ABSTRACT
Cytochrome P450 17A1 (CYP17A1; also P450c17and P450sccII) is a critically important enzyme in humans that catalyzes the formation of all endogenous androgens. It is an atypical cytochrome P450 enzyme in that it catalyzes two distinct types of substrate oxidation. Through its hydroxylase activity, it catalyzes the 17α-hydroxylation of pregnenolone to 17α-OH pregnenolone. Subsequently, through its C17,20lyase activity, it can further convert 17α-OH pregnenolone to the androgen dehydroepiandrosterone, which is a precursor to androstenedione, testosterone, and dihydrotestosterone. The importance of androgens in diseases such as prostate cancer has been appreciated for decades and the discovery of extra-testicular formation of androgens has helped clarify the pathology of the disease, especially the castrate- resistant disease. Therefore, specific inhibition of CYP17A1 by therapeutic intervention has been an area of considerable effort in several research laboratories. This basic research has led to the discovery of several promising drug candidates followed by the conduct of several clinical trials. Recently, all these efforts have culminated in the first approval by FDA of an inhibitor of CYP17A1 for the treatment of castrate-resistant prostate cancer. Ongoing clinical trials are now evaluating the agent in earlier stages of prostate cancer and even rare forms of androgen-dependent breast cancer. Accordingly, this review focuses on the biochemistry, chemistry, and clinical inhibitors of CYP17A1.
Subject(s)
Enzyme Inhibitors/pharmacology , Prostatic Neoplasms/drug therapy , Steroid 17-alpha-Hydroxylase/antagonists & inhibitors , Steroid 17-alpha-Hydroxylase/metabolism , Animals , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/therapeutic use , Humans , Male , Molecular Conformation , Pregnenolone/analogs & derivatives , Pregnenolone/chemistry , Pregnenolone/metabolism , Prostatic Neoplasms/enzymologyABSTRACT
SN2310 is an injectable emulsion composed of vitamin E, a succinate derivative, as well as 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan. Single intravenous doses of 15, 20, 25, and 30 mg/m(2) of SN2310 emulsion were administered in a total of 26 patients with advanced solid malignancies. Serial blood samples were collected and concentrations of SN2310, SN-38, and SN-38 glucuronide were assayed. Mean systemic clearance of SN2310 ranged between 1.91 and 2.02 L/h/m(2) . Peak concentrations of SN-38 were observed at the end of infusion, suggesting a fast metabolic conversion of SN2310 to its active form, SN-38. Mean t1/2 values of SN-38 across the 20-30 mg/m(2) dose levels (131-199 h) were 33-55-fold longer than those observed for SN2310. The systemic exposure of SN-38 increased in a proportional manner over the dose range studied. SN2310 emulsion displayed an improved safety profile as compared with irinotecan. The most significant safety risk was neutropenia. Considering the rapid formation of SN-38, the proportional increase in exposure levels, and its longer elimination half-life, less frequent dosing of SN2310 emulsion may be considered for the treatment of patients with advanced solid malignancies.
