Chemically programmed antibodies: Endothelin receptor targeting CovX-Bodies TM Venkata R. Doppalapudi, * Nancy Tryder, Lingna Li, Teresa Aja, David Griffith, Francesca-Fang Liao, Giovanni Roxas, Mysore P. Ramprasad, Curt Bradshaw and Carlos F. Barbas, III CovX Research LLC, 9381 Judicial Drive, Suite 200, San Diego, CA 92130, USA Received 22 September 2006; accepted 5 October 2006 Available online 7 October 2006 Abstract—Aryl sulfonamide-based endothelin antagonists were synthesized and covalently linked to the reactive lysine of the m38C2 antibody to create a series of CovX-Bodies. These chemically programmed antibodies behaved as potent endothelin receptor antag- onists in vitro and had antitumor efficacy in a prostate cancer xenograft model which, on a molar basis, far exceeded the activity of the parent small molecule. Ó 2006 Elsevier Ltd. All rights reserved. Monoclonal antibodies (mAbs) have proven effective as therapeutics across a spectrum of diseases, including cancer, heart disease, infection, and immune disorders, as shown by the growing list of mAbs that have been ap- proved by the US Food and Drug Administration and by the European Medicines Agency. 1 The therapeutic potential of antibodies can be expanded by arming them with drugs, toxins, and radionuclides. 2 Although anti- bodies offer high target specificity, long serum half-life, and Fc-mediated effector functions, development re- quires years of research and is costly. On the other hand, small molecule or peptide-based leads with excellent activity can be straightforward to find but are often pla- gued with poor drug-like properties. In recent publications, Barbas demonstrated that the strengths of certain small synthetic molecules and anti- bodies could be uniquely combined using an aldolase antibody. 3–5 In this approach, a reversible, covalent enaminone bond forms in a well-controlled fashion be- tween a b-diketone and active site lysine of the aldolase antibody m38C2. When the b-diketone is incorporated into an extended pharmacophore, the result is a well- characterized, bivalent antibody termed a CovX-Body TM (Fig. 1). This approach effectively combines the function of certain small molecules and peptides with the long serum half-life of an antibody into one unique therapeu- tic. Barbas discovered a CovX-Body prototype that is based on an integrin targeting pharmacophore. 3,5 Here, we further expand the technology to include endothelin antagonists, and describe the design and synthesis of endothelin-A (ET A ) antagonist CovX-Bodies. In addi- tion, we also show that ET A -targeting CovX-Bodies bind ET A and ET B receptors and have anti-tumor effica- cy in tumor xenograft models. Endothelins (ET-1, ET-2, and ET-3) constitute a family of vasoconstrictor peptides, produced by the endotheli- um of blood vessels and many other tissues. 6 Endothe- lins exert their physiological effects via two specific G- protein coupled receptors termed ET A and ET B . Both receptor subtypes are found on smooth muscle cells and mediate vasoconstriction and/or proliferative disor- ders. The endothelins and their receptors ET A and ET B play a major role in tumor growth, proliferation, apop- tosis, angiogenesis, and bone metastasis. 7 ET-1 pro- motes cell growth and suppresses apoptosis of cancer cells. Extensive preclinical and clinical studies with ET A receptor antagonists (and to a lesser degree ET B antagonists) have shown potential therapeutic benefits in disease states such as heart failure, pulmonary hyper- tension atherosclerosis, restenosis, systemic hyperten- sion, various models of cancer, and chronic renal failure. 6–9 0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2006.10.009 Keywords: Monoclonal antibodies; Aldolase antibody; CovX-Body TM ; Endothelin-A; Endothelin-A (ET A ) antagonists; Antitumor efficacy. * Corresponding author. Tel.: +1 858 964 2026; fax: +1 858 964 2090; e-mail: dvramana@covx.com Bioorganic & Medicinal Chemistry Letters 17 (2007) 501–506