Modification of radiation-induced carcinogenesis in mice by misonidazole and WR-2721

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.

Tumor Induction in Mice After Localized Single- or Fractionated-Dose Irradiation: Differences in Tumor Histotype and Genetic Susceptibility Based on Dose Scheduling

PURPOSE

To investigate differences in tumor histotype, incidence, latency, and strain susceptibility in mice exposed to single-dose or clinically relevant, fractioned-dose γ-ray radiation.

METHODS AND MATERIALS

C3Hf/Kam and C57BL/6J mice were locally irradiated to the right hindlimb with either single large doses between 10 and 70 Gy or fractionated doses totaling 40 to 80 Gy delivered at 2-Gy/d fractions, 5 d/wk, for 4 to 8 weeks. The mice were closely evaluated for tumor development in the irradiated field for 800 days after irradiation, and all tumors were characterized histologically.

RESULTS

A total of 210 tumors were induced within the radiation field in 788 mice. An overall decrease in tumor incidence was observed after fractionated irradiation (16.4%) in comparison with single-dose irradiation (36.1%). Sarcomas were the predominant postirradiation tumor observed (n=201), with carcinomas occurring less frequently (n=9). The proportion of mice developing tumors increased significantly with total dose for both single-dose and fractionated schedules, and latencies were significantly decreased in mice exposed to larger total doses. C3Hf/Kam mice were more susceptible to tumor induction than C57BL/6J mice after single-dose irradiation; however, significant differences in tumor susceptibilities after fractionated radiation were not observed. For both strains of mice, osteosarcomas and hemangiosarcomas were significantly more common after fractionated irradiation, whereas fibrosarcomas and malignant fibrous histiocytomas were significantly more common after single-dose irradiation.

CONCLUSIONS

This study investigated the tumorigenic effect of acute large doses in comparison with fractionated radiation in which both the dose and delivery schedule were similar to those used in clinical radiation therapy. Differences in tumor histotype after single-dose or fractionated radiation exposures provide novel in vivo evidence for differences in tumor susceptibility among stromal cell populations.

Pre-treatment with amifostine protects against cyclophosphamide-induced disruption of taste in mice

Cyclophosphamide (CYP), a commonly prescribed chemotherapy drug, has multiple adverse side effects including alteration of taste. The effects on taste are a cause of concern for patients as changes in taste are often associated with loss of appetite, malnutrition, poor recovery and reduced quality of life. Amifostine is a cytoprotective agent that was previously shown to be effective in preventing chemotherapy-induced mucositis and nephrotoxicity. Here we determined its ability to protect against chemotherapy-induced damage to taste buds using a mouse model of CYP injury. We conducted detection threshold tests to measure changes in sucrose taste sensitivity and found that administration of amifostine 30 mins prior to CYP injection protected against CYP-induced loss in taste sensitivity. Morphological studies showed that pre-treatment with amifostine prevented CYP-induced reduction in the number of fungiform taste papillae and increased the number of taste buds. Immunohistochemical assays for markers of the cell cycle showed that amifostine administration prevented CYP-induced inhibition of cell proliferation and also protected against loss of mature taste cells after CYP exposure. Our results indicate that treatment of cancer patients with amifostine prior to chemotherapy may improve their sensitivity for taste stimuli and protect the taste system from the detrimental effects of chemotherapy.

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.

In vivo Study to Evaluate the Protective Effects of Amifostine on Radiation-Induced Damage of Testis Tissue

OBJECTIVE

To investigate the early protective effects of amifostine against radiation-induced damage on rat testis tissue.

METHODS

Eighty adult male Wistar rats were randomized to 4 groups: Saline solution was given to group A for control, 200 mg/kg amifostine (WR-2721) to group B, a single fraction of 6 Gy local irradiation to testes in group C and 200 mg/kg amifostine 15-30 min before 6 Gy testicular irradiation to group D. Animals were sacrificed 3 weeks after treatment and their testes were removed for macroscopic, microscopic and ultrastructural histopathological examination.

RESULTS

The weights, widths and lengths of testes in the last 3 groups had decreased significantly when compared with the control group, but the decrease in widths after irradiation was found to be significantly less only in the amifostine plus radiation group. There was a significant reduction of testis weights in relation to the individual body weights in the irradiated testes compared with the other groups (p < 0.005), while there was no significant change of testis weight/total body weight ratio in amifostine plus irradiation group. Spermatogonium A and primary spermatocyte counts were also less in the treatment groups, and primary spermatocyte numbers were significantly higher in amifostine plus radiation group when compared with radiation alone group (p < 0.005). Pretreatment with amifostine reduced the decrease of primary spermatocyte counts by a factor of 1.28. Electron microscopic analysis did not show any cytotoxic effect of amifostine alone, and furthermore, ultrastructural findings were normal with the addition of amifostine prior to irradiation, though there was damage in the radiation exposure group.

CONCLUSION

Amifostine when given alone by itself appears to cause adverse alterations in testis tissue; however, it has a radioprotective effect on spermiogenetic cells when used prior to radiation.

Cytoprotection in Acute Myelogenous Leukemia (AML) therapy

Planning therapy for acute myelogenous leukemia (AML) is difficult because of the heterogeneous nature of the disease and varying patient age at presentation. Cytogenetics and patient age at the time of diagnosis are two major factors determining treatment outcome in AML. Patients with poor-risk cytogenetics have much lower complete remission rates than other groups. In addition, AML in patients greater than 55 to 60 years of age often exhibits a resistant phenotype, more akin to secondary AML or AML arising from myelodysplastic syndromes. This group is also characterized by lower complete remission rates, and often requires the delivery of intensive therapy to a patient population that is the least likely to tolerate it. At the Jefferson Health System (Philadelphia, PA), we wished to develop a regimen that was maximally intensive to treat stubborn disease, but gentle enough to be given to all patients regardless of age. Toward this end, 33 patients received a maximal dose of the cytoprotective agent, amifostine, before each infusion of idarubicin in the "7 + 3" regimen, escalating the dose of idarubicin in a phase I fashion to a maximum dose of 24 mg/m2 . The data indicate that the addition of amifostine to "7 + 3" AML induction therapy enables a substantial escalation of the idarubicin dose through the 21-mg/m2 dose level, without a concomitant increase in side effects, thus providing a regimen that is both intensive and applicable to patients of all ages. Currently, phase II studies are ongoing on a national basis to evaluate the efficacy of this regimen.

Preclinical modeling of improved amifostine (Ethyol) use in radiation therapy

Amifostine (Ethyol) has been evaluated clinically as a radioprotective agent for the prevention of xerostomia and mucositis for patients receiving radiotherapy (RT). Currently, amifostine is approved for the prevention of xerostomia in head and neck cancer patients receiving RT when administered intravenously (IV) before RT. For the clinician, there would be several advantages to administering the drug subcutaneously and to being able to show its protective effects on mucositis. The authors have developed a rat RT model to examine the protective effects of amifostine after IV and subcutaneous (SC) administration in a mucositis model. Rats (5 per group) were given 200 mg/kg (human dose equivalent of approximately 1,300 mg/m(2)) of amifostine either IV or SC, and their head and neck regions were exposed to 15.3 Gy of gamma radiation 0.5, 2, 4, and 8 hours after amifostine administration. For 10 days after treatment, the oral cavities of the rats were examined for signs of mucositis. Mucosal erythema and mucosal edema were scored according to 0 through 5 and 0 through 2 scales, respectively, with the scores added to indicate overall mucositis. The average mucositis score for the untreated animals was 3.5. Rats were protected from mucositis up to 4 hours when given amifostine either IV or SC. Rats that received amifostine SC, but not IV, were protected from mucositis 8 hours after administration. Preliminary pharmacokinetic data have revealed slightly higher active metabolite (WR-1065) levels in the parotid gland and small intestine in the rats given amifostine SC compared with IV and equivalent levels in the plasma and kidney. The data showed that SC administration of amifostine gave radioprotection comparable to IV administration up to 4 hours before RT and may be more effective than IV administration at longer pretreatment intervals.

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: chemotherapeutic and radiotherapeutic protective effects

Amifostine (Ethyoltrade mark, Alza Pharmaceuticals) is an inorganic thiophosphate cytoprotective agent known chemically as ethanethiol, 2-[3- aminopropyl)amino]dihydrogen phosphate. It is a prodrug of free thiol (WR-1065) that may act as a scavenger of free radicals generated in tissues exposed to cytotoxic drugs and binds to reactive metabolites of such drugs. Amifostine was originally developed as a radioprotective agent in a classified nuclear warfare project. Following declassification of the project it was evaluated as a cytoprotective agent against toxicity of the alkylating drugs and cisplatin. Differences in the alkaline phosphatase concentration of normal versus tumour tissues can result in greater conversion of amifostine in normal tissues. Inside the cell, WR-1065 provides an alternative target to DNA and RNA for the reactive molecules of alkylating or platinum agents and acts as a potent scavenger of the oxygen free radicals induced by ionizing radiation and some chemotherapy agents. Preclinical animal studies have demonstrated that the administration of amifostine protects against a variety of chemotherapy-related toxicities including cisplatin-induced nephrotoxicity, cisplatin-induced neurotoxicity, cyclophosphamide- and bleomycin-induced pulmonary toxicity and the cytotoxicities (including cardiotoxicity) induced by doxorubicin and related chemotherapeutic agents. Amifostine has been shown to protect a variety of animal species from lethal doses of radiation. Amifostine gives haematological protection from cyclophosphamide, carboplatin, mitomycin C, fotemustine and radiotherapy; renal and peripheral nerve protection from cisplatin; mucosa, skin and salivary gland protection from radiotherapy. Multiple Phase I studies were carried out with amifostine in combination with chemotherapy for various neoplasms. Appropriate doses of amifostine were found to be 740 - 910 mg/m(2) in single-dose regimens and 340 mg/m(2) in multiple-dose regimens. In radioprotection, doses are generally 200 - 350 mg/m(2). For all these characteristics, amifostine has been recently approved and suggested in ASCO clinical practice guidelines as a radioprotector for head and neck cancer treatment and supportive agent during cisplatin-based chemotherapy, in lymphomas and solid tumours. Moreover, its spectrum of possible applications is enlarging. As data have been provided indicating that amifostine stimulates haematopoiesis, it has been employed with intriguing results in the treatment of myelodysplastic syndromes (MDS).

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.

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.

Radiation-induced lymphoid tumors and radiation lethality are inhibited by combined treatment with small doses of zinc aspartate and WR 2721

Combined small doses of zinc aspartate and WR 2721 provided additive protection against radiation lethality in mice. Survival obtained with a small dose of WR 2721 which was ineffective alone could be enhanced to 83% by combining the drug with zinc aspartate, which on its own also displayed no effect. The survival of 25% provided by a higher dose of WR 2721 was increased significantly by adding zinc aspartate. Additivity was also tested in a model of radiation carcinogenesis. For this purpose, lethality and occurrence of lymphoid tumors induced by fractionated total-body irradiation were studied in C57B1/6 mice treated with zinc aspartate and WR 2721. In order to reveal additive effects, both agents were used at sub-optimal dosages. In mice subjected to 5 daily exposures of 1.9 Gy, the combination of zinc aspartate and WR 2721 was effective and enhanced the survival to 83% as compared with 25% afforded by WR 2721 alone (p < 0.005). Similarly, histological assessment of organ involvement with lymphoma revealed that zinc aspartate and WR 2721 alone did not bring about a significant reduction of lymphoma incidence. On the other hand, the combined agents diminished organ involvement with lymphoma to 9.1% as against 90% in the controls (p < 0.0005) and 62.5% with WR 2721 alone (p < 0.025). Thus, combined treatment with zinc aspartate and WR 2721 also inhibited radiation-induced lymphoid tumors.