Abstract 5530: A novel bacterial anticancer treatment modality targeting hypoxic solid tumors as an enzyme-prodrug using non-pathogenic Bifidobacterium longum expressing cytosine deaminase

Abstract

Abstract Solid tumors generally exhibit anaerobic or hypoxic regions compared with normal tissues, which causes a potential therapeutic problem because hypoxic tumor cells are resistant to radiotherapy and chemotherapy. Furthermore, recent studies have suggested that tumor hypoxia is associated with malignant progression, including enhanced invasiveness, angiogenesis and distant metastasis. We previously reported that a strain of domestic, nonpathogenic and anaerobic bacteria, Bifidobacterium longum (B. longum) selectively localized and proliferated within solid tumors after systemic administration. In addition, we reported that a transformed B. longum (prototype APS001) with a shuttle-plasmid encoding the cytosine deaminase (CD) gene, which deaminates the pro-drug 5-fluorocytosine (5-FC) to the active agent 5-fluorouracil (5-FU), induced tumor regression in chemically-induced rat mammary tumors. This enzyme/pro-drug therapeutic strategy was described as the BifidobactErial Selective Targeting-Cytosine Deaminase (BEST-CD) therapy. In this study, we developed an improved B. longum transformant with a plasmid that expressed a CD gene that had been modified by a point mutation. This newly transformed bacterium (APS001F) was about 10 times more potent in vitro in CD-activity compared with the prototype bacteria (APS001) harboring the original CD, and it produced higher levels of 5-FU in the tumors of animals in vivo without increasing the 5-FU in normal tissues. In this series of preclinical studies using tumor-bearing animal models, APS001F was selectively localized in solid tumor tissue but not in normal organs or tissues, and the high concentrations of 5-FU in the tumor tissues correlated positively with the number of intra-tumoral colonies of APS001F. When combined with oral administration of 5-FC, 2 days after the last APS001F injection (i.v.), significant tumor suppression was observed in nude mice with KPL-1 human mammary carcinoma. Furthermore, the anti-tumor activity of APS001F was confirmed in nude rats with MKN45 human stomach carcinoma after 2 hours of infusion once a day for 3 consecutive days followed by oral 5-FC administration for 3 weeks, which would be a typical clinical dosing regimen. There were no significant adverse events or abnormal symptoms in any of the APS001F- treated rats. Taken together, this transformed B. longum with the modified CD gene is thought to be a safe and attractive new anticancer treatment modality that is able to selectively deliver an active drug to various hypoxic solid tumors as an enzyme/pro-drug therapy. We are currently investigating the combination therapy of APS001F with some anticancer drugs, such as molecular-targeted drugs or anti-angiogenic drugs. 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 5530.