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Purpose: Sabizabulin, an oral cytoskeleton disruptor, was tested in a phase Ib/II clinical study in men with metastatic castration-resistant prostate cancer (mCRPC). Patients and Methods: The phase Ib portion utilized a 3+3 design with escalating daily oral doses of 4.5–81 mg and increasing schedule in 39 patients with mCRPC treated with one or more androgen receptor–targeting agents. Prior taxane chemotherapy was allowed. The phase II portion tested a daily dose of 63 mg in 41 patients with no prior chemotherapy. Efficacy was assessed using PCWG3 and RECIST 1.1 criteria. Results: The MTD was not defined in the phase Ib and the recommended phase II dose was set at 63 mg/day. The most common adverse events (>10% frequency) at the 63 mg oral daily dosing (combined phase Ib/II data) were predominantly grade 1–2 events. Grade ≥3 events included diarrhea (7.4%), fatigue (5.6%), and alanine aminotransferase/aspartate aminotransferase elevations (5.6% and 3.7%, respectively). Neurotoxicity and neutropenia were not observed. Preliminary efficacy data in patients treated with ≥1 continuous cycle of 63 mg or higher included objective response rate in 6 of 29 (20.7%) patients with measurable disease (1 complete, 5 partial) and 14 of 48 (29.2%) patients had PSA declines. The Kaplan–Meier median radiographic progression-free survival was estimated to be 11.4 months (n = 55). Durable responses lasting >2.75 years were observed. Conclusions: This clinical trial demonstrated that chronic oral daily dosing of sabizabulin has a favorable safety profile with preliminary antitumor activity. These data support the ongoing phase III VERACITY trial of sabizabulin in men with mCRPC.

Purpose: A blood test to detect colon cancer at a preventable stage would represent a major advancement. We have previously identified colon cancer–specific markers using focused proteomics analysis of nuclear structural proteins. Two of these markers, colon cancer–specific antigen (CCSA)-3 and CCSA-4, have been developed into blood-based markers that are able to distinguish individuals with colorectal cancer from those without. CCSA-2 is a distinct novel colon cancer marker identified using focused proteomics.Experimental Design: Using an indirect ELISA on serum samples obtained from two institutions, we evaluated CCSA-2 as a serum-based colon cancer marker. A total of 111 serum samples from individuals who underwent colonoscopy and were subsequently diagnosed as either being normal or having hyperplastic polyps, nonadvanced adenomas, advanced adenomas, and colorectal cancer were evaluated. A diverse control population that consisted of 125 serum samples was also included in this study.Results: Receiver operating characteristic analyses were used to measure the sensitivity and specificity of CCSA-2. CCSA-2 at a cutoff of 10.8 μg/mL has overall specificity of 78.4% [95% confidence interval (95% CI), 67.3-87.1%] and sensitivity of 97.3% (95% CI, 85.8-99.5%) in separating individuals with advanced adenomas and colorectal cancer from normal, hyperplastic, and nonadvanced adenoma populations. The receiver operating characteristic curve for CCSA-2 has an area under the curve of 0.90 (95% CI, 0.83-0.95).Conclusion: Our initial study shows that CCSA-2 is a potential serum-based marker for colon cancer detection with high sensitivity and specificity.

Supplementary Table from A Phase Ib/II Study of Sabizabulin, a Novel Oral Cytoskeleton Disruptor, in Men with Metastatic Castration-resistant Prostate Cancer with Progression on an Androgen Receptor–targeting Agent

Suppl. Methods

Purpose:Sabizabulin, an oral cytoskeleton disruptor, was tested in a phase Ib/II clinical study in men with metastatic castration-resistant prostate cancer (mCRPC).Patients and Methods:The phase Ib portion utilized a 3+3 design with escalating daily oral doses of 4.5–81 mg and increasing schedule in 39 patients with mCRPC treated with one or more androgen receptor–targeting agents. Prior taxane chemotherapy was allowed. The phase II portion tested a daily dose of 63 mg in 41 patients with no prior chemotherapy. Efficacy was assessed using PCWG3 and RECIST 1.1 criteria.Results:The MTD was not defined in the phase Ib and the recommended phase II dose was set at 63 mg/day. The most common adverse events (>10% frequency) at the 63 mg oral daily dosing (combined phase Ib/II data) were predominantly grade 1–2 events. Grade ≥3 events included diarrhea (7.4%), fatigue (5.6%), and alanine aminotransferase/aspartate aminotransferase elevations (5.6% and 3.7%, respectively). Neurotoxicity and neutropenia were not observed. Preliminary efficacy data in patients treated with ≥1 continuous cycle of 63 mg or higher included objective response rate in 6 of 29 (20.7%) patients with measurable disease (1 complete, 5 partial) and 14 of 48 (29.2%) patients had PSA declines. The Kaplan–Meier median radiographic progression-free survival was estimated to be 11.4 months (n = 55). Durable responses lasting >2.75 years were observed.Conclusions:This clinical trial demonstrated that chronic oral daily dosing of sabizabulin has a favorable safety profile with preliminary antitumor activity. These data support the ongoing phase III VERACITY trial of sabizabulin in men with mCRPC.

Supplementary Figures S1-S2 from Evaluation of Colon Cancer–Specific Antigen 2 as a Potential Serum Marker for Colorectal Cancer

Supplementary Data from A Phase Ib/II Study of Sabizabulin, a Novel Oral Cytoskeleton Disruptor, in Men with Metastatic Castration-resistant Prostate Cancer with Progression on an Androgen Receptor–targeting Agent

Supplementary Figures and Tables

Supplementary Figure from A Phase Ib/II Study of Sabizabulin, a Novel Oral Cytoskeleton Disruptor, in Men with Metastatic Castration-resistant Prostate Cancer with Progression on an Androgen Receptor–targeting Agent

Purpose:Androgen receptor (AR)-targeting prostate cancer drugs, which are predominantly competitive ligand-binding domain (LBD)-binding antagonists, are inactivated by common resistance mechanisms. It is important to develop next-generation mechanistically distinct drugs to treat castration- and drug-resistant prostate cancers.Experimental Design:Second-generation AR pan antagonist UT-34 was selected from a library of compounds and tested in competitive AR binding and transactivation assays. UT-34 was tested using biophysical methods for binding to the AR activation function-1 (AF-1) domain. Western blot, gene expression, and proliferation assays were performed in various AR-positive enzalutamide-sensitive and -resistant prostate cancer cell lines. Pharmacokinetic and xenograft studies were performed in immunocompromised rats and mice.Results:UT-34 inhibits the wild-type and LBD-mutant ARs comparably and inhibits the in vitro proliferation and in vivo growth of enzalutamide-sensitive and -resistant prostate cancer xenografts. In preclinical models, UT-34 induced the regression of enzalutamide-resistant tumors at doses when the AR is degraded; but, at lower doses, when the AR is just antagonized, it inhibits, without shrinking, the tumors. This indicates that degradation might be a prerequisite for tumor regression. Mechanistically, UT-34 promotes a conformation that is distinct from the LBD-binding competitive antagonist enzalutamide and degrades the AR through the ubiquitin proteasome mechanism. UT-34 has a broad safety margin and exhibits no cross-reactivity with G-protein–coupled receptor kinase and nuclear receptor family members.Conclusions:Collectively, UT-34 exhibits the properties necessary for a next-generation prostate cancer drug.

Colon cancer–specific antigen (CCSA)-3 and CCSA-4 are novel colon cancer markers identified by focused proteomic analysis of nuclear structural proteins. The goal of these studies was to evaluate serum-based CCSA-3 and CCSA-4 in the detection of individuals with preneoplastic and neoplastic lesions using ELISAs. Serum samples from 107 subjects undergoing colonoscopy, 28 subjects with colorectal cancer, and 125 subjects with benign disease or other types of cancer were evaluated. Individuals who underwent colonoscopy were classified into mutually exclusive categories, including normal colon, hyperplastic polyp, nonadvanced adenoma, and advanced adenoma. Sensitivity and specificity for both CCSA-3 and CCSA-4 were evaluated using receiver operating characteristic (ROC) curves. At a cutoff of 2 μg/mL for CCSA-3 and 0.3 μg/mL for CCSA-4, each marker detected all 28 colorectal cancers, for a sensitivity of 100% (lower 95% confidence bound, 89.8%). The sensitivity for detection of the combined end point of colorectal cancer and advanced adenoma for CCSA-3 was 89.1% [95% confidence interval (95% CI), 76.4–96.4%] and for CCSA-4 was 84.8% (95% CI, 71.1–93.7%) and 91.3% (95% CI, 79.2–97.6%) for either marker positive. The specificity in individuals with normal, hyperplastic polyps, or nonadvanced adenomas was 82.0% (95% CI, 72.4–89.4%) and 91.0% (95% CI, 83.0–96.0%) for CCSA-3 and CCSA-4, respectively. ROC curves for CCSA-3 and CCSA-4 reveal an area under the curve of 0.94 (95% CI, 0.90–0.98%). In these initial analyses, CCSA-3 and CCSA-4 show promise as potential serum markers for detection of colorectal cancer and advanced adenomas. [Cancer Res 2007;67(12):5600–5]

Supplementary Figure 1 - PDF file 202K, (A), expression of RBM3 in different human tissues. Data are mean � s.d. (n = 3). (B), expression of CIRBP in CD133+ and CD133- PrEC cells. mRNA levels of RBM3 and CIRBP was determined by RT-PCR. Data are mean � s.d. (n = 4). (C), mRNA levels of RBM3 were detected in the PC3-GFP and PC3-RBM3 clones by RT-PCR. Data are mean � s.d. (n = 3), *P < 0.05. (D), RBM3 protein was detected in both cytoplasmic (Cyto) and nuclear (Nu) components of PC3-GFP and PC3-RBM3 clones. Tubulin and Lammn A/C were used as loading controls for cytoplasmic and nuclear fractions, respectively. In all panels: G#1, PC3-GFP-clone #1; G#2, PC3-GFP-clone #2; R#1, PC3-RBM3-clone #1; R#6, PC3-RBM3-clone #6

Supplementary Figure 2 - PDF file 68K, (A), expression of cancer-related miRNAs was detected in the PC3-RBM3 and PC3-GFP clones using a cancer-specific miRNA PCR array. Left panel, selected miRNAs whose expression levels differed more than 1.5 fold in the clone R#1 compared to G#1. Red bars, differentiation-related miRNAs; black bars, other cancer-related miRNAs. Right panel, the up-regulation of miR-9 in PC3-RBM3 clones was validated by RT-PCR. Values are mean � s.d. (n = 3), *P < 0.05. (B), left panel, β3-tubulin expression was detected by Western blot in PC3-GFP and PC3-RBM3 clones. Right panel, quantitative evaluation of protein levels of β3-tubulin. Values are mean � s.d. (n = 3), *P < 0.05. (C), the immunohistochemical staining of RBM3 and β3-tubulin in the nerve fibers observed in human prostate tissue. Upper panels, low magnification; lower panels, high magnification. Scale bars, 100 �m. In all panels: G#1, PC3-GFP-clone #1; G#2, PC3-GFP-clone #2; R#1, PC3-RBM3-clone #1; R#6, PC3-RBM3-clone #6.expression of CDH2 in PC3-GFP and PC3-RBM3 clones

Supplementary Table 2 - PDF file 33K, Calculated size of PCR products for CD44 splicing variants

Supplementary Figure 5 - PDF file 104K, (A), mRNA levels of CD44v8-v10 (CD44v) were determined in human normal and prostate cancer tissues by RT-PCR. Normal, normal prostate tissue (n = 19); OC-PCa, organ-confined prostate cancer (n = 79); Met-PCa, metastatic prostate cancer (n = 23). (B), mRNA levels of CD44v were compared between patients with recurrent PCa (Rec, n = 44) and those without recurrent disease (Non-rec, n = 30). (C) and (D), mRNA levels of standard CD44 (CD44s) (C) or CD44v (D) were compared between patients with low grade PCa (Gleason score � 6, n = 21) and those with high grade disease (Gleason score > 6, n = 53). All experiments were repeated three times. Bars indicate median values

Supplementary Figures 1-2 from Initial Analyses of Colon Cancer–Specific Antigen (CCSA)-3 and CCSA-4 as Colorectal Cancer–Associated Serum Markers

Supplementary Figure 4 - PDF file 146K, mRNA expression of Cyclin D1 was evaluated in PC3 cells (A) and DU145 cells (B) that formed colonies in soft agar or those grew in the regular 2D culture condition by qRT-PCR. Values are mean � s.d. (n = 4). (C), PC3 cells were cultured under 32˚C for 0 hr to 144 hr, and mRNA level of cyclin D1 was detected by qRT-PCR. Values are mean � s.d. (n = 4). (D) Over-expression of CD44 variant and standard construct. LNCaP cells were transfected with pLenti-III-CD44s (CD44s), pLenti-III-CD44v8-v10 (CD44v8-10) or empty vector. After 48 hr of transfection, cells were collected and the expression of mRNA and protein of CD44 were detected by RT-PCR and Western blot, respectively. Data are mean � s.d. (n = 3), *P < 0.05

Supplementary Figure 3 - PDF file 244K, (A), CD44 variant mRNAs were amplified by PCR using the general primers c13 and hs3'. The PCR products at size of 650 bp and 250 bp were cut and subjected to direct DNA sequencing. The numbers in the block are exons number of CD44. N, negative control; G#1, PC3-GFP-clone #1. (B), schematic diagram of designing siRNAs specific to CD 44 variant exons v8-v10 (siC1, siC2) and primers specific to CD44v8-v10 (CD44v) or standard CD44 (CD44s). Primers c13 and hs3' can amplify both CD44s and CD44v. Primers p1 and p2 can only amplify CD44v8-v10, while primers p3 and p4 are specific to standard CD44s. Primer hs5' is the outside primer of the nest PCR. (C), the specificity of siRNAs targeting for CD44v8-v10. Variant exon-specific PCR was performed using primer p1 and p2. CD44s was amplified using CD44 standard-specific primer p3 and p4. siN, non-target siRNA. Data are mean � s.d. (n = 3), *P < 0.05. (D), the efficiency of siRNA pool targeting RBM3. Cells were treated with siRBM3 or non-targeting siRNA (siN) for 48 hr. The expression of mRNA and protein of CD44 were detected by RT-PCR and Western blot, respectively. R#1, PC3-RBM3-clone #1; R#6, PC3-RBM3-clone #6. Data are mean � s.d. (n = 3), *P < 0.05

Supplementary Table 1 - PDF file 43K, mRNA expression of stem cell-related gene using a Stem Cell PCR array

Supplementary documents - PDF file 122K, Supplementary methods and supplementary figures legends

Targeting the androgen receptor (AR) may be the next important endocrine therapy for women with advanced breast cancer. AR is the most abundantly expressed steroid receptor in breast cancer and has been demonstrated to be a tumor suppressor when activated. Enobosarm is an oral selective nonsteroidal agonist that activates the AR in breast cancer. Enobosarm has an extensive clinical experience in 25 clinical trials and 1,450 dosed subjects including in breast cancer where three Phase 2 studies have been conducted two of which were in women (158 subjects) who had AR+/ER+/HER2- metastatic breast cancer (MBC).The larger Phase 2 clinical trial (G200802) evaluated 9mg and 18mg enobosarm daily oral dosing in 136 women with ER+/HER2- MBC who previously responded to endocrine treatment. Patients were heavily pretreated having progressed on an average of 3 endocrine treatments and 90% had prior chemotherapy. Enobosarm showed efficacy activity in the overall study with a clinical benefit rate at 6 months of 32% (95% CI: 19.5%,46.7%) for the 9 mg and 29% (95% CI: 17.1%,43.1%) for the 18 mg evaluable cohorts. Quality of life assessments showed significant improvement from baseline for both enobosarm cohorts (p=0.002). Enobosarm was well tolerated at both doses. In a post-hoc analysis in all patients (9mg and 18mg) with known AR status and measurable disease (n=84), AR expression in breast. cancer tissue (%AR nuclei staining) correlated with efficacy outcomes. When comparing AR nuclei staining ≥40% (n=47) compared to patients with an AR nuclei staining Citation Format: Adam Brufsky, Hannah Linden, Hope Rugo, Charles Vogel, Joyce A O'Shaughnessy, Robert H Getzenberg, K. Gary Barnette, Domingo Rodriguez, Mitchell S Steiner, Erica Mayer. Randomized, multicenter, international phase 3 ARTEST study to evaluate the efficacy and safety of enobosarm versus active control for the treatment of AR+ ER+ HER2- metastatic breast cancer in patients who progressed on a nonsteroidal aromatase inhibitor, fulvestrant and CDK 4/6 inhibitor [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-17-01.

Introduction: Hormonal agents remain the most effective therapies for estrogen receptor positive (ER+) HER2- breast cancer. The androgen receptor (AR) is the most highly expressed steroid receptor found in up to 95% of ER+ breast cancer patients. Androgen agonists have antiproliferative activity in ER+ breast cancer and have been used in treatment, however their lack of availability and virilizing side effects have limited their use. Enobosarm is a non-steroidal tissue-selective AR modulator that that is being developed for AR targeted treatment of ER+/AR+ breast cancer. Methods: An international, Phase 2, open label, parallel design, randomized study was conducted in 136 patients (pts) to investigate the efficacy and safety of enobosarm in postmenopausal women with metastatic ER+/AR+ breast cancer that progressed on previous endocrine therapy. Pts were randomized to receive 9 mg (n=72) or 18 mg (n=64) of oral daily enobosarm. The primary endpoint was clinical benefit rate (CBR) at 24 weeks (defined as CR, PR or SD) by RECIST 1.1. Secondary endpoints included objective response rate, best overall response rate (BOR), progression free survival (PFS), duration of clinical benefit. Results: The study population consisted of heavily pre-treated pts with a mean of 4 (range 1-6) prior hormone therapies and >90% receiving one prior course of chemotherapy. Median age was 60.8 years (35-83) for 9 mg and 62.1 (42-81) for the 18 mg cohort. AR positivity was centrally confirmed in 73.6% and 81.2% in the 9 and 18 mg cohorts, respectively. Efficacy: In the evaluable pts, 50 in the 9 mg arm and 52 in the 18 mg arm (AR confirmed), 32% of the 9mg cohort met the primary endpoint of CBR at 24 weeks (95% CI, 19.5%; 46.7%) and 29% (95% CI, 17.1%; 43.1%) in the 18 mg cohort. The BOR was 2 CRs, 10 PRs in the 9 mg and 3 CRs,7 PRs in the 18 mg group by central review. Median PFS was 5.6 (2.9 to 27.5) and 4.2 (2.8 to 11) months (mo) in the 9 mg and 18 mg groups. The median duration of treatment was 4.0 months (0.23-30.3 months) in the 9 mg group and 3.8 months (0.5-16.7 months) in the 18 mg group. At the time the study was terminated, the median duration of clinical benefit was not reached (NR) in the 9 mg group (range 8.2 mo to NR) and 14.1 mo (range 11.0 to 16.5) in the 18 mg group. QOL: Using a standardized instrument of generic health status (EQ-5D), a significant percentage of pts reported improvement in measurements including mobility (40%, 50%), anxiety/depression (50%, 29%) and pain discomfort (50%, 31%) for the 9 and 18 mg groups, respectively. Drug related severe adverse events (SAEs) (Grades 3-4) were observed in 6 (8.0%) at the 9 mg and 10 (16.4%) at the 18 mg dose. The SAEs (Grade 3-4) attributed to the study drug by the site investigator were for the 9 mg group: fatigue (1), elevated transaminases (2), headache (1), hypercalcemia (2) and anemia (1). For the 18 mg group the drug attributable SAEs (Grade 3-4) were: dry mouth (1), increased aminotransferase (2), decreased white blood cell count (1), fatigue (2), hypercalcemia (1), decreased appetite (1), headache (1), tumor flare (2), agitation (1), lymphadenopathy (1) and acute kidney injury (1). Conclusions: In this Phase 2 parallel design study, enobosarm (9 mg and 18 mg) has significant clinical activity and was well tolerated in heavily pretreated patients with ER+/AR+ metastatic breast cancer. Given the limited options of hormonal therapy for metastatic ER+ breast cancer, enobosarm merits further clinical development in a Phase 3 clinical program as an AR targeted treatment for metastatic ER+AR+ breast cancer. Citation Format: Carlo Palmieri, Hannah Linden, Stephen Birrell, Elgene Lim, Lee S Schwartzberg, Hope S Rugo, Patrick Cobb, Kirti Jain, Charles Vogel, Joyce A O’Shaughnessy, Robert H Getzenberg, Mitchell S Steiner, Adam Brufsky, Beth Overmoyer. Efficacy and safety of enobosarm, a selective androgen receptor modulator, to target AR in women with advanced ER+/AR+ breast cancer - final results from an international Phase 2 randomized study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD8-10.

It is now widely recognized that carcinoma-associated fibroblasts which are believed to be myofibroblasts, promote the transformation of prostate epithelial cells to cancer cells, enhance their proliferation and invasiveness, and induce the acquisition of resistance to cancer therapy and immune evasiveness. Prostate-associated gene 4 (PAGE4) is an intrinsically disordered protein that is remarkably prostate-specific. PAGE4 is also a stress-response protein that functions as a transcriptional regulator and is upregulated in early-stage prostate cancer (PCa) and its precursor lesions. However, PAGE4 is downregulated in high-grade PCa and metastatic disease. Here, we show that PAGE4 is highly expressed in the stromal cells surrounding the cancer-adjacent "normal" glands and low-grade PCa lesions but not in lesions proximal to high-grade PCa. Overexpression of PAGE4 in a stromal cell line inhibits the migration and invasion of PCa epithelial cells in multiple coculture systems. PAGE4 overexpression also inhibits the downregulation of E-cadherin in PCa epithelial cells when cocultured with stromal cells. Furthermore, signaling via tumor necrosis factor-α and transforming growth factor-β pathways is decreased in the stromal cells overexpressing PAGE4 suggesting that PAGE4 appears to play a protective role against disease progression by perturbing interactions between epithelial cells and stromal cells in PCa. Taken together, these findings support previous observations that upregulation of PAGE4 in PCa correlates with a better prognosis and highlight PAGE4 as a novel therapeutic target for early-stage "low-risk" disease.

5049 Background: Sabizabulin is a novel oral cytoskeleton disruptor being developed for use in metastatic castration resistant prostate cancer (mCRPC). A Phase 1b/2 clinical study was conducted to establish the maximum tolerated dose (MTD) and evaluate the preliminary efficacy in men with mCRPC resistant to androgen receptor targeting agents. Methods: The Phase 1b portion of the study in 39 men utilized escalating and expanding dose and duration. The Phase 2 portion studied 41 men with mCRPC at the recommended Phase 2 dose of 63 mg daily. Efficacy was assessed by bone/CT scans. A final analysis of the safety and efficacy data including the primary endpoint, the median progression-free survival was conducted. Results: Although the MTD was not reached in the Phase 1b, the recommended Phase 2 dose was set at 63 mg/day to maximize GI tolerability. The most common adverse events (> 10% frequency) at the 63 mg oral daily dosing (combined Phase 1b/2 data) were predominantly Grade 1-2. Grade ³3 events included diarrhea (7.4%), fatigue (5.6%) and ALT/AST elevations (5.6% and 3.7%, respectively). Neurotoxicity and neutropenia were not observed. Preliminary efficacy data in patients treated with ≥1 continuous cycle (21 days) of 63 mg or higher (n = 55) included an objective response rate of 6/29 (20.7%) in patients with measurable disease (1 complete, 5 partial). 14/48 (29.2%) of the patients had PSA declines. The Kaplan-Meier median radiographic progression-free survival was estimated to be 11.4 months (95% C.I. 29.63-65.79) (n = 55). Durable responses lasting > 2.75 years were observed with 14.5% (8/55) demonstrating a response greater than 12 months. Conclusions: This clinical trial demonstrated that chronic oral daily dosing of sabizabulin has a favorable safety profile with significant preliminary cytotoxic and cytostatic antitumor activity. These data support the ongoing Phase 3 VERACITY trial of sabizabulin in men with mCRPC who have progressed on an androgen receptor targeting agent. Clinical trial information: NCT03752099.

TPS1121 Background: Targeting the androgen receptor (AR) may be the next important endocrine therapy for advanced breast cancer. The AR has been demonstrated to be a tumor suppressor when activated. Enobosarm is an oral selective AR targeting agonist that activates the AR in breast cancer. Preclinical studies in CDK4/6 inhibitor resistant PDX models demonstrated combinatorial synergistic activity of enobosarm plus CDK 4/6 inhibitors. An open-label, Phase 2 study, was conducted in 136 women with heavily pretreated ER+ HER2- metastatic breast cancer that were randomized to oral daily enobosarm at a dose of 9 or 18 mg. The efficacy evaluable (EE) group were patients that were AR positive (> 10% AR nuclear staining). In the EE population with measurable disease at baseline, 10 patients had received prior endocrine therapy + a CDK 4/6 inhibitor. Subsequent treatment with enobosarm resulted in a clinical benefit rate of 50% and the best overall response rate (ORR) was 30% (2CRs and 1 PR). Of the 10 patients, 7 had AR nuclear staining ≥40%. None of the patients with AR nuclear staining < 40% responded to enobosarm. Although a small subset of the study, it appears that enobosarm has activity in patients who had ≥40% AR staining and who had progressed on standard endocrine therapy with a CDK 4/6 inhibitor. Overall, treatment with enobosarm was well tolerated with significant positive effects on quality-of-life measurements. Methods: The ENABLAR-2 trial is an ongoing Phase 3, randomized, open-label, efficacy and safety study in patients with AR+ ER+ HER2- MBC with AR nuclear staining of ≥40%, who have progressed after one line of systemic therapy comprising estrogen blocking agent and palbociclib. The planned sample size is 186 patients randomized 1:1 to enobosarm + abemaciclib OR fulvestrant if the first line of therapy for MBC was a non-steroidal AI plus palbociclib, until disease progression, toxicity, or loss of clinical benefit. If first line therapy for metastatic breast cancer was fulvestrant plus palbociclib, then the patient will be randomized 1:1 to either enobosarm + abemaciclib OR an AI. Randomization will be stratified by AR% nuclear staining, ≥60% versus < 60%, as well as by estrogen blocking agent such that each cohort will have the same number of subjects previously receiving fulvestrant + palbociclib in first line therapy. The key objectives are to determine the safety and efficacy of enobosarm and abemaciclib combination versus an alternative estrogen blocking agent with the primary endpoint of PFS. Secondary endpoints include ORR, duration of response, overall survival, change from baseline in Short Physical Performance Battery (SPPB), change in EORTC Quality of Life Questionnaire (EORTC-QLQ) and change in body composition as measured by DEXA. Clinical trial information: NCT05065411.

TPS5102 Background: Sabizabulin is a first-in-class, oral agent that inhibits microtubule polymerization disrupting the cytoskeleton and arresting cellular proliferation. A Phase 1b/2 clinical study was conducted to establish the MTD and evaluate the preliminary efficacy in men with metastatic castrate resistant prostate cancer (mCRPC) who progressed on at least one androgen receptor targeting agent (ARTA). The most common AEs reported were mild to moderate diarrhea, fatigue, nausea, and vomiting with no clinically relevant neurotoxicity or neutropenia. In the Phase 1b/2, the median radiographic progression free survival for the 63mg dose (n = 55) was 11.4 months (range 6-36+ months) in the Phase 1b portion including responses > 2.75 years. The Phase 3 reformulation which had improved bioavailability is 32mg PO qd. Methods: VERACITY is an ongoing Phase 3 multicenter, randomized, active-control study designed to evaluate sabizabulin in the treatment of mCRPC who have progressed on at least one ARTA. Patients on the study will be chemotherapy naive. Subjects (n = 245) are being randomized in a 2:1 ratio to receive sabizabulin (32 mg/d oral) or active control (alternative ARTA) and will remain on study until radiographic progression-free survival (rPFS). Randomization will be stratified by: measurable disease vs bone-only disease and by prior exposure to ARTA (progressed on one vs more than one prior ARTA). The primary efficacy endpoint of the study is median rPFS. Secondary endpoints include: objective response rate (ORR), duration of objective response, overall survival and time to intravenous (IV) chemotherapy. The Phase 3, VERACITY registration clinical trial is current ongoing in approximately 45 clinical sites with enrollment anticipated to be completed in 2022 and with unblinded results presented in 2023 Based upon the Phase 1b/2 clinical trial, sabizabulin daily chronic oral dosing has a favorable safety profile, is feasible to administer chronically, and has significant and durable antitumor activity. mCRPC that has progressed following ARTAs and prior to taxane chemotherapy, remains an urgent unmet medical need for patients with advanced disease. Sabizabulin is an exciting first-in-class agent that may add to the armamentarium for the treatment of mCRPC following progression on ARTA’s. Clinical trial information: NCT04844749.

110 Background: Sabizabulin is a novel oral cytoskeleton disruptor being developed for use in metastatic castration resistant prostate cancer (mCRPC). A phase 1b/2 clinical study was conducted to establish the maximum tolerated dose (MTD) and evaluate the preliminary efficacy in men with mCRPC resistant to androgen receptor targeting agents (ARTAs). Methods: The phase 1b portion of the study in 39 men utilized escalating and expanding dose and duration. The phase 2 portion studied 41 men with mCRPC at the recommended phase 2 dose (RP2D) of 63 mg daily. Based upon the phase 1b/2 data, sabizabulin appears to have both cytotoxic and cytostatic activity. A analysis was conducted evaluating the best clinical response (BCR) defined as either an objective response assessed by PCWG3 criteria and/or stable disease defined as ≥5 cycles (≥15 weeks) of continuous treatment. Results: Of the combined 80 patients in the phase 1b/2 portions of the study, the BCR was 37.5% (30/80) and 5 of the responders remain on study with the longest being treated for more than 30 months. Of the patients with measurable disease at study entry, the BCR was 59% (17/29). Prior to study entry, 11/30 (37%) of those with a BCR had previously been treated with and subsequently progressed on a minimum of 2 ARTAs. The remaining 19/30 (63%) had progressed on a single ARTA agent. 11 (37%) were previously treated with enzalutamide or apalutamide and 8 (27%) with abiraterone as single agents. 8 (27%) received enzalutamide and abiraterone and 3 (10%) patients received more than two ARTAs. As described previously, the safety profile continues to be favorable with no clinically relevant neutropenia or neurotoxicity. Conclusions: In this analysis, sabizabulin has demonstrated not only cytotoxic, but also significant cytostatic activity with similar responses in men that have progressed on a single or multiple ARTA agents. Sabizabulin is a novel agent with the potential provide men with mCRPC a well-tolerated chronic treatment cytostatic option after progressing on an ARTA and is being tested in the open phase 3 VERACITY trial. Clinical trial information: NCT03752099.

Current clinical tests for prostate cancer (PCa), such as the PSA test, are not fully capable of discerning patients that are highly likely to develop metastatic prostate cancer (MPCa). Hence, more accurate prediction tools are needed to provide treatment strategies that are focused on the different risk groups. Cancer/testis antigens (CTAs) are expressed during embryonic development and present aberrant expression in cancer making them ideal tumor specific biomarkers. Here, the potential use of a panel of CTAs as a biomarker for PCa detection as well as metastasis prediction is explored. We initially identified eight CTAs (CEP55, NUF2, PAGE4, PBK, RQCD1, SPAG4, SSX2andTTK) that are differentially expressed in MPCa when compared to local disease and used this panel to compare the gene and protein expression profiles in paired PCa and normal adjacent prostate tissue. We identified differential expression of all eight CTAs at the protein level when comparing 80 paired samples of PCa and the adjacent non-cancer tissue. Using multiple logistic regression we also show that a panel of these CTAs present high accuracy to discriminate normal from tumor samples. In summary, this study provides evidence that a panel of CTAs, differentially expressed in aggressive PCa, is a potential biomarker for diagnosis and prognosis to be used in combination with the current clinically available tools and is also a potential target for immunotherapy development.

Purpose: Androgen receptor (AR)-targeting prostate cancer drugs, which are predominantly competitive ligand-binding domain (LBD)-binding antagonists, are inactivated by common resistance mechanisms. It is important to develop next-generation mechanistically distinct drugs to treat castration- and drug-resistant prostate cancers. Experimental Design: Second-generation AR pan antagonist UT-34 was selected from a library of compounds and tested in competitive AR binding and transactivation assays. UT-34 was tested using biophysical methods for binding to the AR activation function-1 (AF-1) domain. Western blot, gene expression, and proliferation assays were performed in various AR-positive enzalutamide-sensitive and -resistant prostate cancer cell lines. Pharmacokinetic and xenograft studies were performed in immunocompromised rats and mice. Results: UT-34 inhibits the wild-type and LBD-mutant ARs comparably and inhibits the in vitro proliferation and in vivo growth of enzalutamide-sensitive and -resistant prostate cancer xenografts. In preclinical models, UT-34 induced the regression of enzalutamide-resistant tumors at doses when the AR is degraded; but, at lower doses, when the AR is just antagonized, it inhibits, without shrinking, the tumors. This indicates that degradation might be a prerequisite for tumor regression. Mechanistically, UT-34 promotes a conformation that is distinct from the LBD-binding competitive antagonist enzalutamide and degrades the AR through the ubiquitin proteasome mechanism. UT-34 has a broad safety margin and exhibits no cross-reactivity with G-protein–coupled receptor kinase and nuclear receptor family members. Conclusions: Collectively, UT-34 exhibits the properties necessary for a next-generation prostate cancer drug.

INTRODUCTION AND OBJECTIVES:VERU-111 is a novel, oral α and β tubulin inhibitor that blocks tubulin polymerization and is not a substrate for multi-drug resistance. In xenograft mouse models of tax...

5056 Background: VERU-111 is an oral cytoskeletal disruptor that disrupts microtubules supporting the cytoskeleton and has no affinity for multidrug resistance proteins. A phase 1b/2 clinical study has been conducted to establish the maximum tolerated dose (MTD) and evaluate the preliminary efficacy in men with mCRPC also resistant to androgen receptor targeting agents. Methods: In the phase 1b component of the study, a 3+3 design with escalating oral dosing of 4.5 mg to 81 mg (7 days on drug/14 days off per 21-day cycle) was utilized. The schedule was also expanded to continuous dosing/cycle. The phase 2 portion utilized 63 mg daily dosing to evaluate efficacy in approximately 40 taxane-naïve men with mCRPC that have failed at least one androgen receptor targeting agent. Results: In the phase 1b portion of the study, 30 taxane-naïve men with mCRPC and a median age of 76 (61-92) were enrolled. 8 had received prior enzalutamide, 12 abiraterone and 10 both. 8 men had bone mets, 5 lymph node, 5 mixed and 1 had soft tissue metastases at study entry. The MTD of VERU-111 is 72mg (3/11 men had grade 3 diarrhea) and the recommended phase 2 dose is 63mg. Grade 3 diarrhea was not observed at doses ≤ 63mg per day and the most common non-dose limiting AEs were mild to moderate nausea, vomiting, diarrhea, and fatigue, with no observed neurotoxicity or neutropenia. Efficacy was assessed by PSA and bone/CT scans. In men treated for ≥ 4 continuous 21-day cycles, 6/10 (60%) had PSA declines, 4(40%) men had ≥ 30% declines and 2(20%) ≥ 50% declines compared to their 21-day cycle baseline PSA. Median PFS is currently 12 months (6-23+ months) with 3 patients continuing on study, 2 of which have been on study for approximately 2 years. In patients receiving at least a single dose of ≥ 63 mg daily (n=19), objective tumor responses were seen in 3 men (16%). The median rPFS in these patients is currently 12.4 months. In the phase 2 portion of the study, 55% of the patients had bone only metastases, 11% had nodal only, 32% had mixed bone and nodal disease and 3% had visceral disease at study entry. 6/32 (19%) were previously treated with abiraterone alone, 12/32 (38%) with enzalutamide alone, and 14/32 (44%) had abiraterone in combination with enzalutamide, proxalutamide or apalutamide. The phase 2 portion of the study is ongoing and objective tumor responses have been observed including a CR and PRs and PSA decreases >50%. Patients have been on study as long as 9 months. Conclusions: This phase 1b/2 clinical trial, demonstrates that oral daily dosing of VERU-111 has a favorable safety profile and that chronic dosing is feasible. The recommended phase 2 dose of 63mg daily has significant durable antitumor activity. These data support a potential prominent role of VERU 111 for the treatment of men with mCRPC who previously failed an androgen receptor targeting agent and prior to the administration of intravenous chemotherapy. Clinical trial information: NCT03752099.

1020 Background: The AR is expressed in up to 90% of ER+ breast cancer where it acts as a tumor suppressor. Historically, therapy with synthetic androgens had efficacy, but virilizing side effects and toxicity limited their use. Enobosarm is a selective AR activating agent that does not cause masculinization and has positive attributes such as promotion of bone and improvement of physical function. In a phase 2 study, correlation between the degree of AR staining and antitumor activity in AR+/ER+ patients with metastatic breast cancer (MBC) was examined. Methods: A phase 2, open label, parallel design randomized study was conducted in 136 patients to evaluate the efficacy and safety of enobosarm in heavily pretreated women with AR+/ER+ MBC. Patients were randomized to 9 mg (n=72) or 18 mg (n=64) of oral daily enobosarm. AR expression (%AR nuclei staining) in breast cancer samples was determined centrally by immunohistochemistry. The correlation between %AR staining and clinical outcomes was examined with a focus on the 9mg dose, selected for the phase 3 study and the optimal %AR staining established. Results: Tumor objective outcomes correlated with percent AR staining (Table). Further, using a 40% AR staining cutoff in patients with measurable disease, the clinical benefit rate (CBR) for ≥40% AR is 80% and

Stress urinary incontinence (SUI), a prevalent condition, is represented by an involuntary leakage of urine that results, at least in part, from weakened or damaged pelvic floor muscles and is triggered by physical stress. Current treatment options are limited with no oral therapies available. The pelvic floor is rich in androgen receptor and molecules with anabolic activity including selective androgen receptor modulators (SARMs) may serve as therapeutic options for individuals with SUI. In this study, two SARMs (GTx-024 and GTx-027) were evaluated in a post-menopausal animal model in order to determine their effect on pelvic floor muscles. Female C57BL/6 mice were ovariectomized and their pelvic muscles allowed to regress. The animals were then treated with vehicle or doses of GTx-024 or GTx-027. Animal total body weight, lean body mass, and pelvic floor muscle weights were measured along with the expression of genes associated with muscle catabolism. Treatment with the SARMs resulted in a restoration of the pelvic muscles to the sham-operated weight. Coordinately, the induction of genes associated with muscle catabolism was inhibited. Although a trend was observed towards an increase in total lean body mass in the SARM-treated groups, no significant differences were detected. Treatment of an ovariectomized mouse model with SARMs resulted in an increase in pelvic floor muscles, which may translate to an improvement of symptoms associated with SUI and serves as the basis for evaluating their clinical use. J. Cell. Biochem. 118: 640-646, 2017. © 2016 Wiley Periodicals, Inc.

A causal link between benign prostatic hyperplasia (BPH) and prostate cancer has long been suspected but not widely accepted. A new model is proposed that supports such a connection. In contrast to the prevailing wisdom, our model, that draws on dynamical systems theory, suggests that in response to stress, epithelial cells in the unstable gland can give rise to both types of diseases via a phenotypic switching mechanism. The central idea is that phenotypic switching is a stochastic process which exploits the plasticity of the epithelial cell. It is driven by 'noise' contributed by the conformational dynamics of proteins that are intrinsically disordered. In a system that is noisy when stressed, disorder promotes promiscuity, unmasks latent information, and rewires the network to cause phenotypic switching. Cells with newly acquired phenotypes can transcend the traditional zonal boundaries to give rise to BPH or prostate cancer depending on the microenvironment. Establishing causality between the two diseases may provide us with an opportunity to better understand their etiology and guide prevention and treatment strategies. J. Cell. Biochem. 117: 2235-2240, 2016. © 2016 Wiley Periodicals, Inc.

131 Background: VERU-111 is an oral, cytoskeletal disruptor that crosslinks α & ß tubulin and inhibits microtubule polymerization with no affinity for multidrug resistance proteins. A Phase 1b/2 clinical study has been conducted to establish the maximum tolerated dose (MTD) and evaluate the preliminary efficacy in men with progressive mCRPC resistant to androgen receptor targeting agent (ARTA). Methods: In the Phase 1b portion of the study, a 3+3 design with escalating oral dosing of 4.5 - 81 mg (7 days on drug/14 days off per 21 day cycle) was utilized. After no dose limiting toxicity was observed, the dose was increased in the next cohort. The schedule was also expanded in those completing the 7 days on/14 days off cycle to continuous dosing/cycle. The recommended Phase 2 study dose is 63 mg daily and the trial is fully enrolled with 40 taxane-naiive men with mCRPC that have failed at least one ARTA. Results: In the Phase 1 portion of the study, 30 taxane-naïve mCRPC men with a median age of 76 (61-92) were enrolled. 8 received prior enzalutamide, 12 abiraterone and 10 both. 8 men had bone mets, 5 lymph node, 5 mixed and 1 had soft tissue metastases. The MTD of VERU-111 is 72mg (3 /11 men had Grade 3 diarrhea). No Grade 3 diarrhea was observed at doses < 72 mg per day. At doses < 72mg/d, the most common AEs were mild to moderate nausea, vomiting, diarrhea, and fatigue, with no observed neurotoxicity or neutropenia. In the Phase 1b, antitumor activity was assessed by PSA and bone/CT scans in men that were treated for ≥ 4 continuous 21-day cycles. 6/10 (60%) had PSA declines: 4 (40%) men had ≥ 30% and 2(20%) ≥ 50% declines compared to their 21 day cycle baseline. Based on PCWG3/RECIST 1.1 criteria, objective tumor responses were seen in 2 men (soft tissue and bone). Median duration of response is 11 months (6-18+ months). In the Phase 2 portion of the study, 49% had bone only metastases, 54% have bone only metastases, 11% have nodal disease, 32% had mixed bone and nodal disease and 3% had visceral disease. This portion of the study is ongoing and results will be reported. 9/29 (31%) had previously abiraterone, 10/29 (34%)( enzalutmide, 7/29 (24%) both enzalutmide and abiraterone and 4/29 (14%) apalutamide. Conclusions: Based upon this Phase 1b/2 clinical trial, oral VERU-111 has a favorable safety profile allowing for chronic administration and significant and durable antitumor activity. The daily dose of 63mg is being tested in the fully enrolled Phase 2 portion. Oral administration, safe long-term treatment and evidence of antitumor activity highlight a potential prominent role of VERU 111 for the treatment of men with mCRPC who failed an androgen receptor targeting agent. Clinical trial information: NCT03752099.

Resistance is a significant limitation to the effectiveness of cancer therapies. The PI3K/Akt and MAP kinase pathways play important roles in a variety of normal cellular processes and tumorigenesis. This study is designed to explore the relationship of these signaling pathways with multidrug resistance in prostate cancer (PCa). The PI3K/Akt and MAP kinase pathways were investigated utilizing paclitaxel resistant DU145-TxR PCa cells and their parental non-resistant DU145 cells to determine their relationship with resistance to paclitaxel and other anticancer drugs. Our results demonstrate that the PI3K/Akt and MAP kinase pathways are upregulated in DU145-TxR cells compared to the DU145 cells. Inactivating these pathways using the PI3K/Akt pathway inhibitor LY294002 or the MAP kinase pathway inhibitor PD98059 renders the DU145-TxR cells more sensitive to paclitaxel. We investigated the effects of these inhibitors on other anticancer drugs including docetaxel, vinblastine, doxorubicin, 10-Hydroxycamptothecin (10-HCPT) and cisplatin and find that both inhibitors induces DU145-TxR cells to be more sensitive only to the microtubule-targeting drugs (paclitaxel, docetaxel and vinblastine). Furthermore, the treatment with these inhibitors induces cleaved-PARP production in DU145-TxR cells, suggesting that apoptosis induction might be one of the mechanisms for the reversal of drug resistance. In conclusion, the PI3K/Akt and MAP kinase pathways are associated with resistance to multiple chemotherapeutic drugs. Inactivating these pathways renders these PCa cells more sensitive to microtubule-targeting drugs such as paclitaxel, docetaxel and vinblastine. Combination therapies with novel inhibitors of these two signaling pathways potentially represents a more effective treatment for drug resistant PCa.

Background A need remains for new therapeutic approaches for men with advanced prostate cancer, particularly earlier in the disease course. Objective To assess the ability of an oral selective estrogen receptor α agonist (GTx-758) to lower testosterone concentrations compared with leuprolide while minimizing estrogen deficiency–related side effects of androgen-deprivation therapy. Design, setting, and participants Hormone-naive advanced prostate cancer patients were randomized to oral GTx-758 1000mg/d, 2000mg/d, or leuprolide depot. Intervention GTx-758 and leuprolide. Outcome measurements and statistical analysis The primary end point was the proportion of patients achieving total testosterone ≤50 ng/dl by day 60. Secondary end points included serum free testosterone, prostate-specific antigen (PSA), sex hormone-binding globulin, hot flashes, bone turnover markers, and insulin-like growth factor (IGF)-1 levels. Results and limitations Of 159 randomized patients, leuprolide reduced total testosterone to ≤50 ng/dl in a greater proportion of patients than GTx-758 by day 60 (43.4%, 63.6%, and 88.2% of subjects receiving GTx-758 1000mg [ p p =0.004], and leuprolide, respectively). GTx-758 reduced free testosterone and PSA earlier and to a greater degree than leuprolide. GTx-758 led to fewer hot flashes, decreases in bone turnover markers, and alterations in IGF-1 compared with leuprolide. A higher incidence of venous thromboembolic events (VTEs) was seen with GTx-758 (4.1%) compared with leuprolide (0.0%). Conclusions Although leuprolide reduced total testosterone to ≤50 ng/dl in a greater proportion of patients compared with GTx-758, GTx-758 was superior in lowering free testosterone and PSA. GTx-758 reduced estrogen deficiency side effects of hot flashes, bone loss, and insulin resistance but with a higher incidence of VTEs. Patient summary This paper reports findings that leuprolide lowered total testosterone more than GTx-758 but that GTx-758 lowered free testosterone and prostate-specific antigen more than leuprolide. GTx-758 also reduced estrogen deficiency side effects, albeit at a higher rate of vascular events. Trial registration Clinicaltrials.gov identifier NCT01615120.