Radiolabelling and biodistribution of IgE antibodies

Abstract

Antibodies used for cancer treatment and immune therapy have, to date, been of the IgG class. Efficacy might be improved by using the IgE class of antibodies as these have higher affinity for their Fc-receptors. IgE has a greater tissue penetration and longer half-life in tissue and IgE bound to IgE-receptor-expressing effector cells is thought to actively infiltrate tumours. IgE has not been subject of in vivo imaging studies to date. Objectives: The aim was to radiolabel both anti-CSPG4-IgE and MOV18-IgE, and their IgG counterparts targeted to the same antigen, while maintaining the functionality of the antibodies; and subsequently, to compare IgE with IgG in in vivo imaging and biodistribution studies in a disease model. Methods: IgE’s and their antigen-matched IgG counterparts were engineered against two different tumour antigens. Tumour models were developed to assess targeting in vivo and imaging and biodistribution studies using radiolabelled IgE were carried out. Six antibodies were engineered for comparison: MOv18-IgE and -IgG antibody targeted against the folate receptor alpha (FR ) expressed on ovarian cancer cells; A MOv18-IgE and -IgG chimeric rat/mouse were engineered for evaluation in a new syngeneic immunocompetent rat model to mimic the immunotherapeutic antibody (human/mouse chimeric MOv18-IgE and -IgG) planned for a clinical study; and a second antibody, anti-CSPG4-IgE, targeted against the chondroitin sulfate proteoglycan 4 (CSPG4), expressed in melanoma cancer was compared to its IgG counterpart. The antibodies were analysed in a NOD/SCID xenograft mouse model with splenic engraftment of human peripheral blood lymphocytes. All antibodies were labelled with 111In using the same bifunctional chelator and labelling conditions (p-SCN-CHX-A"-DTPA) and radiolabelled with 111In at room temperature. Functional assays using FACS were carried out to assure binding to the target and high- and low-affinity Fc-binding to Fc"R expressing immune effector cells. NanoSPECT/CT imaging and biodistribution studies were used to determine targeting and clearance of IgE in vivo. Results: 111In-CHX-A"-DTPA-IgE and -IgG antibodies were labelled with high efficiency (>98%). Binding of the conjugated antibody to the target antigen and Fc"R expressing immune effector cells was identical to that of the native antibody. IgE showed a higher liver uptake in biodistribution (up to 75% ID IgE vs 5% ID IgG 8 h post injection) compared with the IgG counterpart as well as more than 10 times faster blood clearance where as IgG showed prolonged half-life (2.5 days) in blood. Tumour-to-blood and tumour-to-muscle ratios of IgE and IgG showed significant (tbr: P<0.05; tmr: P<0.0005) differences. Conclusion: Similar conjugation and radiolabelling of all antibodies as well as the in vivo assessment allowed the evaluation of targeting, biodistribution and clearance of IgE compared with its IgG counterpart. Observed characteristics of IgE like the rapid blood clearance and the higher liver uptake were found to be fundamentally different compared to its IgG counterpart and suggest a different and mostly unknown mode of action.

Date of Award	2015
Original language	English
Awarding Institution	King's College London
Supervisor	Philip Blower (Supervisor) & James Spicer (Supervisor)