title: Combination therapy targeting Raf-1 and MEK causes apoptosis of HCT116             colon cancer cells.
abstract: Members of the Ras protooncogene family are mutated in approximately 75%             of colon cancers. The Raf kinases (Raf-1, b-Raf and a-Raf) directly interact with             Ras and serve as mediators of mitogenic signals. Expression of the constitutively             active alleles of Raf or Ras gene families results in oncogenesis in a number             of model systems. Previous studies emphasized the importance of Raf-1 and b-Raf             in preventing apoptosis in addition to their roles in cell growth. In the present             study, we examined whether inhibition of the Raf-1 or b-Raf kinase decreases cell             growth and increases apoptosis in colon cancer cells. c-Raf and b-Raf were depleted             in colon cancer cell lines, such as HCT116, HT29 and Colo205, containing Ras or             b-Raf mutations by RNA interference (RNAi). The results showed that colon cancer             cells with activating Ras mutations undergo apoptosis following Raf-1 inhibition,             as determined by cell cycle analysis and the release of cytochrome c. Moreover,             in b-Raf mutant colon cancers, the inhibition of b-Raf as compared to Raf-1 is             crucial for cancer cell death. There is increasing evidence for both MEK-independent             Raf signaling and Raf-independent MEK signaling. Thus, we investigated whether             targeting multiple points of the mitogen-activated protein kinase (MAPK) pathway             with a MEK inhibitor and Raf RNAi increases cancer cell death. The results showed             that combination therapy, inhibiting Raf and MEK kinases simultaneously, increased             apoptosis in colon cancer cells. Taken together, our data demonstrate that combination             therapy targeting the MAPK pathway at two distinct points, Raf kinase and MEK,             has greater efficacy in increasing cancer cell death and is likely to improve             therapeutic outcomes for patients.
authors.affiliation: Department of Cancer Biology, Dana-Farber Cancer Institute and Department of Pathology, Harvard Medical School, Boston, MA 02115, USA. romesh.r.subramanian@gmail.com
authors.forename: Romesh R
authors.initials: RR
authors.lastname: Subramanian
authors.forename: Akio
authors.initials: A
authors.lastname: Yamakawa
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000628:therapy*; D015972:Gene Expression Regulation, Neoplastic; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors*; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference
chemical_list: D019908:Proto-Oncogene Proteins c-raf; D020929:Mitogen-Activated Protein Kinase Kinases