George Seed

DNA-Repair Defects and Olaparib in Metastatic Prostate Cancer

BACKGROUND Prostate cancer is a heterogeneous disease, but current treatments are not based on molecular stratification. We hypothesized that metastatic, castration-resistant prostate cancers with DNA-repair defects would respond to poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibition with olaparib. METHODS We conducted a phase 2 trial in which patients with metastatic, castration-resistant prostate cancer were treated with olaparib tablets at a dose of 400 mg twice a day. The primary end point was the response rate, defined either as an objective response according to Response Evaluation Criteria in Solid Tumors, version 1.1, or as a reduction of at least 50% in the prostate-specific antigen level or a confirmed reduction in the circulating tumor-cell count from 5 or more cells per 7.5 ml of blood to less than 5 cells per 7.5 ml. Targeted next-generation sequencing, exome and transcriptome analysis, and digital polymerase-chain-reaction testing were performed on samples from mandated tumor biopsies. RESULTS Overall, 50 patients were enrolled; all had received prior treatment with docetaxel, 49 (98%) had received abiraterone or enzalutamide, and 29 (58%) had received cabazitaxel. Sixteen of 49 patients who could be evaluated had a response (33%; 95% confidence interval, 20 to 48), with 12 patients receiving the study treatment for more than 6 months. Next-generation sequencing identified homozygous deletions, deleterious mutations, or both in DNA-repair genes--including BRCA1/2, ATM, Fanconis anemia genes, and CHEK2--in 16 of 49 patients who could be evaluated (33%). Of these 16 patients, 14 (88%) had a response to olaparib, including all 7 patients with BRCA2 loss (4 with biallelic somatic loss, and 3 with germline mutations) and 4 of 5 with ATM aberrations. The specificity of the biomarker suite was 94%. Anemia (in 10 of the 50 patients [20%]) and fatigue (in 6 [12%]) were the most common grade 3 or 4 adverse events, findings that are consistent with previous studies of olaparib. CONCLUSIONS Treatment with the PARP inhibitor olaparib in patients whose prostate cancers were no longer responding to standard treatments and who had defects in DNA-repair genes led to a high response rate. (Funded by Cancer Research UK and others; ClinicalTrials.gov number, NCT01682772; Cancer Research UK number, CRUK/11/029.).

Decline in Circulating Tumor Cell Count and Treatment Outcome in Advanced Prostate Cancer

Background Treatment response biomarkers are urgently needed for castration-resistant prostate cancer (CRPC). Baseline and post-treatment circulating tumor cell (CTC) counts of ≥5 cells/7.5 ml are associated with poor CRPC outcome. Objective To determine the value of a ≥30% CTC decline as a treatment response indicator. Design, setting, and participants We identified patients with a baseline CTC count ≥5 cells/7.5 ml and evaluable post-treatment CTC counts in two prospective trials. Intervention Patients were treated in the COU-AA-301 (abiraterone after chemotherapy) and IMMC-38 (chemotherapy) trials. Outcome measures and statistical analysis The association between a ≥30% CTC decline after treatment and survival was evaluated using univariable and multivariable Cox regression models at three landmark time points (4, 8, and 12 wk). Model performance was evaluated by calculating the area under the receiver operating characteristic curve (AUC) and c-indices. Results Overall 486 patients (122 in IMMC-38 and 364 in COU-AA-301) had a CTC count ≥5 cells/7.5 ml at baseline, with 440, 380, and 351 patients evaluable at 4, 8, and 12 wk, respectively. A 30% CTC decline was associated with increased survival at 4 wk (hazard ratio [HR] 0.45, 95% confidence interval [CI] 0.36–0.56; p < 0.001), 8 wk (HR 0.41, 95% CI 0.33–0.53; p < 0.001), and 12 wk (HR 0.39, 95% CI 0.3–0.5; p < 0.001) in univariable and multivariable analyses. Stable CTC count (<30% fall or <30% increase) was not associated with a survival benefit when compared with increased CTC count. The association between a 30% CTC decline after treatment and survival was independent of baseline CTC count. CTC declines significantly improved the AUC at all time-points. Finally, in the COU-AA-301 trial, patients with CTC ≥5 cells/7.5 ml and a 30% CTC decline had similar overall survival in both arms. Conclusions A 30% CTC decline after treatment from an initial count ≥5 cells/7.5 ml is independently associated with CRPC overall survival following abiraterone and chemotherapy, improving the performance of a multivariable model as early as 4 wk after treatment. This potential surrogate must now be prospectively evaluated. Patient summary Circulating tumor cells (CTCs) are cancer cells that can be detected in the blood of prostate cancer patients. We analyzed changes in CTCs after treatment with abiraterone and chemotherapy in two large clinical trials, and found that patients who have a decline in CTC count have a better survival outcome.

Second-Generation HSP90 Inhibitor Onalespib Blocks mRNA Splicing of Androgen Receptor Variant 7 in Prostate Cancer Cells

Resistance to available hormone therapies in prostate cancer has been associated with alternative splicing of androgen receptor (AR) and specifically, the expression of truncated and constitutively active AR variant 7 (AR-V7). The transcriptional activity of steroid receptors, including AR, is dependent on interactions with the HSP90 chaperone machinery, but it is unclear whether HSP90 modulates the activity or expression of AR variants. Here, we investigated the effects of HSP90 inhibition on AR-V7 in prostate cancer cell lines endogenously expressing this variant. We demonstrate that AR-V7 and full-length AR (AR-FL) were depleted upon inhibition of HSP90. However, the mechanisms underlying AR-V7 depletion differed from those for AR-FL. Whereas HSP90 inhibition destabilized AR-FL and induced its proteasomal degradation, AR-V7 protein exhibited higher stability than AR-FL and did not require HSP90 chaperone activity. Instead, HSP90 inhibition resulted in the reduction of AR-V7 mRNA levels but did not affect total AR transcript levels, indicating that HSP90 inhibition disrupted AR-V7 splicing. Bioinformatic analyses of transcriptome-wide RNA sequencing data confirmed that the second-generation HSP90 inhibitor onalespib altered the splicing of at least 557 genes in prostate cancer cells, including AR. These findings indicate that the effects of HSP90 inhibition on mRNA splicing may prove beneficial in prostate cancers expressing AR-V7, supporting further clinical investigation of HSP90 inhibitors in malignancies no longer responsive to androgen deprivation. Cancer Res; 76(9); 2731-42. ©2016 AACR.

Validation and utilisation of high-coverage next-generation sequencing to deliver the pharmacological audit trail.

Background:Predictive biomarker development is a key challenge for novel cancer therapeutics. We explored the feasibility of next-generation sequencing (NGS) to validate exploratory genomic biomarkers that impact phase I trial selection.Methods:We prospectively enrolled 158 patients with advanced solid tumours referred for phase I clinical trials at the Royal Marsden Hospital (October 2012 to March 2013). After fresh and/or archived tumour tissue were obtained, 93 patients remained candidates for phase I trials. Results from tumour sequencing on the Illumina MiSeq were cross-validated in 27 out of 93 patients on the Ion Torrent Personal Genome Machine (IT-PGM) blinded to results. MiSeq validation with Sequenom MassARRAY OncoCarta 1.0 (Sequenom Inc., San Diego, CA, USA) was performed in a separate cohort.Results:We found 97% concordance of mutation calls by MiSeq and IT-PGM at a variant allele frequency ⩾13% and ⩾500 × depth coverage, and 91% concordance between MiSeq and Sequenom. Common ‘actionable’ mutations involved deoxyribonucleic acid (DNA) repair (51%), RAS-RAF-MEK (35%), Wnt (26%), and PI3K-AKT-mTOR (24%) signalling. Out of 53, 29 (55%) patients participating in phase I trials were recommended based on identified actionable mutations.Conclusions:Targeted high-coverage NGS panels are a highly feasible single-centre technology well-suited to cross-platform validation, enrichment of trials with molecularly defined populations and hypothesis testing early in drug development.

Sarcopenia and change in body composition following maximal androgen suppression with abiraterone in men with castration-resistant prostate cancer

Background:Standard medical castration reduces muscle mass. We sought to characterize body composition changes in men undergoing maximal androgen suppression with and without exogenous gluocorticoids.Methods:Cross-sectional areas of total fat, visceral fat and muscle were measured on serial CT scans in a post-hoc analysis of patients treated in Phase I/II trials with abiraterone followed by abiraterone and dexamethasone 0.5 mg daily. Linear mixed regression models were used to account for variations in time-on-treatment and baseline body mass index (BMI).Results:Fifty-five patients received a median of 7.5 months abiraterone followed by 5.4 months abiraterone and dexamethasone. Muscle loss was observed on single-agent abiraterone (maximal in patients with baseline BMI >30, −4.3%), but no further loss was observed after addition of dexamethasone. Loss of visceral fat was also observed on single-agent abiraterone, (baseline BMI >30 patients −19.6%). In contrast, addition of dexamethasone led to an increase in central visceral and total fat and BMI in all the patients.Interpretation:Maximal androgen suppression was associated with loss of muscle and visceral fat. Addition of low dose dexamethasone resulted in significant increases in visceral and total fat. These changes could have important quality-of-life implications for men treated with abiraterone.

The molecular underpinnings of prostate cancer: impacts on management and pathology practice

Prostate cancer (PCa) is a clinically heterogeneous disease and current treatment strategies are based largely on anatomical and pathological parameters. In the recent past, several DNA sequencing studies of primary and advanced PCa have revealed recurrent patterns of genomic aberrations that expose mechanisms of resistance to available therapies and potential new drug targets. Suppression of androgen receptor (AR) signalling is the cornerstone of advanced prostate cancer treatment. Genomic aberrations of the androgen receptor or alternative splicing of its mRNA are increasingly recognised as biomarkers of resistance to AR‐targeted therapies such as abiraterone or enzalutamide. Genomic aberrations of the PI3K–AKT axis, in particular affecting PTEN, are common in PCa, and compounds targeting different kinases in this pathway are showing promise in clinical trials. Both germline and somatic defects in DNA repair genes have been shown to sensitise some patients to therapy with PARP inhibition. In addition, abnormalities in mismatch‐repair genes are associated with response to immune checkpoint inhibition in other solid tumours and present a tantalising therapeutic avenue to be pursued. Aberrations in CDK4/6–RB1 pathway genes occur in a subset of PCas, may associate with differential sensitivity to treatment, and are likely to have clinical implications beyond prognostication. Inhibitors of CDK4/6 are already being tested in prostate cancer clinical trials. Furthermore, deletions of RB1 are strongly associated with a neuroendocrine phenotype, a rare condition characterized by a non‐AR‐driven transcriptomic profile. Finally, aberrations in genes involved in regulating the chromatin structure are an emerging area of interest. Deletions of CHD1 are not infrequent in PCa and may associate with increased AR activity and genomic instability, and these tumours could benefit from DNA‐damaging therapies. This review summarises how genomic discoveries in PCa are changing the treatment landscape of advanced CRPC, both by identifying biomarkers of resistance and by identifying vulnerabilities to be targeted. Copyright

Abstract CT322: DNA repair defects and antitumor activity with PARP inhibition: TOPARP, a phase II trial of olaparib in metastatic castration resistant prostate cancer

Introduction: Next generation sequencing (NGS) has identified genomic aberrations causing DNA repair defects in sporadic metastatic castration resistant prostate cancer (mCRPC). We hypothesized that single agent olaparib would have antitumor activity in a sub-population of mCRPC patients (pts) and that exome and transcriptome studies would identify this population. Methods: TOPARP is an open-label, investigator-initiated phase II trial with a novel multi-step adaptive design (CRUK/11/029). The first part of the study (TOPARP-A) has a two-stage design evaluating the antitumor activity of single agent olaparib in unselected mCRPC pts (p0 = 0.05; p1 = 0.20; α = 0.02; β = 0.10) with a preplanned analysis to identify a biomarker defined sensitive subgroup. Primary endpoint, response rate (RR), was defined as objective response by RECIST 1.1 and/or PSA fall ≥50% and/or confirmed circulating tumor cell (CTC) count falls from ≥5 to Results: Fifty pts were enrolled from 7 UK centers; all had had prior docetaxel, 48 (96%) prior abiraterone and 29 (58%) prior cabazitaxel. Overall, 16 of 49 evaluable pts experienced a response (RR 32.7%, 95% CI: 20.0 to 47.5), with 11 and 4 pts having been on treatment for >6 and >12 months respectively at data cut-off. NGS identified homozygous deletions and/or putatively deleterious mutations in DNA repair genes in 15/49 (30.6%) evaluable pts. While a majority of these genomic aberrations occurred in BRCA2 and ATM, biallelic loss of other relevant genes, including members of the Fanconi Anemia complementation group and CHEK2, were also observed. Among these fifteen pts, 13 (86.7%) responded to olaparib. All seven pts with BRCA2 loss (somatic [4/7] or germline [3/7]) and 4/5 pts with ATM truncating mutations responded to olaparib. The specificity of the biomarker suite was 94% in this population. Conversely, PTEN loss and ERG rearrangements were not associated with response. Finally, consistent with previous studies of olaparib, anemia (10/50, 20%) and fatigue (6/50, 12%) were the most common grade>3 adverse events, with 13 (26%) pts requiring a dose reduction. Conclusions: Olaparib has durable antitumor activity in heavily pre-treated pts with sporadic mCRPC with a 32.7% overall response rate. Genomic defects in DNA repair genes associate with olaparib sensitivity in sporadic mCRPC, offering a possibility for the very first molecular treatment stratification of advanced prostate cancer. Citation Format: Joaquin Mateo, Shahneen Sandhu, Susana Miranda, Suzanne Carreira, Suneil Jain, Christy Ralph, Andrew Protheroe, Syed Hussain, Robert Jones, Tony Elliot, Ursula McGovern, Alexa Gillman, Claire Paulding, Helen Mossop, Nuria Porta, Diletta Bianchini, Zafeiris Zafeiriou, Gunther Boysen, Daniel Nava Rodrigues, Penelope Flohr, George Seed, Jane Goodall, Ines Figueiredo, Raquel Perez-Lopez, Nina Tunariu, Aurelius Omlin, Roberta Ferraldeschi, Lakshmi P. Kunju, Rosalind Eeles, Gerhardt Attard, Dan Robinson, Arul Chinnaiyan, Emma Hall, Johann S. de Bono. DNA repair defects and antitumor activity with PARP inhibition: TOPARP, a phase II trial of olaparib in metastatic castration resistant prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT322. doi:10.1158/1538-7445.AM2015-CT322

Plasma Cell-free DNA Concentration and Outcomes from Taxane Therapy in Metastatic Castration-resistant Prostate Cancer from Two Phase III Trials (FIRSTANA and PROSELICA)

Background Noninvasive biomarkers are needed to guide metastatic castration-resistant prostate cancer (mCRPC) treatment. Objective To clinically qualify baseline and on-treatment cell-free DNA (cfDNA) concentrations as biomarkers of patient outcome following taxane chemotherapy. Design, setting, and participants Blood for cfDNA analyses was prospectively collected from 571 mCRPC patients participating in two phase III clinical trials, FIRSTANA (NCT01308567) and PROSELICA (NCT01308580). Patients received docetaxel (75 mg/m2) or cabazitaxel (20 or 25 mg/m2) as first-line chemotherapy (FIRSTANA), and cabazitaxel (20 or 25 mg/m2) as second-line chemotherapy (PROSELICA). Outcome measurements and statistical analysis Associations between cfDNA concentration and prostate-specific antigen (PSA) response were tested using logistic regression models. Survival was estimated using Kaplan-Meier methods for cfDNA concentration grouped by quartile. Cox proportional hazard models, within each study, tested for associations with radiological progression-free survival (rPFS) and overall survival (OS), with multivariable analyses adjusting for baseline prognostic variables. Two-stage individual patient meta-analysis combined results for cfDNA concentrations for both studies. Results and limitations In 2502 samples, baseline log10 cfDNA concentration correlated with known prognostic factors, shorter rPFS (hazard ratio [HR] = 1.54; 95% confidence interval [CI]: 1.15–2.08; p = 0.004), and shorter OS on taxane therapy (HR = 1.53; 95% CI: 1.18–1.97; p = 0.001). In multivariable analyses, baseline cfDNA concentration was an independent prognostic variable for rPFS and OS in both first- and second-line chemotherapy settings. Patients with a PSA response experienced a decline in log10 cfDNA concentrations during the first four cycles of treatment (per cycle −0.03; 95% CI: −0.044 to −0.009; p = 0.003). Study limitations included the fact that blood sample collection was not mandated for all patients and the inability to specifically quantitate tumour-derived cfDNA fraction in cfDNA. Conclusions We report that changes in cfDNA concentrations correlate with both rPFS and OS in patients receiving first- and second-line taxane therapy, and may serve as independent prognostic biomarkers of response to taxanes. Patient summary In the past decade, several new therapies have been introduced for men diagnosed with metastatic prostate cancer. Although metastatic prostate cancer remains incurable, these novel agents have extended patient survival and improved their quality of life in comparison with the last decade. To further optimise treatment allocation and individualise patient care, better tests (biomarkers) are needed to guide the delivery of improved and more precise care. In this report, we assessed cfDNA in over 2500 blood samples from men with prostate cancer who were recruited to two separate international studies and received taxane chemotherapy. We quantified the concentration of cfDNA fragments in blood plasma, which partly originates from tumour. We identified that higher concentrations of circulating cfDNA fragments, prior to starting taxane chemotherapy, can be used to identify patients with aggressive prostate cancer. A decline in cfDNA concentration during the first 3–9 wk after initiation of taxane therapy was seen in patients deriving benefit from taxane chemotherapy. These results identified circulating cfDNA as a new biomarker of aggressive disease in metastatic prostate cancer and imply that the study of cfDNA has clinical utility, supporting further efforts to develop blood-based tests on this circulating tumour-derived DNA.

Targeting Bromodomain and Extra-Terminal (BET) Family Proteins in Castration-Resistant Prostate Cancer (CRPC)

Purpose: Persistent androgen receptor (AR) signaling drives castration-resistant prostate cancer (CRPC) and confers resistance to AR-targeting therapies. Novel therapeutic strategies to overcome this are urgently required. We evaluated how bromodomain and extra-terminal (BET) protein inhibitors (BETi) abrogate aberrant AR signaling in CRPC. Experimental Design: We determined associations between BET expression, AR-driven transcription, and patient outcome; and the effect and mechanism by which chemical BETi (JQ1 and GSK1210151A; I-BET151) and BET family protein knockdown regulates AR-V7 expression and AR signaling in prostate cancer models. Results: Nuclear BRD4 protein expression increases significantly (P ≤ 0.01) with castration resistance in same patient treatment-naïve (median H-score; interquartile range: 100; 100–170) and CRPC (150; 110–200) biopsies, with higher expression at diagnosis associating with worse outcome (HR, 3.25; 95% CI, 1.50–7.01; P ≤ 0.001). BRD2, BRD3, and BRD4 RNA expression in CRPC biopsies correlates with AR-driven transcription (all P ≤ 0.001). Chemical BETi, and combined BET family protein knockdown, reduce AR-V7 expression and AR signaling. This was not recapitulated by C-MYC knockdown. In addition, we show that BETi regulates RNA processing thereby reducing alternative splicing and AR-V7 expression. Furthermore, BETi reduce growth of prostate cancer cells and patient-derived organoids with known AR mutations, AR amplification and AR-V7 expression. Finally, BETi, unlike enzalutamide, decreases persistent AR signaling and growth (P ≤ 0.001) of a patient-derived xenograft model of CRPC with AR amplification and AR-V7 expression. Conclusions: BETi merit clinical evaluation as inhibitors of AR splicing and function, with trials demonstrating their blockade in proof-of-mechanism pharmacodynamic studies. Clin Cancer Res; 24(13); 3149–62. ©2018 AACR.

Circulating tumour cell increase as a biomarker of disease progression in metastatic castration-resistant prostate cancer patients with low baseline CTC counts

Background The development of treatment response and surrogate biomarkers for advanced prostate cancer care is an unmet clinical need. Patients with baseline circulating tumour cell (BLCTCs) counts <5/7.5 mL represent a good prognosis subgroup but are non-evaluable for response assessment (decrease in CTCs). The aim of the study is to determine the value of any increase in CTCs (CTC progression) as an indicator of progression in prostate cancer patients with low pre-treatment CTCs (<5). Patients and methods We carried out a post hoc analysis of patients with BLCTCs < 5 treated in the COU-AA-301 (abiraterone or placebo + prednisone) and IMMC-38 (chemotherapy) trials. The association of CTC progression (increase in CTCs at 4, 8 or 12 weeks) with overall survival (OS) was evaluated in multi-variable Cox regression models. Performance of survival models with and without CTC progression was evaluated by calculating ROC curve area under the curves (AUCs) and weighted c-indices. Results Overall, 511 patients with CTCs < 5 (421 in COU-AA-301 and 90 in IMMC-38) were selected; 212 (41.7%) had CTC progression at 4, 8 or 12 weeks after treatment initiation. CTC progression was associated with significantly worse OS [27.1 versus 15.1 m; hazard ratio (HR) 3.4 (95% confidence interval [CI] 2.5-4.5; P < 0.001)], independent of baseline CTCs and established clinical variables. Adding CTC progression to the OS model significantly improved ROC AUC (0.77 versus 0.66; P < 0.001). Models including CTC progression had superior ROC AUC (0.77 versus 0.69; P < 0.001) and weighted c-index [0.750 versus 0.705; delta c-index: 0.045 (95% CI 0.019-0.071)] values than those including CTC conversion (increase to CTCs ≥ 5). In COU-AA-301, the impact of CTC progression was independent of treatment arm. Conclusions Increasing CTCs during the first 12 weeks of treatment are independently associated with worse OS from advanced prostate cancer in patients with baseline CTCs < 5 treated with abiraterone or chemotherapy and improve models with established prognostic variables. These findings must be prospectively validated.