Prostate cancer: Bicalutamide dose increase in castration-resistant disease

Preclinical models of prostate cancer - modelling androgen dependency and castration resistance in vitro, ex vivo and in vivo

Prostate cancer is well known to be dependent on the androgen receptor (AR) for growth and survival. Thus, AR is the main pharmacological target to treat this disease. However, after an initially positive response to AR-targeting therapies, prostate cancer will eventually evolve to castration-resistant prostate cancer, which is often lethal. Tumour growth was initially thought to become androgen-independent following treatments; however, results from molecular studies have shown that most resistance mechanisms involve the reactivation of AR. Consequently, tumour cells become resistant to castration - the blockade of testicular androgens - and not independent of AR per se. However, confusion still remains on how to properly define preclinical models of prostate cancer, including cell lines. Most cell lines were isolated from patients for cell culture after evolution of the tumour to castration-resistant prostate cancer, but not all of these cell lines are described as castration resistant. Moreover, castration refers to the blockade of testosterone production by the testes; thus, even the concept of "castration" in vitro is questionable. To ensure maximal transfer of knowledge from scientific research to the clinic, understanding the limitations and advantages of preclinical models, as well as how these models recapitulate cancer cell androgen dependency and can be used to study castration resistance mechanisms, is essential.

Bicalutamide 150 mg as secondary hormonal therapy for castration-resistant prostate cancer

PURPOSE

This study was aimed to evaluate the effect and tolerability of bicalutamide 150 mg therapy in patients with castration-resistant prostate cancer (CRPC).

METHODS

A total of 48 patients with histologically confirmed prostate cancer were included. They had been treated with continuous maximal androgen blockade therapy, but their serum prostate-specific antigen (PSA) increased after initial hormonal therapy. Patients were given bicalutamide (150 mg per day). Serum PSA testing was performed every 3 months. The response was defined according to PSA decline from baseline: PSA decline ≥85% as complete response, ≥50 % but <85% as partial response, and <50 % as failure. Response duration was defined as the time from PSA response until PSA increased ≥25 % or ≥2 ng/mL from the nadir. The potential predictive factors (Gleason score, clinical stage and serum PSA) were investigated.

RESULTS

The time of follow-up was 3-30 months. A PSA decline ≥50% was observed in 37 of 48 patients including 18 ≥ 50% but <85% and 19 ≥ 85% responders. The median response duration was 12 months for partial responders and 20 months for complete responders. Patients with lower Gleason score, lower serum PSA and using flutamide as first-line nonsteroidal antiandrogen achieved more benefits. Moreover, bicalutamide 150 mg therapy was well tolerated.

CONCLUSIONS

Bicalutamide 150 mg therapy was an appropriate therapeutic method for patients of CRPC, especially for those with lower Gleason score, lower serum PSA and using flutamide as first-line nonsteroidal antiandrogen.