We investigated whether platelets prime colon cancer cells for metastasis and whether pharmacological inhibition of platelet function may prevent it. Coculturing HT29 human colon carcinoma cells with human platelets led to the induction of mesenchymal-like cancer cells characterized by downregulation of E-cadherin and upregulation of Twist1, enhanced cell mobility and a proaggregatory action on platelets. These changes were prevented by different antiplatelet agents, aspirin[an inhibitor of cyclooxygenase(COX)-1], DG-041[an antagonist of prostaglandin(PG)E2 EP3 receptor] and ticagrelor (a P2Y12 receptor antagonist). The injection of HT29 cells, exposed to platelets in vitro, into the tail vein of humanized immunodeficient mice led to higher incidence of lung metastasis compared to the injection of untreated HT29 cells. This effect was associated with enhanced systemic biosynthesis of thromboxane(TX)A2 and PGE2 in vivo. Platelet COX-1 inhibition by aspirin administration to mice prevented the increased rate of metastasis as well as the enhanced production of TXA2 and PGE2 induced by the in vitro priming of HT29 cells by platelets. In conclusion, targeting platelet COX-1 with low-dose aspirin exerts an antimetastatic action by averting the stem cell mimicry of cancer cells associated with enhanced proaggregatory effects induced by platelet-tumor cell interactions. These effects may be shared by other antiplatelet drugs.

Aspirin taken for several years at doses of at least 75 mg daily reduced long-term incidence and mortality due to colorectal cancer. The finding of aspirin benefit at low-doses given once daily, used for cardioprevention, locates the antiplatelet effect of aspirin at the center of its antitumor efficacy. In fact, at low-doses, aspirin acts mainly by an irreversible inactivation of platelet cyclooxygenase (COX)-1 in the presystemic circulation, which translates into a long-lasting inhibition of platelet function. Given the short half-life of aspirin in the human circulation(approximately 20 min) and the capacity of nucleated cells to resynthesize the acetylated COX-isozyme(s), it seems unlikely that a nucleated cell could be the target of aspirin chemoprevention. These findings convincingly suggest that colorectal cancer and atherothrombosis may share a common mechanism of disease, i.e. platelet activation in response to epithelial(in tumorigenesis) and endothelial(in tumorigenesis and atherothrombosis) injury. Activated platelets may also enhance the metastatic potential of cancer cells (through a direct interaction and/or the release of soluble mediators or exosomes) at least in part by inducing the overexpression of COX-2. COX-independent mechanisms of aspirin, such as the inhibition of NF-kB signaling and Wnt/β-catenin signaling and the acetylation of extra-COX proteins, have been suggested to play a role in its chemopreventive effects. However, their relevance remains to be demonstrated in vivo at clinical doses.

No abstract

Conventional medical treatment for rheumatoid arthritis and osteoarthritis includes the use of NSAIDs (traditional and selective inhibitors of cyclooxygenase [COX]-2), because they provide unmistakable and significant health benefits in the treatment of pain and inflammation. However, they are associated with an increased risk of serious gastrointestinal (GI) and cardiovascular (CV) adverse events. Both beneficial and adverse effects are due to the same mechanism of action, which is inhibition of COX-dependent prostanoids. Since CV and GI risk are related to drug exposure, a reduction in the administered dose is recommended. However, this strategy will not eliminate the hazard owing to a possible contribution of individual genetic background. Further studies will be necessary to develop genetic and/or biochemical markers predictive of the CV and GI risk of NSAIDs.

Non-steroidal anti-inflammatory drugs (NSAIDs) are a chemically heterogeneous group of compounds that provide unmistakable and significant health benefits in the treatment of pain and inflammation. They include traditional NSAIDs (tNSAIDs), which act by inhibiting both cyclooxygenase (COX)-1 and COX-2 and selective COX-2 inhibitors (coxibs). The development of biomarkers predictive of the impact of NSAIDs on COX-1 and COX-2 activities in vitro, ex vivo and in vivo has been essential to read out the clinical consequences of selective and non-selective inhibition of COX isozymes in human beings. The analgesic and anti-inflammatory effects of NSAIDs are COX-2-dependent effects, unrelated to COX-2 selectivity. The intensity and duration of these effects are influenced by dose and half-life of the NSAID. However, the inhibition of COX-1 in cells of the gastrointestinal (GI) system and COX-2 in vascular cells translates into increased risk of serious GI adverse events and atherothrombosis and hypertension, respectively. The COX-2 selectivity of NSAIDs can predict, at least in part, the GI toxicity. In contrast, the CV effects are largely COX-2-dependent effects, unrelated to COX-2 selectivity but are dose dependent. The reduction in the dose is recommended and presumably will limit the number of patients exposed to a CV or a GI hazard by NSAIDs and coxibs. It will not, however, eliminate the risk on an individual level because there is a marked variability in how different people react to these drugs, based on their genetic background. The challenge of the next future will be to develop biomarkers useful to identify the individuals who react abnormally to COX inhibition.