S-(-)-Camptothecin is primarily used in cancer treatment due to its potent antitumor properties. It works by inhibiting the enzyme topoisomerase I, which is crucial for DNA replication in cancer cells. This inhibition leads to DNA damage and ultimately induces apoptosis in the cancerous cells. It serves as a precursor for the synthesis of other chemotherapeutic agents like topotecan and irinotecan, which are FDA-approved drugs for treating various cancers, including ovarian, colorectal, and small cell lung cancer. Additionally, it is being studied for its potential in combination therapies to enhance efficacy and reduce drug resistance in oncology.