Design and application of hybrid cyclic-linear peptide-doxorubicin conjugates as a strategy to overcome doxorubicin resistance and toxicity

Doxorubicin (Dox) is used for breast cancer, leukemia, and lymphoma treatment as an effective chemotherapeutic agent. However, Dox use is restricted due to inherent and acquired resistance and an 8-fold increase in the risk of potentially fatal cardiotoxicity. Hybrid cyclic-linear peptide [R5K]W7A and linear peptide R5KW7A were conjugated with Dox through a glutarate linker to afford [R5K]W7A-Dox and R5KW7A-Dox conjugates to generate Dox derivatives. Alternatively, [R5K]W7C was conjugated with Dox via a disulfide linker to generate [R5K]W7C–S–S-Dox conjugate, where S–S is a disulfide bond. Comparative antiproliferative assays between conjugates [R5K]W7A-Dox, [R5K]W7C–S–S-Dox, linear R5KW7A-Dox, the corresponding physical mixtures of the peptides, and Dox were performed in normal and cancer cells. [R5K]W7A-Dox conjugate was 2-fold more efficient than R5KW7A-Dox, and [R5K]W7C–S–S-Dox conjugates in inhibiting the cell proliferation of human leukemia cells (CCRF-CEM). Therefore, hybrid cyclic-linear [R5K]W7A-Dox conjugate was selected for further studies and inhibited the cell viability of CCRF-CEM (84%), ovarian adenocarcinoma (SK-OV-3, 39%), and gastric carcinoma (AGS, 73%) at a concentration of 5 μM after 72 h of incubation, which was comparable to Dox (5 μM) efficacy (CCRF-CEM (85%), SK-OV-3 (33%), and AGS (87%)). While [R5K]W7A-Dox had a significant effect on the viability of cancer cells, it exhibited minimal cytotoxicity to normal kidney (LLC-PK1, 5–7%) and heart cells (H9C2,