ABSTRACT
The mammalian target of rapamycin (mTOR) regulates cell growth by integrating nutrient and growth factor signaling and is strongly implicated in cancer. But mTOR is not an oncogene, and which tumors will be resistant or sensitive to new adenosine triphosphate (ATP) competitive mTOR inhibitors now in clinical trials remains unknown. We screened a panel of over 600 human cancer cell lines to identify markers of resistance and sensitivity to the mTOR inhibitor PP242. RAS and phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) mutations were the most significant genetic markers for resistance and sensitivity to PP242, respectively; colon origin was the most significant marker for resistance based on tissue type. Among colon cancer cell lines, those with KRAS mutations were most resistant to PP242, whereas those without KRAS mutations most sensitive. Surprisingly, cell lines with co-mutation of PIK3CA and KRAS had intermediate sensitivity. Immunoblot analysis of the signaling targets downstream of mTOR revealed that the degree of cellular growth inhibition induced by PP242 was correlated with inhibition of phosphorylation of the translational repressor eIF4E-binding protein 1 (4E-BP1), but not ribosomal protein S6 (rpS6). In a tumor growth inhibition trial of PP242 in patient-derived colon cancer xenografts, resistance to PP242-induced inhibition of 4E-BP1 phosphorylation and xenograft growth was again observed in KRAS mutant tumors without PIK3CA co-mutation, compared with KRAS wild-type controls. We show that, in the absence of PIK3CA co-mutation, KRAS mutations are associated with resistance to PP242 and that this is specifically linked to changes in the level of phosphorylation of 4E-BP1.
Subject(s)
Adenosine Triphosphate/metabolism , Antineoplastic Agents/pharmacology , Binding, Competitive/drug effects , Carrier Proteins/metabolism , Drug Resistance, Neoplasm/drug effects , Indoles/pharmacology , Phosphoproteins/metabolism , Purines/pharmacology , TOR Serine-Threonine Kinases/antagonists & inhibitors , Adaptor Proteins, Signal Transducing , Animals , Cell Cycle Proteins , Cell Line, Tumor , Class I Phosphatidylinositol 3-Kinases , Colonic Neoplasms/pathology , Eukaryotic Initiation Factors , Female , Humans , MAP Kinase Signaling System/drug effects , Mice , Mutation , Phosphatidylinositol 3-Kinases/genetics , Phosphorylation/drug effects , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins p21(ras) , Ribosomal Protein S6/metabolism , TOR Serine-Threonine Kinases/metabolism , Xenograft Model Antitumor Assays , ras Proteins/geneticsABSTRACT
BACKGROUND: Comprehensive molecular characterization of cancer that has metastasized to bone has proved challenging, which may limit the diagnostic and potential therapeutic opportunities for patients with bone-only metastatic disease. METHODS: We describe successful tissue acquisition, DNA extraction, and whole-exome sequencing from a bone metastasis of a patient with metastatic, castration-resistant prostate cancer (PCa). RESULTS: The resulting high-quality tumor sequencing identified plausibly actionable somatic genomic alterations that dysregulate the phosphoinostide 3-kinase pathway, as well as a theoretically actionable germline variant in the BRCA2 gene. CONCLUSIONS: We demonstrate the feasibility of diagnostic bone metastases profiling and analysis that will be required for the widespread application of prospective 'precision medicine' to men with advanced PCa.
Subject(s)
Bone Neoplasms/secondary , Exome , Prostatic Neoplasms/genetics , Prostatic Neoplasms/pathology , Biopsy , Bone Neoplasms/diagnostic imaging , Bone Neoplasms/pathology , Germ-Line Mutation , High-Throughput Nucleotide Sequencing , Humans , Male , Middle Aged , Mutation , Prostatic Neoplasms, Castration-Resistant/genetics , Prostatic Neoplasms, Castration-Resistant/pathology , RadiographyABSTRACT
Immune escape describes a critical event whereby tumor cells adopt an immunoresistant phenotype to escape adaptive surveillance. We show that expression of a pivotal negative regulator of T-cell function, B7-H1, correlates with PI(3) kinase activation in breast and prostate cancer patients. B7-H1-mediated immunoresistance can be attenuated by inhibitors of the PI(3) kinase pathway, and is dependent on S6K1-mediated translational regulation of B7-H1 protein. Breast and prostate carcinoma cells with activated PI(3) kinase lose the immunoresistant phenotype after treatment with B7-H1 siRNA. Conversely, breast and prostate carcinoma cells with minimal PI(3) kinase activation adopt an immunoresistant phenotype when engineered to overexpress B7-H1 protein. These observations describe a mechanism for immune escape from tumor dormancy in humans that relates to oncogenesis.
