Biodistribution study of Re-188-labeled trisuccin-HuCC49 and trisuccin-HuCC49 Delta CH2 conjugates in athymic nude mice bearing intraperitoneal coloncancer xenografts

The trihydroxamate bifunctional chelating agent (BCA), trisuccin, has been shown to be a potential ligand for radiolabeling of monoclonal antibodies ( MAbs) with rhenium radioisotopes, through an indirect postconjugation appro ach. The use of this trihydroxamate BCA made it possible to prepare stable BCA-MAb conjugates in pure form that could be radiolabeled with carrier-fre e Re-188. The anti-TAG-72 murine MAb, CC49, and its humanized derivatives a re promising agents in the treatment of a number of malignancies with the C H2 domain-deleted MAb (HuCC49 Delta CH2), which is of particular interest d ue to its rapid blood clearance. The biodistribution of Re-188-labeled conj ugates of trisuccin,vith both humanized CC49 (HuCC49) and HuCC49 Delta CH2 in athymic nude mice implanted i.p. with LS174T human colon carcinoma was s tudied. Trisuccin-MAb conjugates were synthesized at different BCA:MAb rati os by the 6-oxoheptanoic acid method using trisuccin hydrazide. The conjuga tes were analyzed by matrix-assisted laser desorption/ionization time-of-fl ight mass spectroscopy for the number of incorporated trisuccin molecules. The conjugates were radiolabeled with carrier-free, generator-produced Re-1 88 and purified by gel filtration on Sephadex G-25. Labeling yields and hom ogeneity of the labeled conjugates were analyzed by high-pressure liquid ch romatography and instant TLC. Athymic nude mice were injected i.p. with LS1 74T human colon carcinoma cells, 7 days prior to injection of the labeled a ntibodies, Re-188. labeled MAbs were injected i.p., and the mice were sacri ficed 24 h postinjection. Matrix-assisted laser desorption/ ionization time -of-flight analyses showed stable incorporation of trisuccin into each MAb, with the measured ligand:MAb values positively correlating with the theore tical ratios. Labeling of the conjugates with Re-188 proceeded with high yi elds, producing homogeneous Re-188-MAbs with good stabilities as shown by i nstant TLC and biodistribution analyses. Biodistribution of the radiolabele d MAbs at 24 h after injection showed median tumor uptake values of 23.5 %I D/g and 17.6%ID/g for the Re-188.HuCC49 Delta CH2 and Re-188- HuCC49, respe ctively. The blood clearance of the domain-deleted MAb was faster than that of the intact antibody, The blood values at 24 h after injection were 0.7% ID/g for Re-188.HuCC49 Delta CH2 and 3.2%ID/g for Re-188-HuCC49. The result s indicate that trisuccin is a promising agent for postconjugation labeling of antibodies with Re-188. Additionally, these results illustrate the pote ntial of Re-188.HuCC49 Delta CH2 in radioimmunodiagnosis and radioimmunothe rapy of cancer.