1. Design, Synthesis, and Structure-Activity Relationship Study of Biologically Active Compounds of Medicinal Interest

Discovery and development of new and potent taxoid anticancer agents, anti-thrombotic agents, cardiovascular agents, various enzyme inhibitors are our major focus in collaboration with oncologists, pharmacologists, cell biologists, hematologists, and toxicologists. These agents are being designed based on molecular modeling, synthesized by using new and efficient organic syntheses, and evaluated their potency which feeds back newer and better design. We have been developing a variety of methods for the syntheses of these agents, e.g., extremely effective asymmetric synthesis of nonprotein amino acids, peptides, peptide mimetics, and taxoids using b-Lactam Synthon Method.

I. Design, synthesis, and structure-activity relationship study of biologically active taxoids analogs:

Paclitaxel and docetaxel are potent anticancer reagents. Extensive SAR studies of paclitaxel and its congeners in our laboratories led to the discovery of second-generation taxoids and advanced second-generation taxoids bearing modification at different positions including C-2, C-10 and C-3’ on the taxoid structure. These taxoids exhibit excellent activities particularly against multidrug resistant (MDR) cancer cell lines as well as tumors and some of them including SB-T-101131 and SB-T-1213 are orally active. SB-T-101131 "Orataxel" (IDN5109, Bay 55-8862) is currently in phase I human clinical trials, and its phase II trials are scheduled to start in December 2001. Further SAR studies are actively underway in these laboratories.

II. Design and synthesis of macrocyclic taxoids:

Recently, several structural dissimilar natural products (epothilones, eleutherobin, discodermolide and laulimalide) were found to share the same mechanism of action with paclitaxel. Based on extensive SAR studies and molecular modeling, we have proposed a plausible common pharmacophore for those microtubule-stabilizing agents. Based on this common pharmacophore model, a series of macrocyclic taxoids as hybrid constructs has been designed and synthesized. Various hybrid taxoids have been designed and synthesized. Further extension of this line of research to the design and synthesis of de novo microtubule-stabilizing agents that do not have taxane skeleton is under active investigation.

A new computational docking protocol has been developed and used in combination with conformational information inferred from REDOR-NMR experiments on microtubule bound 2-(p-fluorobenzoyl)paclitaxel to delineate a unique tubulin binding structure of paclitaxel. A conformationally constrained macrocyclic taxoid bearing a linker between the C-14 and C-3'N positions has been designed and synthesized to enforce this "REDOR-taxol" conformation. The novel taxoid SB-T-2053 inhibits the growth of MCF-7 and LCC-6 human breast cancer cells (wild-type and drug resistant) on the same order of magnitude as paclitaxel. Moreover, SB-T-2053 induces in vitro tubulin polymerization at least as well as paclitaxel, which directly validates our drug design process. These results open a new avenue for drug design of next generation taxoids and other microtubule-stabilizing agents based on the refined structural information of drug-tubulin complexes, in accordance with typical enzyme-inhibitor medicinal chem. precepts.

III. Design and synthesis of de novo cytotoxic alkaloids through mimicking taxoid skeleton:

Based on a common pharmacophore model and the hypothesis that the baccatin core of taxoids is a scaffold securing the proper orientation of the side chains, a bicyclic alkaloid scaffold was designed as a baccatin surrogate. Using this scaffold, two novel macrocyclic and open-chain taxoid-mimicking' compounds were synthesized. Two of these 'taxoid-mimics', I and II, were found to possess cytotoxicity with micromolar level IC50 values against human breast cancer cell lines.

IV. Taxoids for Potent Cytotoxic Agents in Tumor-Activated Prodrugs (TAPs):

One of the key problems with conventional chemotherapy is its toxicity: In addition to killing cancer cells, anticancer drugs destroy healthy tissue, causing the side effects usually associated with this type of treatment. ImmunoGen has developed the technology known as "tumor-activated prodrugs," (TAPs), in which the anticancer agents are linked chemically to certain type of monoclonal antibodies. Those antibodies may specifically bind to antigens that are known to be expressed predominantly on cancer cell surfaces. The anticancer drug is inactive until it enters the tumor cell to which it is targeted by the monoclonal antibody. In this way, the anticancer drugs are exclusively delivered to the cancer cells, leaving the normal cells intact. We have designed and synthesized novel taxoids used as cytotoxic agents in TAPs. Preliminary biological tests showed very impressive results.

In this first-generation mAb-taxoid conjugates, the orginal taxoid molecule was not released because of the compromised modification of the taxoid molecule to attach the disulfide linker. Accordingly, the cytotoxicity of the taxoid released in these conjugates was 8-10 times weaker than the parent taxoid. In order to solve this problem, we have been developing the second-generation mechanism-based disulfide linkers. One of our approaches is the glutathione-triggered cascade drug release, forming a thiolactone as a side product.

V. Novel fatty acid-second-generation taxoid conjugates as promising anticancer agents:

Polyunsatd. fatty acids such as docosahexaenoic acid (DHA), linolenic acid, and linoleic acid were linked to the C-2' position of the second-generation taxoids that could overcome MDR caused by overexpressed ABC transporters. The new conjugates, tested in vivo, exhibited strong activity against drug-resistant colon cancer and drug-sensitive ovarian cancer xenografts in mice. Two of the new conjugates, DHA-SB-T-1214 and DHA-SB-T-1213, were found to achieve the total regression of drug-resistant and drug-sensitive tumors, resp., in the animal models with substantially reduced systemic toxicity.

VI. Noncytotoxic taxanes as novel antituberculosis agents:

FtsZ, the bacterial tubulin homologue, is an essential cell-division protein that polymerizes into a cytokinetic ring at the septum site.  Based on the structural homology with tubulin, we hypothesized that compounds that stabilize microtubules should inhibit the (de)polymerization of FtsZ from Mycobacterium tuberculosis (MTB).  Subsequently, screening of 120 taxanes identified a number of compounds that exhibited significant anti-tuberculosis activity.  Through systematic rational drug design, we discovered that C-seco-TRAs are non-cytotoxic at the upper limit of detection (>80 µM), while maintaining MIC₉₉ values of 1.25-2.5 µM against drug-resistant and drug-sensitive MTB strains.  Polymerization assays demonstrated that these C-seco-TRAs inhibited MTB FtsZ polymerization in a dose dependent manner. Thus, these novel taxanes specifically target FtsZ, but not microtubules.

Phone: (631)632-7947 or (631)632-7890 (Patricia Marinaccio, Project Staff Assistant)

Fax: (631)632-7942

Email: iojima@notes.cc.sunysb.edu