2-[(Aminopropyl)amino]ethanethiol (WR1065) is anti-neoplastic and anti-mutagenic when given during 60Co gamma-ray irradiation

Cancer Incidence in C3H Mice Protected from Lethal Total-Body Radiation after Amifostine

Amifostine is a potent antioxidant that protects against ionizing radiation effects. In this study, we evaluated the effect of Amifostine administered before total-body irradiation (TBI), at a drug dose that protects against TBI lethality, for potential protection against radiation-induced late effects such as a shortened lifespan and cancer. Three groups of mice were studied: 0 Gy control; 10.8 Gy TBI with Amifostine pretreatment; and 5.4 Gy TBI alone. Animals were monitored for their entire lifespan. The median survival times for mice receiving 0, 5.4 or 10.8 Gy TBI were 706, 460 and 491 days, respectively. Median survival of both irradiated groups was significantly shorter compared to nonirradiated mice ( P < 0.0001). Cancer incidence (hematopoietic and solid tumors) was similar between the irradiated groups and was significantly greater than for the 0 Gy controls. The ratio of hematopoietic-to-solid tumors differed among the groups, with the 5.4 Gy group having a higher incidence of hematopoietic neoplasms compared to the 10.8 Gy/Amifostine group (1.8-fold). Solid tumor incidence was greater in the 10.8 Gy/Amifostine group (1.6-fold). There are few mouse lifespan studies for agents that protect against radiation-induced lethality. Mice treated with 10.8 Gy/Amifostine yielded a lower incidence of hematopoietic neoplasms and higher incidence of solid neoplasms. In conclusion, mice protected from lethal TBI have a shortened lifespan, due in large part to cancer induction after exposure compared to nonexposed controls. Amifostine treatment did protect against radiation-induced hematopoietic tumors, while protection against solid neoplasms was significant but incomplete.

Antioxidant dietary supplementation in mice exposed to proton radiation attenuates expression of programmed cell death-associated genes

Dietary antioxidants have radioprotective effects after ionizing radiation exposure that limit hematopoietic cell depletion. We sought to determine the mechanism of proton-induced hematopoietic cell death in animals receiving a moderate dose of whole-body proton radiation. In addition, animals were maintained on diets supplemented with or without dietary antioxidants. In the presence of the dietary antioxidants, total bone marrow mRNA and protein expression of apoptosis-related genes were decreased compared to the expression profiles in the irradiated mice not receiving the antioxidant formulation. These data confirm high-energy proton-induced gene expression of classical apoptosis markers including BAX, caspase-3 and PARP-1. Antioxidant supplementation resulted in decreased expression of these genes in addition to increased protein expression of the anti-apoptosis markers Bcl2 and Bcl-xL. In conclusion, oral supplementation with antioxidants appears to be an effective approach for radioprotection against hematopoietic cell death.

SOD2-mediated effects induced by WR1065 and low-dose ionizing radiation on micronucleus formation in RKO human colon carcinoma cells

RKO36 cells exposed to either WR1065 or 10 cGy X rays show elevated SOD2 gene expression and SOD2 enzymatic activity. Cells challenged at this time with 2 Gy exhibit enhanced radiation resistance. This phenomenon has been identified as a delayed radioprotective effect or an adaptive response when induced by thiols or low-dose radiation, respectively. In this study we investigated the relative effectiveness of both WR1065 and low-dose radiation in reducing the incidence of radiation-induced micronucleus formation in binucleated RKO36 human colon carcinoma cells. The role of SOD2 in this process was assessed by measuring changes in enzymatic activity as a function of the inducing agent used, the level of protection afforded, and the inhibitory effects of short interfering RNA (SOD2 siRNA). Both WR1065 and 10 cGy X rays effectively induced a greater than threefold elevation in SOD2 activity 24 h after exposure. Cells irradiated at this time with 2 Gy exhibited a significant resistance to micronucleus formation (P < 0.05; Student's two-tailed t test). This protective effect was significantly inhibited in cells transfected with SOD2 siRNA. SOD2 played an important role in the adaptive/delayed radioprotective response by inhibiting the initiation of a superoxide anion-induced ROS cascade leading to enhanced mitochondrial and nuclear damages.

WR-1065, the active metabolite of amifostine, mitigates radiation-induced delayed genomic instability

Compounds that can protect cells from the effects of radiation are important for clinical use, in the event of an accidental or terrorist-generated radiation event, and for astronauts traveling in space. One of the major concerns regarding the use of radio-protective agents is that they may protect cells initially, but predispose surviving cells to increased genomic instability later. In this study we used WR-1065, the active metabolite of amifostine, to determine how protection from direct effects of high- and low-LET radiation exposure influences genomic stability. When added 30 min before irradiation and in high concentrations, WR-1065 protected cells from immediate radiation-induced effects as well as from delayed genomic instability. Lower, nontoxic concentrations of WR-1065 did not protect cells from death; however, it was effective in significantly decreasing delayed genomic instability in the progeny of irradiated cells. The observed increase in manganese superoxide dismutase protein levels and activity may provide an explanation for this effect. These results confirm that WR-1065 is protective against both low- and high-LET radiation-induced genomic instability in surviving cells.

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.

Amifostine in clinical oncology: current use and future applications

Amifostine (Ethyol), an inorganic thiophosphate, is a selective broad-spectrum cytoprotector of normal tissues that provides cytoprotection against ionizing radiation and chemotherapeutic agents, thus preserving the efficacy of radiotherapy and chemotherapy. This review summarizes the preclinical data and clinical experience with amifostine, and provides insight into future clinical directions. Amifostine, an inactive pro-drug, is transformed to an active thiol after dephosphorylation by alkaline phosphatase found in the normal endothelium. The absence of alkaline phosphatase in the tumoral endothelium and stromal components, and the hypovascularity and acidity of the tumor environment, may explain its cytoprotective selectivity. The cytoprotective mechanism of amifostine is complicated, involving free radical scavenging, DNA protection and repair acceleration, and induction of cellular hypoxia. Intravenous administration of amifostine 740-900 mg/m(2) before chemotherapy and 250-350 mg/m(2) before each radiotherapy fraction are widely used regimens. The US Food and Drug Administration has approved the use of amifostine as a cytoprotector for cisplatin chemotherapy and for radiation-induced xerostomia. Ongoing trials are being conducted to determine the efficacy of amifostine in reducing radiation-induced mucositis and other toxicities. Novel schedules and routes of administration are under investigation, and may further simplify the use of amifostine and considerably broaden its applications.

Amifostine: mechanisms of action underlying cytoprotection and chemoprevention

Amifostine is an important drug in the new field of cytoprotection. It was developed by the Antiradiation Drug Development Program of the US Army Medical Research and Development Command as a radioprotective compound and was the first drug from that Program to be approved for clinical use in the protection of dose limiting normal tissues in patients against the damaging effects of radiation and chemotherapy. Its unique polyamine-like structure and attached sulfhydryl group give it the potential to participate in a range of cellular processes that make it an exciting candidate for use in both cytoprotection and chemoprevention. Amifostine protects against the DNA damaging effects of ionizing radiation and chemotherapy drug associated reactive species. It possesses anti-mutagenic and anti-carcinogenic properties. At the molecular level, it has been demonstrated to affect redox sensitive transcription factors, gene expression, chromatin stability, and enzymatic activity. At the cellular level it has important effects on growth and cell cycle progression. This review focuses on relating its unique chemical design to mechanisms of action that underlie its broad usefulness as both a cytoprotective and chemopreventive agent for use in cancer therapy.

Amifostine

Amifostine (WR-2721) is a cytoprotective agent that protects a broad range of normal tissues from the toxic effects of chemotherapy and radiotherapy without attenuating tumour response. This selective protection is due to the greater conversion and uptake of the active metabolite, WR- 1065, in normal versus neoplastic tissues. In a pivotal phase III trial, 242 patients with advanced ovarian cancer were randomised to receive treatment with cisplatin 100 mg/m2 and cyclophosphamide 1000 mg/m2 every 3 weeks with or without pretreatment with intravenous amifostine 910 mg/m2. Over 6 cycles of therapy, amifostine significantly reduced haematological, renal and neurological toxicities: treatment delays, treatment discontinuation and days in hospital related to these adverse events were also significantly reduced in patients receiving amifostine versus patients receiving chemotherapy alone. In another randomised phase III trial in 303 patients with head and neck cancer undergoing irradiation therapy (total dose 50 to 70Gy), pretreatment with intravenous amifostine 200 mg/m2 significantly reduced the incidence of acute and late grade > or =2 xerostomia. However, mucositis was not significantly reduced in amifostine recipients compared with patients receiving radiotherapy alone, although this has been shown in smaller randomised trials. Amifostine (340 mg/m2) also provided significant protection against pneumonitis and oesophagitis in patients with lung cancer receiving thoracic irradiation in a preliminary report from a phase III trial (n = 144). Other studies have demonstrated protective effects of amifostine in other tumour types and other chemotherapy, radiation and radiochemotherapy regimens; however, evidence is still limited in these indications. No evidence of tumour protection by amifostine has been demonstrated in any clinical trials. Amifostine has also been shown to stimulate haematopoietic stem cells and has been investigated as a therapy for patients with myelodysplastic syndrome in number of small preliminary studies. At the recommended dose and schedule, amifostine is generally well tolerated. Adverse effects are usually reversible and manageable and those most frequently experienced include nausea and vomiting, transient hypotension and somnolence and sneezing.

CONCLUSION

The results of phase III trials have confirmed the safety and efficacy of amifostine as a cytoprotectant to ameliorate cisplatin-induced cumulative renal toxicity, for which it is the only agent proven to be effective, and neutropenia in patients with advanced ovarian cancer, and to reduce xerostomia in patients with head and neck cancer receiving irradiation therapy. Depending on the outcome of numerous ongoing clinical trials, amifostine may eventually find broader clinical applications, both as a cytoprotectant and as a potential therapy in myelodysplastic syndrome.

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.

Genomic instability and tumorigenic induction in immortalized human bronchial epithelial cells by heavy ions

Carcinogenesis is postulated to be a progressive multistage process characterized by an increase in genomic instability and clonal selection with each mutational event endowing a selective growth advantage. Genomic instability as manifested by the amplification of specific gene fragments is common among tumor and transformed cells. In the present study, immortalized human bronchial (BEP2D) cells were irradiated with graded doses of either 1GeV/nucleon 56Fe ions or 150 keV/micrometer alpha particles. Transformed cells developed through a series of successive steps before becoming tumorigenic in nude mice. Tumorigenic cells showed neither ras mutations nor deletion in the p16 tumor suppressor gene. In contrast, they harbored mutations in the p53 gene and over-expressed cyclin D1. Genomic instability among transformed cells at various stage of the carcinogenic process was examined based on frequencies of PALA resistance. Incidence of genomic instability was highest among established tumor cell lines relative to transformed, non-tumorigenic and control cell lines. Treatment of BEP2D cells with a 4 mM dose of the aminothiol WR-1065 significantly reduced their neoplastic transforming response to 56Fe particles. This model provides an opportunity to study the cellular and molecular mechanisms involved in malignant transformation of human epithelial cells by heavy ions.

Chromatographic and mass spectral analysis of the radioprotector and chemoprotector S-3-(3-methylaminopropylamino)propanethiol (WR-151326) and its symmetrical disulfide (WR-25595501)

Metabolically active forms of the radioprotective and chemoprotective drug S-3-(3-methylaminopropylamino)propylphosphorothioic acid (WR-151327) are S-3-(3-methylaminopropylamino)propanethiol (WR-151326) and its symmetrical disulfide (WR-25595501). This paper describes applications of sensitive and specific procedures such as capillary column gas chromatography with flame ionization detection, electron impact mass spectrometry and liquid chromatography with electrochemical detection for structural characterization and analysis of the active forms of WR-151327. These chromatographic procedures provide reproducible linear calibration graphs for a relatively wide range of concentrations of the active forms of WR-151327. The described procedures will further facilitate in vivo and in vitro investigations of chemoprotective and radioprotective properties of WR-151327 and its active metabolites.

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.

Induction of micronuclei by bleomycin in G0 human lymphocytes: II. Potentiation by radioprotectors

Dimethylsulfoxide (DMSO) and WR-1065 are radioprotectors, in that they reduce the effectiveness with which ionizing radiation causes genetic damage. Unlike their protective effects with radiation, these agents potentiate the induction of micronuclei by bleomycin in the cytokinesis-block assay in G0 human lymphocytes. High concentrations of DMSO (1 M) are required to cause potentiation. In contrast, WR-1065 causes dose-dependent potentiation at relatively low concentrations (1.25 to 10 mM). Cytogenetic analysis supports the results from the micronucleus assay, showing higher levels of genetic damage induced by the combination of bleomycin with DMSO or WR-1065 than by bleomycin alone. Possible mechanisms of potentiation are proposed.

Effects of WR-1065 and WR-151326 on survival and neoplastic transformation in C3H/10T1/2 cells exposed to TRIGA or JANUS fission neutrons

We demonstrated the ability of aminothiols WR-1065 and WR-151326, each at concentration 1 mM, to protect C3H/10T1/2 cells against the transforming effects of fission neutrons under two distinct sets of experimental conditions. Experiments with WR-1065 were performed with stationary cultures of C3H/10T1/2 cells, and a TRIGA reactor-generated fission neutron field at the Armed Forces Radiobiology Research Institute (USA). Experiments with WR-151326 were performed with proliferating cultures of C3H/10T1/2 cells and a JANUS reactor-generated fission neutron field at the Argonne National Laboratory (USA). Radioprotectors were present before, during, and after irradiation for total-periods of 35 min (WR-151326; 10 min pre-incubation) or 1 h (WR-1065; 30 min pre-incubation). Bioavailability of WR-1065 and WR-151326 in extracellular medium under experimental conditions simulating those of the transformation experiments was studied by measuring oxidation rates in the presence of attached C3H/10T1/2 cells in plateau and exponential phase of growth for periods of up to 5 h. Estimated half-lives for autoxidation of WR-1065 or WR-151326 were approximately 8 min or 1 h regardless of the proliferative status of cells. In the absence of WR-compounds, dose-response data for transformation induction by neutrons from TRIGA and JANUS reactors were fitted to a common curve with a linear coefficient of about 7 x 10(-4)/Gy. WR-151326 and WR-1065 were found to provide significant radioprotection by factors of 1.79 +/- 0.08 and 3.23 +/- 0.19, respectively, against fission neutron-induced neoplastic transformation. No significant protection against neutron-induced cell lethality was observed.

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

The antimutagenic effects of the radiation protective agent, S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721), were studied against fission-spectrum-neutron- and 60Co-gamma-ray-induced mutagenesis in mice. Mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus was measured 56 days following whole-body irradiation with JANUS neutrons (single doses, 50-150 cGy) or 60Co photons (single doses, 250-750 cGy). Splenic T lymphocytes from B6CF1 mice were grown in round-bottomed 96-microwell culture plates with or without the selective agent 6-thioguanine (6-TG). The mutant frequency, as a result of exposure to neutrons or 60Co photons, increased 100-fold with dose. Doses of 150 cGy neutrons and 750 cGy 60Co photons were equally mutagenic. When animals were injected with WR-2721 at a dose of 400 mg/kg body weight, i.p., 30 min before whole-body irradiation with JANUS neutrons or 60Co photons, mutant frequencies were significantly reduced at all radiation doses (i.e. protection factors of 1.4 and 2.4, respectively). Thus, the aminothiols are effective antimutagens. A novel clinical application of these compounds could be in their use to protect against radiation- and/or chemotherapy-induced genotoxic damage to normal cells.

Radioprotection by polysaccharides alone and in combination with aminothiols

We demonstrated that glucan, a beta-1,3 polysaccharide immunomodulator, enhances survival of mice when administered before radiation exposure. Glucan's prophylactic survival-enhancing effects are mediated by several mechanisms including (1) increasing macrophage-mediated resistance to potentially lethal postirradiation opportunistic infections, (2) increasing the D(o) of hematopoietic progenitor cells, and (3) accelerating hematopoietic reconstitution. In addition, even when administered shortly after some otherwise lethal doses of radiation, glucan increases survival. Glucan's therapeutic survival-enhancing effects are also mediated through its ability to enhance macrophage function and to accelerate hematopoietic reconstitution; glucan's therapeutic potential, however, is ultimately dependent on the survival of a critical number of hematopoietic stem cells capable of responding to glucan's stimulatory effects. Preirradiation administration of the traditional aminothiol radioprotectants WR-2721 and WR-3689 has been previously demonstrated to be an extremely effective means to increase hematopoietic stem cell survival. Therapeutic glucan treatment administered in combination with preirradiation WR-2721 or WR-3689 treatment synergistically increases both hematopoietic reconstitution and survival. Such combined modality treatments offer new promise in treating acute radiation injury.

Chemical protection and cell-cycle effects on radiation-induced mutagenesis

Chinese hamster ovary cells in the exponential phase of growth were harvested and separated by the method of centrifugal elutriation into subpopulations enriched with up to 95% G1 phase, 70% S phase and 65% G2 + M phase cells. Cell cycle distributions were routinely monitored by flow cytometry. Following elutriation, aliquots of cells from each of the enriched cell fractions were incubated in the presence or absence of 4 mM of 2-[(aminopropyl)amino] ethanethiol (WR-1065) for 30 min at 37 degrees C. The cells were then irradiated with 60Co gamma-rays or fission-spectrum neutrons from the JANUS research reactor. Both cell killing and mutagenesis were determined. Regardless of the radiation quality used, cells enriched in G1 phase were the most sensitive to radiation-induced mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase locus. The relative magnitude of protection exerted by WR-1065 differed for each of the elutriator separated cell populations. The greatest magnitude of protection, however, was observed for G1-enriched populations, regardless of the radiation quality used or the biological end-point tested.

Reversion of radiosensitivity in azacytidine-treated XRS5 cells does not result in full radioprotection by WR-1065

A series of cell lines were previously generated from the radiation sensitive Chinese hamster ovary line xrs5 after treatment with azacytidine. Six of these lines have been examined for their resistance to killing by 0 to 20 Gray of 60Co gamma rays and the amount of radioprotection afforded by treatment with the drug 2-[(aminopropyl)amino]ethanethiol (WR-1065). As xrs5 cells have lost the ability to be protected by WR-1065, studies were performed to determine whether reversion to radio-resistance correlated with recovery of aminothiol radioprotection. Treatment of azacytidine-treated, radiation sensitive and resistant cells with four millimolar WR-1065 30 minutes prior to irradiation enhanced survival after exposure to gamma radiation, although the enhancement in survival was less than for wild type Chinese hamster ovary K1 cells. The data suggest that there is not an absolute linkage between recovery of gamma ray radiation resistance and protection by WR-1065 and other factors, such as chromatin organization, must play a role.

Protection by WR-2721 and WR-151327 against late effects of gamma rays and neutrons

Two thiophosphoroate compounds WR-2721 and WR-151327 were assessed for their ability to modify the deleterious effects (life shortening and carcinogenesis) of fission-spectrum neutrons (kerma-weighted mean energy of 0.85 MeV) or gamma rays on B6CF1 hybrid mice. Male and female mice, 200 of each sex per experimental group, were irradiated individually at 110 days of age. Radioprotectors (400 mg/kg of WR-2721 or 580 mg/kg of WR-151327) were administered intraperitoneally 30 min prior to irradiation. Neutron doses were 10 cGy or 40 cGy and gamma ray doses were 206 cGy or 417 cGy. Animals were housed five to a cage; cage locations in the holding rooms were randomized by computer. Animals were checked daily and all deceased animals were necropsied. WR-2721 afforded protection against both neutron- and gamma-ray-induced carcinogenesis and subsequent life shortening. Cumulative survival curves for unirradiated mice of either sex were unaffectecd by protectors. WR-2721 protected irradiated groups against life shortening by approximately 10 cGy of neutrons or 100 cGy of gamma rays. WR-151327 was as effective as WR-2721 against neutron irradiation.

Differential radioprotection of cultured human diploid fibroblasts and fibrosarcoma cells by WR1065

The present studies were performed to determine whether WR1065, the dephosphorylated, free-thiol active metabolite of WR2721, could provide differential radioprotection of normal and tumor cell lines in vitro and secondly to investigate potential mechanisms for the selective nature of the radioprotection at the cellular and molecular level. When 4 mM WR1065 was administered 30 min prior to and during irradiation, a protection factor of 1.9 was obtained in clonogenic assays performed with normal human diploid fibroblasts (AG1522) while no protection of fibrosarcoma cells (HT1080) was observed. Some radioprotection of fibrosarcoma cells was observed with higher drug concentrations (10-40 mM), but the increase in survival was considerably less than the plateau level reached with the diploid fibroblasts (3-fold vs 24-fold at 6 Gy). The observation of such a selective effect in vitro with WR1065 indicates that differences in tissue-specific variables such as blood flow, pH, pO2, and drug dephosphorylation cannot solely account for the selective nature of the radioprotection afforded by WR2721 in vivo. Incubation of nucleoids with increasing concentrations of the DNA intercalating dye propidium iodide was used to titrate the ability of DNA to undergo supercoiling changes. The relaxation and rewinding of supercoiled DNA loops in isolated nucleoids serves as an indicator of both the presence of DNA damage and inherent differences in DNA loop characteristics. Fibrosarcoma cells had a much larger propidium iodide-relaxable DNA loop size than fibroblasts. The rewinding phase of the DNA supercoiling response is impaired by the presence of radiation-induced DNA strand breaks. Four mM WR1065 resulted in a significant reduction in the amount of rewinding inhibition observed after a dose of 10 Gy in diploid fibroblasts (protection factor = 1.43) but did not alter the response of irradiated fibrosarcoma cells. These results, indicating that WR1065 had a preferential radioprotective effect in vitro on both survival and the manifestation of DNA damage at the nucleoid level, are consistent with the hypothesis that cell type differences in chromatin organization and DNA-drug associations could play a role in the selective radioprotection.

Effect of thiols on micronucleus frequency in gamma-irradiated mammalian cells

The effects of the thiols cysteamine, WR-1065, and WR-255591 on radiation-induced micronucleus (MN) frequency and cell killing were compared in cultured Chinese hamster ovary cells. MN were measured using the cytochalasin B assay of Fenech and Morley (1985), which minimizes the effect of cytokinetic perturbations on MN expression. The dose-response curves for MN induction were curvilinear both for control cells at doses between 1.5 and 4.5 Gy and for thiol-treated cells at doses between 3 and 9 Gy. Protection against MN induction by each thiol was independent of radiation dose. Furthermore, there was a close correlation between the degree of modification of MN induction and cell survival by each thiol, i.e., the MN frequency closely predicted the survival level regardless of the presence of absence of the thiols. A similar predictive relationship has also been reported by us for cell survival and DNA double-strand break (DSB) induction in this cell line following treatment with these same thiols. Collectively, these data support the hypothesis that, for DNA-repair-proficient mammalian cells treated with radiomodifying agents that do not alter DNA-repair processes, MN and DSB induction are predictive of the level of radiation lethality and of each other.

New protective agents for bone marrow in cancer therapy

WR-2721 is a unique bone marrow protective agent which also protects other normal tissues against the toxic effects of radiation therapy and chemotherapy, especially with cisplatin and alkylating agents. In addition to protection against acute toxicities, WR-2721 has also been shown to protect against mutagenesis, cell transformation, and carcinogenesis which might be termed subacute and late toxicities. The protective mechanisms are not fully elucidated but oxygen free radical scavenging certainly plays a role and effects of enzymatic DNA repair mechanisms have also been reported. In the field of reduction of toxicity from anticancer treatment modalities, the properties of CSFs and other substances have been contrasted with WR-2721 the former being stimulators of bone marrow (and the immune system) rather than true protectors. Nonetheless, they also have a clinical role and combinations of a protector and stimulator may prove useful in the future. WR-2721 offers the prospect of increasing the therapeutic index of current cancer treatment and may allow the administration of higher than currently would be considered maximal tolerated doses (MTD). This may, in turn, lead to improved efficacy and the full potential of this agent is now being explored in a variety of randomized, controlled clinical trials.

Conformational changes in chromatin structure induced by the radioprotective aminothiol, WR 1065

WR 1065, 2-[(minopropyl) amino] ethanethiol is an effective scavenger of free radicals. When present during irradiation it reduces cellular DNA damage as analysed by alkaline elution from filters. The same technique indicates that without irradiation, WR 1065 has no effect of DNA integrity. Using nucleoid analysis, where DNA damage is detected at the level of replicon clusters, WR 1065 distorts replicon supercoiling without breaking the DNA molecule. This confirmational change in nucleoid structure occurs with no detectable change in nucleoid protein content. It is proposed that perturbation of replicon supercoiling affects the process of normal DNA synthesis and strand break rejoining, allowing a longer time for the accurate repair of DNA damage.

The effect of 2-[(aminopropyl)amino] ethanethiol on fission-neutron-induced DNA damage and repair

The effect(s) of the radioprotector 2-[(aminopropyl)amino] ethanethiol (WR 1065) on fission-neutron-induced DNA damage and repair in V79 Chinese hamster cells was determined by using a neutral filter elution procedure (pH 7.2). When required, WR1065, at a final working concentration of 4 mM, was added to the culture medium, either 30 min before and during irradiation with fission spectrum neutrons (beam energy of 0.85 MeV) from the JANUS research reactor, or for selected intervals of time following exposure. The frequency of neutron-induced DNA strand breaks as measured by neutral elution as a function of dose equalled that observed for 60Co gamma-ray-induced damage (relative biological effectiveness of one). In contrast to the protective effect exhibited by WR1065 in reducing 60Co-induced DNA damage, WR1065 was ineffective in reducing or protecting against induction of DNA strand breaks by JANUS neutrons. The kinetics of DNA double-strand rejoining were measured following neutron irradiation. In the absence of WR1065, considerable DNA degradation by cellular enzymes was observed. This process was inhibited when WR1065 was present. These results indicate that, under the conditions used, the quality (i.e. nature), rather than quantity, of DNA lesions (measured by neutral elution) formed by neutrons was significantly different from that formed by gamma-rays.

Mechanisms of inhibition of free-radical processes in mutagenesis and carcinogenesis

Mechanisms of the defense system against genotoxic damage, with emphasis on free-radical processes, are presented. Components of the defense system, interrelationships between components, and the stages in defense are discussed. Examples of free-radical mechanisms of protective agents (mannitol, DMSO) and repair agents (thiols and antioxidants), and the kinetics of their reactions are reviewed. Future trends in the development of novel protective agents are invoked.

Cell cycle redistribution of cultured cells after treatment with chemical radiation protectors

The effect of two radioprotective agents (WR-1065 and WR-151326) was tested for their ability to modify cell cycle progression. Each protector was administered at a concentration of 4 mmol to exponentially growing cultures of V79 cells for periods of time up to 3 h. Under these conditions no cell toxicity was observed. At selected times up to and after removal of the protector, aliquots of cells were removed, counted and fixed in cold 70% ethanol. The cells were stained with DAPI in a 0.1% citrate solution and DNA histograms were obtained using a PARTEC PAS-II flow cytometer. The coefficient of variation of the G1 peaks obtained for unperturbed cell samples routinely ranged from 1.5 to 2.5%. During exposure, both radioprotectors effectively perturbed cell cycle progression, as characterized by a build-up of cells in S and G2 phases. After the protectors were removed, cells began to redistribute throughout the cell cycle. Twelve hours were required before cells exposed to WR-1065 approached levels commensurable with controls. In contrast, cells treated with WR-151236 required about 24 h to redistribute to control levels. These data demonstrate that different thiol-containing radioprotective compounds can differentially affect the progression and redistribution of exposed cells.

Radioprotectors in tumor radiotherapy: factors and settings determining therapeutic ratio

WR-2721 and DDC have been used most frequently in our studies on radioprotective agents. WR-2721 was a much more potent radioprotector of murine normal tissues, both against early and late injuries of several organs and tissues, than was DDC. Protection factors for WR-2721 usually ranged between 1.5 and 2.5. Both agents protected solid murine tumors only minimally. While WR-2721 increased therapeutic ratios commonly, DDC did so only rarely. Micrometastatic foci were amenable to radioprotection more than established solitary tumors. Additional factors that influenced the degree of therapeutic benefit included dose of WR-2721, dose of irradiation (single versus fractionated), and time of WR-2721 administration in relation to radiation delivery. The ability of WR-2721 to prevent radiation-induced immunosuppression, metastatic spread, and carcinogenesis are additional benefits in the therapeutic use of this agent. Our current research on the improvement of radioprotectors for therapeutic use is focused on (a) a search for new radioprotective agents that are equal to or better than WR-2721 but less toxic and/or more specific for normal tissue, (b) understanding the basic mechanisms of action of these radioprotective agents at the molecular level, both in cells and tissues, and thus understanding the mechanisms leading to selective or preferential radioprotection of normal tissues, and (c) in vitro testing of primary human tumor cultures for their (non)susceptibility to radioprotection.

The effect of 2-[(aminopropyl)amino] ethanethiol (WR-1065) on radiation induced DNA double strand damage and repair in V79 cells

Radiation induced DNA double strand breaks are believed to be important lesions involved in processes related to cell killing, induction of chromosome aberrations and carcinogenesis. This paper reports the effects of the radioprotector 2-[(aminopropyl)amino]ethanethiol (WR-1065) on radiation-induced DNA damage and repair in V79 cells using the neutral elution method performed at pH 7.2 or pH 9.6. WR-1065 (4 mM) was added to the culture medium either 30 minutes prior to and during irradiation with Cobalt-60 gamma rays (for dose response experiments) or during the repair times tested (for DNA rejoining experiments). The results indicate that WR-1065 is an effective protector against the formation of radiation-induced double-strand breaks in DNA as measured using a neutral elution technique at either pH. The protector reduced the strand scission factors by 1.44 and 1.77 in experiments run at pH 9.6 and pH 7.2, respectively. The kinetics of DNA double-strand rejoining were dependent upon the pH at which the neutral elution procedure was performed. Unlike the results obtained with alkaline elution, rejoining of DNA breaks was unaffected by the presence of WR-1065 at either pH.

The effect of 2-[(aminopropyl)amino] ethanethiol (WR1065) on radiation-induced DNA damage and repair and cell progression in V79 cells

The radioprotector 2-[(aminopropyl)amino] ethanethiol (WR1065) was investigated with respect to its ability to affect radiation-induced DNA damage and repair in V79 cells. Studies were performed to evaluate the protector under conditions in which it is known to be effective in reducing the cytotoxic and mutagenic effects of gamma-irradiation. At a concentration of 4 mM, WR1065 protected against the formation of single strand breaks (SSB), as determined by the method of alkaline elution, when it was present during irradiation. The protector appeared, however, to inhibit the subsequent postirradiation repair or rejoining of SSB. While repair was complete within 24 h, the protector reduced the rate of repair by a factor of 3. This inhibitory effect on the rate of repair did not correlate with either measured differences in cell survival or mutagenesis. The radioprotector was also investigated with respect to its ability to affect cell cycle progression. WR1065 present in the growth medium inhibited the progression of cells through S-phase, and cell-doubling time following a 3 h exposure to the protector was increased from 11 to 18 h. These data are consistent with the well characterized property of thiols to inhibit DNA polymerase activity. It was concluded that, while the presence of WR1065 during irradiation reduced SSB-DNA damage, its effect on the subsequent rejoining of these breaks could not be correlated with its observed effect on protecting against radiation-induced mutagenesis. It may be that the inhibition of cell-cycle progression by the protector allowed more time to enhance the fidelity of repair as measured by the protector's ability to protect against radiation-induced mutagenesis.

Protective effects of 2-[(aminopropyl)amino] ethanethiol against bleomycin and nitrogen mustard-induced mutagenicity in V79 cells

This study examines the effects of the radioprotector 2-[(aminopropyl)amino] ethanethiol (WR-1065) on bleomycin (BLM) and nitrogen mustard- (HN2) induced cytotoxicity, DNA damage, and mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus in V79 Chinese hamster cells. The anti-mutagenic effect of WR-1065 on cis-diamminedichloroplatinum (cis-DDP) and radiation- (XRT) induced HGPRT mutations was also evaluated for comparative purposes. WR-1065 (4 mM) was added prior to exposure of cells to therapy agents. All exposure times were 30 min. and both cell survival and mutagenesis were assayed. WR-1065 was effective in protecting against both effects. The induction of mutants corrected for background by BLM, HN2, cis-DDP, or XRT was linear in all cases. Mutation frequencies without WR-1065 were 78 X 10(-6) per unit BLM, 66 X 10(-7) per microgram HN2, 25 X 10(-7) per microgram cis-DDP; and 87 X 10(-7) per Gy of XRT. With WR-1065, these were reduced to 37 X 10(-6) per unit BLM, 40 X 10(-7) per microgram HN2, 1 X 10(-7) per microgram cis-DDP, and 44 X 10(-7) per Gy of XRT. Mutation protection factors (MPF), a ratio of the corresponding slopes of the mutation induction curves, with and without WR-1065 were: BLM, MPF = 2.8; HN2, MPF = 3.4; cis-DDP, MPF = 7.1; and XRT, MPF = 5.1. Single-strand-break (SSB) formation in DNA by BLM or HN2, assayed by alkaline elution, was protected against by WR-1065. WR-1065 did not induce SSB in control cells. The reduction of the mutagenic effects of agents used in radiation and chemotherapy by radioprotectors may be an important additional benefit for consideration in their use in cancer treatment.