DDB and betulinic acid-derivatives as potent chemosensitizing, chemopreventive, and anti-HIV agents

The overall goals of this research are to design and synthesize novel DDB and betulinic acid derivatives to evaluate their chemosensitizing, chemopreventive, and anti-HIV activities. Structure-activity relationships (SAR) are established in order to discover novel chemical entities, and to explore the mechanism(s) of action.;Dimethyl diphenyl bicarboxylate (DDB) and its analog, bicyclol, were reported to have chemosensitizing activity in several multidrug resistant cancer cell lines. In a continuing study, an easy modification was accomplished by reduction to 2,2'-bismethylhydroxy DDB followed by esterification with various acids. This synthetic route was applied to develop a series of compounds and establish SAR. SAR studies on these compounds revealed that analogs with aromatic and bulky aliphatic side chains at the 2,2'-hydroxymethyl positions effectively and significantly sensitized MDR-1 over-expressed cells to three anticancer drugs, paclitaxel (TAX), vincristine (VCR), and doxorubicin (DOX). DDB derivatives 83 and 90 were five to ten times more effective than verapamil (VRP) for TAX and VCR reversal ability. Analog 73 also showed five times greater chemosensitizing effect than VRP against DOX. The mechanism of action studies showed that DDB analogs elevate cellular concentration of DOX via inhibition of P-glycoprotein.;Nineteen DDB analogs were evaluated in an in vitro short-term Epstein Barr virus early antigen (EBA-EA) activation assay. Three of the most potent compounds (83, 85 and 106) were also tested for inhibitory effects on skin tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test. Compound 106 with a prenyl ether had the most significant cancer preventive activity in vitro, and it also exhibited a remarkable inhibitory effect on skin tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test.;Importantly, active DDB analogs displayed no cytotoxicity either in chemoreversal or cancer prevention assays, suggesting that they are good leads for further development.;In chapter 5, another natural product, betulinic acid, was studied since our group has focused on modification of this molecule for years. Most researches were on the modifications of positions 3, 19 and 28. Modifications on ring A were largely under investigation. Therefore, thirteen new betulinic acid derivatives were designed, synthesized, and evaluated for anticancer, cancer prevention, or anti-HIV activity. In the cytotoxic activity evaluation, compounds 120, 123, 126, and 129 exhibited GI50 < 10 μM, and compound 120 with a 3-methyl ester and 4, 2β-vinyl group was the most potent. SAR study showed that the 3-methyl ester and 4, 23-vinyl group are important for potency. A C-3 carboxylic acid modification totally abolished the activity. A carboxylic acid was better than an N-heptane acetamide at C-28. In the cancer prevention assay, compound 121 showed the strongest inhibition in EBV-EA activation, and was more potent than curcumin, even at low concentrations. The SAR trends were similar to those for anticancer activity, except that a C-3 carboxylic acid was preferred. In the anti-HIV assay, only compound 119 with an lactone A-ring and 28-N heptane acetamide showed weak activity, and was identified as an entry inhibitor. However, its activity was weaker than a known entry inhibitor, A43-D, with the same C-28 side chain.