Advancing antileishmanial treatments through innovative nanotechnology in vitro approaches and characterization of novel therapeutic compounds

Abstract

[eng] Leishmaniasis is a vector-borne disease, caused by the parasite Leishmania spp. and transmitted by sand flies of the genus Phlebotomus or Lutzomyia. There are over 12 million people infected worldwide and around one million new cases each year, which represents a significant global health challenge. Actually, leishmaniasis is the second deadliest parasitic disease in the world after malaria, but it is still considered a neglected tropical disease. The current treatment options of leishmaniasis face challenges, such as long regimens, drug resistance, side effects, issues related to the parenteral administration, limited availability in endemic regions, and high costs. Thus, there is an urgent need to develop new safer treatments with a better patient compliance and more effective than the actual antileishmanial drugs. In this work, three strategies are proposed to overcome some of the challenges mentioned above. Firstly, nanotechnology was applied with the aim of developing nanoformulations to encapsulate high amounts of pentamidine (one of the antileishmanial drugs currently used for clinical purposes) and, using heparin and chondroitin sulfate (CS) as targeting elements, to direct the nanoformulations to the free parasite or to macrophages infected with the parasite. Such specific delivery allowed for (i) increasing the targeting to macrophages when liposomes were coated with either heparin or CS, (ii) significantly reducing the IC50 of the drug on L. infantum and L. pifanoi promastigotes when liposomes were coated with heparin or chondroitin sulfate, (iii) significantly reducing the cytotoxicity on human umbilical endothelial cells, and (iv) obtaining a higher deposition of the nebulized liposomal preparations in the deeper stages of a human lung airway simulator when compared to free pentamidine. The second approach was focused on the search for new drugs with a different mechanism of action than the current antileishmanial drugs. In here, different compounds which interfere with protein aggregation showed some extent of antileishmanial activity. In particular, the bis(styrylpyridinium) salt YAT2150 had a better activity against L. infantum than most of the currently used drugs for the clinical treatment of leishmaniasis, including pentamidine, miltefosine and paromomycin. In relation to the mode of action of YAT2150, a reduction in the overall protein aggregation in a culture of L. infantum promastigotes was observed, according to Thioflavin T analysis. This finding aligns with the proposed mode of action of YAT2150 in P. falciparum determined in a previous study. The encapsulation of YAT2150 in liposomes or immunoliposomes functionalized with an antibody against LPG, significantly increased the selectivity index of the drug above 100. Therefore, the activity of YAT2150 against both Leishmania and Plasmodium represents a promising opportunity for the treatment of co-infections with these parasites. The third strategy was spurred by the urgent need to develop ligands that specifically recognise the parasite, and that could be used, e.g., for the functionalization of drug delivery systems or as diagnostic tools. GP63, is the major surface protein present in Leishmania promastigotes and constitutes one of its main virulence factors, playing a role in the adhesion of the parasite to the macrophage and in the survival of amastigotes. DNA aptamers were developed against a L. infantum mature form of GP63 (LiGP63m), using the systematic evolution of ligands by exponential enrichment (SELEX) method. After 7 SELEX cycles, 5 individual aptamer sequences were selected, showing a high affinity for endogenous LiGP63 within a promastigote lysate, with a binding affinity in the μM range, according to an Aptamer Linked Immobilized Sorbent Assay (ALISA). In conclusion, the aptamers discussed here hold promise for interventions against leishmaniasis as potential diagnostic tools and as targeting molecules for drug delivery nanocarriers.

[spa] La leishmaniasis es una enfermedad transmitida por vectores del género Phlebotomus o Lutzomyia y causada por el parásito Leishmania spp. Afecta a más de 12 millones de personas en todo el mundo con aproximadamente un millón de nuevos casos anuales, representando un desafío para la salud global. Es la segunda enfermedad parasitaria más mortal después de la malaria, aunque sigue siendo una enfermedad tropical desatendida. Los tratamientos actuales presentan diversas limitaciones, entre ellas: su larga duración, la resistencia a los medicamentos, los efectos secundarios, los problemas asociados con la administración parenteral, la baja disponibilidad en regiones endémicas y los altos costes. Por lo tanto, es urgente desarrollar tratamientos más seguros, más efectivos y con mejor adherencia. En esta tesis se proponen tres estrategias para superar estos desafíos: - Nanotecnología: Se desarrollaron liposomas para encapsular pentamidina, un fármaco leishmanicida clásico, y se dirigieron específicamente al parásito libre o a macrófagos infectados utilizando heparina y sulfato de condroitina para recubrir los liposomas. La conjugación de estos ligandos aumentó la captación de los liposomas recubiertos por parte de los macrófagos, redujo significativamente la IC50 del fármaco en promastigotes de L. infantum y L. pifanoi, disminuyó la citotoxicidad en células endoteliales humanas y aumentó la deposición del fármaco en los niveles más profundos de un simulador de vías respiratorias humanas cuando se comparó con la pentamidina libre. - Nuevos medicamentos: Se probó la actividad leishmanicida de compuestos que interfieren con la agregación proteica. En particular, la sal de bis(estirilpiridinio) YAT2150 mostró mejor actividad contra L. infantum que muchos medicamentos usados actualmente. La encapsulación de YAT2150 en liposomas aumentó significativamente el índice de selectividad hasta un valor superior a 50. - Aptámeros: Se desarrollaron aptámeros de ADN contra la proteína de superficie GP63 de L. infantum. Estos mostraron una alta afinidad y especificidad por dicha proteína, tanto en su forma recombinante purificada, como en la proteína endógena. Estos aptámeros son prometedores como una potencial herramientas de diagnóstico y como moléculas para dirigir específicamente sistemas de liberación de fármacos. Estas estrategias buscan mejorar el tratamiento y diagnóstico de la leishmaniasis, ofreciendo nuevas esperanzas en la lucha contra esta enfermedad.