Aminoglutethimide: theoretical considerations and clinical results in advanced prostate cancer

Potential impact of combined inhibition of 3α-oxidoreductases and 5α-reductases on prostate cancer

Prostate cancer (PCa) growth and progression rely on the interaction between the androgen receptor (AR) and the testicular ligands, testosterone and dihydrotestosterone (DHT). Almost all men with advanced PCa receive androgen deprivation therapy (ADT). ADT lowers circulating testosterone levels, which impairs AR activation and leads to PCa regression. However, ADT is palliative and PCa recurs as castration-recurrent/resistant PCa (CRPC). One mechanism for PCa recurrence relies on intratumoral synthesis of DHT, which can be synthesized using the frontdoor or primary or secondary backdoor pathway. Androgen metabolism inhibitors, such as those targeting 5α-reductase, aldo-keto-reductase family member 3 (AKR1C3), or cytochrome P450 17A1 (CYP17A1) have either failed or produced only modest clinical outcomes. The goal of this review is to describe the therapeutic potential of combined inhibition of 5α-reductase and 3α-oxidoreductase enzymes that facilitate the terminal steps of the frontdoor and primary and secondary backdoor pathways for DHT synthesis. Inhibition of the terminal steps of the androgen metabolism pathways may be a way to overcome the shortcomings of existing androgen metabolism inhibitors and thereby delay PCa recurrence during ADT or enhance the response of CRPC to androgen axis manipulation.

Roles for the backdoor pathway of androgen metabolism in prostate cancer response to castration and drug treatment

Almost all men who present with advanced prostate cancer (CaP) and many men who fail potentially curative therapy are treated with androgen deprivation therapy (ADT). ADT is not curative and CaP recurs as the lethal phenotype. The goal of this review is to describe the evolution of adrenal androgen blockade, how new androgen measurement methods have furthered understanding of androgen metabolism, and how further understanding of the backdoor pathway of androgen metabolism may lead to interventions that extend survival even more.

Randomised phase III study of intravenous vinorelbine plus hormone therapy versus hormone therapy alone in hormone-refractory prostate cancer

BACKGROUND

Vinorelbine (VRL) has been shown to be active in hormone-refractory prostate cancer (HRPC) in phase II studies, alone or in combination. Its moderate toxicity profile is well tolerated in elderly patients.

PATIENTS AND METHODS

Patients with metastatic prostate cancer, progressive after primary hormonal therapy, were randomised to receive intravenous VRL 30 mg/m2 on days 1 and 8 every 3 weeks, and hydrocortisone 40 mg/day or hydrocortisone alone until disease progression. Centres could choose to add aminoglutethimide 1000 mg/day to hydrocortisone as second-line hormone therapy (HT) for all their patients. Randomisation was stratified by centre. Further chemotherapy was allowed after progression. The primary end point was progression-free survival (PFS). The final analysis was performed on a total of 414 patients. Reported results were all based on intention-to-treat analyses. All progressions and responses were reviewed by an independent panel.

RESULTS

PFS was significantly prolonged in the VRL plus HT arm compared with the HT alone arm, according to the statistical hypothesis of the protocol (P=0.055 in the two-sided log-rank test with a pre-specified significance level of 10%). The 6-month PFS rates were 33.2% versus 22.8%, and the median durations of PFS were 3.7 versus 2.8 months. In the multivariate Cox analysis, which included age, Karnofsky performance status (PS), haemoglobin, alkaline phosphatase at study entry and number of prior hormonal treatments, the P value was decreased to 0.005. The prostate-specific antigen (PSA) response rate (> or =50% decline sustained for at least 6 weeks) was significantly higher for VRL plus HT compared with HT (30.1% versus 19.2%; P=0.01). Clinical benefit, defined as a decrease in pain intensity or analgesic consumption or an improvement of Karnofsky PS for at least 9 weeks, and at least stable assessment in the other two, was also more frequently observed in patients who received VRL plus HT versus HT alone (30.6% and 19.2%; P=0.008). There was no statistical difference in overall survival. Forty-three per cent of patients in the HT arm received at least one line of further chemotherapy after progression, compared with 28% of patients in the VRL-based arm. Aminoglutethimide did not seem to result in better efficacy for either arm. VRL plus HT was well tolerated, with a median administered relative dose intensity of 90%; grade 4 neutropenia occurred in 6.5% of patients and non-haematological toxicity was rare.

CONCLUSIONS

The combination of VRL and hydrocortisone compared with hydrocortisone alone resulted in improved clinical benefit, PFS and PSA response rate. This therapeutic gain is similar to that previously reported with mitoxantrone in combination with low-dose corticosteroids. There was no gain in survival; however, the combination is well tolerated in this elderly group of patients, who often present cardiac co-morbidities, and therefore offers an active and safe therapeutic option for patients with hormone-refractory prostate cancer.

Phase II trial and pharmacokinetic assessment of intravenous melphalan in patients with advanced prostate cancer

Alkylating agents have been reported to yield response rates of up to 20% in hormone-refractory prostate cancer. Melphalan was studied in four small trials in which the drug was given orally. In this phase II trial, melphalan (30 mg/m2) was given intravenously every 28 days to 27 patients with hormone-refractory prostate cancer. Pharmacokinetic sampling was performed so as to describe the clearance of melphalan in this population and in an attempt to carry out pharmacodynamic modeling for toxicity and response. Prostate-specific antigen (PSA) was also assessed prospectively. No objective responses to this regimen were documented. The median survival for patients on this trial was 11.5 months. There was no correlation between drug clearance and measured creatinine clearance and no relationship between systemic exposure and toxicity. A decrease of > 50% in serum PSA that was sustained for > 6 weeks was documented in two patients, most notably in one patient who has survived for more than 29 months. Intravenous melphalan is not an active agent in hormone-refractory prostate cancer.