放射增敏剂研究进展

放射增敏剂在肿瘤放疗中具有很大的实用价值，因而对它的研究日益受到重视，已先后合成并筛选出ＭＩＳＯ等乏氧细胞放射增敏剂，对这些化合物的药效、毒性及临床都做了大量工作，同时还对具有放射增敏活性的生物还原剂及合并用药等作了研究。     

N-（5-硝基吲唑-3-甲酰）酪氨酸钠的制备、乏氧增敏与体内分布研究

目的：在硝基吲唑母核上引入酪氨酸并成盐,制备N-（5-硝基吲唑-3-甲酰）酪氨酸钠并考察其乏氧增敏活性和体内分布情况。方法用缩合剂法合成N-（5-硝基吲唑-3-甲酰）酪氨酸钠,通过小鼠移植瘤模型评价其乏氧增敏活性,通过放射性碘标记法考察其在荷瘤小鼠体内的分布情况。结果合成了目标化合物并对结构进行了确证。移植瘤模型增敏实验表明其对H22移植瘤具有一定的乏氧增敏活性,平均放射增敏比为1．5。体内分布实验中其在肿瘤部位与脑和肌肉部位的分布比值均大于5,表明其具有较好的体内分布特性。结论 N-（5-硝基吲唑-3-甲酰）酪氨酸钠具有良好的乏氧增敏活性和体内分布特性,具有进一步开发价值。     

放射增敏剂研究概况

肿瘤乏氧是导致放疗失败的一个重要原因,放射增敏剂由于能提高乏氧细胞对射线的敏感性而受到广泛重视。目前,放射增敏剂的研究包括传统硝基咪唑类化合物、乏氧细胞毒性物、一氧化氮供体、血红蛋白别构效应物和金属卟啉等,它们通过不同作用机制改善组织氧合状态或选择性杀死乏氧细胞,从而提高细胞对射线敏感性。由于肿瘤微环境极其复杂,尽管已合成了大量不同类型的化合物,但尚未发现真正能适用于临床的药物。     

放射增敏剂研究概况

肿瘤乏氧是导致放疗失败的一个重要原因,放射增敏剂由于能提高乏氧细胞对射线的敏感性而受到广泛重视,目前,放射增敏剂的研究包括传统硝基咪唑类化合物,乏氧细胞毒性物,一氧化氮供体,血红蛋白别构效应物和金属卟啉等,它们通过不同作用机制改善组织氧合状态或选择性杀死乏氧细胞,从而提高细胞对射线敏感性,由于肿瘤微环境极其复杂,尽管已合成了大量不同类型的化合物,但尚未发现真正能适用于临床的药物。     

放射增敏剂与肿瘤治疗

放射增敏剂已经使用很多年了,目前主要用于增敏乏氧细胞。肿瘤组织中有乏氧细胞存在,过去曾用高压氧使乏氧细胞增敏,但不同的试验结果不尽一致。因为动物全身长时间高压氧处理产生的生理反应使血管闭合,从而影响氧的增敏效果。后来有人试图用负π介子和中子来解决乏氧细胞的问题,虽有一定作用但未能完全使乏氧细胞增敏,而且设备非常昂贵。因此,Gray实验室开始着手化学放射增敏剂的研究。Adams研究了许多带有机环结构的化合物,目前已有甲硝哒唑(metronidazole)、misonidazole和9963等放射增敏剂。一种化合物是否有放射增敏作用,主要看其治疗增益,即对肿瘤组织的增敏是否比正常组织增敏大,否则就起不到放射增敏的作用。肿瘤组织中存有许多乏氧细胞,而正常组织中都没有。因此,增敏剂能提高肿瘤组织的放射敏感性。     

5-硝基吲唑衍生物对HeLa细胞的放射增敏作用

目的 研究5-硝基吲唑-3-甲酰亚氨基二乙酸的细胞毒性,以及对HeLa细胞的放射增敏作用。方法 取指数生长期的HeLa细胞,接种于96孔板,加入不同浓度的药物作用后,用噻唑蓝比色法(MTT法)测定存活分数,并比较不同药物剂量加照射的实验组与单纯照射组的细胞存活分数。结果 5-硝基吲唑-3-甲酰亚氨基二乙酸对HeLa细胞的毒性较小。该药物对HeLa细胞有放射增敏作用,且乏氧处理的效果优于有氧处理:0、6、12、24、48、96μg/ml药物乏氧处理,存活率分别为0.91、0.87、0.84、0.81、0.76、0.60;48、96μg/ml药物有氧处理,存活率分别为0.85和0.73。结论 5-硝基吲唑-3-甲酰亚氨基二乙酸对HeLa细胞的毒性较小,且具有一定的乏氧放射增敏剂特征。     

放射增敏剂AK和MISO的临床药物动力学和疗效比较研究

放射增敏剂ＡＫ和ＭＩＳＯ的临床药物动力学和疗效比较研究骆传环，鲍云华，王作华，王友茹，俞受程肿瘤组织中的乏氧细胞对射线敏感性低，限制了放疗效果。因此，人们研制了放射增敏剂，以提高肿瘤的放疗效果，并打破肿瘤治疗中的不良循环。目前研究最多的是硝基咪唑类化...     

辐射增敏剂和生物还原剂的作用机理与近期发展概况

辐射增敏剂的基本原理是它能够增加细胞(特别是乏氧细胞)对射线的生物学效应,其中研究得较多的是具有亲电子性的2-硝基咪唑类化合物,如SR-2508,Ro03-8799和RSU-1069等,这些辐射增敏剂都具有较强的增敏作用及各自的特点.在RSU-1069基础上发展起来的双功能性化合物,即具有辐射增敏与生物还原毒性的化合物,能在乏氧条件下通过酶的作用(如细胞色素P450酶系)转变为一系列对乏氧细胞有选择性毒性的代谢物.     

烟酰胺在体内的放射增敏作用:增加肿瘤损伤比正常组织大

一般认为,实体瘤中的乏氧细胞是肿瘤放射治疗存在的主要问题。解决这一问题的最有希望的疗法之一是应用亲电子制剂,增强放射对乏氧细胞的致死效应。最有效的放射增敏剂是硝基咪唑类化合物Misonidazole(MISO)和第二代类似物SR2508与RO03-8799。这三个化合物现已进行广泛的临床试用,但由于神经毒副作用限制了疗效。本文作者试图克服神经毒副作用,研究了结构与硝基咪唑不同、特别是不含硝基的化合物,报告烟酰胺在小鼠体内作用特性的实验结果。资料指出了烟酰胺对小鼠的一般毒性、药代动力学和三种不同肿瘤与二种正常组织的放射增敏作用,并讨论了     

放射增敏剂增强细胞毒药物的作用

乏氧细胞放射增敏剂Misonidazole(MISO)现正被临床广泛试用。有两个因素与这种增敏有关,一是它的电子亲和性(electron affinity),一是它的亲脂性(lipophilicity)。因此最近证明放射增敏剂不但具有放射增敏作用,而且远具有“化学增敏作用”(“Chemosensitizing”effect),即它能增加化学治疗药物的细胞毒性作用。例如,乏氧的V79细胞在生理温度下对于博莱霉素(Bleomycin)是具有抵抗性的,但是与MISO合并使用,便变得敏感起来。     

Hypoxia-selective Radiosensitization of Mammalian Cells by Nitracrine,an Electron-affinic DNA Intercalator

Summary

The radiosensitizing ability of the 1-nitroacridine nitracrine (NC) is of interest since it is an example of a DNA intercalating agent with an electron-affinic nitro group. NC radiosensitization was evaluated in Chinese hamster ovary cell (AA8) cultures at 4°C in order to suppress the rapid metabolism and potent cytotoxicity of the drug. Under hypoxic conditions, submicromolar concentrations of NC resulted in sensitization (SER = 1·6 at 1 µmol dm^?3). Sensitization was also seen under aerobic conditions but a concentration more than 10-fold higher was required. In aerobic cultures NC radiosensitization was independent of whether cells were exposed before and during, or after, irradiation. Postirradiation sensitization was not observed under hypoxic conditions. The time dependence of NC uptake and the development of radiosensitization were similar (maximal at 30 min at 4°C under hypoxia) suggesting that sensitization, unlike cytotoxicity, is due to unmetabolized drug. NC is about 1700 times more potent as a radiosensitizer than misonidazole. This high potency is adequately accounted for by the electron affinity of NC (E(1) value at pH 7 of ?275mV versus NHE) and by its accumulation in cells to give intracellular concentrations approximately 30 times greater than in the medium. However, concentrations of free NC appear to be low in AA8 cells, presumably because of DNA binding. If radiosensitization by NC is due to bound rather than free drug, it suggests that intercalated NC can interact very efficiently with DNA target radicals. This is despite a binding ratio in the cell estimated as less than 1 NC molecule/400 base pairs under conditions providing efficient sensitization. This work suggests a new approach in the search for more effective clinical radiosensitizers, and poses questions on the means by which intercalated drugs can interact with DNA damage.     

Characterization of metronidazole-phosphate, a water-soluble metronidazole derivative, as a radiosensitizer of hypoxic cells.

A water-soluble derivative of metronidazole (Flagyl) was synthetized with the purpose to overcome some practical difficulties in the clinical administration of the drug. The derivative, a phosphate ester of metronidazole, was characterized for different physical-chemical properties. It had a low toxicity both in vitro and in vivo. In vitro, it retained a radiosensitizing effect specific for hypoxic cells which was, however, decreased in comparison with the parent compound. The decreased sensitization was related to a decreased one-electron reduction potential and octanol/water partition coefficient. In mice, metronidazole-phosphate had a prolonged blood life in comparison to metronidazole.     

Radiosensitization by quaternary salts of 5-nitroimidazole derivatives

The radiosensitizing effects of five newly synthesized quaternary salts of 5-nitroimidazole derivatives on the survival of TC-SV40 mammalian cells have been measured. A toxicity study was carried out in order to determine the concentrations to be used in the radiosensitizing experiments. The oxygen enhancement ratio (OER) for TC-SV40 cells was 2.74. None of the five 5-nitroimidazole derivatives showed radiosensitizing activity in aerobic conditions, while in hypoxia their dose-modifying factors (DMF) at the concentration of 0.2 mmol dm-3 range from 1.52 to 1.03 in this order: unsubstituted pyridinium greater than carbamoyl pyridinium greater than trimethyl pyridinium greater than t-butyl pyridinium greater than imidazolium. This latter product at the concentration of 2 mmol dm-3 has a DMF of 1.64. As comparison, metronidazole was also tested on this cell line and its DMF at 0.2 mmol dm-3 was 1.35. The response-concentration dependences for the unsubstituted pyridinium 5-nitroimidazole derivative and for metronidazole (comparing charged and uncharged structures) showed the flattening response-concentration curve of quaternary compounds. The electron affinity was evaluated through the CNDO/S theoretical method, and an exponential relationship between these values and the DMFs of the pyridinium derivatives was demonstrated.     

In vitro hypoxic cytotoxicity and hypoxic radiosensitization

Background and purpose

Tumor hypoxia is a major problem in radiation therapy of solid tumors because of the radiosensitizing effect of oxygen. Nitroimidazole-containing compounds are oxygen mimetics accumulating in hypoxic tumor areas. However, the broad use of 2-nitroimidazoles as a hypoxic radiosensitizer is limited by their partially low efficacy and/or high neurotoxicity.

Materials and methods

Here, we characterized the in vitro hypoxic cytotoxicity and hypoxic radiosensitizing efficacy of N,N,N-tris [2-(2-nitro-1H-imidazol-1-yl)ethyl]amine (PRC) in a hypoxia-sensitive lymphoma and a hypoxia-resistant glioblastoma cell line by colony formation assay and flow cytometry.

Results

PRC exerted high hypoxic cytotoxic and radiosensitizing action on both cell lines at almost absent toxicity under normoxic conditions. In particular, under hypoxia, but not normoxia, PRC targeted the mitochondria resulting in oxidative stress, G₂/M cell cycle arrest, and triggering of the intrinsic apoptosis pathway.

Conclusion

Our in vitro findings suggest that PRC might be a promising new 2-nitroimidazole for improving radiation therapy of hypoxic tumors in vivo.     

Radiosensitization of E. coli B/r by arylhydrazonopropanedinitriles

Several arylhydrazonopropanedinitriles and an arylhydrazonopropane-diethyl ester (derivatives of well-known uncouplers of oxidative phosphorylation) have been studied with respect to their ability to radiosensitize E. coli B/r under oxic and hypoxic conditions. Of the compounds studied, 2-carboxyphenylhydrazono-propanedinitrile and 2-carboxyphenylhydrazonopropanediethylester were found to be the most efficient radiosensitizers under hypoxia, whilst the former compound was also found to provide radiosensitization under oxic conditions. Increased radiosensitization by 4-carboxyphenylhydrazonopropanedinitrile was observed on decreasing the pH of the irradiation incubation medium. The results are discussed with respect to the physicochemical properties of these compounds and their reactivity with thiols, for which data are presented.     

Studies in radiosensitizing effects of misonidazole and SR-2508 on C3H/He mouse mammary tumors

The radiosensitizing efficacy of SR-2508, a new 2-nitroimidazole, which is less neurotoxic than misonidazole (MISO) was studied using transplantable mammary carcinoma of C3H/He mice. Tumor responses to treatments were evaluated by growth-delay time assay. In single irradiations, the enhancement ratios of 0.5 mmole/kg of MISO and 1.5 mmole/kg of SR-2508, which were equitoxic to C3H/He mice, were 1.42 and 1.84 respectively. In fractionated irradiations with three fractions over two days or five fractions over four days, the enhancement ratios of 1.5 mmole/kg of SR-2508 were 1.40 and 1.34 respectively. On the other hand the enhancement ratios of MISO at the above mentioned dose in respective fractionated irradiations were 1.15 or 1.11. SR-2508 is considered promising as a hypoxic cell radiosensitizer for clinical use.     

Radiosensitization by Nickel Lapachol

The properties of interest in the radiosensitization of a metal complex, nickel lapachol, are compared with those of the 2-nitroimidazole, misonidazole. These very different compounds were found to be surprisingly similar in terms of their reduction potential (? 370 mV), enhancement ratios for killing of hypoxic Chinese hamster ovary cells by X-irradiation, and enhancement of DNA breaks in hypoxia. For nitroimidazoles, the sensitization depends on ‘electron affinity’, reduction of the nitro group; for nickel lapachol it is the metal which is necessary for reduction, yet the sensitization efficiencies are remarkably close. However, the metal complex has additional activities (some sensitization in aerobic cells; increased sensitization with preincubation) which are as yet unexplained but are assumed to be related to the nature of the naphthoquinone ligand, rather than to the reduction of the metal.     

Radiosensitization by metal complexes of 4(5)-nitroimidazole

Four closely-related cis-platinum (Pt) complexes of 4(5)-nitroimidazole have been examined with respect to properties of radiobiological interest, to test the hypothesis that targeting a nitroimidazole (NO2Im) to DNA could enhance its radiosensitizing ability: I [PtCl2(5-NO2Im)2]; II [PtCl2(4-NO2Im)2]; III [PtCl2(NH3)(5-NO2Im)]; IV [PtCl2(NH3)(4-NO2Im)]. The reduction potential was affected to the same extent on metal binding in all of the complexes (delta E1/2 = +200 mV, cf. ligand measured polographically). Higher sensitization by 5-NO2 complexes I, III (cf. II, IV) was found. Only the mono complexes III and IV bind to DNA (in an assay using inhibition of restriction endonuclease activity); these radiosensitize as well as, or better than, free ligand in hypoxic CHO cells, and better than the bis complexes (I and II). The toxicity of the mono complexes is higher than ligand, and parallels the binding (III, IV, mono bis analogues). The complexes are compared with 4-nitroimidazole complexes of ruthenium, with respect to toxicity, binding and radiosensitization.     

Development and testing of new hypoxic cell radiosensitizers.

Several new electron-affinic compounds have been shown to possess radiosensitizing ability in hypoxic mammalian cells. The correlation between chemical structure and biological activity can aid in the design and synthesis of new agents with potentially greater hypoxic cell radiosensitizing ability.     

In vitro and in vivo radiosensitizing effects of 2-nitroimidazole derivatives with sugar component

A new type of hypoxic cell sensitizer, 2-nitroimidazole substituted with an acyclic sugar analogue at the N-1 position of the imidazole ring (RK compounds) has been developed and tested on HeLa S3 and Chinese hamster V79 cells. As might be expected from their electron affinities, which are stronger than that of misonidazole, the abilities of RK compounds to sensitize hypoxic cells were correspondingly increased. One millimole of RK28 [1-(4'-hydroxy-2'-butenoxy)methyl-2-nitroimidazole] gave an enhancement ratio of 1.56 or 1.84 in comparison with 1.40 or 1.71 for the same concentration of misonidazole to HeLa S3 or V79 cells, respectively. RK28 showed slight cytotoxicity to aerobic HeLa S3 cells at a concentration of 5 mM after a three-hour exposure, whereas under hypoxic conditions, the agent was markedly cytotoxic. In vivo radiosensitization studies in ICR mice with Ehrlich ascites tumor indicated that RK28 produced an increase in DMF to hypoxic tumor cells with increased dose of the compound. Their DMF values were 1.63, 1.97 and 2.34 at 0.075, 0.15 and 0.3 mg/gbw of RK28, respectively. A dose of 0.3 mg/gbw of RK28 produced a DMF around 1.5 to two times greater than that resulting from the same dose of misonidazole. Pharmacokinetic studies of RK28 in ICR mice with Sarcoma-180 revealed a faster clearance from the serum and a slower decrease in the tumor than with misonidazole.