STEALTH liposomal CKD-602, a topoisomerase I inhibitor, improves the therapeutic index in human tumor xenograft models.

BACKGROUND CKD-602, a topoisomerase I inhibitor, has antitumor activity in a broad spectrum of tumor types. STEALTH liposomal CKD-602 (S-CKD602) prolongs circulation of CKD-602 in plasma, increases drug exposure in tumors and improves efficacy compared with free drug. MATERIALS AND METHODS Different dosing regimens of S-CKD602, free CKD-602 and topotecan were compared for antitumor activity in female athymic nude mice bearing human A375 melanoma, ES-2 ovarian, H82 SCLC or HT-29 colon tumor xenografts. RESULTS S-CKD602 was more efficacious than free drug in all tumor types studied. The therapeutic index (TI) of S-CKD602 was estimated to be approximately 6-fold greater than that of free CKD-602 in ES-2 and approximately 3-fold greater in H82 tumors. TI of S-CKD602 was approximately 2-fold greater than that of free CKD-602 and approximately 5-fold greater than that of topotecan in A375, and > or = 3-fold greater in HT-29 tumors. In A375 tumors, once-weekly dosing of S-CKD602 was superior to once every 2 weeks or twice weekly schedules. CONCLUSION The therapeutic index of S-CKD602 was greater than that of free CKD-602 and topotecan in several human tumor types.