Nhin Lu

A Clinically Relevant Androgen Receptor Mutation Confers Resistance to Second-Generation Antiandrogens Enzalutamide and ARN-509

UNLABELLED Despite the impressive clinical activity of the second-generation antiandrogens enzalutamide and ARN-509 in patients with prostate cancer, acquired resistance invariably emerges. To identify the molecular mechanisms underlying acquired resistance, we developed and characterized cell lines resistant to ARN-509 and enzalutamide. In a subset of cell lines, ARN-509 and enzalutamide exhibit agonist activity due to a missense mutation (F876L) in the ligand-binding domain of the androgen receptor (AR). AR F876L is sufficient to confer resistance to ARN-509 and enzalutamide in in vitro and in vivo models of castration-resistant prostate cancer (CRPC). Importantly, the AR F876L mutant is detected in plasma DNA from ARN-509-treated patients with progressive CRPC. Thus, selective outgrowth of AR F876L is a clinically relevant mechanism of second-generation antiandrogen resistance that can potentially be targeted with next-generation antiandrogens. SIGNIFICANCE A missense mutation in the ligand-binding domain of the androgen receptor F876L confers resistance to the second-generation antiandrogens enzalutamide and ARN-509 in preclinical models of AR function and prostate cancer and is detected in plasma DNA from ARN-509-treated patients with progressive disease. These results chart a new path for the discovery and development of next-generation antiandrogens that could be coupled with a blood-based companion diagnostic to guide treatment decisions.

Identification of GDC-0810 (ARN-810), an Orally Bioavailable Selective Estrogen Receptor Degrader (SERD) that Demonstrates Robust Activity in Tamoxifen-Resistant Breast Cancer Xenografts

Approximately 80% of breast cancers are estrogen receptor alpha (ER-α) positive, and although women typically initially respond well to antihormonal therapies such as tamoxifen and aromatase inhibitors, resistance often emerges. Although a variety of resistance mechanism may be at play in this state, there is evidence that in many cases the ER still plays a central role, including mutations in the ER leading to constitutively active receptor. Fulvestrant is a steroid-based, selective estrogen receptor degrader (SERD) that both antagonizes and degrades ER-α and is active in patients who have progressed on antihormonal agents. However, fulvestrant suffers from poor pharmaceutical properties and must be administered by intramuscular injections that limit the total amount of drug that can be administered and hence lead to the potential for incomplete receptor blockade. We describe the identification and characterization of a series of small-molecule, orally bioavailable SERDs which are potent antagonists and degraders of ER-α and in which the ER-α degrading properties were prospectively optimized. The lead compound 11l (GDC-0810 or ARN-810) demonstrates robust activity in models of tamoxifen-sensitive and tamoxifen-resistant breast cancer, and is currently in clinical trials in women with locally advanced or metastatic estrogen receptor-positive breast cancer.

The selective estrogen receptor downregulator GDC-0810 is efficacious in diverse models of ER+ breast cancer

ER-targeted therapeutics provide valuable treatment options for patients with ER+ breast cancer, however, current relapse and mortality rates emphasize the need for improved therapeutic strategies. The recent discovery of prevalent ESR1 mutations in relapsed tumors underscores a sustained reliance of advanced tumors on ERα signaling, and provides a strong rationale for continued targeting of ERα. Here we describe GDC-0810, a novel, non-steroidal, orally bioavailable selective ER downregulator (SERD), which was identified by prospectively optimizing ERα degradation, antagonism and pharmacokinetic properties. GDC-0810 induces a distinct ERα conformation, relative to that induced by currently approved therapeutics, suggesting a unique mechanism of action. GDC-0810 has robust in vitro and in vivo activity against a variety of human breast cancer cell lines and patient derived xenografts, including a tamoxifen-resistant model and those that harbor ERα mutations. GDC-0810 is currently being evaluated in Phase II clinical studies in women with ER+ breast cancer.

Optimization of an indazole series of selective estrogen receptor degraders: Tumor regression in a tamoxifen-resistant breast cancer xenograft

Selective estrogen receptor degraders (SERDs) have shown promise for the treatment of ER+ breast cancer. Disclosed herein is the continued optimization of our indazole series of SERDs. Exploration of ER degradation and antagonism in vitro followed by in vivo antagonism and oral exposure culminated in the discovery of indazoles 47 and 56, which induce tumor regression in a tamoxifen-resistant breast cancer xenograft.

Abstract 4757: A novel class of selective estrogen receptors degraders regresses tumors in pre-clinical models of endocrine-resistant breast cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA 80% of all breast cancers express the estrogen receptor alpha (ERα) and thus are treated with anti-hormonal therapies that directly block ER function (e.g.Tamoxifen) or hormone synthesis (Aromatase Inhibitors). While these therapies are initially effective, acquired resistance invariably emerges and disease progression ensues. Importantly, the majority of these tumors continue to depend on ERα for growth and survival via both ligand-dependent and ligand-independent pathways. The emerging evidence that ERα can be activated in the absence of estrogens via point mutations in ERα or cellular signaling pathways supports the development of agents that are not only competitive ERα antagonists but also reduce steady state levels of the receptor and thus limit both ligand dependent and independent signaling. We have identified two novel series of non-steroidal ERα antagonists, series I exemplified by ARN-810, now in clinical trials for treatment of endocrine resistant breast cancer, and series II, both of which induce degradation of ERα at picomolar concentrations resulting in significant reduction in steady state ERα protein levels in breast cancer cell lines. Using peptide-based conformational profiling, we show that both series induce ERα conformations that are distinct from both fulvestrant and tamoxifen indicating novel mechanism of action. In vitro, both ligand series are active on wild-type and the constitutively active ERα mutants found in endocrine resistant breast cancer patients. Importantly, these compounds yield tumor regression in both tamoxifen-sensitive and -resistant models of breast cancer in vivo. Based on their unique in vitro profile, and good pharmacokinetics following oral dosing, these compounds represent a novel class of Selective Estrogen Receptor Degraders (SERDs) that hold promise as a next generation therapy for the treatment of ER+ breast cancer as monotherapy, as well as in combination with agents that target other pathways involved in both intrinsic and acquired endocrine resistance. Citation Format: James D. Joseph, Beatrice Darimont, Steven Govek, Dan Brigham, Jing Qian, John Sensintaffar, Gang Shao, Anna Aparicio, Mehmet Kahraman, Andiliy Lai, Kyoung-Jin Lee, Nhin Lu, Johnny Nagasawa, Michael Moon, Peter Rix, Nick Smith, Jeff Hager. A novel class of selective estrogen receptors degraders regresses tumors in pre-clinical models of endocrine-resistant breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4757. doi:10.1158/1538-7445.AM2014-4757

Identification of an Orally Bioavailable Chromene-Based Selective Estrogen Receptor Degrader (SERD) That Demonstrates Robust Activity in a Model of Tamoxifen-Resistant Breast Cancer

About 75% of breast cancers are estrogen receptor alpha (ER-α) positive, and women typically initially respond well to antihormonal therapies such as tamoxifen and aromatase inhibitors, but resistance often emerges. Fulvestrant is a steroid-based, selective estrogen receptor degrader (SERD) that both antagonizes and degrades ER-α and shows some activity in patients who have progressed on antihormonal agents. However, fulvestrant must be administered by intramuscular injections that limit its efficacy. We describe the optimization of ER-α degradation efficacy of a chromene series of ER modulators resulting in highly potent and efficacious SERDs such as 14n. When examined in a xenograft model of tamoxifen-resistant breast cancer, 14n (ER-α degradation efficacy = 91%) demonstrated robust activity, while, despite superior oral exposure, 15g (ER-α degradation efficacy = 82%) was essentially inactive. This result suggests that optimizing ER-α degradation efficacy in the MCF-7 cell line leads to compounds with robust effects in models of tamoxifen-resistant breast cancer derived from an MCF-7 background.

Abstract 5053: Discovery of GDC-0810 a novel, non-steroidal selective estrogen receptor degrader with robust activity in pre-clinical models of endocrine-resistant breast cancer

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA The majority of breast cancers express estrogen receptor alpha (ERα) and thus are treated with anti-hormonal therapies that directly block ER function (e.g.Tamoxifen) or hormone synthesis (Aromatase Inhibitors). While these therapies are initially effective, acquired resistance emerges and disease progression ensues. Importantly, the majority of these tumors continue to depend on ERα for growth and survival via both ligand-dependent and ligand-independent pathways. The emerging evidence that ERα can be activated in the absence of estrogens via point mutations in ERα or cellular signaling pathways supports the development of agents that are not only competitive ERα antagonists but also reduce steady state levels of the receptor and thus limit both ligand dependent and independent signaling. Here we disclose the discovery of ARN-810, also known as GDC-0810. ARN-810 is an oral, potent antagonist of ER that also induces degradation of ERα at picomolar concentrations. ARN-810 treatment results in significant reduction in steady state ERα protein levels in breast cancer cell lines. Using peptide-based conformational profiling, we show ARN-810 induces ERα conformations that are distinct from both fulvestrant and tamoxifen indicating novel mechanism of action. In vitro, ARN-810 is active on wild-type and the constitutively active ERα mutants found in endocrine resistant breast cancer patients. Importantly, ARN-810 is active in cell-line and in vivo models of ESR1 wild-type and mutant, primary and endocrine-resistant breast cancers including patient derived xenograft (PDX) models. These preclinical data indicate that ARN-810, a novel Selective Estrogen Receptor Degrader (SERD), holds promise as a next generation therapy for the treatment of ER+ breast cancer as monotherapy, as well as in combination with agents that target other pathways involved in both intrinsic and acquired endocrine resistance. ARN-810 is in clinical development for the treatment of ER+ breast cancer. Citation Format: James Joseph, Steven Govek, Beatrice Darimont, Daniel Brigham, Anna Aparicio, Eric Bischoff, Mehmet Kahraman, Michelle Nannini, Joshua Kaufman, Andily Lai, Kyoung-Jin Lee, Jason Oeh, Nhin Lu, Wei Zhou, Michael Moon, Jing Qian, John Sensintaffar, Gang Shao, Deepak Sampath, Lori S. Friedman, Peter Rix, Richard A. Heyman, Nicholas Smith, Jeffrey H. Hager. Discovery of GDC-0810 a novel, non-steroidal selective estrogen receptor degrader with robust activity in pre-clinical models of endocrine-resistant breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5053. doi:10.1158/1538-7445.AM2015-5053

Abstract A37: A novel class of selective estrogen receptor degraders display activity in pre-clinical models of ERα+ ovarian cancer

Greater than 50% of high grade serous ovarian cancers express the estrogen receptor alpha (ERα). This observation, in addition to multiple lines of epidemiological and preclinical data, suggests that, similar to breast and endometrial cancer, estrogen receptor signaling may play a role in the development and progression of ovarian cancer. Unfortunately, unlike in breast cancer, therapeutically targeting ERα signaling in patients with recurrent ovarian cancer typically yields only marginal clinical responses. However, patient selection based solely on ERα expression increases the response rate of aromatase inhibitors suggesting that ERα may be a viable therapeutic target in a subset of ovarian cancer patients. Given the presentation of late-stage disease, the mutational complexity and alteration of multiple signaling pathways known to induce ligand independent ERα activity in ovarian cancer, additional levels of patient stratification as well as novel therapeutics that target both the ligand dependent and independent ERα signaling, have the potential to yield better therapeutic outcomes. We have identified novel, orally bioavailable non-steroidal ERα antagonists that induce ERα degradation at picomolar concentrations in vitro resulting in significant reduction in steady state ERα protein levels in multiple cancer cell lines. Using peptide-based conformational profiling, we show that these ligands induce estrogen receptor conformations that are distinct from both fulvestrant and tamoxifen indicating novel mechanism of action. Importantly, these compounds block the growth of tamoxifen-sensitive and -resistant models of breast cancer and endometrial cancer in vivo. Similar to the breast and endometrial cancer models, these compounds antagonize ER target gene expression and induce ERα degradation in two ER+ ovarian cancer cell lines, OVSAHO and OVKATE, whereas the first generation ER antagonist tamoxifen antagonizes transcription but stabilizes ERα in this setting. Consistent with their transcriptional antagonist and degrader activities, these compounds also inhibit the hormone-dependent growth of these cell lines in vivo. Based on these findings, these compounds represent a novel class of Selective Estrogen Receptor Degraders (SERDs) that may hold promise as a next generation therapy for the treatment of ER+ ovarian cancer as monotherapy and importantly as combination therapy with agents that target the key nodal points critical to malignant progression or new, emergent agents displaying promising activity. Citation Format: James D. Joseph, Beatrice Darimont, Steven Govek, Dan Brigham, Anna Aparicio, Mehmet Kahraman, Andiliy Lai, Kyoung-Jin Lee, Nhin Lu, Johnny Nagasawa, Josh Kaufman, Michael Moon, Rene Prudente, Jing Qian, John Sensintaffar, Gang Shao, Peter Rix, Nick Smith, Jeff Hager. A novel class of selective estrogen receptor degraders display activity in pre-clinical models of ERα+ ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A37.

Abstract C16: Targeting AR in castration-resistant prostate cancer: Development of ARN-509 and second-generation antiandrogen resistance models

Abstract The androgen receptor (AR) plays a central role in the development and progression of prostate cancer. Recent studies demonstrate that AR remains essential in the majority of castration resistant prostate cancer (CRPC) after classical androgen ablation therapies have failed. The clinical efficacies of MDV3100 and abiraterone acetate, both of which target the AR pathway in the castrate resistant setting, support these findings. ARN-509 is a 2nd generation competitive AR antagonist that, unlike bicalutamide, maintains full antagonist activity in preclinical CRPC models. ARN-509 does not robustly induce AR nuclear localization or DNA binding. However, ARN-509 displays maximal efficacy in the LNCaP/AR xenograft model of CRPC at lower dose and steady state plasma concentrations compared to MDV3100, suggesting potential for higher therapeutic index and ability to deliver the maximally efficacious dose in man. To date, ARN-509 has shown promising antitumor activity in mCRPC patients enrolled in a Phase 1 study. Given that approximately 50% of CRPC patients have suboptimal response to MDV3100 and abiraterone acetate as well as the observation that resistance eventually develops in patients who initially respond to therapy, we sought to determine whether AR remains a viable therapeutic target in the MDV3100 and ARN-509 resistant setting. To this end, we generated several MDV3100 and ARN-509 resistant derivatives of the LNCaP and LNCaP/AR cell lines. While work is underway to determine the molecular mechanisms of resistance, a subset of cell lines does not require androgens for growth in vitro. These androgen independent derivatives express AR at levels comparable to LNCaP/AR (approximately 3X LNCaP) or 2-3 fold LNCaP-AR. When representative lines are injected into castrated mice, they demonstrate a decreased latency of tumor formation compared to the parental cell line both in the presence and absence of ARN-509. Importantly, in all lines tested, small interfering RNA mediated reduction in AR levels dramatically impaired the ability of the androgen independent resistant cell lines to proliferate in the absence of androgens. These data support the hypothesis that AR remains a viable therapeutic target for second generation anti-androgen resistant prostate cancer and is the first step toward establishing a platform to screen for next generation anti-androgens. Citation Format: James D. Joseph, Anna Aparicio, Josh Kaufman, Jackie Julien, Celine Bonnefous, Nicholas D. Smith, Peter Rix, Michael E. Jung, Charles L. Sawyers, Richard A. Heyman, Jeffrey H. Hager, Nicola J. Clegg, John Sensintaffar, Nhin Lu, Kate Grillot, Eric Bischoff, Gang Shao, Jing Qian, Beatrice Darimont. Targeting AR in castration-resistant prostate cancer: Development of ARN-509 and second-generation antiandrogen resistance models [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C16.