Peptide‐drug conjugate designated for targeted delivery to HER2‐expressing cancer cells

Targeted therapy of the highest globally incident breast cancer shall resolve the issue of off‐target toxicity concurring with augmented killing of specific diseased cells. Thus, the goal of this study was to prepare a peptide‐drug conjugate targeting elevated expression of HER2 receptors in breast cancer. Towards this, the rL‐A9 peptide was conjugated with the chemotherapeutic drug doxorubicin (DOX) through a N ‐succinimidyl‐4‐( N ‐maleimidomethyl) cyclohexane‐1‐carboxylate (SMCC) linker. The synthesized peptide‐drug conjugate, rL‐A9‐DOX, was characterized by mass spectrometry. Molecular docking studies, based on binding energy data, suggested a stronger interaction of rL‐A9‐DOX with the HER2 receptor in comparison to the unconjugated peptide, rL‐A9. The cytotoxic effect of the rL‐A9‐DOX conjugate was observed to be higher in HER2‐positive SKOV3 cells compared to HER2‐negative MDA‐MB‐231 cells, indicating selective cell killing. Cellular internalization of the rL‐A9‐DOX conjugate was evident from the flow cytometry analysis, where a noticeable shift in mean fluorescent intensity (MFI) was observed for the conjugate compared to the control group. This data was further validated by confocal microscopy, where the fluorescent signal ascertained nuclear accumulation of rL‐A9‐DOX. The present studies highlight the promising potential of rL‐A9‐DOX for targeted delivery of the drug into a defined group of cancer cells.