Marketed Drugs Can Inhibit Cytochrome P450 27A1, a Potential New Target for Breast Cancer Adjuvant Therapy

Abstract

Cytochrome P450 CYP27A1 is the only enzyme in humans converting cholesterol to 27-hydroxycholesterol, an oxysterol of multiple functions, including tissue-specific modulation of estrogen and liver X receptors. Both receptors seem to mediate adverse effects of 27-hydroxycholesterol in breast cancer when the levels of this oxysterol are elevated. The present work assessed druggability of CYP27A1 as a potential antibreast cancer target. We selected 26 anticancer and noncancer medications, most approved by the Food and Drug Administration, and evaluated them first in vitro for inhibition of purified recombinant CYP27A1 and binding to the enzyme active site. Six strong CYP27A1 inhibitors/binders were identified. These were the two antibreast cancer pharmaceuticals anastrozole and fadrozole, antiprostate cancer drug bicalutamide, sedative dexmedetomidine, and two antifungals ravuconazole and posaconazole. Anastrozole was then tested in vivo on mice, which received subcutaneous drug injections for 1 week. Mouse plasma and hepatic 27-hydroxycholesterol levels were decreased 2.6- and 1.6-fold, respectively, whereas plasma and hepatic cholesterol content remained unchanged. Thus, pharmacologic CYP27A1 inhibition is possible in the whole body and individual organs, but does not negatively affect cholesterol elimination. Our results enhance the potential of CYP27A1 as an antibreast cancer target, could be of importance for the interpretation of Femara versus Anastrozole Clinical Evaluation Trial, and bring attention to posaconazole as a potential complementary anti-breast cancer medication. More medications on the US market may have unanticipated off-target inhibition of CYP27A1, and we propose strategies for their identification.

Fig. 1.

Chemical structures of the drugs evaluated in the present work. The structures in orange are of the strong CYP27A1 inhibitors or binders.

Fig. 2.

Effect of drugs on CYP27A1 cholesterol 27-hydroxylase activity in the screening assay. Assay conditions are described in Materials and Methods. The results represent mean ± S.D. of three independent measurements. Numbers above the bars indicate percentage of CYP27A1 activity relative to control incubations containing no drug.

Fig. 3.

Absolute and difference (right side insets) spectra of CYP27A1 in the absence (black dashed line) and presence (orange line) of different drugs. Numbers above and below the spectra indicate the wavelengths of absorption maxima or minima. Absolute spectra were recorded using 1.2 μM CYP27A1 and 50 μM drug. Difference spectra were recorded using 0.4 μM CYP27A1 and a varying drug concentration against increasing amounts of drug vehicle. The buffer was 50 mM KP_i (pH 7.2) containing 1 mM EDTA, 0.01% CYMAL-7, 10% glycerol, and 0.1 M NaCl.

Fig. 4.

The IC₅₀ plots for the inhibition of cholesterol 27-hydroxylation by bicalutamide, anastrozole, fadrozole, and posaconazole. Assay conditions are described in Materials and Methods. The results represent mean ± S.D. of three independent measurements.

Fig. 5.

Effect of anastrozole treatment on the levels of 27HC and cholesterol in mouse plasma and liver. Anastrozole treatment is described in Materials and Methods. The results represent mean ± S.D. of the measurements in individual animals. Ctrl, control (vehicle-treated animals); Tx, anastrozole-treated mice. ***P < 0.001.