Abstract 1792: MAPK1 p.D321N mutation confers sensitive to erlotinib in head and neck squamous cell carcinoma (HNSCC)

The annual incidence of head and neck squamous cell carcinoma (HNSCC) is ~0.88 million worldwide (IARC, WHO 2018). Despite great success of precision medicine in major cancers such as lung cancer and breast cancers, there are limited precision therapies for HNSCC. We previously reported an HNSCC patient whose tumor harbored a somatic MAPK1 p.E322K mutation demonstrating exceptional clinical response to erlotinib, an EGFR inhibitor. Subsequent laboratory investigation confirmed the ability of MAPK1 p.E322K to hyperactivate EGFR, thus causing erlotinib sensitivity in HNSCC models, both in vitro and in vivo. Here, we sequenced 105 tumors from Hong Kong (HK) HNSCC patients by next-generation sequencing (NGS) on MAPK1 gene and we found a 5.71% rate (6/105 tumors) of MAPK1 somatic mutation in HK-HNSCC. This rate appears to be relatively higher than the 1.75% (9/521 tumors) rate in the US-TCGA HNSCC cohort (P=0.0288). Apart from the MAPK1 p.E322K mutation found in the US-TCGA HNSCC cohort, we identified novel MAPK1 p.R135K and p.D321N mutations in our HK cohort which were absent in the US TCGA HNSCC. Pan-cancer mapping of MAPK1 somatic mutations revealed that MAPK1 p.R135K and p.D321N mutations are also recurrent hotspot mutation in TCGA pan-cancers (32 cancer types). Strikingly, based on the X-ray crystallography of the human MAPK1 protein, R135 and D321 amino acid residues both reside on the same kinase interaction motif (KIM) domain as E322 (all are within a 13Å distance in 3D). Thus, we further investigated if MAPK1 p.R135K and p.D321N mutations might function similarly as MAPK1 p.E322K mutant in terms of their abilities to drive HNSCC growth, and erlotinib sensitivity in HNSCC models. We employed the same FaDu retroviral infection method to study these mutations as we did previously, and we found that MAPK1 p.D321N (P