(N-(2-Hydroxypropyl)methacrylamide (HPMA)) copolymers have seen extensive development as sophisticated lysosomotropic drug carriers. They can be used for site-specific drug delivery by incorporation of appropriate targeting groups and here we report their conjugation to antitumour monoclonal antibodies (the murine IgG, antibody B72.3 and its Fab' and Fab'2 fragments) and assessment as vehicles for tumour-specific drug delivery. Conjugates were synthesised containing an average 5 copolymer units (Mw 20kD) per antibody molecule. Kinetics of elimination and body distribution of radiolabelled conjugates in mice were substantially modified compared with native antibody and fragments, showing prolonged circulation in the bloodstream. Notably, the half-time for bloodclearance of the Fab' fragment (35min) was extended ten-fold following conjugation (6h). The conjugates provoked only a low immune response in A/J mice, following three injections in adjuvant (IgG titre-1 less than 100), and were resistant (up to 50%) to proteolytic degradation by preparations of rat liver lysosomal enzymes. The parent antibody targeted efficiently to human colorectal carcinoma (LS174T) xenografts in nude mice (up to 25%/g); the conjugates, however, showed no tumour-targeting, probably due to masking by polymer chains (which are attached by non-specific aminolysis). Conjugates designed to maintain immunoreactivity following linkage through oxidised carbohydrates are currently being synthesised. Nevertheless, the conjugates display increased rates of extravasation, compared with proteins of the same hydrodynamic size, and the decreased charge is anticipated to accelerate diffusion through tumour interstitium.
Two proteins (model targeting residues) human immunoglobulin fraction (IgG) and human transferrin have been conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer and the antibody titer elicited, after subcutaneous or intraperitoneal administration to A/J and B10 mice of free and conjugated protein, was measured using the ELISA technique. The measured IgG titer against protein-HPMA copolymer conjugates was always higher than the IgM titer. Also, the titer (IgG) measured against native protein was up to 250-fold greater than that raised against protein-HPMA copolymer conjugates. This reduction in antibody titer against conjugate had a limited de pendence on its molecular weight.
152The cross-reactivity of antisera against the specified antigens showed a relatively low interaction of anti-IgG antisera with IgG-HPMA copolymer conjugate. In contrast, there was a high degree of interaction of anti-conjugate antisera with IgG. Little cross-reactivity of anti-transferrin antisera was seen against the transferrin-HPMA copolymer conjugate and similarly the anticonjugate antisera showed little interaction with transferrin. The data presented indicate that it may be possible to give multiple doses of protein-HPMA copolymer conjugates before an immune response becomes limiting.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.