Repression of c-myc gene expression by the thiol and disulfide forms of the cytoprotector amifostine

Amifostine does not protect thyroid cancer cells in DNA damaging in vitro models

BACKGROUND

Amifostine is a potent scavenger of reactive oxygen species that is used for the salivary gland protection during therapy with radioactive iodine for thyroid cancer. There are no data on the potential effect of amifostine on thyroid cancer cells.

METHODS

We investigated the effects of the active form of amifostine (WR-1065) on the response of thyroid cancer cells to treatment with DNA-damaging agents. WR-1065 was examined in human thyroid cancer cell lines (FTC133, TPC1, BCPAP and C643) and embryonic fibroblast cells NIH3T3. DNA damage was induced by exposure to H₂O₂ (0.1 mM), by treatment with the radiomimetic neocarzinostatin (NCS 250 ng/mL) and by γ-radiation (6 Gy). DNA damage, cell viability and apoptosis were examined.

RESULTS

We demonstrated the selective action of WR-1065 (0.1 mM), which prevented oxidative stress-induced DNA damage in fibroblasts, but did not protect thyroid cancer cells from DNA damage and apoptosis documented by caspase-3 and PARP cleavage after exposure to H₂O₂, NCS and γ-radiation. Prolonged exposure to WR-1065 (0.1 mM for 24 h) was toxic for thyroid cancer cells; this treatment decreased the number of viable cells by 8% in C643 cells, 47% in TPC cells, 92% in BCPAP cells and 82% in FTC 133 cells. The cytotoxic effects of WR-1065 were not associated with induction of apoptosis.

CONCLUSIONS

Our data show that amifostine has no protective effect on thyroid cancer cells against DNA-damaging agents in vitro and suggest that amifostine will not attenuate the efficacy of radioiodine treatment in patients with thyroid cancer.

Mitigating the risk of radiation-induced cancers: limitations and paradigms in drug development

The United States radiation medical countermeasures (MCM) programme for radiological and nuclear incidents has been focusing on developing mitigators for the acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), and biodosimetry technologies to provide radiation dose assessments for guiding treatment. Because a nuclear accident or terrorist incident could potentially expose a large number of people to low to moderate doses of ionising radiation, and thus increase their excess lifetime cancer risk, there is an interest in developing mitigators for this purpose. This article discusses the current status, issues, and challenges regarding development of mitigators against radiation-induced cancers. The challenges of developing mitigators for ARS include: the long latency between exposure and cancer manifestation, limitations of animal models, potential side effects of the mitigator itself, potential need for long-term use, the complexity of human trials to demonstrate effectiveness, and statistical power constraints for measuring health risks (and reduction of health risks after mitigation) following relatively low radiation doses (<0.75 Gy). Nevertheless, progress in the understanding of the molecular mechanisms resulting in radiation injury, along with parallel progress in dose assessment technologies, make this an opportune, if not critical, time to invest in research strategies that result in the development of agents to lower the risk of radiation-induced cancers for populations that survive a significant radiation exposure incident.

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.

Amifostine modulates radio-induced apoptosis of peripheral blood lymphocytes in head and neck cancer patients

Head and neck cancer is treated mainly with surgery and radiotherapy. Xerostomia and mucositis are common adverse effects of radiation therapy. One of the strategies aimed at decreasing radiation toxicity is the use of radioprotective agents, such as amifostine. We previously reported that radio induced apoptosis of peripheral blood lymphocytes was statistically associated with normal tissue toxicity in the form of severe xerostomia. The aim of the present study was to explore the effects of amifostine on the radiation-induced apoptosis of peripheral blood lymphocytes from patients suffering head and neck cancer. Eighteen consecutive patients with squamous cell carcinoma of the head and neck were included in the study. Peripheral blood lymphocytes were isolated before and after the treatment with amifostine. Then, cells were irradiated at 0, 1, 2 and 8 Gy during 24 hours. Apoptosis was measured by flow cytometry using annexin V/propidium iodide. As expected, radio-induced apoptosis values fitted to a semi logarithmic equation as follows: RIA = β ln(Gy) + α. The administration of amifostine prior to radiation therapy modulates radio-induced apoptosis of peripheral blood lymphocytes: 13.68 vs. 13.37 (P = 0.027), 19.11 vs. 17.64 (P = 0.001) and 30.70 vs. 28.84 (P = 0.001), before and after the administration of the drug for 1, 2 and 8 Gy respectively. α and β decreased significantly after the administration of the drug: 13.58 vs. 12.99 (P = 0.009) and 8.21 vs. 7.53 (P = 0.017), respectively. Our results provide new information about the biological actions of amifostine in vivo.

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.

Effect of Amifostine on Response Rates in Locally Advanced Non–Small-Cell Lung Cancer Patients Treated on Randomized Controlled Trials: A Meta-Analysis

PURPOSE

Amifostine can reduce the cytotoxic effects of chemotherapy and radiotherapy in patients with locally advanced non-small-cell lung cancer, but concerns remain regarding its possible tumor-protective effects. Studies with sufficient statistical power to address this question are lacking.

METHODS AND MATERIALS

We performed a meta-analysis of all published clinical trials involving locally advanced non-small-cell lung cancer patients treated with radiotherapy with or without chemotherapy, who had been randomized to treatment with amifostine vs. no amifostine or placebo. Random effects estimates of the relative risk of overall, partial, and complete response were obtained.

RESULTS

Seven randomized trials involving 601 patients were identified. Response rate data were available for six studies (552 patients). The pooled relative risk (RR) estimate was 1.07 (95% confidence interval, 0.97-1.18; p = 0.18), 1.21 (95% confidence interval, 0.83-1.78; p = 0.33), and 0.99 (95% confidence interval, 0.78-1.26; p = 0.95) for overall, complete, and partial response, respectively (a RR >1 indicates improvement in response with amifostine compared with the control arm). The results were similar after sensitivity analyses. No evidence was found of treatment effect heterogeneity across the studies.

CONCLUSIONS

Amifostine has no effect on tumor response in patients with locally advanced non-small-cell lung cancer treated with radiotherapy with or without chemotherapy.

Interaction of amifostine and ionizing radiation on transcriptional patterns of apoptotic genes expressed in human microvascular endothelial cells (HMEC)

PURPOSE

Amifostine is a prodrug that requires dephosphorylation by alkaline phosphatase to become activated. This process occurs rapidly within the bloodstream after its i.v. administration to patients undergoing cancer treatment with selected radiation and chemotherapies. Vascular endothelial cells will, therefore, represent a normal cell system that is among the first to experience the radioprotective effects of this agent. Amifostine's active free thiol WR-1065 was investigated to determine its effect on radiation-induced changes in transcriptional patterns and subsequent apoptosis in human microvascular endothelial cells (HMEC) growing in vitro.

METHODS AND MATERIALS

Human microvascular endothelial cells were grown to confluency and then exposed to WR-1065 at a concentration of 4 mM for 30 min, radiation doses that ranged from 0 to 6 Gy, and WR-1065 at a concentration of 4 mM for 30 min before exposure to ionizing radiation. Cell survival was assessed by clonogenic assay, cell cycle phase was analyzed by flow cytometry, apoptosis was also assessed by flow cytometry in which Anexin V staining and sub-G1 fraction analysis were applied, and gene expression was analyzed by the Clontech Atlas Human cDNA array to identify synergistic and antagonistic effects as a function of amifostine and radiation exposure conditions with a focus on apoptotic-related factors.

RESULTS

Exposure of HMEC to 4 mM WR-1065 30 min before irradiation resulted in a protection enhancement factor of 2.0; that is, D(O-IRR) of 1.25 Gy and D(O-IRR+WR) of 2.56 Gy. Expression profiling revealed 29 genes that were synergistically activated by the combined action of WR-1065 and ionizing radiation, and an additional 12 genes were synergistically or additively suppressed. In particular, a subset of apoptosis-related genes that included caspases 2, 4, and 9 and different members of the bcl family, along with apoptosis-related receptors, were identified as being significantly affected by the combined treatment of WR-1065 and radiation exposure. In addition, a number of cell cycle-related genes that express cyclins A, G1, G2, and D3 and DNA damage/check point proteins ATM, DNA-PK and RAD23B were also found to be significantly affected. Functional assays of apoptosis were also performed that demonstrated the ability of WR-1065 to protect against radiation-induced apoptosis.

CONCLUSIONS

WR-1065, the active thiol form of amifostine, is an effective radioprotector of HMEC as determined by use of clonogenic and apoptotic assays for cell survival. Expression profiling successfully defined the transcriptional response of HMEC to both WR-1065 and ionizing radiation exposure, either alone or in combination, and demonstrated both synergistic and antagonistic effects on the expression of different cellular genes, along with corresponding functional responses. The radioprotective effects of amifostine are not limited to its well-characterized physiochemical properties, which include free-radical scavenging, auto-oxidation leading to intracellular hypoxia, and chemical repair by hydrogen atom donation, but include its ability to modulate the complex transcriptional regulation of genes that are involved in apoptosis, cell cycle, and DNA repair.

Amifostine has antiangiogenic properties in vitro by changing the redox status of human endothelial cells

Amifostine is a broad-spectrum cytoprotective agent, selective for normal tissues. It is a pro-drug metabolised to the free thiol WR-1065 that may act as a scavenger of free radicals, generated in tissues exposed to chemotherapeutic agents or radiation. WR-1065 can be further oxidized to its symmetric disulfide WR-33278 or degraded to hydrogen peroxide (H2O2). Both WR-1065 and WR-33278 resemble endogenous polyamines. Although amifostine is used in some cases in the clinic, there are only few studies concerning its actions at the cellular level. We have previously shown that amifostine inhibits angiogenesis in vivo, affecting the expression of several angiogenic genes. In the present work, we studied the effect of amifostine on human umbilical vein endothelial cell (HUVEC) functions in vitro, in order to further clarify its mechanism(s) of action. Amifostine increased HUVEC proliferation, an effect that was reversed by the intracellular H2O2 scavenger sodium pyruvate, agents that increase intracellular cAMP levels and L-valine. On the other hand, amifostine decreased HUVEC migration, an effect that was reversed by L-valine or L-arginine but not sodium pyrouvate. The decrease in migration was in line with decreased tube formation on matrigel and decreased amounts of metalloproteinase-2 released into the culture medium of HUVEC. Finally, amifostine reduced tyrosine nitration of the cytoskeletal proteins actin and alpha-tubulin in a time dependent manner. This last action could be due to the reduced production of nitric oxide (NO) or to other not yet identified mechanisms. Collectively, our results suggest that amifostine acts on endothelial cells through pathways that affect the redox status of the cells, either by producing H2O2 or by modulating NO production.

The cytoprotective aminothiol WR1065 activates p53 through a non-genotoxic signaling pathway involving c-Jun N-terminal kinase

WR1065 is an aminothiol with selective cytoprotective effects in normal cells compared with cancer cells. In a previous study (North, S., El-Ghissassi, F., Pluquet, O., Verhaegh, G., and Hainaut, P. (2000) Oncogene 19, 1206-1214), we have shown that WR1065 activates wild-type p53 in cultured cells. Here we show that WR1065 induces p53 to accumulate through escape from proteasome-dependent degradation. This accumulation is not prevented by inhibitors of phosphatidylinositol 3-kinases and is not accompanied by phosphorylation of Ser-15, -20, or -37, which are common targets of the kinases activated in response to DNA damage. Furthermore, WR1065 activates the JNK (c-Jun N-terminal kinase), decreases complex formation between p53 and inactive JNK, and phosphorylates p53 at Thr-81, a known site of phosphorylation by JNK. A dominant negative form of JNK (JNK-APF) reduces by 50% the activation of p53 by WR1065. Thus, WR1065 activates p53 through a JNK-dependent signaling pathway. This pathway may prove useful for pharmacological modulation of p53 activity through non-genotoxic mechanisms.

Activation of p53 by the cytoprotective aminothiol WR1065: DNA-damage-independent pathway and redox-dependent modulation of p53 DNA-binding activity

WR1065 is an aminothiol with selective cytoprotective effects in normal compared to cancer cells, which is used to protect tissues against the damaging effect of radiation and chemotherapeutic drugs. WR1065 has been shown to induce wild-type p53 accumulation and activation in cultured cells, suggesting a role of p53 in cytoprotection. However, the molecular mechanisms by which WR1065 activates p53 remain unclear. Here, we demonstrated that p53 accumulation by WR1065 in MCF-7 cells did not result from the formation of DNA-damage as measured by DNA fragmentation and Comet assay, nor from oxidative stress as detected by measurement of glutathione levels, lipid peroxidation and reactive oxygen species production. p53 activation by WR1065 was not prevented by inhibition of PI-3 kinases, and was still detectable in MCF-7 cells stably transfected with the oncoprotein E6, which repressed p53 induction by DNA damage. These data provided evidence that WR1065 induces p53 by a pathway different than the one elicited by DNA-damage. Direct reduction by WR1065 of key cysteines in p53 may play an important role in this alternative pathway, as shown by the fact that WR1065 activated the redox-dependent, DNA-binding activity of p53 in vitro.

p53 protein regulates the effects of amifostine on apoptosis, cell cycle progression, and cytoprotection

To determine the role of p53 protein on the cellular effects of amifostine, we used molecularly engineered HCT116 colon cancer cells in which the p53 gene was inactivated by targeted homologous recombination or p53 protein was degraded by high-level expression of papillomavirus E6 protein. Amifostine induced a G1 arrest and protected against paclitaxel toxicity in p53-proficient but not in p53-deficient cells. In the absence of p53 protein, amifostine enhanced the cytotoxicity of paclitaxel. In addition, treatment of HCT116 cells with amifostine alone resulted in apoptotic cell death. Compared with p53-deficient cells, p53-proficient cells exhibited low-level resistance to amifostine-induced apoptosis. Amifostine induced the expression of p53 protein in p53-proficient cells and the expression of p21 protein in both p53-proficient and -deficient cells. These findings indicate that amifostine-induced G1 arrest and cytoprotection are mediated via a pathway that is dependent on p53 protein and that amifostine-induced expression of p21 protein is not sufficient to sustain a G1 arrest or to mediate cytoprotection. In addition, these findings identify p53 protein as a mechanism of resistance to amifostine-induced apoptosis.British

Amifostine inhibits angiogenesis in vivo

Amifostine (WR-2721) is an inorganic thiophosphate-cytoprotective agent developed to selectively protect normal tissues against the toxicity of chemotherapy and radiation. We have previously shown that amifostine protects both chicken embryo chorioallantoic membrane (CAM) vessels and cells from the effects of X-rays. In the present work, we studied the effect of amifostine on angiogenesis in vivo, using the CAM model. Amifostine decreased the number of CAM vessels in a dose-dependent manner, without being toxic for the tissue. It also decreased the mRNA levels of both vascular endothelial growth factor (VEGF) isoforms VEGF(165) and VEGF(190), 6 and up to 48 h after its application onto the CAM. Similarly, it decreased the mRNA levels of inducible nitric-oxide synthase, 24 and 48 h after drug application. Furthermore, amifostine decreased the deposited amounts of laminin and collagen I 24 h after its application, without affecting the expression of the corresponding genes. The protein amounts and activity of matrix metalloproteinase-2 were not affected, whereas the expression of the corresponding gene was decreased up to 48 h after drug application. Finally, the activity of plasmin was increased 6 h after amifostine application and remained increased at later time points. These findings suggest that amifostine alters the expression of several molecules implicated in the angiogenesis process and affects the composition of the extracellular matrix in a way that leads to inhibition of angiogenesis. Such an antiangiogenic action of amifostine, together with its radioprotective effects, further supports its use in combination with radiotherapy for increased therapeutic efficacy.

Activation of the nuclear transcription factor kappaB (NFkappaB) and differential gene expression in U87 glioma cells after exposure to the cytoprotector amifostine

PURPOSE

Amifostine has been approved as a therapy to decrease the incidence of moderate-to-severe xerostomia in patients undergoing postoperative radiation treatment for head-and-neck cancer. As a reducing agent capable of participating in intracellular reductive/oxidative processes, it has the potential to affect redox-sensitive transcription factors and gene expression. Amifostine's active free thiol WR-1065 was investigated to determine its effect on nuclear transcription factor kappaB (NFkappaB) activation and subsequent gene expression in U87 glioma cells.

METHODS AND MATERIALS

The human glioma cell line U87 was grown to confluency and then exposed to WR-1065 at a concentration of 40 microM for times ranging from 30 min to 24 h. Changes in cell cycle were monitored by flow cytometry. The effect of WR-1065 on NFkappaB activation was determined by a gel shift assay. Changes in gene expression as a function of time of exposure to WR-1065 were determined by Northern blot and the Atlas Human cDNA Expression Array (Clontech, Palo Alto, CA). Changes in gene expression using the Atlas Array were verified by reverse transcriptase-polymerase chain reaction (RT-PCR) with gene-specific primers.

RESULTS

Exposure of U87 cells to 40 microM WR-1065 resulted in a marked activation of NFkappaB between 30 min and 1 h after treatment. Expression of MnSOD, an NFkappaB-responsive gene, was enhanced by over 2-fold after 16 h of treatment and remained elevated at 24 h. During this period of time, no changes in cell cycle distribution were observed. To assess changes in the expression levels of NFkappaB-responsive genes as a function of WR-1065 exposure, cDNA arrays containing 49 genes identified as having DNA-binding motifs for NFkappaB were used. Only five genes were found to be significantly affected at 1, 4, and/or 16 h of treatment. GST-3 and c-myc were repressed up to 2- and 4-fold, respectively. The expression levels of IL-2Ra, RANTES, and c-myb, in contrast, were enhanced up to 14-, 3-, and 2-fold, respectively. The remaining genes having NFkappaB-responsive elements in their promoter regions were either not expressed (20 genes) or were not affected (24 genes) by exposure to WR-1065.

CONCLUSIONS

The redox-sensitive transcription factor NFkappaB can be activated in U87 glioma cells by the active thiol form of the cytoprotector amifostine. Activation of NFkappaB by the antioxidant WR-1065 is accompanied by a reduced expression of the oncogene c-myc and an enhanced expression of the antioxidant gene MnSOD, a gene whose expression in tumor cells is relatively low, but when overexpressed has been correlated with a suppression of the malignant phenotype. Activation of NFkappaB by WR-1065, however, results in selective rather than global changes in the expression of genes containing NFkappaB-responsive elements.

Amifostine does not protect malignant lymphoma cell lines from the cytotoxic effects of various chemotherapeutics in vitro

The effect of amifostine on the cytotoxicity of melphalan, BCNU, doxorubicin and etoposide in lymphoma cell lines; HTB-61 (Burkitt), HTB-142 (nonspesified neck lymphoma), HTB-146 (Hodgkin's) and HTB 176 (Sezarýs syndrome) and a normal human fibroblast cell line was studied in vitro. Amifostine decreased etoposide induced cell kill in the fibroblast cell line. Pretreatment with the same amifostine concentration did not decrease the cytotoxic effects of etoposide, doxorubicin, melphalan and carmustine in lymphoma cell lines. Moreover, it even enhanced the cell killing effects of chemotherapeutics in especially HTB61 cell line. Our results indicate that amifostine does not decrease cytotoxicity of the chemotherapeutics and favor the testing of this drug in accordance with lymphoma treatments in clinical trials.

Activation of NFkappaB and MnSOD gene expression by free radical scavengers in human microvascular endothelial cells

The effect of nonprotein thiol (NPT) free radical scavengers WR-1065 (SH) and WR-33278 (SS), the active thiol and disulfide metabolites of amifostine, N-acetylcysteine (NAC; both L- and D- isomers), mesna, captopril, and dithiothreitol (DTT) on NFkappaB activation in human microvascular endothelial cells (HMEC) was investigated and contrasted to TNFalpha. The use of each of these NPTs at millimolar concentrations independent of oxidative damage-inducing agents resulted in a marked activation of NFkappaB, with the maximum effect observed between 30 min and 1 h after treatment. Only the SH and SS forms of amifostine, however, were effective in activating NFkappaB when administered at micromolar levels. Using a supershift assay, SH and SS equally affected the p50-p65 heterodimer, but not homodimers or heterodimers containing p52 or c-Rel subunits of NFkappaB. Neither catalase nor pyruvate when added to the culture medium to minimize hydrogen peroxide production had an effect on NFkappaB activation by SH. Thus, while oxidative damage is known to activate NFkappaB, the intracellular redox environment may also be affected by the addition of free radical scavenging agents such as NPT, and these in turn are capable of activating the redox sensitive transcription factor NFkappaB. There does not appear to be a significant role, if any, for the production of H(2)O(2) as an intermediate step in the activation of NFkappaB by either the SH or the SS form of amifostine. Rather, the underlying mechanism of action, especially for the SS form, may be related to the close structural and functional similarities of these agents to polyamines, which have been reported to be capable of activating NFkappaB. In contrast to TNFalpha, exposure of cells to either 40 microM or 4 mM of SH for 30 min did not induce intercellular adhesion molecule-1 (ICAM-1) gene expression, but did increase manganese superoxide dismutase (MnSOD) gene expression. MnSOD expression rose by 2-fold and remained elevated from 4 to 22 h following SH exposure.

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.

Bone marrow purging by photodynamic treatment in children with acute leukemia: cytoprotective action of amifostine

In order to evaluate the combined effect of Amifostine and Merocyanine 540 during photoirradiation in neoplastic cells, bone marrow cells from children with acute leukemia (AL), age-matched controls as well as HL-60 cell line were studied. Cell suspensions were incubated with Amifostine, then with MC 540 and they were subsequently exposed to different irradiation doses by Argon Laser 514 nm. Cell survival was estimated by trypan blue supravital stain following a 24-h incubation. The leukemic cell line was studied in continuous liquid cell cultures for 4 weeks. The survival of normal bone marrow progenitors has been estimated by colony formation assay in methylcellulose cultures. Our results showed that Amifostine enhances the photokilling effect of MC 540 on leukemic cells and significantly protects bone marrow nucleated and committed progenitors (BFU-E and CFU-GM) from children with AL under chemotherapy. In conclusion, Amifostine seems to be a promising cytoprotective agent in the clinical use of purging with MC 540 mediated phototherapy.

Cytoprotection by WR-1065, the active form of amifostine, is independent of p53 status in human malignant glioma cell lines

PURPOSE

This study tests the hypothesis that p53 status, i.e. wild type versus mutant form, is a determinant in radiation protection of human glioma cells by WR-1065, the active thiol form of amifostine (WR-2721).

MATERIALS AND METHODS

The cytoprotective effectiveness of WR-1065 when present during irradiation was investigated using four well-characterized human glioma cell lines. The p53 positive lines were U87 and D54, and the mutant p53 lines were U251 (mutant at codon 273; CGT/CAT; Arg/His) and A172 (mutant at codon 242; TGC/TTC; Cys/Phe). Treatment conditions included exposure of cells to a range of doses (0-10Gy) alone or in combination with 4mM of WR-1065 added 30min prior to irradiation. Resultant survival curves were obtained using a clonogenic assay and protection factors, the ratio of terminal slopes +/- WR-1065, were determined for each glioma cell line.

RESULTS

The Do values of wild-type U87 and D54 were 1.62 and 1.89Gy while those of p53 mutants U251 and A172 were 1.64 and 1.68 Gy, respectively. Protection factors were determined to be 2.4 and 1.9 for U87 and D54, and 2.6 and 2.8 for U251 and A172, respectively.

CONCLUSIONS

The p53 status of the four human glioma cell lines tested was not a predictor for either their relative sensitivity to ionizing radiation or ability to be protected by WR-1065. It is concluded that cytoprotection exhibited by cells exposed to WR-1065 during irradiation is independent of their p53 status.

The cytoprotective aminothiol WR1065 activates p21waf-1 and down regulates cell cycle progression through a p53-dependent pathway

The phosphoaminothiol WR1065, the active metabolite of the pro-drug amifostine (WR2721), protects cultured cells and tissues against cytotoxic exposure to radiation or chemotherapeutic agents. We show here that WR1065 and the pro-drug WR2721 activate the p53 tumor suppressor protein and induce the expression of the cyclin-dependent kinase inhibitor p21waf-1 in the breast cancer cell line MCF-7, and in the mouse fibroblast cell line balb/c 3T3. Using two MCF-7 derived cell lines, MN1 and MDD2, we show that induction of p21waf-1 is detectable in MN1 (expressing a functional p53) but not in MDD2 (p53 disabled). These effects are observed at concentrations of WR1065 (0.5 to 1 mM) identical to those required to protect against cytotoxicity by hydrogen peroxide. Induction of p53 is not prevented by addition of aminoguanidine, an inhibitor of Cu-dependent amine-oxidases which blocks the extra-cellular degradation of WR1065 into toxic metabolites. Moreover, spermidine, a natural polyamine structurally related to amifostine, does not activate p53. Induction of p53 by WR1065 results in a delay in the G1/S transition in MCF-7 and MN-1 cells, but not in the p53 disabled cells MDD2. These data indicate that WR1065, a polyamine analog with thiol anti-oxidant properties, activates a cell cycle check-point involving p53.

Inhibitory effects of WR-2721 and cysteamine on tumor initiation in mammary glands of pregnant rats by radiation

We evaluated the effect of WR-2721 [S-2-(3-aminopropylamino)-ethylphosphorothioic acid] and cysteamine (2-mercaptoethylamine) on the development of radiation-induced mammary tumors in rats. Pregnant rats were treated with WR-2721 or cysteamine 30 min prior to whole-body irradiation with gamma rays from a (60)Co source at a dose of 1.5 or 2.6 Gy. Additional pregnant rats were given saline and then exposed to gamma rays at a dose of 0, 1.5 or 2.6 Gy as a control. All rats were implanted with pellets of diethylstilbestrol, a tumor promoter, 1 month after termination of nursing and were observed for 1 year to detect palpable mammary tumors. No mammary tumors developed in the saline-injected nonirradiated rats. However, when rats were irradiated with 1.5 or 2. 6 Gy after saline treatment, the incidence of mammary tumors was high (71.4 and 92.3%, respectively). Administration of WR-2721 or cysteamine prior to irradiation with 1.5 Gy significantly decreased the tumor incidence (23.8 and 20.8%, respectively). Tumor prevention by either agent was less effective at the higher dose. The appearance of the first mammary tumor occurred later in rats treated with WR-2721 or cysteamine than in the control rats. An increasing rate of adenocarcinoma in the control group was observed with increasing dose from 1.5 Gy up to 2.6 Gy. However, the development of adenocarcinoma did not increase after pretreatment with WR-2721 or cysteamine in rats irradiated with 2.6 Gy. Many of the mammary tumors that developed in the control rats were of the ER(+)PgR(+) type. Administration of WR-2721 produced no tumors of the ER(+)PgR(+) type. Cysteamine treatment increased the development of ER-negative tumors. The serum concentration of progesterone was significantly higher in rats treated with WR-2721 or cysteamine than in the control rats. On the other hand, the estradiol-17beta concentration was reduced by treatment with WR-2721, but not significantly compared to the control. WR-2721 and cysteamine had no effect on the prolactin concentration of the irradiated rats. The results suggest that administration of WR-2721 or cysteamine prior to the irradiation has a potent preventive effect on theinitiation phase during mammary tumorigenesis.

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.