Immunization of ovarian cancer patients with a synthetic Lewis(y)-protein conjugate vaccine: a phase 1 trial.

As the initial step in developing carbohydrate-based vaccines for the treatment of ovarian cancer patients in an adjuvant setting, 25 patients were immunized with a Lewis(y) pentasaccharide (Le(y))-keyhole limpet hemocyanin (KLH)-conjugate vaccine together with the immunological adjuvant QS-21. Four different doses of the vaccine, containing 3, 10, 30, and 60 microg of carbohydrate were administered s.c. at 0, 1, 2, 3, 7, and 19 weeks to groups of 6 patients. Sera taken from the patients at regular intervals were assayed by ELISA for reactivity with naturally occurring forms of Le(y) (Le(y)-ceramide and Le(y) mucin) and by flow cytometry and a complement-dependent cytoxicity assay for reactivity with Le(y)-expressing tumor cells. The majority of the patients (16/24) produced anti-Le(y) antibodies as assessed by ELISA, and a proportion of these had strong anti-tumor cell reactivity as assessed by flow cytometry and complement-dependent cytotoxicity. One serum, analyzed in detail, was shown to react with glycolipids but not with glycoproteins or mucins expressed by ovarian cancer cell line OVCAR-3. The vaccine was well tolerated and no gastrointestinal, hematologic, renal, or hepatic toxicity related to the vaccine was observed. On the basis of this study, Le(y)-KLH should be a suitable component for a polyvalent vaccine under consideration for the therapy of epithelial cancers.

A second generation synthesis of the MBr1 (globo-H) breast tumor antigen: new application of the n-pentenyl glycoside method for achieving complex carbohydrate protein linkages.

A new synthesis of the hexasaccharide MBr1 antigen (globo-H) is reported. A revised construction with improved efficiency was necessary because an anti-cancer vaccine containing this antigen is entering phase II and phase III clinical trials for prostate cancer. The key feature of this second generation synthesis is the preparation of globo-H as its n-pentenyl glycoside. This group serves as an anomeric protecting group and as a linker for bioconjugation to carrier protein. The resultant synthesis allows for the production of suitable quantities of globo-H for clinical trials.

Polyclonal antibodies from patients immunized with a globo H-keyhole limpet hemocyanin vaccine: isolation, quantification, and characterization of immune responses by using totally synthetic immobilized tumor antigens.

We have previously reported on a carbohydrate-based vaccine program for immunotherapy in cancer patients. One such vaccine, based on the globo H antigen conjugated to the protein keyhole limpet hemocyanin (KLH), has been in clinical evaluation. Although this and other carbohydrate vaccines have been shown to induce antibody responses, there are currently no quantitative data on the antibody levels achieved in immunized patients by these or other anti-cancer vaccines. We report herein an efficient route to complex synthetic oligosaccharides attached to an affinity matrix for identifying and isolating antibodies elicited against such a carbohydrate-based vaccine in humans. Pre- and postvaccination profiles from serum samples of patients immunized with globo H-KLH were compared. All anti-globo H antibody activity was efficiently separated from other serum constituents. The isolated antibodies were readily quantified, and their specificities were analyzed. Since no comparable data were available on antibodies resulting from the vaccination of other cancer patients, we compared the observed levels with those quoted in studies with bacterial polysaccharide vaccines that had been quantified. Remarkably, cancer patients immunized with globo H-KLH produce anti-globo H antibody levels often exceeding those formed by immunization with bacterial polysaccharides. In addition, substantial quantities of both IgG and IgM antibodies were elicited, clearly indicating a class switch to IgG. Taken together, these analyses serve to clarify several aspects of the immune response to the vaccine and give several new insights to the carbohydrate-based vaccination strategy. Furthermore, antibodies so isolated could well have applications in clinical therapy.

Reversal of anticancer multidrug resistance by the ardeemins.

Two "reverse prenyl" hexahydropyrroloindole alkaloids, 5-N-acetylardeemin and 5-N-acetyl-8-demethylardeemin, were evaluated as reversal agents in cells exhibiting a multidrug resistant (MDR) phenotype. These ardeemins (i) reversed drug resistance to vinblastine (VBL) or to taxol as much as 700-fold at relatively noncytotoxic concentrations in vitro; (ii) as a single agent at high concentrations killed MDR cells more efficaciously than the respective parent wild-type cells; and (iii) exhibited strong synergistic effects with doxorubicin (DX) and VBL against the growth of MDR neoplastic cells, and to a lesser extent, of the parent wild-type cells. Mechanistic studies showed that photoaffinity labeling of P-glycoprotein (Pgp) with [3H] azidopine was competitively inhibited by the ardeemins. Resistance to DX in MDR-[Pgp+ and MDR-associated protein (MRP)+], MDR-Pgp+, lung resistance protein (LRP)+-expressing, and wild-type lung cancer cells were reversed 110- to 200-fold, 50- to 66-fold, 7- to 15-fold, and 0.9- to 3-fold, respectively, by 20 microM of the ardeemins. Moreover, these compounds increased the intracellular accumulation of VBL and markedly decreased its efflux. Finally, in vivo combination studies demonstrated that nontoxic doses of the ardeemins with DX significantly improved the chemotherapeutic effects in B6D2F1 mice bearing DX-resistant P388 leukemia, and nude mice bearing human MX-1 mammary carcinoma xenografts. The above features indicate that the ardeemins may have utility in the therapy of cancer.

The practical synthesis of a methylenebisphosphonate analogue of benzamide adenine dinucleotide: inhibition of human inosine monophosphate dehydrogenase (type I and II).

beta-Methylene-BAD (8), a nonhydrolyzable analogue of benzamide adenine dinucleotide (BAD), was synthesized as potential inhibitor of human inosine monophosphate dehydrogenase (IMPDH). Treatment of 2',3'-O-isopropylideneadenosine 5'-methylenebisphosphonate (15) with DCC afforded P1,P4-bis(2',3'-O-isopropylideneadenosine) 5'-P1,P2:P3,P4-dimethylenetetrakisphosphonate (17). This compound was further converted with DCC to an active intermediate 18 which upon reaction with 3-(2',3'-O-isopropylidene-beta-D-ribofuranosyl)benzamide (19) gave, after hydrolysis and deisopropylidenation, the desired beta-methylene-BAD (8) in 95% yield. In a similar manner, treatment of 18 with 2',3'-O-isopropylidenetiazofurin (21) followed by hydrolysis and deprotection afforded beta-methylene-TAD (5) in 91% yield. Compound 8 (IC50 = 0.665 microM) was found to be a 6-8 times less potent inhibitor of IMPDH than 5 (IC50 = 0.107 microM) and was almost equally potent against IMPDH type I and type II. Although TAD and beta-methylene-TAD were bound by LADH with the same affinity, the binding affinity of 8 toward LADH (Ki = 333 microM) was found to be 50-fold lower than that of the parent pyrophosphate 7 (Ki = 6.3 microM).

Chemical synthesis of benzamide adenine dinucleotide: inhibition of inosine monophosphate dehydrogenase (types I and II).

Treatment of 3-(2,3-O-isopropylidene-beta-D-ribofuranosyl)benzamide (6) with POCl3 in (EtO)3-PO afforded only little phosphorylation product (8, 5%), but the major product was 5'-chlorobenzamide riboside (7, 85%). Reaction of 6 with 2-cyanoethyl N,N-diisopropylchlorophosphoramidite followed by 2-cyanoethanol/tetrazole treatment and oxidation with tert-butyl peroxide gave a 1:1 mixture of the desired 5'-O-bis(2-cyanoethyl) phosphate 9 and the chloro derivative 7. This mixture was treated with methanolic ammonia and partitioned between CHCl3 and water. The 2',3'-O-isopropylidenebenzamide mononucleotide (8) was obtained in 21.2% overall yield from the aqueous layer. Compound 8 was then converted into the corresponding imidazolide 11b which, upon coupling with 2',3'-O-acetonide of AMP, afforded the acetonide of benzamide adenine dinucleotide (15) in 94% yield together with small amounts of symmetrical pyrophosphates P1,P2-bis(2',3'-O-isopropylideneadenosin-5'-yl)pyrophosphate (13, 3%) and P1,P2-bis(2',3'-O-isopropylidene-3-(carbamoylphenyl)-5'-ribosyl)py rophosphate (14, 2%). Deprotection of 15 with Dowex 50/H+ in water afforded the desired benzamide adenine dinucleotide (BAD) in 93% yield. BAD inhibits inosine monophosphate dehydrogenase type I (IC50 = 0.78 microM) and type II (IC50 = 0.88 microM) with same degree of potency.

NAD-analogues as potential anticancer agents: conformational restrictions as basis for selectivity.

Cofactor type inhibitors (NAD-analogues) of IMP-dehydrogenase (IMPDH) were synthesized and their application as potential anticancer agents are discussed. C-nucleoside isosteres of NAD, C-NAD and C-PAD, showed an effective competitive inhibition of IMPDH, C-NAD but not C-PAD caused extremely potent inhibition of alcohol dehydrogenase. We also synthesized compounds in which nicotinamide riboside was replaced with tiazofurin (TAD-analogues) and the 2' and 3'-positions of adenosine part were fluorinated. The ribose ring of 2'-deoxy-2'-fluoroadenosine is in the C3'-endo conformation whereas 3'-deoxy-3'-fluoroadenosine favors the C2'-endo sugar pucker. These derivatives are good inhibitors of IMPDH type II, the isoenzyme dominant in neoplastic cells. In contrast, all these analogues showed rather week inhibitory activity against alcohol dehydrogenase. Nicotinamide riboside derivatives in which the base and the sugar are linked through an oxygen or a methylene bridge were synthesized. NAD-analogues containing such conformationally restricted nicotinamide nucleoside moiety (syn or anti) are expected to be selective inhibitors of B-specific (IMPDH) or A-specific dehydrogenases, respectively.

Potent inhibitors of human inosine monophosphate dehydrogenase type II. Fluorine-substituted analogues of thiazole-4-carboxamide adenine dinucleotide.

Three analogues of thiazole-4-carboxamide adenine dinucleotide (TAD) (1-3) containing a fluorine atom at the C2' of the adenine nucleoside (in the ribo and arabino configuration) and at the C3' (in the ribo configuration) were synthesized in high yield from the corresponding 5'-monophosphates of 2'-deoxy-2'-fluoroadenosine (9), 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-adenine (17), and 3'-deoxy-3'-fluoroadenosine (14), respectively. Pure 2',3'-O-isopropylidene-tiazofurin 5'-phosphorimidazolide (8) was obtained by phosphorylation of the protected tiazofurin followed by treatment with carbonyldiimidazole and HPLC purification. Reaction of 8 with 9 in DMF-d7 (monitored by 1H and 31P NMR) afforded the desired dinucleotide 12, which after deisopropylidenation gave 1 in 82% yield. Small amounts of symmetrical dinucleotides AppA (10, 7.2%) and TRppTR (11, 8.0%) were also isolated during HPLC purification of the major product 12. In a similar manner, compounds 2 and 3 were obtained by coupling of 8 with 14 and 17 in 80% and 76% yield, respectively. All newly prepared fluoro-substituted compounds as well as beta-CF2-TAD, earlier synthesized by us, showed good inhibitory activity against inosine monophosphate dehydrogenase type II, the isozyme which is predominant in neoplastic cells. Binding of 1 (Kis = 0.5 microM), 2 (Kis = 0.7 microM), and 3 (Kis = 2.9 microM) was comparable to that of TAD (Ki = 0.2 microM). The difluoromethylene bisphosphonate analogue, beta-CF2-TAD (Ki = 0.17 microM), was found to be equally effective as the best cofactor-type inhibitor, beta-CH2-TAD (Ki = 0.11 microM). Interestingly, the level of inhibition of horse liver alcohol dehydrogenase by these compounds was found to be much lower (0.1 mM for 1 and 2 and no inhibition up to 10 mM for 3). These findings show that inhibition of tumor-induced inosine monophosphate dehydrogenase type II is selective and may be of therapeutic interest.

Synthesis of thiazole-4-carboxamide-adenine difluoromethylenediphosphonates substituted with fluorine at C-2' of the adenosine.

Synthesis of an analogue 3 of thiazole-4-carboxamide adenine-dinucleotide (TAD) in which the beta-oxygen atom of the pyrophosphate bridge is replaced by a difluoromethylene group has been achieved. Likewise, 2'-deoxy-2'-fluoroadenosine containing analogues of TAD (4) and its difluoromethylenediphosphonate congener (5) have been synthesized. Adenosine 5'-difluoromethylenediphosphonate (8) was prepared from 5'-O-tosyladenosine (6) and tris(tetra-n-butylammonium)difluoromethylenediphosphonate (7) by a modified procedure of Poulter's. Compound 8 was converted into the 2',3'-cyclic carbonate 9 by treatment with triethyl orthoformate. Treatment of 9 with 2',3'-O-isopropylidenetiazofurin (10) in pyridine in the presence of DCC gave a mixture of dinucleotide 11 and the isopropylidene-protected diadenosine tetraphosphonate 12. After deprotection of 11, the desired beta-difluoromethylene TAD (3) was separated by HPLC as the minor product. The diadenosine tetraphosphonate 12, an analogue of Ap4A, was obtained as the major component. Alternatively, 2',3'-O-isopropylidenetiazofurin (10) was tosylated, and the product 13 was further converted into the corresponding difluoromethylenediphosphonate 14 by coupling with 7. DCC-catalyzed coupling of 14 with 2'-deoxy-2'-fluoroadenosine (15) followed by deisopropylidenation afforded the analogue 5. Again the corresponding tetraphosphonate analogue of tiazofurin 17 was the predominant product. Dinucleotide 4 was obtained by coupling of the carbonyldiimidazole-activated tiazofurin 5'-monophosphate with 2'-deoxy-2'-fluoroadenosine 5'-monophosphate. 2'-Deoxy-2'-fluoroadenosine (15) was prepared efficiently from the known N6-benzoyl-3'-O-tetrahydropyranyladenosine (18), which was converted into 3'-O-tetrahydropyranyl-2'-O-triflyl-5'-O-trityladenosine (20) by tritylation and triflation. Treatment of 20 with sodium acetate in hexamethylphosphoric triamide, followed by deacetylation afforded 9-(3-O-tetrahydropyranyl-5-O-trityl-beta-D- arabinofuranosyl)-N6-benzoyladenine (22), which was then treated with DAST. After deprotection of the product, 15 was obtained in good yield.