5‘-bromoacetamido-5‘-deoxyadenosine. A novel reagent for labeling adenine nucleotide sites in proteins

Daunorubicin conjugated to a monoclonal anti-CA125 antibody selectively kills human ovarian cancer cells

The present study was designed to test the in vitro efficacy for human ovarian cancer cells of daunorubicin (DNR) conjugated to a monoclonal antibody (OC125). The OC125 antibody specifically binds to the antigenic protein CA125 from human ovarian carcinoma. New analogs of DNR containing various linker groups were conjugated to mouse monoclonal anti-CA125 antibody (DNR-OC125); nonspecific murine IgG1 (DNR-IgG1); or bovine serum albumin (DNR-BSA). The DNR-protein conjugates were all stable for several days in neutral solutions at room temperature. The DNR-OC125 conjugates selectively killed dividing cell populations but not nondividing cell populations of two human ovarian cancer cell lines (SK-OV-3 or OVCAR-3) that express the CA125 antigen. Equivalent concentrations of DNR-IgG1 or DNR-BSA conjugates were neither toxic to the dividing nor the nondividing populations of SK-OV-3 or OVCAR-3 cells. Only those DNR-protein conjugates linked to OC125 were cytotoxic to dividing cell populations of both cell lines. This indicates that cytotoxicity is dependent on OC125 antibody-CA125 antigen binding which concentrates DNR on the ovarian cancer cells. We advance the hypothesis that following antibody-antigen binding, DNR is released from the conjugate and it intercalates in DNA by a mechanism similar to that of the unmodified DNR. The new DNR-OC125 conjugate may be useful for delivering DNR to ovarian tumors that express the CA125 antigen because the drug-antibody conjugates (1) retain the cytotoxic characteristics of the unmodified drug: (2) specifically kill the human ovarian cancer cells that express the CA125 antigen; and (3) are completely stable for days in neutral solutions at room temperature.

Affinity labeling of the cofactor-binding site of estradiol 17 beta-dehydrogenase of human placenta by 5'-p-fluorosulfonylbenzoyl adenosine

An analogue of adenosine nucleotide, 5'-p-fluorosulfonylbenzoyl adenosine (5'-FSB-Ado), appears to interact irreversibly with the cofactor-binding site of estradiol 17 beta-dehydrogenase of human placenta. This conclusion is based on the following observations: (1) The estradiol 17 beta-dehydrogenase is inhibited by 5'-FSB-Ado. When NAD+ is the variable component in the presence of saturated amount of steroid, the type of the inhibition is competitive in nature. When the steroid is the variable component, mode of the inhibition becomes non-competitive. The results suggest reversible binding of 5'-FSB-Ado to the cofactor-binding site of the dehydrogenase. (2) 5'-FSB-Ado inactivates irreversibly the estradiol 17 beta-dehydrogenase in time- and concentration-dependent manners, following pseudo-first-order kinetics. But, no inactivation is observed in the presence of p-fluorosulfonylbenzoic acid, suggesting that adenosine moiety of 5'-FSB-Ado is essential for the affinity labeling of estradiol 17 beta-dehydrogenase. (3) NADP+ protects completely estradiol 17 beta-dehydrogenase from the inactivation of 5'-FSB-Ado, whereas NAD(H) is partially protective against the inactivation, suggesting that phosphate moiety at 2'-position of NADP+ disturbs the covalent binding of 5'-FSB-Ado at or near the cofactor-binding site of the enzyme. (4) 2',5'-ADP shows the significant protection against the inactivation by 5'-FSB-Ado, but less effect is observed in the presence of nicotinamide mononucleotides. These results suggest that 5'-FSB-Ado is an affinity ligand for binding-site of adenosine nucleotide moiety of the cofactor.