“Catch-and-Release” Anti-Carcinoembryonic Antigen Monoclonal Antibody Leads to Greater Plasma and Tumor Exposure in a Mouse Model of Colorectal Cancer

Abstract

In this study, we examined the effects of target expression, neonatal Fc receptor (FcRn) expression in tumors, and pH-dependent target binding on the disposition of monoclonal antibodies (mAbs) in murine models of colorectal cancer. A panel of anti-carcinoembryonic antigen (CEA) mAbs was developed via standard hybridoma technology and then evaluated for pH-dependent CEA binding. Binding was assessed via immunoassay and radioligand binding assays. 10H6, a murine IgG1 mAb with high affinity for CEA at pH = 7.4 ( = 12.6 ± 1.7 nM) and reduced affinity at pH = 6.0 ( = 144.6 ± 21.8 nM), and T84.66, which exhibits pH-independent CEA binding ( = 1.1 ± 0.11 and 1.4 ± 0.16 nM at pH 7.4 and 6.0), were selected for pharmacokinetic investigations. We evaluated pharmacokinetics after intravenous administration to control mice and to mice bearing tumors with (MC38, LS174T) and without (MC38) CEA expression and with or without expression of murine FcRn, at doses of 0.1, 1, and 10 mg/kg. 10H6 displayed linear pharmacokinetics in mice bearing MC38 or MC38 tumors. T84.66 displayed linear pharmacokinetics in mice with MC38 tumors but dose-dependent nonlinear pharmacokinetics in mice bearing MC38 In addition to the improved plasma pharmacokinetic profile (i.e., linear pharmacokinetics, longer terminal half-life), 10H6 exhibited improved exposure in MC38 tumors relative to T84.66. In mice bearing tumors with CEA expression, but lacking expression of murine FcRn (LS174T), 10H6 demonstrated nonlinear pharmacokinetics, with rapid clearance at low dose. These data are consistent with the hypothesis that pH-dependent CEA binding allows mAb dissociation from target in acidified endosomes, enabling FcRn-mediated protection from target-mediated elimination in mice bearing MC38 tumors.

Antibody engineering to generate SKY59, a long-acting anti-C5 recycling antibody

“…Alternatively, combinatorial histidine scanning libraries have conferred pH-dependent antigen binding on lead antibodies [21,22]. In addition, pH-dependent antibodies have been identified directly from a histidine-rich library [23], and also generated naturally in animals [17,24,25]. As we have reported, the pH-dependent interaction between C5 and SKY59 was partly due to histidine residues found in the epitope on C5 [17].…”

“…This accumulation occurs because the antigen is synthesized continuously in vivo but the clearance of the antigen is reduced by the administered antibody [8,9], which generally has a long plasma half-life because of neonatal Fc receptor (FcRn)-mediated recycling [10]. The property by which an antibody binds to an antigen pH dependently has been studied strenuously in recent years [11–25] in hopes of achieving longer-lasting efficacy and a lower dose for treatment by suppressing the antigen accumulation. An antibody that binds to its antigen pH-dependently, also known as a recycling or sweeping antibody, is capable of dissociating its bound antigen in the acidic endosome, which lets the antigen-free antibody be recycled back to plasma by the FcRn-mediated recycling.…”

Physiologically Based Modeling of the Pharmacokinetics of “Catch-and-Release” Anti-Carcinoembryonic Antigen Monoclonal Antibodies in Colorectal Cancer Xenograft Mouse Models

“…Anti-CEA mAb pharmacokinetic data used for these modeling exercises were previously generated within our laboratory 24, 37 Briefly, the plasma pharmacokinetics of T84.66, a murine IgG1 mAb with pH-independent CEA binding (i.e., with high affinity for CEA at pH 5.5 and at pH 7.4), and the newly developed catch-and-release anti-CEA mAb, 10H6, were studied in C57BL/6 mice bearing MC38 tumor cells, a murine colorectal cancer cell line that does not express human CEA (abbreviated MC38 CEA− for clarity) and in mice bearing MC38 cells that have been transfected to express human CEA (MC38 CEA+ ). C57BL/6 mice (5/group) bearing MC38 CEA− or MC38 CEA+ tumors were injected intravenously with 0.1, 1, or 10 mg/kg of T84.66 or 10H6, along with tracer quantities of 125 I-labeled mAb.…”

“…47,48 T84.66 equilibrium dissociation and binding rate constants K D,CEA , k off,CEA , and k on,CEA were fixed based on estimates reported previously. 49 T84.66 demonstrates no substantial changes in CEA binding at acidic pH 24 ; therefore, binding constants were fixed to values reported for pH 7.4 (Table IV). The equilibrium dissociation constant for CAR mAb 10H6 at pH 7.4 was estimated through use of a 125 I-radioligand binding assay (Fig.…”

“…We have recently shown that 10H6, an IgG1κ murine mAb, exhibits pH-dependent, CAR binding to carcinoembryonic antigen (CEA). 24 CEA (also known as CEACAM5 or CD66e) is a 180 kDa cell surface glycoprotein that has low expression in the colon of healthy adults. 25 Although previously believed to be a non-internalized cell surface protein, it was recently demonstrated that CEA internalizes with an endocytosis half-time of 10–16 hours.…”