Ribozymes targeting serine/threonine kinase Akt1 sensitize cells to anticancer drugs

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Abstract
The serine/threonine kinase Akt is a key component of the cellular signaling pathway for survival and drug‐resistance in cancer cells. In the present study we confirmed this view by expressing an antagonist of Akt, a dominant negative form of Akt, in HCT116 colon carcinoma cells and observing apoptosis induction in cells in which expression of the mutant protein had been induced. Three isoforms of Akt have been found: Akt1/PKBα, Akt2/PKBβ and Akt3/PKBγ. However, the function of individual isoforms with respect to tumorigenicity and drug‐resistance of cancer cells is largely unknown. We designed ribozymes targeting the Akt1 protein in mammalian cells. Our data indicate that Akt1 ribozymes downregulate Akt1 expression to less than half that of control cells. Downregulation of Akt1 expression appears to sensitize HEK293 and HeLa cells to typical chemotherapeutic agents. However, Akt1 ribozymes had little effect on the proliferative activity of the cells. Thus, Akt as a whole and even just the Akt1 isozyme is an excellent target for chemotherapy. We further suggest a synergistic effect for combination therapy targeting Akt and other vital molecules such as tubulins, topoisomerases and protein kinases. (Cancer Sci 2005; 96: 620 – 626)