C. Subramanian1, T. M. Rajendiran2, T. Soni3, M. S. Cohen1 1University Of Michigan,General Surgery,Ann Arbor, MI, USA 2University Of Michigan,Pathology And Michigan Regional Metabolomics Resource Core,Ann Arbor, MI, USA 3University Of Michigan,Michigan Regional Metabolomics Resource Core,Ann Arbor, MI, USA
Introduction: Of the 60,000 HNSCC cases diagnosed annually in the US, 60% present with advanced stage III/IV disease requiring multimodality therapy yet five-year survival rates have not significantly changed in over three decades with a median survival of less than a year. It is therefore imperative to find better therapies for patients with advanced disease and one of the best routes is through identification of novel yet tumor-specific biomarkers from which the drugs can be designed. Since lipids play an important role in tumor development and progression of cancer and can be very specifically overproduced in several tumors, we hypothesized that lipid metabolic profiling of HNSCC is a unique untapped mechanism to identify novel therapeutic targets for HNSCC.
Methods: Mass spectrometry (LC/MS), based shotgun untargeted global lipidomic profiling was used to explore the lipid signatures which included 63 HNSCC patient tumors. Validated HNSCC cell lines UMSCC1,12, 22B and MDA1986 were also grown in 2D culture for tumor xenograft implantation for comparison. Phospholipase A2 activity was measured using the cPLA2 assay kit from Cayman as per the manufacturer’s protocol. UMSCC 22B xenografts were developed and the mice were treated i.p. with10 mg/ kg of cPLA2 inhibitor arachidonyl trifluoromethyl ketone (ATK) or vehicle for 15 days and the tumor volumes were measured.
Results: Unsupervised principal component analysis of the lipid signature showed a very distinct and clear separation between the benign and cancer tissues. A total of 576 lipids were identified of which 322 were significantly different between benign and cancer tissues (p<0.05). Evaluation of the top 40 significantly expressed lipids showed up regulation of free fatty acids (24:1, 24:2,24:3 and 22;3), phospholipids such as lysophosphotidyl choline (LPC) in cancer tissues compared to benign tissues whereas glycero lipids such as triglycerides (TG) were down regulated in cancer tissues. Since upregulation of LPC is catalyzed by PLA2, its activity was measured both in tumor samples as well as in HNSCC cell lines. Tumor samples showed 3.0 fold higher expression levels of cPLA2 compared to benign samples (p<0.01) whereas cell lines showed only 2.5 fold upregulation compared to control fibroblast cell lines (p<0.01). Treatment of HNSCC xenogaft with ATK resulted in significant (>90%) reduction in tumor volume compared to vehicle treatment groups (p<0.01). Animal weight and organs all showed no signs of toxicity with treatment.
Conclusion: Lipid profiling of HNSCC patient tumors identified up regulation of FFA and LPC indicating PLA2 as a potential therapeutic target for HNSCC. Blocking of cPLA2 activity using ATK resulted in significant growth reduction of HNSCC xenografts without any measured toxicity. This is a very exciting, novel, and highly translatable treatment option for HNSCC with high clinical potential that warrants further preclinical validation.