Pharmacogenomics of tumor necrosis factor antagonists in rheumatoid arthritis

Tumor necrosis factor (TNF)-α plays a central role in the pathogenesis of rheumatoid arthritis (RA) and is instrumental in causing joint destruction, the clinical hallmark of the disease. Recognizing this, in recent years biological therapies have been developed that work by blocking the damaging effects of TNF-α on synovium and cartilage. Three such agents are currently approved for treatment in RA - etanercept, infliximab and adalimumab. Although these agents are very effective in slowing the clinical and structural progression in RA, they are expensive, totaling several thousand dollars in yearly costs. Furthermore, only about 60% of patients respond effectively to these agents. As RA is a chronic disease, with most patients expected to remain on these therapies for life, ways to prospectively identify patients most likely to benefit from these agents are being explored. Pharmacogenomic approaches form the basis of most such screening methods. Polymorphisms in genes encoding TNF-α, TNF-α receptors, other cytokines, and the major histocompatibility complex region, and their ability to predict response to anti-TNF therapies, have been the focus of many recent studies. The results from such studies are mixed, with some suggesting that single nucleoticle polymorphisms (SNPs) in these genes are significant, while others conclude that such SNPs are irrelevant in predicting response. Such conflicting results are likely to be due to a variety of factors, as discussed in this article. Whether pharmacogenomics will allow prediction of anti-TNF therapy efficacy in RA remains a question with no clear answers to date. Large, prospective, multicenter studies with the examination of not just individual SNPs, but also multi-SNP haplotypes, are needed to address this question in the future.