Background: Insulinoma-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 ß-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.

Methods: The 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.

Results: In 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.

Conclusions: Improvements 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.

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