Cell biological effects of hyperthermia alone or combined with radiation or drugs: A short introduction to newcomers in the field

Hyperthermia results in protein unfolding that, if not properly chaperoned by Heat Shock Proteins (HSP), can lead to irreversible and toxic protein aggregates. Elevating HSP prior to heating makes cells thermotolerant. Hyperthermia also can enhance the sensitivity of cells to radiation and drugs. This sensitization to drugs or radiation is not directly related to altered HSP expression. However, altering HSP expression before heat and radiation or drug treatment will affect the extent of thermal sensitization because the HSP will attenuate the heat-induced protein damage that is responsible for radiation- or drug-sensitization. For thermal radiosensitization, nuclear protein damage is considered to be responsible for hyperthermic effects on DNA repair, in particular base excision repair. Hyperthermic drug sensitization can be seen for a number of anti-cancer drugs, especially of alkylating agents. Synergy between heat and drugs may arise from multiple events such as heat damage to ABC transporters (drug accumulation), intra-cellular drug detoxification pathways and repair of drug-induced DNA adducts. This may be why cells with acquired drug resistance (often multi-factorial) can be made responsive to drugs again by combining the drug treatment with heat.     

p27~(kip1)表达在食管癌放射抗拒中的意义

目的 探讨p27~(kip1)表达与食管癌放射敏感性变化的关系.方法 通过γ射线反复照射人食管鳞癌细胞EC9706(累计放射剂量6 000 cGy),逐步筛选得到具有放射抗拒性的细胞EC9706R.采用克隆形成实验检测两种细胞的放射敏感性,流式细胞仪分析细胞周期特征,免疫细胞化学检测p27~(kip1)的表达.结果 筛选得到的人食管鳞癌细胞EC9706R较亲本细胞显示出明显的放射抗性,EC9706R细胞SF_2=65.71%,D_0=2.20 Gy,D_q=1.61 Gy,N=2.07;EC9706细胞SF_2=46.72%,D_0=1.61 Gy,D_q=0.99 Gy,N=1.85,EC9706R细胞SF_2、D_0、D_q及N值均高于亲本细胞;细胞周期检测显示EC9706R细胞G_1期比例较亲本细胞明显下降,而S期比例明显增加;免疫细胞化学结果 显示具有放射抗性的EC9706R细胞p27~(kip1)表达明显低于亲本细胞.结论 p27~(kip1)表达下调导致细胞周期变化,可能是食管癌细胞产生放射抗拒的机制之一.     

紫杉醇对人腺样囊性癌细胞ACC-2体外辐射增敏作用机制初探

目的 通过体外实验初步阐述紫杉醇对人腺样囊性癌细胞ACC-2的辐射增敏作用机制。方法 用克隆形成法检测不同时间-浓度条件紫杉醇和／或放射作用后的人腺样囊性癌细胞ACC-2细胞存活分数，计算辐射增敏率(SER)。用流式细胞仪分析不同时间-浓度条件下紫杉醇对细胞周期和细胞凋亡的影响。结果 10100，1000nmol紫杉醇作用24h后SER分别为1．29，1．66和1．23。紫杉醇作用时问和浓度越高，ACC-2细胞G2／M期的比率也越高。100，1000nmol紫杉醇作用24h后，G2／M期比率明显升高。10nmol紫杉醇作用24h细胞凋亡百分率20．7％。结论 紫杉醇的辐射增敏作用可能是一个多因素事件，紫杉醇的G2／M期阻滞作用和诱导细胞凋亡作用在其中起重要作用。     

沙纳唑对体外培养的小鼠骨髓粒系造血祖细胞的放射增敏作用

目的:本实验旨在研究沙纳唑以及合并γ射线照射对体外培养小鼠骨髓粒系造血祖细胞(CFU-GM)集落形成的影响,分析沙纳唑是否对其有放射增敏作用.方法:从小鼠骨髓分离CFU-CM,在37℃、5%CO2条件下培养,当细胞进入呈指数生长期,分别在培养液中加入一系列浓度纱纳唑(0,1,5,12.5,25,50,100,200,400,800μg/ml)进行孵育,接受60Coγ射线照射(剂量为0,0.5,1,2,3,4Gy),观察细胞集落形成比.为评价沙纳唑对CFU-GM的放射增敏性,将CFU-GM接受沙纳唑和γ射线照射(2Gy)处理以及两者合并处来评价沙纳唑对CFU-GM的放射增敏作用.结果:(1)沙纳唑对体外CFU-GM集落形成明显细胞抑制作用,且随剂量增加作用增大.沙纳唑在低剂量(低于20μg/ml)对CFU-GM集落形成抑制作用呈线性关系(r=0.9987,p<0.01)分别为50和120μg/ml.(2)放射照射对CFU-GM也有明显抑制作用,饱和剂量和Do值分别是2.0和0.72Gy.(3)用沙纳唑联合放射照射处理CFU-GM后,对CFU-GM的抑制作用比单一处理都要强,但经统计学分析沙纳唑与放射照射之间无协同作用.结论:纱纳唑对体外培养小鼠骨髓系造血祖细胞有细胞毒性作用,但在低于IC20剂量下复合放射照射对CFU-GM集落形成无放射增敏作用.     

New perspectives of valproic acid in clinical practice

Introduction: Valproic acid (VPA) has been used in clinical practice as an anticonvulsant for more than four decades. Its pharmacokinetics and toxicity are thus well documented. VPA is also a potent class-selective histone deacetylase (HDAC) inhibitor at nontoxic therapeutic concentrations. New areas of application for VPA are currently opening up in clinical practice.

Areas covered: The authors discuss VPA and how it may serve as an effective drug for cancer therapy. This is due to its ability to induce differentiation of a number of cancer cells in vitro and also to decrease tumor growth and metastases in animal models. The authors highlight how the utilization of VPA as an HDAC inhibitor is not limited to a single-agent therapy. Early clinical studies have also revealed promising potency of VPA in combination treatment with classic anticancer drugs. The authors do this by summarizing the published results and providing insight into the potential future developments for this field.

Expert opinion: VPA was shown to restore or improve responsiveness of tumors to conventional therapeutic agents, to enhance the efficacy of adenoviral gene therapy, to sensitize TRAIL-resistant tumor cells to apoptosis, and to enhance radiosensitivity of tumor cells. Drawbacks in VPA medical applications include its teratogenicity and complexity of its effects.     

A DNA double-strand break repair-deficient mutant of CHO cells shows reduced radiosensitization after exposure to hyperthermic temperatures in the plateau phase of growth

Heat response and heat-induced radiosensitization were studied in plateau-phase cultures of CHO cells and their radiation-sensitive counterpart, the xrs-5 cells. The xrs-5 cells were more sensitive to heat alone than were CHO cells. A large enhancement in radiation-induced killing was observed in CHO cells pre-exposed to heat (43°C), expressed as a reduction in the values of D_o and D_q. Contrary to the results obtained with CHO cells, pre-exposure to heat of xrs-5 cells affected radiation sensitivity to a much lesser extent. D_I, the radiation dose required to reduce cell survival to 1%, decreased in CHO cells from 8?7 Gy to 2?5 Gy with increasing heat damage (cell survival after exposure to heat alone), whereas it decreased from 1?4 Gy to 0?9 Gy in xrs-5 cells. These results suggest that heat-induced radiosensitization is compromised in plateau-phase xrs-5 cells. Since xrs-5 cells are deficient in DNA dsb repair, it is hypothesized that DNA dsb repair proficiency is a prerequisite for heat radiosensitization and that heat-induced inhibition of DNA dsb repair is likely to contribute to the radiosensitization observed in repair-proficient cell lines after exposure to high temperatures.     

二甲双胍在恶性肿瘤放疗中的应用研究进展

二甲双胍(C4H11N5)是治疗2型糖尿病的主要药物.有研究显示,二甲双胍可以抑制肿瘤生长,改善恶性肿瘤患者的预后.近年越来越多的研究发现,二甲双胍可以改善肿瘤细胞的放疗敏感性.然而,二甲双胍增强恶性肿瘤放疗敏感性的具体机制尚未完全阐明.本研究将对有关二甲双胍联合放疗应用的最新发现进行综述,并着重介绍其在不同肿瘤中的疗...     

Transfection of human tumour cells with Mre11 siRNA and the increase in radiation sensitivity and the reduction in heat-induced radiosensitization

Double-strand DNA breaks (DSBs) are potentially lethal DNA lesions induced by ionizing radiation. In eukaryotes, DSBs can be repaired by homologous recombination (HR) or non-homologous end-joining (NHEJ). DNA repair protein Mre11 participates in both the NHEJ and HR DNA repair pathways. Hyperthermia has been used clinically as a radiosensitizer. However, the mechanisms by which radiosensitization is induced by hyperthermia, especially moderate hyperthermia (41°C) are not fully understood. Previous studies suggest that 41°C reduces the nuclear Mre11 protein level in a manner that correlates with heat-induced changes in radiation sensitivity. Therefore, siRNA technology was used in the present study to reduce Mre11 gene expression to determine if reduced Mre11 protein levels induced radiosensitization and if such radiosensitization is similar to that induced by moderate hyperthermia. The results show that (1) the cellular level of the Mre11 protein was reduced about 60 ± 18% by a 24-h treatment with siRNA. Results from the Mre11 protein turnover assay showed a half-life of 11.6 ± 0.5?h for the Mre11 protein, which is consistent with reduction in protein level in 24?h after Mre11 siRNA treatment assuming a delay of 4–8?h to reduce RNA levels. After 48?h in siRNA, cellular Mre11 protein levels increased to approximately pretreatment levels. NSY cells were sensitized to ionizing radiation after 24?h of treatment with Mre11 siRNA. Two hours at 41°C did not increase the radiation sensitivity of cells with a reduced Mre11 protein level following a 24-h siRNA treatment. These data support the conclusion that the DSB repair protein, Mre11, appears to be a target for radiosensitization by moderate hyperthermia.     

Anginex synergizes with radiation therapy to inhibit tumor growth by radiosensitizing endothelial cells

We have demonstrated that the designed peptide anginex displays potent antiangiogenic activity. The aim of our study was to investigate the effect of anginex on established tumor vasculature as an adjuvant to radiation therapy of solid tumors. In the MA148 human ovarian carcinoma athymic mouse model, anginex (10 mg/kg) in combination with a suboptimal dose of radiation (5 Gy once weekly for 4 weeks) caused tumors to regress to an impalpable state. In the more aggressive SCK murine mammary carcinoma model, combination of anginex and a single radiation dose of 25 Gy synergistically increased the delay in tumor growth compared to the tumor growth delay caused by either treatment alone. Immunohistochemical analysis also demonstrated significantly enhanced effects of combined treatment on tumor microvessel density and tumor or endothelial cell proliferation and viability. In assessing physiologic effects of anginex, we observed a reduction in tumor perfusion and tumor oxygenation in SCK tumors after 5-7 daily treatments with anginex with no reduction in blood pressure. To test anginex as a radiosensitizer, additional studies using SCK tumors were performed. Three daily i.p. injections of anginex were able to enhance the effect of 2 radiation doses of 10 Gy, resulting in 50% complete responses, whereas the known antiangiogenic agent angiostatin did not enhance the radiation response of SCK tumors. Mechanistically, it appears that anginex functions as an endothelial cell-specific radiosensitizer because anginex showed no effect on in vitro radiosensitivity of SCK or MA148 tumor cells, whereas anginex significantly enhanced the in vitro radiosensitivity of 2 endothelial cell types. This work supports the idea that the combination of the antiangiogenic agent anginex and radiation may lead to improved clinical outcome in treating cancer patients.