Antitumor Activity In Prostate Cancer Research Articles

Abstract CT159: CYCLONE 1: abemaciclib in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC)

Abstract Background: Treatment options for patients (pts) with heavily pretreated mCRPC are limited. Augmenting endocrine therapy by targeting CDK4/6 with abemaciclib has dramatically improved outcomes in HR+ breast cancer. Similar to ER, AR signaling activates CDK4 & 6 and abemaciclib showed preclinical anti-tumor activity in prostate cancer (PC). This signal seeking single arm Phase 2 study evaluated the safety and clinical activity of abemaciclib monotherapy in pts with heavily pretreated poor prognosis mCRPC who progressed after both a novel hormonal agent (NHA) and two taxanes. Methods: Eligible pts had progressive mCRPC, measurable disease by RECIST1.1, and previously received ≥1 NHA, docetaxel, and cabazitaxel for metastatic PC. Abemaciclib was administered at 200 mg BID on a continuous 28-day dosing schedule. The primary endpoint was investigator-assessed objective response rate without concurrent bone progression (ORR). A target ORR of ≥12.5% was deemed suitable to support further evaluation of abemaciclib monotherapy in this refractory mCRPC setting. Key secondary endpoints included disease control rate (DCR), time to PSA progression, radiographic progression-free survival (rPFS), overall survival (OS), and safety. Results: Forty-four pts (median age 68 yrs; 75% ECOG PS 1, median PSA of 96 ng/mL) were enrolled. In total, 46.5% had visceral metastasis, including 27.9% with liver metastases. Median time from development of mCRPC to study entry was 2.1 yrs and the median number of prior systemic regimens for mCRPC was 3. Median number of treatment cycles was 3 (1-13). Five pts (11.8%) had soft tissue response. The ORR without concurrent bone progression was 6.8%. Eighteen pts (40.9%) had stable disease, of which 6 (13.6%) lasted ≥6 months (mos); DCR was 47.7%. Median rPFS was 2.7 mos (95% CI 1.9, 3.7); 6-mos rPFS rate was 24.9% (95% CI 12.4, 39.5); median time to PSA progression was 6.5 mos. Median OS was 7.6 mos (95% CI 5.6, NE). Any grade (G) TRAEs experienced by ≥50% of pts were diarrhea (79.5%), decreased appetite (52.3%) and fatigue (50%); majority were G1/2. G3 TRAEs in ≥ 5% of pts were neutropenia (22.7%), anemia (6.8%), fatigue (6.8%) and diarrhea (6.8%). There were no G4 or G5 TRAEs. Discontinuation rate due to AE was 13.6%. Conclusions: Abemaciclib demonstrated modest but objective single-agent clinical activity in pts with very heavily pretreated progressive mCRPC. The safety profile of abemaciclib was consistent with the experience in breast cancer. Although the primary endpoint was not formally met, the single agent activity observed in this late line mCRPC setting validates CDK4/6 as a therapeutic target in advanced PC. The CYCLONE 2 and CYCLONE 3 studies are currently evaluating abemaciclib in combination with abiraterone/prednisone to leverage synergy of combined CDK4/6 and hormonal inhibition in first line mCRPC and mHSPC settings, respectively. Citation Format: Neeraj Agarwal, Daniel Castellano Guana, Teresa A. Gordoa, Jose A. Arija, Emeline Colomba, Gwenaelle Gravis, Loic Mourey, Stephanie Oudard, Aude Flechon, Macarena Gonzalez, Pablo Maroto-Rey, Michael Schweizer, Enrique Gallardo, Karim Nacerddine, Adams K. Appiach, Arjun Balar, Erica Johnston, José M. Piulats. CYCLONE 1: abemaciclib in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT159.

Abstract CT121: ARX517, an anti-PSMA ADC targeting mCRPC resistant or refractory to standard therapies: A phase 1 dose escalation and dose expansion study (ARX517-2011, NCT04662580)

Abstract Background: Targeted therapies against prostate-specific membrane antigen (PSMA) have exhibited promising antitumor activity in prostate cancer. With the FDA’s approval of (177) Lu-PSMA-617, PSMA has been validated as a target to treat metastatic castration-resistant prostate cancer (mCRPC). ARX517 is an antibody-drug conjugates (ADC) composed of a fully humanized anti-PSMA mAb site-specifically conjugated to AS269, a potent tubulin inhibitor, yielding a drug-to-antibody (DAR) ratio of 2. After binding to PSMA on the surface of cancer cells, ARX517 is internalized and delivers a cytotoxic payload which inhibits tubulin polymerization and induces cellular apoptosis. ARX517’s site-specific linkage, stable conjugation chemistry, and non-cleavable linker exhibit a homogenous drug-antibody-ratio, mAb-like biophysical properties, and exceptional stability. Therefore, ARX517 promotes highly specific tumor cell apoptosis with minimal off-target bystander activity. Trial Design: The Phase 1 study’s dose escalation and dose expansion evaluates the safety, pharmacokinetics, and preliminary evidence of anti-tumor activity of ARX517 in adults with mCRPC. Patients must have mCRPC which is resistant or refractory to standard therapies, including androgen receptor signaling inhibitors, and show disease progression by Prostate Cancer Working Group 3 (PCWG3) criteria. All patients must have adequate organ function and brain metastases must be radiographically stable. Ascending dose levels of ARX517 administered as a single agent will use an i3+3 design in the dose escalation phase. During the dose expansion phase, ARX517 will be administered at the recommended phase 2 dose (RP2D) or maximum tolerated dose (MTD). Exploratory pharmacodynamic assessment includes PSMA-PET/CT imaging. The total number of subjects is dependent on the number of ascending doses and cohort size before dose expansion. Status: ARX517-2011 began enrolling patients in July 2021. With no dose limiting toxicities through dose level 6 (2.0 mg/kg Q3W), dose escalation remains ongoing. As of January 2023, the APEX-01 study is currently enrolling in cohort 7 (2.4 mg/kg) of dose-escalation. Dose expansion will start after RP2D or MTD. Citation Format: John Shen, Richard Pachynski, Luke Nordquist, Nabil Adra, Mehmet Bilen, Rahul Aggarwal, Zachary Reichert, Michael Schweizer, Dong Xu, Manan Patel, Jin Zhang, Wenge Shi, Darryl Z. L'Heureux, Scott Tagawa. ARX517, an anti-PSMA ADC targeting mCRPC resistant or refractory to standard therapies: A phase 1 dose escalation and dose expansion study (ARX517-2011, NCT04662580) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT121.

230 (PB110) - Efficacy signals, long-term exposure and safety data from a phase 1–2 study of a cell-penetrating peptide antagonist of CEBPβ, a novel target, in patients (pts) with refractory solid tumors

Background: The oncogenic transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) promotes tumor survival and proliferation and inhibits differentiation. ST101 is a peptide antagonist of C/EBPβ, with anti-tumor activity in prostate cancer (PC), glioblastoma (GBM), breast cancer (BC), melanoma, and other pre-clinical models.

Abstract CT211: A phase 1 dose-escalation and dose-expansion study to evaluate the safety, pharmacokinetics, and anti- tumor activity of ARX517 in subjects with advanced solid tumors resistant or refractory to standard therapies (APEX-01 trial, NCT04662580)

Abstract Background: Novel anti-PSMA (prostate-specific membrane antigen) targeted therapies have exhibited encouraging antitumor activity in prostate cancer and most non-prostate solid tumors express PSMA in tumor neovasculature. ARX517 is an antibody drug conjugate composed of a fully humanized anti-PSMA monoclonal antibody linked to pAF-AS269, a potent microtubule inhibitor. Upon binding to PSMA on the surface of cancer cells, ARX517 is internalized and pAF-AS269 is released following lysosomal metabolism. Methods: This Phase 1, dose-escalation and dose-expansion study is evaluating the safety, pharmacokinetics, and preliminary anti-tumor activity of ARX517 in adults with prostate cancer or other solid tumors whose disease is resistant or refractory to standard therapies. Patients must have metastatic castration-resistant prostate cancer refractory to standard therapies, including abiraterone, darolutamide, apalutamide or enzalutamide and progression by Prostate Cancer Working Group criteria. Non-prostate advanced solid tumors must be pathologically confirmed, metastatic, or unresectable solid tumors that have disease progression despite at least 1 prior standard of care systemic treatment and have no satisfactory treatment alternatives. All patients must have adequate organ function and any brain metastasis must demonstrate radiographic stability. Exploratory pharmacodynamic assessment includes PSMA-PET/CT imaging, which is optional for low dose cohorts but required starting at 1.4 mg/kg dose. Dose-escalation will consist of ascending dose levels of ARX517 administered as a single agent and will use a i3+3 design. The number of subjects in the dose-expansion will be based on the number of doses to be expanded for further evaluation of safety, PK, and clinical activity. Through dose levels one and two, no dose limiting toxicities have been observed. Ascending dose levels of ARX517 as a single agent will be administered until the recommended Phase 2 dose or maximum tolerated dose is determined. Status: ARX517-2011 began recruiting patients in July 2021 and as of January 2022 has completed enrollment in the 3rd cohort of dose-escalation. Citation Format: Russell K. Pachynski, Luke Nordquist, Michael T. Schweizer, John Shen, Nabil Adra, Mehmet A. Bilen, Zachery R. Reichert, Rahul Aggarwal, Bilal A. Siddiqui, Matt Li, Dong Xu, Richard Huhn, Darryl Z. L'Heureux, Jinchun Yan, Ying Buechler, Sulan Yao, John Simitzi, Wenge Shi, Shawn Zhang, Scott T. Tagawa. A phase 1 dose-escalation and dose-expansion study to evaluate the safety, pharmacokinetics, and anti- tumor activity of ARX517 in subjects with advanced solid tumors resistant or refractory to standard therapies (APEX-01 trial, NCT04662580) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT211.

Efficacy proof-of-concept from a phase 1 study of a novel therapeutic peptide, ST101, targeting the oncogenic transcription factor C/EBPβ in patients with refractory solid tumors.

3014 Background: The oncogenic transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) promotes tumor survival and proliferation and inhibits differentiation. ST101 is a peptide antagonist of C/EBPβ, with anti-tumor activity in prostate cancer (PC), glioblastoma (GBM), breast cancer (BC), melanoma, and other pre-clinical models. Methods: This phase 1 study enrolled patients (pts) with refractory solid tumors with varying histologies. The primary objective was to evaluate safety/tolerability of ST101 and to determine the recommended phase 2 dose (RP2D). Secondary and exploratory objectives included pharmacokinetics (PK), preliminary efficacy (RECIST 1.1), and pharmacodynamic (PD) evaluation. The study used a 3+3 dose-escalation design, with once-weekly IV infusion dosing of ST101 at 0.5, 1, 2, 4, 6, 9 mg/kg or a flat dose of 500 mg. Results: Enrollment in phase 1 was completed in November 2021 with a total of 25 pts with multi-metastatic disease that were refractory to standard therapy. As of February 15, 2022, five pts remain on study with a median treatment duration of 27 weeks’ (16-77). There were no DLTs, dose modifications, or serious adverse events (SAEs) related to ST101. The only AEs of note were G1-2 histaminergic infusion-related reactions (IRRs), largely pruritis and urticaria, managed with antihistamines, montelukast, and interruption/slowing of infusion. IRRs affected 93% of pts on the first dose at ≥4mg/kg and led to prolongation of infusion time. Intensity and frequency of IRRs decrease with repeat dosing. No other AEs were consistently reported. There was no evidence of accumulation upon continued exposure of ST101 and no anti-drug antibodies. Tumor immunohistochemistry showed dose-proportionate staining for ST101 and decreased tumor proliferation in several pts represented by decreased Ki67 expression. Population PK analysis supported flat dosing in phase 2. Five pts continue on treatment with one confirmed partial response in a patient with cutaneous melanoma lasting >42 weeks and four pts with ongoing stable disease. Conclusions: ST101 demonstrated safety at all doses explored and evidence of efficacy across dose levels, particularly higher doses and in pts with melanoma. PK and PD support a dose relationship for efficacy and selection of 500 mg as the RP2D. Pts are now enrolling in phase 2 cohorts to assess response in cutaneous melanoma, GBM, castrate-resistant PC, and HR+ BC. Clinical trial information: NCT04478279. [Table: see text]

Abstract DDT02-03: AMG 509: A novel, humanized, half-Life extended, bispecific STEAP1 × CD3 T cell recruiting XmAb® 2+1 antibody

Abstract AMG509, a novel STEAP1 x CD3 T cell-recruiting XmAb® 2+1 bispecific immune therapy for the treatment of prostate cancer and Ewing sarcoma. Metastatic castration resistant prostate cancer (mCRPC) and Ewing sarcoma (EWS) are both diseases with unmet medical needs. Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) is a cell surface antigen that is induced by androgens and highly expressed in prostate cancer. STEAP1 is also highly expressed in EWS, and it is a target of the EWS/FLI1 fusion, the primary oncogenic driver in this pediatric malignancy. AMG 509 is a novel, half-life extended, cynomolgus monkey cross-reactive, STEAP1 x CD3 T cell-recruiting XmAb® 2+1 bispecific antibody designed to treat STEAP1-expressing cancers. AMG 509 contains two identical humanized anti-STEAP1 Fab domains that bind STEAP1-expressing cells, an anti-CD3 scFv domain that binds T cells, and an Fc domain engineered to lack effector function and extend serum half-life. We found that membranous STEAP1 expression, as measured by IHC, was absent from most normal tissues (FDA normal organ tissue array, n = 72) except the prostate epithelium and a subset of lung macrophages. In contrast, we found membranous STEAP1 expression by IHC in 80% of primary prostate cancer tumors (n = 80) and moderate to high expression in 83% of metastatic prostate cancer lesions (n = 181) and 77% of bone metastases (n = 31). In addition, we found STEAP1 expression by IHC in all EWS cell lines (n=13) and xenograft models tested (n=12). AMG 509 bound to recombinant human and cynomolgus monkey CD3ϵ with a KD of 27.6 nM and 25.8 nM, respectively, and to 293T cells transfected with human or cynomolgus monkey STEAP1 with an EC50 of 3.8 nM and 3.1 nM, respectively. AMG 509 triggered potent T cell-redirected lysis of STEAP1-positive cancer cells, with a median EC50 of 18.9 pM across 17 different STEAP1-expressing prostate, EWS, gastric, and melanoma cancer cell lines. AMG 509 was 50-fold more potent in inducing the redirected lysis of C4-2B prostate cancer cells in vitro than an XmAb® molecule with a single anti-STEAP1 Fab domain. AMG 509 was also specific, as it showed no activity against C4-2B cancer cells engineered to lack STEAP1 expression. AMG 509 exhibited hallmarks of T-cell engagement in vitro, including T-cell proliferation and cytokine release. It also induced robust in vivo anti-tumor activity in prostate cancer and EWS xenograft models, with concomitant CD8+ T-cell activation and expansion in tumors. Data from a nonclinical safety study conducted in the cynomolgus monkey suggest that AMG 509 can be administered safely at doses that are predicted to be clinically active. AMG 509 is a potent and specific first-in-class T cell-recruiting antibody for the treatment of STEAP1-positive malignancies. We are currently evaluating the safety, tolerability, pharmacokinetics, and efficacy of AMG 509 in a phase 1, first-in-human study in patients with mCRPC (NCT04221542). Citation Format: Olivier Nolan-Stevaux. AMG 509: A novel, humanized, half-Life extended, bispecific STEAP1 × CD3 T cell recruiting XmAb® 2+1 antibody [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr DDT02-03.

SM88/SMK non-hormonal therapy in recurrent or untreated prostate cancer.

e16540 Background: Prostate cancer (PC) has a poor prognosis. Androgen deprivation therapy is effective but has unacceptable short and long term side effects. SM88 (modulators of mTOR, mitochondrial stress, CYP3a4 and tyrosine isomers) is a novel combination of anti-cancer therapies with previously reported favorable results yet low toxicity in a heterogeneous group of 30 patients with cancer. We now report on a PC cohort treated with SM88. Methods: Retrospective chart review. Results: Between 2012 and 2014, 6 men with PC were treated with SM88, administered 5 days/week over a 6-week treatment cycle. SM88 consisted of daily oral and subcutaneous injection of the components. The average age was 54 years (range 32-66). Five (83.3%) were Caucasian, 1 (16.7%) was Hispanic. patients with prostate cancer were treated with SM88 daily, Monday-Friday, for between 6 to 31 wks (median 11). Four patients had castrate resistant disease, two declined ADT. One had failed prior chemotherapy (see Table). All subjects were not receiving other therapy. One subject died of disease complications approximately 3 months after starting treatment but only received approximately 20 days of therapy over a 6 week cycle. Three patients had PSA nadir responses of >90% reduction over pretreatment peak levels (see table). Two others had radiographic SD for between 10-14 wks. There were no significant toxicity except cutaneous hyperpigmentation. The duration of responses ranged from 10-114 weeks. Best overall responses included 2 patients with complete biochemical response. Four subjects improved their ECOG score during treatment and 2 had no change. Conclusions: SM-88 appears to be well tolerated and to have anti-tumor activity in prostate cancer without androgen deprivation toxicity. Additional confirmatory prospective studies in prostate are ongoing and planned in other cancers. [Table: see text]

IGFBP3 and MAPK/ERK signaling mediates melatonin-induced antitumor activity in prostate cancer.

Treatment of prostate cancer (PCa), a leading cause of cancer among males, lacks successful strategies especially in advanced, hormone-refractory stages. Some clinical studies have shown an increase in neuroendocrine-like cells parallel to the tumor progression but their exact role is a matter of debate. The prostate is a well-known target for melatonin, which reduces PCa cells proliferation and induces neuroendocrine differentiation. To evaluate the mechanisms underlying the indole effects on neuroendocrine differentiation and its impact on PCa progression, we used a cell culture model (LNCaP) and a murine model (TRAMP). Persistent ERK1/2 activation was found in both, melatonin and androgen-deprived cells. Melatonin blocked nuclear translocation of androgen receptor (AR), thus confirming anti-androgenic actions of the indole. However, using a comparative genome microarray to check the differentially expressed genes in control, melatonin, or androgen-deprived cells, some differences were found, suggesting a more complex role of the indole. By comparing control cells with those treated with melatonin or depleted of androgen, a cluster of 26 differentially expressed genes (±2.5-fold) was found. Kallikreins (KLK)2 and KLK3 (PSA) were dramatically downregulated by both treatments whereas IGFBP3 and IGF1R were up- and downregulated, respectively, in both experimental groups, thus showing a role for IGF in both scenarios. Finally, melatonin prolonged the survival of TRAMP mice by 33% when given at the beginning or at advances stages of the tumor. Serum IGFBP3 was significantly elevated by the indole in early stages of the tumor, confirming in vivo the role of the IGF signaling in the oncostatic action of the indole.

Combining the pan-aurora kinase inhibitor AMG 900 with histone deacetylase inhibitors enhances antitumor activity in prostate cancer.

Histone deacetylase inhibitors (HDACIs) are being tested in clinical trials for the treatment of solid tumors. While most studies have focused on the reexpression of silenced tumor suppressor genes, a number of genes/pathways are downregulated by HDACIs. This provides opportunities for combination therapy: agents that further disable these pathways through inhibition of residual gene function are speculated to enhance cell death in combination with HDACIs. A previous study from our group indicated that mitotic checkpoint kinases such as PLK1 and Aurora A are downregulated by HDACIs. We used in vitro and in vivo xenograft models of prostate cancer (PCA) to test whether combination of HDACIs with the pan-aurora kinase inhibitor AMG 900 can synergistically or additively kill PCA cells. AMG 900 and HDACIs synergistically decreased cell proliferation activity and clonogenic survival in DU-145, LNCaP, and PC3 PCA cell lines compared to single-agent treatment. Cellular senescence, polyploidy, and apoptosis was significantly increased in all cell lines after combination treatment. In vivo xenograft studies indicated decreased tumor growth and decreased aurora B kinase activity in mice treated with low-dose AMG 900 and vorinostat compared to either agent alone. Pharmacodynamics was assessed by scoring for phosphorylated histone H3 through immunofluorescence. Our results indicate that combination treatment with low doses of AMG 900 and HDACIs could be a promising therapy for future clinical trials against PCA.

Fatostatin Displays High Antitumor Activity in Prostate Cancer by Blocking SREBP-Regulated Metabolic Pathways and Androgen Receptor Signaling

Current research links aberrant lipogenesis and cholesterogenesis with prostate cancer development and progression. Sterol regulatory element-binding proteins (SREBP; SREBP-1 and SREBP-2) are key transcription factors controlling lipogenesis and cholesterogenesis via the regulation of genes related to fatty acid and cholesterol biosynthesis. Overexpression of SREBPs has been reported to be significantly associated with aggressive pathologic features in human prostate cancer. Our previous results showed that SREBP-1 promoted prostate cancer growth and castration resistance through induction of lipogenesis and androgen receptor (AR) activity. In the present study, we evaluated the anti-prostate tumor activity of a novel SREBP inhibitor, fatostatin. We found that fatostatin suppressed cell proliferation and anchorage-independent colony formation in both androgen-responsive LNCaP and androgen-insensitive C4-2B prostate cancer cells. Fatostatin also reduced in vitro invasion and migration in both the cell lines. Further, fatostatin caused G2-M cell-cycle arrest and induced apoptosis by increasing caspase-3/7 activity and the cleavages of caspase-3 and PARP. The in vivo animal results demonstrated that fatostatin significantly inhibited subcutaneous C4-2B tumor growth and markedly decreased serum prostate-specific antigen (PSA) level compared with the control group. The in vitro and in vivo effects of fatostatin treatment were due to blockade of SREBP-regulated metabolic pathways and the AR signaling network. Our findings identify SREBP inhibition as a potential new therapeutic approach for the treatment of prostate cancer.

Phase II Randomized Study of Figitumumab plus Docetaxel and Docetaxel Alone with Crossover for Metastatic Castration-Resistant Prostate Cancer

Figitumumab is a human IgG2 monoclonal antibody targeting insulin-like growth factor 1 receptor (IGF-1R), with antitumor activity in prostate cancer. This phase II trial randomized chemotherapy-naïve men with progressing castration-resistant prostate cancer to receive figitumumab every 3 weeks with docetaxel/prednisone (Arm A) or docetaxel/prednisone alone (Arm B1). At progression on Arm B1, patients could cross over to the combination (Arm B2). Prostate-specific antigen (PSA) response was the primary endpoint; response assessment on the two arms was noncomparative and tested separately; H0 = 0.45 versus HA = 0.60 (α = 0.05; β = 0.09) for Arm A; H0 = 0.05 versus HA = 0.20 (α = 0.05, β = 0.10) for Arm B2. A comparison of progression-free survival (PFS) on Arms A and B1 was planned. A total of 204 patients were randomized and 199 treated (Arm A: 97; Arm B1: 102); 37 patients crossed over to Arm B2 (median number of cycles started: Arm A = 8; B1 = 8; B2 = 4). PSA responses occurred in 52% and 60% of Arms A and B1, respectively; the primary PSA response objective in Arm A was not met. Median PFS was 4.9 and 7.9 months, respectively (HR = 1.44; 95% confidence interval, 1.06-1.96). PSA response rate was 28% in Arm B2. The figitumumab combination appeared more toxic, with more treatment-related grade 3/4 adverse events (75% vs. 56%), particularly hyperglycemia, diarrhea, and asthenia, as well as treatment-related serious adverse events (41% vs. 15%), and all-causality grade 5 adverse events (18% vs. 8%). IGF-1R targeting may merit further evaluation in this disease in selected populations, but combination with docetaxel is not recommended.

Tasquinimod: A Novel Drug in Advanced Prostate Cancer

Tasquinimod, an oral quinolone-3-carboxamide with anti-tumor activity in preclinical models of prostate cancer, has been tested in patients with minimally symptomatic castration-resistant prostate cancer (CRPC), showing promising inhibitory effects on the occurrence of metastasis and delayed disease progression. Although its mode of action is not fully understood, tasquinimod presumably exerts its unique anti-tumor action through inhibition of angiogenesis and immunomodulation. In clinical studies, tasquinimod demonstrated anti-tumor activity in prostate cancer in combination with a mild-to-moderate side effect profile. With single-agent tasquinimod, dose-limiting toxicity was amylase elevation without signs of pancreatitis and sinus tachycardia. The maximum tolerated dose in Phase I studies in patients with CRPC was once daily administration of 0.5-1-mg tasquinimod orally. In a Phase II trial, significant clinical activity has been demonstrated in asymptomatic or minimally symptomatic, chemotherapy-naive, metastatic CRPC (mCRPC) patients. Men were randomized to tasquinimod or placebo in a 2:1 fashion; treatment with tasquinimod resulted in significant improvement of median progression-free survival (7.6 vs 3.3 months with placebo; p = 0.0042). Based on these encouraging effects, a randomized, double-blind, placebo-controlled trial in men with minimally symptomatic mCRPC has been designed. This large Phase III trial, powered for a primary end point of progression-free survival, has now enrolled the target number of 1200 men. If the Phase II data are validated in the Phase III trial a new compound with a unique mode of action might become approved as a future therapy for minimally symptomatic mCRPC patients.

Lumican expression, localization and antitumor activity in prostate cancer

The stromal reaction surrounding tumors leads to the formation of a tumor-specific microenvironment, which may play either a restrictive role or a supportive role in the growth and progression of the tumors. Lumican, a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM), regulates collagen fibrillogenesis. Recently, lumican has also been shown to regulate cell behavior during embryonic development, tissue repair and tumor progression. The role of lumican in cancer varies according to the type of tumor. In this study we analyze the role of lumican in the pathogenesis of prostate cancer both in vivo and in vitro. Overall lumican up-regulation was observed in the primary tumors analyzed through both real-time PCR and immunostaining. The increase in lumican expression was observed in the reactive stroma surrounding prostate primary tumors with fibrotic deposition surrounding the acinar glands. In vitro analysis demonstrated that lumican inhibited both the migration and invasion of metastatic prostate cancer cells isolated from lymph node, bone and brain. Moreover, prostate cancer cells seeded on lumican presented a decrease in the formation of cellular projections, lamellipodia detected by a decreased rearrangement in ZO-1, keratin 8/18, integrin β1 and MT1-MMP, and invadopodia detected by disruption of α-smooth muscle actin, cortactin and N-WASP. Moreover, a significant increase in prostate cancer cell invasion was observed through the peritoneum of lumican knockout mice, further demonstrating the restrictive role lumican present in the ECM has on prostate cancer invasion. In conclusion, lumican present in the reactive stroma surrounding prostate primary tumors plays a restrictive role on cancer progression, and we therefore postulate that lumican could be a valuable marker in prostate cancer staging.

Synthesis, Anti-hypertensive Effect of a Novel Angiotensin II AT1 Receptor Antagonist and its Anti-tumor Activity in Prostate Cancer

Since the first non-peptide Ang II receptor antagonist was originally reported, it has become the most common target in the development of new treatments for hypertension. In recent years, all components of the classical RAS have been reported in the prostate, these results suggest the possibility that ARB is a novel therapeutic class of agents for prostate cancer. In this study, a new compound 2-(4-((2-propyl-5-nitro-1H-benzo[d]imidazol-1-yl) methyl)-1H-indol-1-yl) benzoic acid was synthesized and evaluated as a novel angiotensin II AT1 receptor antagonist by radioligand binding assays, anti-hypertensive assays in vivo and oral acute toxicity test. MTT assays and tests in nude mice were used to demonstrate its anti-tumor activity. This new compound showed high affinity to AT1 receptor and anti-hypertensive activity in spontaneously hypertensive rats and renal hypertensive rats. Moreover, in human prostate cancer cells and in athymic nude mice bearing human prostate cancer cells, we observed this new compound had an efficient antiproliferative activity in vitro and anti-tumor activity in vivo. The preliminary pharmacological characteristics with oral acute toxicity test suggested that this new compound can be considered as a candidate for both anti-hypertensive and anti-tumor drug.

Phase II study of tasquinimod in chemotherapy-naive patients with metastatic castrate-resistant prostate cancer (CRPC): Safety and efficacy analysis including subgroups.

126 Background: Tasquinimod (TASQ) is an oral quinoline-3-carboxamide derivative that binds to S100A9 and displays anti-angiogenic and anti-tumor activity in prostate cancer (PC) models. In a randomized blinded phase II study, 206 (136 TASQ, 70 placebo [P]) men with metastatic castrate resistant (CRPC) were assigned to TASQ/P once-daily at an initial dose level of 0.25 mg/day escalating to 1.0 mg/day over 4 weeks. The primary endpoint to demonstrate an improvement in PCWG2 criteria-defined progression at 6 months was met and presented at ASCO 2010. This abstract provides an update on safety and efficacy including CRPC subgroups. Methods: Subgroups of patients based on baseline criteria were investigated for safety using NCI CTC v 3.0 criteria, PK and efficacy. Results: 201 (134 TASQ, 67 P) pts with a median age of 72.6 years received treatment and were evaluable for efficacy and safety. The updated analysis based on 5 additional PFS events confirmed an improved PFS of 7.6 vs. 3.3 months for pts on TASQ vs. P. Most progression events in both arms were radiological, but more pts progressed on bone scan in the P group. Radiographic PFS was 8.8 vs 4.4 months. Significant PFS improvements were observed in the PCWG2 risk groups with bone metastatic and visceral disease. TASQ treatment led to a transient increase in inflammatory lab markers such as CRP and fibrinogen, as well as asymptomatic increases in amylase/lipase. CRP increase was associated with adverse events (AEs) such as muscle and joint pain, while increased amylase was associated with a lower risk for gastrointestinal AEs. TASQ treatment was associated with anaemia, but did not affect CV risk factors such as hypertension or QTc prolongation, and the rate of composite cardiac events was acceptably low. Clearance of TASQ is decreased with age (1.4 % per year) and patients over 80 often required dose reduction due to increased exposure and toxicities. Conclusions: TASQ improved PFS in men with metastatic CRPC. Side effects are manageable and seem to correlate with laboratory markers. Individualized dosing based on tolerability is recommended and a phase III placebo-controlled study is being initiated. [Table: see text]

A phase II study of 2-methoxyestradiol (2ME2) NanoCrystal® dispersion (NCD) in patients with taxane-refractory, metastatic castrate-resistant prostate cancer (CRPC)

2ME2 (Panzem®) is a non-estrogenic derivative of estradiol with antiproliferative and antiangiogenic activity. Preclinical data support antitumor activity in prostate cancer. This trial evaluated the efficacy of 2ME2 NCD in patients with taxane-refractory, metastatic CRPC. Patients with metastatic CRPC who had progressed on only one prior taxane-based regimen were eligible. All patients received 2ME2 NCD at 1,500 mg orally four times daily, repeated in 28 day cycles. The primary endpoint was progression-free survival at month 6, with a secondary endpoint of PSA response. An exploratory endpoint was metabolic response on FDG-PET imaging. A total of 50 pts was planned. The study was terminated after 21 pts when a futility analysis showed the primary endpoint was unlikely to be reached. The median number of cycles on study was 2 (range <1 to 12). Adverse events (AE) of grade ≥3 related to the study drug occurred in 7 unique patients (33%): elevations in liver function tests, fatigue or weakness, gastrointestinal hemorrhage, and hyponatremia. Paired FDG-PET scans were obtained for 11 pts. No metabolic responses were observed. 2ME2 NCD did not appear to have clinically significant activity in this study. 2ME2 NCD was well-tolerated and showed some evidence of biologic activity. Given the aggressive biology in this taxane-refractory population, the potential benefit from a cytostatic agent like 2ME2 might better be realized in the pre-chemotherapy (or rising PSA only) stage of CRPC.

A randomized, multicenter, international phase II study of tasquinimod in chemotherapy naïve patients with metastatic castrate-resistant prostate cancer (CRPC).

4510 Background: Tasquinimod (TASQ) is a quinoline-3-carboxamide derivative that binds to S100A9 and displays anti-angiogenic properties and anti-tumor activity in prostate cancer (PC) models. Phase I studies in PC indicated that TASQ is well tolerated and may delay PC progression. Methods: 206 patients (pts) with metastatic CRPC were assigned (2:1) to either receive oral TASQ once-daily at an initial dose level of 0.25 mg/day escalating to 1.0 mg/day over 4 weeks, or placebo (P). The primary endpoint was proportion of pts without disease progression (DP) at 6 months, defined by PCWG2 or pain criteria, but excluding PSA. Secondary endpoints comprised safety, progression free survival (PFS), and changes in biological markers, including PSA. Results: 200 (133 TASQ, 67 P) pts with a median age of 72.5 years were evaluable for efficacy and safety. Median baseline characteristics were (TASQ/P): Karnofsky (95/95), Gleason (7/7), LDH (201/206 U/L), Alk Phos (98/87 U/L), Hgb (12.9/13.2 g/dL), PSA (29/19 μ g/L) and PSADT (4.2/5.0 mo). 6-mo progression free proportion for TASQ and P groups was 57% and 33% respectively (p=0.0001) and median PFS was 24.7 vs. 12.9 weeks. In clinical subgroups defined by PCWG2, the PFSs were (weeks/N): nodal 24.3/9 vs. 12.6/12; bone 30.6/90 vs. 13.4/42; visceral 23.9/32 vs. 12.1/10 for pts on TASQ and P. Pts treated with TASQ had significantly decreased serum LDH levels and stabilized bone alkaline phosphatase (BAP) levels, with less pronounced effects on PSA response and progression. Serious vascular events were more common in the TASQ arm (myocardial infarction, heart failure or stroke (3 % vs 0 %), deep vein thrombosis (4 % vs 0 %)). Common (>10%) adverse events (AEs) occurring more frequently in pts receiving TASQ included gastrointestinal disorders, fatigue, and musculoskeletal pains. and asymptomatic elevation of pancreatic enzymes and proinflammatory markers. G3-4 AEs (including labs) were reported in 38% pts on TASQ vs. 10 % on P. Conclusions: TASQ significantly slowed the rate of DP and improved PFS in pts with metastatic CRPC and a phase III study is planned. Side effects were manageable. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Active Biotech Active Biotech Active Biotech Active Biotech

Abstract 3244: Combination of COX-2 inhibitor Celebrex with androgen deprivation synergistically inhibits tumor growth in a syngeneic mouse model of prostate cancer

Abstract Prostate cancer (PC) is the most common solid tumor in men in the United States. Effective treatment options include surgery and radiation therapy for localized tumors, whereas advanced cancer is treated by androgen deprivation. Unfortunately, most patients with metastatic prostate cancer will eventually relapse into a hormone-independent cancer that is notoriously resistant to chemotherapy. Thus, more effective therapeutic strategies are needed to improve this outcome, which leads to about 30 000 deaths every year. Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown efficacy for the prevention or the treatment of several human cancers. Among them, specific COX-2 inhibitors have received particular attention because COX-2 is overexpressed in many epithelial tumors, including prostate, and because a number of studies have shown that they slow the growth of colon, lung and breast tumor xenografts in mice. In addition, COX-2 inhibitors have potent antitumor activity in prostate cancer both in vitro and in vivo. Celebrex (Celecoxib), the only COX-2 inhibitor still approved for clinical use, is being evaluated in clinical trials for the treatment of localized or advanced prostate cancer. In this study, we observed that celebrex in combination with androgen deprivation inhibits tumor growth much more efficiently that either treatment alone. A syngeneic pseudo-orthotropic mouse model and Intravital Microscopy (IVM) were used to measure several parameters of tumor progression and study the effect of Celebrex combined with androgen deprivation. Androgen-dependent TRAMP-C2 mouse prostate cancer cells were co-implanted with prostate tissue into the dorsal skinfold chamber of syngeneic C57Bl/6 mice. Mice were subjected to surgical or hormonal castration, alone or in combination with Celebrex. Tumor growth, apoptosis, mitosis and angiogenesis were measured. We observed that Celebrex alone inhibited tumor growth with no evidence of apoptosis but most likely through growth arrest during mitosis. Interestingly, Celebrex alone had no effect on angiogenesis. Castration alone had a significant angiostatic effect but tumor growth was inhibited only by 20%. In contrast, the combination of castration and Celebrex inhibited tumor growth by 65% and resulted in both increased apoptosis and increased mitotic arrest. Conclusion: our study provides evidence that Celebrex treatment of prostate cancer-bearing mice results in a lower proliferative rate in tumors. In addition, Celebrex potentiates the effect of castration to inhibit tumor growth in vivo. We propose therefore that administration of Celebrex during androgen deprivation may be more efficient than androgen deprivation alone and warrants further study. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3244.

Dasatinib inhibits site-specific tyrosine phosphorylation of androgen receptor by Ack1 and Src kinases

Activation of androgen receptor (AR) may play a role in the development of castration resistant prostate cancer. Two intracellular tyrosine kinases, Ack1 (activated cdc42-associated kinase) and Src, phosphorylate and enhance AR activity and promote prostate xenograft tumor growth in castrated animals. However, the upstream signals that activate these kinases and lead to AR activation are incompletely characterized. In this study, we investigated AR phosphorylation in response to non-androgen ligand stimulation using phospho-specific antibodies. Treatment of LNCaP and LAPC-4 cells with epidermal growth factor (EGF), heregulin, Gas6 (ligand binding to Mer receptor tyrosine kinase and activating Ack1 downstream), interleukin (IL)-6 or bombesin stimulated cell proliferation in the absence of androgen. Treatment of LNCaP and LAPC-4 cells with EGF, heregulin, or Gas6 induced AR phosphorylation at Tyr-267; IL-6 or bombesin treatment did not. AR phosphorylation at Tyr-534 was induced by treatment with EGF, IL-6 or bombesin, but not by heregulin or Gas6. siRNA-mediated knockdown of Ack1 or Src showed that Ack1 mediates heregulin- and Gas6-induced AR Tyr-267 phosphorylation whereas Src mediates Tyr-534 phosphorylation induced by EGF, IL-6, and bombesin. Dasatinib, a Src inhibitor, blocked EGF-induced Tyr-534 phosphorylation. In addition, we show dasatinib also inhibited Ack1 kinase. Dasatinib inhibited heregulin-induced Ack1 kinase activity and AR Tyr-267 phosphorylation. Dasatinib inhibited heregulin-induced AR-dependent reporter activity. Dasatinib also inhibited heregulin-induced expression of endogenous AR target genes. Dasatinib inhibited Ack1-dependent colony formation and prostate xenograft tumor growth in castrated mice. Interestingly, Ack1 or Src knockdown or dasatinib did not inhibit EGF-induced AR Tyr-267 phosphorylation or EGF-stimulated AR activity, suggesting the existence of an additional tyrosine kinase that phosphorylates AR at Tyr-267. These data suggest that specific tyrosine kinases phosphorylate AR at distinct sites and that dasatinib may exert anti-tumor activity in prostate cancer through inhibition of Ack1.

A novel bis-indole destabilizes microtubules and displays potent in vitro and in vivo antitumor activity in prostate cancer

Microtubules are one of the most useful subcellular targets in chemotherapy. We identified a novel indole, (3-(1H-indol-2-yl)phenyl)(1H-indol-2-yl)methanone (15), that inhibits tubulin action and exhibits potent antitumor activity in various preclinical models. In vitro cancer cell growth inhibition was measured by SRB or MTT assay in human cancer cell lines. Apoptosis induced by 15 was examined in LNCaP and PC-3 cells. Effects of 15 on cell cycle distribution and tubulin were investigated via in vitro models. In vivo toxicity and xenograft efficacy studies were conducted in mice. Indole 15 inhibited the in vitro growth of a number of human cancer cell lines, including drug-resistant cell lines that over-express P-glycoprotein, multidrug resistance-associated proteins, and breast cancer resistance protein with IC(50) values in the range of 34-162 nM. Nanomolar concentrations of the compound caused down-regulation of bcl-2, induced PARP cleavage, and induced apoptosis in both LNCaP and PC-3 prostate cancer cells, as confirmed by anti-histone ELISA and DNA laddering. In vitro studies revealed that the compound inhibited polymerization of purified tubulin and induced a strong and concentration-dependent G(2)M arrest in PC-3 cells. In vivo studies in immunodeficient mice bearing PC-3 tumor xenografts showed that the compound effectively inhibited tumor growth. The potent in vitro and in vivo antitumor activities of this novel indole suggest that drugs with this novel chemical scaffold might be developed for treatment of drug-resistant prostate cancer.