Clinical trials of WR-2721 and cis-platinum

The Role of Low-Energy Electron Interactions in cis-Pt(CO)2Br2 Fragmentation

Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo- and secondary electrons that determine the reaction paths of the respective radiation sensitizers. In the latter case, low-energy secondary electrons determine the deposition chemistry. In this contribution, we present a combined experimental and theoretical study on the role of LEE interactions in the fragmentation of the Pt(II) coordination compound cis-PtBr₂(CO)₂. We discuss our results in conjunction with the widely used cancer therapeutic Pt(II) coordination compound cis-Pt(NH₃)₂Cl₂ (cisplatin) and the carbonyl analog Pt(CO)₂Cl₂, and we show that efficient CO loss through dissociative electron attachment dominates the reactivity of these carbonyl complexes with low-energy electrons, while halogen loss through DEA dominates the reactivity of cis-Pt(NH₃)₂Cl₂.

Use of Amifostine for Cytoprotection during Radiation Therapy: A Review

BACKGROUND

Radiation therapy is a cornerstone of the therapeutic modalities used in modern oncology. However, it is sometimes limited in its ability to achieve optimal tumor control by radiation-induced normal tissue toxicity. In delivering radiation therapy, a balance must be achieved between maximizing the dose to the tumor and minimizing any injury to the normal tissues. Amifostine was the first Food and Drug Administration (FDA)-approved clinical radiation protector intended to reduce the impact of radiation on normal tissue, lessening its toxicity and potentially allowing for increased tumor dose/control. Despite being FDA-approved almost 20 years ago, Amifostine has yet to achieve widespread clinical use.

SUMMARY

A thorough review of Amifostine's development, mechanism of action, and current clinical status were conducted. A brief history of Amifostine is given, from its development at Walter Reid Institute of Research to its approval for clinical use. The mechanism of action of Amifostine is explored. The results of a complete literature review of all prospective randomized trials to date involving the use of Amifostine in radiation therapy are presented. The results are arranged by treatment site and salient findings discussed. Side effects and complications to consider in using Amifostine are reviewed. Key Messages: Amifostine has been explored as a radiation protectant in most radiation treatment sites. Studies have demonstrated efficacy of Amifostine in all treatment sites reviewed, but results are heterogeneous. The heterogeneity of studies looking at Amifostine as a clinical radiation protectant has precluded a definitive answer on its efficacy. Complicating its clinical use is its toxicity and delivery requirements. Amifostine has largely fallen out of use with the advent of intensity modulated radiation therapy (IMRT). However, side effects with IMRT remain a challenge and concern. The use of Amifostine in the IMRT era has been poorly explored and is worthy of future study.

Tuning the metabolism of the anticancer drug cisplatin with chemoprotective agents to improve its safety and efficacy

Numerous in vivo studies have shown that the severe toxic side-effects of intravenously administered cisplatin can be significantly reduced by the co-administration of sulfur-containing 'chemoprotective agents'. Using a metallomics approach, a likely biochemical basis for these potentially useful observations was only recently uncovered and appears to involve the reaction of chemoprotective agents with cisplatin-derived Pt-species in human plasma to form novel platinum-sulfur complexes (PSC's). We here reveal aspects of the structure of two PSC's and establish the identification of an optimal chemoprotective agent to ameliorate the toxic side-effects of cisplatin, while leaving its antineoplastic activity largely intact, as a feasible research strategy to transform cisplatin into a safer and more effective anticancer drug.

Pathophysiology of cisplatin-induced acute kidney injury

Cisplatin and other platinum derivatives are the most widely used chemotherapeutic agents to treat solid tumors including ovarian, head and neck, and testicular germ cell tumors. A known complication of cisplatin administration is acute kidney injury (AKI). The nephrotoxic effect of cisplatin is cumulative and dose-dependent and often necessitates dose reduction or withdrawal. Recurrent episodes of AKI may result in chronic kidney disease. The pathophysiology of cisplatin-induced AKI involves proximal tubular injury, oxidative stress, inflammation, and vascular injury in the kidney. There is predominantly acute tubular necrosis and also apoptosis in the proximal tubules. There is activation of multiple proinflammatory cytokines and infiltration of inflammatory cells in the kidney. Inhibition of the proinflammatory cytokines TNF-α or IL-33 or depletion of CD4+ T cells or mast cells protects against cisplatin-induced AKI. Cisplatin also causes endothelial cell injury. An understanding of the pathogenesis of cisplatin-induced AKI is important for the development of adjunctive therapies to prevent AKI, to lessen the need for dose decrease or drug withdrawal, and to lessen patient morbidity and mortality.

Interventions for preventing neuropathy caused by cisplatin and related compounds

BACKGROUND

Cisplatin and several related antineoplastic drugs used to treat many types of solid tumours are neurotoxic, and most patients completing a full course of cisplatin chemotherapy develop a clinically detectable sensory neuropathy. Effective neuroprotective therapies have been sought.

OBJECTIVES

To examine the efficacy and safety of purported chemoprotective agents to prevent or limit the neurotoxicity of cisplatin and related drugs.

SEARCH METHODS

On 4 March 2013, we searched the Cochrane Neuromuscular Disease Group Specialized Register, CENTRAL, MEDLINE, EMBASE, LILACS, and CINAHL Plus for randomised trials designed to evaluate neuroprotective agents used to prevent or limit neurotoxicity of cisplatin and related drugs among human patients.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs in which the participants received chemotherapy with cisplatin or related compounds, with a potential chemoprotectant (acetylcysteine, amifostine, adrenocorticotrophic hormone (ACTH), BNP7787, calcium and magnesium (Ca/Mg), diethyldithiocarbamate (DDTC), glutathione, Org 2766, oxcarbazepine, or vitamin E) compared to placebo, no treatment, or other treatments. We considered trials in which participants underwent evaluation zero to six months after completing chemotherapy using quantitative sensory testing (the primary outcome) or other measures including nerve conduction studies or neurological impairment rating using validated scales (secondary outcomes).

DATA COLLECTION AND ANALYSIS

Two review authors assessed each study, extracted the data and reached consensus, according to standard Cochrane methodology.

MAIN RESULTS

As of 2013, the review includes 29 studies describing nine possible chemoprotective agents, as well as description of two published meta-analyses. Among these trials, there were sufficient data in some instances to combine the results from different studies, most often using data from secondary non-quantitative measures. Nine of the studies were newly included at this update. Few of the included studies were at a high risk of bias overall, although often there was too little information to make an assessment. At least two review authors performed a formal review of an additional 44 articles but we did not include them in the final review for a variety of reasons.Of seven eligible amifostine trials (743 participants in total), one used quantitative sensory testing (vibration perception threshold) and demonstrated a favourable outcome in terms of amifostine neuroprotection, but the vibration perception threshold result was based on data from only 14 participants receiving amifostine who completed the post-treatment evaluation and should be regarded with caution. Furthermore the change measured was subclinical. None of the three eligible Ca/Mg trials (or four trials if a single retrospective study was included) described our primary outcome measures. The four Ca/Mg trials included a total of 886 participants. Of the seven eligible glutathione trials (387 participants), one used quantitative sensory testing but reported only qualitative analyses. Four eligible Org 2766 trials (311 participants) employed quantitative sensory testing but reported disparate results; meta-analyses of three of these trials using comparable measures showed no significant vibration perception threshold neuroprotection. The remaining trial reported only descriptive analyses. Similarly, none of the three eligible vitamin E trials (246 participants) reported quantitative sensory testing. The eligible single trials involving acetylcysteine (14 participants), diethyldithiocarbamate (195 participants), oxcarbazepine (32 participants), and retinoic acid (92 participants) did not perform quantitative sensory testing. In all, this review includes data from 2906 participants. However, only seven trials reported data for the primary outcome measure of this review, (quantitative sensory testing) and only nine trials reported our objective secondary measure, nerve conduction test results. Additionally, methodological heterogeneity precluded pooling of the results in most cases. Nonetheless, a larger number of trials reported the results of secondary (non-quantitative and subjective) measures such as the National Cancer Institute Common Toxicity Criteria (NCI-CTC) for neuropathy (15 trials), and these results we pooled and reported as meta-analysis. Amifostine showed a significantly reduced risk of developing neurotoxicity NCI-CTC (or equivalent) ≥ 2 compared to placebo (RR 0.26, 95% CI 0.11 to 0.61). Glutathione was also efficacious with an RR of 0.29 (95% CI 0.10 to 0.85). In three vitamin E studies subjective measures not suitable for combination in meta analysis each favoured vitamin E. For other interventions the qualitative toxicity measures were either negative (N-acetyl cysteine, Ca/Mg, DDTC and retinoic acid) or not evaluated (oxcarbazepine and Org 2766).Adverse events were infrequent or not reported for most interventions. Amifostine was associated with transient hypotension in 8% to 62% of participants, retinoic acid with hypocalcaemia in 11%, and approximately 20% of participantss withdrew from treatment with DDTC because of toxicity.

AUTHORS' CONCLUSIONS

At present, the data are insufficient to conclude that any of the purported chemoprotective agents (acetylcysteine, amifostine, calcium and magnesium, diethyldithiocarbamate, glutathione, Org 2766, oxcarbazepine, retinoic acid, or vitamin E) prevent or limit the neurotoxicity of platin drugs among human patients, as determined using quantitative, objective measures of neuropathy. Amifostine, calcium and magnesium, glutathione, and vitamin E showed modest but promising (borderline statistically significant) results favouring their ability to reduce the neurotoxicity of cisplatin and related chemotherapies, as measured using secondary, non-quantitative and subjective measures such as the NCI-CTC neuropathy grading scale. Among these interventions, the efficacy of only vitamin E was evaluated using quantitative nerve conduction studies; the results were negative and did not support the positive findings based on the qualitative measures. In summary, the present studies are limited by the small number of participants receiving any particular agent, a lack of objective measures of neuropathy, and differing results among similar trials, which make it impossible to conclude that any of the neuroprotective agents tested prevent or limit the neurotoxicity of platinum drugs.

Amifostine protective effect on cisplatin-treated rat testis

Cisplatin is a potent drug used in clinical oncology but causes spermatogenesis damage. Amifostine is a drug used against toxicity caused by ionizing irradiation and chemotherapeutic drugs. Since cisplatin provokes fertility and induces germ cell apoptosis and necrosis, we proposed to evaluate the amifostine cytoprotective action on testes of cisplatin-treated rats. Thirty-day-old prepubertal Wistar rats received a single cisplatin dose of 5 mg/kg and were killed after 3, 6, and 12 hr. The hematoxylin-eosin stained testicular sections were submitted to histological, morphometric, and stereological analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) method was used to label apoptotic cells. TUNEL-positive and TUNEL-negative germ cells with abnormal nuclear morphology (ANM) were scored. Significant alterations of greater part of the parameters occurred in the cisplatin-treated group (CE) compared to the group that received amifostine before the cisplatin-treatment (ACE); however, testicular weight and volume did not vary between these groups. Tubular diameter was reduced in CE in comparison to ACE rats, while interstitial tissue and lymphatic space volume and volume density were significantly higher in CE rats; interstitial testicular edema probably occurred in cisplatin-treated rats. CE rats showed important histological alterations, which were more accentuated than in ACE rats. The numerical densities of apoptotic germ cells and TUNEL-negative cells with ANM were lower in ACE than in CE rats. In conclusion, the amifostine previously administered to prepubertal rats reduced the testicular damage caused by cisplatin. We conclude that amifostine partially protected the rat seminiferous epithelium against cisplatin toxicity.

A pilot study of addition of amifostine to melphalan, carboplatin, etoposide, and cyclophosphamide with autologous hematopoietic stem cell transplantation in pediatric solid tumors-A pediatric blood and marrow transplant consortium study

Limited information is available regarding the use of amifostine in pediatric hematopoietic stem cell transplant (HSCT) patients. Melphalan, carboplatin, etoposide +/- cyclophosphamide is a commonly used preparatory regimen in pediatric solid tumor HSCT. Therefore, we decided to determine the feasibility of the addition of amifostine (750 mg/m b.i.d. x 4 d) to melphalan (200 mg/m), carboplatin (1200 mg/m), and etoposide (800 mg/m) (level 1) and escalating doses of cyclophosphamide (3000 mg/m and 3800 mg/m, levels 2 and 3, respectively) followed by autologous HSCT. Thirty-two patients with a variety of pediatric solid tumors were studied. Seventeen patients were accrued at level 1, 9 at level 2, and 6 at level 3. Major toxicities during the administration of the preparatory regimen were hypocalcemia, emesis, and hypotension. Hypocalcemia required aggressive calcium supplementation during the conditioning phase. No dose limiting toxicities were encountered at level 3. Amifostine at 750 mg/m b.i.d. for 4 days can be administered with a double alkylator regimen consisting of melphalan (200 mg/m), cyclophosphamide (up to 3800 mg/m), carboplatin (1200 mg/m), and etoposide (800 mg/m) with manageable toxicities.

Cytoprotective Agents Used in the Treatment of Patients With Cancer

OBJECTIVE

To provide a review of the literature of commonly prescribed cytoprotective agents used in the treatment of patients with cancer.

DATA SOURCES

Journal articles, research reports, review articles, and web sites.

CONCLUSION

Multiple agents have been theorized to have cytoprotective properties. Significant evidence exists supporting the use of some cytoprotective agents approved by the US Food and Drug Administration (FDA). More research is needed to determine the efficacy of new cytoprotective agents and expanded indications for those agents currently used.

IMPLICATIONS FOR NURSING PRACTICE

Knowledge of the indications for and side effect profiles of cytoprotective agents is a necessary component of oncology nursing care. Familiarity with evidence-based research that supports or refutes the use of FDA-approved cytoprotective agents or alternative agents is helpful when suggesting, prescribing, or administering such agents.

WR-2721 (Amifostine) ameliorates cisplatin-induced hearing loss but causes neurotoxicity in hamsters: dose-dependent effects

Chemoprotective agents reduce the toxic side effects of chemotherapy agents such as cisplatin. The conventional belief is that the chemoprotective agent WR-2721 (Amifostine), while protecting against most cisplatin-induced side effects, does not protect against cisplatin-induced ototoxicity (i.e., hearing loss). There is no knowledge, however, about the efficacy of high doses of WR-2721 (WR) in possibly protecting against cisplatin-induced ototoxicity. Thus, the dose-dependent effects of WR in possibly ameliorating cisplatin-induced ototoxicity were investigated. Hamsters were given a series of 5 cisplatin injections (3 mg/kg/injection once every other day, i.p.) either alone or in combination with 18, 40, 80, or 400 mg/kg/injection of the rescue agent WR ( n = 5 or 10/group). Other groups received either 80 mg/kg/injection WR alone ( n = 5) or were untreated ( n = 14). Ototoxicity was assessed by auditory brain stem responses (ABR). WR provided dose-dependent rescue from cisplatin's ototoxicity with no protection at the low dose of 18 mg/kg, moderate protection at 40 mg/kg, and nearly complete protection at 80 and 400 mg/kg. However, WR doses of 40 mg/kg or higher caused neurotoxicity as evidenced by prolongations in the ABR's interpeak latencies. Thus, high doses of WR provided the beneficial effect of protecting against cisplatin-induced ototoxicity, but had the harmful side effect of neurotoxicity. Previous failures to find chemoprotection from cisplatin-induced ototoxicity were likely due to the use of WR doses that were too small. The clinical implications of the beneficial and harmful effects of high doses of WR are discussed.

Comparative study between the interaction of dephosphorylated amifostine (WR-1065) and amoxicilline with pBR322 in absence and presence of cisplatin by AFM

The effect of the amoxicilline as a possible cisplatin-action protector on pBR322 DNA has been visually studied by atomic force microscopy in comparison with the modifications caused by the controversed cisplatin protector amifostine. Incubation of amoxicilline with the plasmid DNA showed aggregation and compaction of DNA. Cisplatin incubated in the same conditions with DNA produced kinks and super-coiling of the circular form. In the case of previous treatment of DNA with amoxicilline, the characteristic effect of cisplatin is only partially observed. The amoxicilline seemed to control the action of cisplatin on DNA. The initial effect of dephosphorylated amifostine (WR-1065) when this protector was incubated with the plasmid was also the formation of aggregates and the compaction of DNA. However, addition of cisplatin successively after 1 and 2 h showed the characteristic modification caused by cisplatin but only in a decreasing percentage of molecules of DNA. Both molecules, amoxicilline and WR-1065 seem to control the strong direct action of cisplatin on DNA. This effect can justify the role as protecting agent of amifostine on side effects caused by cisplatin and can open new possibilities to other agents like amoxicilline.

A Phase II trial of cisplatin plus WR-2721 (amifostine) for metastatic breast carcinoma: an Eastern Cooperative Oncology Group Study (E8188)

BACKGROUND

Cisplatin has minimal antitumor activity when used as second- or third-line treatment of metastatic breast carcinoma. Older reports suggest an objective response rate of 8% when 60-120 mg/m2 of cisplatin is administered every 3-4 weeks. Although a dose-response effect has been observed with cisplatin, the dose-limiting toxicities associated with cisplatin (e.g., nephrotoxicity, ototoxicity, and neurotoxicity) have limited its use as a treatment for breast carcinoma. WR-2721 or amifostine initially was developed to protect military personnel in the event of nuclear war. Amifostine subsequently was shown to protect normal tissues from the toxic effects of alkylating agents and cisplatin without decreasing the antitumor effect of the chemotherapy. Early trials of cisplatin and amifostine also suggested that the incidence and severity of cisplatin-induced nephrotoxicity, ototoxicity, and neuropathy were reduced.

METHODS

A Phase II study of the combination of cisplatin plus amifostine was conducted in patients with progressive metastatic breast carcinoma who had received one, but not more than one, chemotherapy regimen for metastatic disease. Patients received amifostine, 910 mg/m2 intravenously over 15 minutes. After completion of the amifostine infusion, cisplatin 120 mg/m2 was administered over 30 minutes. Intravenous hydration and mannitol was administered before and after cisplatin. Treatment was administered every 3 weeks until disease progression.

RESULTS

Forty-four patients were enrolled in the study of which 7 (16%) were ineligible. A median of 2 cycles of therapy was administered to the 37 eligible patients. Six partial responses were observed for an overall response rate of 16%. Most patients (57%) stopped treatment because of disease progression. Neurologic toxicity was reported in 52% of patients. Seven different life-threatening toxicities were observed in patients while receiving treatment.

CONCLUSIONS

The combination of cisplatin and amifostine in this study resulted in an overall response rate of 16%. Neither a tumor-protective effect nor reduced toxicity to normal tissues was observed with the addition of amifostine to cisplatin in this trial.

WR-2721: inhibitor of cisplatin-induced micronuclei

The modulatory effect of S-2-/3-aminopropylamino/ethyl-phosphorothioic acid, (WR-2721, Amifostine) on induction of micronuclei by cis-diamminedichloroplatinum[II] (CDDP) was studied. The adult, male Swiss mice were treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, and/or with CDDP, at a dose 5 mg/kg or 10 mg/kg body weight. WR-2721 was given alone or 30 min before CDDP administration. The frequency of micronucleated polychromatic erythrocytes (MNPCEs) and also the number of polychromatic erythrocytes (PCEs) in the bone marrow and peripheral blood, at 24 h after the drug application, were determined. After administration of CDDP, the frequency of MNPCEs distinctly increased, and the number of PCEs decreased. As compared with the animals injected with CDDP only, in mice treated with WR-2721 before CDDP application, the number of MNPCEs was reduced and the frequency of PCEs was increased. However, WR-2721 given alone, without subsequent administration of cis-diamminedichloroplatinum[II], caused an increase in the number of micronucleated polychromatic erythrocytes and a decrease in the number of PCEs. The geno- and cyto-toxicity and chemoprotection were dependent on the doses of the agents WR-2721 and CDDP applied. In mice injected with CDDP and/or WR-2721, the patterns of changes in the frequency of MNPCEs and PCEs were similar in the bone marrow and peripheral blood, respectively. The protective effect of the aminothiol compound WR-2721 against induction of micronuclei and apoptotic cell death in the erythropoietic system by CDDP was shown.

Protection from toxicant-mediated renal injury in the rat with anti-CD54 antibody

BACKGROUND

The benefit of the potent chemotherapeutic agent cisplatin in treating neoplasms is limited by nephrotoxicity. We tested the hypothesis that CD54 [intercellular adhesion molecule-1 (ICAM-1)] is an important mediator in cisplatin-mediated renal failure.

METHODS

The effect of a monoclonal anti-CD54 antibody was evaluated in a rat model of cisplatin toxicity. Renal function, histopathology, renal myeloperoxidase activity, and mortality were determined in the anti-CD54 and placebo groups.

RESULTS

Renal CD54 mRNA expression was markedly increased by 24 hours after exposure to cisplatin in mice. An improvement in renal function, mortality, and histological abnormalities was evident in animals exposed to cisplatin and treated with anti-CD54 antibody (mAb). Seven days after the administration of cisplatin, the mean creatinine was 0.65+/-0.05 mg/dl in the rats that received anti-CD54 mAb and 4.76+/-1.42 in control animals (P<0.02). Mortality was lower in experimental animals (0 vs. 29% in control rats seven days following cisplatin, P<0.04). Histological evidence of cell injury was markedly attenuated (P<0.04) in the treated compared with the control rats.

CONCLUSION

CD54 may be critical in the pathophysiology of renal injury following cisplatin, perhaps by its effects on leukocyte-endothelial interactions.

Effects of amifostine on cisplatin induced DNA adduct formation and toxicity in malignant glioma and normal tissues in rat

The chemoprotective effect of amifostine (WR2721) was studied in a BDIX rat model with intracerebral BT4C glioma implants. Twenty-one rats were given cisplatin 5 mg/kg i.p., 21 were given amifostine 200 mg/kg i.p. + cisplatin 5 mg/kg i.p. Ten rats served as untreated controls. An immunohistochemical method for analysis of cisplatin-DNA adducts was used to elucidate the adduct formation in tumor, normal brain and kidney. Tumor volume and serum creatinine level were analysed 10 days after treatment. In animals pretreated with amifostine there was a delayed adduct formation rate in the normal brain, and in the kidney cortex the number of tubular cells with extremely high adduct level was reduced. No difference in adduct formation was seen in tumors. Tumor volume was significantly larger following amifostine + cisplatin (66% of controls) compared to cisplatin alone (38% of controls). Weight loss was, however, severe in rats given cisplatin alone. In the tumor growth study only 3 out of 11 rats treated with cisplatin 5 mg/kg alone survived until time of sacrifice at 10 days, whereas all those pretreated with amifostine survived. Mean serum creatinine was 48 micromol/l (controls), 146 micromol/l (cisplatin) and 59 micromol/l (amifostine + cisplatin). A marked reduction of histopathological renal changes was found when amifostine was added. Amifostine thus significantly reduced general and renal toxicity of cisplatin. The tumor growth retardation was stronger when cisplatin was given alone but this is probably related to general toxicity and malnutrition indirectly supported by the fact that amifostine did not significantly reduce cisplatin-DNA adduct formation in tumors. The results of the present study suggest that amifostine may have a role in increasing the therapeutic ratio of cisplatin, also in the treatment of malignant glioma.

Reducing the toxicity of anticancer therapy: new strategies

Cytoprotective agents offer opportunities to reduce the treatment-related toxicity of anticancer therapy and perhaps to increase the dose and dose intensity of radiation and chemotherapy. One such agent is amifostine, an organic thiophosphate. Amifostine selectively protects normal tissues and provides broad-spectrum protection for a variety of organs while remaining minimally toxic. Clinical studies have demonstrated that amifostine protects against myelotoxicity, nephrotoxicity, neurotoxicity, mucositis and esophagitis in patients treated with alkylating and platinum agents, paclitaxel and radiation therapy. In addition, preclinical studies suggest the possibility of protection against anthracycline-induced cardiotoxicity and radiation- and chemotherapy-induced mutagenicity. Preclinical and clinical studies have not demonstrated any diminution of antitumor efficacy. Amifostine is well tolerated in doses of 740 or 910 mg/m2. The most common side effects requiring treatment are transient hypotension, which responds to intravenous fluids, and nausea and vomiting, effectively treated with 5-HT3 antagonists and dexamethasone.

Pharmacokinetics of cisplatin with and without amifostine in tumour-bearing nude mice

Amifostine (Ethyol, WR-2721) is in use in the clinic as a protector against platinum-induced toxicities. We have previously reported that amifostine induced a potentiation of the antitumour activity of carboplatin in human ovarian cancer xenografts. An influence of amifostine on the pharmacokinetics of carboplatin, resulting in higher platinum concentrations in plasma and tissues of the tumour-bearing nude mice, was thought to be the cause of enhancement of the antitumour activity. Therefore, the pharmacokinetics of cisplatin were investigated in tumour-bearing nude mice treated with cisplatin alone or in combination with amifostine. A significant increase in the area under the curve (AUC) of the total platinum concentration in mice treated with amifostine was only observed in the kidney (from 355 to 398 nmol h/g), whereas in the other tissues and plasma no significant changes were measured. The selective protection of normal tissues by amifostine was confirmed by a decrease in the AUC of the cisplatin-DNA adduct levels in normal tissues. The decrease was only significant in the liver (282-240 fmol h/microgram DNA), whereas in tumour tissue a slight increase in the AUC of the cisplatin-DNA adducts could be detected (91.3-110.1 fmol h/microgram DNA). The minor influence of amifostine on the pharmacokinetics of cisplatin may be the reason why amifostine did not potentiate the antitumour activity of cisplatin. The influence of amifostine on cisplatin-DNA adduct levels in normal tissues versus tumour tissues is further evidence for the usefulness of this toxicity modulator in cancer patients.

Phase II evaluation of cisplatin and WR2721 for refractory metastatic breast cancer

Cisplatin, as second-line therapy for metastatic breast cancer (MBC), has at best shown only modest response rates. At high doses, the toxicity profile of this drug may outweigh any potential benefits for MBC patients. We performed a phase II study to determine whether the investigational agent WR2721 would mitigate the toxicity of cisplatin in patients with MBC and to assess the antitumor response of cisplatin as salvage therapy. Thirteen women were enrolled in the study. Cisplatin was administered at a dose of 120 mg/m2 together with WR2721 at a dose of 910 mg/m2 intravenously every 21 days. Response was assessed at the end of two cycles, and toxicity was evaluated after each treatment cycle. No objective antitumor responses were noted. Three patients exhibited toxicity from cisplatin in the form of ototoxicity, nephrotoxicity, myelotoxicity, and persistent delayed nausea and vomiting necessitating discontinuation from the study. There was one death from renal failure. WR2721 itself caused significant but transient hypotension in 46% of the patients. In our experience, salvage chemotherapy with cisplatin in pretreated patients with MBC produced no objective responses. WR2721 did not prevent the occurrence of organ toxicity.

Co-administration of the neurotrophic ACTH(4-9) analogue, ORG 2766, may reduce the cochleotoxic effects of cisplatin

In this study the effect of the neurotrophic ACTH(4-9) analogue, ORG 2766, on cisplatin cochleotoxicity was investigated with both light- and transmission electron microscopy. Guinea pigs were treated with either cisplatin+ORG 2766 (n = 11) or cisplatin + physiological saline (n = 9). All animals treated with cisplatin + physiological saline showed complete loss of outer hair cells (OHC) and degeneration of the organ of Corti in the basal cochlear turns, while partial OHC loss was found in the middle and apical turns. The inner hair cells (IHC) and other cochlear tissues were not affected. Eight animals from the group treated with cisplatin + ORG 2766 demonstrated similar pathological changes, but to a lesser degree, especially in the middle turns. The three remaining animals demonstrated no cochlear alterations at all, light-microscopically, and only minor subcellular changes in the OHCs at the ultrastructural level. Electrophysiologically, these three animals showed normals compound action potential (CAP) amplitudes at stimulus frequencies from 0.5 to 16 kHz and normal cochlear microphonics (CM) in the frequency range from 0.5 to 8 kHz. The other animals treated with cisplatin + ORG 2766 showed a severe loss in their CAPs and CM, except for one showing intermediate loss. All animals from the group treated with cisplatin alone showed a severe loss in their CAPs and CM. Endolymphatic hydrops was present in all animals from the cisplatin- and the cisplatin + ORG 2766-treated groups. These data indicate that daily, concomitant administration of ORG 2766 may reduce OHC loss and subsequent degeneration of the organ of Corti in cisplatin-treated guinea pig cochleas.

Phase II trial of tirapazamine combined with cisplatin in chemotherapy of advanced malignant melanoma

PURPOSE

A phase II study was undertaken to determine the efficacy of tirapazamine (TPZ) combined with cisplatin (cDDP) in patients with metastatic melanoma.

PATIENTS AND METHODS

Between June 1994 and November 1995, 48 patients with metastatic melanoma were treated with TPZ (260 mg/m2, administered intravenously over two hours) followed in one-hour by cDDP (75 mg/m2 over one hour) every 21 days. Sixteen patients had received prior chemotherapy, and 13 of these had failed to respond to prior cDDP. None of the patients had symptomatic brain metastasis.

RESULTS

Nine patients had partial responses, with an overall response rate of 19% (95% confidence interval (95% CI) of 9%-33%). The median duration of response was six months. None of the responders had received prior chemotherapy. Responses were seen in 8 (33%, confidence interval of 16%-55%) of 24 patients with primary cutaneous melanoma who had received no prior chemotherapy and in the only patient with previously untreated conjunctival melanoma. There were no responders among the seven patients with choroidal melanoma and 16 patients with previously treated cutaneous melanoma. Two patients with partial responses were rendered free of gross disease surgically three months after completing eight courses of TPZ-cDDP; they remain free of tumor recurrence. Responses were seen in lymph nodes (27%), lung (26%), skin (20%), adrenal gland (20%), soft tissues (17%) and liver (17%). Common toxicities included muscle cramps, fatigue, gastrointestinal effects and peripheral neuropathy. Fatigue, nausea, vomiting, anorexia, and muscle cramps were grade 3 or 4 in less than 10% of the courses. Neutropenia and thrombocytopenia were rare.

CONCLUSION

The TPZ-cDDP combination has definite activity against chemotherapy-naïve patients with cutaneous melanoma and warrant further studies in combination with other cytotoxic agents.

Medical treatment of metastatic melanoma

The role of combination chemotherapy in the treatment of metastatic melanoma is still a matter of controversy because of the lack of prospective trials directly demonstrating increased response rates and improved survival compared with DTIC alone. Nevertheless, several three-drug regimens have reported response rates between 30% and 50% in single-institution studies. The duration of response medians of these regimens ranges between 6 and 9 months. However, the survival medians of 6 to 11 months are not substantially better than those of DTIC alone. However, survival at 1 and 2 years following initiation of therapy may more clearly demonstrate an impact of therapies for metastatic melanoma.

[Chemoprotectors. Mechanisms of action and clinical applications]

Toxicity of chemotherapy remains an important point in the care of patients with malignancies. Since a few years, new compounds without any intrinsic anti tumoral activity have been developed to decrease the toxicity or to enhance the activity of anti-cancer drugs. From those used against the toxic activity of anti-cancer drugs, two classes could be isolated: the chemoprotectors that interact through a specific of chemotherapy in normal cells, and the chemocorrectors that enhance the spontaneous recovery after exposition to cytotoxic drugs. The most widely used chemoprotector remains the 2-mercaptoethanesulfonate (mesna) which protects against the bladder toxicity of ifosfamide and cyclophosphamide. However, two new drugs, amifostine and dextrazoxane have been recently or will be approved in France against the toxicity of cisplatin and anthracyclines, respectively. Mechanism of action and clinical applications of these new drugs in cancer chemotherapy are reviewed.

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.

Audiological findings in a Phase I protocol investigating the effect of WR 2721, high-dose cisplatin and radiation therapy in patients with locally advanced cervical carcinoma

WR 2721 (ethiofos) protects against the toxic effects of the heavy metal compound cisplatin, which is used in the treatment of solid tumours. In a Phase I protocol designed to determine the maximum dose of WR 2721 which could be tolerated when administered in combination with cisplatin and radiation therapy to patients with cervical carcinoma, 11 patients were evaluated by audiologic testing before and after cisplatin WR 2721 administration in an attempt to identify the degree of ototoxicity. Forty-five per cent were noted to have significant hearing threshold changes, predominantly in the high frequencies. There were no significant changes in the speech frequencies in this series. This contrasts with the greater degrees of ototoxicity observed in controls treated in the same way who received cisplatin without WR 2721 protection.

Inhibition of the clastogenic effect of cyclophosphamide by WR-2721 in the bone marrow of mice

The frequency of micronucleated polychromatic erythrocytes in the bone marrow of Swiss mice treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, 15 or 30 min prior to cyclophosphamide (CP) administration, at a dose of 200 mg/kg body weight, was determined 24 h after CP treatment. In mice injected with CP, the number of micronuclei in polychromatic erythrocytes was significantly increased in comparison with the controls, and in mice treated with WR-2721 and CP, the frequency of micronucleated polychromatic erythrocytes was distinctly decreased in comparison to those given CP alone. The protective effect of WR-2721 against cyclophosphamide-induced clastogenicity was shown. The effect was dependent on the dose of the thiol agent given, and it was more expressed when WR-2721 was applied at the higher dose, 400 mg/kg body weight. However, the protection by the aminothiol appeared not to depend on the time intervals between WR-2721 and CP administration to the mouse organism.

Free-radical repair by a novel perthiol: reversible hydrogen transfer and perthiyl radical formation

2-(3-Aminopropyl-amino) ethaneperthiol (RSSH, the perthiol analogue of the thiol radioprotector, WR-1065) reacts with the alpha-hydroxy alkyl radical (CH3)2C.OH by donating a hydrogen atom as indicated by the characterization of perthiyl radicals (RSS.; lambda max approximately 374 nm, epsilon 374 approximately 1680 +/- 20 dm3 mol-1 cm-1) by pulse radiolysis. The perthiyl radical abstracts a hydrogen from the alcohol to establish a reversible hydrogen-transfer equilibrium. This equilibrium lies predominantly on the side of radical repair since the rate constants for the forward and reverse reactions at pH 4 are: kappa(RSSH+(CH3)2C.OH) = (2.4 +/- 0.1) x 10(9) dm3 mol-1 s-1 and kappa(RSS.+(CH3)2CHOH) = (3.8 +/- 0.3) x 10(3) dm3 mol-1 s-1 respectively. The pKa (RSSH<-->RSS(-)+H+) = 6.2 +/- 0.1 was determined from the pH dependence of the rate of perthiol repair. Identical experiments have been performed with WR-1065 allowing a direct comparison of free-radical repair reactivity to be made with the parthiol analogue. At pH approximately 7.4 the reactivities of the thiol and perthiol were similar, both repairing the alcohol radical with a rate constant of approximately (2.4 +/- 0.1) x 10(8) dm3 mol-1 s-1. However, at pH 5 whilst the hydrogen-donation rate of the thiol was 15-20% higher than at pH 7.4, the perthiol reactivity was over an order of magnitude higher. The thermodynamic driving force for the observed enhanced free-radical repair reactivity of RSSH compared to RSH is attributed to the resonance stabilization energy of 8.8 kJ mol-1 within the RSS. radical. These results indicate a possible application of RSSH/RSS- as DNA-targeted antioxidants or chemoprotectors.

Effects of the modulating agent WR2721 on myelotoxicity and antitumour activity in carboplatin-treated mice

The selective modulation of carboplatin [diammine(1,1-cyclo-butanedicarboxylato)platinum(II)]-induced myelotoxicity was investigated in mice, using the protective agent WR2721 [S-2-(3-aminopropylamino)ethyl-phosphorothioic acid, ethiofos]. In female BALB/c mice, WR2721 (200 mg/kg intraperitoneally, i.p.) partly prevented the reduction of in vitro proliferation of whole bone marrow cells and non-adherent cells when administered at different time points relative to 90 mg/kg carboplatin (i.p.). Protection was highest when WR2721 was administered 5 min prior to carboplatin. In vitro proliferation of whole bone marrow cells and non-adherent cells in liquid culture increased from 15% of control for carboplatin alone to 45% when WR2721 was administered 5 min prior to carboplatin. However, WR2721 did not significantly prevent the loss in clonogenic capacity of early hematopoietic progenitors in the bone marrow, as determined by a bilayered soft agar colony forming units assay. In nude mice, bearing well-established subcutaneous human ovarian carcinoma xenografts OVCAR-3, WR2721 (200 mg/kg i.p.) 5 min prior to intravenous carboplatin allowed a 1.5-fold increase in the maximum tolerated dose of carboplatin as determined by overall weight loss. WR2721 alone did not affect tumour growth. However, WR2721 had a potentiating effect on the tumour growth inhibition of a standard dose of carboplatin in this model. Minimal tumour volume compared to control (T/C) decreased from 9.4% with carboplatin alone to 2.2% with WR2721 5 min prior to the same dose of carboplatin. Specific growth delay (SGD) increased from 7.4 to 10.3. With the 1.5-fold increased, equitoxic dose of carboplatin in combination with WR2721, the antitumour activity was only slightly further increased (T/C = 1.4%, SGD = 10.5).

Randomized clinical trial of mitomycin-C with or without pretreatment with WR-2721 in patients with advanced colorectal cancer

The use of mitomycin for metastatic colorectal cancer has been limited by mitomycin's myelosuppressive potential. The objective of this randomized study was to determine whether WR-2721 would decrease the hematologic toxicity of mitomycin in patients with colorectal cancer resistant to fluorouracil-based therapy. Ninety-seven patients with refractory colorectal cancer were randomized to receive either mitomycin 20 mg/m2 only or the same dose of mitomycin after pretreatment with WR-2721, 910 mg/m2. The principal toxicity in both groups was thrombocytopenia. The platelet nadirs were lower in patients receiving single-agent mitomycin (P = 0.026). Surprisingly, no clinical complete or partial responses were noted in either group, and survival was not different between the two groups. Thus, while WR-2721 decreased the thrombocytopenia associated with mitomycin therapy, mitomycin was ineffective in the treatment of refractory colorectal carcinoma.

Newer insights into cisplatin nephrotoxicity

OBJECTIVE

To review recent advances in the understanding of the mechanisms of cisplatin nephrotoxicity. Factors affecting this toxicity and agents that may protect against it are discussed.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature including reviews. A manual search of bibliographies was performed to include all articles on the subject.

STUDY SELECTION

All available data relating to the mechanisms, modifying factors, and management of cisplatin nephrotoxicity were assessed.

DATA EXTRACTION

As limited human data are available, all animal studies were included. Articles with hypotheses or suggestions not backed by scientific data were excluded from review.

DATA SYNTHESIS

Cisplatin is one of the most effective agents available for treating a variety of solid tumors. Nephrotoxicity is the dose-limiting factor for the use of this drug. Mechanisms for renal toxicity range from definitive histologic changes found in the proximal convoluted tubules to physiologic and biochemical alterations involving a decrease in mitochondrial respiratory function, enzymatic activity in the respiratory chain and glutathione peroxidase, and effects on cellular calcium homeostasis. Important factors related to nephrotoxicity include age, renal irradiation, and concurrent alcohol intake. Agents that appear promising in attenuating the nephrotoxic effects of cisplatin include loading with NaCl solution and/or mannitol, sodium thiosulfate, WR 2721, glutathione, probenecid, and many other compounds under active investigation.

CONCLUSIONS

Cisplatin is a nephrotoxic drug; however, agents that may make cisplatin therapy more safe and rewarding will be available in the near future.

WR2721 as a modulator of cisplatin- and carboplatin-induced side effects in comparison with other chemoprotective agents: a molecular approach

Cisplatin is an active cytostatic that became successful in the treatment of several types of solid tumours after its nephrotoxic potential was controlled by hydration and diuresis. Thiol compounds were tested to reduce further cisplatin-induced nephrotoxicity. Thiosulphate is rapidly excreted by the kidneys and protects against cisplatin-induced nephrotoxicity by inactivating reactive platinum species in the kidney. Due to inactivation of cisplatin in the circulation, thiosulphate also interferes with its antitumour activity. Therefore, it is mainly used in two-route schedules, whereby cisplatin is delivered locally to the tumour (i.p. or i.a.) while systemic (i.v.) thiosulphate protects the kidneys. Diethyldithiocarbamate was shown to protect against cisplatin-induced nephrotoxicity in several animal models by reversing cellular damage. However, in the clinic it has been less successful, partly due to its central nervous system toxicity. The endogenous thiol compounds glutathione and metallothionein have been shown to reduce cisplatin-induced toxicity both in animal models and in clinical trials. However, the results are rather preliminary and a reduction in therapeutic efficacy may be expected, for both glutathione and metallothionein have been reported to be involved in platinum resistance. The thioether methionine has been shown to reduce cisplatin-induced nephrotoxicity in animal models but it has not yet been tested in the clinic. Cisplatin-induced acute emesis can be sufficiently controlled with a new class of 5-hydroxytryptamine-3 (5HT3)-receptor blockers, but delayed emesis remains a problem. High-dose cisplatin regimens with protection of the kidneys induces ototoxicity, peripheral neuropathy and myelotoxicity, which become dose-limiting. Neurotoxicity was partly reversed by the neurogenerative agent ORG2766, but this agent does not reduce other cisplatin-induced toxicities. Therefore, an agent capable of protecting multiple non-tumour tissues is needed. Carboplatin is a second-generation analogue of cisplatin with less nephro-, neuro- and ototoxicity. Carboplatin is at least as active as cisplatin at its maximum tolerated dose, which is defined by its myelotoxicity. Protection from carboplatin-induced myelotoxicity may be controlled by autologous bone marrow transplantation and/or hematopoietic growth factor infusions. High-dose carboplatin schedules may cause nephrotoxicity, neurotoxicity and ototoxicity. Again, the protection of multiple non-tumour tissues is needed. WR2721 appears to be such a modulating agent capable of protecting multiple non-tumour tissues. It was shown to be preferentially metabolized and taken up as the thiol metabolite WR1065 by non-tumour tissues as compared with (hypoxic) solid tumours. It was shown to protect mice from cisplatin-induced nephrotoxicity and from cisplatin- and carboplatin-induced myelotoxicity without interfering with the antitumour activity.(ABSTRACT TRUNCATED AT 400 WORDS)

para-sulfobenzoyloxybromobimane: a new membrane-impermeable reagent useful for the analysis of thiols and their export from cells

para-Sulfonylbenzoyloxybromobimane (sBBr) was shown to be similar to the fluorescent labeling agent monobromobimane (mBBr) in reacting rapidly and selectively with thiols to produce stable derivatives which are readily separated by HPLC. Chromatography of the sBBr derivative provides a useful means of confirming the identification of an unknown thiol based upon the chromatography of its mBBr derivative and can be useful for quantitative determination of polycationic thiols for which chromatography of the mBBr derivative is unsatisfactory. Unlike mBBr, which readily penetrates cells, sBBr was found not to be taken up by cells. These characteristics allow sBBr to be used, in conjunction with mBBr, to quantify the export of thiols from cells, as illustrated for GSH and the radioprotective drug WR1065, from V79 cells. Simultaneous determination of GSH and glutathione disulfides in cell culture medium could be achieved by labeling of thiols with sBBr followed by reduction of disulfides with dithiothreitol, labeling of the resulting thiols with mBBr, and HPLC analysis for both glutathione derivatives.

Postirradiation treatment with granulocyte colony-stimulating factor and preirradiation WR-2721 administration synergize to enhance hemopoietic reconstitution and increase survival

These studies tested whether WR-2721 could be used to protect hemopoietic stem cells, which after irradiation could be stimulated by granulocyte colony-stimulating factor (G-CSF) to proliferate and reconstitute the hemopoietic system. Female C3H/HeN mice were administered WR-2721 (4 mg/mouse, i.p.) 30 min before 60Co irradiation and G-CSF (2.5 micrograms/mouse/day, s.c.) from days 1-16 after irradiation. In survival studies, saline, G-CSF, WR-2721, and WR-2721 + G-CSF treatments resulted in LD50/30 values of 7.85 Gy, 8.30 Gy, 11.30 Gy, and 12.85 Gy, respectively. At these LD50/30 values, the dose reduction factor (DRF) of 1.64 obtained in combination-treated mice was more than additive between the DRF's of G-CSF-treated mice (1.06) and WR-2721-treated mice (1.44). Bone marrow and splenic multipotent hemopoietic stem cell (CFU-s) and granulocyte-macrophage progenitor cell (GM-CFC) recoveries were also accelerated most in mice treated with WR-2721 + G-CSF. In addition, mice treated with WR-2721 + G-CSF exhibited the most accelerated peripheral blood white cell, platelet, and red cell recoveries. These studies (a) demonstrate that therapeutically administered G-CSF accelerates hemopoietic reconstitution from WR-2721-protected stem and progenitor cells, increasing the survival-enhancing effects of WR-2721 and (b) suggest that classic radioprotectants and recombinant hemopoietic growth factors can be used in combination to reduce risks associated with myelosuppression induced by radiation or radiomimetic drugs.

Behavioral toxicity of selected radioprotectors

Effective radioprotection with minimal behavioral disruption is essential for the selection of protective agents to be used in manned spaceflight. This overview summarizes the studies on the behavioral toxicity of selected radioprotectors classified as phosphorothioates (WR-2721, WR-3689), bioactive lipids (16, 16 dimethylprostaglandin E2(DiPGE2), platelet activating factor (PAF), leukotriene C4), and immunomodulators (glucan, synthetic trehalose dicorynomycolate, and interleukin-1). Behavioral toxicity was examined in laboratory mice using a locomotor activity test. For all compounds tested, there was a dose-dependent decrease in locomotor behavior that paralleled the dose-dependent increase in radioprotection. While combinations of radioprotective compounds (DiPGE2 plus WR-2721) increased radioprotection, they also decreased locomotor activity. The central nervous system stimulant, caffeine, was able to mitigate the locomotor decrement produced by WR-3689 or PAF.

1,2-dithiol-3-thione and dithioester analogues: potential radioprotectors

Several 1,2-dithiol-3-thione and dithioester compounds were assayed for radioprotective capabilities in EMT6 cells in vitro. The 1,2-dithiol-3-thiones were generally more cytotoxic than the dithioesters and in some instances were more cytotoxic toward hypoxic cells than toward normally oxygenated cells. When the drugs were present at a concentration of 500 microM for 1 h prior to and during radiation delivery, the 5-(2-thienyl)-1,2-dithiol-3-thione produced a radiation protection factor (RPF) of 2.7 at 1 log of cell kill. The 4-methyl analogue of this same compound was, however, much less effective, producing a RPF of only 1.2. The 4-ethoxycarbonyl analogue was moderately active, producing a RPF of 1.7. The 4-methyl-5-(2-pyrazinyl)-1,2-dithiol-3-thione (Oltipraz) was least effective, yielding a RPF of only 1.1. Of the dithioesters tested, methyl 3-pyrrolidino-2-phenylpropene dithiocarboxylate produced a RPF of 2.6, methyl 3-piperidino-2-phenylpropenedithiocarboxylate a RPF of 2.7, and the corresponding 3-morpholino and 3-thiomorpholino derivatives RPF values of 2.7 and 2.9, respectively. The iodide salt of 4-ethoxycarbonyl-5-(2-thienyl)-1,2-dithiol-3-thione produced a RPF of 2.6 Methyl 3-cyclohexylamino-2-phenylpropenedithiocarboxylate was equally effective (RPF = 2.6). Finally, methyl 3-morpholino-3-thienyl-2-methylpropenedithiocarboxylate and methyl 3-morpholino-3-(2-pyrazinyl)-2-methylpropenedithiocarboxylate were less effective, producing RPF values of 2.0 and 1.6, respectively. These results demonstrate that several of these compounds are highly effective radioprotectors. In vitro and in vivo studies testing their efficacy are underway.