Biodistribution of Charged F(ab')2 Photoimmunoconjugates in a Xenograft Model of Ovarian Cancer

Abstract

The effect of charge modification of photoimmunoconjugates (PICs) on their biodistribution in a xenograft model of ovarian cancer was investigated. Chlorine(e6) c(e6) was attached site specifically to the F(ab')(2) fragment of the murine monoclonal antibody OC125, directed against human ovarian cancer cells, via poly-l-lysine linkers carrying cationic or anionic charges. Preservation of immunoreactivity was checked by enzyme-linked immunosorbent assay (ELISA). PICs were radiolabelled with I-125 and compared with non-specific rabbit IgG PICs after intraperitoneal (i.p.) injection into nude mice. Samples were taken from normal organs and tumour at 3 h and 24 h. Tumour to normal I-125 ratios showed that the cationic OC125F(ab')(2) PIC had the highest tumour selectivity. Ratios for c(e6) were uniformly higher than for I-125, indicating that c(e6) became separated from I-125. OC125F(ab')(2) gave highest tissue values of I-125, followed by cationic OC125F(ab')(2) PIC; other species were much lower. The amounts of c(e6) delivered per gram of tumour were much higher for cationic OC125F(ab')(2) PIC than for other species. The results indicate that cationic charge stimulates the endocytosis and lysosomal degradation of the OC125F(ab')(2)-pl-c(e6) that has bound to the i.p. tumour. Positively charged PICs may have applications in the i.p. photoimmunotherapy of minimal residual ovarian cancer.