328. Transcriptionally Targeted Cancer Gene Therapy for Small Cell Lung Cancer
Authors: Nina Pedersen, Thomas T. Poulsen, Mikkel W. Pedersen, Michael S. Lan, Mary B. Breslin, Hans S. Poulsen
Journal: Molecular Therapy (2006)

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Small Cell Lung Cancer (SCLC) is an aggressive, highly metastatic disease for which there is currently no satisfactory treatment. Therefore development of novel treatment modalities is highly in demand. As SCLC is a disseminated disease, treatment must be administered systemically and therefore requires a high level of targeting. This can be achieved by transcriptionally targeted cancer gene therapy. We have identified promoters regions from several genes, which confer very high and SCLC specific mRNA expression - genes normally either only active during early developmental differentiation or associated with high proliferation.

The insulinoma-associated 1 (INSM1) gene encodes a transcriptional repressor normally exclusively expressed transiently during early embryonic development in neuroendocrine regions, but has been found highly re-activated in neuroendocrine tumours, including SCLC. A 1.7 kb region of this promoter has very high activity in most SCLC cell lines and no activity in normal and other cancer cell lines. We have demonstrated that this promoter region confers sufficient activity when expressing a therapeutic gene to cause SCLC specific cell death in vitro and in vivo.

The Achaete-Scute Homolog 1 (ASCL1) encoding a transcription factor transiently expressed during early development of neural and neuroendocrine progenitor cells, is also re-expressed in SCLC. A proximal 0.7 kb region of the ASCL1 promoter demonstrated high expression in a subset of SCLC cell lines with low or no expression in other cell lines. Addition of a suggested distal 2.5 kb repressor region gave no significant increase in specificity, but a general decrease in activity. The 0.7 kb promoter region regulating expression of a therapeutic gene was found to be sufficiently active to mediate SCLC specific cell death in vitro.

The Enhancer of Zeste Homolog 2 (EZH2) gene is a member of the Polycomb group of proteins important for maintaining the silenced state of homeotic genes in the adult and is associated with high proliferation. EZH2 has been found highly overexpressed in a number of cancers, including SCLC. All tested cell lines (normal or cancer) have high expression of EZH2 mRNA, thus reflecting their high proliferative state. However, a 1.1 kb region of the EZH2 promoter displayed very high activity in SCLC cell lines, but not in other cell lines and was sufficiently active to mediate SCLC cell death in vitro. This short region of the EZH2 promoter has previously been shown to be activated by transcription factors from the E2F family. Preliminary results indicate that the high activity of the promoter region in SCLC is due to the lack of functional RB, which normally down regulates the activities of the E2F family. Therefore this short region of the promoter has potential for gene therapy for RB deficient cancers.

The promoter regions from all three genes are currently being tested in mouse tumour models for activity and specificity using a novel liposomal delivery system for systemic application.