Intrarectal amifostine suspension may protect against acute proctitis during radiation therapy for prostate cancer: a pilot study

Advances of Amifostine in Radiation Protection: Administration and Delivery

Amifostine (AMF, also known as WR-2721) is the only approved broad-spectrum small-molecule radiation protection agent that can combat hematopoietic damage caused by ionizing radiation and is used as an antitumor adjuvant and cell protector in cancer chemotherapy and radiotherapy. Amifostine is usually injected intravenously before chemotherapy or radiotherapy and has been used in the treatment of head and neck cancer. However, the inconvenient intravenous administration and its toxic side effects such as hypotension have severely limited its further application in clinic. In order to reduce the toxic and side effects, scientists are trying to develop a variety of drug administration methods and are devoted to developing a wide application of amifostine in radiation protection. This paper reviews the research progress of amifostine for radiation protection in recent years, discusses its mechanism of action, clinical application, and other aspects, with focus on summarizing the most widely studied amifostine injection administration and drug delivery systems, and explored the correlation between various administrations and drug efficacies.

Potential applications of drug delivery technologies against radiation enteritis

INTRODUCTION

The incidence of abdominal tumors, such as colorectal and prostate cancers, continually increases. Radiation therapy is widely applied in the clinical treatment of patients with abdominal/pelvic cancers, but it often unfortunately causes radiation enteritis (RE) involving the intestine, colon, and rectum. However, there is a lack of suitable treatment options for effective prevention and treatment of RE.

AREAS COVERED

Conventional clinical drugs for preventing and treating RE are usually applied by enemas and oral administration. Innovative gut-targeted drug delivery systems including hydrogels, microspheres, and nanoparticles are proposed to improve the prevention and curation of RE.

EXPERT OPINION

The prevention and treatment of RE have not attracted sufficient attention in the clinical practice, especially compared to the treatment of tumors, although RE takes patients great pains. Drug delivery to the pathological sites of RE is a huge challenge. The short retention and weak targeting of conventional drug delivery systems affect the therapeutic efficiency of anti-RE drugs. Novel drug delivery systems including hydrogels, microspheres, and nanoparticles can allow drugs long-term retention in the gut and targeting the inflammation sites to alleviate radiation-induced injury.

Aloe vera for Prevention of Acute Radiation Proctitis in Colorectal Cancer a Preliminary Randomized, Placebo-Controlled Clinical Trial

OBJECTIVE

To examine the preventive effects of Aloe vera in colorectal cancer patients undergoing radiotherapy.

MATERIAL AND METHOD

Twenty colorectal cancer patients, who received radiation, were randomized to receive Aloe vera 3% or placebo ointment, 1 g twice daily for 6 weeks. At weekly visits, acute radiation proctitis (ARP) was evaluated by Radiation Therapy Oncology Group and clinical presentation criteria as the primary endpoint. We also evaluated secondary endpoints of quality of life, psychosocial status, by applying Hospital Anxiety-Depression (HAD) Scale and laboratory measures of quantitative measurement of C-reactive protein (CRP) as a marker for systemic inflammation.

RESULTS

There was a significant improvement in the symptom index (before treatment vs. after treatment with Aloe vera) for diarrhea (p = 0.029, median score: 0.5 vs. 0.001). The overall primary and secondary outcomes favored Aloe group, while the measures of toxicity did not achieve a statistical significant difference. The lifestyle score improved significantly with A. vera (p = 004), and they also had a lower depression score in HAD scale (p = 0.008). Furthermore, quantitative CRP decreased significantly during the course of treatment with Aloe vera.

CONCLUSION

The use of topical formulation of Aloe vera 3% diminishes the severity of ARP in colorectal cancer patients.

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.

Radiation Modifiers

Radiation therapy is one of the most commonly used treatments for cancer. Radiation modifiers are agents that alter tumor or normal tissue response to radiation, such as radiation sensitizers and radiation protectors. Radiation sensitizers target aspects of tumor molecular biology or physiology to enhance tumor cell killing after irradiation. Radioprotectors prevent damage of normal tissues selectively. Radiation modifiers remain largely investigational at present, with the promise that molecular characterization of tumors may enhance the capacity for successful clinical development moving forward. A variety of radiation modifiers are described.

Intra-rectal use of epinephrine in radiotherapy of prostate cancer

Purpose: The aim of the study was to evaluate the feasibility and toxicity of intra-rectal epinephrine during prostatic radiotherapy.

Materials and methods: A total of 34 patients with prostate cancer were randomized to receive daily intra-rectal epinephrine (4 mg in 40 mL, n=16) or placebo (40 mL normal saline, n=18) 5 min before daily radiotherapy. Physical examination including systolic blood pressure (SBP) and heart rate (HR) was performed before, 5 min after, and 20 min after intra-rectal use. Toxicities were graded using the Radiation Therapy Oncology Group standard. A two-sided Fisher's exact test was used to compare proportions between groups. A mixed-effects model was used to analyze multiple measurements of SBP and HR. Survival curves were calculated using the Kaplan–Meier method and compared between groups using the log-rank test.

Results: All patients completed the protocol treatment and reported no cardiovascular symptoms after intra-rectal administration. There were no differences in SBP and HR between these two groups at any time point (before, 5 min after, and 20 min after epinephrine). At 5 weeks after the start of radiotherapy, the incidence of rectal toxicity≥grade 2 was 27.8% (5/18) for the control group versus 12.5% (2/16) for the epinephrine group, but was not statistically significant (p=0.4). There was no rectal toxicity≥grade 2 in these two groups beyond 2-year follow-up. The 5-year biochemical relapse-free survival was 75.0% and 72.2% for the epinephrine and control group, respectively.

Conclusion: Results of this pilot randomized trial have demonstrated that intra-rectal administration of epinephrine is feasible and safe in prostatic radiotherapy. Its radio-protective effect warrants further investigation.

Enteral Activation of WR-2721 Mediates Radioprotection and Improved Survival from Lethal Fractionated Radiation

Unresectable pancreatic cancer is almost universally lethal because chemotherapy and radiation cannot completely stop the growth of the cancer. The major problem with using radiation to approximate surgery in unresectable disease is that the radiation dose required to ablate pancreatic cancer exceeds the tolerance of the nearby duodenum. WR-2721, also known as amifostine, is a well-known radioprotector, but has significant clinical toxicities when given systemically. WR-2721 is a prodrug and is converted to its active metabolite, WR-1065, by alkaline phosphatases in normal tissues. The small intestine is highly enriched in these activating enzymes, and thus we reasoned that oral administration of WR-2721 just before radiation would result in localized production of the radioprotective WR-1065 in the small intestine, providing protective benefits without the significant systemic side effects. Here, we show that oral WR-2721 is as effective as intraperitoneal WR-2721 in promoting survival of intestinal crypt clonogens after morbid irradiation. Furthermore, oral WR-2721 confers full radioprotection and survival after lethal upper abdominal irradiation of 12.5 Gy × 5 fractions (total of 62.5 Gy, EQD2 = 140.6 Gy). This radioprotection enables ablative radiation therapy in a mouse model of pancreatic cancer and nearly triples the median survival compared to controls. We find that the efficacy of oral WR-2721 stems from its selective accumulation in the intestine, but not in tumors or other normal tissues, as determined by in vivo mass spectrometry analysis. Thus, we demonstrate that oral WR-2721 is a well-tolerated, and quantitatively selective, radioprotector of the intestinal tract that is capable of enabling clinically relevant ablative doses of radiation to the upper abdomen without unacceptable gastrointestinal toxicity.

Proctitis 1 Week after Stereotactic Body Radiation Therapy for Prostate Cancer: Implications for Clinical Trial Design

Background

Proctitis following prostate cancer radiation therapy is a primary determinant of quality of life (QOL). While previous studies have assessed acute rectal morbidity at 1 month after stereotactic body radiotherapy (SBRT), little data exist on the prevalence and severity of rectal morbidity within the first week following treatment. This study reports the acute bowel morbidity 1 week following prostate SBRT.

Materials and methods

Between May 2013 and August 2014, 103 patients with clinically localized prostate cancer were treated with 35–36.25 Gy in five fractions using robotic SBRT delivered on a prospective clinical trial. Bowel toxicity was graded using the Common Terminology Criteria for Adverse Events version 4.0 (CTCAEv.4). Bowel QOL was assessed using the EPIC-26 questionnaire bowel domain at baseline, 1 week, 1 month, and 3 months. Time-dependent changes in bowel symptoms were statistically compared using the Wilcoxon signed-rank test. Clinically significant change was assessed by the minimally important difference (MID) in EPIC score. This was defined as a change of 1/2 standard deviation (SD) from the baseline score.

Results

One-hundred and three patients with a minimum of 3 months of follow-up were analyzed. The cumulative incidence of acute grade 2 gastrointestinal (GI) toxicity was 23%. There were no acute ≥ grade 3 bowel toxicities. EPIC bowel summary scores maximally declined at 1 week after SBRT (−13.9, p < 0.0001) before returning to baseline at 3 months after SBRT (+0.03, p = 0.94). Prior to treatment, 4.9% of men reported that their bowel bother was a moderate to big problem. This increased to 28.4% (p < 0.0001) 1 week after SBRT and returned to baseline at 3 months after SBRT (0.0%, p = 0.66). Only the bowel summary and bowel bother score declines at 1 week met the MID threshold for clinically significant change.

Conclusion

The rate and severity of acute proctitis following prostate SBRT peaked at 1 week after treatment and returned to baseline by 3 months. Toxicity assessment at 1 week can therefore minimize recall bias and should aid in the design of future clinical trials focused on accurately capturing and minimizing acute morbidity following SBRT.

Prevention of pelvic radiation disease

Pelvic cancers are among the most frequently diagnosed cancers worldwide. Treatment of patients requires a multidisciplinary approach that frequently includes radiotherapy. Gastrointestinal (GI) radiation-induced toxicity is a major complication and the transient or long-term problems, ranging from mild to very severe, arising in non-cancerous tissues resulting from radiation treatment to a tumor of pelvic origin, are actually called as pelvic radiation disease. The incidence of pelvic radiation disease changes according to the radiation technique, the length of follow up, the assessment method, the type and stage of cancer and several other variables. Notably, even with the most recent radiation techniques, i.e., intensity-modulated radiotherapy, the incidence of radiation-induced GI side effects is overall reduced but still not negligible. In addition, radiation-induced GI side effects can develop even after several decades; therefore, the improvement of patient life expectancy will unavoidably increase the risk of developing radiation-induced complications. Once developed, the management of pelvic radiation disease may be challenging. Therefore, the prevention of radiation-induced toxicity represents a reasonable way to avoid a dramatic drop of the quality of life of these patients. In the current manuscript we provide an updated and practical review on the best available evidences in the field of the prevention of pelvic radiation disease.

Feasibility study of the pharmacology of local application of amifostine (WR-2721) to the buccal mucosa in guinea pigs

BACKGROUND/AIMS

We have undertaken this study to investigate the feasibility of topical application of the radioprotective compound WR-2721 to the buccal mucosa.

METHODS

Saliva samples were collected from 5 volunteers and were reconstituted in 3 amifostine solutions. Measurements of amifostine and WR-1065 contents were performed at 6 different time points. Young-adult guinea pigs were topically administered amifostine 50 and 100 mg to each buccal mucosa. At 0, 15 and 30 min after application, the blood samples obtained from the heart and the buccal tissues were prepared for the analysis of amifostine and WR-1065.

RESULTS

There was no significant difference between the 3 concentrations of amifostine in saliva in vitro at any of the 6 study time points (p > 0.05). No WR-1065 was detected in saliva. In the guinea pigs from groups A and B, there were significant differences in concentrations of amifostine and WR-1065 in the tissues between the 0-min and 15-min subgroups and between the 0-min and 30-min subgroups (p < 0.05). The concentrations of amifostine and WR-1065 from the 15-min and 30-min subgroups did not differ statistically (p > 0.05).

CONCLUSIONS

It is feasible to administer topical amifostine (WR-2721) to mucosa to prevent radiation-induced oral mucositis, and systemic absorption is negligible. Relatively high concentrations of amifostine in human saliva in vitro were maintained, although some inconsistent changes are observed.

Systematic review of agents for the management of gastrointestinal mucositis in cancer patients

PURPOSE

The aim of this study was to review the available literature and define clinical practice guidelines for the use of agents for the prevention and treatment of gastrointestinal mucositis.

METHODS

A systematic review was conducted by the Mucositis Study Group of the Multinational Association of Supportive Care in Cancer/International Society of Oral Oncology (MASCC/ISOO). The body of evidence for each intervention, in each cancer treatment setting, was assigned an evidence level. Based on the evidence level, one of the following three guideline determinations was possible: recommendation, suggestion, and no guideline possible.

RESULTS

A total of 251 clinical studies across 29 interventions were examined. Panel members were able to make one new evidence-based negative recommendation; two new evidence-based suggestions, and one evidence-based change from previous guidelines. Firstly, the panel recommends against the use of misoprostol suppositories for the prevention of acute radiation-induced proctitis. Secondly, the panel suggests probiotic treatment containing Lactobacillus spp., may be beneficial for prevention of chemotherapy and radiotherapy-induced diarrhea in patients with malignancies of the pelvic region. Thirdly, the panel suggests the use of hyperbaric oxygen as an effective means in treating radiation-induced proctitis. Finally, new evidence has emerged which is in conflict with our previous guideline surrounding the use of systemic glutamine, meaning that the panel is unable to form a guideline. No guideline was possible for any other agent, due to inadequate and/or conflicting evidence.

CONCLUSIONS

This updated review of the literature has allowed new recommendations and suggestions for clinical practice to be reached. This highlights the importance of regular updates.

Salvage radiotherapy for prostate cancer: Finding a way forward using radiobiological modeling

PURPOSE

Recent modeling efforts, based on reported outcomes following salvage radiotherapy (SRT) for prostate cancer, predict the likelihood of biochemical control (tumor control probability, TCP) as a function of pre-treatment prostate specific antigen (PSA) and SRT dose. Similar instruments predict the risk of grade ≥ 3 late toxicity (normal tissue complication probability, NTCP) as a function of SRT dose. Here we explore how changes in the parameters of those models might affect the optimal SRT dose and clinical outcomes.

MATERIALS AND METHODS

Baseline TCP and NTCP model parameters were established in a previous report. Pre-treatment PSA was set at 0.4 ng/mL. Model parameters were modified to explore four scenarios: (1) improving the safety of SRT, (2) increasing tumor cell radiosensitivity, (3) increasing the cure rate achievable with SRT and (4) adoption of hypofractionated SRT schedules. The "optimal" SRT dose, defined as the dose that maximized the likelihood of achieving biochemical control without causing late toxicity, was identified for each scenario.

RESULTS

Improving the safety of SRT increased the optimal SRT dose, while radiosensitization decreased the optimal dose. Both changes were predicted to increase the probability of biochemical control and decrease late toxicity rates. Increasing the cure rate achievable with SRT (eg: improving patient selection or combining SRT with effective systemic therapy) provided the greatest gains in TCP. Adoption of a hypofractionated SRT schedule was predicted to improve both biochemical control and late toxicity.

CONCLUSIONS

Modeling exercises demonstrate the significant gains that may be achieved with improved implementation of SRT for prostate cancer. Strategies to realize the effects modeled in this report should be explored in clinical trials.

The efficacy of the combination therapy with oral and topical mesalazine for patients with the first episode of radiation proctitis

BACKGROUND/AIMS

Radiation proctitis is a common complication of pelvic radiation for which an optimal treatment remains undetermined. We assessed the efficacy of oral and topical mesalazine combination therapy for patients with naive radiation proctitis.

METHODS

A total of 23 patients with radiation proctitis were enrolled in the study over a period of 2 years. Three of these patients were excluded due to severe bleeding during the study. Twenty patients (mean age 60.3 years; two males, 18 females) were treated with oral mesalazine (3 × 1 g per day) plus a daily mesalazine suppository (1 g per day at bedtime) for 4 weeks. The efficacy of treatment was assessed according to the Subjective Objective Management Analytic (SOMA) scale for alleviation of clinical symptoms of rectal toxicity and sigmoidoscopic findings.

RESULTS

The mean bleeding score improved significantly from 2.10 to 1.70 (p = 0.002) with mesalazine treatment. However, scores were not improved for pain (0.30-0.20, p = 0.163), tenesmus (0.50-0.45, p = 0.577), or stool frequency (0.35-0.30, p = 0.577). The improvements in the mean telangiectasia score (1.80-1.45, p = 0.005), bleeding point score (1.60-1.05, p < 0.001), and friable mucosa score (1.35-1.00, p = 0.005) were all statistically significant. No side-effects were noted in any of the patients.

CONCLUSIONS

The combination of oral and topical mesalazine therapy for radiation proctitis may be a safe and effective treatment for naive radiation proctitis, especially for hemorrhagic proctitis. A large, randomized controlled trial is required to confirm the results of this pilot study.

Effect of a prostaglandin--given rectally for prevention of radiation-induced acute proctitis--on late rectal toxicity. Results of a phase III randomized, placebo-controlled, double-blind study

BACKGROUND AND PURPOSE

To assess the late effect of a prostaglandin, given rectally during irradiation, on late rectal toxicity. In the acute treatment setting no significant differences in reducing the incidence of acute proctitis symptoms in patients receiving misoprostol, however, significantly more rectal bleeding had been reported.

PATIENTS AND METHODS

A total of 100 patients who had undergone radiotherapy for prostate cancer had been entered into this phase III randomized, placebo-controlled, double-blind study with misoprostol or placebo suppositories. The toxicity was evaluated yearly after cessation of irradiation by the RTOG/LENT-SOMA scale.

RESULTS

The median follow-up was 50 months. 20 patients suffered from grade 1, four patients from grade 2 as well, and three patients only from grade 2 toxicity. Frequency, bleeding and urgency were the most commonly reported symptoms. In keeping with other studies and clinical experience, the symptoms peaked within the first 2 years with a median for grade 1 of 13 months and for grade 2 of 15 months. The presence of acute toxicity grade 2 showed a correlation with the development of any late toxicity (p = 0.03). Any acute rectal bleeding was significant correlated with any late rectal bleeding (p = 0.017).

CONCLUSION

Misoprostol given as once-daily suppository for prevention of acute radiation-induced proctitis does neither influence the incidence and severity of radiation-induced acute nor late rectal toxicity. Misoprostol has no negative impact on the incidence and severity of late rectal bleeding, in contrast to acute rectal bleeding. The routine clinical use of misoprostol suppositories cannot be recommended.

Radioprotection in mice following oral administration of WR-1065/PLGA nanoparticles

PURPOSE

N-(2-mercaptoethyl)1,3-diaminopropane (WR-1065), is the active metabolite of amifostine, a broad spectrum cytoprotective agent used in conjunction with both chemo- and radiotherapy of certain cancers. This report describes for the first time an oral formulation of WR-1065 and follows on from our earlier report of a similar oral formulation of amifostine.

MATERIALS AND METHODS

The nanoparticles of WR-1065 were prepared by spray drying technique using poly lactide-co-glycolide (PLGA) as the polymer matrix. Radioprotection was determined by measuring reductions in radiation-induced: (i) 30-day survival; (ii) bone marrow suppression; and (iii) intestinal injury following 9 Gray (Gy) whole body gamma irradiation in mice. All treatments were given 1 hour pre-irradiation and WR-1065 was tested at the dose of 500 mg/kg.

RESULTS

The WR-1065/PLGA nanoparticles were smooth and spherical with the average diameter of 206 nm and contained 21.7% (w/w) WR-1065. While irradiation markedly reduced 30-day survival in non-treated control mice, and caused significant bone marrow suppression and intestinal injury in surviving mice, oral administration of WR-1065/PLGA nanoparticles resulted in significant radioprotection as evidenced by a marked reduction in all three of the above mentioned parameters of radiation injury.

CONCLUSIONS

These findings clearly demonstrate the feasibility of developing an effective oral formulation of WR-1065 as a radioprotective agent.

Alternate delivery route for amifostine as a radio-/chemo-protecting agent

Amifostine (ethiofos, WR-2721) is an organic thiophosphate prodrug that serves as an antineoplastic adjunct and cytoprotective agent useful in cancer chemotherapy and radiotherapy. The selective protection of certain tissues of the body is believed to be due to higher alkaline phosphatase activity, higher pH and vascular permeation of normal tissues. Amifostine is conventionally administered intravenously before chemotherapy or radiotherapy. It is approved by the Food and Drug Administration (FDA) to reduce cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian cancer. It was originally indicated to reduce the cumulative renal toxicity from cisplatin in non-small cell lung cancer although this indication was withdrawn in 2005. Amifostine is also FDA approved for patients with head and neck cancer to reduce the incidence of moderate to severe xerostomia in patients who are undergoing postoperative radiation treatment where the radiation port includes a substantial portion of the parotid glands. The potential of amifostine as a cytoprotective agent is unlikely to be fully realized if the method of administration is restricted to intravenous administration. Attempts have been made to develop non-invasive methods of delivery such as transdermal patches, pulmonary inhalers, and oral sustained-release microspheres. It is the goal of this article to explore non-intravenous routes of administration associated with better efficacy of the drug. This review will primarily focus on the variety of more recently studied (2002 and later) alternative modes for amifostine administration, including subcutaneous, intrarectal and oral routes.

Intrarectal amifostine during external beam radiation therapy for prostate cancer produces significant improvements in Quality of Life measured by EPIC score

PURPOSE

To test whether intrarectal amifostine limits symptoms of radiation proctitis, measured by using the Radiation Therapy Oncology Group (RTOG) gastrointestinal (GI) toxicity score and the Expanded Prostate Cancer Index Composite (EPIC) score.

METHODS AND MATERIALS

Patients with localized prostate cancer received amifostine as a rectal suspension 30-45 minutes before daily three-dimensional conformal radiation therapy. The first 18 patients received 1 g of amifostine, and the next 12 patients received 2 g. Toxicity was assessed at baseline, during treatment, and at follow-up visits by using RTOG grading and the EPIC Quality of Life (QoL) 50-item questionnaire. The Bowel Function subset of the bowel domain (EPIC-BF), which targets symptom severity, and the Bowel Bother subset of the bowel domain (EPIC-BB), which assesses QoL, were evaluated and compared with the RTOG GI toxicity score.

RESULTS

Median follow-up was 30 months (range, 18-36 months). Overall, EPIC-BF and EPIC-BB scores both tracked closely with the RTOG GI toxicity score. Seven weeks after the start of radiation therapy, the incidence of RTOG Grade 2 toxicity was 33% in the 1-g group (6/18 patients) compared with 0% (0/12 patients) in the 2-g group and tended toward statistical significance (p = 0.06). A significant difference between amifostine groups was observed using the EPIC-BF score at 7 weeks (p = 0.04). A difference in EPIC-BB scores between dose groups was evident at 7 weeks (p = 0.07) and was significant at 12 months (p = 0.04).

CONCLUSIONS

Higher doses of amifostine produced significant improvements in acute and late bowel QoL (up to 1 year after therapy), measured using the EPIC score.

Amifostine: the first selective-target and broad-spectrum radioprotector

After several decades of preclinical and clinical research, the first approved radioprotective drug, amifostine, is being used in clinical practice. Amifostine has been shown to specifically protect normal tissues from damage caused by radiation and chemotherapy. An inactive prodrug, amifostine is converted to an active thiol by dephosphorylation by alkaline phosphatase in the normal endothelium. The hypovascularity and acidity of the tumor environment and the differential expression of alkaline phosphatase in normal and neoplastic tissues contribute to its cytoprotective selectivity. The cytoprotective mechanism of amifostine is complicated, involving free-radical scavenging, DNA protection and repair acceleration, and induction of cellular hypoxia. The U.S. Food and Drug Administration has approved the i.v. use of amifostine to reduce the cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian cancer and to reduce the incidence of moderate to severe xerostomia in patients undergoing postoperative radiation treatment for head and neck cancer, where the radiation port includes a substantial portion of the parotid glands. Nonetheless, amifostine has potential applications in many other oncologic settings. Novel schedules and routes of administration are under investigation and may further simplify the use of amifostine, reduce any undesired effects, and considerably broaden its applications. This review summarizes the clinical experience with amifostine and provides insight into future clinical directions.