Identificación de nuevas dianas terapéuticas potenciales e inhibidores del sistema ubiquitina proteasoma para el tratamiento de la malaria

La malaria es una de las enfermedades infecciosas que producen un mayor número de muertes en el mundo. La mayoría de los casos tienen lugar en África, Ásia y parte de Sudamérica, teniendo un impacto en el desarrollo socioeconómico de los países más pobres. Las formas más severas de malaria son producidas por la infección del parásito protista Plasmodium falciparum (P. falciparum). P. falciparum posee un ciclo de vida complejo, ya que adopta diferentes formas a lo largo de su ciclo vital. La etapa intraeritrocítica es la etapa asociada con la patogénesis, siendo la más estudiada y la principal diana de los fármacos antimaláricos. Sin embargo, la aparición de resistencias frente a todos los antimaláricos conocidos, han llevado a la necesidad de desarrollar nuevos medicamentos con mecanismos de acción novedosos, y a la identificación y validación de nuevas dianas terapéuticas. El Sistema Ubiquitina Proteasoma (UPS) es una de las pocas dianas terapéuticas que pueden ser consideradas como validadas en P. falciparum. Los inhibidores de proteasoma humano inhiben el crecimiento del parásito, incluso en cepas resistentes a antimaláricos y en varias etapas de su ciclo de vida. Un número creciente de compuestos que inhiben alguno de los componentes del UPS humano se encuentran en fases clínicas para el tratamiento de enfermedades como el cáncer. Sin embargo, existe la necesidad de encontrar compuestos que inhiban específicamente alguno de los componentes del UPS de P. falciparum con el fin de evitar cualquier tipo de toxicidad. A pesar de ello, el conocimiento del UPS de P. falciparum es limitado, dificultando el desarrollo de nuevos fármacos..

High-throughput screening of the Plasmodium falciparum cGMP-dependent protein kinase identified a thiazole scaffold which kills erythrocytic and sexual stage parasites.

Antimalarial drug resistance compels the quest for new compounds that target alternative pathways to current drugs. The Plasmodium cyclic GMP-dependent protein kinase (PKG) has essential functions in all of the major life cycle developmental stages. An imidazopyridine PKG inhibitor scaffold was previously shown to clear P. falciparum infection in a rodent model in vivo and blocked transmission to mosquitoes providing proof of concept for this target. To find new classes of PKG inhibitors to serve as alternative chemical starting points, we performed a high-throughput screen of the GSK Full Diversity Collection using recombinant P. falciparum PKG. We developed a robust enzymatic assay in a 1536-well plate format. Promising compounds were then tested for activity against P. falciparum asexual blood stage growth, selectivity and cytotoxicity. By using a scoring system we selected the 66 most promising PKG inhibitors (comprising nine clusters and seven singletons). Among these, thiazoles were the most potent scaffold with mid-nanomolar activity on P. falciparum blood stage and gamete development. Using Kinobeads profiling we identified additional P. falciparum protein kinases targeted by the thiazoles that mediate a faster speed of the kill than PKG-selective compounds. This scaffold represents a promising starting point to develop a new antimalarial

Inhibiting the stringent response blocks Mycobacterium tuberculosis entry into quiescence and reduces persistence

The stringent response enables Mycobacterium tuberculosis (Mtb) to shut down its replication and metabolism under various stresses. Here we show that Mtb lacking the stringent response enzyme RelMtb was unable to slow its replication rate during nutrient starvation. Metabolomics analysis revealed that the nutrient-starved relMtb-deficient strain had increased metabolism similar to that of exponentially growing wild-type bacteria in nutrient-rich broth, consistent with an inability to enter quiescence. Deficiency of relMtb increased the susceptibility of mutant bacteria to killing by isoniazid during nutrient starvation and in the lungs of chronically infected mice. We screened a pharmaceutical library of over 2 million compounds for inhibitors of RelMtb and showed that the lead compound X9 was able to directly kill nutrient-starved M. tuberculosis and enhanced the killing activity of isoniazid. Inhibition of RelMtb is a promising approach to target M. tuberculosis persisters, with the potential to shorten the duration of TB treatment.This work was supported by R01AI083125, R21AI122922, and R21AI114507A to P.C.

METHODOLOGY Open Access

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