Investigation of combretastatin, dihydronaphthalene, benzosuberene, and quinoline-based analogues as inhibitors of tubulin polymerization with potential to function as vascular isrupting gents, and selected compounds as water-soluble prodrug salts and drug-linker conjugates
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Differences from normal and tumor vasculature directed to the concept of discovery of vascular disrupting agents (VDAs), which interfere with oxygen and nutrients supply for tumor, as potential therapeutic agents for cancer chemotherapy. Inspired by the natural products colchicine, combretastatin A1 (CA1) and combretastatin A4 (CA4), the Pinney Group (Baylor University) has developed a variety of potent VDAs, which function as inhibitors of tubulin polymerization, such as combretastatin (KGP06 and KGP08), dihydronaphthalene (KGP05 and OXi6196), benzosuberene (KGP18 and KGP156), benzo[b]thiophene, and indole-based (OXi6196 and OXi6197) analogues. In an effort to extend the structure-activity relationship studies of VDAs bound in the colchicine binding site and using selected Pinney Group VDAs as models, several combretastatin, benzosuberene, dihydronaphthalene, and quinoline-based derivatives were designed and synthesized. For the purpose of improving water solubility and potential bioavailability, synthetic modifications to amino acid prodrug conjugates (AAPCs) of amino variant of the Pinney Group VDAs including KGP05, KGP06, KGP08, and KGP156 were also achieved and afforded both glycinamide and serinamide prodrugs of each parent VDA. These AAPCs were evaluated for their cytotoxicity against selected cancer lines, ability to inhibit tubulin polymerization and colchicine binding, and cleavability by the enzyme leucine aminopeptidase (LAP) to generate parent compound. In addition, both KGP08 and the water-soluble glycinamide hydrochloride salt of KGP05 displayed greater than 95% decrease in bioluminescence (compared to saline control) in a tumor bearing (MDA-MB-231-luc) SCID mouse model 2 and 4 h (respectively) post treatment with administeration of moderate dosage. Antibody-drug conjugates (ADCs) served as novel agents for cancer treatment by combining monoclonal antibody (mAb) with potent anticancer agent, thus taking advantage of specific characteristics of each component. KGP18 and KGP156 were used for the studies of design and synthesis of drug-linker conjugates by using linker payload of FDA-approved ADC (Adcetris®) as template. Ultimately, not only was KGP18 successfully incorporated into the dipeptide linker payload by chemical reactions via initiation of activating KGP18 using para-nitrophenyl chloroformate and utilizing self-immolative spacer N,N'-dimethylenediamine (DMED), but also KGP156 was fruitfully connected with the dipeptide linker payload by synthetic modifications which is beneficial from first formation of isocyanate intermediate using triphosgene.