# CYP11A1 (cholesterol side-chain cleavage enzyme)

Source: https://onco.cc/targets/cyp11a1/  
OnCo record `cyp11a1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CYP11A1 is the first enzyme in making every steroid hormone from cholesterol; the historic breast cancer drug aminoglutethimide blocked it, cutting oestrogen and adrenal steroids, before aromatase inhibitors made that approach precise.

## Summary

CYP11A1 converts cholesterol to pregnenolone inside mitochondria, the rate-limiting first step for cortisol, aldosterone, androgens and oestrogens. Aminoglutethimide, introduced for advanced breast cancer and Cushing's syndrome in the 1960s and 1970s, inhibited CYP11A1 and aromatase, producing a medical adrenalectomy that required cortisol replacement; it was displaced by the selective aromatase inhibitors anastrozole, letrozole and exemestane. Blocking steroid synthesis further downstream at CYP17A1 with abiraterone is the modern equivalent in prostate cancer. The enzyme is also a marker of adrenocortical carcinoma.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Tags: chembl-gap
- Symbol: CYP11A1
- Class: enzyme
- Biology: A mitochondrial cytochrome P450 of adrenal cortex, gonads and placenta; it requires adrenodoxin and adrenodoxin reductase to receive electrons from NADPH.
- Where found: Adrenal cortex, ovary, testis and placenta; Adrenocortical carcinoma and steroid-producing tumours

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Cholesterol_side-chain_cleavage_enzyme
- UniProt P05108: CYP11A1: https://www.uniprot.org/uniprotkb/P05108/entry
- HGNC:2590 CYP11A1: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:2590
- ChEMBL target CHEMBL2033: https://www.ebi.ac.uk/chembl/explore/target/CHEMBL2033

## Connected records

- targets: [Aromatase (CYP19A1)](https://onco.cc/targets/aromatase/), [CYP17A1 (17-alpha-hydroxylase/17,20-lyase)](https://onco.cc/targets/cyp17a1/)
- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Prostate cancer](https://onco.cc/cancers/prostate/)

---
JSON: https://onco.cc/api/v1/entities/cyp11a1.json