# Ribonucleotide reductase (RRM1)

Source: https://onco.cc/targets/rrm1/  
OnCo record `rrm1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The enzyme that makes DNA building blocks from RNA building blocks. Gemcitabine's active form shuts it down and hydroxyurea quenches its catalytic radical, starving dividing cells of the nucleotides they need.

## Summary

Ribonucleotide reductase converts ribonucleoside diphosphates into the deoxyribonucleotides used to make DNA, the rate-limiting step of DNA precursor supply. Gemcitabine diphosphate inhibits the RRM1 large subunit while gemcitabine triphosphate is built into DNA and stops chain extension, a self-potentiating combination that underlies its use in pancreatic, lung, bladder, ovarian and breast cancers. Hydroxyurea scavenges the tyrosyl radical of the small subunit and is used to control blood counts in myeloproliferative neoplasms and chronic myeloid leukaemia. High RRM1 expression is associated with gemcitabine resistance.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Symbol: RRM1
- Class: enzyme
- Biology: Large catalytic subunit of ribonucleotide reductase; target of gemcitabine diphosphate, with the small subunit RRM2 quenched by hydroxyurea.
- Where found: Pancreatic, lung, bladder, ovarian and breast cancers treated with gemcitabine; Myeloproliferative neoplasms treated with hydroxyurea

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/RRM1
- UniProt P23921: RRM1: https://www.uniprot.org/uniprotkb/P23921/entry

## Connected records

- cancers: [Bladder & urothelial cancer](https://onco.cc/cancers/urothelial/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/)
- drugs: [Gemcitabine](https://onco.cc/drugs/gemcitabine/), [Hydroxyurea (hydroxycarbamide)](https://onco.cc/drugs/hydroxyurea/)
- targets: [DNA polymerase alpha (POLA1)](https://onco.cc/targets/pola1/), [Thioredoxin reductase 1](https://onco.cc/targets/txnrd1/)

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JSON: https://onco.cc/api/v1/entities/rrm1.json