RAD18 mediates resistance to ionizing radiation in human glioma cells

Radioresistance remains a major challenge in the treatment of glioblastoma multiforme (GBM). RAD18 a central regulator of translesion DNA synthesis (TLS), has been shown to play an important role in regulating genomic stability and DNA damage response. In the present study, we investigate the relationship between RAD18 and resistance to ionizing radiation (IR) and examined the expression levels of RAD18 in primary and recurrent GBM specimens. Our results showed that RAD18 is an important mediator of the IR-induced resistance in GBM. The expression level of RAD18 in glioma cells correlates with their resistance to IR. Ectopic expression of RAD18 in RAD18-low A172 glioma cells confers significant resistance to IR treatment. Conversely, depletion of endogenous RAD18 in RAD18-high glioma cells sensitized these cells to IR treatment. Moreover, RAD18 overexpression confers resistance to IR-mediated apoptosis in RAD18-low A172 glioma cells, whereas cells deficient in RAD18 exhibit increased apoptosis induced by IR. Furthermore, knockdown of RAD18 in RAD18-high glioma cells disrupts HR-mediated repair, resulting in increased accumulation of DSB. In addition, clinical data indicated that RAD18 was significantly higher in recurrent GBM samples that were exposed to IR compared with the corresponding primary GBM samples. Collectively, our findings reveal that RAD18 may serve as a key mediator of the IR response and may function as a potential target for circumventing IR resistance in human GBM.     

IFNgamma-inducible CXCL10/CXCR3 axis alters the sensitivity of HEp-2 cells to ionizing radiation

Radiotherapy is a conventional approach for anti-cancer treatment, killing tumor cells through damaging cellular DNA. While increasing studies have demonstrated that tumors generated the tolerance to radiation and tumor immune system was found to be correlated to radiotherapy resistance. Therefore, it is critical to identify potential immune factors associated with the efficacy of radiotherapy. Here in this study, we evaluated the sensitivities of different tumor cells to radiation and determined HEp-2 cells as the radio-resistant tumor cells for further investigation. IFNgamma as a key regulator of host immune response showed the potential to sensitize tumors to ionizing radiation (IR). Besides, IFNgamma-induced CXC chemokine ligand 10 (CXCL10) was found to be necessary for effective IR-induced killing of cultured HEp-2 cells. Increased clonogenic survival was observed in CXCL10-depleted HEp-2 cells and CXCL10-KO cells. Additionally, the loss of CXCL10 in HEp-2 cells showed less progression of the G0/G1 phase to G2/M when exposed to IR (8 Gy). Local IR (20 Gy) to nude mice bearing HEp-2 tumors significantly reduced tumor burden, while fewer effects on tumor burden in mice carrying CXCL10-KO tumors were observed. We furtherly evaluated the possible roles the chemokine receptor CXCR3 plays in mediating the sensitivity of cultured HEp-2 cells to IR. Altered expression of CXCR3 in HEp-2 cells affected IR-induced killing of HEp-2 cells. Our data suggest the IFNgamma-activated CXCL10/CXCR3 axis may contribute to the effective radiation-induced killing of HEp-2 cells in vitro.     

Reversal of ABCG2-mediated multidrug resistance by human cathelicidin and its analogs in cancer cells

Multidrug resistance (MDR) of cancer cells to a wide spectrum of anticancer drugs is a major obstacle to successful chemotherapy. It is usually mediated by the overexpression of one of the three major ABC transporters actively pumping cytotoxic drugs out of the cells. There has been great interest in the search for inhibitors toward these transporters with an aim to circumvent resistance. This is usually achieved by screening from natural product library and the subsequent structural modifications. This study reported the reversal of ABCG2-mediated MDR in drug-selected resistant cancer cell lines by a class of host defense antimicrobial peptides, the human cathelicidin LL37 and its fragments. The effective human cathelicidin peptides (LL17-32 and LL13-37) were found to increase the accumulation of mitoxantrone in cancer cell lines with ABCG2 overexpression, thereby circumventing resistance to mitoxantrone. At the effective concentrations of the cathelicidin peptides, cell proliferation of the parental cells without elevated ABCG2 expression was not affected. Result from drug efflux and ATPase assays suggested that both LL17-32 and LL13-37 interact with ABCG2 and inhibit its transport activity in an uncompetitive manner. The peptides were also found to downregulate ABCG2 protein expression in the resistant cells, probably through a lysosomal degradation pathway. Our data suggest that the human cathelicidin may be further developed for sensitizing resistant cancer cells to chemotherapy.     

N-methyl-N''-nitro-N-nitrosoguanidine-induced resistance to ionizing radiation

Summary N-methyl-N-nitro-N-nitrosoguanidine (MNNG) pretreatments increase the resistance of Escherichia coli to -radiation. The increased resistance is dependent on functional polA, recA, recB, recC, and lexA genes and is partly dependent on recN. The MNNG-induced resistance is additive to resistance induced by pretreatment with -radiation but not by increases induced by hydrogen peroxide. The MNNG-induced resistance occurs in adaptive response mutants and at pretreatment levels of MNNG that do not activate cells to reactivate UV-inactivated lambda phage. The MNNG-induced resistance appears to be distinct from other inductions to -radiation resistance.     

Notch1 signaling modulates hypoxia-induced multidrug resistance in human laryngeal cancer cells

Molecular Biology Reports - Laryngeal carcinoma is one of the common malignant tumors of the head and neck. Multidrug resistance (MDR) remains a critical problem in the chemotherapy of patients...     

Veliparib overcomes multidrug resistance in liver cancer cells

Overexpression of ATP-binding cassette (ABC) transporter is one of the most important factors taking responsibility for the progress of multidrug resistance (MDR) in multiple cancers. In this study, we investigated that veliparib, a PARP inhibitor which is in clinical development, could overcome ABCB1-mediated MDR in liver cancer cells. Veliparib could significantly enhance the cytotoxic effects of a series of conventional chemotherapeutic drugs in ABCB1-overexpression liver cancer cells. Mechanism study showed that veliparib could significantly enhance the accumulation of doxorubicin in ABCB1-overexpression liver cancer cells, without down-regulating the expression level of ABCB1. Finally, veliparib could significantly inhibit the ATPase activity of ABCB1 transporter. This study could provide information that combine veliparib with other chemotherapeutic drugs may benefit liver cancer patients.     

Effect of graded doses of ionizing radiation on the human testis

A portable unit was developed to provide uniform irradiation of the human testes. The device had built-in radiological protection and provided a dosage independent of the subject geometry, uniform to within +or- 5%. Single doses, between 8-600 rad were administered to the testes of human subjects. Observations were made both before and following irradiation. Parameters evaluated included sperm concentration, motility and morphology, seminal fluid volume, plasma and urinary gonadotropin and testosterone levels, urinary estrogens, and comparison of testicular biopsies taken before and after irradiation in the same subject. Dose-response relationships and recovery times were determined for each dose range studied.     

Effect of ionizing radiation on Fc-receptors of mouse peritoneal mononuclear cells

The influence of different gamma-radiation doses on the number of mouse peritoneal mononuclears bearing Fc-receptors was studied. At doses of 7 and 9.5 Gy, phase changes were observed in the number of cells bearing Fc-receptors: a short-term rise registered 24 h to 2 days after irradiation was followed by depression. In addition, the total number of peritoneal mononuclears decreased. At a dose of 100 Gy, the number of cells with Fc-receptors was reduced as early as 1 h after irradiation, and the pronounced cell lysis occurred.     

Regulation of multidrug resistance in cancer cells by hyaluronan

Multidrug resistance in cancer cells is often due to ATP-dependent efflux pumps, but is also linked to alterations in cell survival and apoptotic signaling pathways. We have found previously that perturbation of hyaluronan-tumor cell interaction by treatment with hyaluronan oligosaccharides suppresses the phosphoinositide 3-kinase/Akt cell survival signaling pathway in cancer cells and reduces tumor growth in vivo. Here we find that these oligomers suppress both the MAP kinase and phosphoinositide 3-kinase pathways in multidrug resistant tumor cells and sensitize these cells to a variety of chemotherapeutic drugs. On the other hand, increased hyaluronan production induces resistance in drug-sensitive tumor cells. Likewise, increased expression of emmprin, which is a glycoprotein that is present on the surface of most malignant cancer cells and that stimulates hyaluronan production, also induces increased resistance. Thus, perturbation of hyaluronan signaling may provide a dual therapeutic role, since it has intrinsic suppressive effects on tumor growth as well as sensitizing cancer cells to chemotherapeutic agents.     

Autophagy induced by ionizing radiation promotes cell death over survival in human colorectal cancer cells

Autophagy is commonly described as a cell survival mechanism and has been implicated in chemo- and radioresistance of cancer cells. Whether ionizing radiation induced autophagy triggers tumor cell survival or cell death still remains unclear. In this study the autophagy related proteins Beclin1 and ATG7 were tested as potential targets to sensitize colorectal carcinoma cells to ionizing radiation under normoxic, hypoxic and starvation conditions. Colony formation, apoptosis and cell cycle analysis revealed that knockdown of Beclin1 or ATG7 does not enhance radiosensitivity in HCT-116 cells. Furthermore, ATG7 knockdown led to an increased survival fraction under oxygen and glutamine starvation, indicating that ionizing radiation indeed induces autophagy which, however, leads to cell death finally. These results highlight that inhibition of autophagic pathways does not generally increase therapy success but may also lead to an unfavorable outcome especially under amino acid and oxygen restriction.     

Effect of ionizing radiation on DNA synthesis in ataxia telangiectasia cells.

The effect of ionizing radiation on DNA synthesis in control and ataxia telangiectasia (AT) lymphoblastoid cell lines was determined. A dose dependent decrease in DNA synthesis was observed in control cells, and the rate and extent of thi decrease in synthesis increased with time after irradiation. No decrease in DNA synthesis was obtained in AT cells, immediately following irradiation, at doses up to 400 rads. At longer times postirradiation, inhibition of synthesis increased but the extent of inhibition was less in AT cell than controls at all doses used. An immediate depression of DNA synthesis was evident in control cells after a radiation dose of 200 rads reaching a maximum at 90 min postirradiation. Little or no decrease in DNA synthesis was evident in AT cells up to 60 min after the same radiation dose, but a decrease occurred between 60 and 90 min after irradiation. The rate of recovery of DNA synthesis to normal levels was more rapid in AT cells than in controls.     

Survivin expressions in human hepatoma HepG2 cells exposed to ionizing radiation of different LET

Survivin is a member of the inhibitors of apoptosis (IAP) protein family that interferes with post-mitochondrial events including activation of caspases. To examine the regulation of survivin expression in response to irradiation with different linear energy transfer (LET), human hepatoma HepG2 cells were irradiated in vitro with X-rays and carbon ions. Cellular sensitivities to low- and high-LET radiation were determined by colony formation. Survivin expression at mRNA and protein level were measured with RT-PCR and Western blot analyses, respectively. Radiation-induced cell cycle arrest and apoptosis were investigated with flow cytometry. We found that low-LET X-rays induced dose-dependent increases in survivin expression. After exposure to high-LET carbon ions, survivin expression gradually increased from 0 to 4 Gy, and then declined at 6 Gy. More pronounced survivin expression, stronger G(2)/M phase arrest was observed after exposure to carbon ions in comparison with X-rays at doses from 0 to 4 Gy. These observations indicate that there is a differential survivin expression in response to different LET radiations and the cycle arrest mechanism may be associated with it. In addition, our data on induction of apoptosis are compatible with the assumption that survivin expression induced by low-LET X-rays radiation may play a critical role in inhibiting apoptosis. However, after irradiation with ions, an anti-apoptotic function of survivin is not evident, possibly because of the serious damage produced by densely ionizing radiation.     

Exposure of human lymphocytes to ionizing radiation reduces mutagenesis by subsequent ionizing radiation

The effect of prior incubation with [3H]thymidine on survival and mutagenesis after X-irradiation of human lymphocytes was studied by incubating lymphocytes with 0.001-1.0 mu Ci/ml [3H]thymidine for 6 h at 37 degrees C and then irradiating with 150 or 300 rad. Survival was measured using lymphocyte cloning and mutagenesis was measured using 6-thioguanine selection to detect clones mutated at the hypoxanthine phosphoribosyltransferase locus. [3H]Thymidine alone had no effect on survival or mutagenesis and X-radiation alone produced the expected decrease in survival and increase in mutations. [3H]Thymidine prior to X-radiation had no effect on lethality of X-radiation but at concentrations of 0.1 and 1.0 mu Ci/ml produced a significant decrease in the number of mutations induced after both 150 and 300 rad. The results suggest that ionizing radiation, produced by disintegration of 3H, reduces the mutagenic effect of a subsequent exposure to ionizing radiation by induction of a system which prevents or repairs a restricted class of radiation damage.     

Aneugenic effect of ionizing radiation in mammalian and human somatic cells

Aneuploidy is among the most serious impairments of hereditary material in somatic and germline cells of living organisms. Chromosome loss or the appearance of an extra homolog in the chromosome set can result in either cell death or the development of various neoplasms with high probability of malignancy. It was traditionally believed that ionizing radiation produces primarily a clastogenic effect. However, there is apparently an aneugenic component of radiation, with mechanism different from that of structural chromosome damage. The present review focuses on the evidence for the existence of the aneugenic effect of ionizing radiation in mammalian and human somatic cells.     

选择性环氧合酶-2抑制剂塞来昔布抑制胃癌多药耐药基因表达的实验研究

目的:探讨选择性环氧合酶(COX-2)抑制剂塞来昔布对胃癌细胞株BGC823多药耐药(mdr)1表达的影响.方法:胃癌细胞株BGC823经浓度分别为0、10、100μ mol/L的塞来昔布处理后,酶联免疫吸附试验检测塞来昔布对胃癌细胞前列腺素E2(PGE2)分泌的影响,24、48 h后用RT-PCR检测多药耐药(mdr)1 mRNA表达,48 h后用免疫细胞化学染色法检测P-gp表达.结果:塞来昔布可显著抑制胃癌细胞株BGC823 PGE2分泌.并呈浓度依赖性(P<0.05).不同浓度塞来昔布作用于细胞后,胃癌细胞株BGC823的mdrl/P-gp表达受不同程度抑制,100μ mol/L的塞来昔布对mdrl mRNA表达抑制作用强于10μ mol/L(P<0.01).不同浓度药物与测量时间为交互作用,作用48h与24h相比,塞来昔布对mdrl mRNA表达的抑制作用更强(P<0.01).结论:塞来昔布可抑制BGC823的mdrl/P-gp表达,且呈剂量效应关系.塞来昔布可能通过抑制COX-2活性,抑制COX-2下游产物PGE2表达,从而抑制P-gp表达.选择性COX-2抑制剂可能有助于减轻肿瘤细胞对化疗药物的耐药性.