Activity In Castration-resistant Prostate Cancer Research Articles

A phase II trial of cabozantinib (Cabo) in patients (pts) with castrate-resistant prostate cancer (CRPC) metastatic to bone (NCT01428219).

TPS5094 Background: MET overexpression predicts prostate cancer invasion and bone metastasis; inhibition of MET/VEGF pathways has synergistic activity in CRPC (Knudsen et al. Adv Cancer Res 2004; Aftab et al. Clin Transl Oncol 2011). Cabo is a small molecule that inhibits multiple receptor tyrosine kinases, including MET and VEGFR2. A phase II randomized discontinuation trial of Cabo showed clinical activity in CRPC, including reduction of soft tissue lesions, prolongation of progression-free survival (PFS), resolution of bone scans, and reductions in bone turnover markers, pain and narcotic use (Smith et al, JCO 2013). To further define the activity of Cabo in pts with CRPC and bone metastases, we launched a phase II trial to characterize the effects of Cabo on bone metabolism and tumor activity in prostate cancer bone lesions. We hypothesize that the clinical activity of Cabo correlates with measurable pharmacodynamic effects on bone micro-environment. Methods: After informed consent, chemotherapy-naive pts with progressive CRPC and bone metastases accessible to CT-guided biopsy, adequate performance status/organ function, are treated with Cabo 60 mg once daily. Primary endpoint: proportion of pts progression-free (PF) at 12 weeks. Secondary endpoints: safety, PFS, response proportion/duration, PSA response, PSA time-to-progression. A Simon's two-stage mini-max design permits early termination after the first 27 evaluable pts in case of unfavorable results. Alternatively, up to 46 evaluable pts will be accrued. Cabo would not be of interest if the 12-week PF proportion is <0.45; it would be of definite clinical interest if the 12-week PF proportion is >0.65 (5% type I error, 85% power). Perfusion/diffusion-weighted MRI (parametric response maps) and bone lesion biopsies are required at baseline and 6 weeks after starting Cabo. Doxycycline is administered prior to bone biopsy for bone labeling. Bone cores are sent for dynamic histomorphometry and immunohistochemistry (phospho-MET/MET, phospho-VEGFR2/VEGFR2, phospho-Akt/Akt). Serum is collected at several time-points to measure markers of bone metabolism. 13 of 27 first-stage pts have been enrolled and started Cabo. Clinical trial information: NCT01428219.

Effects on androgen receptor nuclear import by docetaxel, cabazitaxel, abiraterone, and enzalutamide: Potential mechanism for cross-resistance in castration-resistant prostate cancer (CRPC).

5064 Background: Recent reports have suggested that paclitaxel and docetaxel, which exert their therapeutic activity primarily through inhibition of microtubule function and mitosis, also impair androgen receptor (AR) signaling. AR signaling is the key therapeutic target for the newly available agents abiraterone and enzalutamide. A recent study suggested impaired efficacy of docetaxel when given after progression on abiraterone in patients with CRPC. To identify potential mechanisms of cross-resistance, we investigated whether and to what extent AR nuclear translocation is affected by docetaxel, cabazitaxel, abiraterone and enzalutamide. Methods: Hep3B cells stably expressing GFP labeled AR were used for AR translocation studies. Cells were seeded on a cover slip in steroid-stripped medium (DCC) and treated with docetaxel (1 µM), cabazitaxel (1 µM), abiraterone (6 µM) and enzalutamide (1 µM). The anthracenedione mitoxantrone (100 nM) that does not target the microtubule cytoskeleton was used as a control cytotoxic agent. Following incubation for 48 hours, the synthetic androgen R1881 was added to study dynamics of AR nuclear import by time-lapse confocal microscopy. Results: Docetaxel and cabazitaxel inhibited R1881 induced AR nuclear translocation with 21% and 34% respectively compared to control, while mitoxantrone did not affect AR transport. Abiraterone inhibited AR translocation with 58% and enzalutamide completely blocked AR translocation. Conclusions: These data point towards a role for microtubules in AR nuclear transport and an additional mechanism of taxane activity in CRPC. Docetaxel, cabazitaxel, abiraterone and enzalutamide all interfere with AR nuclear transport, which is a crucial step in AR signaling. Our findings identify and provide insight in a potential mechanism of clinical cross-resistance between the two taxanes currently registered for treatment in CRPC and the novel agents abiraterone and enzalutamide. Further investigations are warranted in order to define if this potential cross-resistance impacts the most suitable treatment sequence for these drugs in CRPC.

First-in-human phase I study of EZN-4176, a locked nucleic acid antisense oligonucleotide (LNA-ASO) to androgen receptor (AR) mRNA in patients with castration-resistant prostate cancer (CRPC).

5052 Background: EZN-4176 is a third generationLNA-ASO that binds the ligand binding domain of AR mRNA resulting in full length AR mRNA degradation and decreased AR protein expression. Methods: Patients (pts) (performance status ECOG≤1) with progressing CRPC were eligible; prior abiraterone and enzalutamide treatment were allowed. EZN-4176 was administered as a weekly (QW) one-hour intravenous infusion. The starting dose was 0.5 mg/Kg with a 4-week dose-limiting toxicity (DLT) period. After determination of the DLT and the maximum tolerated dose (MTD) for weekly administration, a fortnightly schedule (Q2W) was initiated; a 3+3 modified Fibonacci dose escalation design was pursued. PD studies evaluated AR expression in tissue utilizing antibodies to the amino and carboxy-termini of the AR. Results: 22 pts were enrolled (median age 70.6 years, range 59 – 84 years). One pt was treated with the Q2W schedule. Two DLTs (G3/G4 ALT/AST elevation) occurred at 10 mg/Kg, which was therefore identified as the MTD for the weekly schedule. Multiple pts treated at 6.5 and 10 mg/Kg (5/9 pts, 55%) developed ≥G2 ALT and/or AST elevation after the first cycle requiring dose reduction and treatment delay. The most frequent adverse events (AEs) all-grades were fatigue (21/22 pts, 95.4%), nausea (10/22 pts, 45.4%), constipation (8/22 pts, 36.3%), AST (8/22 pts, 36.3%) and ALT (10/22 pts, 45.4%) elevation. The most frequent G3/4 AEs were AST (4/22 pts, 18.1%) and ALT (5/22 pts, 22.7%) elevation. Maximum PSA and circulating tumor cells (CTCs) declines are summarized below. There were no objective soft tissue responses. PD studies did not document any knockdown of AR expression Conclusions: EZN-4176 has limited antitumour activity in CRPC at its MTD for weekly administration. Safety, PK, PD and efficacy data will be presented. Clinical trial information: NCT01337518. [Table: see text]

NCIC CTG, IND-205: A phase II study of PX-866 in patients with recurrent or metastatic castration-resistant prostate cancer (CRPC).

5042 Background: PX-866 is an irreversible, pan-isoform inhibitor of Class I PI-3K. Mutations in PIK3CA and loss of PTEN activity lead to activation of AKT signaling; alterations in these genes occur frequently in prostate cancers while activation of the PI-3K/AKT signaling pathway is implicated in prostate cancer progression and treatment resistance. Hence, novel inhibitors of the pathway such as PX-866 are of interest. Methods: In this multicenter, two-stage, phase II study, docetaxel-naïve CRPC pts received PX-866, 8mg daily on a 6-week cycle. Primary endpoint was lack of progression at 12 weeks (PCWG2 criteria). Secondary endpoints included PSA and objective response rates and change in circulating tumor cells (CTC) during treatment. If ≤5 of the first 20 pts were progression free at 12 weeks, the study would stop. Otherwise, 40 pts would be accrued and PX-866 deemed worthy of further study if ≥16 pts were progression free at 12 weeks. Results: 43 pts were accrued after the criteria to progress to stage 2 were met. Median age was 70, ECOG PS was 0/1/2 in 27/15/1 pts, 23 pts had measurable disease, 24 patients had CTC ≥5. Median number of cycles was 2 (range 1–8). Most common adverse events (AE) were diarrhea (27 pts), nausea (25), fatigue (15), vomiting (13), anorexia (15) and grade 1 hypomagnesemia (11); 7 pts discontinued because of toxicity (3 GI, 3 LFTs, 1 fatigue). Grade 3 AEs were diarrhea (5 pts), AST/ALT elevation (4), fatigue (3). 11 patients were progression free at 12 weeks. 16 of the 24 pts with measurable disease were evaluable for response; there were no objective responses but 10 pts had stable disease (2.6-13.9m). One pt had a confirmed PSA response. CTC favorable conversion (from 5 at baseline to <5) was observed in 6/24 evaluable patients (25%). Correlative studies are ongoing. Conclusions: PX-866 is well tolerated and showed modest activity in CRPC but did not meet a priori benchmarks for further development as a single agent in unselected patients. As androgen receptor inhibition promotes PI3K activity in PTEN-loss PC models, the addition of PX-866 in pts whose PSA is rising on abiraterone may reverse resistance and phase B of the study is underway to test this hypothesis clinically. Clinical trial information: NCT01331083.

Abstract LB-166: Cabozantinib (cabo) + abiraterone (abi) combination therapy in castration resistant prostate cancer (CRPC): preclinical evaluation and interim results of an investigator-sponsored phase 1 clinical study.

Abstract Introduction: Abi (CYP17A1 and lyase inhibitor) and cabo (multi-targeted receptor tyrosine kinase inhibitor including MET and VEGFR2) have complementary mechanisms of action and both have significant single agent activity in CRPC. Cabo decreases evidence of skeletal disease on 99mTc bone scans to a marked degree. Rationale exists for cabo to enhance abi efficacy. Methods: In vitro proliferation experiments have been done with WST-1 assay to evaluate anti-cancer activity of abi and cabo as single agents and in combination in androgen receptor (AR) positive and negative, hormone sensitive and castration resistant cell lines (PC-3, VCaP, LAPC4 and LAPC4-CR). An in vivo established subcutaneous model of LAPC4-CR in female mice has been used to compare single agents and combination therapy. A phase 1 dose escalation trial using a 3 + 3 design with a fixed dose (1,000 mg) of abi and 5mg BID prednisone with escalating doses of cabo (20mg, 40mg and 60mg) is ongoing in pts who are castration resistant and pre or post chemotherapy. This study includes assessment of therapy response using 18F-NaF and 18F-FDG PET/CT combined with 99mTc bone scan and diagnostic CT abdomen and pelvis. Results: In vitro proliferation studies demonstrated single agent activity between 2 and 10 μM for abi and cabo in all cell lines (including AR negative PC-3) and the ability of cabo to enhance abi activity. In LAPC4 and VCaP, abi plus cabo decreased AR and PSA protein levels to the same degree or more than abi or cabo alone. In vivo LAPC4-CR studies showed abi retarded growth until day 14 only, single agent cabo caused 66% growth suppression at day 25 with effect durable until day 39. At day 39, abi + cabo resulted in no growth from baseline. In the phase 1 trial, 8 pts have been enrolled and no dose limiting toxicities (DLT) have been observed in the first 28 days of therapy for the 3 patient cohorts treated at both 20 mg and 40 mg. Two patients have been treated at 60mg without DLT in the first cycle (third patient enrollment pending). The number of 4 week cycles for the 20mg cohort are: 9+, 9, 8+ (all post docetaxel); 40mg: 2, 3+, 3+; 60mg: 1+, 1+. Preliminary findings from PET/CT studies of 6 patients with baseline and follow-up after 8 weeks of therapy: extent of bone disease and change in SUVmax on NaF PET/CT show potential for better definition of disease burden and therapy response than 99m Tc bone scan plus CT; potential negative prognostic outcome for patients with 18F-FDG-avid disease. Conclusion: Preclinical in vitro and in vivo studies show cabo enhances abi efficacy in prostate cancer. Mechanistic studies are being conducted to identify the biological basis for this finding. The ongoing phase 1 clinical trial with drug trough levels, CTC enumeration and bone turnover assessments will help define the recommended phase 2 dose of abi + cabo combination therapy. Citation Format: Christopher J. Sweeney, Katherine Zukotynski, Xiaodong Wang, Andrew Wick, Amanda Fredericks, Bon Lam, Philip Kantoff. Cabozantinib (cabo) + abiraterone (abi) combination therapy in castration resistant prostate cancer (CRPC): preclinical evaluation and interim results of an investigator-sponsored phase 1 clinical study. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-166. doi:10.1158/1538-7445.AM2013-LB-166

Transdermal Oestradiol in the Management of Castration-resistant and Corticosteroid-resistant Prostate Cancer — a Dose Escalation Study

s / Clinical Oncology 25 (2013) e67ee74 e72 [1]. Prophylactic use of granulopoiesis-stimulating factors, such as granulocyte-colony-stimulating factor (G-CSF), is being increasingly used to prevent chemotherapy-induced neutropaenia [2e4]. To compare the rate of febrile neutropaenia before and after implementation of G-CSF prophylaxis in patients receiving chemotherapy for testicular cancer. To determine the impact of these events on unscheduled care. Materials andmethods: Over an 18month period, we prospectively audited the incidence of febrile neutropaenia before (n 1⁄4 12) and after (n 1⁄4 8) implementation of prophylactic pegylated G-CSF (6mg SC 24 h post-chemotherapy) in patients receiving comparable chemotherapy regimens. Identification of febrile neutropaenic episodes and resultant impact on treatment recorded. There were no significant differences in chemotherapy regimens or other supportive care apart from the use of G-CSF. Results: The rate of neutropaenic sepsis was significantly different between the pre-GCSF and post-GCSF group (42% versus 0%, P 1⁄4 0.05). In the pre-GCSF group, 4 patients developing febrile neutropaenia went on to have G-CSF with subsequent cycles. Those developing febrile neutropaenia in the preGCSF group had a cumulative 31 days of unscheduled inpatient stay. This included one patient admitted to intensive care. There were no unscheduled inpatient stays in the post-GCSF group. Conclusion: Use of prophylactic G-CSF following chemotherapy for testicular cancer significantly reduces the incidence of febrile neutropaenia and subsequent inpatient stays.

Novel Interaction between the Co-chaperone Cdc37 and Rho GTPase Exchange Factor Vav3 Promotes Androgen Receptor Activity and Prostate Cancer Growth*

Elevated androgen receptor (AR) activity in castration-resistant prostate cancer may occur through increased levels of AR co-activator proteins. Vav3, a guanine nucleotide exchange factor, is up-regulated following progression to castration resistance in preclinical models and is overexpressed in a significant number of human prostate cancers. Vav3 is a novel co-activator of the AR. We sought to identify Vav3 binding partners in an effort to understand the molecular mechanisms underlying Vav3 enhancement of AR activity and to identify new therapeutic targets. The cell division cycle 37 homolog (Cdc37), a protein kinase-specific co-chaperone for Hsp90, was identified as a Vav3 interacting protein by yeast two-hybrid screening. Vav3-Cdc37 interaction was confirmed by GST pulldown and, for native proteins, by co-immunoprecipitation experiments in prostate cancer cells. Cdc37 potentiated Vav3 co-activation of AR transcriptional activity and Vav3 enhancement of AR N-terminal-C-terminal interaction, which is essential for optimal receptor transcriptional activity. Cdc37 increased prostate cancer cell proliferation selectively in Vav3-expressing cells. Cdc37 did not affect Vav3 nucleotide exchange activity, Vav3 protein levels, or subcellular localization. Disruption of Vav3-Cdc37 interaction inhibited Vav3 enhancement of AR transcriptional activity and AR N-C interaction. Diminished Vav3-Cdc37 interaction also caused decreased prostate cancer cell proliferation selectively in Vav3-expressing cells. Taken together, we identified a novel Vav3 interacting protein that enhances Vav3 co-activation of AR and prostate cancer cell proliferation. Vav3-Cdc37 interaction may provide a new therapeutic target in prostate cancer.

Cabozantinib Has Activity in Castration-Resistant Prostate Cancer

Abstract The MET/VEGFR2 inhibitor cabozantinib showed antitumor activity in men with metastatic CRPC.

Understanding the Role of MET Kinase in Cancer Therapy

Understanding the Role of MET Kinase in Cancer Therapy

Phase II trial of non-pegylated liposomal doxorubicin and low-dose prednisone in second-line chemotherapy for hormone-refractory prostate cancer

Non-pegylated liposomal doxorubicin (NPLD) (Myocet) has shown marked in vitro activity in castration-resistant prostate cancer (CRPC) and also in docetaxel-resistant cells, higher than that shown by pegylated liposomal doxorubicin. Its activity would seem to be due to a high intracellular drug concentration and induction of Golgi-dependent apoptosis. On the basis of these results, a clinical study was designed to assess the activity of NPLD and low-dose prednisone in second-line therapy. Fifty-four patients were enrolled and evaluated. Eligibility criteria were histologically confirmed CRPC, PSA >20 ng/mL or measurable lesions according to the RECIST criteria, previous docetaxel-based chemotherapy, and adequate cardiac function. Patients were treated with weekly intravenous NPLD 25 mg/m2 and daily prednisone 10 mg until progression. Median patient age was 69 years (range, 52-83) and median baseline PSA concentration was 120 ng/mL (range, 5.35-4350). Sixteen (29.6%) patients had measurable lesions. Objective or PSA responses (>50% reduction) were observed in 8 (14.8%) patients. The median time to progression was 2.8 months and the median overall survival was 11.3 months. Toxicity was generally mild (grade 1-2) and infrequent, with grade 3-4 neutropenia in 12.9% of cases. Grade 3 nonhematological toxicities included nausea in 2 patients (3.7%) and fatigue and stomatitis in 1 case (1.9%). No drug-related serious adverse events were reported. Weekly administration of NPLD is a well tolerated treatment with proven albeit limited activity.

Diethylstilbestrol in castration‐resistant prostate cancer

What's known on the subject? and What does the study add? Diethylstilbestrol (DES) was the first hormone treatment used for prostate cancer and has also shown effectiveness in castration-resistant disease in small studies; however, concerns over thromboembolic toxicity have restricted its use in the past. Over 200 elderly men with castration-resistant prostate cancer were treated with 1-3 mg of DES, given with 75 mg aspirin and breast bud irradiation. Almost 30% of men showed a significant PSA response and the median time to PSA progression was 4.6 months. Almost 20% of patients with pain had a significant analgesic benefit. The most important toxicity was thromboembolism in 10% of men. Overall the drug has an acceptable toxicity profile and offers a palliative benefit in frail elderly men who may not be fit for chemotherapy. • To assess the efficacy and toxicity of diethylstilbestrol (DES) in the management of castration-resistant prostate cancer (CRPC). • A total of 231 patients with CRPC received treatment with DES at the Royal Marsden Hospital between August 1992 and August 2000. • The median pre-treatment prostate-specific antigen (PSA) level was 221 ng/mL. • DES was used at a dose of 1-3 mg daily, with aspirin 75 mg. • The primary endpoint was PSA response rate. • The PSA response rate (using PSA Working Group criteria) was 28.9%. • The median time to PSA progression was 4.6 months. • Of patients with bone pain, 18% had an improvement in their European Organisation for the Research and Treatment of Cancer pain score. • Thromboembolic complications were seen in 9.9% of all patients. • DES has significant activity in CRPC and can be of palliative benefit. • DES has an acceptable toxicity profile in the management of patients with symptomatic CRPC when used at a dose of 1-3 mg, combined with aspirin and prophylactic breast bud radiotherapy.

In Silico Discovery of Androgen Receptor Antagonists with Activity in Castration Resistant Prostate Cancer

Previously available androgen receptor (AR) antagonists (bicalutamide, flutamide, and nilutamide) have limited activity against AR in prostate cancers that relapse after castration [castration resistant prostate cancer (CRPC)]. However, recent AR competitive antagonists such as MDV3100, generated through chemical modifications to the current AR ligands, appear to have increased activity in CRPC and have novel mechanisms of action. Using pharmacophore models and a refined homology model of the antagonist-liganded AR ligand binding domain, we carried out in silico screens of small molecule libraries and report here on the identification of a series of structurally distinct nonsteroidal small molecule competitive AR antagonists. Despite their unique chemical architectures, compounds representing each of six chemotypes functioned in vitro as pure AR antagonists. Moreover, similarly to MDV3100 and in contrast to previous AR antagonists, these compounds all prevented AR binding to chromatin, consistent with each of the six chemotypes stabilizing a similar AR antagonist conformation. Additional studies with the lead chemotype (chemotype A) showed enhanced AR protein degradation, which was dependent on helix 12 in the AR ligand binding domain. Significantly, chemotype A compounds functioned as AR antagonists in vivo in normal male mice and suppressed AR activity and tumor cell proliferation in human CRPC xenografts. These data indicate that certain ligand-induced structural alterations in the AR ligand binding domain may both impair AR chromatin binding and enhance AR degradation and support continued efforts to develop AR antagonists with unique mechanisms of action and efficacy in CRPC.

Nelfinavir inhibits regulated intramembrane proteolysis of sterol regulatory element binding protein‐1 and activating transcription factor 6 in castration‐resistant prostate cancer

Nelfinavir induces apoptosis in liposarcoma by inhibiting site-2 protease (S2P) activity, which leads to suppression of regulated intramembrane proteolysis. We postulate similar effects in castration-resistant prostate cancer because it exhibits a lipogenic phenotype. Nelfinavir inhibited androgen receptor activation in androgen-sensitive prostate cancer and the nuclear translocation of the fusion proteins sterol regulatory element binding protein-1 (SREBP-1)-enhanced green fluorescence protein (EGFP) and activating transcription factor 6 (ATF6)-EGFP in castration-resistant prostate cancer cells, viewed under confocal microscopy. Nelfinavir and site-1 protease (S1P) and S2P small interfering RNAs (siRNAs) reduced the proliferation of castration-resistant prostate cancer and induced apoptosis, which was opposed by autophagy. Inhibition of autophagy with hydroxychloroquine was additive to the apoptotic effect of nelfinavir. Western blotting of S1P and S2P siRNA knockdown and/or nelfinavir-treated cells confirmed the accumulation of precursor SREBP-1 and ATF6. 3,4-Dichloroisocoumarin, an S1P inhibitor, did not affect SREBP-1 processing. In contrast, 1,10-phenanthroline, an S2P inhibitor, reproduced the nelfinavir-treated molecular and biological phenotype. Nelfinavir-mediated inhibition of regulated intramembrane proteolysis led to the accumulation of unprocessed SREBP-1 and ATF6. This resulted in sequential endoplasmic reticulum stress, inhibition of the unfolded protein response, reduced fatty acid synthase expression and apoptosis, which was countered by autophagy. Inhibition of autophagy was at least additive to this pro-apoptotic effect. These findings provide new insights into nelfinavir-induced endoplasmic reticulum stress and cancer cell death, and lead us to propose investigating its clinical activity in castration-resistant prostate cancer. This report validates S2P as a therapeutic target in castration-resistant prostate cancer.

SWOG S0421: Phase III study of docetaxel (D) and atrasentan (A) versus docetaxel and placebo (P) for men with advanced castrate resistant prostate cancer (CRPC).

4511 Background: The endothelin pathway has a mechanistic role in bone metastases (mets). Atrasentan (A), an endothelin receptor antagonist, has reported activity in CRPC. This trial tested the survival impact of A + docetaxel (D) vs. D+ placebo (P) in CRPC pts with bone mets. Methods: Eligible CRPC pts, stratified for progression type, baseline pain index (BPI), extraskeletal mets and bisphosphonate (BisP) use, were randomized 1:1 to D+A vs. D+P for 12 3-wk cycles. Non-progressors could continue blinded drug alone for 16 more wks. Co-primary endpoints: overall (OS) and progression-free survival (PFS). 930 pts were needed to detect a 25% increase in med OS with D+A (1-sided log-rank, α=0.025, 87% power). Results: 991/1,038 pts were eligible: med age 69, 16% non-white, 61% on BisP, 31% prior prostatectomy, 42% worst pain by BPI ≥ 4, 20% PSA only progression and 56% extraskeletal mets. Multivariate analysis of baseline prognostic factors predicting worse OS were: measurable or evaluable disease progression, high BPI and extraskeletal mets (all p<0.02). No differences in median OS, PFS, or response between arms. Toxicities were similar between arms. Most common toxicities were fatigue, dyspnea, neutropenia and anemia. Addition of A trended to worse OS in pts with visceral mets (HR=1.13 p=0.21) and better OS in those without: bone only (HR=0.86, p=0.20). 357 pts continued A or P up to 52 weeks, no OS difference was seen post-chemo for this subset (p=0.92). Conclusions: This phase III study found no benefit for the addition of A to D in CRPC. Unless specific biomarkers can stratify a population for benefit, endothelin modulators have limited future use in advanced CRPC. Further analyses will test putative surrogacy effects of PSA, serum bone markers and circulating tumor cell kinetics for OS. [Table: see text]

The evolving paradigm of second-line hormonal therapy options for castration-resistant prostate cancer

The review examines recent advances in second-line hormonal therapy for the treatment of castrate-resistant prostate cancer (CRPC). Recent data highlight the continued importance of androgen signaling in CRPC. These findings have spurred the development of novel inhibitors of adrenal and intra-tumoral androgen synthesis and novel androgen signaling inhibitors with activity in CRPC. In the past year abiraterone acetate, a CYP17 (17α-hydroxylase/17, 20 lyase) inhibitor, received US FDA approval for use in the treatment of metastatic CRPC in patients previously treated with docetaxel. Additionally, the novel androgen signaling inhibitor MDV3100 has been reported to confer a survival advantage compared to placebo in the same patient population. Here we review the scientific rationale for targeting androgen signaling in CRPC and the recent pivotal trials that support the use of novel second-line hormonal therapies. Additionally, we summarize ongoing preclinical and clinical efforts to ascertain and overcome mechanisms of resistance. Novel inhibitors of extra-gonadal androgen synthesis and androgen receptor function demonstrate the continued importance of androgen signaling in CRPC. These agents have improved clinical outcomes for patients with metastatic CRPC.

Abstract 3848: Preclinical profile of AZD3514: A small molecule-targeting androgen receptor function with a novel mechanism of action and the potential to treat castration-resistant prostate cancer

Abstract The androgen receptor (AR), an important molecular target in the aetiology and progression of prostate cancer, has been found recently to drive key signalling responses in castration resistant prostate cancer (CRPC) after classical androgen ablation therapies have failed. Here we describe the biological characterisation of AZD3514 an oral drug that targets AR function, with a novel mechanism of action that can result in down-regulation of AR protein. AZD3514 binds to the AR ligand binding domain and has selectivity for binding to AR over other nuclear hormone receptors. In vitro AZD3514 inhibits cell growth in prostate cancer cells expressing wild-type (VCaP) and mutated (T877A) AR (LNCaP), but is inactive in AR-negative prostate cancer cells, indicating a dependency on AR for efficacy. In vivo, we assessed activity initially in the Hershberger castrated rat assay in which oral dosing of AZD3514 (100mg/kg once-daily for 7 days) significantly inhibited testosterone-induced growth of sexual accessory organs. Studies to investigate the mode of action of AZD3514 revealed a number of cellular events associated with loss of AR function. Consistent with an inhibition of AR signalling, AZD3514 caused a rapid reduction in PSA synthesis in vitro; with a significant decrease in PSA mRNA being evident in LNCaP cells within 2 - 3 h of compound treatment. Additional experiments in LNCaP cells and U2OS AR-transfected cells, demonstrated that AZD3514 inhibits an androgen-induced translocation of AR from the cytoplasm to the nucleus within a comparable time-frame. In addition to the effects on AR localisation and AR-dependent transcription, AZD3514 treatment also reduced AR protein in LNCaP cells maintained in steroid-depleted conditions; an effect which was evident within 6 - 8h, and maximal at 18 - 24h. The ability to down-regulate AR under such conditions differentiates AZD3514 from the AR antagonists bicalutamide and MDV3100, which do not reduce AR protein levels. Administration of AZD3514 (100 mg/kg/day orally) for 3 days to Copenhagen rats bearing R3327H Dunning prostate tumours, indicates that AZD3514 treatment also reduces tumour AR in vivo. AZD3514 has also been shown to reduce AR protein expression, PSA synthesis and cell growth in vitro in a subclone of cells serially maintained in the presence of bicalutamide (LNCaP-CR) and an androgen-independent subclone of cells that was serially maintained in steroid-depleted medium (LNCaP-AI), suggesting that this novel mechanism of AR inhibition can deliver activity in CRPC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3848. doi:1538-7445.AM2012-3848

Abstract 960: Intratumoral dihydrotestosterone regulation by conversion of androstanediol to dihydrotestosterone in prostate cancer

Abstract Purpose It has become apparent that resurgent androgen receptor activity in castration-resistant prostate cancer can be accounted for in part through intratumoral androgen synthesis. The potent androgen dihydrotestosterone (DHT) yields an inactive androgen 5α-androstane-3α17α-diol (androstanediol/3α-diol) in the prostate. The metabolism of 3α-diol and relationships among other androgens have not been elucidated. Therefore, we studied the metabolism of 3α-diol in prostate cancer cells, as well as the expression of 17α-hydroxysteroid dehydrogenase 6 (17α-HSD6), a key enzyme of oxidative 3α-HSD that converts 3α-diol into DHT, in prostate cancer cells and tissues using real time-PCR and immunohistochemistry. Finally, we studied the correlation between serum 3α-diol G levels and androgens in localized prostate cancer patients. Methods LNCaP and VCaP cells were cultured in the hormone-depleted medium with presence/absence of 3α-diol, and the intracellular levels of androstenedione, testosterone and DHT were concurrently determined by liquid chromatography tandem mass spectrometry. LNCaP and VCaP cells were exposed to 3α-diol and bicalutamide in various concentrations. Prostate-specific antigen (PSA) levels in media were assayed. To examine the long term effect of androgen deprivation, LNCaP was cultured in hormone-depleted medium with 1nM DHEA. Transcriptome expression was analyzed to detect expression levels of 17α-HSD6. Expression scores for 17α-HSD6 in radical prostatectomy specimens treated with or without androgen deprivation therapy (ADT) were evaluated using immunohistochemistry. Seventy-two patients with localized prostate cancer patients were prospectively studied based on blood samples before and after ADT for 6 months. Results DHT was synthesized from 3α-diol in prostate cancer cells. Prostate cancer cells produced PSA in a dose-dependent manner with 3α-diol. Prostate cancer cells pretreated with 3α-diol showed a dose-dependent decrease in PSA production with bicalutamide. In the lower passages LNCaP cells treated with DHEA, expression of 17α-HSD6 showed much less striking change. However, in the higher passage LNCaP cells, 17α-HSD6 was up-regulated. The score for 17α-HSD6 in prostate cancer tissues treated with ADT was significantly higher than that without ADT (p<0.001). There were significant positive relationships between serum DHEA-S and 3α-diol G levels before and after ADT. Conclusion We verified the synthesis of DHT from 3α-diol in prostate cancer cells in this study and elucidated that the serum 3α-diol G level well reflects the adrenal androgen milieu in localized prostate cancer patients. Therefore, 3α-diol can be a potential precursor of the most active androgen DHT in prostate cancer. Our data suggest that the adrenal androgen-DHT axis can be a potential therapeutic target for treating prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 960. doi:1538-7445.AM2012-960

963 HOW DOES 5α-REDUCTASE ACTIVITY CHANGE DURING THE PROGRESSION OF CASTRATION RESISTANT PROSTATE CANCER?

You have accessJournal of UrologyProstate Cancer: Basic Research V1 Apr 2012963 HOW DOES 5α-REDUCTASE ACTIVITY CHANGE DURING THE PROGRESSION OF CASTRATION RESISTANT PROSTATE CANCER? Takeo Kosaka, Akira Miyajima, Eiji Kikuchi, Takahiro Maeda, Hirohiko Nagata, and Mototsugu Oya Takeo KosakaTakeo Kosaka Tokyo, Japan More articles by this author , Akira MiyajimaAkira Miyajima Tokyo, Japan More articles by this author , Eiji KikuchiEiji Kikuchi Tokyo, Japan More articles by this author , Takahiro MaedaTakahiro Maeda Tokyo, Japan More articles by this author , Hirohiko NagataHirohiko Nagata Tokyo, Japan More articles by this author , and Mototsugu OyaMototsugu Oya Tokyo, Japan More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.1062AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Deregulation of the androgen-androgen receptor (AR) pathway is a hallmark of prostate cancer (PCA). Therapies targeting the androgen-AR axis at different levels including de novo steroid synthesis may be quite effective against PCA to improve the prognosis of patients. However, it has not been been fully elucidated how steroid-5α-reductase (SRD5As) contribute to the development of PCA or progression to castration-resistant prostate cancer (CRPC). In this study, we sought to determine the significance of dihydrotestosterone (DHT) and SRD5As activity in CRPC. METHODS Two human CRPC cell lines (C4-2 and C4-2AT6) were used in this study. C4-2AT6 was established from C4-2 grown in androgen ablated condition for six months. The expression of SRD5As was semi-quantified with qPCR. To ascertain the potential SRD5As activity, we cultured C4-2 and C4-2AT6 cells with the steroid precursors modified by stable isotope: 13C-[2,3,4]-androstenedione (13C-A-dione). The sequential biosynthesis of 13C-[2,3,4]-dihydrotestosterone (13C-DHT) and 13C-[2,3,4]-testosterone (13C-T) were analyzed by liquid chromatography/mass spectrometry (LC/MS). RESULTS The C4-2AT6 cells showed 0.48-fold decrease of SRD5A1, 1.4-fold increase in SRD5A2 and 2.6-fold increase in SRD5A3 expression than C4-2 cells. The DHT concentration (0.01 ± 0.008 pg/ml, p<0.001) detected by LC/MS in C4-2AT6 cultured supernatant was significantly lower than that of in C4-2 supernatant (0.46 ± 0.12 pg/ml). These results showed that DHT production was reduced in C4-2AT6 cells. LC/MS analysis can detect significant convergence of 13C-A-dione into 13C-DHT and 13C-T. The concentration of 13C-DHT/13C-T (DHT/T ratio) was thought to reflect the SRD5As activity. The concentration of 13C-DHT in C4-2 and C4-2AT6 was 779.6 ± 210.9 and 150 ± 58.5 pg/mL, respectively (p<0.001). The DHT/T ratio of C4-2 and C4-2AT6 cells was 0.07 ± 0.03 and 0.02 ±0.003, respectively (p<0.001), suggesting reduced SRD5As activity in C4-2AT6. The response of C4-2AT6 cells to DHT was significantly decreased, compared with C4-2 cells, indicating reduced dependency of mRNA expression of PSA and Nkx3.1 on DHT. CONCLUSIONS These results demonstrated that the direct evidences of the change of SRD5As activity, accompanied by the reduced ability to produce DHT in CRPC. These experimental models provide a bland new platform to investigate the significance of DHT and SRD5As in CRPC progression. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e392-e393 Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Takeo Kosaka Tokyo, Japan More articles by this author Akira Miyajima Tokyo, Japan More articles by this author Eiji Kikuchi Tokyo, Japan More articles by this author Takahiro Maeda Tokyo, Japan More articles by this author Hirohiko Nagata Tokyo, Japan More articles by this author Mototsugu Oya Tokyo, Japan More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Phase I study of imatinib mesylate (IM) and sorafenib (S) in patients (pts) with refractory castration-resistant prostate cancer (CRPC).

146 Background: IM is an inhibitor of protein-tyrosine kinases including those that are over-expressed in bone metastases and primary prostatic adenocarcinoma. S is a potent inhibitor of wild-type and mutant BRAF, C-RAF, VEGFR2, VEGFR3, FLT3, and PDGFR-beta with modest activity in CRPC. We combined IM+S to determine the maximum tolerated dose (MTD) and the dose-limiting toxicity (DLT) in CRPC pts. Methods: CRPC pts with measurable disease and adequate organ function who failed chemotherapy were eligible. Dose escalation followed a 3+3 study design. Toxicity was scored following CTCAEv3. Responses were defined by RECIST1.0. IM pharmacokinetics (PK) were determined on day 15, 4 h post-dose with a validated LC-MS assay. Results: Seventeen pts were enrolled; 10 were evaluable. At dose level 0 (DL0), 6 pts received S at 400 mg S with 300 mg of IM both given daily. At DL1, 4 pts received 400 mg S twice/day with 300 mg IM daily; inevaluable pts received &lt;1 cycle (5 withdrew consent, 1 rapid early progression, 1 non-compliant). Median age was 73 (57-89) and median PSA was 284 ng/ml (11.7–9027). Median number of prior non-hormonal therapies was 3 (1–12) and 12 pts had Gleason score ≥7 while 15 pts had bone as the major site of metastases. On DL0, 1/6 pts had DLT (gr 3 hand/foot). On DL1, 2/4 pts had DLT (1 gr 3 hand/foot, 1 gr 3 diarrhea). MTD was 300 mg IM and 400 mg S both qd. No biochemical responses were observed. Two pts on DL1 had stable disease radiographically by RECIST (overall clinical benefit for the entire cohort 20%). Median time to progression was 2 months (1-5) while median OS was 6 months (1-30+) with 3/17 patients (17%) remaining alive at a median follow-up of 21 months. Of patients enrolled, 10 had PK data, which suggested that S reduced IM clearance by 40%, resulting in 60% increased exposure (P = 0.009; two-tailed t-test on log-transformed values, compared to historic data). Conclusions: To our knowledge, this is the first report to show that IM+S can be safely combined in CRPC. The phase II recommended dose for future trials is 300 mg IM and 400 mg S, both given daily. The PK interaction might be of questionable clinical relevance because IM concentrations are within the commonly observed range.

Abstract A11: Categorization of castration-resistant prostate cancer bone metastases according to expression of steroid-converting enzymes and constitutively active androgen receptor variants

Abstract Patients with advanced prostate cancer (PC) are given androgen ablation therapy. After a period of initial remission tumors eventually relapse, predominantly within the bone, and are then termed castration-resistant prostate cancer (CRPC). The majority of CRPC tumors express the androgen receptor (AR) and AR regulated genes. Possible mechanisms behind AR activity in CRPC include steroid synthesis by tumor cells and expression of constitutively active AR variants. We have previously found high levels of cholesterol in prostate cancer bone metastases that theoretically could be the substrate for CYP11 and intra-tumoral synthesis of steroids (Thysell et al, 2010). Steroid-converting enzymes have, as far as we know, not been thoroughly examined in PC bone metastases, and the aim of this study was therefore to analyze the expression of the main enzymes involved in the conversion of cholesterol into testosterone (T) and dihydrotestosterone (DHT) in hormone-naïve (HN) and CRPC bone metastases in comparison to primary tumors. We have previously also shown that the constitutively active AR variant AR-V7 is expressed at high levels in CRPC bone metastases in patients with particularly poor prognosis (Hörnberg et al, 2011). Another aim of this study was therefore to evaluate if CRPC bone metastases could be differentiated according to expression of steroid-converting enzymes and AR-V7 into sub-groups with potentially different mechanisms behind castration-resistance. Expression levels of the enzymes included in the classical and backdoor steroidogenesis pathways were analyzed by applying an Illumina whole-genome array to total RNA extracted from frozen biopsies of prostate tissue obtained at radical prostatectomy and metastasis surgery, respectively. Levels were compared between HN bone metastases (n=10), CRPC bone metastases (n=30), and non-malignant (n=12) and malignant (n=13) areas of the primary tumors. Results were verified using RT-PCR and immunohistochemistry in an extended series of samples. Significant increased gene expression levels of HSD17B10 were found in CRPC compared to HN bone metastases, which possibly indicated enhanced conversion of androstanediol to DHT in CRPC metastases. The CRPC metastases did however not show higher levels of CYP11, CYP17, AKR1C3, HSD3B2, or SRD5A1/2 than the HN metastases, indicating no general induction of the classical steroidogenesis pathway in CRPC bone metastases. The expression levels of AKR1C3 and AKR1C2 were significantly higher, and of SRD5A2 significantly lower, in bone metastases than in primary tumors, with highly variable levels found for AKR1C3. About 20% of the CRPC metastases expressed extremely high levels of AKR1C3 which suggested the likelihood of androstenedione conversion into T in those tumors. Another 20% of the CRPC metastases expressed extreme values of the constitutively active AR-V7. In conclusion, AKR1C3 and AR-V7 expression in bone metastases were able to categorize CRPC patients according to potentially different mechanisms behind castration-resistance, and may furthermore also influence patient response to different types of anti-androgen therapies. Citation Format: Emma Jernberg, Anders Widmark, Sead Crnalic, Anders Bergh, Pernilla Wikström. Categorization of castration-resistant prostate cancer bone metastases according to expression of steroid-converting enzymes and constitutively active androgen receptor variants [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A11.