Abstract LB-276: A novel approach using the telomerase-selective adenoviral marker (OBP-401) for detection of circulation tumor cells in breast cancer patients

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Background: The detection of circulating tumor cells (CTCs) is a potential method to predict survival of metastatic breast cancer patients as well as outcomes of early breast cancer patients. However, no method for CTCs has yet proven to be the golden standard. We developed a new approach for detecting CTCs using the telomerase-selective adenoviral marker (OBP-401, Oncolys Biopharma). This marker contains the replication cassette, in which the human telomerase reverse transcriptase promoter drives expression of E1 genes, and the green fluorescent protein (GFP) gene for monitoring viral replication. Thus, OBP-401 infects viable cancer cells and replicates in them under the telomerase activity, and we can detect viable CTCs as GFP-positive cells. Methods: This system is consisted of the following steps; (1) virus-infection for 7.5 ml whole blood (incubated with 4 × 10sup8 Plaque Forming Unit OBP-401 virus for 24 hours at 37 Celsius), (2) dead cell staining using [L23102][1] (invitrogen), (3) virus-inactivation and RBC elimination, and (4) detection of GFP expressing cells using fluorescence microscopy. In a preclinical study, the sensitivity of this system was assessed using cell lines. Next, we conducted feasibility studies for CTCs detection in 80 healthy individuals, 70 metastatic, and 27 early breast cancer patients. In metastatic and early breast cancer patients, we compared the sensitivity of this system with that of CellSearch® (Veridex). GFP-positive cells (viable CTCs) and [L23102][1] expressing cells measuring ≥ 20 m in diameter (dead CTCs) were considered as CTCs in this system. Preliminary data: The sensitivity of this system, which was determined by a serial dilution of MDA-MB-468 cells against healthy volunteer's blood, was 1 cell per 7.5 ml. Neither viable nor dead CTCs were detected in any of healthy controls. Of 50 metastatic patients, 12% were primary breast cancers with stage IV disease, 24% were in the 1st line chemotherapy setting, and 42 % were heavily pretreated with chemotherapy. The sensitivities of tumor markers (CEA and CA15-3), CellSearch, and OBP-401 were 78%, 54%, and 66%, respectively. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-276. [1]: /lookup/external-ref?link_type=GEN&access_num=L23102&atom=%2Fcanres%2F70%2F8_Supplement%2FLB-276.atom