Bruzek Laura M, Poynter Jenny N, Kaufmann Scott H, Adjei Alex A
Division of Medical Oncology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
Mol Pharmacol. 2005 Aug;68(2):477-86. doi: 10.1124/mol.104.010074. Epub 2005 May 18.
Farnesyl protein transferase inhibitors (FTIs) have demonstrated clinical activity in certain solid tumors and hematological malignancies. Little is known about mechanisms of resistance to these agents. To provide a basis for better understanding FTI resistance, the colorectal carcinoma cell line HCT 116 was selected by stepwise exposure to increasing 4-(2-(4-(8-chloro-3,10-dibromo-6,11-dihydro-5H-benzo-(5,6)-cyclohepta(1,2-b)-pyridin-11(R)-yl)-1-piperidinyl)-2-oxo-ethyl)-1-piperidinecarboxamide (SCH66336) concentrations. The resulting line, HCT 116R, was 100-fold resistant to SCH66336 and other FTIs, including methyl {N-[2-phenyl-4-N[2(R)-amino-3-mercaptopropylamino] benzoyl]}-methionate (FTI-277), but was less than 2-fold resistant to the standard agents gemcitabine, cisplatin, and paclitaxel. Accumulation of the unfarnesylated forms of prelamin A and HDJ-2, two substrates that reflect farnesyl transferase inhibition, was similar in FTI-treated parental and HCT 116R cells, indicating that alterations in drug uptake or inhibition of farnesyl protein transferase is not the mechanism of resistance. Changes in signal-transduction pathways that might account for this resistance were examined by immunoblotting and confirmed pharmacologically. There was no difference in activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase pathway or sensitivity to the MEK1/2 inhibitor 2'-amino-3'-methoxyflavone (PD98059) in HCT 116R cells. In contrast, increased phosphorylation of the molecular target of rapamycin (mTOR) and its downstream target p70 S6 kinase and increased levels of Akt1 and Akt2 were demonstrated in HCT 116R cells. Further experiments demonstrated that the mTOR inhibitor rapamycin selectively sensitized HCT 116R cells to SCH66336 but not to gemcitabine, cisplatin, or paclitaxel. These findings provide evidence that alterations in the phosphatidylinositol-3 kinase/Akt pathway can contribute to FTI resistance and suggest a potential strategy for overcoming this resistance.
法尼基蛋白转移酶抑制剂（FTIs）已在某些实体瘤和血液系统恶性肿瘤中显示出临床活性。关于这些药物的耐药机制知之甚少。为了更好地理解FTI耐药性提供依据，通过逐步暴露于浓度递增的4-(2-(4-(8-氯-3,10-二溴-6,11-二氢-5H-苯并-(5,6)-环庚并(1,2-b)-吡啶-11(R)-基)-1-哌啶基)-2-氧代-乙基)-1-哌啶甲酰胺（SCH66336），选择了结肠癌细胞系HCT 116。所得细胞系HCT 116R对SCH66336和其他FTIs（包括甲基{N-[2-苯基-4-N[2(R)-氨基-3-巯基丙基氨基]苯甲酰基]}-甲硫氨酸酯（FTI-277））具有100倍的耐药性，但对标准药物吉西他滨、顺铂和紫杉醇的耐药性小于2倍。前体核纤层蛋白A和HDJ-2这两种反映法尼基转移酶抑制作用的底物的未法尼基化形式的积累，在FTI处理的亲本细胞和HCT 116R细胞中相似，表明药物摄取的改变或法尼基蛋白转移酶的抑制不是耐药机制。通过免疫印迹检查并经药理学证实可能导致这种耐药性的信号转导途径的变化。在HCT 116R细胞中，丝裂原活化蛋白激酶激酶（MEK）/细胞外信号调节激酶途径的激活或对MEK1/2抑制剂2'-氨基-3'-甲氧基黄酮（PD98059）的敏感性没有差异。相反，在HCT 116R细胞中，雷帕霉素的分子靶点（mTOR）及其下游靶点p70 S6激酶的磷酸化增加，Akt1和Akt2的水平升高。进一步的实验表明，mTOR抑制剂雷帕霉素选择性地使HCT 116R细胞对SCH66336敏感，但对吉西他滨、顺铂或紫杉醇不敏感。这些发现提供了证据，表明磷脂酰肌醇-3激酶/Akt途径的改变可导致FTI耐药，并提出了克服这种耐药性的潜在策略。
