Reduction-Responsive RGD-Docetaxel Conjugate: Synthesis, In Vitro Drug Release and In Vitro Antitumor Activity

Poor selectivity to tumor cells is a major drawback in the clinical application of the antitumor drug docetaxel (DTX). Peptide-drug conjugates (PDCs) constructed by modifying antitumor drugs with peptide ligands that have high affinity to certain overexpressed receptors in tumor cells are increasingly assessed for their possibility of tumor-selective drug delivery. In the present research, DTX is condensed with 3-(pyridin-2-yldisulfanyl) propanoic acid via ester bond to obtain the intermediate Py-SS-DTX. Two conjugates GSS-DTX and RGDC-SS-DTX were obtained by conjugation of Py-SS-DTX with glutathione (GSH) and RGDC peptide through a thiol-disulfide exchange reaction. Afterwards, these two peptide-DTX conjugates were characterized by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and high-resolution mass spectrometry. The GSS-DTX and RGDC-SS-DTX were further evaluated in terms of drug release, cell cycle inhibition, cell apoptosis, and cytotoxicity. The results show that both the GSS-DTX and RGDC-SS-DTX exhibit reduction-responsive drug release and RGDC-SS-DTX exhibit higher reduction-responsiveness. The in vitro antitumor activity study shows that RGDC-SS-DTX exhibits enhanced G2/M phase arrest, cell apoptosis rate, and cytotoxicity as compared to GSS-DTX and free DTX. Besides, RGDC-SS-DTX shows reduced cytotoxicity on normal cells as compared to free DTX. The RGDC-SS-DTX synthesized in this study represents a novel DTX conjugate to effectively and selectively inhibit tumor cells.