New Chemical Scaffolds for Human African Trypanosomiasis Lead Discovery from a Screen of Tyrosine Kinase Inhibitor Drugs

Abstract

Human African trypanosomiasis (HAT) is caused by the protozoan Trypanosoma brucei. New drugs are needed to treat HAT because of undesirable side effects and difficulties in the administration of the antiquated drugs that are currently used. In human proliferative diseases, protein tyrosine kinase (PTK) inhibitors (PTKIs) have been developed into drugs (e.g., lapatinib and erlotinib) by optimization of a 4-anilinoquinazoline scaffold. Two sets of facts raise a possibility that drugs targeted against human PTKs could be "hits" for antitrypanosomal lead discoveries. First, trypanosome protein kinases bind some drugs, namely, lapatinib, CI-1033, and AEE788. Second, the pan-PTK inhibitor tyrphostin A47 blocks the endocytosis of transferrin and inhibits trypanosome replication. Following up on these concepts, we performed a focused screen of various PTKI drugs as possible antitrypanosomal hits. Lapatinib, CI-1033, erlotinib, axitinib, sunitinib, PKI-166, and AEE788 inhibited the replication of bloodstream T. brucei, with a 50% growth inhibitory concentration (GI 50 ) between 1.3 M and 2.5 M. Imatinib had no effect (i.e., GI 50 > 10 M). To discover leads among the drugs, a mouse model of HAT was used in a proof-of-concept study. Orally administered lapatinib reduced parasitemia, extended the survival of all treated mice, and cured the trypanosomal infection in 25% of the mice. CI-1033 and AEE788 reduced parasitemia and extended the survival of the infected mice. On the strength of these data and noting their oral bioavailabilities, we propose that the 4-anilinoquinazoline and pyrrolopyrimidine scaffolds of lapatinib, CI-1033, and AEE788 are worth optimizing against T. brucei in medicinal chemistry campaigns (i.e., scaffold repurposing) to discover new drugs against HAT.

Optimization of physicochemical properties for 4-anilinoquinazoline inhibitors of trypanosome proliferation

“…We previously reported that the human tyrosine kinase inhibitor lapatinib ( 1 ), shown in Figure 1, prevents proliferation of bloodstream T. brucei with an EC 50 of 1.54 μM [17, 18]. Further optimization studies, especially the “tail” region (in red), led to the discovery of 2 (NEU-617), with a potency of 0.042 μM and improved parasite selectivity over 1 [12].…”

Novel Effects of Lapatinib Revealed in the African Trypanosome by Using Hypothesis-Generating Proteomics and Chemical Biology Strategies

“…Identifying pTyr-regulated pathways affected by lapatinib will help our understanding of the drug's antitrypanosomal activity in vitro or in a mouse model of HAT (5). Since pTyr serves as a docking site for effector proteins (12), we reasoned that polypeptides in complex with Tyr-phosphorylated proteins might provide some insight into processes regulated by that posttranslational modification.…”

“…Chemical biology experiments confirmed that lapatinib treatment destabilizes the PFR structure and inhibits endocytosis of transferrin in bloodstream T. brucei. These two biological processes are essential for the parasite's viability, and their perturbation can explain, at least in part, lapatinib's ability to kill trypanosomes (4,5). This hypothesis-generating proteomics and chemical biology strategy could find general use in understanding the mode of action of other antiparasite hits discovered in phenotypic screens (46,47).…”

“…A major goal of this work was to evaluate the pharmacological basis of lapatinib's trypanocidal effects (4,5). In human cells, lapatinib inhibits EGFR (2, 3), but it also binds to other protein kinases (29), and it associates with Pgp ATPase (30) as well as ABCB1 transporters (31).…”

“…Current chemotherapies need improvement, and the desired "target product profile" of new therapies include oral administration and multitargeting (1). Lapatinib, a human epidermal growth factor receptor (EGFR) inhibitor (2,3), was identified as a hit for antitrypanosome drug discovery (4) and subsequently demonstrated to be a lead drug, curing 25% of mice infected with trypanosomes (5). As a promising lead, new analogs of the 4-anilinoquinazoline scaffold in lapatinib are being optimized to improve efficacy and physicochemical properties for HAT drug discovery (6-8).…”