Potential Therapeutic Applications of P2 Receptor Antagonists: From Bench to Clinical Trials

BACKGROUND

Extracellular purines and pyrimidines have important physiological functions in mammals. Purines and pyrimidines act on P1 and P2 purinergic receptors, which are widely expressed in the plasma membrane in various cell types. P2 receptors act as important therapeutic targets and are associated with several disorders, such as pain, neurodegeneration, cancer, inflammation, and thrombosis. However, the use of antagonists for P2 receptors in clinical therapy, with the exception of P2Y12, is a great challenge. Currently, many research groups and pharmaceutical companies are working on the development of specific antagonist molecules for each receptor subtype that could be used as new medicines to treat their respective disorders.

OBJECTIVE

The present review compiles some interesting findings on the application of P2 receptor antagonists in different in vitro and in vivo experimental models as well as the progress of advanced clinical trials with these compounds.

CONCLUSION

Despite all of the exciting results obtained on the bench, few antagonists of P2 receptors advanced to the clinical trials, and once they reach this stage, the effectiveness of the therapy is not guaranteed, as in the example of P2X7 antagonists. Despite this, P2Y12 receptor antagonists have a history of success and have been used in therapy for at least two decades to prevent thrombosis in patients at risk for myocardial infarctions. This breakthrough is the motivation for scientists to develop new drugs with antagonistic activity for the other P2 receptors; thus, in a matter of years, we will have an evolution in the field of purinergic therapy.

Sofosbuvir shows a protective effect against vertical transmission of Zika virus and the associated congenital syndrome in rhesus monkeys

The outbreaks of Zika virus (ZIKV) infection in Brazil, 2015-2016, were associated with severe congenital malformations. Our translational study aimed to test the efficacy of the antiviral agent sofosbuvir (SOF) against vertical transmission of ZIKV and the associated congenital syndrome (CZS), using a rhesus monkey model. Eight pregnant macaques were successfully infected during the organogenesis phase with a Brazilian ZIKV strain; five of them received SOF from two to fifteen days post-infection. Both groups of dams showed ZIKV-associated clinical signals, detectable ZIKV RNA in several specimens, specific anti-ZIKV IgM and IgG antibodies, and maternal neutralizing antibodies. However, malformations occurred only among non-treated dam offspring. Compared to non-treated animals, all SOF-treated dams had a shorter ZIKV viremia and four of five neonates had undetectable ZIKV RNA in blood and tissue samples. These results support further clinical evaluations aiming for the prevention of CZS.

The Search for New Agonists to P2X7R for Clinical Use: Tuberculosis as a Possible Target

Treatment for tuberculosis is effective with the use of proper antibiotics, but the number of drug-resistant cases is increasing. Drug resistance occurred in 650,000 cases of the 20 million patients in treatment worldwide in 2011, which demonstrates the necessity of finding new therapeutic approaches. In this context, the search for new medicines and immunomodulators could help reduce the prevalence and incidence of multi-drug-resistant tuberculosis cases. Thus several preclinical studies demonstrate the involvement of the P2X7 receptor (P2X7R) in the control of Mycobacterium tuberculosis (MTB) infection. Adenosine triphosphate (ATP), a natural agonist for P2X7R, promotes MTB death and the induction of apoptosis in monocytes and macrophages infected with MTB via activation of P2X7R by extracellular ATP. In addition, P2X7R activation in the presence of ATP increases the expression of major histocompatibility complex (MHC) class II by macrophages infected with Mycobacterium bovis (BCG) or MTB, which contributes to the generation of the antimicrobial immune response via T cells. Nevertheless, one idea that seems overlooked by the "purinergic community" is the use of the high-conductance channel associated with P2X7R to increase the passage of hydrophilic drugs to the cytoplasm of cells that express the P2X7 pore, a potential method for a drug delivery system. In this work, we propose the use of P2X7 agonists in conjunction with low molecular weight anti-tuberculosis medicines for the treatment of multi-drug-resistant tuberculosis.