Genomic analyses of squamous cell carcinoma (SCC) have yet to yield significant strategies against pathway activation to improve treatment. Platinum-based chemotherapy remains the mainstay of treatment for SCC of different histotypes either as a single-agent or alongside other chemotherapeutic drugs or radiotherapy; however, resistance inevitably emerges, which limits the duration of treatment response. To elucidate mechanisms that mediate resistance to cisplatin, we compared drug-induced perturbations to gene and protein expression between cisplatinsensitive and -resistant SCC cells, and identified MAPK-ERK pathway upregulation and activation in drug-resistant cells.

Oncogenesis in non-small cell lung cancer (NSCLC) is regulated by a complex signal transduction network. Single-agent targeted therapy fails frequently due to treatment insensitivity and acquired resistance. In this study, we demonstrate that co-inhibition of the MAPK and SRC pathways using a PD0325901 and Saracatinib kinase inhibitor combination can abrogate tumor growth in NSCLC. PD0325901/Saracatinib at 0.25:1 combination was screened against a panel of 28 NSCLC cell lines and 68% of cell lines were found to be sensitive (IC50 < 2 μM) to this combination. In Snail1 positive NSCLC lines, the drug combination complementarily enhanced mesenchymal-epithelial transition (MET), increasing both E-cadherin and Plakoglobin expression, and reducing Snail1, FAK and PXN expression. In addition, the drug combination abrogated cell migration and matrigel invasion. The co-inhibition of MAPK and SRC induced strong G1/G0 cell cycle arrest in the NSCLC lines, inhibited anchorage independent growth and delayed tumor growth in H460 and H358 mouse xenografts. These data provide rationale for further investigating the combination of MAPK and SRC pathway inhibitors in advanced stage NSCLC.

There have been advances in personalized therapy directed by molecular profiles in lung adenocarcinoma, but not in lung squamous cell carcinoma (SCC). The lack of actionable driver oncogenes in SCC has restricted the use of small‐molecule inhibitors. Here, we show that SCC cell lines displayed differential sensitivities to belinostat, a pan‐histone deacetylase inhibitor. Phosphoproteomic analysis of belinostat‐treated SCC cells revealed significant downregulation of the MAPK pathway, along with the induction of apoptosis. In cisplatin‐resistant cells that demonstrated aberrant MAPK activation, combined treatment with belinostat significantly inhibited cisplatin‐induced ERK phosphorylation and exhibited strong synergistic cytotoxicity. Furthermore, belinostat transcriptionally upregulated the F‐box proteins FBXO3 and FBXW10, which directly targeted son of sevenless (SOS), an upstream regulator of the MAPK pathway, for proteasome‐mediated degradation. Supporting this, suppression of SOS/ERK pathway by belinostat could be abrogated by inhibiting proteasomal activity either with bortezomib or with siRNA knockdown of FBXO3/FBXW10. Taken together, these preclinical data offer a novel understanding of the epigenetic mechanism by which belinostat exerts its cytotoxicity and supports the combination with cisplatin in clinical settings for chemorefractory SCC tumors.

<p>MEK inhibition triggers G1 arrest, while cisplatin induced S-phase arrest, in lung SCC cells.</p>

<p>Effects of cisplatin treatment on levels of phosphorylated kinases are assessed in H596 and Calu-1 cells.</p>

<p>Cisplatin-resistant H596 sustained activation of p-ERK after cisplatin treatment.</p>

<p>Cisplatin resistance in head and neck squamous cell carcinoma (HNSCC) cells is associated with activation of MAPK/ERK pathway.</p>

<p>Cisplatin inhibits colony formation of lung squamous cell carcinoma (SCC) cells.</p>