Recent advances in catalytic antibodies

Monoclonal antibodies as surrogate receptors in a high throughput screen for compounds that enhance insulin sensitivity

Monoclonal antibodies (MoAbs) were made to a known insulin sensitivity enhancer (ISE) compound, CS-045. The MoAbs were characterized with respect to binding other known thiazolidinedione ISE compounds using a CS-045 labeled with b-phycoerythrin in a competitive particle concentration fluorescence immunoassay (PCFIA). By comparing the rank order of IC50 values for each compound to its respective potency as an ISE, one MoAb (13E3) was selected for further characterization. This MoAb was also used as a surrogate receptor in a high throughput screen to identify novel compounds that compete for binding to CS-045. Some of the hits were found to have efficacy in reducing blood glucose. Subsequently, another group reported that several compounds with the core thiazolidinedione structure of the ISE compounds bound with high affinity to peroxisome proliferator-activating receptors (PPAR). Therefore, we used the MoAb assay to test these and other compounds that are known to bind to PPARgamma and noted crossreactivity with some of the compounds.

Aspects of antibody-catalyzed primary amide hydrolysis

Because there are many known C-terminally amidated peptides of biological importance, there is great potential in medicine and organic synthesis for antibodies that catalyze primary amide bond hydrolysis or formation. We characterized a catalytic antibody, 13D11, raised to a phosphinate hapten, that hydrolyzed the primary amide of a dansyl-alkylated derivative of (R)-phenylalaninamide (DNS-(R)F-NH2). At pH 9.0, 13D11 hydrolyzed DNS-(R)F-NH2 with a kcat of 1.65 x 10(-7) s-1 (kcat/kuncat = 132) and a Km of 432 microM, and was stereospecifically hapten-inhibited (Ki = 14.0 microM). Control experiments indicated that the catalytic activity was not the result of a contaminating protease. In accordance with the hapten being a transition-state analog of base hydrolysis, the rate of DNS-(R)F-NH2 hydrolysis increased with hydroxide concentration to an optimum pH of 9.5. Above pH 9.5, activity declined rapidly suggesting the antibody was inactivated during the long incubation period. This work demonstrates the feasibility of generating catalytic antibodies to hydrolyze unactivated amide bonds without cofactor assistance.