In vitro and in vivo activities of KRN330, a fully human monoclonal antibody against colon cancer.

Abstract

432 Background: KRN330 is a novel recombinant human IgG1 monoclonal antibody (mAb) targeting A33 surface differentiation antigen that is uniformly expressed on the surface of 95% of colorectal cancer (CRC) cells. In this study, we characterized the activity of KRN330 for its in vitro properties, as well as for its in vivo antitumor activity. Methods: A kinetic analysis of the interaction between KRN330 and recombinant human A33 was conducted using a Biacore 3000. Western blot analysis was conducted using A33 expressing COLO205 lysates under reducing and non-reducing conditions. Binding of KRN330 to human colorectal cancer tissues were investigated using FITC-labeled KRN330. We also developed more conventional staining methods of A33 and investigated A33 expression using human colon cancer tissue microarray (TMA). ADCC and CDC activities of KRN330 were assessed using a standard 51Cr release assay. A33 expression levels of 14 CRC cell lines were analyzed using flow cytometer. In vivo antitumor activities of KRN330 alone or in combination with chemotherapeutic agents against subcutaneous or intraperiotoneal human CRC (COLO205 and LS174T) models were investigated using mice and rats xenograft model. Results: A kinetic analysis revealed that KRN330 showed a high binding affinity to A33. Western blot analysis also showed that antibody recognized not any protein under reducing condition, but non-reducing condition. A33 staining of TMA with 204 different samples revealed the majority of tumor expressed A33. KRN330 exhibited ADCC activity against A33 expressing human colorectal cancer cell lines which include both K-ras wild and mutated types. KRN330 showed dose-dependent antitumor activities in vivo. KRN330 also significantly prolonged survival of human colon tumor bearing mice. In addition, combination treatment of KRN330 with irinotecan showed increased antitumor activitiy and prolongation of survival, compared to either irinotecan or KRN330 alone. Conclusions: These results suggest that KRN330 is a promising candidate of novel therapy for CRC. The phase I/II study of KRN330 plus irinotecan in patients with second line metastatic CRC is ongoing. [Table: see text]