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Proceedings of the Society for Experimental Biology and Medicine 224:45-49 (2000)
© 2000 Society for Experimental Biology and Medicine

Original Article

Anticancer Agents Suppressive for Adult Parasites of Filariasis in Mongolian Jirds

Kenneth E. Kinnamon*,1, Robert R. Engle*, Bing T. Poon*, William Y. Ellis*, John W. McCall{dagger} and Michael T. Dzimianski{dagger}


* Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Washington, D.C. 20307–5100; and
{dagger} Department of Parasitology, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Eight chemical structures not previously reported to possess antifilarial activity have been identified. A total of 79 compounds with anticancer properties were evaluated for possible macrofilaricidal activity against Brugia pahangi and Acanthocheilonema viteae transplanted into male Mongolian jirds (Meriones unguiculatus). All eight active compounds were suppressive for the onchocerciasis type (Acanthocheilonema viteae) of the disease. None was macrofilaricidal for the lymphatic form (Brugia pahangi). These new structures may represent a nucleus around which effective drugs can be synthesized.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
More than one billion people (20%) of the world's population live in areas where they are at risk of infection from lymphatic filariasis (Wucheria bancrofti, Brugia malayi, B. timori) and "river blindness" (Onchocerca volvulus) (1). Drugs used most commonly to cope with these diseases are diethylcarbamazine (DEC) and ivermectin. Although both of these have marked microfilaricidal activity, neither has appreciable action against the adult worms. There is a great need for effective macrofilaricidal drugs. The discovery and development of a macrofilaricide is a mandate of the MACROFIL project of the World Health Organization (2).

A group of compounds with members known to adversely affect parasites of humans, including filaria, are anticancer agents. For example, the antineoplastic antibiotic cyanein has antinematodal activity (3). And, of more than 100 anticancer compounds tested for activity against Trypanosoma brucei rhodesiense infections, 18.3% were found to be positive (4, 5). Similarly, 6.7% showed activity against Trypanosoma cruzi infections (6). Thiosemicarbazones, a class with known antineoplastic action (7), are active against bacteria (8), viruses (9), coccidia (10), malaria (11), and filaria (12). Phosphonylmethoxyalkylpurine analogs (13), levamisole (14) and suramin (15), all structures with antitumor attributes, have been shown to have antiviral (16), general anthelminthic (17), and antifilarial (18) activity, respectively.

Although it is realized that antineoplastic agents display general cellular toxicity, it is appreciated that there is toxicity to the host with virtually all therapeutic agents. The issue is the therapeutic index. With this backdrop of information, it was of interest to us to evaluate compounds with known antineoplastic properties. We chose to evaluate 79 compounds with known anticancer activity. These were supplied to us by the National Cancer Institute.

The evaluations were carried out by assessing the macrofilaricidal activity against Brugia pahangi and Acanthocheilonema viteae in male Mongolian jirds. The animal model employed, using these two parasites, was designed to mimic, in-so-far as possible, respectively, human lymphatic filariasis and "river blindness" (onchocerciasis). The model, actually a double-model, was based upon experience gained during studies following interaction with those of the World Health Organization (19). The creation of these "lymphatic type" (Brugia pahangi) and "onchocerciasis type" (Acanthocheilonema viteae) models is discussed more fully elsewhere (20).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals used were male Mongolian jirds (Meriones unguiculatus) weighing 50–60 g. The experiments reported herein were conducted according to principles set forth in the Guide for the Care and Use of Laboratory Animals, Institute of Laboratory Animal Resources, National Research Council, NIH Pub. no. 85–23. Brugia pahangi was maintained by alternate passage through beagle dogs, and Aedes aegypti mosquitoes (selected Liverpool strain) and A. viteae were cyclically maintained in jirds or outbred Syrian hamsters, and the soft tick, Ornithodoros tartakovski, as described elsewhere (21). The dosage level of the compound selected for testing depended upon the available sample size and toxicity of the drug. Compounds were given once daily, at the mg/kg/day (MKD) dosage shown, for 5 days by subcutaneous injection. All compounds were suspended in hydroxyethylcellulose (0.5%) and Tween 80 (0.1%) by sonication at 20 kilocycles for 10 min. During dosing, suspensions were agitated as needed using a vortex mixer.

The test regimen employed 8-week-old A. viteae collected from donor hamsters and given to jirds (21). Each of these jirds was given 10 (5 male and 5 female) of these adult worms by subcutaneous (SC) transplantation under sodium pentobarbital anesthesia at a level of 48 mg/kg (22). Two weeks later, 20 (10 male and 10 female) adult B. pahangi, taken from jirds infected intraperitoneally (IP) 8 weeks earlier (4) were transplanted into the peritoneal cavity of each of these jirds, under sodium pentobarbital anesthesia. The following week, they were randomly allocated to form a "run," and dosing was initiated (Day 0). Each run consisted of 18 test groups of 3 jirds each, a negative control group of 3–6 jirds given the hydroxyethylcellulose-Tween 80 carrier, and a positive control group of 3 jirds treated subcutaneously with 2 MKD for 5 days of flubendazole. Body weights were recorded daily for 5 days to determine the doses needed and to look for signs of toxicity. A drug was considered to be toxic if jirds were moribund or dead or if there was a 15% (group mean) weight loss. Dosing of a group of jirds was discontinued if toxicity was noted.

All jirds were sacrificed on Day 56 after dosing was initiated to determine the effects of the drugs on the adults of both A. viteae in subcutaneous tissue and between facial planes of muscle and B. pahangi in the peritoneal cavity. Live worms were identified to species, noted as to sex, and counted. The number of dead and/or encapsulated worms was also recorded. If a compound caused a 60% or greater reduction in the adult worm burden of one or both species, it was considered active. Arcsin conversions were done before percentage computations were undertaken.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Results for the eight anticancer agents exhibiting antifilarial activity are shown in Table IGo. The 71 compounds that were inactive are listed in Table IIGo. All eight actives were suppressive for the parasite that causes the onchocerciasis form (A. viteae) of the disease. None of the compounds was found to be effective against the lymphatic filariasis form (B. pahangi). Although Table IIGo enumerates compounds found to be inactive, it is believed that the information is valuable. Among drugs that are listed in Table IIGo are many standard anticancer agents.


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  		Table I.   Active Compounds in Jirds (Meriones unguiculatus) (Three Animals per Test Group) Transplanted with 20 Adult Brugia pahangi (Bp) and 10 Adult Acanthocheilonema viteae (Ac) and Treated Subcutaneously for 5 Consecutive Days
 

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  		Table II.   Inactive Compounds in Jirds (Meriones unguiculatus) (Three Animals per Test Group) Transplanted with 20 Adult Brugia pahangi and 10 Adult Acanthocheilonema viteae and Treated Subcutaneously for 5 Consecutive Days
 
Why hydroxyurea (Compound 3, Table IGo) was more active at 25 MKD than at 50 MKD is not known. The worm location within the test animals at the higher dose level may have been more inaccessible to the subcutaneously administered compound than those at the lower dose level (i.e., 25 MKD). Please note that a similar result was noted for the positive control drug (flubendazole) at 50 MKD and 25 MKD.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
None of the eight compounds found to be suppressive in the present study have been reported previously to possess activity against parasites that produce either the lymphatic form or the onchocerciasis form of filariasis. Why certain anticancer agents are effective against certain parasites is not understood. Some metabolic similarities between neoplastic cells and the African trypanasomes have been offered as a reason for the effectiveness in those organisms (23-25). However, unlike the protozoan diseases in which the parasite undergoes replication within the host, once the infective larvae of helminths have reached the final host, the only cell division that takes place is within the reproductive organs (26).

The antitumor mechanism of action of suramin, the only WHO-recommended macrofilaricidal agent, has been examined. Inhibition of various growth factors favoring cell transformation of tumor progression represents a major mechanism of action by this drug as an anticancer agent (15, 27). As an antifilarial, suramin is known to destabilize filarial DNA (28) and adversely affect protein kinases and enzymes associated with glucose catabolism (i.e., glyceraldehyde-3-phosphate dehydrogenase, lactic dehydrogenase, malic dehydrogenase) (29-31). Its limited efficacy against adult worms in onchocerciasis is not because of the poor penetration of the nodules by the drug (32, 33). How these various attributes might be linked is not presently understood.

Other metabolic similarities of cancerous tissues and parasites worthy of mention are seen in certain polyamine relationships. The interconversion of spermine to spermidine to putrescine is similar in mammalian cells and filarial worms (34, 35). However, it is important to note that this functional reverse pathway, is much more important in filaria than mammals. In the parasite, it is the mechanism by which the worms control and reduce the level of higher polyamines and supply putrescine for recycling via the synthetic pathway. This difference may represent a rewarding avenue by which filaricides may be designed.

The "hits" reported in the present study may represent a nucleus around which chemical analogs can be synthesized. The approach envisioned is not dissimilar to one employed in the search for anticancer agents where the aim is to take advantage of the numerous molecular alterations identified in tumor cells (36). But rather than the focus being on the deviation of the tumor cells from those that are normal in the anticancer drug search, concentration is on the metabolic differences between the host's normal cells and those of the parasitic worm. One can be optimistic that the eight structures identified in the present work represent a harbinger of drugs with therapeutic advantage that can interfere with a critical metabolic step and thus use an effective killing mechanism for the nematode worms without adversely affecting the host.


   Acknowledgments
 
We are indebted to the National Cancer Institute for making the test compounds available. We are especially thankful to Jill Johnson, Chemist, Drug Synthesis & Chemistry Branch.


   Footnotes
 
This investigation received financial support from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases.

The opinions or assertions contained herein are personal views of the authors and should not be construed as official or necessarily reflecting the views of the Walter Reed Army Institute of Research, Uniformed Services University of the Health Sciences, or the Department of Defense.

1 To whom requests for reprints should be addressed at the Department of Preventive Medicine & Biometrics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814–4799. Back


   References
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 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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Received for publication August 31, 1999. Accepted for publication January 19, 2000.





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