{"entity":{"id":"sn-38","kind":"term","name":"SN-38","aka":["7-ethyl-10-hydroxycamptothecin"],"tldr":"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.","asOf":"2026-09-09","wikipedia":"https://en.wikipedia.org/wiki/SN-38","links":[{"label":"Wikipedia","url":"https://en.wikipedia.org/wiki/SN-38"}],"tags":[],"related":["topoisomerase-inhibitors","efflux-pump","irinotecan"],"cancers":[],"sections":[],"technologies":["adc"],"targets":[],"drugs":["sacituzumab-govitecan"],"companies":[],"institutions":[],"pathways":[],"terms":["payload","topoisomerase-i-payloads"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"ADC chemistry"},"route":"/terms/sn-38/","neighbours":{"technology":[{"id":"adc","kind":"technology","name":"Antibody-drug conjugate (ADC)","route":"/technologies/adc/"},{"id":"topoisomerase-inhibitors","kind":"technology","name":"Topoisomerase-I inhibitors (and ADC payloads)","route":"/technologies/topoisomerase-inhibitors/"}],"term":[{"id":"cl2a","kind":"term","name":"CL2A","route":"/terms/cl2a/"},{"id":"efflux-pump","kind":"term","name":"Drug efflux pumps (ABC transporters)","route":"/terms/efflux-pump/"},{"id":"payload","kind":"term","name":"Payload (ADC)","route":"/terms/payload/"},{"id":"topoisomerase-i-payloads","kind":"term","name":"Topoisomerase-I inhibitor payloads","route":"/terms/topoisomerase-i-payloads/"}],"drug":[{"id":"irinotecan","kind":"drug","name":"Irinotecan (and liposomal irinotecan)","route":"/drugs/irinotecan/"},{"id":"sacituzumab-govitecan","kind":"drug","name":"Sacituzumab govitecan","route":"/drugs/sacituzumab-govitecan/"}],"pathway":[{"id":"dna-replication-licensing","kind":"pathway","name":"DNA replication & origin licensing","route":"/pathways/dna-replication-licensing/"},{"id":"drug-efflux-pumps","kind":"pathway","name":"Drug efflux pumps (ABC transporters)","route":"/pathways/drug-efflux-pumps/"}]}}