title: Alternative dosing of dual PI3K and MEK inhibition in cancer therapy.
abstract: BACKGROUND
  PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways are thought to be the central transducers of oncogenic signals in solid malignancies, and there has been a lot of enthusiasm for developing inhibitors of these pathways for cancer therapy. Some preclinical models have suggested that combining inhibitors of both parallel pathways may be more efficacious, but it remains unknown whether dual inhibition with high enough concentrations of the drugs to achieve meaningful target inhibition is tolerable in a clinical setting. Furthermore, the predictive factors for dual inhibition are unknown.
  
  
  METHODS
  Non-small cell lung cancer (NSCLC) cell lines (n=12) with the most frequent oncogenic backgrounds (K-Ras mut n=3, EGFR mut n=3, ALK translocated n=3, and triple-negative n=3) were exposed to PI3K inhibitors (ZSTK474, PI-103) or MEK inhibitor (CI-1040) alone or in combination and analysed with an MTS growth/cytotoxicity assay and statistically by combination index analysis. The activity of the intracellular signaling pathways in response to the inhibitor treatments was analysed with a western blot using phospho-specific antibodies to AKT, ERK1/2, S6, and 4E-BPI. For the differential dosing schedule experiments, additional breast and colon cancer cell lines known to be sensitive to dual inhibition were included.
  
  
  RESULTS
  Two of the 12 NSCLC cell lines tested, H3122 (ALK translocated) and H1437 (triple-negative), showed increased cytotoxicity upon dual MEK and PI3K inhibition. Furthermore, MDA-MB231 (breast) and HCT116 (colon), showed increased cytotoxicity upon dual inhibition, as in previous studies. Activation of parallel pathways in the dual inhibition-sensitive lines was also noted in response to single inhibitor treatment. Otherwise, no significant differences in downstream intracellular pathway activity (S6 and 4E-BPI) were noted between PI3K alone and dual inhibition other than the increased cytotoxicity of the latter. In the alternative dosing schedules two out of the four dual inhibition-sensitive cell lines showed similar cytotoxicity to continuous PI3K and short (15min) MEK inhibition treatment.
  
  
  CONCLUSIONS
  Therapy with a dual PI3K and MEK inhibitor combination is more efficient than either inhibitor alone in some NSCLC cell lines. Responses to dual inhibition were not associated with any specific oncogenic genotype and no other predictive factors for dual inhibition were noted. The maximal effect of the dual PI3K and MEK inhibition can be achieved with alternative dosing schedules which are potentially more tolerable clinically.
authors.affiliation: Department of Medical Oncology and Radiotherapy, Oulu University Hospital, Oulu PB22 90029 OYS, Finland.
authors.forename: Elina
authors.initials: E
authors.lastname: Jokinen
authors.forename: Niina
authors.initials: N
authors.lastname: Laurila
authors.forename: Jussi P
authors.initials: JP
authors.lastname: Koivunen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology; D002450:Cell Communication / Q000502:physiology; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000201:enzymology; D004359:Drug Therapy, Combination; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors