Fabrication of size-controlled SN-38 pure drug nanocrystals through an ultrasound-assisted reprecipitation method toward efficient drug delivery for cancer treatment

•We fabricated pure drug nanocrystals, composed of almost 100% of SN-38 molecules.•Ultrasound-assisted reprecipitation method was used as fabrication technic.•Rod-like SN-38 nanocrystals with ca. 150 nm in a long axis were obtained.•SN-38 nanocrystals exhibited a potent cytostatic activity against cancer cells. Carrier-free drug nanoparticles are a promising drug delivery system for cancer therapy; however, the fabrication of nanoparticles composed of small molecule drugs is challenging. In this study, we fabricated pure drug nanocrystals, with nearly 100% of 7-ethyl-10-hydroxycamptothecin (SN-38) molecules, by using the ultrasound-assisted reprecipitation method. The rod-like nanocrystals with ca. 150 nm in a long axis were obtained through the ultrasound-assisted reprecipitation method, and the nanofibers were obtained without irradiation. Furthermore, the SN-38 nanocrystals exhibited considerably higher cytostatic activity against cancer cells than irinotecan hydrochloride, which is a clinically used prodrug of SN-38. These results demonstrate the potential of the ultrasound-assisted precipitation method as a powerful process to fabricate nanoparticles assembled using only small molecule drugs.