# SN-38

Source: https://onco.cc/terms/sn-38/  
OnCo record `sn-38` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

SN-38 is the active form of the chemotherapy irinotecan and the payload of sacituzumab govitecan. It blocks topoisomerase I so DNA breaks during copying, but it kills cells only at nanomolar concentrations, so the ADC carries roughly eight copies per antibody and uses a linker that releases it in the tumour; slow metabolisers (UGT1A1*28) get more diarrhoea.

## Summary

SN-38 blocks topoisomerase I, the enzyme that relieves twisting in DNA during copying, so the copying machinery collides with trapped complexes and the DNA breaks. It is about a thousand times more potent than irinotecan itself but only nanomolar, which is why sacituzumab govitecan carries roughly eight copies per antibody and uses a linker that lets go in the tumour environment. It is pumped out by the ABCG2 transporter, one route to resistance, and people who metabolise it slowly (UGT1A1*28) get more diarrhoea and low blood counts.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: 7-ethyl-10-hydroxycamptothecin

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/SN-38
- Wikipedia: https://en.wikipedia.org/wiki/SN-38

## Connected records

- technologies: [Antibody-drug conjugate (ADC)](https://onco.cc/technologies/adc/), [Topoisomerase-I inhibitors (and ADC payloads)](https://onco.cc/technologies/topoisomerase-inhibitors/)
- terms: [CL2A](https://onco.cc/terms/cl2a/), [Drug efflux pumps (ABC transporters)](https://onco.cc/terms/efflux-pump/), [Payload (ADC)](https://onco.cc/terms/payload/), [Topoisomerase-I inhibitor payloads](https://onco.cc/terms/topoisomerase-i-payloads/)
- drugs: [Irinotecan (and liposomal irinotecan)](https://onco.cc/drugs/irinotecan/), [Sacituzumab govitecan](https://onco.cc/drugs/sacituzumab-govitecan/)
- pathways: [DNA replication & origin licensing](https://onco.cc/pathways/dna-replication-licensing/), [Drug efflux pumps (ABC transporters)](https://onco.cc/pathways/drug-efflux-pumps/)

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JSON: https://onco.cc/api/v1/entities/sn-38.json