Here we describe a series of CXCR4 antagonist CovX-Bodies, produced by covalently attaching CXCR4 antagonist peptides to a humanized IgG1 molecule with the goal of producing molecules with the potency and specificity of peptides and the pharmacokinetic parameters of an antibody. Extensive SAR was performed on peptides derived from T140, a highly charged 14 amino acid cyclic peptide containing 4 Arginine residues. Both the free peptides and the associated CovX-bodies were potent antagonists of CXCR4 in vitro, and SAR studies were consistent with a model of both allosteric and orthosteric inhibition. However, in vivo pharmacokinetic (PK) studies revealed an unexpected and CXCR4-independent disappearance of the CovX-Bodies from circulation, such that approximately 10% of the injected CovX-Body remained in circulation 1 hour after i.v. injection into mice. Based on the known nonspecific cell-penetrating properties of Arginine-rich peptides, we hypothesized that Arginine replacement and charge neutralization would improve the pharmacokinetics of the CovX-Bodies. We identified substitutions that could replace up to 3 of the 4 Arg residues while retaining potent CXCR4 binding and antagonism, but Arg2 was obligate. However, these CovX-Bodies were only modestly improved in PK, indicating that that the anomalous in vivo behavior was not solely a function of charge or the net number of Arg residues. Only the replacement of Arg2 significantly improved the pharmacokinetics of the CovX-Bodies, but also resulted in a loss of CXCR4 antagonism. Extensive SAR failed to identify a suitable replacement residue for Arg2, nor did alternative structural forms such as 5 member, bicyclic, or reversed ring molecules have significantly improved pharmacokinetics. Based on these data, we conclude that the specific property of the peptide that allows potent inhibition of CXCR4, of which Arg2 is an integral component, also mediates binding to moieties other than CXCR4, leading to the depletion of these molecules from circulation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2849. doi:1538-7445.AM2012-2849