Leonard Katz - US grants

The objective of the proposed work is the biosynthesis of analogs of rapamycin in specifically constructed mutants of Streptomyces hygroscopicus ATCC 29253, the rapamycin producer. These novel compounds will be tested for their biological activity as immunosuppressive agents and will be valuable starting materials for chemical modification. This objective will be accomplished through (1) characterizing the (rap) genes involved in rapamycin biosynthesis, (2) introducing mutations into specific sites in rap DNA and replacing the wild type gene with its mutant counterpart, (3) fermenting the mutants, isolating the rapamycin analogs and determining their structure and (4) evaluating the novel rapamycin analogs for their biological activity. Steps 1 and 2 involve transposon mutagenesis, gene cloning and disruption, nucleotide sequencing and gene replacement which will be done in the Leonard Katz (P.I.) and Richard Hutchinson (Co-P.I.) laboratories at Abbott Laboratories and the University of Wisconsin, respectively. Step 3 will be performed at Abbott under the direction of James McAlpine (Co-P.l.). Novel rapamycin analogs will turned over to K. Mollison and B. Lane at Abbott Laboratories for evaluation of their biological properties. This proposal is based on our recently acquired understanding of the organization of the genes (eryA) involved in the biosynthesis of 6-deoxyerythronolide B (6-dEB), the 14-membered macrocyclic lactone precursor of the macrolide antibiotic erythromycin; on our ability to introduce mutations into eryA which resulted in the formation of structural analogs of 6-dEB of predicted structure; and on our belief that the genes for rapamycin biosynthesis will be organized similarly and amenable to analogous manipulations. Thus it will be possible to pre-select the structure of the compounds desired and construct a family of genetically engineered S. hygroscopicus strains each producing a rapamycin analog carrying a change at a unique functional site of the molecule. These compounds, or their chemically modified derivatives, can be used in binding studies with rapamycin binding proteins, in functional tests for immunosuppressive activity, and in bioavailability studies. The proposed research presents a novel method to make structural analogs of a natural compound that would be difficult to make by conventional chemical approaches. Our work will provide molecules that will shed light on the structure/activity relationships of macrocyclic immunosuppressants and could potentially lead to the discovery of improved forms of such therapeutic agents. It will also expand knowledge about microbial (Streptomyces) genetics and the structure of complex polyketide synthases, thus setting the stage for definitive studies of this unusual enzymology.

Resistance to macrolide antibiotics has increased at alarming rates in recent years, driving the need to develop new and more effective antibiotics. The long term objective of this proposal is to develop a novel 16-membered macrolide antibiotic that is active against erythromycin-resistant Streptococcus pneumoniae and other Gram positive pathogens and which can be produced at reasonable cost. The proposed compound is designed to exhibit its potency through the novel mechanism of synergistic multi-domain ribosomal binding. Consequently, the compound should not induce macrolide resistance and evade all known efflux mechanisms that confer macrolide resistance. Phase I is a proof of principle project to produce a small series of derivatives of a 16- membered macrolide that is a readily available fermentation product, and determine whether the derivatives bind to domain II of the ribosomes and exhibit increased potency against macrolide-resistant strains. Phase II Specific Aims will be to optimize the derivatives to achieve oral bioavailability. Lead compounds will be examined in vitro and in animals for efficacy, toxicity and pharmacokinetics with the intent of advancing one or more to clinical development. PROPOSED COMMERCIAL APPLICATION: Clinical development candidates could be commericialized as anti-infective agents only after approval by the appropriate regulatory authorities.

DESCRIPTION (provided by applicant): The long term objective of this proposal is to generate novel anticancer agents which are commercially feasible to prepare by fermentation processes. Epothilone D, a 16-membered polyketide-derived macrolactone, has promising antitumor activity but is produced in low titers by the native organism, Sorangium cellulosum, and is only sparingly soluble in water. Chemical synthesis of epothilones has been achieved but the methods are elaborate and not feasible for scale-up for pharmaceutical applications. The Phase I Specific Aim of this proposal is to generate a number of epothilone analogs by genetic engineering which are more water soluble than and at least as potent as the parent. These analogs will be tested in cell culture (taxol susceptible and resistant lines) and in vitro assays and water solubility measured (octanol-water partition coefficients). Phase II would involve the generation of additional analogs by diketide feeding. The two best compounds in terms of a) potency, b) water solubility and c) economics of production would be carried forward into further testing. Sufficient amounts of each would be produced to use in animal tumor models and in preliminary animal toxicity and pharmacokinetic studies. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE

DESCRIPTION : (adapted from p.2 of proposal)This is a revised phase II application concerned with developing a method of production of epithilone D. Epothilones are polyketides isolated from the myxobacterium Sorangium cellulosum that have shown great promise as anticancer agents. Although the two compound classes are structurally unrelated, the mechanism of action, stabilization of microtubules, is similar to that of paclitaxel (Taxol). Epithilones are active against Taxol resistant cell lines, are effective against multiple drug resistant cell lines, and are more water-soluble and thus more easily administered than Taxol. Because of these properties, one epithilone, epithilone D, has been chemically synthesized, and is being considered for clinical evaluation. Yields are low, both in the chemical synthesis and in the natural host organism. In phase I the epithilone biosynthesis genes were cloned and sequenced, and expressed in the fast growing heterologous host Streptomyces coelicor. A problem was that expression of epithilone biosynthesis genes was toxic to this host. Phase 2 work seeks to first overcome or circumvent this toxicity. Following this, a series of steps will be taken to maximize biosynthesis of Epithilone D. PROPOSED COMMERCIAL APPLICATION: Not Available

[unreadable] DESCRIPTION (provided by applicant): The long term goal of this project is to prepare novel macrolide antibiotics that are active against methicillin-resistant, macrolide-resistant, Staphylococcus aureus strains, in an attempt to augment chemotherapy of diseases caused by antibiotic-resistant human pathogens. These compounds will simultaneously block protein synthesis by inhibiting the peptidyl transferase (PT) activity of the ribosomes and at the same time overcome the loss of binding of normal macrolides to macrolide-resistant ribosomes by carrying chemical extensions that enable binding to other ribosomal sites. We will test the concept that this approach is feasible by producing a small series of novel molecules that can be chemically modified at different sites to inhibit PT and to bind tightly to ribosomes. The specific aims for the Phase I research are: (1) Construct recombinant microorganisms making a small series of 14-membered macrolides containing the disaccharide mycaminose-mycarose at the C5 position as direct fermentation products. (2) If production of a 14-membered macrolides containing the disaccaride is not possible, construct organisms making a small series of 14-membered macrolides containing the monosaccharide mycaminose at the C5 position. (3) Chemically acylate the sugars of the compounds produced in aims 1 or 2 and determine if PT activity of bacterial ribosomes is inhibited in a variety of assays. (4) Add side chains to the macrolactone backbone of the molecules that inhibit PT activity to enable tight binding to methylated and non-methylated bacterial ribosomes. The lead compounds discovered would be optimized in Phase II research.

DESCRIPTION (provided by applicant): The incidence of aspergillosis, and other invasive mould infections (IMIs), is increasing in hospitals worldwide at an alarming rate. These infections occur primarily in neutropenic patients undergoing cancer chemotherapy and in transplant centers where patients are undergoing immunosuppressive therapy. The treatments employed for these infections consist of the currently available antifungal drugs, often in combination, with failures approaching 50% and high associated mortality. Where successful, treatments are usually long term and usually prolong the hospitalization of the patient. Aspergillus fumigatus, and other Aspergillus species account for about 70% of IMIs, the remainder caused by Scedosporium, Cryptococcus, Fusarium, Rhizopus and other moulds. Current development of antifungal drugs has always targeted Candida infections and has not focused on Aspergillus and other invasive moulds. The ambruticins, polyketides with unusual structures discovered in the 1970s and 1990s from different strains of the myxobacterium Sorangium cellulosum, have high potencies against a number of Aspergillus strains, good oral bioavailability and excellent safety profiles in laboratory animals. In this Phase I proposal, we will make a number of semisynthetic analogs of ambruticin S and ambruticin VS4 and determine their in vitro potencies against a number of Aspergillus species, Cryptococcus, Rhizopus, Scedosporium and Fusarium species. Other in vitro experiments will include the determination of synergy or antagonism of ambruticin with other antifungal agents, and determination of the post-antibiotic effect of these compounds. We will also determine the pharmacokinetic parameters and LD50 of selected compounds. Results obtained during the one year granting period will allow us to make intelligent and systematic choices of molecules for animal efficacy and IND-enabling studies in subsequent Phase II research.