Faculty Bibliography

We recently reported the medicinal chemistry re-optimization of a series of compounds derived from the human tyrosine kinase inhibitor, lapatinib, for activity against Plasmodium falciparum. From this same library of compounds, we now report potent compounds against Trypanosoma brucei brucei (which causes human African trypanosomiasis), T. cruzi (the pathogen that causes Chagas disease), and Leishmania spp. (which cause leishmaniasis). In addition, sub-micromolar compounds were identified that inhibit proliferation of the parasites that cause African animal trypanosomiasis, T. congolense and T. vivax. We have found that this set of compounds display acceptable physicochemical properties and represent progress towards identification of lead compounds to combat several neglected tropical diseases.

Human African trypanosomiasis, Chagas disease, and leishmaniasis are human infections caused by kinetoplastid parasites of the genera Trypanosoma and Leishmania. Besides their severity and global impact, treatments are still challenging. Currently available drugs have important limitations, highlighting the urgent need to develop new drugs. Phosphoglucose isomerase (PGI) is considered a promising target for the development of antiparasitic drugs, as it acts on two essential metabolic pathways, glycolysis and gluconeogenesis. Herein, we describe the identification of new nonphosphorylated inhibitors of Leishmania mexicana PGI ( LmPGI), with the potential for the development of antiparasitic drugs. A fluorescence-based high-throughput screening (HTS) assay was developed by coupling the activities of recombinant LmPGI with glucose-6-phosphate dehydrogenase and diaphorase. This coupled assay was used to screen 42,720 compounds from ChemBridge and TimTec commercial libraries. After confirmatory assays, selected LmPGI inhibitors were tested against homologous Trypanosoma cruzi and humans. The PGI hits are effective against trypanosomatid PGIs, with IC₅₀ values in the micromolar range, and also against the human homologous enzyme. A computational analysis of cavities present on PGI's crystallographic structure suggests a potential binding site for the proposed mixed-type inhibition mechanism.

Discovery of new chemotherapeutic lead agents can be accelerated by optimizing chemotypes proven to be effective in other diseases to act against parasites. One such medicinal chemistry campaign has focused on optimizing the anilinoquinazoline drug lapatinib (1) and the alkynyl thieno[3,2-d]pyrimidine hit GW837016X (NEU-391, 3) into leads for antitrypanosome drugs. We now report the structure-activity relationship studies of 3 and its analogs against Trypanosoma brucei, which causes human African trypanosomiasis (HAT). The series was also tested against Trypanosoma cruzi, Leishmania major, and Plasmodium falciparum. In each case, potent antiparasitic hits with acceptable toxicity margins over mammalian HepG2 and NIH3T3 cell lines were identified. In a mouse model of HAT, 3 extended life of treated mice by 50%, compared to untreated controls. At the cellular level, 3 inhibited mitosis and cytokinesis in T. brucei. Thus, the alkynylthieno[3,2-d]pyrimidine chemotype is an advanced hit worthy of further optimization as a potential chemotherapeutic agent for HAT.

Antiself antibodies are most commonly associated with autoimmune disorders, but a large body of evidence indicates that they are also present in numerous infectious diseases. These autoimmune antibodies appear transiently during infection with a number of viruses, bacteria, and parasites and in some cases have been associated with the development of autoimmune disorders that develop after infection has been cleared. Traditionally these infection-associated autoantibodies are considered an erroneous byproduct of a legitimate immune response, but their possible role in the clearance of microbes and infected cells or inhibition of host-cell invasion suggests that they may be present because of their beneficial protective role against various infections.

Dendritic cells (DCs) are activated by pathogens to initiate and shape immune responses. We found that the activation of DCs by Plasmodium falciparum, the main causative agent of human malaria, induces a highly unusual phenotype by which DCs up-regulate costimulatory molecules and secretion of chemokines, but not of cytokines typical of inflammatory responses (IL-1beta, IL-6, IL-10, TNF). Similar results were obtained with DCs obtained from malaria-naive US donors and malaria-experienced donors from Mali. Contact-dependent cross-talk between the main DC subsets, plasmacytoid and myeloid DCs (mDCs) was necessary for increased chemokine and IFN-alpha secretion in response to the parasite. Despite the absence of inflammatory cytokine secretion, mDCs incubated with P. falciparum-infected erythrocytes activated antigen-specific naive CD4+ T cells to proliferate and secrete Th1-like cytokines. This unexpected response of human mDCs to P. falciparum exhibited a transcriptional program distinct from a classical LPS response, pointing to unique P. falciparum-induced activation pathways that may explain the uncharacteristic immune response to malaria.

Infectious pathogens contribute to the development of autoimmune disorders, but the mechanisms connecting these processes are incompletely understood. Here we show that Plasmodium DNA induces autoreactive responses against erythrocytes by activating a population of B cells expressing CD11c and the transcription factor T-bet, which become major producers of autoantibodies that promote malarial anaemia. Additionally, we identify parasite DNA-sensing through Toll-like receptor 9 (TLR9) along with inflammatory cytokine receptor IFN-gamma receptor (IFN-gammaR) as essential signals that synergize to promote the development and appearance of these autoreactive T-bet+ B cells. The lack of any of these signals ameliorates malarial anaemia during infection in a mouse model. We also identify both expansion of T-bet+ B cells and production of anti-erythrocyte antibodies in ex vivo cultures of naive human peripheral blood mononuclear cells (PBMC) exposed to P. falciprum infected erythrocyte lysates. We propose that synergistic TLR9/IFN-gammaR activation of T-bet+ B cells is a mechanism underlying infection-induced autoimmune-like responses.