A pegylated conjugate of SN-38 (7-ethyl-10-hydroxy-camptothecin), a biologically active metabolite of the prodrug irinotecan, with potential antineoplastic activity. Upon administration, the proprietary linker slowly releases SN-38 from the pegylated SN-38 conjugate PLX038. SN-38 binds to and inhibits topoisomerase I by stabilizing the cleavable complex between topoisomerase I and DNA, resulting in DNA breaks, inhibition of DNA replication, and apoptosis. Compared with irinotecan, this formulation allows higher accumulation in solid tumors due to its nanoparticle size and long half-life.