Maximizing ER-α Degradation Maximizes Activity in a Tamoxifen-Resistant Breast Cancer Model: Identification of GDC-0927.

The further optimization of ER-α degradation efficacy of a series of ER modulators by refining side-chain substitution led to efficacious selective estrogen receptor degraders (SERDs). A fluoromethyl azetidine group was found to be preferred and resulted in the identification of bis-phenol chromene 17ha. In a tamoxifen-resistant breast cancer xenograft model, 17ha (ER-α degradation efficacy = 97%) demonstrated tumor regression, together with robust reduction of intratumoral ER-α levels. However, despite superior oral exposure, 5a (ER-α degradation efficacy = 91%) had inferior activity. This result suggests that optimizing ER-α degradation efficacy leads to compounds with robust effects in a model of tamoxifen-resistant breast cancer. Compound 17ha (GDC-0927) was evaluated in clinical trials in women with metastatic estrogen receptor-positive breast cancer.

Selective estrogen receptor degraders with novel structural motifs induce regression in a tamoxifen-resistant breast cancer xenograft.

Potent estrogen receptor ligands typically contain a phenolic hydrogen-bond donor. The indazole of the selective estrogen receptor degrader (SERD) ARN-810 is believed to mimic this. Disclosed herein is the discovery of ARN-810 analogs which lack this hydrogen-bond donor. These SERDs induced tumor regression in a tamoxifen-resistant breast cancer xenograft, demonstrating that the indazole NH is not necessary for robust ER-modulation and anti-tumor activity.

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.

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.

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.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of nebulized sodium nitrite (AIR001) following repeat-dose inhalation in healthy subjects.

INTRODUCTION: The efficacy of nebulized sodium nitrite (AIR001) has been demonstrated in animal models of pulmonary arterial hypertension (PAH), but it was not known if inhaled nitrite would be well tolerated in human subjects at exposure levels associated with efficacy in these models. METHODS: Inhaled nebulized sodium nitrite was assessed in three independent studies in a total of 82 healthy male and female subjects. Study objectives included determination of the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) under normal and mildly hypoxic conditions, and following co-administration with steady-state sildenafil, assessment of nitrite pharmacokinetics, and evaluation of the fraction exhaled nitric oxide (FENO) and concentrations of iron-nitrosyl hemoglobin (Hb(Fe)-NO) and S-nitrosothiols (R-SNO) as biomarkers of local and systemic NO exposure, respectively. RESULTS: Nebulized sodium nitrite was well tolerated following 6 days of every 8 h administration up to 90 mg, producing significant increases in circulating Hb(Fe)-NO, R-SNO, and FENO. Pulmonary absorption of nitrite was rapid and complete, and plasma exposure dose was proportional through the MTD dosage level of 90 mg, without accumulation following repeated inhalation. At higher dosage levels, DLTs were orthostasis (observed at 120 mg) and hypotension with tachycardia (at 176 mg), but venous methemoglobin did not exceed 3.0 % at any time in any subject. Neither the tolerability nor pharmacokinetics of nitrite was impacted by conditions of mild hypoxia, or co-administration with sildenafil, supporting the safe use of inhaled nitrite in the clinical setting of PAH. CONCLUSION: On the basis of these results, nebulized sodium nitrite (AIR001) has been advanced into randomized trials in PAH patients.

Phase I study of ARN-509, a novel antiandrogen, in the treatment of castration-resistant prostate cancer.

PURPOSE: ARN-509 is a novel androgen receptor (AR) antagonist for the treatment of castration-resistant prostate cancer (CRPC). ARN-509 inhibits AR nuclear translocation and AR binding to androgen response elements and, unlike bicalutamide, does not exhibit agonist properties in the context of AR overexpression. This first-in-human phase I study assessed safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor activity of ARN-509 in men with metastatic CRPC. PATIENTS AND METHODS: Thirty patients with progressive CRPC received continuous daily oral ARN-509 at doses between 30 and 480 mg, preceded by administration of a single dose followed by a 1-week observation period with pharmacokinetic sampling. Positron emission tomography/computed tomography imaging was conducted to monitor [(18)F]fluoro-α-dihydrotestosterone (FDHT) binding to AR in tumors before and during treatment. Primary objective was to determine pharmacokinetics, safety, and recommended phase II dose. RESULTS: Pharmacokinetics were linear and dose proportional. Prostate-specific antigen declines at 12 weeks (≥ 50% reduction from baseline) were observed in 46.7% of patients. Reduction in FDHT uptake was observed at all doses, with a plateau in response at ≥ 120-mg dose, consistent with saturation of AR binding. The most frequently reported adverse event was grade 1/2 fatigue (47%). One dose-limiting toxicity event (grade 3 abdominal pain) occurred at the 300-mg dose. Dose escalation to 480 mg did not identify a maximum-tolerated dose. CONCLUSION: ARN-509 was safe and well tolerated, displayed dose-proportional pharmacokinetics, and demonstrated pharmacodynamic and antitumor activity across all dose levels tested. A maximum efficacious dose of 240 mg daily was selected for phase II exploration based on integration of preclinical and clinical data.

ARN-509: a novel antiandrogen for prostate cancer treatment.

Continued reliance on the androgen receptor (AR) is now understood as a core mechanism in castration-resistant prostate cancer (CRPC), the most advanced form of this disease. While established and novel AR pathway-targeting agents display clinical efficacy in metastatic CRPC, dose-limiting side effects remain problematic for all current agents. In this study, we report the discovery and development of ARN-509, a competitive AR inhibitor that is fully antagonistic to AR overexpression, a common and important feature of CRPC. ARN-509 was optimized for inhibition of AR transcriptional activity and prostate cancer cell proliferation, pharmacokinetics, and in vivo efficacy. In contrast to bicalutamide, ARN-509 lacked significant agonist activity in preclinical models of CRPC. Moreover, ARN-509 lacked inducing activity for AR nuclear localization or DNA binding. In a clinically valid murine xenograft model of human CRPC, ARN-509 showed greater efficacy than MDV3100. Maximal therapeutic response in this model was achieved at 30 mg/kg/d of ARN-509, whereas the same response required 100 mg/kg/d of MDV3100 and higher steady-state plasma concentrations. Thus, ARN-509 exhibits characteristics predicting a higher therapeutic index with a greater potential to reach maximally efficacious doses in man than current AR antagonists. Our findings offer preclinical proof of principle for ARN-509 as a promising therapeutic in both castration-sensitive and castration-resistant forms of prostate cancer.

Pharmacological characterization of KLYP961, a dual inhibitor of inducible and neuronal nitric-oxide synthases.

Nitric oxide (NO) derived from neuronal nitric-oxide synthase (nNOS) and inducible nitric-oxide synthase (iNOS) plays a key role in various pain and inflammatory states. KLYP961 (4-((2-cyclobutyl-1H-imidazo[4,5-b]pyrazin-1-yl)methyl)-7,8-difluoroquinolin-2(1H)-one) inhibits the dimerization, and hence the enzymatic activity of human, primate, and murine iNOS and nNOS (IC(50) values 50-400 nM), with marked selectivity against endothelial nitric-oxide synthase (IC(50) >15,000 nM). It has ideal drug like-properties, including excellent rodent and primate pharmacokinetics coupled with a minimal off-target activity profile. In mice, KLYP961 attenuated endotoxin-evoked increases in plasma nitrates, a surrogate marker of iNOS activity in vivo, in a sustained manner (ED(50) 1 mg/kg p.o.). KLYP961 attenuated pain behaviors in a mouse formalin model (ED(50) 13 mg/kg p.o.), cold allodynia in the chronic constriction injury model (ED(50) 25 mg/kg p.o.), or tactile allodynia in the spinal nerve ligation model (ED(50) 30 mg/kg p.o.) with similar efficacy, but superior potency relative to gabapentin, pregabalin, or duloxetine. Unlike morphine, the antiallodynic activity of KLYP961 did not diminish upon repeated dosing. KLYP961 also attenuated carrageenin-induced edema and inflammatory hyperalgesia and writhing response elicited by phenylbenzoquinone with efficacy and potency similar to those of celecoxib. In contrast to gabapentin, KLYP961 did not impair motor coordination at doses as high as 1000 mg/kg p.o. KLYP961 also attenuated capsaicin-induced thermal allodynia in rhesus primates in a dose-related manner with a minimal effective dose (≤ 10 mg/kg p.o.) and a greater potency than gabapentin. In summary, KLYP961 represents an ideal tool with which to probe the physiological role of NO derived from iNOS and nNOS in human pain and inflammatory states.

Substituted 6-(1-pyrrolidine)quinolin-2(1H)-ones as novel selective androgen receptor modulators.

The androgen receptor is a ligand inducible transcription factor that is involved in a broad range of physiological functions. Here we describe the discovery of a new class of orally available selective androgen receptor modulators. The lead compound, 6-[(2R,5R)-2-methyl-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)pyrrolidin-1-yl]-4-trifluoromethylquinolin-2(1H)-one (6a), showed excellent anabolic activity in muscle with reduced effect on the prostate in a rat model of hypogonadism. The compound also improved bone strength in a rat model of post-menopausal osteoporosis.