CDK4/6 inhibitors promote senescence-associated lysosomal alterations and enhance sensitivity to lysosomotropic agents in breast cancer

Breast cancer remains a leading cause of mortality globally, emphasizing the need to develop more effective and well-tolerated treatments. Pharmacological inhibitors of Cyclin-Dependent Kinases (CDK) 4 and 6 (CDK4/6i) can inhibit breast cancer growth by inducing a senescent-like state. However, long-term treatment efficacy remains hindered by the development of drug resistance and restoration of cell proliferation. Thus, clearance of senescent-like cancer cells may extend the durability of treatment. In this study, we showed that CDK4/6i-treated breast cancer cells exhibit various senescence-associated phenotypes that remain insensitive to common senolytic compounds. By searching for novel vulnerabilities, we identified a significantly increased lysosomal mass and altered lysosomal structure across various breast cancer cell types upon exposure to CDK4/6i in preclinical systems and clinical specimens. We demonstrated that these lysosomal alterations render breast cancer cells sensitive to lysosomotropic agents, such as L-leucyl-L-leucine methyl ester (LLOMe) and salinomycin. Importantly, sequential treatment with CDK4/6i/lysosomotropic agents effectively reduced the growth of both Hormone Receptor-positive (HR+) and triple-negative breast cancer (TNBC) cells in vivo . This sequential therapeutic strategy offers a promising approach to eliminate CDK4/6i-induced senescent(-like) cells, potentially reducing tumor recurrence and enhancing the overall efficacy of breast cancer therapy.