Farah Ibrahim O, Begum Rowshan A, Ishaque Ali B
Department of Biology, Jackson State University, Jackson, MS 39217, USA.
Biomed Sci Instrum. 2007;43:116-21.
In response to genotoxic agents, normal tissue cells are instructed by p53 either to perform DNA repair or to undergo apoptosis. Studies showed that chemo and/or radiotherapy damage both normal and cancerous cells indiscriminately. To this end, severe side effects inflicted by p53 activation in normal tissues, would possibly be abrogated by p53 inhibition. Pifithrin-alpha (PFT-alpha) is a reversible inhibitor of p53-mediated apoptosis, p53-dependent gene transcription, as well as down stream responsive gene function. The objective of this study was (1) to evaluate PFT-alpha for differential cellular protection in response to arsenic trioxide and cadmium chloride exposure of normal and neoplastic cells, and (2) to evaluate the transcriptional activation of p53 and p53-responsive genes in rat liver cells and HepG2 carcinoma cell line. Cell survival was detected by fluorescein diacetate (FDA) and fluorospectroscopy. Mean LC50 and (SD) for HepG2 cells following exposure to arsenic were 13.7 (+/-1.0) microg/ml with PFT- alpha and 13.4 (+/- 0.5) microg/ml without PFT-alpha (p>0.05). For rat liver cells it was 670 (+/- 8.15) microg/ml with and 573.15 (+/-1.0) microg/ml without PFT-alphha (p<0.05). On exposure to cadmium Chloride, LC50's were 6.95 (+/-2.5) microg/ml for HepG2 cell line in presence of PFT-alpha and 7.35 (+/-1.9) microg/ml in its absence (p>0.5). The results revealed significant differences from controls only upon exposure of rat liver cells to arsenic trioxide in presence of PFT-alpha. PFT-alpha inhibited the transactivation of p53 in rat liver cells and resulted in repression of Bcl2, PCNA, MDM2, Cyclin G and P21 genes by arsenic trioxide. HepG2 cells exposed to arsenic trioxide and PFT-alpha showed expression of only the P53 and PCNA genes. We conclude that PFT-alpha exhibits cytoprotective effect, modifies the detrimental influences of known genotoxic agents in normal cells and has the potential for use as an adjuvant to cancer therapy.
在对基因毒性剂的反应中，正常组织细胞受p53调控，要么进行DNA修复，要么发生凋亡。研究表明，化疗和/或放疗会不加区分地损伤正常细胞和癌细胞。为此，p53在正常组织中激活所造成的严重副作用，可能会通过抑制p53来消除。pifithrin-α（PFT-α）是一种p53介导的凋亡、p53依赖性基因转录以及下游反应性基因功能的可逆抑制剂。本研究的目的是：（1）评估PFT-α在正常细胞和肿瘤细胞暴露于三氧化二砷和氯化镉时的细胞差异保护作用；（2）评估大鼠肝细胞和HepG2癌细胞系中p53及其反应性基因的转录激活情况。通过荧光素二乙酸酯（FDA）和荧光光谱法检测细胞活力。HepG2细胞暴露于砷后，使用PFT-α时的平均半数致死浓度（LC50）及标准差为13.7（±1.0）μg/ml，不使用PFT-α时为13.4（±0.5）μg/ml（p>0.05）。对于大鼠肝细胞，使用PFT-α时为670（±8.15）μg/ml，不使用时为573.15（±1.0）μg/ml（p<0.05）。暴露于氯化镉时，HepG2细胞系在有PFT-α存在时的LC50为6.95（±2.5）μg/ml，不存在时为7.35（±1.9）μg/ml（p>0.5）。结果显示，仅在大鼠肝细胞暴露于有PFT-α存在的三氧化二砷时，与对照组有显著差异。PFT-α抑制大鼠肝细胞中p53的反式激活，并导致三氧化二砷对Bcl2、PCNA、MDM2、细胞周期蛋白G和P21基因的抑制。暴露于三氧化二砷和PFT-α的HepG2细胞仅显示P53和PCNA基因的表达。我们得出结论，PFT-α具有细胞保护作用，可改变已知基因毒性剂对正常细胞的有害影响，有潜力用作癌症治疗的辅助药物。
