Adenoviral insulinoma-associated protein 1 promoter-driven suicide gene therapy with enhanced selectivity for treatment of neuroendocrine cancers.

backgroundInsulinoma-associated protein 1 (INSM1) is a zinc finger transcriptional repressor with a limited spatial and temporal embryonic expression pattern in neuronal and neuroendocrine tissues. Interestingly, INSM1 activity is reactivated in neuroendocrine tumors such as small-cell lung cancer (SCLC), neuroblastoma, medulloblastoma, and retinoblastoma. Adenoviral constructs with the 1.7-kilobase pair INSM1 promoter-driven herpes simplex virus thymidine kinase (HSV-tk) gene could effectively suppress D283 Med subcutaneous xenograft tumor growth. Undesirably, sequences in the adenoviral backbone overrode promoter specificity in vivo. Incorporation of both the chicken β-globin HS4 insulator sequence and 2 copies of the mouse nicotinic acetylcholine receptor (nAchR) neuronal restrictive silencer element abolished the nonspecific activation of the INSM1 promoter in vivo.

methodsThe luciferase reporter gene was replaced with the HSV-tk suicide gene to generate the Ad-K5 virus. Both in vitro cell viability assays and in vivo tumor regression studies were used to determine the efficacy of the improved configuration INSM1 promoter adenoviral construct against a panel of neuroendocrine cell lines.

resultsIn vitro cell viability assays with the Ad-K5 HSV-tk-expressing construct further reinforced that the Ad-K5 virus could eradicate SCLC, insulinoma, medulloblastoma, and neuroblastoma cells. Further, Ad-K5 virus treatment of a D283 Med subcutaneous xenograft tumor showed a superior antitumor effect over the control Ad-RSV (Rous sarcoma virus)-HSV-tk.

conclusionsImprovements to the INSM1 promoter resulted in a stronger and more selective adenovirus. Treatment of a panel of neuroendocrine carcinomas with the Ad-K5 virus revealed enhanced antitumor activity over the RSV control, demonstrating its usefulness for the treatment of a variety of neuroendocrine tumors.