Efficacy and Microfilaricidal Kinetics of Imatinib for the Treatment of Loa Loa

Overview

Background: Many people who live in west or central Africa are at risk for infection from a very small worm called Loa loa. This infection is acquired through the bite of a fly. Baby worms called microfilariae live in the blood. The infection most commonly causes skin itching, mild temporary limb swelling, and sometimes a adult worm can be seen in the white of the eye of an infected individual. Very rarely, people with this infection can develop problems with the kidneys and heart as a result of the worm's effect on the immune system. Because the vast majority of people with the infection have minimal symptoms, people in Cameroon usually do not get treated. But infection with Loa loa can cause serious problems in people who are being treated for infections with other parasites (namely, river blindness and lymphatic filariasis). Researchers want to find out of a drug called imatinib can treat Loa loa infection so that patients with this infection can safely receive other drugs to cure river blindness and lymphatic filariasis. Researchers believe imatinib can be a safe drug to use on Loa loa, because in the lab this drug kills the worms slowly, whereas other drugs which can cause treatment reactions usually kill the worms very quickly. Objective: To test if imatinib can treat Loa loa infection by killing the worms slowly. Eligibility: People ages 18-65 with non-severe Loa loa infection who are otherwise healthy Design: Participants will be screened with a physical exam and blood and urine tests. Participants will have a baseline visit. This will include a physical exam and blood and urine tests. It may include a stool sample. Participants will be randomly assigned to get 1 dose of either imatinib or a placebo. Participants will return to the clinic every day for 1 week, then once a week for 3 weeks. Visits will include a physical exam and blood tests. They will have urine tests in the first week. Participants will have follow-up visits 3, 6, and 12 months after taking the imatinib or placebo. These include a physical exam and blood tests. They may include urine and stool samples. If participants develop side effects, they will be treated for them.

With the discovery that people experiencing severe treatment reactions following mass drug administration (MDA) with ivermectin for onchocerciasis and lymphatic filariasis control were co-infected with Loa loa, there has been a need for new filaricidal drugs. Currently, Loa loa infection, considered relatively nonpathogenic, is not treated in endemic areas. However, because treatment for Loa loa can result in toxicity in people who are being concurrently treated for onchocerciasis and lymphatic filariasis, finding a new treatment for Loa loa has become a priority. Imatinib has recently been shown to be microfilaricidal in vitro at concentrations physiologically achievable after a single oral dose in humans. The current standard in loiasis treatment outside of endemic areas is to treat those with low microfilarial (MF) levels (less than approximately 8,000MF/mL) with diethylcarbamazine (DEC). However, at high MF concentrations (\>20,000 MF/mL) serious side effects including encephalopathy and death have occurred with administration of DEC or ivermectin, a widely distributed microfilaricide throughout Africa. In endemic areas, this risk is avoided by not treating loiasis altogether. The adverse reactions are believed to be due release of a large antigen load due to rapid killing of large numbers of MF. The rapidity of killing is believed to be the main driver of these reactions seen at high MF counts. The purpose of this study is to assess how imatinib acts as a slow microfilaricide at levels (\<2,500 MF/mL) that have been safely treated previously with DEC and ivermectin. We aim to perform a dose escalation study to identify the minimum single oral dose that will be effective as a slow microfiaricidal drug against Loa loa. If imatinib is found to be effective and have kinetics which favor slow microfilarial killing, then this can serve as the basis for a larger study in which patients with very high microfilarial loads would be treated, as this is the at risk population in current MDA campaigns. This is a double blind, randomized, pilot phase 2 dose-escalation trial. Subjects will receive a dose of imatinib at 200, 400 or 600 (n = 5 each). Symptoms and blood microfilarial concentration will be assessed at baseline, daily for the first 7 days, then weekly for the next 21 days, then at 3, 6, and 12 months. These will be compared against an untreated placebo-controlled group of 5 subjects who will have the same data collected at these respective days.