Value of Early Circulating Tumor Cells Dynamics to Estimate Docetaxel Benefit in Metastatic Castration-Resistant Prostate Cancer (mCRPC) Patients.

Circulating tumor cell (CTC) enumeration and changes following treatment have been demonstrated to be superior to PSA response in determining mCRPC outcome in patients receiving AR signaling inhibitors but not taxanes. We carried out a pooled analysis of two prospective studies in mCRPC patients treated with docetaxel. CTCs were measured at baseline and 3-6 weeks post treatment initiation. Cox regression models were constructed to compare 6-month radiographical progression-free survival (rPFS), CTCs and PSA changes predicting outcome. Among the subjects, 80 and 52 patients had evaluable baseline and post-treatment CTC counts, respectively. A significant association of higher baseline CTC count with worse overall survival (OS), PFS and time to PSA progression (TTPP) was observed. While CTC response at 3-6 weeks (CTC conversion (from ≥5 to <5 CTCs), CTC30 (≥30% decline in CTC) or CTC0 (decline to 0 CTC)) and 6-month rPFS were significantly associated with OS (all p < 0.005), the association was not significant for PSA30 or PSA50 response. CTC and PSA response were discordant in over 50% of cases, with outcome driven by CTC response in these patients. The c-index values for OS were superior for early CTC changes compared to PSA response endpoints, and similar to 6-month rPFS. Early CTC declines were good predictors of improved outcomes in mCRPC patients treated with docetaxel in this small study, offering a superior and/or earlier estimation of docetaxel benefit in comparison to PSA or rPFS that merits further confirmation in larger studies.

Novel, gross chromosomal alterations involving PTEN cooperate with allelic loss in prostate cancer.

There is increasing evidence that multiple chromosomal rearrangements occur in prostate cancer. PTEN loss is considered to be a key event in prostate carcinogenesis but the mechanisms of loss remain to be fully elucidated. We hypothesised that gross rearrangements may exist that cause disruption of the PTEN gene in the absence of genomic deletion. We therefore designed a novel fluorescence in situ hybridisation (FISH) assay with probes overlying regions 3' and 5' of PTEN and a third probe overlying the gene. We aimed to identify both genomic deletions and gross rearrangements of PTEN that would be overlooked by previously reported single-probe FISH assays. We proceeded to evaluate a tissue microarray with radical prostatectomy and trans-urethral resection of the prostate specimens from 187 patients. We identified PTEN genomic loss in 45/150 (30%) radical prostatectomy patients and 16/37 (43%) trans-urethral resection of the prostate patients. Importantly, our assay detected novel chromosomal alterations in the PTEN gene (characterised by splitting of FISH signals) in 13 tumours (6.9% of all prostate cancers; 21% of PTEN-lost cancers). All PTEN-rearranged tumours had genomic loss at the other allele and had no expression of PTEN by immunohistochemistry. PTEN-rearranged tumours were significantly more likely to have an underlying ERG rearrangement. Our assay differentiated loss of the probe overlying PTEN in isolation or in combination with either one of or both the probes overlying the 3' and 5' regions. This gave an indication of the size of genomic loss and we observed considerable inter-tumoural heterogeneity in the extent of genomic loss in PTEN-lost tumours. In summary, gross rearrangements of the PTEN locus occur in prostate cancer and can be detected by a 'break-apart' FISH assay. This observation could explain the absence of PTEN protein expression in a subgroup of tumours previously classified as having heterozygous genomic loss using single-probe traditional FISH assays.

Clinical and biochemical consequences of CYP17A1 inhibition with abiraterone given with and without exogenous glucocorticoids in castrate men with advanced prostate cancer.

CONTEXT: Abiraterone acetate is a small-molecule cytochrome P450 17A1 (CYP17A1) inhibitor that is active in castration-resistant prostate cancer. OBJECTIVE: Our objective was to determine the impact of abiraterone with and without dexamethasone treatment on in vivo steroidogenesis. DESIGN AND METHODS: We treated 42 castrate, castration-resistant prostate cancer patients with continuous, daily abiraterone acetate and prospectively collected blood and urine before and during abiraterone treatment and after addition of dexamethasone 0.5 mg daily. RESULTS: Treatment with single-agent abiraterone acetate was associated with accumulation of steroids with mineralocorticoid properties upstream of CYP17A1. This resulted in side effects, including hypertension, hypokalemia, and fluid overload, in 38 of 42 patients that were generally treated effectively with eplerenone. Importantly, serum and urinary androgens were suppressed by more than 90% from baseline. Urinary metabolites of 17-hydroxypregnenolone and 17-hydroxyprogesterone downstream of 17α-hydroxylase remained unchanged. However, 3α5α-17-hydroxypregnanolone, which can be converted via the backdoor pathway toward 5α-dihydrotestosterone, increased significantly and correlated with levels of the major 5α-dihydrotestosterone metabolite androsterone. In contrast, urinary metabolites of 11-deoxycortisol and active glucocorticoids declined significantly. Addition of dexamethasone to abiraterone acetate significantly suppressed ACTH and endogenous steroids, including 3α5α-17-hydroxypregnanolone. CONCLUSION: CYP17A1 inhibition with abiraterone acetate is characterized by significant suppression of androgen and cortisol synthesis. The latter is associated with a rise in ACTH that causes raised mineralocorticoids, leading to side effects and incomplete 17α-hydroxylase inhibition. Concomitant inhibition of 17,20-lyase results in diversion of 17-hydroxyprogesterone metabolites toward androgen synthesis via the backdoor pathway. Addition of dexamethasone reverses toxicity and could further suppress androgens by preventing a rise in substrates of backdoor androgen synthesis.

The CT flare response of metastatic bone disease in prostate cancer.

BACKGROUND: New or worsening bone lesions in patients responding to treatment, known as the flare phenomenon is well described on (99m)Tc-MDP bone scintigraphy, but to our knowledge has not previously been described on CT. The appearance of new or worsening bone sclerosis on CT in patients with prostate cancer may therefore be erroneously classified as disease progression. PURPOSE: To assess the incidence of osteoblastic healing flare response at 3-month CT assessment in patients with castrate-resistant prostate cancer and to identify associated features that enable differentiation from progressive metastatic bone disease at 3 months. MATERIAL AND METHODS: CT scans of 67 patients with castrate-resistant prostate cancer undergoing treatment were reviewed by a radiologist blinded to clinical outcome. Changes in number, size, and density of metastatic bone lesions were documented and Response Evaluation Criteria in Solid Tumours (RECIST) in soft tissue lesions, alkaline phosphatase, prostate specific antigen, and (99m)Tc-MDP bone scans were used for correlation. RESULTS: Of the 39 patients who had 3- and 6-month follow-up, eight patients (21%) demonstrated an increase in number, size, or density of sclerotic lesions on the 3-month CT scan despite improvement in PSA and soft tissue lesions. Three out of eight patients (8%) maintained partial response/remained stable at follow-up and were defined as showing a flare response: in this group bone metastases evident on CT showed a qualitative and quantitative increase in density and no lesions faded at 3 months. In contrast, in all patients who progressed at 3 months by PSA/RECIST criteria (n = 8) bone lesions showed a mixed pattern with some lesions increasing and others decreasing in density. CONCLUSION: The incidence of flare response of metastatic bone disease evident at 3-month post-treatment CT in patients with prostate cancer undergoing systemic treatment is 8%. In patients with falling PSA and stable/responding soft tissue disease at 3 months an increase in bone sclerosis in the absence of fading bone metastases can be interpreted as flare and is likely to represent a response.

Significant and sustained antitumor activity in post-docetaxel, castration-resistant prostate cancer with the CYP17 inhibitor abiraterone acetate.

PURPOSE: The principal objective of this trial was to evaluate the antitumor activity of abiraterone acetate, an oral, specific, irreversible inhibitor of CYP17 in docetaxel-treated patients with castration-resistant prostate cancer (CRPC). PATIENTS AND METHODS: In this multicenter, two-stage, phase II study, abiraterone acetate 1,000 mg was administered once daily continuously. The primary end point was achievement of a prostate-specific antigen (PSA) decline of > or = 50% in at least seven of 35 patients. Per an attained phase II design, more than 35 patients could be enrolled if the primary end point was met. Secondary objectives included: PSA declines of > or = 30% and > or = 90%; rate of RECIST (Response Evaluation Criteria in Solid Tumors) responses and duration on study; time to PSA progression; safety and tolerability; and circulating tumor cell (CTC) enumeration. RESULTS: Docetaxel-treated patients with CRPC (N = 47) were enrolled. PSA declines of > or = 30%, > or = 50% and > or = 90% were seen in 68% (32 of 47), 51% (24 of 47), and 15% (seven of 47) of patients, respectively. Partial responses (by RECIST) were reported in eight (27%) of 30 patients with measurable disease. Median time to PSA progression was 169 days (95% CI, 113 to 281 days). The median number of weeks on study was 24, and 12 (25.5%) of 47 patients remained on study > or = 48 weeks. CTCs were enumerated in 34 patients; 27 (79%) of 34 patients had at least five CTCs at baseline. Eleven (41%) of 27 patients had a decline from at least five to less than 5 CTCs, and 18 (67%) of 27 had a > or = 30% decline in CTCs after starting treatment with abiraterone acetate. Abiraterone acetate was well tolerated. CONCLUSION: Abiraterone acetate has significant antitumor activity in post-docetaxel patients with CRPC. Randomized, phase III trials of abiraterone acetate are underway to define the future role of this agent.

Targeting the PI3K/AKT pathway for the treatment of prostate cancer.

Despite recent advances in our understanding of the biological basis of prostate cancer, the management of the disease, especially in the castration-resistant phase, remains a significant challenge. Deregulation of the phosphatidylinositol 3-kinase pathway is increasingly implicated in prostate carcinogenesis. In this review, we detail the role of this pathway in the pathogenesis of prostate cancer and the rapidly evolving therapeutic implications of targeting it. In particular, we highlight the importance of the appropriate selection of agents and combinations, and the critical role of predictive and pharmocodynamic biomarkers.

A first-in-man phase i and pharmacokinetic study on CHR-2797 (Tosedostat), an inhibitor of M1 aminopeptidases, in patients with advanced solid tumors.

PURPOSE: To determine the maximum tolerated dose, dose-limiting toxicity, pharmacokinetics, and preliminary therapeutic activity profile of CHR-2797 (tosedostat), a novel, orally bioavailable inhibitor of the M1 family of aminopeptidases with antiproliferative and antiangiogenic activity in vitro. EXPERIMENTAL DESIGN: A phase I study of accelerated titration design that escalated through nine doses (10-320 mg) in patients (Eastern Cooperative Oncology Group performance status, < or =2) with advanced solid tumors. CHR-2797 was administered once daily. RESULTS: Forty patients (median age, 60 years; range, 24-80 years; male, 27; female, 13) were treated in 12 cohorts with once daily doses (10-320 mg). Dose-limiting toxicities were thrombocytopenia, dizziness, and visual abnormalities in one patient, and anemia, blurred vision, and vomiting in a second patient at 320 mg, resulting in an inability to complete 28 days of study drug. The most commonly observed toxicities were fatigue, diarrhea, peripheral edema, nausea, dizziness, and constipation. One patient had a partial response (renal cell carcinoma) and four patients had stable disease for >6 months. CHR-2797 and its active metabolite, CHR-79888, show dose-proportional increases in plasma AUC and C(max). The terminal half-life for CHR-2797 is approximately 1 to 3.5 hours and between 6 and 11 hours for CHR-79888. Intracellular (packed blood cells) exposure to CHR-79888 is consistent with intracellular levels that proved to be efficacious in xenograft models. CONCLUSION: CHR-2797 is well tolerated and can be safely administered at doses that result in intracellular levels of CHR-79888 that are associated with activity in preclinical models. The recommended dose for single agent therapy in solid tumors is 240 mg/d.

Antitumor activity with CYP17 blockade indicates that castration-resistant prostate cancer frequently remains hormone driven.

Abiraterone acetate is a potent, selective, and orally bioavailable small molecule inhibitor of CYP17, an enzyme that catalyzes two key serial reactions (17 alpha hydroxylase and 17,20 lyase) in androgen and estrogen biosynthesis. Clinical trials have confirmed that specific inhibition of CYP17 is safe and results in clinically important antitumor activity in up to 70% of castrate patients with advanced prostate cancer resistant to currently available endocrine therapies. These clinical data indicate that castration-resistant prostate cancer frequently remains hormone dependent and has confirmed that this disease should no longer be described as "hormone resistant or refractory". Biomarker studies, including the analysis of ETS gene fusion status, on patients treated with abiraterone acetate may allow enrichment of patients with a sensitive phenotype in future studies of therapeutics targeting CYP17.

A novel, spontaneously immortalized, human prostate cancer cell line, Bob, offers a unique model for pre-clinical prostate cancer studies.

INTRODUCTION: New in vitro models of castration-resistant prostate cancer (CRPC) are urgently required. METHODS: Trans-rectal needle biopsies (TRBP) of the prostate were performed for research purposes on progressing CRPC patients who had not received prior treatment to the prostate. Biopsies were immediately digested with collagenase and plated onto collagen-coated flasks with a feeder layer of 3T6 cells and cultured in cytokine-supplemented keratinocyte serum-free medium. RESULTS: Biopsies from 25 patients were collected and one of these, following an initial period of crisis, spontaneously immortalized. A series of cell lines called Bob were then established from a clone that survived CD133-selection followed by 4 weeks under adhesion-independent conditions in methylcellulose. Gains and losses previously described in clinical prostate tumors, most notably loss of 8(p) and gain of 8(q), were identified on comparative genomic hybridization and long-term growth in culture, survival in methylcellulose and invasion through matrigel confirmed the malignant phenotype of Bob. Furthermore, Bob expressed high levels of p53 and markers of early differentiation, including K8, prostatic acid phosphatase and prostate stem cell antigen. There was, however, no in vivo growth and ERG and ETV1 were not rearranged. Growth in serum permitted some differentiation. CONCLUSION: This is the first spontaneously immortalized prostate cancer cell line to be established from a TRBP of a patient with CRPC. Bob is a novel pre-clinical model for functional studies in CRPC and especially for studying the CRPC "basal" phenotype.

Selective inhibition of CYP17 with abiraterone acetate is highly active in the treatment of castration-resistant prostate cancer.

PURPOSE: It has been postulated that castration-resistant prostate cancer (CRPC) commonly remains hormone dependent. Abiraterone acetate is a potent, selective, and orally available inhibitor of CYP17, the key enzyme in androgen and estrogen biosynthesis. PATIENTS AND METHODS: This was a phase I/II study of abiraterone acetate in castrate, chemotherapy-naive CRPC patients (n = 54) with phase II expansion at 1,000 mg (n = 42) using a two-stage design to reject the null hypothesis if more than seven patients had a prostate-specific antigen (PSA) decline of > or = 50% (null hypothesis = 0.1; alternative hypothesis = 0.3; alpha = .05; beta = .14). Computed tomography scans every 12 weeks and circulating tumor cell (CTC) enumeration were performed. Prospective reversal of resistance at progression by adding dexamethasone 0.5 mg/d to suppress adrenocorticotropic hormone and upstream steroids was pursued. RESULTS: A decline in PSA of > or = 50% was observed in 28 (67%) of 42 phase II patients, and declines of > or = 90% were observed in eight (19%) of 42 patients. Independent radiologic evaluation reported partial responses (Response Evaluation Criteria in Solid Tumors) in nine (37.5%) of 24 phase II patients with measurable disease. Decreases in CTC counts were also documented. The median time to PSA progression (TTPP) on abiraterone acetate alone for all phase II patients was 225 days (95% CI, 162 to 287 days). Exploratory analyses were performed on all 54 phase I/II patients; the addition of dexamethasone at disease progression reversed resistance in 33% of patients regardless of prior treatment with dexamethasone, and pretreatment serum androgen and estradiol levels were associated with a probability of > or = 50% PSA decline and TTPP on abiraterone acetate and dexamethasone. CONCLUSION: CYP17 blockade by abiraterone acetate results in declines in PSA and CTC counts and radiologic responses, confirming that CRPC commonly remains hormone driven.

Characterization of ERG, AR and PTEN gene status in circulating tumor cells from patients with castration-resistant prostate cancer.

Hormone-driven expression of the ERG oncogene after fusion with TMPRSS2 occurs in 30% to 70% of therapy-naive prostate cancers. Its relevance in castration-resistant prostate cancer (CRPC) remains controversial as ERG is not expressed in some TMPRSS2-ERG androgen-independent xenograft models. However, unlike these models, CRPC patients have an increasing prostate-specific antigen, indicating active androgen receptor signaling. Here, we collected blood every month from 89 patients (54 chemotherapy-naive patients and 35 docetaxel-treated patients) treated in phase I/phase II clinical trials of an orally available, highly specific CYP17 inhibitor, abiraterone acetate, that ablates the synthesis of androgens and estrogens that drive TMPRSS2-ERG fusions. We isolated circulating tumor cells (CTC) by anti-epithelial cell adhesion molecule immunomagnetic selection followed by cytokeratin and CD45 immunofluorescence and 4',6-diamidino-2-phenylindole staining. We used multicolor fluorescence in situ hybridization to show that CRPC CTCs, metastases, and prostate tissue invariably had the same ERG gene status as therapy-naive tumors (n=31). We then used quantitative reverse transcription-PCR to show that ERG expression was maintained in CRPC. We also observed homogeneity in ERG gene rearrangement status in CTCs (n=48) in contrast to significant heterogeneity of AR copy number gain and PTEN loss, suggesting that rearrangement of ERG may be an earlier event in prostate carcinogenesis. We finally report a significant association between ERG rearrangements in therapy-naive tumors, CRPCs, and CTCs and magnitude of prostate-specific antigen decline (P=0.007) in CRPC patients treated with abiraterone acetate. These data confirm that CTCs are malignant in origin and indicate that hormone-regulated expression of ERG persists in CRPC.

Phase I clinical trial of a selective inhibitor of CYP17, abiraterone acetate, confirms that castration-resistant prostate cancer commonly remains hormone driven.

PURPOSE: Studies indicate that castration-resistant prostate cancer (CRPC) remains driven by ligand-dependent androgen receptor (AR) signaling. To evaluate this, a trial of abiraterone acetate-a potent, selective, small-molecule inhibitor of cytochrome P (CYP) 17, a key enzyme in androgen synthesis-was pursued. PATIENTS AND METHODS: Chemotherapy-naïve men (n = 21) who had prostate cancer that was resistant to multiple hormonal therapies were treated in this phase I study of once-daily, continuous abiraterone acetate, which escalated through five doses (250 to 2,000 mg) in three-patient cohorts. RESULTS: Abiraterone acetate was well tolerated. The anticipated toxicities attributable to a syndrome of secondary mineralocorticoid excess-namely hypertension, hypokalemia, and lower-limb edema-were successfully managed with a mineralocorticoid receptor antagonist. Antitumor activity was observed at all doses; however, because of a plateau in pharmacodynamic effect, 1,000 mg was selected for cohort expansion (n = 9). Abiraterone acetate administration was associated with increased levels of adrenocorticotropic hormone and steroids upstream of CYP17 and with suppression of serum testosterone, downstream androgenic steroids, and estradiol in all patients. Declines in prostate-specific antigen >or= 30%, 50%, and 90% were observed in 14 (66%), 12 (57%), and 6 (29%) patients, respectively, and lasted between 69 to >or= 578 days. Radiologic regression, normalization of lactate dehydrogenase, and improved symptoms with a reduction in analgesic use were documented. CONCLUSION: CYP17 blockade by abiraterone acetate is safe and has significant antitumor activity in CRPC. These data confirm that CRPC commonly remains dependent on ligand-activated AR signaling.