Notch and Hedgehog Signalling Axis Drive Senescence in HER2-Positive Breast Cancer Resistant to Trastuzumab

Objective: Cellular senescence halts the proliferation of damaged or preneoplastic cells, playing a vital role in cancer control. In HER2-positive breast cancer, resistance to trastuzumab, a HER2-targeted monoclonal antibody, remains a significant obstacle. Although the trastuzumab and cilengitide combination reduces stemness and epithelial-mesenchymal transition, its effect on senescence remains unclear. Additionally, inhibiting the Notch and Hedgehog pathways can induce senescence by impairing proliferation, stemness, and cell cycle progression, making them promising therapeutic targets. This study aimed to evaluate the effect of trastuzumab/cilengitide on cellular senescence in HER2-positive trastuzumab-resistant breast cancer cells and to elucidate the roles of Notch and Hedgehog signalling in this process.Materials and Methods:: HER2-positive breast cancer cell lines HCC1954 and SKBR3, along with their trastuzumab-resistant variants, were treated with trastuzumab, cilengitide, or both. Senescence markers were assessed by real-time PCR. Notch and Hedgehog pathway activity was evaluated, with additional experiments using specific inhibitors Fli06 (Notch) and GANT61 (Hedgehog).Results: The trastuzumab-cilengitide combination significantly upregulated senescence markers relative to monotherapy. This response was associated with a marked decrease in Notch and Hedgehog pathway activity. Further combined inhibition of these pathways enhanced senescence marker expression, underscoring their involvement in drug-induced senescence. Conclusion: The trastuzumab-cilengitide combination induces senescence in trastuzumab-resistant HER2-positive breast cancer cells, potentially through Notch and Hedgehog inhibition. These findings support targeting senescence pathways as a novel strategy to overcome trastuzumab resistance and improve therapeutic outcomes. Further research is warranted to assess the clinical potential of such combination therapies.