Dual FGFR-targeting and pH-activable Smart Ruthenium-Peptide Conjugates for targeted therapy of Breast Cancer

Dysregulation of Fibroblast Growth Factor Receptors (FGFRs) signaling has been associated with breast cancer, yet employing FGFR-targeted delivery systems to improve cytotoxic agents is still sparsely exploited. Herein, we report four new bi-functional ruthenium-peptide conjugates (RuPCs) with FGFR-targeting and pH-dependent releasing abilities, envisioning the selective delivery of cytotoxic Ru complexes to FGFR(+)-breast cancer cells, upon specific accumulation and controlled activation at the acidic tumoral microenvironment. The antiproliferative potential of the RuPCs and active Ru complexes was evaluated in four breast cancer cell lines with different FGFR expression levels (SK-BR-3, MDA-MB-134-VI, MCF-7, and MDA-MB-231) and in the normal human dermal fibroblasts (HDF) cell line, at pH 6.8 and 7.4 that mimics the tumor microenvironment and normal tissues/bloodstream, respectively. The RuPCs showed higher cytotoxicity in cells with higher level of FGFR expression at acidic pH. Additionally, RuPCs showed up to 6-fold higher activity in the FGFR(+) breast cancer lines compared to the normal line. The release profile of Ru complexes from RuPCs corroborates the antiproliferative effects observed. Remarkably, the cytotoxicity and releasing ability of RuPCs were shown to be strongly dependent on the peptide conjugation position in the Ru complex. Complementary molecular dynamic simulations and computational calculations were performed to help interpret these findings at the molecular level. In summary, we identified a lead bi-functional RuPC that holds strong potential as a FGFR-targeted chemotherapeutic agent.