Metformin sensitizes non-small cell lung cancer to CDK4/6 inhibitor treatment by reducing lysosomal trapping

The hyperactivation of cyclin D1-CDK4/6 signaling is correlated with tumour metastasis and poor prognosis in patients with non-small cell lung cancer (NSCLC), suggesting the therapeutic potential of targeting CDK4/6 to treat NSCLC. Our preliminary data indicate CDK4/6 inhibitors are sequestered in lysosomes in NSCLC cells, a phenomenon that is termed lysosomal trapping and is associated with intrinsic drug resistance. It is promising to search for new compounds that could be co-administered with CDK4/6 inhibitors to reduce lysosomal trapping, thereby enhancing the sensitivity of NSCLC cells. Here, we find that metformin reduces the activity of the lysosomal pathway through genome-wide analyses; consistently, metformin reduces lysosomal trapping of CDK4/6 inhibitors in NSCLC cells. Biologically, metformin enhances the suppressive effects of CDK4/6 inhibitors on cell cycle progression, cell proliferation, and colony formation. Mechanistically, metformin suppresses lysosomal trapping by: (i) reducing translocation of TFEB into nuclei that leads to decreased lysosome biogenesis and (ii) disrupting lysosomal acidic environment through reduced V-ATPase activity and decreased interaction between LAMP1/LAMP2 and TMEM175. Clinically, combined treatment with metformin and CDK4/6 inhibitors decreased the growth of mouse xenografts and tumour cell organoids. In conclusion, our study provides a new mechanism for utilizing metformin to treat NSCLC by reducing lysosomal trapping, thereby increasing cellular sensitivity to CDK4/6 inhibitors.