Aspirin attenuates melanoma tumor growth via PGF2α‐SOX‐2 dependent pathways

Abstract

IntroductionExposure to pro‐oxidative stressors including cancer therapies via its ability to generate reactive oxygen species (ROS) produce potent oxidized lipid mediator, platelet‐activating factor (PAF) and PAF‐like agonists. We have shown that these PAF‐agonists significantly: 1) augmented the growth of subcutaneously implanted murine B16F10 melanoma tumors in a PAF‐receptor (PAF‐R) dependent manner; 2) impeded the efficacy of cancer chemotherapeutic agents and radiation therapy in murine melanoma models and; 3) detected in the perfusates and tumors collected from chemotherapy and radiation therapy‐treated melanoma and non‐melanoma cancer patients. As melanoma tumors often acquire resistance to the known chemotherapy, radiation therapy and even novel targeted therapeutic regimens, it is necessary to investigate an alternative approach for its intervention. Aspirin (ASN) has classically been used as an anti‐inflammatory drug and also possesses anti‐cancer activity in‐part via its ability to inhibit enzyme cyclooxygenases. While anti‐carcinogenic activity of ASN has been shown in other cancers, little is known about its effects in melanoma.ObjectivesThe current studies were sought to investigate the mechanism and test the hypothesis if ASN‐mediated anti‐melanoma activity is via inhibition of PAF‐R activation.MethodologyCell proliferation and survival assay, apoptosis by caspase 3/7 luminescence assay, immunoblotting, gene array, quantitative real time PCR and flow cytometry studies were performed. These assays were conducted in stably PAF‐R‐expressing (B16‐PAFR) and deficient melanoma (B16‐MSCV) cells and C57BL/6‐wild‐type (WT) and PAF‐R knockout (PAFR−/−) mice.Results and DiscussionWe demonstrate that ASN inhibits the survival of B16‐PAFR and B16‐MSCV cells at similar rates in a time and dose dependent manner via inducing apoptosis as measured increased caspase 3/7 activity. These ASN‐mediated effects were blocked by PGF2α addition but not by PGE2. Importantly, ASN‐mediated significant suppression of murine B16‐PAFR and B16‐MSCV melanoma tumor growth was independent to both cellular and stromal PAF‐R expression. Moreover, gene array analysis of melanoma tumors revealed an inhibition of SOX‐2 oncogene by ASN. Furthermore, PGF2α add back upregulated SOX‐2 and rescued melanoma cells from ASN‐mediated inhibition of cell survival and induction of apoptosis.ConclusionASN targets PGF2α and downstream SOX‐2 to inhibit melanoma tumor growth in a PAF‐R independent pathway and provide the rationale for its implication as a novel melanoma therapy.Support or Funding InformationNIH K22 ES023850 and WSU‐RIF 190002