Development of Novel Peptide-Doxorubicin Conjugates for Targeting Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive and difficult to treat subtype of breast cancer. Chemotherapy is an active treatment option in combination with other treatments; however, the side effects limit the effective therapeutic dose. To selectively target the cancer cells, I have synthesized three peptide-drug conjugates (PDCs) to specifically target the TNBC cells. The first PDC contains peptide 18-4 with an additional cysteine in the N-terminal (NH2- CWxEAAYQrFL-CONH2) linked to aldoxorubicin (Aldox), a modified version of a common chemotherapy drug doxorubicin (Dox). The cytotoxicity of the PDC and free Dox (positive control) were assessed against MDA-MB-231, MDA-MB-468, and MCF-10A cells using MTT assay. The PDC showed similar toxicity as free Dox towards the TNBC cell lines and was less toxic towards the normal cells. The in vivo efficacy experiments and pharmacokinetics studies with PDC were completed using MDA-MB-231 subcutaneous xenograft in NOD-SCID mice. The mice treated with PDC had lower tumor volume and showed better body weight maintenance and stable overall health compared to the mice treated with Dox. The PDC increased the total drug (PDC and Dox metabolized from PDC) circulation time compared to free Dox. The Dox metabolized from the PDC accumulated in the tumor more than free Dox, thus increasing the therapeutic efficacy of Dox for the treatment of TNBC. This PDC is expected to bind to keratin 1 (K1); therefore, K1 overexpression on the cell surface of a TNBC cell line, MDA-MB-436 compared to a normal breast cell line, MCF-10A was assessed by VII immunohistochemistry which showed the higher cell-surface expression of K1 in MDA-MB-436 cells. The second and third PDCs in this study were synthesized using a cyclic peptide (NH2- NVIKHWYGYTPE-COOH) that targets overexpressed EGFR in TNBC cells. The cyclic peptide was synthesized and linked to Dox via a hydrazone bond to give cyPDC1 and succinimidyl thioether linker to give cyPDC2. The cyPDC1 was synthesized by linking the cyclic peptide to Aldox and cyPDC2 was synthesized by linking the cyclic peptide to Dox using an SMCC linker. In vitro stability, toxicity assay, and in vivo studies will be done with the cyPDC2 in future studies