SBIR-STTR Award

In the malaria parasite, Plasmodium falciparum, resistance to drugs that inhibit dihydrofolate reductase (DHFR) results from point mutations in the DHFR gene. We have engineered yeast whose growth depends upon the DHFR enzyme from drug-sensitive P. falciparum, and shown that these yeast are killed by antimalarial DHFR inhibitors at concentrations in the therapeutic range. This is a collaborative project initiated with Jacobus Pharmaceutical, Inc., manufacturers of a new class of biguanide antifols. The first of these drugs, PS-15, is effective even against alleles of Pf-DHFR resistant to all currently test drugs of this class. The Sibley lab will use yeast that depend upon P. falciparum DHFR as rapid system to screen newly synthesized analogs of the activated triazine form of PS- 15 called WR-99210. We will use saturation mutagenesis of the PF- DHFR to identify any mutations in DHFR that can confer resistance to each drug, Jacobus Pharmaceutical will synthesize derivatives of the triazine (WR99210), based on the structure activity relationships identified in the initial yeast screen. This yeast system is a rapid, inexpensive system to identify drugs or combinations to which resistant mutants are selected most slowly. We will test the hypothesis that mutations that confer resistance to WR-99210 encode an enzyme that is more sensitive to currently used antifolate drugs like pyrimethamie. The goal is to gather the basic information necessary to move into animal and finally human trials so that this promising new antimalarial drug can be brought to market. The system is a prototype; it can be modified to screen drugs directed against other parasite targets in P. falciparum, the related human parasites, Toxoplasma, Pneumocystis, Cryptosporidium or the agricultural parasites, Eimeria, Theileria or Babesia. PROPOSED COMMERCIAL APPLICATION: Information will be generated which will greatly decrease the risk of quick development of resistance to this drug series in the field and will also provide insight into which combinations of drugs from this series with other DHFR inhibitors are least likely to be lead to the quick development of resistance strains of malaria. This will greatly increase the value of the drug and therefore its attractiveness for commercial development.

Thesaurus Terms:
lasmodium falciparum, antimalarial agent, dihydrofolate reductase, drug resistance, drug screening /evaluation gene mutation

Plasmodium falciparum is the parasitic protozoan responsible for fatal malaria in humans. It causes about 300 million clinical case of malaria and 2-3 million deaths annually. There is no vaccine against malaria, so selection of drug resistant malaria parasites has been a major factor in increased malaria morbidity and mortality in the last two decades. The few drugs that have been developed are too expensive for routine use in malaria treatment in most developing countries where the main burden of disease is felt. Inhibitors of the enzyme dihydrofolate reductase (DHFR) like pyrimethamine have been excellent antimalarials, but point mutations in the target gene compromised its effectiveness. The PS series of drugs are biguanides that are metabolized to triazines that also inhibit the P. falciparum DHFR. In Phase I, we have shown that these triazines do not show cross-resistance to any of the previously tested inhibitors of the P. falciparum DHFR, pyrimethamine, cycloguanil or chlorcycloguanil. In addition, we have recently discovered that these compounds are effective inhibitors of the DHFR enzyme from P. vivax, the most prevalent human malaria parasite. A clinical candidate has been selected based on 90 day oral studies in mice. This proposal is to support the preclinical safety assessment to bring this candidate to the clinic, to continue the yeast genetics program providing field monitoring for the development of resistance, and to extend the mechanism of action studies.

Thesaurus Terms:
Plasmodium falciparum, antimalarial agent, dihydrofolate reductase, drug resistance, drug screening /evaluation enzyme inhibitor, fungal genetics, gene mutation, pharmacokinetics, pyrimethamine, triazine laboratory mouse, polymerase chain reaction