Camptothecin is a quinoline-based alkaloid found in the barks of the Chinese camptotheca tree and the Asian nothapodytes tree. It and its close chemical relatives (aminocamptothecin, CPT-11 irinotecan, DX-8951f, and topotecan) are the only known naturally-occurring DNA topoisomerase I inhibitors. It's one of the newer chemotherapy drugs, and as such cancer researchers are really interested in it, but some incarnations of the drug aren't FDA-approved yet (it and some of its chemical relatives are in clinical trials to treat breast cancers, ovarian cancers, colon cancers, malignant melanoma, small-cell lung cancer, and leukemia).

The major side effects of camptothecin drugs are potentially severe diarrhea, nausea, hair loss, anemia, and lowered leukocyte (white blood cell) counts. The drug may also damage bone marrow.