Therapeutic Discovery Killing of Kras-Mutant Colon Cancer Cells via Rac-Independent Actin Remodeling by the b GBP Cytokine , a Physiological PI 3 K Inhibitor Therapeutically Effective In Vivo

Activating mutations in Kras are the most frequent mutations in human cancer. They define a subset of patients who do not respond to current therapies and for whom prognosis is poor. Oncogenic Kras has been shown to deregulate numerous signaling pathways of which the most intensively studied are the Ras/ extracellular signal–regulated kinase cascade and the phosphoinositide 3-kinase (PI3K)/Akt cascade. However, to date, there are no effective targeted therapies in the clinic against Kras-mutant cancers. Here, we report that the b-galactoside–binding protein (bGBP) cytokine, a physiologic inhibitor of class I PI3Ks, is a potent activator of apoptosis in Kras-mutant colorectal cancer cells, even when coharboring mutant-activated PIK3CA. Our study unveils an elective route to intrinsic and extrinsic apoptosis, which involves the cytoskeleton. Early events are inhibition of PI3K activity and Rac-independent actin rearrangement assignable to phosphoinositide changes at the plasma membrane. Cyclin E deregulation, arrest of DNA synthesis, and checkpoint kinase 2 activation underscore events critical to the activation of an intrinsic apoptotic program. Clustering of CD95/Fas death receptors underscore events critical to the activation of extrinsic apoptosis. In nudemice,wepresent thefirst evidence that xenograft tumordevelopment is strongly inhibitedbyHu-r-bGBP. Taken together, our results open a new therapeutic opportunity to a subset of patients refractive to current treatments. This first demonstration of therapeutic efficacy againstKras-mutant colon cancer suggests thatHur-bGBPmay also be therapeutically effective against other cancers harboring activating Ras mutations as well as PIK3CA mutations. Mol Cancer Ther; 11(9); 1–10. 2012 AACR. Introduction Activating mutations in the Ras genes (H,K,N; ref. 1), themost commononcogenicmutations in human cancers, are dominant determinants of drug resistance. Most frequent in Kras, Kras mutations define tumors refractory to conventional chemotherapy and radiation therapy (2, 3) and to more recently introduced therapies based on EGF receptor tyrosine kinase inhibitors (4–7). Locked in the GTP-bound mode, oncogenic Ras constitutively activates the Raf/MEK/extracellular signal–regulated kinase (ERK) cascade and an integrated signaling network, which controls cell proliferation and cell survival (8, 9) to be a major mediator of tumorigenesis. The importance of activating mutations in the Ras oncogenes in human cancers has made Ras and downstream effectors elective targets for therapeutic intervention, but the value of targeting inhibitors in the clinic remains doubtful. For example, prevention of Ras anchorage at the cell membrane by farnesyltransferase inhibitors has been shown to be effective in mice expressing oncogenic Ras but not in patients with solid tumors (10). Similarly, in more recent studies, CI-1040, a MEK inhibitor, was found to induce significant shrinkage of Kras-driven lung carcinomas in mice (11), but had no significant effect in patients with advanced lung, breast, colon, and pancreatic cancers (12). Using a different approach, a number of compounds with efficacy against cells with mutant-activated Kras have been identified by high-throughput screening (13–16) and shown to inhibit xenograft growth (13,15, 16); however, the mechanisms by which these compounds operate are not fully understood and their anticancer efficacy in the clinic remains uncertain. Recently, the necessary role played by the phosphoinositide 3-kinase (PI3K)/Akt pathway in maintaining tumor growth has made this pathway a target for small Authors' Affiliations: School of Biomedical and Health Sciences, King's College London; CancerResearchUKLondonResearch Institute; NYU in London, London, United Kingdom;Department of Experimental Medicine, La Sapienza University, Rome; and Unit of General Pathology, Aging Research Center, G. D'Annunzio University Foundation, Chieti, Italy Note: Current address for D. -y. Shi: Department of Biochemistry and Molecular Biology, Shanghai Medical College of Fudan University, 200032 Shanghai, PR China. Corresponding Author: Livio Mallucci, School of Biomedical and Health Sciences, King's College London, Franklin Wilkins Building, 150 Stamford Street, SE1 9NH London, United Kingdom. Phone: 44-207-848-4257; Fax: 44-207-848-4500; E-mail: livio.mallucci@kcl.ac. uk doi: 10.1158/1535-7163.MCT-11-1041-T 2012 American Association for Cancer Research. Molecular Cancer Therapeutics www.aacrjournals. org OF1 on June 22, 2017. © 2012 American Association for Cancer Research. mct.aacrjournals. org Downloaded from Published OnlineFirst July 2, 2012; DOI: 10.1158/1535-7163.MCT-11-1041-T