Cooperative inhibitory effect of novel mixed backbone oligonucleotide targeting protein kinase A in combination with docetaxel and anti-epidermal growth factor-receptor antibody on human breast cancer cell growth

Type I protein kinase A (PKAI) is overexpressed in the majority of human tu mors and plays a relevant role in neoplastic transformation, conveying mito genic signals of different growth factors and oncogenes, Inhibition of PKAI by antisense oligonucleotides targeting its RI alpha regulatory subunit re sults in cancer cell growth inhibition in vitro and in vivo. We have recent ly shown that a mixed backbone oligonucleotide targeting RI alpha can coope ratively inhibit human cancer cell growth when combined with selected cytot oxic drugs. In the present study, we have used HYB 165, a novel DNA/RNA hyb rid mixed backbone oligonucleotide that exhibits improved pharmacokinetic a nd bioavailability properties in vivo and is presently undergoing Phase I t rials. We have shown that HYB 165 exhibits a dose-dependent inhibitory effe ct on ZR-75-1 cells and a cooperative activity with docetaxel, a cytotoxic drug active in breast cancer. The antiproliferative activity is accompanied by increased apoptosis, as compared with each single agent. On the basis o f our previous demonstration of a structural and functional relation betwee n PKAI and epidermal growth factor receptor, we have performed a double blo ckade of these pathways (MAb) C225, an anti-epidermal growth factor recepto r chimeric MAb, The two compounds determined a cooperative growth inhibitor y effect on ZR-75-1 cells and increased apoptosis, To study whether differe nt biological agents and cytotoxic drugs can interact together, low doses o f HYB 165, MAb C225, and docetaxel were combined causing an even greater co operative effect toward growth inhibition. Finally, we have demonstrated th at each single agent is able to induce bcl-2 phosphorylation and that the t hree agents, used in combination at suboptimal doses, determine a greater d egree of bcl-2 phosphorylation and cause apoptosis of the majority of ZR-75 -1 cells. These findings provide the basis for a novel strategy of treatmen t of breast cancer patients because both HYB 165 and MAb C225 are presently under clinical evaluation.