Antibodies prodrug activation

Roffler, S.R., and Tseng, T.-L. (1994) Enhanced serum half-life and tumor localization of PEG-modified antibody-enzyme conjugates for targeted prodrug activation. Antibody Engineering Conference. San Diego, California. 

An alternative approach is the use of a tumour-specific antibody to which a prodrug activating enzyme has been attached. Therapeutically inactive prodrugs could be administered by,... 

P. H. J. Houba, R. G. G. Leenders, E. Boven, J. W. Scheeren, H. M. Pinedo, H. J. Hais-ma, Characterization of Novel Anthracycbne Prodrugs Activated by Human /3-Glucuronidase for Use in Antibody-Directed Enzyme Prodrug Therapy , Biochem. Pharmacol. 

Fig. 2. Structure of the antibody Fab fusion protein expressed from the vector in Fig. 1 The antigen-binding region is formed by the VH and VL domains, the foreign protein (FP) fused to the truncated hinge region (H1) may be a toxin or prodrug activating enzyme.

Catalytic antibodies were first reported in 1986 by Lerner and Schultz for the hydrolysis of simple esters. Since then over 100 different reactions have been catalyzed by antibodies, from enantioselective preparative reactions to prodrug activations in vivo [1]. New methods have been developed, including specific immunization protocols, direct screening assays for catalysis, and manipulations with recombinant antibodies via phage display. This article gives an overview of work done towards applying catalytic antibodies for synthetic organic reactions by our and other laboratories. 

Houba PHJ, Leenders RGG. Boven E, Scheeren JW, Pinedo HM, Haisma HJ. Characterization of novel anthracyciine prodrugs activated by human p-glticuronidase for use in antibody-directed enzyme prodiug therapy. Biochem Pharmacol 1996 52 455-463. 

In an interesting study on antibody-catalysed prodrug activation, the phosphonate 205 was prepared by Mitsunobu condensation of the phosphonic acid with the 3 -t2-Tbdms derivative of FdU. This hapten was linked to keyhole limpet hemocyanin and bovine serum albumin via the carboxylate group. The monoclonal antibodies specific for 205 were found to catalyse the hydrolysis of 5 -C -(/V-acetyl-D-valyl)-FdU, an FdU prodrug that was not hydrolysed by endogenous esterases, and a combination of 205 and antibody was as effective as FdU itself in preventing the growth of E.coli in vitro. ... 

Shabat D, Lode H, Perd U, Reisfeld RA, Rader C, Lerner RA, Barbas CF III (2001) In vivo activity in a catalyic antibody-prodrug system Antibody catalyzed etoposide prodrug activation for selective chemotherapy. Proc Natl Acad Sci USA 98 7528-7533... 

Retro-aldol Reactions in Human Therapy Prodrug Activation by Aldolase Antibody... 

An important application of aldolase antibodies is prodrug activation in chemotherapeutic strategies. Activation of a prodrug into an active drug at the tumor site enables selective destruction of those tumor cells. This type of site-specific targeting is known as antibody-directed enzyme prodrug therapy (ADEPT) [25]. The ADEPT complex serves two functions. The antibody portion of the complex enables delivery of the drug directly to the tu-... 

Incorporation of an additional 8.4-A linker, as shown in prodrugs 65 and 66, enables a diverse group of drugs to be used for application of aldolase antibody-catalyzed prodrug activation. Aldolase antibody 33F12 has an active site lysine e-amino group at 10A depth in a narrow pocket (Section 6.6). 

Because aldolase antibodies operate by an enamine mechanism, they also catalyze other reactions that proceed by a similar mechanism. For example, as described in the section on prodrug activation reactions, antibodies 38C2 and 33F12 catalyze / -elimination (retro-Michael) reactions (Section 6.3.6). These antibodies also catalyze decarboxylation of j5-keto acids (Scheme 6.12)... 

Figure 13.7 Outline of antibody-directed enzyme prodrug therapy (ADEPT). Subsequent to its enzymatic activation, the active drug is taken up by the cell, upon which it exhibits a cytocidal effect. Refer to text for specific detail...

Because of its catalytic nature, a single antibody-enzyme conjugate would activate many molecules of the prodrug in question. Much of the active cytocidal agent released at the tumour surface would be taken up by the tumour cells via simple diffusion or carrier-mediated active transport. 

Fig. 42 Prodrug [128] is an acylated derivative of the anticancer drug 5-fluoro-deoxyuridine. Antibody 49.AG.659.12, raised against phosphonate [127] was found to activate the prodrug [128] in vitro, thereby inhibiting the growth of E. coli.

Fig. 6.13. Schematic representation of a selective delivery obtained by antibody-directed en-zyme-prodrug therapy (ADEPT). An exogenous enzyme is coupled to a monoclonal antibody (mAb) targeted for tumor cells. In a second step, a prodrug is administered, which, as a selective substrate of the exogenous enzyme, will be selectively activated at the tumor site.

---