In vitro evaluation of novel SN-38 prodrug activated by α-rhamnosidase of exogenous enzyme

This study introduces the α-rhamnose (Rham)-conjugated prodrug of SN-38 (Rham-SN-38) as a promising alternative to irinotecan. α-rhamnosidase, responsible for SN-38 release from Rham-SN-38, does not express in human cells, minimizing individual variability and side effects. The injection of the α-rhamnosidase into the tumor tissues makes it possible, for the first time, to activate the Rham-SN-38. Furthermore, α-rhamnosidase demonstrates significantly higher activity than carboxylesterase, the specific enzyme activating irinotecan. SN-38 release mediated by α-rhamnosidase completes within 2 h, with a k_cat/K_m value approximately 5.0 × 10⁴-fold higher than that of irinotecan. The 50% inhibition concentration (IC₅₀) of Rham-SN-38 against three types of cancer cells and one normal cell exceeds 4.5 × 10³ nM. The addition of α-rhamnosidase significantly increases cytotoxicity, with IC₅₀ comparable to free SN-38. The QIC₅₀, an index reflecting the difference in cytotoxicity with and without α-rhamnosidase, exceeds approximately 1.0 × 10²-fold. Rham-SN-38, synthesized in this study, demonstrates significant potential as a prodrug for cancer therapy.