Antimutagenic effects of radioprotector WR-2721 against fission-spectrum neurons and 60Co gamma-rays in mice

Metabolomic studies in tissues of mice treated with amifostine and exposed to gamma-radiation

Although multiple radioprotectors are currently being investigated preclinically for efficacy and safety, few studies have investigated concomitant metabolic changes. This study examines the effects of amifostine on the metabolic profiles in tissues of mice exposed to cobalt-60 total-body gamma-radiation. Global metabolomic and lipidomic changes were analyzed using ultra-performance liquid chromatography (UPLC) quadrupole time-of-flight mass spectrometry (QTOF-MS) in bone marrow, jejunum, and lung samples of amifostine-treated and saline-treated control mice. Results demonstrate that radiation exposure leads to tissue specific metabolic responses that were corrected in part by treatment with amifostine in a drug-dose dependent manner. Bone marrow exhibited robust responses to radiation and was also highly responsive to protective effects of amifostine, while jejunum and lung showed only modest changes. Treatment with amifostine at 200 mg/kg prior to irradiation seemed to impart maximum survival benefit, while the lower dose of 50 mg/kg offered only limited survival benefit. These findings show that the administration of amifostine causes metabolic shifts that would provide an overall benefit to radiation injury and underscore the utility of metabolomics and lipidomics to determine the underlying physiological mechanisms involved in the radioprotective efficacy of amifostine. This approach may be helpful in identifying biomarkers for radioprotective efficacy of amifostine and other countermeasures under development.

Modifiers of radiation effects in the eye

World events, including the threat of radiological terrorism and the fear of nuclear accidents, have highlighted an urgent need to develop medical countermeasures to prevent or reduce radiation injury. Similarly, plans for manned spaceflight to a near-Earth asteroid or journey to Mars raise serious concerns about long-term effects of space radiation on human health and the availability of suitable therapeutic interventions. At the same time, the need to protect normal tissue from the deleterious effects of radiotherapy has driven considerable research into the design of effective radioprotectors. For more than 70 years, animal models of radiation cataract have been utilized to test the short and long-term efficacy of various radiation countermeasures. While some compounds, most notably the Walter Reed (WR) class of radioprotectors, have reported limited effectiveness when given before exposure to low-LET radiation, the human toxicity of these molecules at effective doses limits their usefulness. Furthermore, while there has been considerable testing of eye responses to X- and gamma irradiation, there is limited information about using such models to limit the injurious effects of heavy ions and neutrons on eye tissue. A new class of radioprotector molecules, including the sulfhydryl compound PrC-210, are reported to be effective at much lower doses and with far less side effects. Their ability to modify ocular radiation damage has not yet been examined. The ability to non-invasively measure sensitive, radiation-induced ocular changes over long periods of time makes eye models an attractive option to test the radioprotective and radiation mitigating abilities of new novel compounds.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part I. Radiation sub-syndromes, animal models and FDA-approved countermeasures

PURPOSE

The increasing global risk of nuclear and radiological accidents or attacks has driven renewed research interest in developing medical countermeasures to potentially injurious exposures to acute irradiation. Clinical symptoms and signs of a developing acute radiation injury, i.e. the acute radiation syndrome, are grouped into three sub-syndromes named after the dominant organ system affected, namely the hematopoietic, gastrointestinal, and neurovascular systems. The availability of safe and effective countermeasures against the above threats currently represents a significant unmet medical need. This is the first article within a three-part series covering the nature of the radiation sub-syndromes, various animal models for radiation countermeasure development, and the agents currently approved by the United States Food and Drug Administration for countering the medical consequences of several of these prominent radiation exposure-associated syndromes.

CONCLUSIONS

From the U.S. and global perspectives, biomedical research concerning medical countermeasure development is quite robust, largely due to increased government funding following the 9/11 incidence and subsequent rise of terrorist-associated threats. A wide spectrum of radiation countermeasures for specific types of radiation injuries is currently under investigation. However, only a few radiation countermeasures have been fully approved by regulatory agencies for human use during radiological/nuclear contingencies. Additional research effort, with additional funding, clearly will be needed in order to fill this significant, unmet medical health problem.

Radiation damage and radioprotectants: new concepts in the era of molecular medicine

Exposure to ionising radiation results in mutagenesis and cell death, and the clinical manifestations depend on the dose and the involved body area. Reducing carcinogenesis in patients treated with radiotherapy, exposed to diagnostic radiation or who are in certain professional groups is mandatory. The prevention or treatment of early and late radiotherapy effects would improve quality of life and increase cancer curability by intensifying therapies. Experimental and clinical data have given rise to new concepts and a large pool of chemical and molecular agents that could be effective in the protection and treatment of radiation damage. To date, amifostine is the only drug recommended as an effective radioprotectant. This review identifies five distinct types of radiation damage (I, cellular depletion; II, reactive gene activation; III, tissue disorganisation; IV, stochastic effects; V, bystander effects) and classifies the radioprotective agents into five relevant categories (A, protectants against all types of radiation effects; B, death pathway modulators; C, blockers of inflammation, chemotaxis and autocrine/paracrine pathways; D, antimutagenic keepers of genomic integrity; E, agents that block bystander effects). The necessity of establishing and funding central committees that guide systematic clinical research into evaluating the novel agents revealed in the era of molecular medicine is stressed.

WR1065 mitigates AZT-ddI-induced mutagenesis and inhibits viral replication

The success of nucleoside reverse transcriptase inhibitors (NRTIs) in treating HIV-1 infection and reducing mother-to-child transmission of the virus during pregnancy is accompanied by evidence that NRTIs cause long-term health risks for cancer and mitochondrial disease. Thus, agents that mitigate toxicities of the current combination drug therapies are needed. Previous work had shown that the NRTI-drug pair zidovudine (AZT)-didanosine (ddI) was highly cytotoxic and mutagenic; thus, we conducted preliminary studies to investigate the ability of the active moiety of amifostine, WR1065, to protect against the deleterious effects of this NRTI-drug pair. In TK6 cells exposed to 100 muM AZT-ddI (equimolar) for 3 days with or without 150 muM WR1065, WR1065 enhanced long-term cell survival and significantly reduced AZT-ddI-induced mutations. Follow-up studies were conducted to determine if coexposure to AZT and WR1065 abrogated the antiretroviral efficacy of AZT. In human T-cell blasts infected with HIV-1 in culture, inhibition of p24 protein production was observed in cells treated with 10 muM AZT in the absence or presence of 5-1,000 muM WR1065. Surprisingly, WR1065 alone exhibited dose-related inhibition of HIV-1 p24 protein production. WR1065 also had antiviral efficacy against three species of adenovirus and influenza A and B. Intracellular levels of unbound WR1065 were measured following in vitro/in vivo drug exposure. These pilot study results indicate that WR1065, at low intracellular levels, has cytoprotective and antimutagenic activities against the most mutagenic pair of NRTIs and has broad spectrum antiviral effects. These findings suggest that the activities have a possible common mode of action that merits further investigation.

Incidence of tissue toxicities in gamma ray and fission neutron-exposed mice treated with Amifostine

PURPOSE

To determine the effects of Amifostine or WR-151,327 on the incidence of lethal and non-lethal toxicities in a large cohort of mice exposed to gamma-ray or fission-spectrum neutron radiation.

METHODS

To analyze data from 4000 B6CF1 mice which received a single whole body irradiation (WBI) with 206 cGy or 417 cGy cobalt-60 gamma rays or 10 cGy or 40 cGy of fission-spectrum neutrons (average energy 0.85 MeV) produced by the Janus reactor at Argonne National Laboratory. In the neutron cohort, Amifostine, WR-151,327, saline or nothing was injected once, intraperitoneally, 30 minutes before irradiation. In the cobalt-60 cohort, WR-151327 was omitted from the same protocol. At the time of natural death, tissue toxicities found in these mice were recorded, and these records were analyzed. While all previous studies focused on the modulation of life shortening effects of WBI by Amifostine, in this study we calculated changes in the frequencies of 59 tissue toxicities and changes in the total number of toxicities per animal.

RESULTS

Amifostine protected against specific non-tumor pathological complications (67% of the non-tumor toxicities induced by gamma irradiation, 31% of the neutron induced specific toxicities), as well as specific tumors (56% of the tumor toxicities induced by gamma irradiation, 25% of the neutron induced tumors). Amifostine also reduced the total number of toxicities per animal for both genders in the gamma ray exposed mice and in males in the neutron exposed mice.

CONCLUSIONS

Amifostine was protective against many, but not all, tissue toxicities caused by WBI gamma and neutron irradiation.

Amifostine protection against mitomycin-induced chromosomal breakage in fanconi anaemia lymphocytes

Fanconi anaemia (FA) is a rare genetic chromosomal instability syndrome caused by impairment of DNA repair and reactive oxygen species (ROS) imbalance. This disease is also related to bone marrow failure and cancer. Treatment of these complications with radiation and alkylating agents may enhance chromosomal breakage. We have evaluated the effect of amifostine (AMF) on basal and mitomycin C (MMC)-induced chromosomal breakage in FA blood cells using the micronucleus assay. The basal micronuclei count was higher among FA patients than healthy subjects. Pre-treatment with AMF significantly inhibited micronucleation induced by MMC in healthy subjects (23.4 ± 4.0 – MMC vs 12.3 ± 2.9 – AMF → MMC) MN/1000CB, p < 0.01, one way ANOVA) as well as in FA patients (80.0 ± 5.8 – MMC vs 40.1 ± 5.8 – AMF → MMC) MN/1000CB, p < 0.01, ANOVA). Release of ROS by peripheral blood mononuclear cells treated with AMF → MMC and measured by chemoluminometry showed that AMF-protection was statistically higher among FA patients than in healthy individuals. Based on these results we suggest that AMF prevents chromosomal breakage induced by MMC, probably by its antioxidant effect.

Studies of thioguanine-resistant lymphocytes induced by in vivo irradiation of mice

The frequency of Hprt-deficient lymphocytes in mice after in vivo gamma irradiation, has been found to vary as a function of time elapsed after exposure and irradiation dose. The frequency of mutant lymphocytes in spleen was determined using an in vitro, clonogenic assay for thioguanine-resistant T-lymphocytes. Mice were exposed to single doses of 0-400 cGy from cesium-137 or to eight daily doses of 50 cGy. The time to maximum-induced mutant frequency was 3 weeks. The dose response was strikingly curvilinear at 3-5 weeks after irradiation, but less precisely defined for 10-53 weeks after exposure, being fit by either linear or quadratic dependence. Three weeks after eight daily 50 cGy exposures, mutant frequency was elevated above controls and mice exposed to 50 cGy (which were not distinct from the nonirradiated controls), but only 17% in that of mice given a single 400 cGy fraction. This fractionation effect and the curvilinearity of the early dose-response curve suggested that saturation of repair increased the yield of mutations at higher acute doses. The decline of spleen mutant frequency in mice observed between 5 and 10 weeks after irradiation may reflect selection against some mutants. The marked variation of mutant frequency, as a function of time after irradiation and of dose rate, emphasize the need to evaluate these variables carefully and consistently in future studies.

Effects of thiols on topoisomerase-II alpha activity and cell cycle progression

Thiol containing compounds exhibiting antioxidant properties are currently being evaluated for use in cytoprotection and chemoprevention. Many of these have also been found to be effective in inhibiting cell cycle progression and cellular proliferation. N-Acetyl-L-cysteine (L-NAC), along with its nonmetabolically active stereoisomer N-acetyl-D-cysteine (D-NAC), together with captopril and dithiothreitol (DTT) were investigated to assess their effects on cell cycle progression as determined by flow cytometry. Topoisomerase-IIa (topo-II alpha) activity, an enzyme involved in DNA synthesis, was also monitored as a function of drug dose using a kinetoplast DNA (kDNA) decatenation assay. Chinese hamster ovary (CHO) AA8 cells were exposed to each thiol at concentrations ranging from 4 microM to 4 mM for a period of 3 h. Following the removal of the thiols, cell cultures were followed for an additional 5 h to assess changes in cell cycle progression. L-NAC, which also serves as a precursor for glutathione (GSH) synthesis, effectively inhibited topo-IIa activity by at least 50% at all concentrations tested. Associated with this reduction in enzyme activity was a sixfold increase in the relative number of cells accumulating in G2phase. D-NAC, which is unable to participate in GSH synthesis, was only half as effective as L-NAC at each concentration tested in inhibiting topo-IIa activity as well as perturbing cell progression through G2. In comparison, captopril, an inhibitor of angiotensin converting enzyme (ACE), had little effect on the progression of cells into G2 phase. In contrast to the repressive effects of L-NAC and D-NAC, it enhanced topo-IIa activity over control values by approximately 20%. DTT, a well characterized thiol known to be capable of reducing disulphides in proteins, was observed to be relatively ineffective in either perturbing cell cycle progression or affecting topo-IIa activity. This suggests an involvement of a mechanism(s) in addition to thiol mediated affects on reduction/oxidation processes. The inhibitory effects of L-NAC and D-NAC on topo-IIa activity, in contrast to the other two thiols, may be due in part to the presence of amine groups which could allow for their participation in polyamine related processes. The difference in the magnitude of the effect exhibited by L-NAC, as compared to D-NAC, on the repression topo-IIa activity also suggests a role for GSH in this process. Inhibition of cellular progression and proliferation by thiols can therefore be mediated by diverse mechanisms which include both cycle-phase specific (i.e. L-NAC and D-NAC) and non cell cycle specific (i.e. captopril) processes.

Antimutagenicity of WR-1065 in L5178Y cells exposed to accelerated (56)Fe ions

The ability of the aminothiol WR-1065 [N-(2-mercaptoethyl)-1,3-diaminopropane] to protect L5178Y (LY) cells against the cytotoxic and mutagenic effects of exposure to accelerated (56)Fe ions (1.08 GeV/nucleon) was determined. It was found that while WR-1065 reduced the mutagenicity in both cell lines when it was present during the irradiation, the addition of WR-1065 after the exposure had no effect on the mutagenicity of the radiation in either cell line. No marked protection against the cytotoxic effects of exposure to (56)Fe ions was provided by WR-1065 when added either during or after irradiation in either cell line. We reported previously that WR-1065 protected the LY-S1 and LY-SR1 cell lines against both the cytotoxicity and mutagenicity of X radiation when present during exposure, but that its protection when administered after exposure was limited to the mutagenic effects in the radiation-hypersensitive cell line, LY-S1. The results indicate that the mechanisms involved differ in the protection against cytotoxic compared to mutagenic effects and in the protection against damage caused by accelerated (56)Fe ions compared to X radiation.

Sparing of radiation-induced damage to the physis: fractionation alone compared to amifostine pretreatment

PURPOSE

The purpose of this study was to determine the relative benefits of sparing longitudinal bone growth by fractionation alone compared to pretreatment with amifostine, a chemical that provides differential radioprotection of normal tissues.

METHODS AND MATERIALS

Twenty-four weanling 4-week-old male Sprague-Dawley rats were randomized into 2 overall treatment groups: fractionation alone (n = 12) and amifostine pretreatment (n = 12). The distal femur and proximal tibia in the right leg of each animal were exposed to a therapeutic X-irradiation dose (17.5 Gy total in 3 or 5 fractions) with the contralateral left leg as control. In 12 of the animals, amifostine (100 mg/kg) was administered intraperitoneally 20 min before radiation exposure. Six weeks later, growth was calculated based upon measurement of the bone lengths.

RESULTS

Fractionated radiation resulted in a mean percent overall limb growth loss of 21. 1 +/- 7.0%. The addition of amifostine brought the mean percent overall limb growth loss to 16.3% +/- 4.6%, which showed a strong trend toward significance compared to fractionation alone (p = 0. 061). The addition of radioprotection with amifostine to 5 fractions irradiation significantly reduced the femoral and overall percentage growth arrest and limb length discrepancy compared to 5 fractions alone.

CONCLUSIONS

These results support further investigation of amifostine and other radioprotectants in combination with fractionation for use in growing children requiring radiotherapy to the extremity for malignant tumors.

Radioprotective thiolamines WR-1065 and WR-33278 selectively denature nonhistone nuclear proteins

Differential scanning calorimetry was used to study the interactions of nuclei isolated from Chinese hamster V79 cells with the radioprotector WR-1065, other thiol compounds, and polyamines. Differential scanning calorimetry monitors denaturation of macromolecules and resolves the major nuclear components (e.g. constrained and relaxed DNA, nucleosome core, and nuclear matrix) of intact nuclei on the basis of thermal stability. WR-1065 treatment (0.5-10 mM) of isolated nuclei led to the irreversible denaturation of nuclear proteins, a fraction of which are nuclear matrix proteins. Denaturation of 50% of the total nonhistone nuclear protein content of isolated nuclei occurred after exposure to 4.7 mM WR-1065 for 20 min at 23 degrees C. In addition, a 22% increase in the insoluble protein content of nuclei isolated from V79 cells that had been treated with 4 mM WR-1065 for 30 min at 37 degrees C was observed, indicating that WR-1065-induced protein denaturation occurs not only in isolated nuclei but also in the nuclei of intact cells. From the extent of the increase in insoluble protein in the nucleus, protein denaturation by WR-1065 is expected to contribute to drug toxicity at concentrations greater than approximately 4 mM. WR-33278, the disulfide form of WR-1065, was approximately twice as effective as the free thiol at denaturing nuclear proteins. The proposed mechanism for nucleoprotein denaturation is through direct interactions with protein cysteine groups with the formation of destabilizing protein-WR-1065 disulfides. In comparison to its effect on nuclear proteins in isolated nuclei, WR-1065 had only a very small effect on non-nuclear proteins of whole cells, isolated nuclear matrix, or the thiol-rich Ca(2+)ATPase of sarcoplasmic reticulum, indicating that WR-1065 can effectively denature protein only inside an intact nucleus, probably due to the increased concentration of the positively charged drug in the vicinity of DNA.

A randomized study of very accelerated radiotherapy with and without amifostine in head and neck squamous cell carcinoma

PURPOSE

The aim of this study was to assess whether amifostine could minimize acute mucositis induced by a very accelerated irradiation regimen in patients with advanced head and neck squamous cell carcinoma (HNSCC).

METHODS AND MATERIALS

Between May 1996 and February 1998, 26 patients with an inoperable nonmetastatic Stage IV HNSCC were entered in this study. The treatment consisted of very accelerated radiotherapy given 64 Gy in 3.5 weeks. The patients were randomized to receive or not 150 mg/m(2), amifostine (Ethyol, U.S. Bioscience) 15-30 min prior to each radiation session.

RESULTS

Of the 13 patients who received amifostine, definitive interruption of amifostine occurred in 5 cases (38%), due to tolerance problems (vomiting, liver enzyme elevation, generalized erythema). The distribution of Grade 4 mucositis (WHO) was 1 case versus 8 cases, with and without amifostine, respectively. The mean duration of "at least Grade 3" mucositis (WHO) was 25.1 days versus 49.2 days with and without amifostine (p = 0.03). In the amifostine group, 11/13 of the patients required a feeding tube (nasogastric tube or medical gastrostomy), because of acute mucositis, whereas in the control group a feeding tube was necessary in all cases. The mean duration of the use of this feeding tube was 1 month versus 2.5 months with and without amifostine respectively (p < 0.01). Local-regional control was not different between both arms with a median follow-up of 15 months.

CONCLUSION

Despite the limited number of patients, this pilot randomized study suggests that amifostine was able to markedly reduce the severity and duration of mucositis induced by very accelerated radiotherapy. However, the tolerance of this twice daily amifostine schedule was relatively poor.

The sulfhydryl containing compounds WR-2721 and glutathione as radio- and chemoprotective agents. A review, indications for use and prospects

Radio- and chemotherapy for the treatment of malignancies are often associated with significant toxicity. One approach to reduce the toxicity is the concomitant treatment with chemoprotective agents. This article reviews two sulfhydryl compounds, namely the agent WR-2721 (amifostine), a compound recently registered for use in human in many countries, and the natural occurring compound glutathione (GSH). GSH is not registered as a chemoprotective agent. WR-2721 is an aminothiol prodrug and has to be converted to the active compound WR-1065 by membrane-bound alkaline phosphatase. WR-1065 and GSH both act as naturally occurring thiols. No protective effect on the tumour has been found when these compounds are administered intravenously. There is even in vitro evidence for an increased anti-tumour effect with mafosfamide after pretreatment with WR-2721, and in vivo after treatment with carboplatin and paclitaxel. Randomized clinical studies have shown that WR-2721 and GSH decrease cisplatin-induced nephrotoxicity and that WR-2721 reduces radiation radiotherapy-induced toxicity. Side-effects associated with WR-2721 are nausea, vomiting and hypotension, GSH has no side-effects. An exact role of WR-2721 and GSH as chemoprotectors is not yet completely clear. Future studies should examine the protective effect of these drugs on mucositis, cardiac toxicity, neuro- and ototoxicity, the development of secondary neoplasms and their effect on quality of life.

Sparing radiation-induced damage to the physis by radioprotectant drugs: laboratory analysis in a rat model

The radioprotectant compound amifostine (S-2[3-aminopropylamino]-ethylphosphorothioic acid), administered prior to radiotherapy, has been demonstrated to provide differential protection of normal cells from the damaging effects of ionizing radiation. The aim of this pilot was to determine if amifostine could preserve the integrity of, or minimize the damage to, the physis during exposure to radiation in an animal model. Thirty weanling Sprague-Dawley rats were randomized into five groups of six animals each. Groups 1 and 2 received a single exposure to radiation consisting of 12.5 and 17.5 Gy, respectively. Groups 3 and 4 received similar exposures of 12.5 and 17.5 Gy, respectively, but with prior administration of amifostine at 100 mg/kg. Group 5 (control) received neither radiation nor amifostine. At 6 weeks, femoral and tibial lengths were measured in treated and untreated hindlimbs and compared with the baseline lengths to calculate growth. Concordant with previous reports in the literature, the radiation doses of 12.5 and 17.5 Gy reduced net femoral growth in length by a mean of 23% (range = 12-33%, SD = 7.41) and 59% (range = 54-64%, SD = 4.45), respectively, in the irradiated limb. Amifostine reduced anticipated growth loss normally resulting from a single 12.5-Gy radiation dose by 48.9% in the femur, 13.1% in the tibia, and 27.6% overall in the total limb (p < or = 0.05). Similarly, anticipated growth loss from a single 17.5-Gy radiation dose was reduced by 30.8% in the femur, 20.3% in the tibia, and 25.7% overall in the total limb (p < or = 0.05). Amifostine administered prior to clinically relevant radiation exposures significantly reduced the amount of anticipated growth arrest in our animal model.

Synthesis and radioprotective effects of adamantyl substituted 1,4-dihydropyridine derivatives

A series of 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid diesters substituted at the N-1 and/or C-4 positions of the dihydropyridine ring was synthesized. The in vitro cytotoxicity and in vitro and in vivo radioprotective efficacy of these agents were evaluated in Chinese hamster (V-79) cells and CD2F1 male mice, respectively. Compounds with at least one adamantyl substituent afforded better radioprotection than those without this substituent. Substitution of an aromatic ring at the C-4 position of the dihydropyridine ring did not enhance the radioprotectant action of the compounds.

The inhibition of radiation-induced mutagenesis by the combined effects of selenium and the aminothiol WR-1065

In order to evaluate the anti-mutagenic effects of the potential chemoprotective compounds selenium and (S)-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-1065), CHO AA8 cells were exposed to both compounds either individually or in combination prior to irradiation. Mutation frequency following exposure to 8 Gy was evaluated by quantitation of the mutations detected at the hprt locus of these cells. Protection against radiation-induced mutation was observed for both 30 nM sodium selenite or 4 mM WR-1065. In addition, the protection against mutation induction provided by the combination of these agents appeared additive. In contrast, sodium selenite did not provide protection against radiation toxicity when provided either alone or in conjunction with WR-1065. In order to evaluate the possible mechanisms of the anti-mutagenic effects observed in these cells, glutathione peroxidase (GPx) activity was evaluated following exposure to the chemopreventative compounds. The addition of sodium selenite to the culture media resulted in a 5-fold increase in GPx activity, which was unaltered by the presence of the WR-1065. Northern analysis of RNA derived from these cells indicated that selenium supplementation resulted in a marginal increase in the mRNA for the cytosolic GPx (GSHPx-1) which was insufficient to account for the stimulation of GPx activity observed in cellular extracts. These results suggest that selenium and WR-1065 offer protection via independent mechanisms and that GPx stimulation remains a possible mechanism of the anti-mutagenic effect of selenium.

The preclinical basis for broad-spectrum selective cytoprotection of normal tissues from cytotoxic therapies by amifostine (Ethyol)

Administered prior to cytotoxic chemotherapy or radiation, the aminothiol amifostine provides broad-spectrum cytoprotection of various normal tissues without attenuating antitumour response. The basis for the selectivity of action resides in the anabolism of amifostine at the normal tissue site by membrane-bound alkaline phosphatase. Dephosphorylation to the free thiol, WR-1065, is followed by rapid uptake into normal tissues by a carrier mediated, facilitated diffusion process; in contrast, uptake into tumour tissue is slow to negligible. Preclinical studies have shown that pretreatment with amifostine provides protection of normal tissues from the cytotoxic effects of alkylating agents, organoplatinums, anthracyclines, taxanes and radiation. Normal tissues protected include bone marrow, kidney, neural tissues, the heart, intestinal crypt cells and pulmonary tissues. Additionally, the mutagenic and carcinogenic effects of these modalities are also attenuated. With respect to bone marrow, preclinical studies have shown significant protection of progenitor cells that give rise to the red and white cells and platelets. Comparative in vitro and in vivo studies using murine and human tumour xenografts show no decrease of antitumour effects of these same therapies despite the protection of normal organs. The unique preclinical profile of amifostine serves as a model for the clinical development programme for this important new broad-spectrum cytoprotective agent.

WR-1065, the active metabolite of amifostine (Ethyol), does not inhibit the cytotoxic effects of a broad range of standard anticancer drugs against human ovarian and breast cancer cells

Amifostine (WR-2721, Ethyol), a phosphorylated thiol, demonstrates the unique ability to protect normal but not tumour tissue from cytotoxic damage induced by radiation therapy and chemotherapy. This study tested the effect of amifostine's active metabolite, the free thiol, WR-1065, on the cytotoxicity of standard anticancer drugs against human A2780 ovarian and MCF7 breast cancer cell lines in vitro, using the well-characterised sulphorhodamine B assay. 50% inhibitory concentration (IC50) values were determined for each of 16 different anticancer drugs in the presence and absence of the highest nontoxic dose of WR-1065 from concentration-response curves constructed in triplicate and based on 18 replicate cell culture plates for each tested drug concentration. Pretreatment with WR-1065 had no statistically significant effect on the IC50 value of any of the 16 drugs tested against either the A2780 or MCF7 human tumour cells. These data expand upon previous reports showing that amifostine does not protect tumours from the cytotoxic effects of anticancer agents. The ability of amifostine to protect against dose-limiting toxicity to a variety of normal tissues without protection of tumour should enhance the efficacy ratio of a wide range of standard anticancer drugs.

Amifostine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential as a radioprotector and cytotoxic chemoprotector

Amifostine (WR-2721) was originally developed as a radioprotective agent. In animals, it protects normal tissues from the damaging effects of irradiation and, as shown in more recent studies, of several cytotoxic agents. Protection of tumours is generally reduced compared with that of normal tissues in animals, suggesting that amifostine may increase the therapeutic window of cytotoxic therapies. Clinical data concerning amifostine suggest that cytotoxic chemotherapy-induced haematological toxicity and cisplatin-induced neurotoxicity, nephrotoxicity and ototoxicity are decreased upon administration of amifostine prior to cytotoxic drugs. Similarly, amifostine reduces damage to normal tissues caused by radiotherapy. Available data show that this protection is achieved without adversely affecting tumour response or patient survival. In 1 large trial, the reduction in cyclophosphamide- and cisplatin-related toxicities manifested as a decrease in the incidence and severity of neutropenia-related fever and sepsis and in the number of patients with ovarian cancer who discontinue therapy before completion of treatment, thus improving the tolerability of this antineoplastic regimen. In addition, the incidences of cisplatin-induced nephro- and neurotoxicity were reduced. Increased doses of cytotoxic therapy have also been administered when amifostine was given prior to therapy, which may increase tumour response. The predominant adverse effect associated with amifostine are hypotension, nausea and vomiting, somnolence and sneezing. Thus, amifostine is likely to be a useful adjuvant to the treatment of patients with malignancy, particularly those receiving cyclophosphamide plus cisplatin. discontinued therapy before completion of treatment, thus improving the tolerability of this antineoplastic regimen. In addition, the incidences of cisplatin-induced.

Dietary supplements of antioxidants reduce hprt mutant frequency in splenocytes of aging mice

The level of spontaneous and gamma-radiation-induced mutations in the hypoxanthine-guanine phosphoribosyl-transferase (hprt) locus as well as the decrease in frequency of these mutations in mice of various age pretreated with dietary supplements of an antioxidant mixture (vitamins C, E, beta-carotene, rutin, selenium, zinc) were studied in splenocytes of young (8-14-week-old) and aged (102-110-week-old) male C57BL/6 mice. The frequency of spontaneous mutations in splenocytes of 102-110-week-old mice was higher by 68-88% than that in mice aged 8-14 weeks. On gamma-irradiation (0.5-5.0 Gy) of mice, the frequency of radiation-induced mutations (Vf assay) in aged mice was 2.3 to 3.6 times (depending on dose) higher than in young ones. Daily supplements of an antioxidant mixture to the diet of mice prior to irradiation showed an antimutagenic effect. The values of mutant frequency reduction factor (MFRF) for 14-110-week-old mice fed with dietary antioxidants during 6 weeks prior to gamma-irradiation with doses of 2.0 and 5.0 Gy were 5.4 and 3.7, respectively. The frequency of radiation-induced mutations prevented or not prevented by antioxidants was much higher in aged mice than in young ones.

Induction of micronucleated erythrocytes by MEA, AET, WR-2721 and X-rays

The induction of micronucleated polychromatic erythrocytes (MNPCEs) was assessed in the bone marrow of adult male Swiss mice treated with MEA (cysteamine HCl), AET (2-aminoethylisothiouronium Br.HBr), or WR-2721 (S-2-(3-aminopropylamino)ethyl phosphorothioic acid), at a dose of 200 mg/kg body weight, and/or exposed to 6 Gy X-rays. MEA, AET, or WR-2721 was given alone or 15 min prior to X-ray exposure, and the frequency of MNPCEs was determined 24 h after the aminothiol treatment and X-irradiation of mice. A genotoxic effect was shown for MEA, AET, WR-2721, and X-rays, as well as a protective effect of the aminothiols against X-ray-induced genotoxicity in the mouse erythropoietic system. The aminothiol drugs given alone, without subsequent X-irradiation, elevated the frequency of MNPCEs, and WR-2721 appeared to be less toxic than AET and MEA. After exposure of mice to X-rays, the number of MNPCEs was distinctly increased. MEA, AET, or WR-2721 administration prior to X-irradiation resulted in a reduction of the X-ray-induced elevation of the frequency of micronuclei, but a stronger radioprotective effect was obtained following WR-2721 and AET treatment than after MEA application. So, the genotoxic and radioprotective effect of the aminothiols was dependent on the compound applied.

Protection of normal tissues from the cytotoxic effects of chemotherapy and radiation by amifostine (WR-2721): preclinical aspects

Amifostine is a radioprotective agent that prevents radiation- and chemotherapy-induced cellular injury through free-radical scavenging, hydrogen donation, and inhibition of DNA damage. Amifostine is metabolised and accumulated to a much greater extent in normal cells than in tumour cells. As a result, it exerts a protective effect from toxicity on normal tissues induced by chemo- or radiotherapy without reducing the antitumour effects of cancer therapy. Extensive preclinical studies have shown that amifostine protects against radiation damage and against the myelotoxic, nephrotoxic and neurotoxic effects of chemotherapeutic agents such as alkylating agents and platinum compounds. In some cases, the antitumour effects of these agents have been potentiated by amifostine. Amifostine has also been shown to protect against radiation- and chemotherapy-induced mutagenesis and, as a result, carcinogenesis. Use of amifostine allows for safer and more effective administration of radio- and anticancer therapy.

Dose and dose-rate dependence of the frequency of HPRT deficient T lymphocytes in the spleen of the 137Cs gamma-irradiated mouse

The frequency of hypoxanthine phosphoribosyl transferase (HPRT) deficient splenic T lymphocytes was measured in the 137Cs gamma-irradiated mouse by the T cell cloning method. Doses from 0.3 to 6 Gy were applied at the dose-rates 0.5 Gy/min, 1 Gy/day and 1 Gy/week. Mutants were determined 8-10 and 30-40 weeks after the end of exposure. Radiation-induced mutant frequency (MFi) was calculated by subtracting the age corrected spontaneous mutant frequency (MFsp) from total mutant frequency (MF) found in irradiated animals. Data were fitted to linear and linear-quadratic dose-response models. MFi depended markedly on dose, dose-rate and time after exposure. When mutants were determined 8-10 weeks after acute irradiation (0.5 Gy/min) the dose-effect curve fitted the linear-quadratic equation MFi = 6.9 x 10(-6) Gy + 1.2 x 10(-6) Gy2, whereas in low dose-rate experiments (1 Gy/day, 1 Gy/week) the dose-effect curves were linear. The slope of the linear regression was about 3 x 10(-6). When low dose-rate-irradiated animals were killed 30-40 weeks after irradiation, MFi was about one-third of that observed after 8 weeks. The dose dose-rate effectiveness factor (DDREF) for radiation mutagenicity was calculated in animals that had been exposed 8-10 weeks previously. For doses < 2 Gy the reduction in effectiveness was about 1.5 when the irradiation dose-rate was < or = 1 Gy/day. For higher doses DDREF was 3-5.

Altered protein expression detected in the F1 offspring of male mice exposed to fission neutrons

Liver protein expression in F1 offspring arising from spermatogonia exposed to 60 cGy of fission spectrum neutrons from the JANUS reactor was compared to that in offspring from unexposed spermatogonia by using two-dimensional electrophoresis (2DE). Approximately 100 protein spots in 2DE patterns from 167 control offspring and 530 offspring from irradiated sires were monitored for quantitative decreases of 50%, indicative of mutation events causing the loss of one normal copy of a structural gene. Reproducible abnormalities were found only in 3 patterns, all from the offspring of neutron-irradiated sires. Two of the three patterns were from littermates (brother and sister) and both showed an approximately 70% decrease in the amount of liver protein MSN188. The third pattern was from a male mouse sired by a different male and showed an approximately 50% decrease in the abundance of protein MSN94. The decreased abundance of MSN188 and MSN94 was assumed to be due to mutation events referred to as NEUT1 and NEUT2, respectively. Sibling crosses between the 2 mice showing the NEUT1 trait produced offspring with control, decreased and undetectable levels of MSN188 in a ratio of 0.25:0.5:0.25. Test crosses between the F1 offspring expressing the NEUT2 trait back to C57BL/6JANL mice produced offspring expressing normal or decreased amounts of MSN94 in a ratio of 0.5:0.5. Inbreeding of individuals expressing decreased amounts of MSN94 produced mice expressing control, decreased amounts, or no detectable amount of that protein in a ratio of 0.25:0.5:0.25. These results indicate that the decreased abundance of MSN188 or MSN94 originally detected in the F1 offspring is due to a genetically transmissible event. Unlike the heritable protein changes observed previously in the F1 offspring of sires exposed to N-ethyl-N-nitrosourea in which a protein variant was produced, both the NEUT1 and NEUT2 mutation events appear to prevent the production of any protein product. These 2 mutations may thus represent mutation lesions other than point mutations (e.g., deletions or translocations) detectable as quantitative changes in protein expression in the F1 generation.