Synergistic growth inhibition and induction of apoptosis by a novel mixed backbone antisense oligonucleotide targeting CRIPTO in combination with C225 anti-EGFR monoclonal antibody and 8-Cl-cAMP in human GEO colon cancer cells

We have evaluated the antiproliferative effect of a novel mixed backbone an tisense oligonucleotide generated against the 5'-coding region of the human CRIPTO mRNA in GEO human colon cancer cells. We have also evaluated the ef fects of this anti-CRIPTO antisense oligonucleotide in combination with a c himeric anti-human epidermal growth factor receptor (EGFR) monoclonal antib ody (MAb C225) and with 8-Cl-cAMP, a cAMP analog that specifically inhibits type I protein kinase A (PKAI), since a functional EGFR-driven autocrine p athway is operative and PKAI is overexpessed in GEO colon cancer cells. Tre atment with a single agent at low doses determined a 15-35% growth inhibiti on. A synergistic antiproliferative effect was observed when combinations o f two agents were used with a co- operativity quotient ranging between 1.5 and 2.2. Furthermore, the combined treatment with all three drugs caused an almost complete suppression of the ability of GEO cells to form colonies i n soft agar. We next evaluated whether any combination of 8-Cl-cAMP, the an ti-CRIPTO antisense oligonucleotide and MAb C225 could induce programmed ce ll death in GEO cells. Treatment with each agent alone at all doses tested did not cause DNA fragmentation. The treatment with any combination of two agents was not able to induce apoptosis. In contrast, treatment with all th ree compounds determined an approximately three-fold increase in DNA fragme ntation. In conclusion, the combination of selective antineoplastic agents directed against different but related key signal tranduction pathways effi ciently inhibits cell growth and causes apoptosis in human colorectal cance r cells.