Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or...
Reexamination Certificate
1998-06-23
2004-03-02
McGarry, Sean (Department: 1635)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
C435S006120, C435S007100
Reexamination Certificate
active
06699654
ABSTRACT:
This invention relates uses of components of plant-like metabolic pathways not including psbA or PPi phosphofructokinase and not generally operative in animals or encoded by the plastid DNA, to develop compositions that interfere with Apicomplexan growth and survival. Components of the pathways include enzymes, transit peptides and nucleotide sequences encoding the enzymes and peptides, or promoters of these nucleotide sequences to which antibodies, antisense molecules and other inhibitors are directed. Diagnostic and therapeutic reagents and vaccines are developed based on the components and their inhibitors.
BACKGROUND
Apicomplexan parasites cause the serious diseases malaria, toxoplasmosis, cryptosporidiosis, and eimeriosis. Malaria kills more than 2 million children each year. Toxoplasmosis is the major opportunistic brain infection in AIDS patients, causes loss of life, sight, hearing, cognitive and motor function in congenitally infected infants, and considerable morbidity and mortality in patients immunocompromised by cancer, transplantation, autoimmune disease and their attendant therapies. Cryptosporidiosis is an untreatable cause of diarrhea in AIDS patients and a cause of epidemics of gastrointestinal disease in immunocompetent hosts. Eimeria infections of poultry lead to billions of dollars in losses to agricultural industries each year. Other Apicomplexan infections, such as babesiosis, also cause substantial morbidity and mortality. Although there are some methods for diagnosis and treatment of Apicomplexan caused diseases, some of these treatments are ineffective and often toxic to the subject being treated.
The tests available to diagnose Apicomplexan infections include assays which isolate the parasite, or utilize light, phase, or fluorescence microscopy, ELISAs, agglutination of parasites or parasite components to detect antibodies to parasites, or polymerase chain reaction (PCR) to detect a parasite gene. Most of the assays utilize whole organisms or extracts of whole organisms rather than recombinant proteins or purified parasite components. In many instances, the available assays have limited ability to differentiate whether an infection was acquired remotely or recently, and are limited in their capacity to diagnose infection at the outpatient or field setting.
The primary antimicrobial agents used to treat toxoplasmosis are pyrimethamine (a DHFR inhibitor) and sulfadiazine (a PABA antagonist). The use of pyrimethamine is limited by bone marrow toxicity which can be partially corrected by the concomitant administration of folinic acid.
T. gondii
cannot utilize folinic acid but mammalian cells can. Another problem is that pyrimethamine is potentially teratogenic in the first trimester of pregnancy. The use of sulfonamides is limited by allergy, gastrointestinal intolerance, kidney stone formation and Stevens-Johnson syndrome.
There are a small number of antimicrobial agents utilized less frequently to treat toxoplasmosis. These include clindamycin, spiramycin, azithromycin, clarithromycin and atovaquone. Usefulness of these medicines for treatment of toxoplasmosis is limited by toxicities including allergy and antibiotic-associated diarrhea, (especially
Clostridium difficile
toxin associated colitis with clindamycin use). Lesser or uncertain efficacy of macrolides such as spiramycin, azithromycin, and clarithromycin also limits use of these antimicrobial agents. Atovaquone treatment of toxoplasmosis may be associated with lack of efficacy and/or recrudescent disease. There are no medicines known to eradicate the latent, bradyzoite stage of
T. gondii,
which is very important in the pathogenesis of toxoplasmosis in immunocompromised individuals or those with recurrent eye disease.
Medicines used to treat malaria include quinine sulfate, pyrimethamine, sulfadoxine, tetracycline, clindamycin, chloroquine, mefloquine, halofantrine, quinidine gluconate, quinidine dihydrochloride, quinine, primaquine and proguanil. Emergence of resistance to these medicines and treatment failures due to resistant parasites pose major problems in the care of patients with malaria. Toxicities of mefloquine include nausea, vomiting, diarrhea, dizziness, disturbed sense of balance, toxic psychosis and seizures. Melfoquine is teratogenic in animals. With halofantrene treatment, there is consistent, dose-related lengthening of the PR and Qt intervals in the electrocardiogram. Halofantrene has caused first degree heart block. It cannot be used for patients with cardiac conduction defects. Quinidine gluconate or dihydrochloride also can be hazardous. Parenteral quinine may lead to severe hypoglycemia. Primaquine can cause hemolytic anemia, especially in patients whose red blood cells are deficient in glucose 6-phosphate dehydrogenase. Unfortunately, there are no medicines known to be effective in the treatment of cryptosporidiosis.
To more effectively treat Apicomplexan infections, there is an urgent need for discovery and development of new antimicrobial agents which are less toxic than those currently available, have novel modes of action to treat drug resistant parasites that have been selected by exposure to existing medicines, and which are effective against presently untreatable parasite life cycle stages (e.g.,
Toxoplasma gondii
bradyzoites) and presently untreatable Apicomplexan parasites (e.g.,
Cryptosporidium parvum
). Improved diagnostic reagents and vaccines to prevent these infections are also needed.
Information available on Apicomplexan parasites has not yet provided keys to solutions to health problems associated with the parasites. Analogies to other organisms could provide valuable insights into the operations of the parasite. There are reports of Apicomplexan parasites having plastids, as well as the nuclear encoded proteins, tubulin, calmodulin, PPi phosphofructokinase and enolase, which are reported to be similar in part to, or homologous with, counterparts in plant-like, lower life forms and higher plants. There are reports of a plastid genome and components of a protein synthetic system in a plastid-like organelle of Apicomplexans. Plasmodium and
T. gondii
plastid DNA sequences were reported to have homologies to algal plastid DNA sequences. The plastid membrane of
T. gondii
was reported to be composed of multiple membranes that appear morphologically similar to those of plant/algal chloroplasts, except for the presence of two additional membranes in the
T. gondii
plastid, suggesting that it may have been an ancient algal endosymbiont. Some of these Apicomplexan proteins such as tubulin, calmodulin and enolase with certain plant-like features also are found in animals, and therefore may appear in the host as well as the parasite. A homologue to a gene, psbA encoding a plant protein important for photosynthesis, also was said to be present in Apicomplexans.
Certain herbicides have been reported to inhibit the growth of Apicomplexans. The herbicides which affect growth of Apicomplexans are known to affect plant microtubules or a plant photosynthetic protein. In addition, a compound, salicylhydroxamic acid, (SHAM), had been found to inhibit
Plasmodium falciparum
(malaria) and
Babesia microti.
Techniques of medicinal chemistry and rational drug design are developed sufficiently to optimize rational construction of medicines and their delivery to sites where Apicomplexan infections occur, but such strategies have not yet resulted in medicines effective against Apicomplexans. Rational development of antimicrobial agents has been based on modified or alternative substrate competition, product competition, change in enzyme secondary structure, and direct interference with enzyme transport, or active site. Antisense, ribozymes, catalytic antibodies, disruption of cellular processes using targeting sequences, and conjugation of cell molecules to toxic molecules are newly discovered strategies employed to interrupt cellular functions and can be utilized to rationally develop novel antimicrobial compounds, but they have not yet been utilized to design medic
Johnson Jennifer J.
McLeod Rima L. W.
Mets Laurens
Roberts Craig W.
Roberts Fiona
Barnes & Thornburg
Martin Alice O.
McGarry Sean
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