Combined blockade of protein kinase A and bcl-2 by antisense strategy induces apoptosis and inhibits tumor growth and angiogenesis

Protein kinase A type I (PKAI) plays a key role in neoplastic transformatio n, conveys mitogenic signals from different sources, and is overexpressed i n the majority of human tumors. Inhibition of PKAI by different tools resul ts in cancer-cell growth inhibition in vitro and in vivo. We and others hav e recently shown that a novel class of mixed-backbone oligonucleotides targ eting the PKAI subunit RI alpha exhibits improved pharmacokinetic propertie s and antitumor activity accompanied by increased apoptosis in several huma n cancer types in vitro and in vivo. The role of bcl-2 in the control of ap optosis has been widely documented, and the inhibition of bcl-2 expression and function may have important therapeutic implications. In fact, oligonuc leotides antisense bcl-2 have shown antitumor activity in animal models and have successfully completed early clinical trials. Recent studies have dem onstrated a direct role of PKA in the regulation of the bcl-2-dependent apo ptotic pathway. Therefore, we have investigated the combined blockade of PK A and bcl-2 by antisense strategy as a potential therapeutic approach. The novel hybrid DNA/RNA mixed-backbone oligonucleotide antisense Riot (AS RI a lpha) in combination with the antisense bcl-2 (AS bcl-2), cooperatively inh ibited bcl-2 expression and soft agar growth and induced apoptosis in diffe rent human cancer cell lines. p.o. administration of AS RI alpha in combina tion with i.p. AS bcl-2 caused a marked antitumor effect and a significant prolongation of survival in nude mice bearing human colon cancer xenografts . Moreover, histochemical analysis of tumor specimens showed inhibition of RI alpha and Ki67 expression, inhibition of angiogenesis, and parallel indu ction of apoptosis in vivo. The results of our study imply an interaction b etween the PKA and bcl-2 signaling pathways and, because both antisenses ha ve now entered Phase II trials, provide the rationale to translate this nov el therapeutic strategy in a clinical setting.