Intrinsic differences in cisplatin sensitivity of head and neck cancer cell lines: Correlation to lysosomal pH

BACKGROUND: Cisplatin treatment is beneficial for approximately 20% of patients with head and neck squamous cell carcinoma (HNSCC). Tools to predict the clinical outcome and evaluate intrinsic cisplatin sensitivity are, therefore, required. METHODS: Cisplatin sensitivity, lysosomal pH, and cell death pathway was studied in 5 HNSCC lines and compared with normal oral keratinocytes. RESULTS: We identified a linear relationship between lysosomal pH and cisplatin sensitivity. Reduced lysosomal acidification was correlated to decreased expression of the V(0)V(1)-ATPase B2 subunit, which is part of the lysosomal acidifying complex. Cisplatin caused apoptosis accompanied by lysosomal membrane permeabilization, and inhibition of lysosomal proteases (cathepsins) partly prevented cell death. CONCLUSION: Cisplatin-induced apoptosis of HNSCC is more efficient in cell lines with low lysosomal pH and is mediated by the release of lysosomal content. Lysosomal pH and expression of V(0)V(1)-ATPase subunits are possible future markers of intrinsic cisplatin sensitivity.