Establishing an in vitro tumor multicellular spheroid model to investigate antibody therapy

Monday, October 24, 2011 — Poster Session I
Noon – 2:00 p.m.	Natcher Conference Center	NCI	CANCER-18

Authors

• Y Phung
• X Xiang
• H Mitchell

Abstract

Tumor microenvironments present significant barriers to penetration by antibodies and immunoconjugates and are difficult to study in vitro. Cells cultured as monolayers exhibit less resistance to therapy than those grown in vivo and an alternative research model more representative of in vivo tumors is desirable. SS1P is an immunotoxin composed of the Fv portion of a mesothelin-specific antibody fused to a bacterial toxin that is presently undergoing clinical trials in mesothelioma. We examined how the tumor microenvironment affects the penetration and killing activity of SS1P in a novel 3D spheroid model cultured in vitro using a human mesothelioma cell line and two primary patient cell lines. Mesothelioma cells grown as monolayers or as spheroids express comparable levels of mesothelin; however, spheroids are at least 100 times less affected by SS1P. The penetration of fluorescence-labeled SS1P molecules within spheroids was limited after 4 hours. Interestingly, a greater number of tight junctions in the core area was observed. Expression of E-Cadherin, a protein involved in the assembly and sealing of tight junctions that is highly expressed in malignant mesothelioma, was significantly increased in spheroids compared to monolayers. Moreover, siRNA silencing and antibody inhibition targeting E-Cadherin enhances SS1P immunotoxin therapy.

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