A Glutathione-Responsive L-Carnitine-Modified Camptothecin Oral Nano-Prodrug for Cancer Therapy

Abstract

Glutathione (GSH)-responsive disulfide bonds have been widely utilized in the design of anti-cancer prodrugs with controlled release capabilities. In this study, we developed a simple amphiphilic camptothecin (CPT) prodrug, Lc-ss-CPT, by conjugating the hydrophobic CPT with the hydrophilic molecule L-carnitine (Lc) via a cleavable disulfide carbonate linker. The prodrugs could self-assemble into spherical nanoparticles (Lc-ss-CPT NPs) in aqueous solution. Leveraging the specific affinity between L-carnitine and organic cation transporter 2 (OCTN2), which is overexpressed on intestinal epithelial cell membranes, Lc-ss-CPT NPs demonstrated enhanced intestinal absorption. These nanoparticles were efficiently transported into the bloodstream through transcytosis, facilitated by the Golgi apparatus and endoplasmic reticulum, enabling tumor accumulation. The zwitterionic nature of L-carnitine conferred Lc-ss-CPT NPs with excellent high nonfouling behavior to proteins and high stability in systemic circulation, resulting in improved pharmacokinetics and significantly higher oral bioavailability compared to free CPT. Upon entering cancer cells via endocytosis, Lc-ss-CPT NPs released CPT in response to intracellular GSH. Also, this process triggered the depletion of intracellular GSH, leading to elevated levels of reactive oxygen species (ROS). The synergistic effect of CPT-mediated topoisomerase I (Topo I) inhibition and ROS overproduction induced G2/M cell cycle arrest, apoptosis, and potent cancer cell-specific cytotoxicity. Orally administered Lc-ss-CPT NPs effectively inhibited the growth of MC38 tumors while exhibiting minimal systemic toxicity. This study demonstrates the potential of Lc-ss-CPT NPs as a promising oral nanoprodrug for targeted and efficient anti-cancer therapy.

Note:
Funding declaration:  The work was supported by National Natural Science Foundation of China (No. 22101002), Shandong Provincial Natural Science Foundations (No. ZR2021LSW001, ZR2015BM024), Research Foundation of Liaocheng University (No. 318012026), and the Ministry of Education industry-School Cooperative Education Project (Grant No. 220605042200513).

Conflict of Interests:  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethical Approval:  All animal experiments were conducted in strict compliance with the Guidelines for Animal Experimentation of Liaocheng University, and the experimental protocol was approved by the Institutional Animal Ethics Committee.

Keywords: Camptothecin, L-carnitien, Oral nano-prodrug, GSH depletion, Targeted anti-cancer