Disulfide-Linked Antibody-Maytansinoid Conjugates: Optimization of In Vivo Activity by Varying the Steric Hindrance at Carbon Atoms Adjacent to the Disulfide Linkage
ABSTRACT In this report, we describe the synthesis of a panel of disulfide-linked huC242 (anti-CanAg) antibody maytansinoid conjugates (AMCs), which have varying levels of steric hindrance around the disulfide bond, in order to investigate the relationship between stability to reduction of the disulfide linker and antitumor activity of the conjugate in vivo. The conjugates were first tested for stability to reduction by dithiothreitol in vitro and for plasma stability in CD1 mice. It was found that the conjugates having the more sterically hindered disulfide linkages were more stable to reductive cleavage of the maytansinoid in both settings. When the panel of conjugates was tested for in vivo efficacy in two human colon cancer xenograft models in SCID mice, it was found that the conjugate with intermediate disulfide bond stability having two methyl groups on the maytansinoid side of the disulfide bond and no methyl groups on the linker side of the disulfide bond (huC242-SPDB-DM4) displayed the best efficacy. The ranking of in vivo efficacies of the conjugates was not predicted by their in vitro potencies, since all conjugates were highly active in vitro, including a huC242-SMCC-DM1 conjugate with a noncleavable linkage which showed only marginal activity in vivo. These data suggest that factors in addition to intrinsic conjugate potency and conjugate half-life in plasma influence the magnitude of antitumor activity observed for an AMC in vivo. We provide evidence that bystander killing of neighboring nontargeted tumor cells by diffusible cytotoxic metabolites produced from target cell processing of disulfide-linked antibody-maytansinoid conjugates may be one additional factor contributing to the activity of these conjugates in vivo.
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09/2012; 1(2). DOI:10.5539/cco.v1n2p49
- "The fact that epirubicin-(C 3 -amide)-SS-[anti- HER2/neu] also did not exert an enhanced level of cytotoxic anti-neoplastic activity against chemotherapeutic -resistant mammary adenocarcinoma (SKBr-3) may therefore reflect a cell biology related variable that explains a lack of enhanced efficacy. Interestingly, minimal or no correlation frequently exists between the in-vitro and in-vivo potency of covalent immunochemotherapeutics with synthetically introduced disulfide bond structures (Kellogg et al., 2011) which is in marked contrast to covalent immunochemotherapeutics devoid of this same internal chemical structure. Differences in cytotoxic anti-neoplastic potency to this degree in-vivo have been attributed to the influence of hepatic metabolization and variations in the creation of lipophilic and hydrophilic metabolites that determine the extent of distribution within fluid compartments and penetration across intact cancer cell membranes (Erickson et al., 2010) . "
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ABSTRACT: Biodegradability can be incorporated into cationic polymers via use of disulfide linkages that are degraded in the reducing environment of the cell cytosol. In this work, N-(2-hydroxypropyl)methacrylamide (HPMA) and methacrylamido-functionalized oligo-l-lysine peptide monomers with either a non-reducible 6-aminohexanoic acid (AHX) linker or a reducible 3-[(2-aminoethyl)dithiol] propionic acid (AEDP) linker were copolymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Both of the copolymers and a 1:1 (w/w) mixture of copolymers with reducible and non-reducible peptides were complexed with DNA to form polyplexes. The polyplexes were tested for salt stability, transfection efficiency, and cytotoxicity. The HPMA-oligolysine copolymer containing the reducible AEDP linkers was less efficient at transfection than the non-reducible polymer and was prone to flocculation in saline and serum-containing conditions, but was also not cytotoxic at charge ratios tested. Optimal transfection efficiency and toxicity were attained with mixed formulation of copolymers. Flow cytometry uptake studies indicated that blocking extracellular thiols did not restore transfection efficiency and that the decreased transfection of the reducible polyplex is therefore not primarily caused by extracellular polymer reduction by free thiols. The decrease in transfection efficiency of the reducible polymers could be partially mitigated by the addition of low concentrations of EDTA to prevent metal-catalyzed oxidation of reduced polymers.International Journal of Pharmaceutics 08/2011; 427(1):113-22. DOI:10.1016/j.ijpharm.2011.08.015 · 3.65 Impact Factor
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ABSTRACT: Antibody conjugates are a diverse class of therapeutics consisting of a cytotoxic agent linked covalently to an antibody or antibody fragment directed toward a specific cell surface target expressed by tumor cells. The notion that antibodies directed toward targets on the surface of malignant cells could be used for drug delivery is not new. The history of antibody conjugates is marked by hurdles that have been identified and overcome. Early conjugates used mouse antibodies; cytotoxic agents that were immunogenic (proteins), too toxic, or not sufficiently potent; and linkers that were not sufficiently stable in circulation. Investigators have explored 4 main avenues using antibodies to target cytotoxic agents to malignant cells: antibody-protein toxin (or antibody fragment-protein toxin fusion) conjugates, antibody-chelated radionuclide conjugates, antibody-small-molecule drug conjugates, and antibody-enzyme conjugates administered along with small-molecule prodrugs that require metabolism by the conjugated enzyme to release the activated species. Only antibody-radionuclide conjugates and antibody-drug conjugates have reached the regulatory approval stage, and nearly 20 antibody conjugates are currently in clinical trials. The time may have come for this technology to become a major contributor to improving treatment for cancer patients.Clinical Cancer Research 10/2011; 17(20):6389-97. DOI:10.1158/1078-0432.CCR-11-1417 · 8.19 Impact Factor