Jing Wang

PURPOSE: Estrogen receptor (ER) alpha signaling is a known driver of ER-positive (ER+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer. Combining endocrine therapy (ET) such as fulvestrant with CDK4/6, mTOR, or PI3K inhibitors has become a central strategy in the treatment of ER+ advanced breast cancer. However, suboptimal ER inhibition and resistance resulting from the ESR1 mutation dictates that new therapies are needed. EXPERIMENTAL DESIGN: A medicinal chemistry campaign identified vepdegestrant (ARV-471), a selective, orally bioavailable, and potent small molecule PROteolysis-TArgeting Chimera (PROTAC) degrader of ER. We used biochemical and intracellular target engagement assays to demonstrate the mechanism of action of vepdegestrant, and ESR1 wild-type (WT) and mutant ER+ preclinical breast cancer models to demonstrate ER degradation-mediated tumor growth inhibition (TGI). RESULTS: Vepdegestrant induced ≥90% degradation of wild-type and mutant ER, inhibited ER-dependent breast cancer cell line proliferation in vitro, and achieved substantial TGI (87%-123%) in MCF7 orthotopic xenograft models, better than those of the ET agent fulvestrant (31%-80% TGI). In the hormone independent (HI) mutant ER Y537S patient-derived xenograft (PDX) breast cancer model ST941/HI, vepdegestrant achieved tumor regression and was similarly efficacious in the ST941/HI/PBR palbociclib-resistant model (102% TGI). Vepdegestrant-induced robust tumor regressions in combination with each of the CDK4/6 inhibitors palbociclib, abemaciclib, and ribociclib; the mTOR inhibitor everolimus; and the PI3K inhibitors alpelisib and inavolisib. CONCLUSIONS: Vepdegestrant achieved greater ER degradation in vivo compared with fulvestrant, which correlated with improved TGI, suggesting vepdegestrant could be a more effective backbone ET for patients with ER+/HER2- breast cancer.

<div>AbstractPurpose:<p>Estrogen receptor (ER) alpha signaling is a known driver of ER-positive (ER<sup>+</sup>)/human epidermal growth factor receptor 2 negative (HER2<sup>−</sup>) breast cancer. Combining endocrine therapy (ET) such as fulvestrant with CDK4/6, mTOR, or PI3K inhibitors has become a central strategy in the treatment of ER<sup>+</sup> advanced breast cancer. However, suboptimal ER inhibition and resistance resulting from the <i>ESR1</i> mutation dictates that new therapies are needed.</p>Experimental Design:<p>A medicinal chemistry campaign identified vepdegestrant (ARV-471), a selective, orally bioavailable, and potent small molecule PROteolysis-TArgeting Chimera (PROTAC) degrader of ER. We used biochemical and intracellular target engagement assays to demonstrate the mechanism of action of vepdegestrant, and <i>ESR1</i> wild-type (WT) and mutant ER<sup>+</sup> preclinical breast cancer models to demonstrate ER degradation-mediated tumor growth inhibition (TGI).</p>Results:<p>Vepdegestrant induced ≥90% degradation of wild-type and mutant ER, inhibited ER-dependent breast cancer cell line proliferation <i>in vitro,</i> and achieved substantial TGI (87%–123%) in MCF7 orthotopic xenograft models, better than those of the ET agent fulvestrant (31%–80% TGI). In the hormone independent (HI) mutant ER Y537S patient-derived xenograft (PDX) breast cancer model ST941/HI, vepdegestrant achieved tumor regression and was similarly efficacious in the ST941/HI/PBR palbociclib-resistant model (102% TGI). Vepdegestrant-induced robust tumor regressions in combination with each of the CDK4/6 inhibitors palbociclib, abemaciclib, and ribociclib; the mTOR inhibitor everolimus; and the PI3K inhibitors alpelisib and inavolisib.</p>Conclusions:<p>Vepdegestrant achieved greater ER degradation <i>in vivo</i> compared with fulvestrant, which correlated with improved TGI, suggesting vepdegestrant could be a more effective backbone ET for patients with ER<sup>+</sup>/HER2<sup>−</sup> breast cancer.</p></div>

<p>Extended Methods</p>

Yan Zhou,1,2 Genyan Zhang,2 Feng Wang,2 Jin Wang,2 Yanwei Ding,2 Xinyu Li,2 Chongtie Shi,2 Jiakui Li,2 Chengkon Shih,2 Song You1 1The School of Life Science and Biopharmaceutical, Shenyang Pharmaceutical University, Shenyang, 2Department of Project Management, Medicinal Chemistry, Pharmacology, Drug Metabolism, and Pharmacokinetics, Toxicology, Xuanzhu Pharma, Jinan, China Abstract: This study presents a process of developing a novel PI3K–mTOR inhibitor through the prodrug of a metabolite. The lead compound (compound 1) was identified with similar efficacy as that of NVP-BEZ235 in a tumor xenograft model, but the exposure of compound 1 was much lower than that of NVP-BEZ235. After reanalysis of the blood sample, a major metabolite (compound 2) was identified. Compound 2 exerted similar in vitro activity as compound 1, which indicated that compound 2 was an active metabolite and that the in vivo efficacy in the animal model came from compound 2 instead of compound 1. However, compound 1 was metabolized into compound 2 predominantly in the liver microsomes of mouse, but not in the liver microsomes of rat, dog, or human. In order to translate the efficacy in the animal model into clinical development or predict the pharmacokinetic/pharmacodynamic parameters in the clinical study using a preclinical model, we developed the metabolite (compound 2) instead of compound 1. Due to the low bioavailability of compound 2, its prodrug (compound 3) was designed and synthesized to improve the solubility. The prodrug was quickly converted to compound 2 through both intravenous and oral administrations. Because the prodrug (compound 3) did not improve the oral exposure of compound 2, developing compound 3 as an intravenous drug was considered by our team, and the latest results will be reported in the future. Keywords: PI3K, mTOR, NVP-BEZ235, prodrug, metabolite, antitumor

<p>Extended Methods</p>