Telomerase-Specific Replication-Selective Virotherapy for Human Cancer

Abstract

Purpose: Replication-selective tumor-specific viruses present a novel approach for treating neoplastic disease. These vectors are designed to induce virus-mediated lysis of tumor cells after selective viral propagation within the tumor. Telomerase activation is considered to be a critical step in carcinogenesis, and its activity is closely correlated with human telomerase reverse transcriptase (hTERT) expression. We investigated the antitumor effect of the hTERTspecific replication-competent adenovirus on human cancer cells.Experimental Design: We constructed an adenovirus 5 vector [tumor-or telomerase-specific replication-competent adenovirus (TRAD)], in which the hTERT promoter element drives expression of E1A and E1B genes linked with an internal ribosome entry site, and we examined the selective replication and antitumor effect in human cancer cells in vitro and in vivo.Results: TRAD induced selective E1A and E1B expression in human cancer cells, but not in normal cells such as human fibroblasts. TRAD replicated efficiently and induced marked cell killing in a panel of human cancer cell lines, whereas replication as well as cytotoxicity was highly attenuated in normal human fibroblasts lacking telomerase activity. In nu/nu mice carrying s.c. human lung tumor xenografts, intratumoral injection of TRAD resulted in a significant inhibition of tumor growth. No evidence of TRAD was identified in tissues outside of the tumors, despite the presence of TRAD in the circulation. Moreover, TRAD replication in the distant, noninjected tumors was demonstrated.Conclusions: Our results suggest that the hTERT promoter confers competence for selective replication of TRAD in human cancer cells, an outcome that has important implications for the treatment of human cancers.

Potent antitumor effects of combined therapy with a telomerase-specific, replication-competent adenovirus (OBP-301) and IL-2 in a mouse model of renal cell carcinoma

“…OBP-301 has potent anticancer activities against many types of human malignancies such as lung, colon and prostate cancer. 6,9 The in vitro assay with mouse RCC cells showed the cytotoxic effect of OBP-301. Conversely, no cytotoxic effect was induced by IL-2 treatment alone.…”

“…6,7 Before use, these viruses were purified by CsCl 2 step-gradient followed by CsCl 2 linear-gradient ultracentrifugation. Recombinant human IL-2 protein was kindly provided by Shionogi Co. (Osaka, Japan), and this protein was diluted in the culture medium just before use for the in vitro studies, and in phosphate-buffered saline (PBS) for the in vivo studies.…”

“…Previous study developed a unique strategy for oncolytic virotherapy based on the replicative capacity of the adenovirus by placing the envelope-1 (E1) gene under the control of an hTERT promoter. [6][7][8][9][10] OBP-301 (telomelysin), a cancer-selective, replication-competent oncolytic adenovirus, can induce cell lysis in human non-small-cell lung cancer and prostate cancer cells. 6,9 OBP-301 has the ability to replicate within tumors, enter the blood circulation and then replicate in distant metastatic tumors after the intratumoral administration.…”

“…[6][7][8][9][10] OBP-301 (telomelysin), a cancer-selective, replication-competent oncolytic adenovirus, can induce cell lysis in human non-small-cell lung cancer and prostate cancer cells. 6,9 OBP-301 has the ability to replicate within tumors, enter the blood circulation and then replicate in distant metastatic tumors after the intratumoral administration. 9 Interleukin-2 (IL-2) is a member of the immunocytokine family and was approved by Food and Drug Administration (FDA) of the United States for treatment of metastatic RCC.…”

Clinical development directions in oncolytic viral therapy

“…57 Earlier studies have shown that hTERT promoter can control the expression of exogenous genes in telomerase-positive cancer cells, and can serve as an excellent candidate for cancer-specific control of oncolytic adenoviral replication. 58 Additional modifications of Telomelysin include the replacement of the normal transcriptional element of viral E1B gene by an IRES (Internal Ribosomal Entry Site) sequence. Furthermore, Telomelysin is the first replication-competent adenovirus that retains a fully functional viral E3 region.…”