18F-16β-fluoro-5α-dihydrotestosterone (FDHT) PET as a prognostic biomarker for survival in patients with metastatic castrate-resistant prostate cancer (mCRPC)

4517

Background: At present there is no imaging biomarker for patients with mCRPC as the disease primarily metastasizes to bone, which is difficult to visualize and quantify using standard techniques. We have conducted clinical trials in which patients with progressive mCRPC are scanned using FDG-PET to examine glucose metabolism, and FDHT-PET. FDHT is a novel tracer and structural analog of dihydrotestosterone that binds to the androgen receptor (AR) to demonstrate AR overexpression, a key biologic feature of mCRPC. We previously reported an association between baseline FDG-PET and overall survival in mCRPC. We now present the prognostic utility of baseline FDHT-PET. Methods: We prospectively scanned mCRPC patients with FDG and FDHT-PET prior to a change in therapy as part of imaging clinical trials. PET results were represented as the hottest lesion (SUVmax), or average of the five hottest lesions (SUVmaxavg). Five lesions per patient were recorded. If less than 5 lesions were captured, a value of 1 was imputed for the remaining lesions. Clinical and lab parameters were collected. Univariate analysis was performed on PET, clinical and lab variables for association with overall survival (OS). Multivariate models of prognostic factors were constructed. Results: 170 mCRPC patients were imaged with FDG and 116 also had FDHT-PET at baseline. Median survival was 21.2 months (95%CI: 19.1-24.0). On univariate analysis, FDHTmax, FDHTmaxavg, FDGmaxavg, PSA, hemoglobin, alkaline phosphatase, and LDH were associated with OS. FDHTmax and FDHTmaxavg were significantly correlated with one another. In a multivariate model, FDHTmaxavg and LDH were prognostic of survival. In a separate model assessing FDG, FDGmaxavg and LDH were also prognostic. Conclusions: FDHT not only allows for a visual assessment of the AR axis in prostate cancer, but appears to associate with overall survival in mCRPC. Increased AR activity as measured by FDHT SUVmaxavg held greater prognostic value than PSA or Gleason score. FDHT is also being evaluated as a clinical response indicator and pharmacodynamic measure with AR directed therapies.

Interim analysis (IA) results of COU-AA-302, a randomized, phase III study of abiraterone acetate in chemotherapy-naive patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

LBA4518

The full, final text of this abstract will be available at abstract.asco.org at 12:01 AM (EDT) on Saturday, June 2, 2012, and in the Annual Meeting Proceedings online supplement to the June 20, 2012, issue of Journal of Clinical Oncology. Onsite at the Meeting, this abstract will be printed in the Saturday edition of ASCO Daily News.

Exploratory analysis of survival benefit and prior docetaxel (D) treatment in COU-AA-301, a phase III study of abiraterone acetate (AA) plus prednisone (P) in metastatic castration-resistant prostate cancer (mCRPC)

4558

Background: AA, a selective androgen biosynthesis inhibitor, blocks the action of CYP17, thereby inhibiting adrenal and intratumoral androgen production. AA has demonstrated improved overall survival (OS) by 4.6 months (mos) vs placebo (HR=0.74) in patients (pts) previously treated with D. Methods: COU-AA-301 is a randomized double blind study of AA (1 g) + P (5 mg po BID) vs placebo + P administered to mCRPC pts post-D with a primary endpoint of OS. To further evaluate primary survival result robustness, we performed post hoc exploratory analyses to assess whether the timing of first and last dose of D and reason for D discontinuation impacted OS. Results: At randomization, treatment arms were balanced with respect to baseline characteristics, prior D use, and reasons for discontinuation. In both arms, almost half (45%) discontinued D due to progressive disease (PD); remainder discontinued D after completing all planned cycles (37%), due to toxicity (12%), or for other reasons (5%) per investigator. Median OS from first and last dose of D were longer with AA vs placebo (Table). Median OS was longer with AA vs placebo in pts who discontinued D for PD, or for all other reasons. Conclusions: These exploratory analyses suggest that the OS benefit of AA in mCRPC was maintained when calculated from first or last dose of prior D, and whether or not pts discontinued D for PD. Pts in AA arm of this study had a prolonged median OS of > 32 mos from time of initial D therapy. Congruity among these analyses and lack of dependence on D timing demonstrate robustness of the primary survival result. [Table: see text]

Predictive biomarkers in circulating tumor cells (CTC) from patients with castration-resistant prostate cancer (CRPC) through genomic analysis

4562

Background: Mutations in the ligand binding domain of androgen receptor (AR) in prostate cancer cells may alter their sensitivity to treatment with specific antiandrogens. To predict for tumor sensitivity to treatment with novel AR targeted therapies, we explored the frequency of mutation detection and copy number alteration in CTC isolated from patients with CRPC enrolled on trials with these targeted therapies. Methods: We used fluorescence-activated cell sorting (FACS) methodology to enrich EpCAM+, CD45-, DAPI- cells. For mutation detection and genomic copy number alteration in CTC in low number of cancer cells found in clinical samples, we optimized next-gen deep sequencing by Illumina. Results: In patients with progressive CRPC , >10 or >50 EpCAM+ events (EPE) were isolated by FACS in 88% or 58% of patients, in whom 32% and 10% had unfavorable (>5 cells/7.5 ml) CTC counts using CellSearch. EPE, expressing prostate-specific mRNAs, provide sufficient high quality DNA for genomic sequencing and copy number analysis. Adequate coverage was obtained from as few 50 EPE, with a recovery rate of 89% from FACS sorted samples. The detection threshold of a mutation was established at 1:4 alleles. To further expand genomic profiling in CTC, we optimized Nimblegen exome mutation detection by deep sequencing on HiSeq PE101. Our initial analysis established the polymorphism frequency detection thresholds in heterogeneous cell populations, and confirmed the sequencing coverage. Somatic missense mutations in AR, APC and TP53 found in CTC but not in paired WBC were confirmed by Sanger sequencing. In parallel, copy number alterations in CTC are studied. Conclusions: Somatic mutations detected in CTC isolated from patients with CRPC can serve as predictive markers of tumor sensitivity to targeted therapies. We established standard operating procedures for specimen processing, and confirmed the sequencing coverage and polymorphism detection thresholds in heterogeneous cell population. Currently we are proceeding to clinical samples to study the associations between specific molecular alterations in CTC as predictive markers of sensitivity and clinical outcomes.

A phase I study of the androgen signaling inhibitor ARN-509 in patients with metastatic castration-resistant prostate cancer (mCRPC)

4548

Background: ARN-509 is a novel small molecule AR antagonist that impairs AR nuclear translocation and binding to DNA, inhibiting tumor growth and promoting apoptosis, with no partial agonist activity. (Clegg et al., 2012) We conducted a phase I trial to assess safety, pharmacokinetics (PK), and determine the recommended phase II dose (RP2D). Methods: Eligible patients with mCRPC received ARN-509 orally on a continuous daily dosing schedule. Seven doses (30, 60, 90, 120, 180, 240, and 300 mg) were tested using standard 3x3 dose escalation criteria. Once drug concentrations were achieved that met or exceeded optimal levels predicted preclinically, an additional 2 dose levels were tested to further confirm the safety margin of ARN-509 (390 and 480 mg). Anti-tumor activity was assessed by PSA, radiographic responses, and FDHT-PET imaging. Results: Thirty patients were enrolled. The most common grades 1-2 treatment-related adverse events were fatigue (38%), nausea (29%), and pain (24%). There was only 1 treatment-related grade 3 adverse event (abdominal pain) at 300 mg, possibly related to a higher pill burden. PK was shown to be linear and dose-dependent. At 12 weeks, 42% of patients have had ≥ 50% PSA declines. Eleven (37%) patients have discontinued the study due to progression, with the longest patient still on study for more than 16 months. FDHT-PET imaging demonstrated AR blockade at 4 weeks across multiple dose levels. Conclusions: In this phase I study, ARN-509 was shown to be safe and well tolerated with linear PK. Based on promising activity across all dose levels and pharmacodynamic evidence of AR antagonism, an optimal biologic dose of 240 mg daily was selected for phase II investigation. DOD/PCF PCCTC trial sponsored by Aragon Pharmaceuticals.

Cabozantinib (XL184) in chemotherapy-pretreated metastatic castration resistant prostate cancer (mCRPC): Results from a phase II nonrandomized expansion cohort (NRE)

4513

Background: Cabozantinib (cabo) inhibits MET and VEGFR2. High rates of bone scan resolution, pain relief and overall disease control, independent of PSA changes, were previously reported in a phase II study in mCRPC patients (pts). This is a NRE cohort in docetaxel (D)-pretreated pts with a novel primary endpoint of bone scan response based on computer-aided quantitative assessment of bone scan lesion area (BSLA) and a double-reader, independent, blinded review (Nucl Med Commun, in press). Methods: D-pretreated (≥225 mg/m2) CRPC pts with bone metastasis were required to have progressed in soft-tissue or bone within 6 months of last dose of D. Pts received 100 mg cabo qd. Tumor response was assessed q6 wks. Bone scan response (BSR) was defined by a ≥30% decline in BSLA. Pain intensity (worst pain over the past 24 hrs; BPI scale 0-10) and interference with sleep and daily activity were prospectively assessed using an IVR system. Analgesic use was collected by diary. Bone turnover markers and CTCs were assessed. Results: 93 D-pretreated pts were enrolled (89 evaluable with ≥6 wks f/u). Median age was 67, 46% received cabazitaxel and/or abiraterone, 32% had visceral disease, 51% had fatigue, and 18% had anemia. 44% had worst pain ≥4 of which 95% were taking narcotics. Median CTC count was 49 and 80% had ≥5. Median f/u was 125 days (range, 23-305). Of 85 pts evaluable for BSR, 51 (60%) had a PR, 24 (28%) SD, 5 (6%) PD and 5 (6%) d/c’d prior to f/u scan. 21/30 pts (70%) had reduction of measurable disease.16/33 pts (49%) with BPI ≥4 and ≥12 wks f/u had pain reduction durable for ≥6 wks; 46% had decreased narcotic use, including 27% who discontinued use. Sleep and daily activity were improved in pts with pain relief. Among pts with elevated serum levels, 74%, 67% and 47% had declines on treatment of ≥30% in CTx, NTx and bALP, respectively. In 59 pts with CTCs ≥5, 92% had a decrease of ≥30% and 39% converted to <5 CTCs at weeks 6 or 12. 12% discontinued cabo due to AEs. Most common Gr 3/4 AEs were fatigue (19%), nausea (10%) and anemia (10%). Conclusions: Cabo treatment resulted in high rates of bone scan response, durable pain relief, and reductions in bone turnover markers and CTCs in D-pre-treated CRPC pts with bone metastases.

Targeting castration resistant prostate cancer (CRPC) with autologous PSMA-directed CAR+ T cells

TPS4700

Background: Based on our preclinical animal models, we initiated a phase I dose-escalating study to assess safety, dose requirement and targeting efficiency of genetically directed autologous human T cells targeted to Prostate Specific Membrane Antigen (PSMA). Our approach is based on the infusion of autologous PSMA-targeted T cells utilizing the P28z second generation chimeric antigen receptor (CAR) in patients (pts) with metastatic CRPC, following iv cyclophosphamide (Cy) (trial NCT01140373). For safety, the herpes simplex virus-1 thymidine kinase (hsvtk) gene is co-expressed with the P28z receptor, and renders T cells sensitive to ganciclovir for immediate T cell elimination if needed. The expression of hsvtk enables PET imaging using radiolabeled FIAU to localize adoptively transferred T cells. The aims of the trial are to assess: (1) safety of PSMA-targeted T cells; (2) biologic and anti-tumor effects; (3) T cell persistence at tumor site; and (4) immune response. Methods: Autologous T cells are activated from a leukapheresis product using anti-CD3/CD28 Dynabeads. Release criteria include mean vector copy number by Q-PCR and vector identity by Southern blot, absence of Replication Competent Retrovirus and residual Dynabeads. Pts will be treated at 3 dose levels from 107 to 108 CAR+ T cells/kg. Four patients have been enrolled; 3 have been treated with 300mg/m2 of Cy one day before infusion of 107 CAR+ T cells/kg. Pts underwent baseline and post treatment CT, bone and PET scans. Pts are followed weekly, then monthly with blood work including immune and vector sequence monitoring. Results: The first 3 pts within the first cohort were successfully treated without toxicity. Two had stable disease for greater than 6 months with the third patient having disease progression. There were no acute adverse events. Conclusion: We have established an ex vivo transduction, expansion and therapeutic protocol for the generation and testing of safe, clinical-grade, PSMA targeted T cells. Pts enrolled at the next dose level of 3 x 107 CAR+ T cells/kg will be assessed as described and by imaging the transduced T cell population using 18F-FIAU as a radiotracer. The data pertaining to the planned T cell imaging will be presented as well.

Primary, secondary, and quality-of-life endpoint results from the phase III AFFIRM study of MDV3100, an androgen receptor signaling inhibitor

4519^

Background: MDV3100, a novel androgen receptor signaling inhibitor (ARSI), inhibits: 1) binding of androgens to AR, 2) AR nuclear translocation, and 3) association of AR with DNA. MDV3100 was active in a phase I-II trial enrolling pre- and post-docetaxel castration-resistant prostate cancer (CRPC) patients. The AFFIRM trial evaluated whether MDV3100 could provide benefit to men with post-docetaxel CRPC. Methods: In this double-blind, multinational phase III study, patients who had received docetaxel-based chemotherapy were randomized 2:1 to MDV3100 160 mg/day or placebo. Treatment with corticosteroids was allowed but not required. Patients were stratified by baseline ECOG and mean brief pain inventory score. The primary endpoint was overall survival (OS). Other efficacy endpoints included radiographic progression-free survival (rPFS), time to PSA progression (TTPP), soft tissue objective response (PR+CR), PSA response, and quality of life (QoL) response (FACT-P). Results: 800 patients were randomized to MDV3100 and 399 to placebo with respective median treatment durations of 8.3 and 3.0 months.Based on a planned interim analysis at 520 deaths, the Independent Data Monitoring Committee recommended the study be unblinded and placebo patients offered MDV3100. Efficacy results are presented (Table). The most common MDV3100 events with an incidence higher than placebo were fatigue (34% vs 29%), diarrhea (21% vs 18%), and hot flush (20% vs 10%). Grade >3 events of interest were cardiac disorders (0.9% MDV3100 vs 2% placebo), fatigue (6% MDV3100 vs 7% placebo), seizure (0.6% MDV3100 vs. 0% placebo), and LFT abnormalities (0.4% MDV3100 vs 0.8% placebo). Conclusions: MDV3100, a novel ARSI, is well-tolerated and significantly prolongs OS, slows disease progression, and improves QoL in men with post-docetaxel CRPC. [Table: see text]

CA184-043: A randomized, double-blind, phase III trial comparing ipilimumab versus placebo following a single dose of radiotherapy (RT) in patients (pts) with castration-resistant prostate cancer (CRPC) who have received prior treatment with docetaxel (D)

TPS4689

Background: Ipilimumab (Ipi), a fully human monoclonal antibody which blocks CTLA-4, augments antitumor immune responses. Ipi has shown antitumor effects in prostate cancer model systems and clinical activity (via prostate-specific antigen [PSA] declines and RECIST response) in Phase 1/2 investigations in CRPC, with a side effect profile reflective of its mechanism of action. Preclinical data suggest that RT given prior to CTLA-4 blockade may increase antitumor activity. Methods: In this study, pts with CRPC who have progressed during or after D are randomized 1:1 to receive either a single dose of bone-directed RT followed by Ipi 10mg/kg, or RT followed by placebo. Within 2 days of RT administration (up to 5 lesions at 8 Gy on a single day) patients receive their initial dose of Ipi/placebo; Ipi/placebo is then given every 3 weeks for a total of 4 doses. Eligible pts may continue to receive blinded study drug every 12 weeks until they meet treatment stopping criteria, withdraw consent, are lost to follow-up, or study closure. The primary endpoint is overall survival (OS). Secondary endpoints include progression-free survival, pain response, and safety. The study is designed to detect a 3.8 month difference (HR=0.76) in median OS with 90% power and 0.05 2-sided type one error. The enrollment goal is 800 randomized patients, with a single interim analysis for superiority of OS planned at 435 events at approximately 33 months from first patient first visit (ClinicalTrials.gov identifier: NCT00861614). [Table: see text] [Table: see text]

A validated whole-blood RNA transcript-based prognostic model that predicts survival in men with castration-resistant prostate cancer

4516

Background: Survival for patients with castration resistant prostate cancer (CRPC) is highly variable. We developed a whole blood RNA transcript-based model as a prognostic biomarker in CRPC. Methods: Peripheral blood was collected from 62 men with CRPC in a training set and from 140 patients with CRPC in a validation set on various treatment regimens. A panel of 168 inflammation and prostate cancer-related genes was evaluated using optimized quantitative polymerase chain reaction to assess biomarkers predictive of survival. A 2-class proportional hazard model was developed from time of CRPC diagnosis and time of blood draw. Results: A 6-gene model (consisting of ABL2, SEMA4D, ITGAL, and C1QA, TIMP1, CDKN1A) separated CRPC patients into two classes: higher risk men who died within 2·2 years of developing CRPC and lower risk men who lived over 2·2 years (log rank p=0·00083). The results were similar regardless of the survival time definition (CRPC diagnosis versus blood draw) and did not depend on whether they received chemotherapy in addition to hormone treatment. The model successfully validated in an independent cohort of men with CRPC (p= 0.000001·7). Conclusions: Transcriptional profiling of whole blood yields critical prognostic information in men with CRPC independent of treatment. The 6-gene model suggests possible dysregulation of the immune system, a finding that warrants further study. This model may play an important role in patient counseling, in patient stratification for clinical trials, and potentially as a predictive biomarker for immune-based therapeutic strategies.

Evidence for efficacy of new Hsp90 inhibitors revealed by ex vivo culture of human prostate tumors

PURPOSE

Targeting Hsp90 has significant potential as a treatment for prostate cancer, but prototypical agents such as 17-allylamino-17 demethoxygeldanamycin (17-AAG) have been ineffective in clinical trials. Recently, a phase I study aimed at defining a biologically active dose reported the first response to an Hsp90 inhibitor in a patient with prostate cancer, which supports the development of new generation compounds for this disease.

EXPERIMENTAL DESIGN

The biological actions of two new synthetic Hsp90 inhibitors, NVP-AUY922 and NVP-HSP990, were evaluated in the prostate cancer cell lines PC-3, LNCaP, and VCaP and in an ex vivo culture model of human prostate cancer.

RESULTS

In cell lines, both NVP-AUY922 and NVP-HSP990 showed greater potency than 17-AAG with regard to modulation of Hsp90 client proteins, inhibition of proliferation, and induction of apoptotic cell death. In prostate tumors obtained from radical prostatectomy that were cultured ex vivo, treatment with 500 nmol/L of NVP-AUY922, NVP-HSP990, or 17-AAG caused equivalent target modulation, determined by the pharmacodynamic marker Hsp70, but only NVP-AUY922 and NVP-HSP990 showed antiproliferative and proapoptotic activity.

CONCLUSIONS

This study provides some of the first evidence that new generation Hsp90 inhibitors are capable of achieving biologic responses in human prostate tumors, with both NVP-AUY922 and NVP-HSP990 showing potent on-target efficacy. Importantly, the ex vivo culture technique has provided information on Hsp90 inhibitor action not previously observed in cell lines or animal models. This approach, therefore, has the potential to enable more rational selection of therapeutic agents and biomarkers of response for clinical trials.

A phase I trial of docetaxel and pulse-dose 17-allylamino-17-demethoxygeldanamycin in adult patients with solid tumors

PURPOSE

To define maximum tolerated dose (MTD), clinical toxicities, and pharmacokinetics of 17-allylamino-17-demethoxygeldanamycin (17-AAG) when administered in combination with docetaxel once every 21 days in patients with advanced solid tumor malignancies.

EXPERIMENTAL DESIGN

Docetaxel was administered over 1 h at doses of 55, 70, and 75 mg/m(2). 17-AAG was administered over 1-2 h, following the completion of the docetaxel infusion, at escalating doses ranging from 80 to 650 mg/m(2) in 12 patient cohorts. Serum was collected for pharmacokinetic and pharmacodynamic studies during cycle 1. Docetaxel, 17-AAG, and 17-AG levels were determined by high-performance liquid chromatography. Biologic effects of 17-AAG were monitored in peripheral blood mononuclear cells by immunoblot.

RESULTS

Forty-nine patients received docetaxel and 17-AAG. The most common all-cause grade 3 and 4 toxicities were leukopenia, lymphopenia, and neutropenia. An MTD was not defined; however, three dose-limiting toxicities were observed, including 2 incidences of neutropenic fever and 1 of junctional bradycardia. Dose escalation was halted at docetaxel 75 mg/m(2)-17-AAG 650 mg/m(2) due to delayed toxicities attributed to patient intolerance of the DMSO-based 17-AAG formulation. Of 46 evaluable patients, 1 patient with lung cancer experienced a partial response. Minor responses were observed in patients with lung, prostate, melanoma, and bladder cancers. A correlation between reduced docetaxel clearance and 17-AAG dose level was observed.

CONCLUSIONS

The combination of docetaxel and 17-AAG was well tolerated in adult patients with solid tumors, although patient intolerance to the DMSO formulation precluded further dose escalation. The recommended phase II dose is docetaxel 70 mg/m(2) and 17-AAG 500 mg/m(2).

Population pharmacokinetic analysis of 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) in adult patients with solid tumors

PURPOSE

To identify sources of exposure variability for the tumor growth inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) using a population pharmacokinetic analysis.

METHODS

A total 67 solid tumor patients at 2 centers were given 1 h infusions of 17-DMAG either as a single dose, daily for 3 days, or daily for 5 days. Blood samples were extensively collected and 17-DMAG plasma concentrations were measured by liquid chromatography/mass spectrometry. Population pharmacokinetic analysis of the 17-DMAG plasma concentration with time was performed using nonlinear mixed effect modeling to evaluate the effects of covariates, inter-individual variability, and between-occasion variability on model parameters using a stepwise forward addition then backward elimination modeling approach. The inter-individual exposure variability and the effects of between-occasion variability on exposure were assessed by simulating the 95 % prediction interval of the AUC per dose, AUC(0-24 h), using the final model and a model with no between-occasion variability, respectively, subject to the five day 17-DMAG infusion protocol with administrations of the median observed dose.

RESULTS

A 3-compartment model with first order elimination (ADVAN11, TRANS4) and a proportional residual error, exponentiated inter-individual variability and between occasion variability on Q2 and V1 best described the 17-DMAG concentration data. No covariates were statistically significant. The simulated 95% prediction interval of the AUC(0-24 h) for the median dose of 36 mg/m(2) was 1,059-9,007 mg/L h and the simulated 95 % prediction interval of the AUC(0-24 h) considering the impact of between-occasion variability alone was 2,910-4,077 mg/L h.

CONCLUSIONS

Population pharmacokinetic analysis of 17-DMAG found no significant covariate effects and considerable inter-individual variability; this implies a wide range of exposures in the population and which may affect treatment outcome. Patients treated with 17-DMAG may require therapeutic drug monitoring which could help achieve more uniform exposure leading to safer and more effective therapy.

Pain control and delay in time to skeletal-related events (SREs) in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with abiraterone acetate (AA): Long-term follow-up

183

Background: In study COU-AA-301, the androgen biosynthesis inhibitor AA significantly increased overall survival in mCRPC post-docetaxel (D) in both interim and updated analyses at 552 and 775 events, respectively. Interim data also showed a significant benefit of AA on patient (pt) reported pain. We present long-term outcomes of the effect of AA on pain and SREs.

Methods: In this international randomized double blind study of AA (1 g QD) + prednisone (P) (5 mg BID) vs placebo + P in mCRPC post-D, pain was assessed at baseline and each treatment cycle until treatment discontinuation using the BPI-SF questionnaire. Palliation/progression of pain intensity (P-INT) and pain interference (P-INF) were evaluated using a priori definitions. P-INT palliation was defined as ≥ 30% improvement in pt reported “worst pain in last 24 h” (on 0-10 numerical rating scale) durable for ≥ 28 d without increased analgesic use (by WHO criteria) in eligible pts (those with significant baseline pain). Conversely, P-INT progression was defined as ≥ 30% deterioration, or increased analgesic use, over ≥ 28 d.

Results: 797 pts were randomized to AA + P, 398 to placebo + P. Median follow-up was 20.2 mos. Median time to SRE was 25.0 mos (AA + P) vs 20.3 mos (placebo + P), p = 0.0001. Pain data were available for most patients; the cumulative amount of missing data ranged from 5% at Cycle 1 to 7% at Cycle 20. AA + P improved P-INT outcomes (Table); P-INF benefits were similar and also highly significant.

Conclusions: Benefits of AA + P observed in the interim analysis, including superior and more durable pain relief and delay of pain progression and SREs, were maintained with longer follow-up. Additional analyses of the potential relationships between pain/SREs and other outcomes, as well as of prednisone’s effect on pain palliation in the control arm, are ongoing.

[Table: see text]

Comparison of PSA, FDG-PET, and Prostate Cancer Working Group 2 (PCWG2) criteria to interpret apparent progression on first post-treatment bone scan

20

Background: The risk of prematurely discontinuing effective therapy in patients with metastatic castrate resistant prostate cancer (mCRPC) because of apparent initial progression on bone scan has repercussions for drug development and clinical practice. We evaluated three methods to distinguish disease progression (POD) from non-progressive bone disease or flare response.

Methods: The dataset was comprised of men with mCRPC enrolled in contemporary clinical trials using AR-directed or targeted therapy. To be included, a worsened bone scan (increased size, intensity, or number of lesions) at the time of initial follow-up at 8-12 wks (FU1), a concurrently performed FDG-PET and PSA, and a second follow-up bone scan (FU2) > 6 wks after FU1 were required. Pts were evaluated by three methods: 1) PSA-guided approach: POD was defined as a PSA increase >25% from baseline at FU1; for non-progressors, a special category was created for flare response defined as a PSA decline >50% and a FU2 bone scan documenting stability/improvement; 2) FDG-PET approach: POD was defined as a new bone lesion or increase in SUV >10% at FU1; 3) Bone scan only approach: POD was defined by PCWG2 requiring 2 new bone scan lesions at FU1 and 2 additional lesions at FU2.

Results: 66 pts registered to trials conducted between 2007-2011 were examined; 38/66 (57.6%) pts had a worsened bone scan at FU1, 23 of whom had a FU2 bone scan and were considered evaluable for this analysis.

Conclusions: Over half of mCRPC pts have a worsening bone scan during the first three months of therapy. PCWG2 controls for flare without use of PSA, confirms radiographic POD, and maintains pts on study longer than use of early post-treatment PSA changes. FDG-PET at first assessment appears to identify an identical percentage of progressors as PCWG2 did at the second assessment. PCWG2 is undergoing prospective validation in phase III trials; the use of FDG PET as an early response biomarker is currently under investigation.

[Table: see text]

Effect of MDV3100, an androgen receptor signaling inhibitor (ARSI), on overall survival in patients with prostate cancer postdocetaxel: Results from the phase III AFFIRM study

LBA1

Background: MDV3100, a novel androgen receptor signaling inhibitor (ARSI), competitively inhibits binding of androgens to the androgen receptor (AR), inhibits AR nuclear translocation, and inhibits association of the AR with DNA (Tran et al, Science. 2009;324:787). MDV3100 was selected for development based on activity in prostate cancer model systems with overexpressed AR, and was active in a phase I-II trial enrolling pre- and post-chemotherapy treated patients with progressive castration resistant disease (CRPC) (Scher et al, Lancet. 2010;375:1437). The AFFIRM trial evaluated whether MDV3100 could prolong overall survival (OS) in men with CRPC who progressed following docetaxel-based chemotherapy.

Methods: In this randomized, double-blind, placebo-controlled, multinational phase III study ( NCT00974311 ), patients who had received ≤ 2 regimens of docetaxel-based chemotherapy were randomized 2:1 to MDV3100 160 mg/day or placebo. Treatment with corticosteroids was allowed but not required. Patients were stratified by baseline ECOG performance status and mean brief pain inventory score. The primary endpoint was OS. Other efficacy endpoints included radiographic progression-free survival (PFS), time to first skeletal-related event, time to prostate-specific antigen (PSA) progression, and circulating tumor cell count conversion rate.

Results: 1,199 patients were randomized between Sep 2009 and Nov 2010. Based on a planned interim analysis at 520 death events, the Independent Data Monitoring Committee (IDMC) recommended the study be unblinded and placebo patients offered MDV3100 due to a significant OS benefit (p<0.0001; hazard ratio 0.631). The estimated median OS was 18.4 months for MDV3100 treated compared to 13.6 months for placebo treated men, a median OS difference of 4.8 months. Data to be available include PFS, time to PSA progression, and safety.

Conclusions: MDV3100, a novel ARSI, significantly improves OS in men with postdocetaxel-treated CRPC reducing the risk of death by 37% relative to placebo. The IDMC determined the risk:benefit of MDV3100 was favorable and recommended the phase III AFFIRM trial be unblinded.

Ipilimumab (IPI) in metastatic castrate-resistant prostate cancer (mCRPC): Results from an open-label, multicenter phase I/II study

25

Background: IPI is a fully human, anti-CTLA-4 monoclonal antibody capable of enhancing anti-tumor immunity. Preclinically, radiotherapy (XRT) and CTLA-4 blockade have synergistic anti-tumor activity. This phase 1/2 study in patients (pts) with mCRPC was designed to assess: safety of IPI at various doses, feasibility of combining IPI with XRT, and activity.

Methods: mCRPC pts with or without prior chemotherapy were enrolled. In the dose-escalation phase, 33 pts (³6 pts per cohort) received IPI q3 weeks x 4 doses at 3, 5, or 10 mg/kg, or with XRT at 3 or 10 mg/kg. Single dose XRT (8 Gy/lesion, up to 3 lesions per pt) was given 24 to 48 h before the first IPI dose. The 10 mg/kg ± XRT cohorts were expanded to 50; 34 received IPI + XRT (Table). Based on clinical benefit, pts received additional doses of IPI. Endpoints were safety, and activity as assessed by serum prostate-specific antigen (PSA) and RECIST criteria. PSA was monitored monthly, with scans q3 months (mos).

Results: There were no dose-limiting toxicities; 10 mg/kg ± XRT cohorts were, therefore, expanded for phase 2 evaluation. Treatment-related adverse events (AEs) and immune-related AEs (irAEs) were common across all cohorts with or without XRT. Common (≥ 15%) treatment-related AEs of any grade in the 10 mg/kg ± XRT group were fatigue (50%), diarrhea (54%), nausea (24%), colitis (22%), decreased appetite (22%), vomiting (18%), rash (32%) and pruritus (20%). Most common grade 3/4 irAEs were colitis (16%), diarrhea (8%) and hepatitis (10%). irAEs were generally responsive to immunosuppressives. Of 50 PSA-evaluable pts in the 10 mg/kg ± XRT group, 8 had PSA response (Table) lasting between 3 and 13+ mos. Of the 28 tumor-evaluable pts receiving 10 mg/kg ± XRT, 1 had complete response and 6 had stable disease.

Conclusions: In pts with mCRPC, IPI 10 mg/kg alone or in combination with XRT showed clinical antitumor activity with disease control in some patients, and a generally manageable safety profile. The combination (IPI 10 mg/kg ± XRT) and monotherapy (IPI 10 mg/kg) are being explored in randomized phase 3 trials.

[Table: see text]

Phase I/II safety and pharmacokinetic (PK) study of ARN-509 in patients with metastatic castration-resistant prostate cancer (mCRPC): Phase I results of a Prostate Cancer Clinical Trials Consortium study

43

Background: In CRPC, androgen receptor (AR) overexpression is associated with resistance to first-generation anti-androgen therapy such as bicalutamide. ARN-509 is a novel small molecule AR antagonist that impairs AR nuclear translocation and binding to DNA, inhibiting tumor growth and promoting apoptosis, with no partial agonist activity. Preclinical data shows that ARN-509 binds AR with 5-fold greater affinity than bicalutamide, and induces tumor regression in hormone-sensitive and CRPC xenograft models.

Methods: In this open-label, Phase 1/2 study, mCRPC patients received ARN-509 orally on a continuous daily dosing schedule. In Phase 1 , 7 doses (30, 60, 90, 120, 180, 240, 300 mg) were tested using standard 3x3 dose escalation criteria to assess safety, PK, and determine the recommended Phase 2 dose (RP2D). Preliminary anti-tumor activity was assessed by PSA kinetics, radiographic responses, circulating tumor cells (CTCs), and FDHT-PET imaging.

Results: Twenty-four patients (median age 68 yrs, Gleason Score 8; prior docetaxel 13%) were enrolled. The most common Grade 1-2 treatment-related adverse events were fatigue (38%), nausea (29%), and pain (24%). There was only 1 treatment-related Grade 3 adverse event (abdominal pain) at 300 mg, possibly related to a higher pill burden, which led to an additional 3 patients being enrolled at the highest dose with no further dose limiting toxicities. PK was shown to be linear and dose-dependent. Twelve patients (55%) had ≥ 50% PSA declines. To date, 7 patients have discontinued the study due to progression, with the longest patient still on study for more than 1 year. FDHT-PET imaging demonstrated AR blockade at 4 weeks across multiple dose levels. Based on preclinical assessment of maximum efficacious dose, PK, and promising activity across all doses, 240 mg was selected as the RP2D.

Conclusions: In this Phase 1 study, ARN-509 was shown to be safe and well tolerated, with promising preliminary activity based on PSA and pharmacodynamic evidence of AR antagonism. The Phase 2 portion of the study will enroll up to 90 patients with treatment-naïve non-metastatic and mCRPC.

Exploratory analysis of survival benefit and prior docetaxel (D) treatment in COU-AA-301, a phase III study of abiraterone acetate (AA) plus prednisone (P) in metastatic castration-resistant prostate cancer (mCRPC)

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Background: AA, a selective androgen biosynthesis inhibitor, blocks the action of CYP17, thereby inhibiting adrenal and intratumoral androgen synthesis. AA has demonstrated improved overall survival (OS) by 4.6 months (mos) vs placebo (HR=0.74) in patients (pts) previously treated with D.

Methods: COU-AA-301 is a randomized double-blind study of AA (1 g) + P (5 mg po BID) vs placebo + P administered to mCRPC pts post-D with a primary endpoint of OS. To evaluate the robustness of the primary survival results, we performed post hoc exploratory analyses to assess whether the timing of first and last dose of D and reason for D discontinuation impacted OS.

Results: At the time of randomization, treatment arms were balanced with respect to baseline characteristics, prior D use, and reasons for discontinuation. In both arms, almost half (45%) discontinued D due to progressive disease (PD); the remainder discontinued D as part of planned treatment (37%), toxicity (12%), or for other reasons (5%) per investigator reporting. Median OS from first and last dose of D were longer with AA vs placebo (Table). Median OS was longer with AA vs placebo in pts who discontinued D for PD or for all other reasons.

Conclusions: These exploratory analyses suggest that the survival benefit of AA in mCRPC was maintained when calculated from first or last dose of prior D, and whether or not pts discontinued D for PD. Pts in the AA arm of this study had a prolonged median OS of > 32 mos from the time of initial D therapy. Congruity among these analyses demonstrates the robustness of the primary survival result.

[Table: see text]

Predictive biomarkers in circulating tumor cells (CTC) from patients with castration-resistant prostate cancer (CRPC) through genomic analysis

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Background: Although designed to retain activity against known androgen receptor (AR) mutants, it is predicted that new MDV3100-resistant mutations may predict for sensitivity to the drug in clinic. To predict for tumor sensitivity to treatment with novel AR targeted therapies, we explored the frequency of mutation detection and copy number alteration in CTC isolated from patients with CRPC enrolled on a trial with MDV3100.

Methods: We used fluorescence-activated cell sorting (FACS) methodology to enrich EpCAM+, CD45−, DAPI− cells. For mutation detection and genomic copy number alteration in CTC in low number of cancer cells found in clinical samples, we optimized next-gen deep sequencing by Illumina.

Results: In patients with progressive CRPC, >10 or >50 EpCAM+ events (EPE) were isolated by FACS in 88% or 58% of patients, in whom 32% and 10% had unfavorable (>5 cells/7.5 ml) CTC counts using CellSearch. EPE, expressing prostate-specific mRNAs, provide sufficient high quality DNA for genomic sequencing and copy number analysis. Adequate coverage was obtained from as few 50 EPE, with a recovery rate of 89% from FACS sorted samples. The detection threshold of a mutation was established at 1:4 alleles. To further expand genomic profiling in CTC, we optimized Nimblegen exome mutation detection by deep sequencing on HiSeq PE101. Our initial analysis established the polymorphism frequency detection thresholds in heterogeneous cell populations, and confirmed the sequencing coverage. Somatic missense mutations in AR, APC and TP53 found in CTC but not in paired WBC were confirmed by Sanger sequencing. In parallel, copy number alterations in CTC are studied.

Conclusions: Somatic mutations detected in CTC isolated from patients with CRPC can serve as predictive markers of tumor sensitivity to targeted therapies. We established standard operating procedures for specimen processing, and confirmed the sequencing coverage and polymorphism detection thresholds in heterogeneous cell population. Currently we are proceeding to clinical samples to study the associations between specific molecular alterations in CTC as predictive markers of sensitivity and clinical outcomes.

Abstract IA22: Molecular Imaging of androgen receptor signalling in CRPC

Androgen receptor (AR) plays a key role in development of castrate-resistant prostate cancer (CRPC), the lethal form of the disease. For this reason we have developed Molecular Imaging (MI) methods to study AR, both in laboratory and clinic. For this work we have used a radiotracer that is highly specific for AR, a flourine-18 analog of dihydrotestoterone, (FDHT) the most abundant androgen at the tissue level in human cancers. In the laboratory for example, we have used FDHT to document AR binding of novel drugs and to determine their relative affinity and the number of AR receptor sites in human prostate cancer cell lines and xenografts. In the clinic we have imaged patients with CRPC to determine the impact of therapies on AR expression. During the course of this work we have developed quantitative kinetic models based on PET imaging and have shown the FDHT binding and uptake into cancers is AR dependent, and that the metabolites of FDHT do not bind appreciably to AR. We have compared FDHT and FDG in CRPC patients and have determined that there are an average of 17 tumors per patient (n=107), and the 90% of metabolically active tumors for FDG or FDHT express AR, but that there is a group of lesions that do not but are detected by metabolism of FDG. We have shown that drugs which target AR displace FDHT completely when used in full pharmacologic doses. So far the data is consistent with the view that this type of displacement is a necessary condition for tumor response, but clearly some patients whose AR binding is completely blocked have lesions which continue to progress through unknown mechanisms. We believe that molecular imaging using antibodies labeled with PET emitters will add greatly to our knowledge about CRPC, and studies in man with 89Zr-DFO J591, and antibody targeting PSMA are just beginning. The impact of AR signaling on PSMA expression has been shown in the laboratory to be down regulation, and we intend to explore the use of antibodies to provide a pharmacodynamic biomarker of AR signaling in man during therapy with AR blockers in the clinic.

Citation Format: Steven M. Larson, Joe Fox, Michael Morris, Michael Evans, Jason Lewis, John Humm, Charles L. Sawyers, Howard I. Scher. Molecular Imaging of androgen receptor signaling in CRPC [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 IA22.

A novel automated platform for quantifying the extent of skeletal tumour involvement in prostate cancer patients using the Bone Scan Index

BACKGROUND

There is little consensus on a standard approach to analysing bone scan images. The Bone Scan Index (BSI) is predictive of survival in patients with progressive prostate cancer (PCa), but the popularity of this metric is hampered by the tedium of the manual calculation.

OBJECTIVE

Develop a fully automated method of quantifying the BSI and determining the clinical value of automated BSI measurements beyond conventional clinical and pathologic features.

DESIGN, SETTING, AND PARTICIPANTS

We conditioned a computer-assisted diagnosis system identifying metastatic lesions on a bone scan to automatically compute BSI measurements. A training group of 795 bone scans was used in the conditioning process. Independent validation of the method used bone scans obtained ≤3 mo from diagnosis of 384 PCa cases in two large population-based cohorts. An experienced analyser (blinded to case identity, prior BSI, and outcome) scored the BSI measurements twice. We measured prediction of outcome using pretreatment Gleason score, clinical stage, and prostate-specific antigen with models that also incorporated either manual or automated BSI measurements.

MEASUREMENTS

The agreement between methods was evaluated using Pearson's correlation coefficient. Discrimination between prognostic models was assessed using the concordance index (C-index).

RESULTS AND LIMITATIONS

Manual and automated BSI measurements were strongly correlated (ρ=0.80), correlated more closely (ρ=0.93) when excluding cases with BSI scores≥10 (1.8%), and were independently associated with PCa death (p<0.0001 for each) when added to the prediction model. Predictive accuracy of the base model (C-index: 0.768; 95% confidence interval [CI], 0.702-0.837) increased to 0.794 (95% CI, 0.727-0.860) by adding manual BSI scoring, and increased to 0.825 (95% CI, 0.754-0.881) by adding automated BSI scoring to the base model.

CONCLUSIONS

Automated BSI scoring, with its 100% reproducibility, reduces turnaround time, eliminates operator-dependent subjectivity, and provides important clinical information comparable to that of manual BSI scoring.

ARN-509: a novel antiandrogen for prostate cancer treatment

Continued reliance on the androgen receptor (AR) is now understood as a core mechanism in castration-resistant prostate cancer (CRPC), the most advanced form of this disease. While established and novel AR pathway-targeting agents display clinical efficacy in metastatic CRPC, dose-limiting side effects remain problematic for all current agents. In this study, we report the discovery and development of ARN-509, a competitive AR inhibitor that is fully antagonistic to AR overexpression, a common and important feature of CRPC. ARN-509 was optimized for inhibition of AR transcriptional activity and prostate cancer cell proliferation, pharmacokinetics, and in vivo efficacy. In contrast to bicalutamide, ARN-509 lacked significant agonist activity in preclinical models of CRPC. Moreover, ARN-509 lacked inducing activity for AR nuclear localization or DNA binding. In a clinically valid murine xenograft model of human CRPC, ARN-509 showed greater efficacy than MDV3100. Maximal therapeutic response in this model was achieved at 30 mg/kg/d of ARN-509, whereas the same response required 100 mg/kg/d of MDV3100 and higher steady-state plasma concentrations. Thus, ARN-509 exhibits characteristics predicting a higher therapeutic index with a greater potential to reach maximally efficacious doses in man than current AR antagonists. Our findings offer preclinical proof of principle for ARN-509 as a promising therapeutic in both castration-sensitive and castration-resistant forms of prostate cancer.

Prostate cancer in 2011: Hitting old targets better and identifying new targets

Options to treat late-stage castration-resistant prostate cancer continued to increase in 2011, as three agents with different mechanisms of action prolonged life and a fourth reduced the morbidity of skeletal metastases. These outcomes contrasted with the heightened controversy generated by the recommendation against PSA screening and other early detection strategies.