Targeting Triple Negative Breast Cancer Cells with Novel Cytotoxic Peptide–Doxorubicin Conjugates

In this study, we have designed and synthesized two novel peptide-drug conjugates (PDCs) where the drug, doxorubicin (Dox), is linked to the peptide via a succinimidyl thioether bond or a hydrazone linker. A highly specific and proteolytically stable breast cancer cell targeting peptide (WxEAAYQrFL) is conjugated to Dox to synthesize peptide-Dox thioether (1) or hydrazone (2) conjugate. The evaluation of the stability in water, media, and human serum showed that the conjugate 1 with the succinimidyl thioether linkage is more stable compared to the acid-sensitive hydrazone containing conjugate 2. The cytotoxicity studies showed that the two PDCs were as toxic as free Dox toward the triple negative breast cancer (TNBC) cells and were 7-30 times less toxic (IC50 1.2-4.7 μM for TNBC cells versus 15-39 μM for noncancerous cells) toward the noncancerous breast cells compared to the free doxorubicin (IC50 0.35-1.5 μM for TNBC cells versus 0.24 μM for noncancerous cells). The results from the comparative study of the two PDCs suggest that both may have translational potential for TNBC treatment.