Abstract 4042: N-121, a novel polypeptide conjugate of SN-38, demonstrated enhanced intratumoral accumulation and sustained release of free SN-38 with potent antitumor activity

Abstract Introduction: SN-38 is a critical chemotherapeutic agent active against a variety of solid tumors including advanced colorectal cancer. Clinical use of SN-38 is hampered by its poor solubility in pharmaceutically acceptable solvents. Although irinotecan, the only approved prodrug of SN-38, is widely used, its efficacy is limited by low conversion to the active SN-38 as well as hematologic and gastrointestinal dose-limiting toxicities. In an attempt to improve the water solubility, antitumor activity and safety profiles of SN-38, we synthesized a water soluble polypeptide-SN-38 conjugate (N-121) and examined its antitumor activity and pharmacokinetics (PK) in mouse models. Methods: Antitumor activity and PK of SN-38, administered as N-121 or irinotecan, was evaluated following tail vein injection in male nude mice with subcutaneous orthotopic xenografts of the HCT116 human colon cancer. Mice received N-121 400 mgk (mg/kg) (32 mkg of eq. SN-38) or irinotecan 80 mgk once a week for 2 weeks and were followed for up to 46 days. Results: N-121 drastically improved by over 1000 fold the water solubility of SN-38. At a SN-38 equivalent dose of less than half of that of irinotecan, N-121 resulted in a much longer tumor growth delay (36 days) than irinotecan (14 days). The more durable tumor growth inhibition with N-121 was consistent with its enhanced intratumoral accumulation: intratumoral trough levels of SN-38 were about 250-fold higher than those observed in plasma, compared with only 15-fold with irinotecan. With N-121, Intratumoral levels of SN-38 remained stable over the PK observation period (48 h), contrasting to a marked decline in SN-38 levels with irinotecan; intratumoral trough levels of SN-38 from N-121 were about 50-fold higher than those achieved with irinotecan. N-121 was well tolerated with a slight weight loss of 7.2%. Conclusion: N-121, a novel water soluble polypeptide-SN-38 conjugate, exhibited enhanced and sustained intratumoral exposure of SN-38 with high antitumor activity in a mouse xenograft tumor model. These promising results warrant further evaluation of N-121. Note: This abstract was not presented at the meeting. Citation Format: Haojun Wang, Wei Li, Xiaojian Zhou, Liuyi Wan, Guanghui Wen. N-121, a novel polypeptide conjugate of SN-38, demonstrated enhanced intratumoral accumulation and sustained release of free SN-38 with potent antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4042. doi:10.1158/1538-7445.AM2017-4042