title: Utilization of quantitative in vivo pharmacology approaches to assess combination effects of everolimus and irinotecan in mouse xenograft models of colorectal cancer.
abstract: OBJECTIVE
  The PI3K/AKT/mTOR pathway is frequently dysregulated in cancers and inhibition of mTOR has demonstrated the ability to modulate pro-survival pathways. As such, we sought to determine the ability of the mTOR inhibitor everolimus to potentiate the antitumor effects of irinotecan in colorectal cancer (CRC).
  
  
  METHODS
  The combinatorial effects of everolimus and irinotecan were evaluated in vitro and in vivo in CRC cell lines harboring commonly found mutations in PIK3CA, KRAS and/or BRAF. Pharmacokinetically-directed dosing protocols of everolimus and irinotecan were established and used to assess the in vivo antitumor effects of the agents. At the end of treatment, 3-6 tumors per treatment arm were harvested for biomarker analysis by NMR metabolomics.
  
  
  RESULTS
  Everolimus and irinotecan/SN38 demonstrated synergistic anti-proliferative effects in multiple CRC cell lines in vitro. Combination effects of everolimus and irinotecan were determined in CRC xenograft models using clinically-relevant dosing protocols. Everolimus demonstrated significant tumor growth inhibition alone and when combined with irinotecan in HT29 and HCT116 tumor xenografts. Metabolomic analysis showed that HT29 tumors were more metabolically responsive than HCT116 tumors. Everolimus caused a decrease in glycolysis in both tumor types whilst irinotecan treatment resulted in a profound accumulation of lipids in HT29 tumors indicating a cytotoxic effect.
  
  
  CONCLUSIONS
  Quantitative analysis of tumor growth and metabolomic data showed that the combination of everolimus and irinotecan was more beneficial in the BRAF/PIK3CA mutant HT29 tumor xenografts, which had an additive effect, than the KRAS/PIK3CA mutant HCT116 tumor xenografts, which had a less than additive effect.
authors.affiliation: Division of Medical Oncology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America. Erica.Pierce@ucdenver.edu
authors.forename: Erica L
authors.initials: EL
authors.lastname: Bradshaw-Pierce
authors.forename: Todd M
authors.initials: TM
authors.lastname: Pitts
authors.forename: Gillian
authors.initials: G
authors.lastname: Kulikowski
authors.forename: Heather
authors.initials: H
authors.lastname: Selby
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Merz
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Gustafson
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Serkova
authors.forename: S Gail
authors.initials: SG
authors.lastname: Eckhardt
authors.forename: Colin D
authors.initials: CD
authors.lastname: Weekes
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000819:agonists / Q000494:pharmacology*; D002166:Camptothecin / Q000819:agonists / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D058534:Class I Phosphatidylinositol 3-Kinases; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004357:Drug Synergism; D000068338:Everolimus; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000819:agonists / Q000494:pharmacology*; D000077146:Irinotecan; D055442:Metabolome / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D009368:Neoplasm Transplantation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D020123:Sirolimus / Q000819:agonists / Q000031:analogs & derivatives* / Q000494:pharmacology; D014183:Transplantation, Heterologous; D023041:Xenograft Model Antitumor Assays; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D007166:Immunosuppressive Agents; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D000077146:Irinotecan; D000068338:Everolimus; D019869:Phosphatidylinositol 3-Kinases; D058534:Class I Phosphatidylinositol 3-Kinases; C484760:PIK3CA protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D020123:Sirolimus; D002166:Camptothecin