Development of a Novel ω‐6 Polyunsaturated Fatty Acid Based Treatment Strategy for Non‐Melanoma Skin Cancer by Inhibiting Delta‐5‐Desaturase

Abstract

BackgroundCyclooxygenase‐2 (COX‐2) overexpression has been considered as one of the culprits for cancer progression, due to precancerous prostaglandin production from downstream ω‐6 polyunsaturated fatty acid (PUFA), arachidonic acid (AA), in the majority of the cancers including, Nonmelanoma skin cancer (NMSC). However, COX‐2 inhibitors have failed to provide protection against cancer in clinics. As per the recent studies from our lab, manipulation of ω‐6 PUFA metabolism by genetically inhibiting delta‐5‐desaturase (D5D), requires for metabolism of an upstream ω‐6 PUFA, dihomo gamma‐linolenic acid (DGLA), to AA, results in accumulation of DGLA which undergo peroxidation by COX‐2 to produce an anti‐cancer product, 8‐Hydroxyoctanoic acid (8‐HOA) in pancreatic and colon cancer model. However, this approach was associated with limitations, such as the degradation of D5D siRNA by endonuclease and the inability to cross the cell membrane. Hence in order to overcome the limitation and to get a sustained production of 8‐HOA inside the tumor, we developed a novel D5D inhibitor (D5Di) and hypothesized that D5Di could stimulate 8‐HOA production, which exerts anti‐cancer activity in NMSC.MethodsIn vitro studies like colony formation assay for proliferation analysis and PI Annexin V double staining assay for apoptosis analysis using A431 cell line and in vivo studies using xenograft mouse model evaluating the protective effect of D5Di against NMSC were performed. In order to dissect the molecular pathway, Western blot analysis, and immunohistochemistry studies were performed.ResultsD5Di treatment in the presence of DGLA resulted in a significant increase in apoptosis by 14.23±1.01% and reduction in survival fraction by 29.91±0.70%. Similar to the in vitro study, treatment with D5Di in animals receiving the DGLA supplement displayed a significant reduction in tumor size. The reduction in tumor size was due to a significantly high level of 8‐HOA (1.32±0.122μM) and a low PGE2/PGE1 ratio. In addition, an increase in cleaved PARP and reduction in Ki‐67 were observed by immunohistochemistry, which were indicating inhibitory effect of D5Di on tumor growth. Moreover, treatment with D5Di also caused downregulation of anti‐apoptotic factors such as procaspase‐3, procaspase‐9, and increased DNA damage marker, γH2Ax, both in vitro and in vivo.ConclusionThese results concluded that the novel strategy of providing D5Di with DGLA could be a new therapeutic approach for advanced and high‐risk NMSC.Support or Funding InformationThis research work is supported by NIH R15CA195499.