An open-label, phase 2 trial of bicalutamide dose escalation from 50 mg to 150 mg in men with CAB and castration resistance. A Canadian Urology Research Consortium Study.

BACKGROUND: Bicalutamide is a widely used, relatively non-toxic anti-androgen, particularly when used in combination with androgen deprivation. In men on combined androgen blockade (CAB), the typical dose is 50 mg per day. For men receiving monotherapy with bicalutamide anti-androgen, the dose is 150 mg per day. The objective was to determine the PSA response rate to increasing bicalutamide to 150 mg per day in men who develop castrate-resistant prostate cancer (CRPC) on CAB with goserelin acetate and bicalutamide 50 mg per day. METHODS: A national, multicentre, phase 2, open-label study in men on CAB with a rising PSA>2.0. The primary end point of the trial was PSA response at 12 months, defined as a decline by 50% or more compared with baseline value. Partial response was defined as a PSA decline of 10-49%. Secondary end points were duration of PSA response, change in slope of serum PSA, change in ratio of free PSA: total PSA at 3 months, 6 months and 12 months as compared with baseline; duration of the bicalutamide withdrawal response after discontinuation; the rate of cardiovascular events; and toxicity. The study was initially planned to accrue 100 patients, but was closed early due to diminishing accrual. RESULTS: Sixty-four patients were accrued; 61 patients received trial treatment and constituted the intention-to-treat (ITT) cohort. 70% were M0. Among 59 evaluable ITT patients, 13 (22%) patients had a >50% PSA decline, 5 (8%) had a decline between 10 and 50%, 4 (7%) had stabilization and 37 (63%) had PSA progression. The median duration was 3.7 months (95% confidence interval of 0.92-6.21 months). CONCLUSION: In patients with early biochemical failure on CAB with bicalutamide 50 mg, an increase in dose to 150 mg of bicalutamide resulted in a PSA response of ⩾ 50% in 22% of patients. Toxicity was mild. Bicalutamide dose intensification may benefit a subset of patients with CRPC. We believe this relatively inexpensive approach warrants further evaluation.

Effect of detergents on ligand binding and translocation activities of solubilized/reconstituted nucleoside transporters.

Purification of equilibrative nucleoside transporters has been hampered by the functional instability of the detergent-solubilized proteins. A variety of nonionic detergents were compared with octylglucoside (the most commonly used detergent in this regard) for their abilities to solubilize functionally stable nucleoside transporter proteins from Ehrlich cell plasma membranes. Transporter stability was assessed through the binding of the specific probe [3H]nitrobenzylthioinosine to freshly solubilized and stored (48 h/6 degrees C) preparations. The most promising detergents were decylmaltoside and cyclohexylbutylmaltoside, both of which, like octylglucoside, solubilized over 70% of the transporters from the membrane. Decylmaltoside- and cyclohexylbutylmaltoside-solubilized transport proteins retained 61 and 83%, respectively, of their [3H]-nitrobenzylthioinosine binding activity upon storage, compared to about 30% using octylglucoside. Decylmaltoside was also superior to octylglucoside in its capacity to solubilize the transporter in a state that retained its high affinity for the transport inhibitors dilazep (Ki = 11 nM, vs 75 nM in octylglucoside) and dipyridamole (Ki = 260 nM, vs 12 microM in octylglucoside). Reconstitution studies indicated that both the decylmaltoside- and cyclohexylbutylmaltoside-solubilized transporters were capable of mediating the uptake of [3H]uridine. Decylmaltoside was superior to cyclohexylbutylmaltoside, however, in both the enhanced transport activity of the resulting proteoliposomes (Vi = 21 pmol/mg/s vs 13 pmol/mg/s, respectively) and the lower nonmediated uptake observed in the decylmaltoside-derived vesicles (27% of total uptake at 4 min incubation). Nevertheless, cyclohexylbutylmaltoside may be useful in initial solubilization procedures due to its ability to selectively solubilize the nucleoside transporter from the plasma membrane. The rational use of these detergents will enable a more extensive purification of functional nucleoside transporters.