# Activation of androgen biosynthesis and drug metabolism by cytochrome b5

> **NIH NIH R01** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2021 · $397,808

## Abstract

Abstract
 Cytochrome b5 (b5) profoundly influences the catalytic efficiency of many cytochrome P450-catalyzed
reactions, yet the mechanism(s) of this action of b5 on P450 enzymes are controversial. Among these b5-
regulated activities is the 17,20-lyase activity of P450 17A1 (CYP17A1, steroid 17-hydroxylase/17,20-lyase),
which is a key step in the biosynthesis of androgens. Diseases of androgen excess and androgen dependence,
including polycystic ovary syndrome and prostate cancer, are extremely common, and the P450 17A1 inhibitor
abiraterone acetate (AA) is used to treat prostate cancer, proving the relevance of P450 17A1 in human disease.
By indiscriminately inhibiting the 17-hydroxylase activity of P450 17A1 in addition to its 17,20-lyase activity,
however, AA causes hypertension and potassium loss unless a potent glucocorticoid is co-administered.
Consequently, an unmet clinical need is a selective inhibitor of the 17,20-lyase reaction, which will safely lower
testosterone production. We hypothesize that a drug, which disrupts the interaction of b5 with P450 17A1, will
selectively block the 17,20-lyase reaction and lower testosterone production without disturbing drug metabolism
or requiring chronic glucocorticoid therapy.
 Our long-term goal is to elucidate the biochemical and physical properties of the b5-P450 17A1 complex
that enhance the 17,20-lyase reaction. Our central hypothesis is that b5 binding restricts the dynamics of P450
17A1 and bound substrate, which reduces uncoupling of the 17,20-lyase reaction. Consequently, the objectives
of this renewal application are to define the biochemical and biophysical nature of the b5-P450 17A1 interaction,
determine the rate-limiting step(s) of the 17,20-lyase reaction, and to probe allosteric sites on the complex.
 In Aim 1, we will probe the conformational dynamics of P450 17A1 and the changes induced upon binding
of substrate and/or b5 using hydrogen-deuterium exchange and mass spectrometry. In Aim 2, with the Scott
laboratory, we will use site-directed mutagenesis, rigorous enzymology studies, and x-ray crystallography to
probe the functional properties of a second non-active-site steroid-binding site on P450 17A1 and its influence
on the individual steps of the 17,20-lyase reaction. In Aim 3, with the Waskell laboratory, we will employ pre-
steady state kinetic experiments to dissect the rates of individual steps in the catalytic cycle in the presence and
absence of b5. In this manner, we will systematically define the mechanism of action of b5 on the 17,20-lyase
activity of P450 17A1 and pave the way for development of better drugs to safely inhibit androgen (and estrogen)
production for the treatment of human diseases.

## Key facts

- **NIH application ID:** 10136618
- **Project number:** 5R01GM086596-11
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** RICHARD J. AUCHUS
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $397,808
- **Award type:** 5
- **Project period:** 2009-09-30 → 2023-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10136618

## Citation

> US National Institutes of Health, RePORTER application 10136618, Activation of androgen biosynthesis and drug metabolism by cytochrome b5 (5R01GM086596-11). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10136618. Licensed CC0.

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