Increased serum stability and prolonged biological half-life of neocarzinostatin covalently bound to monoclonal antibodies.

Abstract

The pharmacokinetics of neocarzinostatin (NCS) have been compared to NCSconjugates with monoclonal antibodies using Balb/c and tumor bearing nude mice. Data on blood and whole body clearance revealed that the high MWconjugate persists in the body far longer and at a higher level than the free drug. Excretion of the free drug occurs with an extremely rapid renal clearance and localization of the remaining drug in the kidney, whereas the NCSimmunoconjugate remained in circulation far longer allowing time for tumor localization to occur without renal accumulation of drug.In addition, NCSconjugated to monoclonal antibody was found to retain its activity in human serum better than free drug, in agreement with data obtained for other NCS-derivatives. Half-time ofinactivation was greatly extended whenmeasured under relevant conditions in a DNAstrand-break assay.The results indicate that two of the most important requirements for the successful targeting of NCSin vivo, decreased clearance rate and increased serum stability are achieved by conjugation to antibody. Both results increase the probability of NCSaccumulating in tissue while still in its active form.Coupling ofNCSto monoclonalantibody decreases clearance and inactivation rate and increases localization of the active drug in tumor tissue.The antitumor antibiotic neocarzinostatin (NCS) has been used in clinical trials for the chemotherapy of human cancers in recent years.1>2) It is evident, however, from both in vitro and in vivo experiments, that both pharmacokinetics as well as serum stability of NCSare disadvantageous. The drug exhibits an extremely rapid renal clearance and becomes inactivated in serum with a half-life in the order of minutes.2~4)The drug consists of an apoprotein and a non covalently associated chromophorethat is very sensitive to light and heat.5) The primary structure of the apoprotein has been elucidated and revised,6) and the binding site involved in the association of the non-protein chromophore as well as the regions for hydrophobic interactions have been described.7) It was noted that the only two amino-groups present in the protein (one a-amino-group at Ala 1, one e-amino-group at Lys 20) are not involved in the cytotoxic action and therefore modification at one or both of these functionalities results in no loss of biological activity.8) Conjugates of NCSand a variety of markers such as fluorescein,9) rhodamine or biotin (Gottschalk, U.; A. Maibucher and K. Trutschler-Ebert; unpublished data), peroxidase,10) SMA,1 1} succinyl,12) transferrin13) and monoclonal antibodies14) have been prepared via the NH2-groups in studies on NCSand its possible role in tumor therapy. In the present study the pharmacokinetics and serum stability of conjugates of NCSand the monoclonal antibody 791T/36 have been examined. This has

Synthesis, Bioanalysis and Biodistribution of Photosensitizer Conjugates for Photodynamic Therapy

“…Examples are known of drug–antibody conjugates that have severely reduced serum stability [33]. On the other hand, there is a report of increased serum stability [34]. …”

Antibody–drug conjugates: the success of failure

“…The toxic conjugate would then be released from the antibody within the lysosomal degradation pathway, killing the target cells via a phenomenon known today as apoptosis. Our favored drugs were the streptomycetes metabolites neocarcinostatin and bleomycin, both of which introduce double-strand breaks into DNA and were therefore known as 'radiomimetics' [1]. Along with our EU partners, we enthusiastically developed in vitro and in vivo models to prove the efficacy of our concept and -to cut a long story short -we failed.…”