Targeting tyrosine phosphatase SHP2 in oral cancers
Authors: Pandruvada Subramanya , Still Merrell , Goertzen Jack , Kelly Abigail , Neville Brad , Huja Sarandeep , Ogretmen Besim , Day Terrence 
Published: April 2020

Head and neck squamous cell carcinomas (HNSCC) are the sixth most common cancer worldwide and account for approximately 65,000 new diagnoses and 35,000 cancer‐related deaths every year in US alone. A range of cancer cell autonomous cues and tumour microenvironment factors account for the heterogeneous responses and failures often encountered during therapies. Recent studies have implicated the presence of tumour infiltrating immune cells as independent prognostic markers in HNSCC. However, it remains unclear how cancer‐cell‐signalling regulates tumour immunogenicity and immune cell infiltration. Aberrant levels of protein tyrosine phosphatase SHP2 have shown to play a role in tumorigenesis of several cancers including HNSCC. While studies indicate PI3K/AKT activation together with frequent alterations in tumour suppressor PTEN are causative factors of tumorigenesis, we hypothesized that SHP‐2/PI3K axis plays a role in dictating cancer‐cell‐secretome and tumour development. Further, we show that decreased PTEN expression displayed activated AKT and PI3K 110alpha catalytic subunit (PIK3CA) which were dependent on SHP2 activation status in HNSCC cell lines. Expressing SHP2C459S mutation (dead phosphatase) restored PTEN expression while inhibiting PI3K‐AKT signaling in specific PTENlow HNSCC cell lines suggesting a potential link between these players. Interestingly, in comparison to SHP2WT or SHP2E76Q mutant (constitutively active mutation), expression of SHP2C459S mutation as well as allosteric SHP2 inhibitor SHP099 treatment have shown a decreased cancer cell migration and matrigel invasion with no effect on cell viability. Furthermore, cell culture‐conditioned media (CM) obtained from SHP2‐modulated HNSCC cell lines presented a distinct and selective immune cell chemoattraction in vitro with increased CD8+T cells while limiting monocyte/macrophage migration suggesting altered secretome composition following SHP2 inhibition and a probable anti‐tumour response. In addition, we observed decreased cancer cell invasion and migration following SHP2 knockdown using shRNA, endorsing altered secretome following SHP‐2 inhibition. Cell culture‐conditioned media analysis conducted using antibody arrays and mass spectrometry further confirmed the altered secretome. These findings led us to conclude that SHP2‐dependent downstream pathways drive oral cancer tumorigenesis with a distinct secretome. Validation of these findings using enzymatically inactive or constitutively active SHP2 mutants in vivo on the outcome of modulating the PI3K/PTEN signalling and immune cell infiltration in humanized mice with HNSCC xenografts are studies in progress. Our findings support that SHP‐2/PI3K axis inhibition strategies may have therapeutic potential in inhibiting tumorigenesis in HNSCC patients.

Support or Funding Information

Supported in part by pilot research funding from an American Cancer Society Institutional Research Grant awarded to the Hollings Cancer Center, Medical University of South Carolina and Faculty Startup research funds from College of Dental Medicine.