title: Pharmacologic synergy between dual phosphoinositide-3-kinase and mammalian target of rapamycin inhibition and 5-fluorouracil in PIK3CA mutant gastric cancer cells.
abstract: Phosphoinositide-3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors are an emerging class of anti-cancer agents. Here, we tested the hypothesis that the dual PI3K/mTOR inhibitor, PI103, could synergize with the chemotherapeutic agent, 5-fluorouracil (5-FU) by inhibiting E2F1, thymidylate synthase (TS) and enhancing DNA damage. Drug combination effects were assessed in gastric cancer cells using the median-effect equation. The specific effects of inhibition of E2F1 and PIK3CA were examined by siRNA, and mTOR by rapamycin exposure. Protein expression and apoptosis pre- and post-treatment was measured using standard methods. PI103 and 5-FU was synergistic in 3/5 gastric cancer cell lines tested. Synergy was associated with PI3KCA mutation, reduced TS and E2F1 protein levels, increased H2AX phosphorylation and apoptosis. E2F1 siRNA enhanced sensitivity to 5-FU only in cells displaying synergy. Excess thymidine exposure converted synergism to antagonism in all cells. Inhibition of PI3K and mTOR alone enhanced 5-FU cytotoxicity in only 2/3 cell lines that displayed synergy each. In AGS cells, PI3K inhibition alone enhanced 5-FU sensitivity as much as dual PI3K/mTOR inhibition. In HGC27 cells, dual inhibition increased 5-FU sensitivity more than single PI3K or mTOR inhibition. Combined PI103 and 5-FU treatment reduced in vivo tumor growth more than treatment with single agents. PI3K/mTOR inhibitors can enhance 5-FU cytotoxicity in vitro and in vivo, especially in PIK3CA mutant tumor cells. Dual, rather than single, PI3K/mTOR inhibitors may combine better with 5-FU due to cellular heterogeneity in sensitivity to PI3K and mTOR inhibition.
authors.affiliation: Cancer Science Institute of Singapore, National University of Singapore, Singapore, Singapore.
authors.forename: Bhaskar
authors.initials: B
authors.lastname: Bhattacharya
authors.forename: Mohamed
authors.initials: M
authors.lastname: Akram
authors.forename: Indirikumar
authors.initials: I
authors.lastname: Balasubramanian
authors.forename: Kimberley K Y
authors.initials: KK
authors.lastname: Tam
authors.forename: King X
authors.initials: KX
authors.lastname: Koh
authors.forename: Mei Q
authors.initials: MQ
authors.lastname: Yee
authors.forename: Richie
authors.initials: R
authors.lastname: Soong
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D004357:Drug Synergism; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage / Q000494:pharmacology*; D005663:Furans / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009687:Nuclear Proteins / Q000235:genetics*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011725:Pyridines / Q000008:administration & dosage / Q000494:pharmacology*; D011743:Pyrimidines / Q000008:administration & dosage / Q000494:pharmacology*; D013274:Stomach Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D014157:Transcription Factors / Q000235:genetics*; D023041:Xenograft Model Antitumor Assays
chemical_list: D005472:Fluorouracil; D005663:Furans; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011725:Pyridines; D011743:Pyrimidines; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; C522973:PI103; C503859:PI3KCA protein, human; C546842:MTOR protein, human