International Journal of Molecular Sciences Review Folic Acid Antagonists: Antimicrobial and Immunomodulating Mechanisms and Applications Daniel Fernández-Villa 1, Maria Rosa Aguilar 1,2 and Luis Rojo 1,2,* 1 Instituto de Ciencia y Tecnología de Polímeros, Consejo Superior de Investigaciones Científicas, CSIC, 28006 Madrid, Spain;
[email protected] (D.F.-V.);
[email protected] (M.R.A.) 2 Consorcio Centro de Investigación Biomédica en Red de Bioingeniería, Biomateriales y Nanomedicina, 28029 Madrid, Spain * Correspondence:
[email protected]; Tel.: +34-915-622-900 Received: 18 September 2019; Accepted: 7 October 2019; Published: 9 October 2019 Abstract: Bacterial, protozoan and other microbial infections share an accelerated metabolic rate. In order to ensure a proper functioning of cell replication and proteins and nucleic acids synthesis processes, folate metabolism rate is also increased in these cases. For this reason, folic acid antagonists have been used since their discovery to treat different kinds of microbial infections, taking advantage of this metabolic difference when compared with human cells. However, resistances to these compounds have emerged since then and only combined therapies are currently used in clinic. In addition, some of these compounds have been found to have an immunomodulatory behavior that allows clinicians using them as anti-inflammatory or immunosuppressive drugs. Therefore, the aim of this review is to provide an updated state-of-the-art on the use of antifolates as antibacterial and immunomodulating agents in the clinical setting, as well as to present their action mechanisms and currently investigated biomedical applications. Keywords: folic acid antagonists; antifolates; antibiotics; antibacterials; immunomodulation; sulfonamides; antimalarial 1.