Targeting Transcription Factors for Cancer Gene Therapy

A high proportion of oncogenes and tumor suppressor genes encode transcription factors. Deregulated expression or activation and inactivation of transcription factors as well as mutations and translocations play critical roles in tumorigenesis. Furthermore, the majority of oncogenic signaling pathways converge on sets of transcription factors that ultimately control gene expression patterns resulting in tumor formation and progression as well as metastasis. Under normal physiological conditions whole sets of genes with similar functions are regulated by highly specific, tightly regulated upstream transcriptional regulators, whereas in cancer aberrant activation of these transcription factors leads to deregulated expression of multiple gene sets associated with tumor development and progression. The activity of these transcription factors can be modulated by multiple mechanisms including posttranslational modifications. Activation or inactivation of transcription factors promote cancer development, cell survival and proliferation and induce tumor angiogenesis. Since many of these transcription factors are inactive under normal physiological conditions and their expression and activities are tightly regulated, these transcription factors represent highly desirable and logical points of therapeutical interference in cancer development and progression. Three major families of transcription factors have emerged as important players in human cancer and are validated targets in drug discovery for cancer therapy: 1) the NF-kappaB and AP-1 families of transcription factors, 2) the STAT family members and 3) the steroids receptors. This review aims to elucidate the divergent molecular mechanisms involved in the deregulated activation of transcription factor signaling in malignant transformation, although additional transcription factor families such as the Ets factors, ATF family members, basic helix-loop-helix transcription factors etc. are additional critical transcriptional regulators in human cancer. We explore new approaches to specifically inhibit these transcription factors in cancer in order to validate them as a drug targets. Efforts to develop novel viral vectors for therapeutic applications are also discussed.