Abstract 4095: Paradoxical activation of the RAF-MEK-ERK pathway in response to nilotinib induces synthetic lethality with MEK inhibition in head and neck cancer cells.
Authors: Sen Banibrata , Mazumdar Tuhina , Peng Shaohua , Hale Katherine S. , Glisson Bonnie S. , Johnson Faye M. 
Published: August 2014

Abstract
Cancers of the head and neck are difficult to treat because both the therapy and the tumor impact essential functions such as speech and swallowing and they can significantly alter facial appearance. The RAS/RAF/MEK/ERK cascade is one of the major signaling pathways that leads to head and neck squamous cell carcinoma (HNSCC) cell survival. There are three RAS genes (HRAS, KRAS, and NRAS) and together, they are mutated in about 30% of human cancers. RAS can also be activated by upstream signaling. Paradoxically RAF inhibition induces RAF-dimerization and causes subsequent activation of MEK/ERK pathway in presence of activated RAS in melanoma. Similarly the ABL inhibitor nilotinib acts as weak inhibitor of RAF kinase and also induces RAF-dimerization and subsequent activation of MEK/ERK in the presence of activated RAS in leukemia and pancreatic cancer cells. Nilotinib synergizes with MEK inhibitition to kill nilotinib-resistant leukemia cells (Abl T351I). We hypothesized that nilotinib and the MEK inhibitor MEK162 would be synergistic in HNSCC due to the frequent activation of RAS via upstream growth factor receptors. RAS mutations are relatively uncommon in HNSCC. We screened 60 validated HNSCC cell lines through sequenome analysis and we found three HNSCC cell lines with activating HRAS mutations (G12D and Q61L) [∼5%]. We found that nilotinib induces significant RAF dimerization and subsequent activation of MEK-ERK pathway irrespective of RAS mutational status. We next investigated how paradoxical MEK/ERK pathway activation affected the growth of HNSCC cells. In this context we treated a panel of HNSCC cell lines harboring WT and mutated HRAS with nilotinib and MEK162. Nilotinib alone had nearly no effect on cell viability and MEK162 had a moderate effect on some HNSCC lines. The combination of nilotinib and MEK162 synergized to inhibit the growth of HNSCC cells independent of RAS mutational status. The drug combination led to an accumulation of cells in G1 and a significant reduction in cell proliferation as measured with BrDU incorporation and colony formation. HNSCC cells with mutant HRAS undergo apoptosis in presence of both the drugs. In contrast none of these drugs induce senescence in HNSCC cell lines. Here we show that in HNSCC, nilotinib as single agent drives the paradoxical activation of RAF-MEK-ERK pathway in RAS mutation-independent manner and we uncovered a synthetic lethal pathway that can be used treat HNSCC. Animal studies are planned.
This work was supported by University of Texas SPORE in Head and Neck Cancer P50 CA097007.
Citation Format: Banibrata Sen, Tuhina Mazumdar, Shaohua Peng, Katherine S. Hale, Bonnie S. Glisson, Faye M. Johnson. Paradoxical activation of the RAF-MEK-ERK pathway in response to nilotinib induces synthetic lethality with MEK inhibition in head and neck cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4095. doi:10.1158/1538-7445.AM2013-4095