Data from Treatment of Human Colon Cancer Xenografts with TRA-8 Anti-death Receptor 5 Antibody Alone or in Combination with CPT-11

Abstract

<div>Abstract<p><b>Purpose:</b> This study was designed to evaluate the <i>in vitro</i> cytotoxicity and <i>in vivo</i> efficacy of TRA-8, a mouse monoclonal antibody that binds to the DR5 death receptor for tumor necrosis factor–related apoptosis-inducing ligand (also called Apo2L), alone and in combination with CPT-11, against human colon cancer cells and xenografts.</p><p><b>Experimental Design:</b> DR5 expression was assessed on human colon cancer cell lines using flow cytometry, and cellular cytotoxicity after TRA-8 treatment, alone and in combination with SN-38, was determined by measuring cellular ATP levels. Tumor growth inhibition and regression rates of well-established subcutaneous COLO 205, SW948, HCT116, and HT-29 colon cancer xenografts in athymic nude mice treated with TRA-8 or CPT-11 alone and in combination were determined. <sup>99m</sup>Tc-TRA-8 was used to examine tumor localization of TRA-8 in animals bearing each of the four xenografts. In addition, whole-body biodistribution and imaging was carried out in COLO 205–bearing animals using <i>in vivo</i> single-photon emission computed tomography imaging and tissue counting.</p><p><b>Results:</b> DR5 expression was highest on HCT116, intermediate on SW948 and COLO 205 cells, and lowest on HT-29 cells. COLO 205 cells were the most sensitive to TRA-8–induced cytotoxicity <i>in vitro</i>, SW948 and HCT116 cell lines were moderately sensitive, and HT-29 cells were resistant. Combination treatment with TRA-8 and SN-38 produced additive to synergistic cytotoxicity against all cell lines compared with either single agent. The levels of apoptosis in all cell lines, including HT-29, were increased by combination treatment with SN-38. <i>In vivo</i>, combination therapy with TRA-8 and CPT-11 was superior to either single-agent regimen for three of the xenografts: COLO 205, SW948, and HCT116. COLO 205 tumors were most responsive to therapy with 73% complete regressions after combination therapy. HT-29 cells derived no antitumor efficacy from TRA-8 therapy. Tumor xenografts established from the four colon cancer cell lines had comparable specific localization of <sup>99m</sup>Tc-TRA-8.</p><p><b>Conclusions:</b><i>In vitro</i> and <i>in vivo</i> effects of TRA-8 anti-DR5 monoclonal antibody on four different colon cancer cell lines and xenografts were quite variable. The HT-29 cell line had low surface DR5 expression and was resistant to TRA-8 both <i>in vitro</i> and <i>in vivo</i>. Three cell lines (COLO 205, SW948, and HCT116) exhibited moderate to high sensitivity to TRA-8–mediated cytotoxicity which was further enhanced by the addition of SN-38, the active metabolite of CPT-11. <i>In vivo</i>, the combination of TRA-8 and CPT-11 treatment produced the highest antitumor efficacy against xenografts established from the three TRA-8–sensitive tumor cell lines. All four colon cancer xenografts had comparable localization of <sup>99m</sup>Tc-TRA-8. These studies support the strategy of TRA-8/CPT-11 combined treatment in human colon cancer clinical trials.</p></div>