Purpose: Steroidal androgens suppress androgen receptor and estrogen receptor positive (AR/ER þ ) breast cancer cells and were used to treat breast cancer, eliciting favorable response. The current study evaluates the activity and efficacy of the oral selective AR modulator RAD140 in in vivo and in vitro models of AR/ER þ breast cancer.Experimental Design: A series of in vitro assays were used to determine the affinity of RAD140 to 4 nuclear receptors and evaluate its tissue-selective AR activity. The efficacy and pharmacodynamics of RAD140 as monotherapy or in combination with palbociclib were evaluated in AR/ER þ breast cancer xenograft models.Results: RAD140 bound AR with high affinity and specificity and activated AR in breast cancer but not prostate cancer cells. Oral administration of RAD140 substantially inhibited the growth of AR/ER þ breast cancer patient-derived xenografts (PDX). Activation of AR and suppression of ER pathway, including the ESR1 gene, were seen with RAD140 treatment. Coadministration of RAD140 and palbociclib showed improved efficacy in the AR/ER þ PDX models. In line with efficacy, a subset of AR-repressed genes associated with DNA replication was suppressed with RAD140 treatment, an effect apparently enhanced by concurrent administration of palbociclib.Conclusions: RAD140 is a potent AR agonist in breast cancer cells with a distinct mechanism of action, including the ARmediated repression of ESR1. It inhibits the growth of multiple AR/ER þ breast cancer PDX models as a single agent, and in combination with palbociclib. The preclinical data presented here support further clinical investigation of RAD140 in AR/ER þ breast cancer patients.

1014 Background: The treatment of advanced ER+ breast cancer remains a clinical challenge with the majority of patients eventually progressing due to resistance to endocrine therapy. RAD1901 is a novel, nonsteroidal, oral SERD that has demonstrated dose dependent degradation of ER, and ER regulated genes in preclinical studies. In multiple in vivo patient derived xenograft models of breast cancer, including those harboring ESR1 mutations, RAD1901 demonstrated significant antitumor activity. Methods: In a phase-1 Study RAD1901-005 (ClinicalTrials.gov ID: NCT02338349), patients with advanced ER+ breast cancer were enrolled in dose escalation cohorts, followed by a safety expansion cohort. Key inclusion criteria include postmenopausal women aged 18 years or older, with advanced ER+, HER2- breast cancer, who have received ≤ 2 prior chemotherapy regimens in the metastatic setting and > 6 months of prior endocrine therapy. ESR1 mutation status was determined from circulating tumor DNA (ctDNA) samples. Clinical outcomes were evaluated based on RECIST v1.1 criteria. Results: As of January 25, 2017, total of 39 patients were enrolled at the 400 mg qd dose. Patients were heavily pre-treated (median lines of prior therapy = 3), with 38% and 41% having previously received fulvestrant and palbociclib/CDK4/6 inhibitor, respectively. RAD1901 was generally well-tolerated, with the most common adverse events being low grade nausea (Grade 3/4 = 0%) and dyspepsia (Grade 3/4 = 0%). ESR1 mutations, including D538G, Y537S/N/C, L536H/P/R, S436P and E380Q, were detected at baseline in 44% of patients and dynamic changes in the allele frequency of ESR1 mutations were observed in response to treatment. Confirmed partial responses were observed in patients with ESR1 mutations, and those who had previously received fulvestrant and palbociclib. Conclusions: RAD1901 has demonstrated evidence of single agent activity, with confirmed partial responses in heavily pre-treated patients with advanced ER+ breast cancer, including those with ESR1 mutations, warranting additional clinical development. Clinical trial information: NCT02338349.

BackgroundTAK-573, a humanized, anti-CD38, IgG4, monoclonal antibody genetically fused to two attenuated IFNα2b molecules, was designed for targeted delivery of attenuated IFNα2b to CD38 expressing (CD38+) cells, utilizing a unique epitope of CD38 that does not compete with current anti-CD38 therapies. Preclinical evaluation of TAK-573 confirmed activation of type I IFN signaling in CD38+ cells inducing direct anti-proliferative effects on multiple myeloma (MM) cells and direct and indirect immune cell activation. Here we provide the preliminary analyses of the pharmacodynamic data currently available from the ongoing Ph I/II TAK-573-1501 clinical study in patients with relapsed/refractory MM (NCT03215030).MethodsPeripheral blood (PB) and bone marrow (BM) aspirates were collected from patients at pre- and post-dose time points for exploratory biomarker analyses. CD38 receptor occupancy (RO) and receptor density (RD) were determined using a 9-color flow cytometry assay. Whole transcriptome sequencing of bulk RNA was performed and analyzed to assess the type I IFN gene signature. Serum samples were analyzed using Olink’s Proximity Extension Assay Immuno-Oncology panel to measure changes in cytokine levels. Mass cytometry-based immunophenotyping was utilized to characterize changes in immune cell prevalence and activation status of cryopreserved cells.ResultsAdministration of TAK-573 resulted in a dose dependent increase in CD38 RO of PB-derived immune cells with saturation detected 4 hours after the end of infusion (EOI) at doses ≥ 0.2 mg/kg. The duration of saturation was dose dependent with doses ≥ 0.75 mg/kg saturating CD38 RO through 24 hours. All dose levels tested resulted in increases in the type I IFN gene signature at 24 hours. Consistent with CD38 being an IFN stimulated gene, TAK-573 treatment resulted in CD38 RD increases most notably on NK cells, but also on other CD38+ cells including MM cells. Circulating levels of IFN-associated cytokines were also elevated, with maximal induction 4 hours after the EOI. CD8+ T-cells in BM showed increased CD69 expression in 7 of 9 patients analyzed, 3 of whom also showed increases in both IFNγ and granzyme B positivity suggesting TAK-573 treatment results in increased BM cytolytic CD8+ T-cells, in a subset of patients.Abstract 357 Figure 1Proposed Mechanism of Action of TAK-573ConclusionsThese preliminary biomarker data indicate that TAK-573 is a pharmacologically active molecule that mediates its effect through IFNAR pathway modulation. Additional data are being collected to further refine the mechanism of action (Image 1), which will inform the recommended phase 2 dose and optimal schedule of administration for the development of TAK-573.Trial RegistrationClinicalTrials. gov: NCT03215030Ethics ApprovalThe TAK-573-1501 study is approved by WIRB-Copernicus Group, University of Nebraska Medical Center, Dana Farber Cancer Institute and Advarra IRBs.

<div>Abstract<p><b>Purpose:</b> Steroidal androgens suppress androgen receptor and estrogen receptor positive (AR/ER⁺) breast cancer cells and were used to treat breast cancer, eliciting favorable response. The current study evaluates the activity and efficacy of the oral selective AR modulator RAD140 in <i>in vivo</i> and <i>in vitro</i> models of AR/ER⁺ breast cancer.</p><p><b>Experimental Design:</b> A series of <i>in vitro</i> assays were used to determine the affinity of RAD140 to 4 nuclear receptors and evaluate its tissue-selective AR activity. The efficacy and pharmacodynamics of RAD140 as monotherapy or in combination with palbociclib were evaluated in AR/ER⁺ breast cancer xenograft models.</p><p><b>Results:</b> RAD140 bound AR with high affinity and specificity and activated AR in breast cancer but not prostate cancer cells. Oral administration of RAD140 substantially inhibited the growth of AR/ER⁺ breast cancer patient-derived xenografts (PDX). Activation of AR and suppression of ER pathway, including the <i>ESR1</i> gene, were seen with RAD140 treatment. Coadministration of RAD140 and palbociclib showed improved efficacy in the AR/ER⁺ PDX models. In line with efficacy, a subset of AR-repressed genes associated with DNA replication was suppressed with RAD140 treatment, an effect apparently enhanced by concurrent administration of palbociclib.</p><p><b>Conclusions:</b> RAD140 is a potent AR agonist in breast cancer cells with a distinct mechanism of action, including the AR-mediated repression of <i>ESR1</i>. It inhibits the growth of multiple AR/ER⁺ breast cancer PDX models as a single agent, and in combination with palbociclib. The preclinical data presented here support further clinical investigation of RAD140 in AR/ER⁺ breast cancer patients. <i>Clin Cancer Res; 23(24); 7608–20. ©2017 AACR</i>.</p></div>