3356

For small cell lung cancer (SCLC) there is currently no satisfactory treatment, wherefore development of novel modalities, such as gene therapy, is highly in demand. As SCLC is a disseminated disease, treatment must be administered systemically and therefore requires a high level of targeting. Unspecific receptors or virus can be used for delivery of the therapeutic gene, if the expression of the gene is regulated by a cancer specific promoter. Using a global gene expression analysis (oligonucleotide arrays), we have identified a number of highly and specifically expressed genes in SCLC (Pedersen, N et al., Cancer Res 63, p1943, 2003). Several of the genes identified by the analysis are known to be transcriptionally regulated in a developmental manner and several reflect the neuroendocrine origin of SCLC. One of these genes is the insulinoma-associated 1 (INSM1), which is normally exclusively expressed during early embryonic development, but has been found highly re-activated in neuroendocrine tumours. A 1.7 kb region of the human INSM1 promoter has previously been shown to confer correct spatial and temporal expression in transgenic mice (Breslin, MB et al., J Biol Chem 278: 38991, 2003). Transfection of a large panel of SCLC cell lines with a reporter gene regulated by this promoter region demonstrated very high expression in most SCLC cell lines (up to 12 times higher levels than from the SV40 promoter with the SV40 enhancer) and no expression in cell lines from other cancer types or normal tissue. The relative expression levels correlated well with the endogenous levels of INSM1 mRNA. This was in contrast to a gastrin releasing peptide promoter region, which has previously been suggested for gene therapy for SCLC, where the levels were lower and did not correlate with endogenous mRNA levels. Expression of the Herpes Simplex Virus Thymidine Kinase (HSV-TK) suicide gene from the INSM1 promoter conferred cell death after treatment with the prodrug ganciclovir in SCLC cell lines with high expression of INSM1, and not in cell lines with low or no expression of INSM1. Preliminary in vivo experiments using xenografted tumours show that HSV-TK expressed by the INSM1 promoter cause significant tumour regression after ganciclovir treatment. We have therefore demonstrated that the activity of INSM1 promoter is sufficient for gene therapy approaches and that this promoter confers the cancer specificity needed for systemic treatment.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]