Amphotericin B Analogs

DESCRIPTION (provided by applicant): Current antifungal therapy is limited by the types of drugs available to treat systemic infections due to emerging and comparatively rare fungi different from the common strains of pathogenic Candida, Aspergillus, Cryptococcus and the Zygomycoses. Neutropenic and immunocompromised patients, such as those with hematologic cancer, AIDS or an organ transplant, are especially prone to invasive fungal infection. Amphotericin B (AMB) continues to be an important drug for invasive aspergillosis, candidemia, mucormycosis, fusariosis and Cryptococcosis meningitis because of its potency, broad spectrum of activity and the low incidence of drug resistance associated with its use. Nonetheless, the well-known nephrotoxicity of AMB severely limits long term use of this polyene macrolide antibiotic. The toxicity is related to AMB's high lipophilicity, which causes it to localize in cell membranes, disrupting membrane integrity and causing leakage of ions. The structural alterations of AMB carried out to date have not resulted in an approved drug that retains the potency and activity spectrum of the parent drug while minimizing its nephrotoxicity and improving its water solubility for ease of formulation. Centrose proposes to use its CarboConnectTM technology for rapidly synthesizing libraries of small molecules with attached sugars of diverse structure to seek novel AMB analogs with lesser toxicity and greater water solubility, together with sufficient potency and spectrum of activity. Precedents among other types of small molecule drugs for improvement of their potency and pharmacokinetics (PK), or diminishment of their toxic liability, by sugar addition or modification provide additional support for our belief that attractive AMB analogs can be discovered in this way. Our rapid, empirical approach to drug lead discovery is sensible for a molecule in which the existing sugar is known to be vital for antifungal activity, yet for which the models of the mechanism of action are inadequate to design a structure-based rationale for systematic exploration and drug lead identification. Assays of library members for antifungal potency and spectrum of activity in vitro together with the results of an in vitro surrogate assay for potential nephrotoxicity should allow identification of leads for in vivo testing. That will involve determining the acute nephrotoxicity, antifungal efficacy and PK characteristics in a rodent. The specific aims of Phase are: 1) to synthesize a 50 member library of sugar conjugates representing a diverse array of mono- and disaccharides from the 19- oximino-OCH2CH2N(H)OCH3 derivative of AMB methyl ester aglycon; 2) to examine the feasibility of synthesizing a 40 member library of 3'-N-glycosyl derivatives of AMB methyl ester by the Amidori rearrangement using novel monosaccharides; 3) to screen the resulting neoglycosides and 3'-N-sugar conjugates for antifungal activity in vitro (MIC values) against a panel of six important fungal pathogens; 4) to determine the IC50 for red blood cell hemolysis of the compounds with MIC's =5 micrograms/ml as a surrogate for in vivo nephrotoxicity; and 5) based on all of the results, to select up to 5 AMB analogs for determination of their acute nephrotoxicity, antifungal activity against two fungal pathogens and PK characteristics in a rodent. PUBLIC HEALTH RELEVANCE:The research aims to discover new forms of the broad spectrum antifungal drug, amphotericin B, with lesser toxicity and greater water solubility, together with sufficient potency and spectrum of activity to be selected for development into an new antifungal drug.