions of the holmium (Ho), erbium (Er), and thulium (Tm) cations that constitute the cores of these nanoprobes make them attractive candidates for optical molecular imaging of multiple disease biomarkers. Methods SWIR-emitting rare-earth-doped albumin nanocomposites (ReANCs) were synthesized using controlled coacervation, with visible light-emitting fluorophores additionally incorporated during the crosslinking phase for validation purposes. Specifically, HoANCs, ErANCs, and TmANCs were co-labeled with rhodamine-B, FITC, and Alexa Fluor 647 dyes respectively. These Rh-HoANCs, FITC-ErANCs, and 647-TmANCs were further conjugated with the targeting ligands daidzein, AMD3100, and folic acid respectively. Binding specificities of each nanoprobe to distinct cellular subsets were established by in vitro uptake studies. Quantitative whole-body SWIR imaging of subcutaneous tumor bearing mice was used to validate the in vivo targeting ability of these nanoprobes. Results Each of the three ligand-functionalized nanoprobes showed significantly higher uptake in the targeted cell line compared to untargeted probes. Increased accumulation of tumor-specific nanoprobes was also measured relative to untargeted probes in subcutaneous tumor models of breast (4175 and MCF-7) and ovarian cancer (SKOV3). Preferential accumulation of tumor-specific nanoprobes was also observed in tumors overexpressing targeted biomarkers in mice bearing molecularly-distinct bilateral subcutaneous tumors, as evidenced by significantly higher signal intensities on SWIR imaging. Conclusions The results from this study show that tumors can be detected in vivo using a set of targeted multispectral SWIR-emitting nanoprobes. Significantly, these nanoprobes enabled imaging of biomarkers in mice bearing bilateral tumors with distinct molecular phenotypes. The findings from this study provide a foundation for optical molecular imaging of heterogeneous tumors and for studying the response of these complex lesions to targeted therapy.

Background: Preclinical studies have shown that activation of the glucocorticoid receptor (GR) leads to resistance to antiandrogens, which is reversed by GR inhibition. ORIC-101 is a potent, selective, orally bioavailable small molecule GR antagonist undergoing clinical development in combination with enzalutamide in patients with metastatic prostate cancer (NCT04033328). Methods: Ten patients were enrolled in the dose escalation portion of the Phase 1b study during which three dose levels of ORIC-101 given once daily were evaluated in combination with 160 mg enzalutamide. Translational markers were measured both pre-treatment and on study, including PD biomarkers, blood cortisol, GR and AR protein levels, and genomic alterations. PD biomarkers FKBP5, GILZ and PER1 were assessed by RT-qPCR in peripheral blood mononuclear cells (PBMCs), collected on multiple days and times in the first two cycles before and after dosing. PD modulation and target coverage were evaluable in 9 out of 10 patients. In tumor biopsies with >50 tumor cells, GR, AR and PTEN protein status were evaluated by immunohistochemistry (IHC). Liquid biopsies were collected before treatment, at the end of Cycle 2, and/or the end of treatment: nuclear GR and ARv7 protein levels were measured on circulating tumor cells (CTCs) by immunofluorescence (Epic Sciences, San Diego, CA), mutations and copy number alterations in cancer genes were captured in plasma with the 500-gene GuardantOMNI® ctDNA assay (Redwood City, CA). Results: PD suppression after one dose of ORIC-101 was observed in PBMCs of all patients. ORIC-101 reached steady-state target engagement within the first cycle in 6 out of 9 evaluable patients across dose levels, including at the RP2D. Nuclear GR protein was detected by IHC in the 6 pre-treatment biopsies, with H-scores ranging from 11 to 298 (median 95, IQR 55-148). Reduction of GR protein was observed in 3 out of 4 matched on study biopsies (pre-treatment H-scores 110-298), indicating potential elimination of GR positive tumor cells, while the fourth patient had low baseline GR levels (H-score 11). Pre-treatment AR protein levels were consistently high (IHC H-scores 230-300). AR alterations observed in ctDNA or CTCs were L702H (n=1 patient), H875Y (n=1), amplification (n=2), and ARv7 (n=2). PTEN protein aberrations were identified in two patients. The amount of tumor shedding in this cohort ranged from 0.24 to 82% (median 2.2%, IQR 0.54-12.1%), comparable to a clinical cohort of ~10,000 prostate tumors profiled with Guardant360® (Guardant Health). Prevalent genomic alterations at time of enrollment included TP53, RB1, BRCA2, ATM and SPOP, with minimal new genomic changes occurring on treatment. Conclusions: Biomarker data from patients enrolled in the Phase 1b study provide evidence of PD modulation, steady-state target coverage, and on-target tumor cell eradication at all dose levels. Tumor characterization in association with clinical outcome provides an opportunity to refine the patient population during the ongoing dose expansion portion of the study. Citation Format: Anneleen Daemen, Shravani Barkund, Ann Johnson, Aleksandr Pankov, Amber W. Wang, Haiying Zhou, Pratik S. Multani, Edna Chow Maneval, Lori S. Friedman, Rupal Patel. Biomarker results supporting selection of RP2D from a phase 1b study of ORIC-101, a glucocorticoid receptor antagonist, in combination with enzalutamide in patients with metastatic prostate cancer progressing on enzalutamide [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P015.

Androgen deprivation therapy (ADT) with or without antiandrogens such as enzalutamide is the mainstay of treatment in advanced prostate cancer (PC). However, new therapeutic strategies are needed for patients who relapse on antiandrogen therapy. The glucocorticoid receptor (GR) has been implicated as a potential antiandrogen bypass mechanism. We previously showed that ORIC-101, a potent and selective, orally bioavailable small molecule GR antagonist, reverses GR-mediated resistance to enzalutamide in preclinical PC models. In the clinic, we are evaluating ORIC-101 in combination with enzalutamide in patients with metastatic prostate cancer (NCT04033328). Activation of the PI3K/AKT pathway through PTEN loss is a poor prognostic factor and another potential resistance mechanism to anti-hormone directed therapies. Reciprocal crosstalk between androgen signaling and PI3K/AKT pathway activation forms the basis for the clinical development of AKT inhibitors (AKTi) in combination with ADT or antiandrogens (NCT03072238, NCT04087174). In this study, we tested preclinically whether activated GR confers resistance to the combination of AKT inhibitors with enzalutamide and whether co-treatment with ORIC-101 reverses GR-mediated resistance to an enzalutamide/AKTi doublet. We first evaluated the effects of enzalutamide plus AKTi treatment on GR levels, GR target genes and activity in three prostate cancer cell lines: PTEN-null line LNCaP and PTEN-wildtype lines VCaP and CWR22PC. We tested three AKT inhibitors: the ATP-competitive inhibitors ipatasertib (GDC-0068) and capivasertib (AZD5363), in addition to the allosteric inhibitor MK2206, in CSS media and 10% FBS, with or without supplementation of the synthetic glucocorticoid, dexamethasone. An increase in the protein and mRNA levels of GR and GR target genes was observed after 7 days of enzalutamide treatment. In the AKTi plus enzalutamide setting, AKT inhibition did not block the enzalutamide-mediated GR upregulation in either PTEN-null or PTEN-wildtype cells. We next evaluated whether increased GR activity mediates resistance to the enzalutamide/AKTi doublet with ipatasertib or capivasertib, and whether this resistance can be reversed with ORIC-101. GR activation with dexamethasone promoted tumor cell growth and androgen-regulated gene expression in the presence of enzalutamide and ipatasertib or capivasertib, using a 21-day proliferation assay in CWR22PC cells. ORIC-101 was able to reverse these dexamethasone-induced effects, confirmed by reduced secreted PSA levels and cell number measured at end of study. These findings indicate that GR upregulation and activation, an established resistance mechanism for antiandrogens, may drive resistance when combined with an AKT inhibitor, and the GR antagonist ORIC-101 is able to overcome this resistance and restore antitumor activity. Citation Format: Shravani Barkund, Haiying Zhou, Lori S. Friedman, Anneleen Daemen. GR antagonist ORIC-101 overcomes GR-mediated resistance to the combination of AR and AKT inhibition in preclinical prostate cancer cell lines [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 1420.

The polycomb repressive complex 2 (PRC2) is responsible for the methylation of histone 3 at lysine 27 (H3K27) which leads to long-term transcriptional silencing. Through this epigenetic chromatin silencing mechanism, PRC2 plays a key role in regulating cellular functions such as cell growth and differentiation. PRC2 comprises three core subunits: the catalytic subunit enhancer of zeste homolog 2 (EZH2), embryonic ectoderm development (EED) and suppressor of zeste 12 (SUZ12). EED directly interacts with histone H3K27me3 and is essential for the histone methyltransferase activity of PRC2. PRC2 dysregulation occurs in multiple solid tumors and hematological malignancies, resulting in elevated levels of PRC2 activity and H3K27 trimethylation, and has been linked to poor prognosis in patients with metastatic prostate cancer. First-generation PRC2 inhibitors which target EZH2 have demonstrated clinical activity in several cancers, yet the pharmacological and ADME properties of these compounds require high doses that only achieve partial target inhibition at clinically active levels and exhibit drug-drug interaction (DDI) liabilities. As an alternative strategy to fully inhibit the PRC2 complex, we developed ORIC-944, a potent and highly selective allosteric inhibitor of PRC2 via binding the EED subunit. This unique EED targeting strategy can more completely inhibit PRC2, for example, in the presence of innate or acquired resistance mutations in EZH2, and by addressing the potential compensatory escape mechanism of EZH1-driven tumor growth. ORIC-944 has potential best-in-class drug properties compared to first generation PRC2 inhibitors, including superior potency and improved DDI liabilities. In diffuse large B-cell lymphoma (DLBCL) xenografts in vivo, ORIC-944 significantly depleted H3K27 trimethylation and induced tumor regressions in a dose-dependent manner. ORIC-944 demonstrated strong tumor growth inhibition as a single agent with once daily oral dosing in both enzalutamide-responsive and enzalutamide-resistant prostate cancer models. ORIC-944 caused a significant reduction in tumor cell proliferation and anti-apoptotic signaling, as measured by Ki67 and survivin, respectively. Moreover, in PK/PD assessments, ORIC-944 strongly depleted H3K27me3 in treated tumors. These in vivo studies established that effective single agent inhibition of PRC2 via EED results in decreased tumor cell growth in PRC2-dependent prostate cancer models. In summary, ORIC-944 is a potent, highly selective, allosteric, orally bioavailable PRC2 inhibitor via the EED subunit that represents a differentiated strategy to block PRC2 activity in selected cancers. We are developing ORIC-944 as a best-in-class PRC2 inhibitor for the treatment of patients with advanced prostate cancer and expect to file an IND in the second half of 2021. Citation Format: Anneleen Daemen, Jessica D. Sun, Aleksandr Pankov, Frank L. Duong, Natalie Yuen, Shravani Barkund, Shelly Kaushik, Jae H. Chang, David M. Briere, Niranjan Sudhakar, Andrew Calinisan, Aaron Burns, John M. Ketcham, Matthew A. Marx, Peter Olson, James G. Christensen, Melissa R. Junttila, Lori S. Friedman. ORIC-944, a potent and selective allosteric PRC2 inhibitor, demonstrates robust in vivo activity in prostate cancer models [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 1131.

3110 Background: Preclinical studies have shown that activation of the glucocorticoid receptor (GR) leads to resistance to chemotherapeutics (eg taxanes) and antiandrogens across multiple tumor types, while GR inhibition enhances therapeutic efficacy. ORIC-101 is a potent, selective, and orally bioavailable small molecule GR antagonist undergoing clinical development in combination with nab-paclitaxel in patients with advanced solid tumors and in combination with enzalutamide in patients with metastatic prostate cancer. Methods: 21 patients were enrolled in the dose escalation portion of the phase 1b study, which evaluated both intermittent (5 days on, 2 days off for 21 days) and continuous dosing regimens of ORIC-101 across 5 cohorts (NCT03928314). Tumor tissue was obtained pre-treatment for 19 out of 21 patients, and on study or at the end of treatment for 11 patients. GR protein status was retrospectively evaluated using a proprietary IHC assay optimized for staining nuclear GR in the epithelial compartment of major tumor type tissues. Biopsies were also profiled with RNA-seq to evaluate a proprietary GR activation signature as a potentially predictive and pharmacodynamic (PD) biomarker. Blood-derived peripheral blood mononuclear cells (PBMCs) were collected for 20 patients along with the pre-treatment biopsy, in the morning of days 1, 5 and/or 8 of Cycle 1, and 2.5 or 6 hours after ORIC-101 administration. Blood cortisol levels were also simultaneously measured. PD modulation in PBMCs was assessed by RT-qPCR for biomarkers FKBP5, GILZ and PER1, selected for their consistent stimulation by GR and reversal with ORIC-101 in preclinical studies and observed PD modulation in healthy volunteers administered ORIC-101. Results: Nuclear GR protein was detected in most pre-treatment biopsies regardless of tumor type, and on treatment reduction of GR protein was observed across dose levels. At physiological systemic cortisol levels, ORIC-101 demonstrated PD suppression in PBMCs on days 1, 5 and 8 in the majority of patients. Cortisol levels increased post-dose in these patients due to negative feedback between cortisol and GR. Steady-state target engagement was not consistently demonstrated with the intermittent regimen. In healthy volunteer studies of ORIC-101, steady-state target suppression was consistently achieved after 7 consecutive daily doses of 200 or 350 mg of ORIC-101. Thus, continuous ORIC-101 administration was selected as the recommended phase 2 dose (RP2D) regimen, aimed at achieving sustained GR suppression for optimal chemotherapy re-sensitization. Conclusions: Biomarker data from patients enrolled in the phase 1b study provide evidence of on-target tumor cell eradication and PD modulation and support the RP2D and the tumor types selected for the ongoing dose expansion portion of the study. Clinical trial information: NCT03928314.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer and one of the most lethal cancers, with a 5-year survival rate of 8%. Chemotherapy remains the main treatment option for patients with advanced and metastatic tumors. However, intrinsic resistance to chemotherapeutics and lack of effective targeted therapies are major factors contributing to the dismal prognosis. Activation of glucocorticoid receptor (GR) signaling confers resistance to chemotherapy in solid tumors, making GR antagonism an attractive combination treatment strategy to overcome chemotherapeutic resistance. ORIC-101 is a novel selective GR antagonist under clinical evaluation in combination with anticancer therapies. We previously reported that ORIC-101 can sensitize triple-negative breast cancer cells to chemotherapy by reversing multiple GR-modulated pathways. Here, we investigate the effects of ORIC-101 in preclinical models of PDAC. Employing in vitro functional assays and gene expression analysis, ORIC-101 exhibited chemo-potentiation in a panel of PDAC cell lines. Biomarker analysis of transcription activity following ORIC-101 treatment in vitro confirmed pharmacodynamic (PD) modulation of core GR target genes, indicative of suppressed GR signaling. Extending these findings in vivo across several PDAC xenograft models (SW1990, BxPC3, and HPAC) revealed that ORIC-101 blocks GR transcriptional activity induced by dexamethasone in a dose-dependent manner. The PD modulation observed in vivo correlated with ORIC-101 plasma exposure. Consistent with ORIC-101's ability to suppress GR activity, in vivo efficacy studies in combination with paclitaxel significantly inhibited PDAC tumor growth compared to the paclitaxel control group. These results in PDAC preclinical models support the clinical development of ORIC-101 in overcoming GR-driven chemoresistance. A phase 1b study of ORIC-101 in combination with nab-paclitaxel in patients with advanced or metastatic solid tumors is ongoing (NCT03928314). Citation Format: Jessica D. Sun, Haiying Zhou, Wayne Kong, Natalie Yuen, Frank L. Duong, Shravani Barkund, Aleksandr Pankov, Dan McWeeney, Qiuping Ye, Omar Kabbarah, Lori S. Friedman, Anneleen Daemen, Melissa Junttila. ORIC-101 overcomes glucocorticoid receptor-mediated chemoresistance in pancreatic cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4123.

Preclinical studies have shown that GR activation leads to decreased response to antimetabolites, taxanes, and platinum agents, while GR inhibition enhances therapeutic efficacy. The novel, selective GR antagonist ORIC-101 is under clinical evaluation in combination with anticancer therapies. In this study we set out to assess which cancer types and chemotherapeutics are responsive to combination with ORIC-101. Specifically, we employed caspase assays, in vitro and in vivo tumor growth inhibition studies, and transcriptional profiling in a panel of preclinical models spanning triple-negative breast, ovarian, non-small cell lung cancers, pancreatic ductal adenocarcinoma, hepatocellular carcinoma, sarcoma, and renal cell carcinoma. We found that ORIC-101 reverses GR-mediated antiapoptosis effects towards diverse chemotherapeutics, including paclitaxel, gemcitabine, and cisplatin, across the seven cancer types. Furthermore, ORIC-101 completely overcomes GR-driven chemoprotection and tumor growth in colony formation assays in vitro and in xenograft studies in vivo. At the molecular level, transcriptional profiling and pathway enrichment analysis showed that ORIC-101 fully reverses GR-activated pathways that are directly involved in drug resistance, such as epithelial-to-mesenchymal transition and antiapoptosis, supporting a pan-cancer role of GR as a mediator of therapy resistance. Altogether, ORIC-101, a selective and potent GR antagonist, overcomes resistance to common chemotherapeutics across multiple cancer models. Clinical evaluation of ORIC-101 in combination with nab-paclitaxel is currently ongoing in advanced solid tumors. Citation Format: Haiying Zhou, Shravani Barkund, Aleksandr Pankov, Ganapati Hegde, Wayne Kong, Padmini Narayanan, Jessica D. Sun, Omar Kabbarah, Lori S. Friedman, Anneleen Daemen. ORIC-101 overcomes resistance to diverse chemotherapeutics across cancer types [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4121.

Preclinical studies have established a role for the Glucocorticoid Receptor (GR) in mediating resistance to both anti-hormonal therapies and conventional chemotherapies in epithelial cancers. Studies in breast cancer models have established that the chemoprotective effect afforded by GR activation is facilitated, at least partially, through upregulation of genes involved in anti-apoptosis, epithelial-to-mesenchymal transition (EMT), and metastasis - thus suggesting that GR inhibition may enhance therapeutic responses. A novel GR antagonist, ORIC-101, is in early clinical development in combination with nab-paclitaxel in advanced solid tumors (NCT03928314). We set out to understand the transcriptional consequences of activating GR in a panel of 9 triple negative breast cancer (TNBC), 12 non-small cell lung cancer (NSCLC) and 12 pancreatic ductal adenocarcinoma (PDAC) cell lines, covering three indications likely to be encountered in clinical trials. Cell lines were selected to capture the transcriptional variability across subtypes of each indication, and transcriptome profiling using RNA-sequencing was performed on these cell lines after treatment with the synthetic glucocorticoid dexamethasone (Dex) in the presence or absence of ORIC-101. We present a comprehensive evaluation of GR-mediated signaling across 3 key indications and 33 cancer cell lines. Overall, Dex resulted in transcriptional regulation of hundreds of genes. While there was a high degree of variation in the specific genes regulated by GR across TNBC, NSCLC, and PDAC models, a set of 11 genes emerged as consistently upregulated by GR, termed the “GR activation signature”. The addition of ORIC-101 completely reverted the expression of these 11 signature genes back to vehicle condition levels. We further validated a subset of signature genes as ORIC-101 pharmacodynamic biomarkers that may be used to inform target engagement status within a patient population in clinical trials. Despite the high degree of variability in the GR-driven transcriptional programs at the gene level, pathway enrichment analysis revealed biological convergence towards a common set of GR regulated pathways including EMT, apoptosis, stemness, hypoxia, inflammation/immune regulation, and extracellular matrix. These molecular processes associated with GR were observed across TNBC, NSCLC, and PDAC cell lines, suggesting a common drug resistance mechanism of GR across the cancer types. Importantly, ORIC-101 completely reversed these Dex-induced changes at both the gene and the pathway level. Our results not only elucidate the direct mechanism of GR-mediated chemotherapy resistance but also showcase the ability of ORIC-101 to revert all transcriptional changes caused by GR activation. Citation Format: Aleksandr Pankov, Haiying Zhou, Shravani Barkund, Ganapati Hegde, Padmini Narayanan, Omar Kabbarah, Lori S. Friedman, Anneleen Daemen. ORIC-101 comprehensively inhibits glucocorticoid pathways to overcome therapeutic resistance in pan-cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4120.

ORIC-101 is a novel and selective glucocorticoid receptor (GR) antagonist currently in Ph1 clinical evaluation in solid tumors. In preclinical models, ORIC-101 potently sensitized triple-negative breast cancer (TNBC) cells to chemotherapy by inhibiting GR-mediated resistance through the epithelial-to-mesenchymal transition and anti-apoptosis pathways, both in vitro and in vivo. To inform the clinical development of ORIC-101, we identified pharmacodynamic (PD) biomarkers and established a relationship between those biomarkers, pharmacokinetics (PK), and efficacy in preclinical models. Using genome-wide profiling, we developed a GR activation signature that includes the direct GR transcriptional targets FKBP5 and GILZ, and subsequently validated both genes as ORIC-101 PD biomarkers in a panel of cell lines. We demonstrated that FKBP5 and GILZ are transcriptionally induced by glucocorticoids in a dose-dependent manner, and that the degree of their transcriptional activation is correlated with basal levels of GR in these models. We showed that ORIC-101 robustly inhibits the transcriptional induction of FKBP5 and GILZ and fully reverses GR-mediated chemoresistance in vitro and in vivo. Furthermore, FKBP5 and GILZ are reliable PD biomarkers for ORIC-101 in human-derived peripheral blood mononuclear cells (PBMCs). Importantly, by integrating PK, PD, and efficacy results from numerous preclinical studies, we captured the relationship between ORIC-101 PK, PD biomarker modulation, and chemopotentiation. Altogether, FKBP5 and GILZ mRNA levels are robust PD biomarkers to measure GR pathway engagement and modulation which corresponds with efficacy in response to GR antagonist treatment in preclinical models. These findings will guide the clinical development of ORIC-101 in TNBC. Citation Format: Haiying Zhou, Qiuping Ye, Aleksandr Pankov, Wayne Kong, Shravani Barkund, Lori S. Friedman, Jessica D. Sun, Omar Kabbarah. ORIC-101 robustly inhibits the glucocorticoid pathway and overcomes chemoresistance in triple-negative breast cancer [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 P6-03-24.

Prostate cancer is the second leading cause of cancer-related death in men. Androgen deprivation is commonly used to treat hormone-sensitive prostate cancer, while second-generation antiandrogens, including enzalutamide and abiraterone, benefit patients with castration-resistant prostate cancer (CRPC). New therapeutic strategies are needed for patients who relapse with metastatic CRPC. The glucocorticoid receptor (GR) has been implicated as a major bypass mechanism to escape androgen blockade in patients with CRPC, indicating that GR-targeted therapies may provide an avenue to overcome therapeutic resistance in this clinical setting. We discovered a novel, selective, oral GR antagonist, ORIC-101, which fully reverses GR-driven resistance to enzalutamide in a dose-dependent manner in preclinical models. Specifically, we show that GR is widely expressed in prostate cancer cell lines, organoids, and tumor tissue, and that GR levels are upregulated upon enzalutamide treatment. We demonstrate in preclinical studies that physiological levels of glucocorticoids promote tumor cell growth, stimulate androgen-regulated gene expression, and drive resistance to enzalutamide. Importantly, these effects were completely reversed by ORIC-101, suggesting ORIC-101 overcomes GR-driven resistance to enzalutamide. To inform the clinical development of ORIC-101 in combination with enzalutamide, we identified FKBP5 and KLK3 as direct transcriptional targets of both androgen receptor and GR. We subsequently validated that secreted PSA, a product of the KLK3 gene, can be induced by glucocorticoids and this induction is fully inhibited by ORIC-101. These findings confirm that targeting GR may help overcome resistance to enzalutamide in CRPC, and that FKBP5 and KLK3 are rational PD biomarkers that may be used in clinical trials of ORIC-101, along with PSA. Citation Format: Haiying Zhou, Shravani Barkund, Aleksandr Pankov, Sharvani Sinha, Dena Sutimantanapi, Lori S. Friedman, Omar Kabbarah. ORIC-101 overcomes glucocorticoid-driven resistance to enzalutamide in castration-resistant prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A10. doi:10.1158/1535-7163.TARG-19-LB-A10