OSCC Lines Represent Multiple Molecular Subtypes With Different Drug Sensitivities

Objectives: Oral squamous cell carcinoma (OSCC) is the 8th most common cancer in adults and its 5-year survival rate of 60% has not improved in 4 decades. There is a critical need to understand OSCC from a molecular perspective to improve therapy and overall survival. Recent whole exome sequencing studies revealed several molecular features of OSCC including inactivating mutations in the Notch signaling pathway. It is not known if the Notch signaling pathway impacts drug sensitivity in OSCC. Our objectives are to determine whether OSCC cell lines exhibit differential sensitivity to clinically used anticancer drugs and whether these differences are related to Notch signaling.
Methods: The sensitivity of nine OSCC cells lines to six anticancer drugs representing DNA damaging agents, microtubule targeting agents, and tyrosine kinase inhibitors was evaluated using the sulforhodamine B assay. Whole cell lysates were prepared for each cell line to determine relative expression of proteins involved in Notch signaling. All experiments incorporated vehicle controls and were performed in triplicate.
Results: Significant differences in drug sensitivity were identified among the OSCC cell lines, with several groups of cell lines sharing sensitivities across drug classes. While it has been suggested that drug sensitivity is due to proliferation rate, this was not the case as differences in drug sensitivity did not correlate with the doubling time of the cell lines. Significant differences in the expression of many key proteins including EGFR, Src, Notch receptors and Notch target gene products were seen among the cell lines. Surprisingly, groups of cell lines with comparable drug class sensitivities tended to express similar levels of Notch pathway components.
Conclusions: Differences in Notch signaling may underlie differential sensitivity of OSCC to anticancer agents. This result implicates the Notch signaling pathway as a basis for molecular subtypes in OSCC.