Mutant HRas Signaling and Rationale for Use of Farnesyltransferase Inhibitors in Head and Neck Squamous Cell Carcinoma

Epithelial‑derived head and neck squamous tumourigenesis (Review)

Head and neck squamous cell carcinomas (HNSCCs), a heterogeneous group of cancers that arise from the mucosal epithelia cells in the head and neck areas, present great challenges in diagnosis, treatment and prognosis due to their complex aetiology and various clinical manifestations. Several factors, including smoking, alcohol consumption, oncogenic genes, growth factors, Epstein‑Barr virus and human papillomavirus infections can contribute to HNSCC development. The unpredictable tumour microenvironment adds to the complexity of managing HNSCC. Despite significant advances in therapies, the prediction of outcome after treatment for patients with HNSCC remains poor, and the 5‑year overall survival rate is low due to late diagnosis. Early detection greatly increases the chances of successful treatment. The present review aimed to bring together the latest findings related to the molecular mechanisms of HNSCC carcinogenesis and progression. Comprehensive genomic, transcriptomic, metabolomic, microbiome and proteomic analyses allow researchers to identify important biological markers such as genetic alterations, gene expression signatures and protein markers that drive HNSCC tumours. These biomarkers associated with the stages of initiation, progression and metastasis of cancer are useful in the management of patients with cancer in order to improve their life expectancy and quality of life.

Inactivation of Ymr1, Sjl2/3 phosphatases promotes stress resistance and longevity in wild type and Ras2G19V yeast

In Saccharomyces cerevisiae, RAt Sarcoma (Ras) activity plays a central role in mediating the effect of glucose in decreasing stress resistance and longevity, with constitutive Ras activation mutations promoting cell growth and oncogenesis. Here, we used transposon mutagenesis in yeast to identify suppressors of the constitutively active Ras2G19V, orthologue of the KRASG12C mammalian oncogene. We identified mutations in Yeast Myotubularin Related (YMR1), SynaptoJanin-Like (SJL2) and SJL3 phosphatases, which target phosphatidylinositol phosphates, as the most potent suppressors of constitutive active Ras, able to reverse its effect on stress sensitization and sufficient to extend longevity. In sjl2 mutants, the staining of Ras-GTP switched from membrane-associated to a diffuse cytoplasmic staining, suggesting that it may block Ras activity by preventing its localization. Whereas expression of the Sjl2 PI 3,4,5 phosphatase mediated stress sensitization in both the Ras2G19V and wild type backgrounds, overexpression of the phosphatidylinositol 3 kinase VPS34 (Vacuolar Protein Sorting), promoted heat shock sensitization only in the Ras2G19V background, suggesting a complex relationship between different phosphatidylinositol and stress resistance. These results provide potential targets to inhibit the growth of cancer cells with constitutive Ras activity and link the glucose-dependent yeast pro-aging Ras signaling pathway to the well-established pro-aging PhosphoInositide 3-Kinase(PI3K) pathway in worms and other species raising the possibility that the conserved longevity effect of mutations in the PI3K-AKT (AK strain Transforming) pathway may involve inhibition of Ras signaling.

Multi-kinase compensation rescues EGFR knockout in a cell line model of head and neck squamous cell carcinoma

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is a debilitating disease with poor survival rates. While the epidermal growth factor receptor (EGFR)-targeting antibody Cetuximab is approved for treatment, responses are limited and the molecular mechanisms driving resistance remain incompletely understood.

METHODS

To better understand how cells survive without EGFR activity, we developed an EGFR knockout derivative of the UM-SCC-92 cell line using CRISPR/Cas9 technology. We then characterized changes to the transcriptome with RNAseq and changes in response to kinase inhibitors with resazurin cell viability assays. Finally, we tested if inhibitors with activity in the EGFR knockout model also had synergistic activity in combination with EGFR inhibitors in either wild type UM-SCC-92 cells or a known Cetuximab-resistant model.

RESULTS

Functional and molecular analysis showed that knockout cells had decreased cell proliferation, upregulation of FGFR1 expression, and an enhanced mesenchymal phenotype. In fact, expression of common EMT genes including VIM, SNAIL1, ZEB1 and TWIST1 were all upregulated in the EGFR knockout. Surprisingly, EGFR knockout cells were resistant to FGFR inhibitor monotherapies, but sensitive to combinations of FGFR and either XIAP or IGF-1R inhibitors. Accordingly, both wild type UM-SCC-92 and Cetuximab-resistant UM-SCC-104 cells with were sensitive to combined inhibition of EGFR, FGFR and either XIAP or IGF-1R.

CONCLUSIONS

These data offer insights into EGFR inhibitor resistance and show that resistance to EGFR knockout likely occurs through a complex network of kinases. Future studies of cetuximab-resistant HNSCC tumors are warranted to determine if this EMT phenotype and/or multi-kinase resistance is observed in patients.