Targeting Filarial Abl-like Kinases: Orally Available, Food and Drug Administration-Approved Tyrosine Kinase Inhibitors Are Microfilaricidal and Macrofilaricidal

Abstract

Background: Elimination of onchocerciasis and lymphatic filariasis is targeted for 2020. Given the coincident Loa loa infections in Central Africa and the potential for drug resistance development, the need for new microfilaricides and macrofilaricides has never been greater. With the genomes of L. loa, Onchocerca volvulus, Wuchereria bancrofti, and Brugia malayi available, new drug targets have been identified.

Methods: The effects of the tyrosine kinase inhibitors imatinib, nilotinib, and dasatinib on B. malayi adult males, adult females, L3 larvae, and microfilariae were assessed using a wide dose range (0-100 µM) in vitro.

Results: For microfilariae, median inhibitory concentrations (IC50 values) on day 6 were 6.06 µM for imatinib, 3.72 µM for dasatinib, and 81.35 µM for nilotinib; for L3 larvae, 11.27 µM, 13.64 µM, and 70.98 µM, respectively; for adult males, 41.6 µM, 3.87 µM, and 68.22 µM, respectively; and for adult females, 42.89 µM, 9.8 µM, and >100 µM, respectively. Three-dimensional modeling suggests how these tyrosine kinase inhibitors bind and inhibit filarial protein activity.

Conclusions: Given the safety of imatinib in humans, plans are underway for pilot clinical trials to assess its efficacy in patients with filarial infections.

Keywords: Brugia malayi; Loa loa; Wuchereria bancrofti; filaria; lymphatic filariasis; macrofilaricide; mass drug administration; microfilaricide; onchocerciasis.

Figure 1.

Phylogenic interrelationships between parasite and human Abl-like kinases. A, Multiple sequence alignment of the catalytic domain of human c-Abl, to which imatinib, nilotinib, and dasatinib bind, compared with the sequences of Abl-like proteins found in Wuchereria bancrofti, Brugia malayi, Loa loa, Onchocerca volvulus, Schistosoma mansoni, and Echinococcus multilocularis, with black shading denoting amino acids that are identical to those found in the human protein. B, Phylogenic tree of the human Abl and parasite Abl-like proteins. Bootstrap values are depicted. C, Percentage identities of the filarial c-Abl-like protein sequence to the entire human protein sequence and of the filarial drug-binding pocket to the human active domain.

Figure 2.

Survival curves of Brugia malayi microfilariae (MF), L3 larvae, adult males (AM), and adult females (AF) for imatinib, nilotinib, and dasatinib. Shown is the percentage survival of each stage following exposure to varying concentrations of imatinib, nilotinib, or dasatinib and of negative controls (water for imatinib and nilotinib and dimethyl sulfoxide [DMSO] for dasatinib) as a function of time in days following drug administration. *P < .05, by the log-rank test.

Figure 3.

Median inhibitory concentrations (IC₅₀ values) for imatinib, dasatinib, and nilotinib against each of the Brugia malayi life stages. A, Representative IC₅₀ curve for imatinib against microfilariae (MF). B, IC₅₀ values and 95% confidence intervals (CIs) for B. malayi MF, L3 larvae, and adult males and females for imatinib, dasatinib, and nilotinib at day 6 following drug administration.

Figure 4.

Projected model of Loa loa Abl-like protein interacting with imatinib, nilotinib, and dasatinib. Loa protein model (red; projected) is superimposed on human (blue; based on x-ray crystallography data: PDB ID 3CS9 [nilotinib], 2GQG [dasatinib], and 2HYY [imatinib]). All residues within 3Å of the inhibitor and known binding sites for the human protein are listed next to the corresponding residue on the Loa model.

Figure 5.

Electron microscopy of microfilariae (MF) following imatinib administration. A and B, Scanning electron micrograph (10 000× original magnification) of MF on day 7 following no drug (A) or exposure to 25 µM imatinib (B). C and D, Transmission electron microscopy (7000× original magnification) of MF on day 7 following no drug (C) or exposure to 25 µM imatinib (D).