alpha-difluoromethylornithine ototoxicity. Chemoprevention clinical trial results

Ototoxicity Review: A Growing Number of Non-Platinum-Based Chemo- and Immunotherapies

OBJECTIVE

To raise awareness of the growing list of non-platinum-based chemo- and immunotherapeutic agents that have been associated with ototoxicity and to introduce the possible mechanism of ototoxicity of these agents.

DATA SOURCES

PubMed, Embase, and Web of Science.

REVIEW METHODS

A systematic review was performed following the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analyses). PubMed, Embase, and Web of Science databases were searched for published reports of ototoxicity from non-platinum-based chemo- and immunotherapeutic agents in adult and pediatric patients. Therapies that utilized any platinum-based agent were excluded.

CONCLUSIONS

Ototoxicity from non-platinum-based chemo- and immunotherapies is an evolving problem. There were 54 reports-39 case reports and 15 cohort studies-documenting ototoxicity from 7 agents/combination therapies. Of these reports, 37 (69%) were published within the last 15 years (after 2005). No recovery of hearing was documented in 21 of 56 cases (38%). Pretreatment audiograms were uncommon (19/54 studies, 35%), despite documented ototoxic associations.

IMPLICATIONS FOR PRACTICE

There is a growing number of novel, ototoxic, non-platinum-based chemo- and immunotherapeutic agents with various potential mechanisms of action. Otolaryngologists will need to prioritize awareness of these agents. This growing list of agents, many of which have reversible effects, suggest a need for standardized ototoxicity monitor protocols so that appropriate and timely management options can be implemented.

Ototoxicity of Long-Term α-Difluoromethylornithine for Skin Cancer Prevention

OBJECTIVE

Evaluate the effects of α-difluoromethylornithine (DFMO) on hearing thresholds as part of a randomized, double-blind, placebo-controlled trial.

METHODS

Subjects were randomized and assigned to the control (placebo) or experimental (DFMO) group. DFMO or placebo were administered orally (500 mg/m2 /day) for up to 5 years.

RESULTS

Subjects taking DFMO had, on average, increased hearing thresholds from baseline across the frequency range compared to subjects in the control group. Statistical analysis revealed this was significant in the lower frequency range.

CONCLUSIONS

This randomized controlled trial revealed the presence of increased hearing thresholds associated with long-term DFMO use. As a whole, DFMO may help prevent and treat certain types of cancers; however, it can result in some degree of hearing loss even when administered at low doses. This study further highlights the importance of closely monitoring hearing thresholds in subjects taking DFMO. Laryngoscope, 133:676-682, 2023.

Structure based design of inhibitory peptides targeting ornithine decarboxylase dimeric interface and in vitro validation in human retinoblastoma Y79 cells

Polyamine synthesis in human cells is initiated by catalytic action of Ornithine decarboxylase (ODC) on Ornithine. Elevated levels of polyamines are manifested proliferating cancer cells and are found to promote tumour cell adhesion. Di-flouro methyl orninthine is a known inhibitor of ODC, however its usage is limited due its low affinity quick clearance and incompetent cellular uptake, thus posing a need for potential inhibitors. Currently, peptides are substituting drugs, as these are highly selective, specific and potent. Hence, in this study, the interacting interfaces of native homodimeric form of ODC and its heterodimer with Antizyme were probed to design inhibitory peptides targeting ODC. The designed peptides were validated for structural fitness by extensive molecular dynamics simulations and Circular dichroism studies. Finally, these peptides were validated in Y79 retinoblastoma cells for impact on ODC activity, cytotoxicity cell cycle and cell adhesion. On collective analysis, Peptide3 (Pep 3) and Peptide4 (Pep 4) were found to be potentially targeting ODC, as these peptides showed significant decrease in intracellular polyamine levels, cell adhesion and cell cycle perturbation in Y79 cells. Thus, Pep 3 and Pep 4 shall be favourably considered as therapeutic agents for targeting ODC mediated proliferation in retinoblastoma.Communicated by Ramaswamy H. Sarma.

Virtual screening of natural inhibitors targeting ornithine decarboxylase with pharmacophore scaffolding of DFMO and validation by molecular dynamics simulation studies

Ornithine decarboxylase (ODC) is an enzyme that initiates polyamine synthesis in human. Polyamines play key roles in cell-cell adhesion, cell motility and cell cycle regulation. Higher synthesis of polyamines also occurs in rapidly proliferating cancer cells are mediated by ODC. As per earlier studies, di-flouro-methyl-orninthine (DFMO) is a proven efficient inhibitor ODC targeting the catalytic activity, however, its usage is limited due to side effects. Targeting ODC is considered as a potential therapeutic modality in the treatment of cancer. In this study, it is attempted to use DFMO scaffold to build a ligand-based pharmocophore query using MOE to screen similar active compounds from Universal Natural Products Database with better ADMET properties. The identified compounds were virtually screened against the active cavity of ODC using Glide. Further, potential natural hits targeting ODC were shortlisted based on Molecular Mechanics/Generalized-Born/Surface Area (MM-GBSA) score. Finally, molecular dynamics simulations were performed for the natural molecule hit and DFMO in complex with ODC using Desmond. Among the hits shortlisted, 2-amino-5, 9, 13, 17-tetramethyloctadeca-8, 16-diene-1, 3, 14-triol (UNPD208110) was found to be highly potential, as it showed a higher binding affinity in terms of interactions with key active cavity residues, and also showed better ADMET property, HUMO-LUMO gap energy and more stable complex formation with ODC compared to DFMO. Hence, the proposed molecule (UNPD208110) shall be favourably considered as a potential natural inhibitor targeting ODC-mediated disease conditions.

Alpha-Difluoromethylornithine, an Irreversible Inhibitor of Polyamine Biosynthesis, as a Therapeutic Strategy against Hyperproliferative and Infectious Diseases

The fluorinated ornithine analog α-difluoromethylornithine (DFMO, eflornithine, ornidyl) is an irreversible suicide inhibitor of ornithine decarboxylase (ODC), the first and rate-limiting enzyme of polyamine biosynthesis. The ubiquitous and essential polyamines have many functions, but are primarily important for rapidly proliferating cells. Thus, ODC is potentially a drug target for any disease state where rapid growth is a key process leading to pathology. The compound was originally discovered as an anticancer drug, but its effectiveness was disappointing. However, DFMO was successfully developed to treat African sleeping sickness and is currently one of few clinically used drugs to combat this neglected tropical disease. The other Food and Drug Administration (FDA) approved application for DFMO is as an active ingredient in the hair removal cream Vaniqa. In recent years, renewed interest in DFMO for hyperproliferative diseases has led to increased research and promising preclinical and clinical trials. This review explores the use of DFMO for the treatment of African sleeping sickness and hirsutism, as well as its potential as a chemopreventive and chemotherapeutic agent against colorectal cancer and neuroblastoma.

Insights on ornithine decarboxylase silencing as a potential strategy for targeting retinoblastoma

Ornithine Decarboxylase (ODC) is a key enzyme involved in polyamine synthesis and is reported to be up regulated in several cancers. However, the effect of ODC gene silencing in retinoblastoma is to be understood for utilization in therapeutic applications. Hence, in this study, a novel siRNA (small interference RNA) targeting ODC was designed and validated in Human Y79 retinoblastoma cells for its effects on intracellular polyamine levels, Matrix Metalloproteinase 2 & 9 activity and Cell cycle. The designed siRNA showed efficient silencing of ODC mRNA expression and protein levels in Y79 cells. It also showed significant reduction of intracellular polyamine levels and altered levels of oncogenic LIN28b expression. By this study, a regulatory loop is proposed, wherein, ODC silencing in Y79 cells to result in decreased polyamine levels, thereby, leading to altered protein levels of Lin28b, MMP-2 and MMP-9, which falls in line with earlier studies in neuroblastoma. Thus, by this study, we propose ODC silencing as a prospective strategy for targeting retinoblastoma.

Polyamine inhibitors for treatment of feline oral squamous cell carcinoma: a proof-of-concept study

This study assessed proof-of-concept for use of polyamine inhibitor 2-diluoromethylornithine (DFMO) as a treatment for oral squamous cell carcinoma (SCC) in client-owned cats. Polyamine levels in tumor tissue and normal oral mucosa were quantified before and after treatment. DFMO was administered orally to 14 client-owned cats with histologically confirmed oral SCC. Patients were monitored for gastrointestinal, dermatologic, auditory, hematological, and biochemical abnormalities. Total polyamine levels in tumor tissue decreased after treatment, as did the specific polyamine putrescine in both tumor tissue and normal mucosa. Ototoxicity was observed in 5 of 6 cats receiving pre- and post-treatment brainstem auditory evoked potential tests. Subclinical thrombocytopenia was observed in 6 of 14 cats. One cat showed mild post-anesthetic tremors that resolved without treatment. Oral administration of DFMO at doses used in this study resulted in significantly decreased tumor polyamine levels without life-threatening clinical or hematological toxicities. Further studies are warranted to explore pathophysiology of polyamine biochemistry and use of polyamine inhibitors in treatment of cats with oral SCC.

Oral and systemic photoprotection

Photoprotection can be provided not only by ultraviolet (UV) blockers but also by oral substances. Epidemiologically identified associations between foods and skin cancer and interventional experiments have discovered mechanisms of UV skin damage. These approaches have identified oral substances that are photoprotective in humans. UV inhibits adenosine triphosphate (ATP) production causing an energy crisis, which prevents optimal skin immunity and DNA repair. Enhancing ATP production with oral nicotinamide protects from UV immunosuppression, enhances DNA repair and reduces skin cancer in humans. Reactive oxygen species also contribute to photodamage. Nontoxic substances consumed in the diet, or available as oral supplements, can protect the skin by multiple potential mechanisms. These substances include polyphenols in fruit, vegetables, wine, tea and caffeine-containing foods. UV-induced prostaglandin E2 (PGE2 ) contributes to photodamage. Nonsteroidal anti-inflammatory drugs and food substances reduce production of this lipid mediator. Fish oils are photoprotective, at least partially by reducing PGE2 . Orally consumed substances, either in the diet or as supplements, can influence cutaneous responses to UV. A current research goal is to develop an oral supplement that could be used in conjunction with other sun protective strategies in order to provide improved protection from sunlight.

DFMO: targeted risk reduction therapy for colorectal neoplasia

Strategies to decrease intracellular polyamine levels have been studied for their efficacy in reducing colorectal cancer (CRC) risk. A successful strategy combined agents that decreased polyamine synthesis by inhibiting ornithine decarboxylase with difluoromethylornithine (DFMO), and increased cellular export of polyamines by activating the spermidine/spermine acetyl transferase with non-steroidal anti-inflammatory drugs (NSAIDs). A Phase III trial treating resected adenoma patients with DFMO plus sulindac demonstrated marked reduction of metachronous adenomas, advanced adenomas and multiple adenomas compared to placebo. This combination regimen was well-tolerated, however there was a non-significant excess of cardiovascular events in the treatment arm compared to placebo as well as modest ototoxicity. Targeting this therapy to people at elevated risk of CRC, and employing clinical and genetic predictors, should improve patient benefit and reduce the risk of side effects to improve the acceptability of this strategy.

Phase I/II clinical trial of 2-difluoromethyl-ornithine (DFMO) and a novel polyamine transport inhibitor (MQT 1426) for feline oral squamous cell carcinoma

Polyamines are essential for cell proliferation. Their production is dysregulated in many cancers and polyamine depletion leads to tumour regression in mouse models of squamous cell carcinoma (SCC). The purpose of this study was to determine the maximally tolerated dose of the polyamine transport inhibitor, MQT 1426, when combined with the ornithine decarboxylase (ODC) inhibitor, DFMO, and to determine whether this therapy results in reduction in tumour polyamine levels. Thirteen cats with oral SCC received both drugs orally and serial tumour biopsies were obtained for polyamine measurement. Cats were monitored for response to therapy and toxicity. A maximum tolerated dose (MTD) of MQT 1426 when combined with DFMO was determined. Dose-limiting toxicity was vestibular in nature, but was fully reversible. Spermidine and total polyamine levels decreased significantly in tissues, two cats experienced objective tumour regression and six cats had stable disease. These results suggest that further study of polyamine depletion therapies is warranted.

Longitudinal assessment of air conduction audiograms in a phase III clinical trial of difluoromethylornithine and sulindac for prevention of sporadic colorectal adenomas

A phase III clinical trial assessed the recurrence of adenomatous polyps after treatment for 36 months with difluoromethylornithine (DFMO) plus sulindac or matched placebos. Temporary hearing loss is a known toxicity of treatment with DFMO, thus a comprehensive approach was developed to analyze serial air conduction audiograms. The generalized estimating equation method estimated the mean difference between treatment arms with regard to change in air conduction pure tone thresholds while accounting for within-subject correlation due to repeated measurements at frequencies. Based on 290 subjects, there was an average difference of 0.50 dB between subjects treated with DFMO plus sulindac compared with those treated with placebo (95% confidence interval, -0.64 to 1.63 dB; P = 0.39), adjusted for baseline values, age, and frequencies. In the normal speech range of 500 to 3,000 Hz, an estimated difference of 0.99 dB (-0.17 to 2.14 dB; P = 0.09) was detected. Dose intensity did not add information to models. There were 14 of 151 (9.3%) in the DFMO plus sulindac group and 4 of 139 (2.9%) in the placebo group who experienced at least 15 dB hearing reduction from baseline in 2 or more consecutive frequencies across the entire range tested (P = 0.02). Follow-up air conduction done at least 6 months after end of treatment showed an adjusted mean difference in hearing thresholds of 1.08 dB (-0.81 to 2.96 dB; P = 0.26) between treatment arms. There was no significant difference in the proportion of subjects in the DFMO plus sulindac group who experienced clinically significant hearing loss compared with the placebo group. The estimated attributable risk of ototoxicity from exposure to the drug is 8.4% (95% confidence interval, -2.0% to 18.8%; P = 0.12). There is a <2 dB difference in mean threshold for patients treated with DFMO plus sulindac compared with those treated with placebo.

Spermine synthase deficiency leads to deafness and a profound sensitivity to alpha-difluoromethylornithine

Male gyro (Gy) mice, which have an X chromosomal deletion inactivating the SpmS and Phex genes, were found to be profoundly hearing impaired. This defect was due to alteration in polyamine content due to the absence of spermine synthase, the product of the SpmS gene. It was reversed by breeding the Gy strain with CAG/SpmS mice, a transgenic line that ubiquitously expresses spermine synthase under the control of a composite cytomegalovirus-IE enhancer/chicken beta-actin promoter. There was an almost complete loss of the endocochlear potential in the Gy mice, which parallels the hearing deficiency, and this was also reversed by the production of spermine from the spermine synthase transgene. Gy mice showed a striking toxic response to treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO). Within 2-3 days of exposure to DFMO in the drinking water, the Gy mice suffered a catastrophic loss of motor function resulting in death within 5 days. This effect was due to an inability to maintain normal balance and was also prevented by the transgenic expression of spermine synthase. DFMO treatment of control mice or Gy-CAG/SpmS had no effect on balance. The loss of balance in Gy mice treated with DFMO was due to inhibition of polyamine synthesis because it was prevented by administration of putrescine. Our results are consistent with a critical role for polyamines in regulation of Kir channels that maintain the endocochlear potential and emphasize the importance of normal spermidine:spermine ratio in the hearing and balance functions of the inner ear.

Effect of dietary green tea extract and aerosolized difluoromethylornithine during lung tumor progression in A/J strain mice

Chemoprevention strategies to prevent the development of lung cancer in at-risk individuals are a key component in disease management. In addition to being highly effective, an ideal chemopreventive agent will require low toxicity as patients are likely to require treatment for several years before their risk of cancer is lowered to background levels. In principle, a combination of safe agents that work through distinct mechanisms will improve efficacy while simultaneously maintaining a favorable safety profile. Here, we describe the use of the decaffeinated green tea extract Polyphenon E (Poly E) (1% in diet) and aerosolized difluoromethylornithine (DFMO) (20 mg/kg/day, 5 days/week) in a mouse lung cancer chemoprevention study using a progression protocol. Female A/J mice were injected with benzo[a]pyrene (B[a]P) at 8 weeks of age and precancerous lesions allowed to form over a period of 21 weeks before chemoprevention treatment for an additional 25 weeks. Poly E treatment did not significantly inhibit average tumor multiplicity but reduced per animal tumor load. Analysis of tumor pathology revealed a specific inhibition of carcinomas, with the largest carcinomas significantly decreased in Poly E-treated animals. Aerosolized DFMO did not have a significant effect on lung tumor progression. Magnetic resonance imaging of B[a]P-induced lung tumors confirmed the presence of a subset of large, rapidly growing tumors in untreated mice. Our results suggest a potential role for green tea extracts in preventing the progression of large, aggressive lung adenocarcinomas.

Functional Consequences of Polyamine Synthesis Inhibition by l-α-Difluoromethylornithine (DFMO)

L-Alpha-difluoromethylornithine (DFMO) is a chemopreventive agent for colon cancer in clinical trials. Yet, the drug produces an across-frequency elevation of the hearing threshold, suggesting that DFMO may affect a common trait along the cochlear spiral. The mechanism for the ototoxic effects of DFMO remains uncertain. The cochlear duct is exclusively endowed with endocochlear potential (EP). EP is a requisite for normal sound transduction, as it provides the electromotive force that determines the magnitude of the receptor potential of hair cells. EP is generated by the high throughput of K(+) across cells of the stria vascularis, conferred partly by the activity of Kir4.1 channels. Here, we show that the ototoxicity of DFMO may be mediated by alteration of the inward rectification of Kir4.1 channels, resulting in a marked reduction in EP. These findings are surprising given that the present model for EP generation asserts that Kir4.1 confers the outflow of K(+) in the stria vascularis. We have proposed an alternative model. These findings should also enable the rational design of new pharmaceuticals devoid of the untoward effect of DFMO.

Polyamines and cancer: old molecules, new understanding

The amino-acid-derived polyamines have long been associated with cell growth and cancer, and specific oncogenes and tumour-suppressor genes regulate polyamine metabolism. Inhibition of polyamine synthesis has proven to be generally ineffective as an anticancer strategy in clinical trials, but it is a potent cancer chemoprevention strategy in preclinical studies. Clinical trials, with well-defined goals, are now underway to evaluate the chemopreventive efficacy of inhibitors of polyamine synthesis in a range of tissues.

Irreversible Ototoxicity Associated with Difluoromethylornithine

Difluoromethylornithine (DFMO) is a potent, irreversible inhibitor of ornithine decarboxylase, the rate-limiting enzyme in the synthesis of polyamines that promote cellular proliferation. DFMO has been tested as a potential cancer therapeutic and chemopreventive agent in clinical trials. Reversible hearing loss is a recognized toxicity of DFMO that usually occurs at doses above 2 g/m2/d, and generally when the cumulative dose exceeds 250 g/m2. In a recently completed Barrett's esophagus chemoprevention trial, a participant developed a 15-dB decrease in hearing at frequencies of 250, 2,000, and 3,000 Hz in the right ear and a ≥20-dB decrease in hearing at 4,000 to 6,000 Hz in the left ear after taking 0.5 g/m2/d DFMO for approximately 13 weeks (cumulative dose of 45 g/m2). The threshold shifts persisted 7 months after DFMO was discontinued. There was no obvious impact on the participant's clinical hearing, but these findings were consistent with irreversible hearing loss. This is the first case reported of irreversible ototoxicity in a clinical trial participant receiving DFMO and, thus, trial participants should be made aware of this small but important risk.

Difluoromethylornithine-Induced Reversible Hearing Loss Across a Wide Frequency Range

OBJECTIVES

Alpha-difluoromethylornithine (DFMO) is an antineoplastic agent that causes reversible hearing loss (HL) by an unknown mechanism. Previous neonatal gerbil studies have identified a dosing regimen of 1 g/kg per day of DFMO given for 3 weeks that results in reversible HL on click-evoked auditory brainstem response (ABR). The objectives of this study are 1) to measure HL and recovery at several frequencies in neonatal gerbils after DFMO therapy at two different dosing regimens and 2) to identify any effects of DFMO on cochlear histology.

STUDY DESIGN

Prospective, nonrandomized, experimental design with placebo controls.

METHODS

ABR to tone pips at 2, 4, 8, 16, and 32 kHz were recorded on 62 21-day-old Mongolian gerbils after daily subcutaneous injections of DFMO (group A at 1 g/kg, group B at 750 mg/kg) or saline from day 3 to day 20 after birth. Thirty-seven animals were retested after a 3-week drug-free recovery period. Twenty-seven animals were killed for analysis of cochlear histology.

RESULTS

Animals that were administered DFMO demonstrated higher ABR thresholds across all five frequencies, with mean threshold differences of 21 to 29 dB in group A and 11 to 17 dB in group B as compared with controls. Higher thresholds were demonstrated at higher frequencies. Fewer side effects were noted at the lower dose. After a 3-week drug-free recovery period, auditory thresholds returned to pretreatment levels. No significant cochlear structural abnormalities were identified under light microscopy.

CONCLUSION

An 18-day regimen of 750 mg/kg per day of DFMO given subcutaneously in neonatal gerbils causes minimal side effects with broad-frequency HL that, after 3 weeks of recovery, is fully reversible.

Primary prevention: phytoprevention and chemoprevention of colorectal cancer

Considering the various stages of carcinogenesis and the numerous tumor types and available chemoprevention agents, knowledge of the etiology and the type of cancer to be treated, or possibly prevented, and understanding of the mechanisms by which agents exert their chemoprevention benefits may provide for improved strategy in designing therapeutic regimens. Because cancer usually develops over a 10- to 20-year period, it may be necessary for some agents to be provided before or early in the initiation steps of carcinogenesis to have beneficial effects. On the other hand, some agents may be more suitable for CRC prevention if provided at a later stage of carcinogenesis. Gene array, genomics, and proteomics are useful tools in advancing our understanding of the molecular events involved in carcinogenesis and in identifying markers of risk and surrogate end-points for colorectal cancer progression. These techniques may also serve for screening, identifying, and providing treatment targets for high-risk patients populations. Treatment could be developed depending on a patient's individual needs and genomic tumor profile. Clinical markers and surrogate end-points should be considered, together with molecular measurements, to more accurately assess risk. NSAIDs and COXIBs are clinically recognized as chemoprevention agents, and clinical trials evaluating their efficacy are ongoing. Treatment protocols, including dose and timing, remain to be determined, however. DFMO may best be used in combination with other chemoprevention agents. Dietary fiber and calcium supplements, as part of an overall low-fat diet, may decrease CRC risk. Long-term compliance with this regimen may be necessary to effect a beneficial outcome. Folate holds promise but needs further investigation, especially because its beneficial effects may depend on cancer type. Phytochemicals have been identified as strong candidates for use as agents to prevent colorectal cancer in cell culture and in rodent models of carcinogenesis. Their potential as chemoprevention agents must be demonstrated in clinical trials. In vitro and animal studies indicated that combination therapy may be a promising strategy over the monotherapy approach; clinical trials addressing the safety and efficacy of some combinations (DFMO/sulindac, fiber/calcium) are underway. The gastrointestinal tract and other organs are constantly exposed to a mixture of potentially toxic compounds and molecules considered favorable to health. Homeostasis between stress-mediated by toxic compounds and defensive mechanisms, is key for the maintenance of health and the prevention of disease. Whereas aggressive pharmacologic treatment may be necessary for patients at high risk for cancer, dietary supplements may be useful for populations at normal risk. The message for cancer prevention in the general population may well remain: keep a balanced healthy diet, eating a variety from all food groups, as part of a healthy lifestyle that includes moderate exercise.

Delayed, Reversible Hearing Loss Caused by Difluoromethylornithine (DFMO)

OBJECTIVES/HYPOTHESIS

Difluoromethylornithine (DFMO) is an anticancer experimental drug that is ototoxic. The objectives of these three experiments were to: 1) determine a dose and dosing schedule of DFMO that produces significant hearing loss (HL) in newborn gerbils; 2) compare the HL level for control and newborn gerbils receiving daily subcutaneous injections of DFMO; and 3) to determine if DFMO-related HL is significantly reversible following discontinuation of DFMO treatment.

STUDY DESIGN

Prospective, non-randomized experimental design with placebo controls.

METHODS

Click-evoked auditory brainstem response (ABR) testing was performed for 21-day-old Mongolian gerbils following daily subcutaneous injections of DFMO or saline. Three experiments were carried out using different injection schedules and doses of DFMO. In experiment 3, animals were retested at 42 days of age following a 3-week recovery from DFMO.

RESULTS

Animals administered an 18-day regimen of DFMO at 1 g/kg per day (from day 3 to day 20) had click thresholds of 25 to 65 dB nHL, whereas animals receiving daily injections of saline had thresholds of 5 to 20 dB nHL. Animals retested after 3 weeks of recovery from DFMO treatment had thresholds ranging from 5 to 20 dB nHL. Differences were statistically significant.

CONCLUSIONS

DFMO causes mild to moderate HL in neonatal gerbils that recovers after discontinuation of the drug.

Recommendations for cancer prevention trials using potentially ototoxic test agents

PURPOSE

Preventive oncology applies pharmacologic agents to reverse, retard, or halt progression of neoplastic cells to invasive malignancy, a process that may require administration of agents over long periods of time. Although ototoxicity may be a tolerable side effect of anticancer or antimicrobial therapy, even modest ototoxicity may not be acceptable in agents developed for preventive oncology that are routinely administered to subjects who neither are, nor necessarily will become, clinically ill.

MATERIALS AND METHODS

Age-related shifts in hearing may occur over the course of longterm or open-ended therapy; consequently, age-adjusted norms enable researchers to better distinguish hearing loss caused by drugs from that caused by aging. Norms for hearing sensitivity are derived from the Baltimore Longitudinal Study of Aging and are the basis for the proposed audiologic monitoring recommendations.

RESULTS

Audiologic monitoring recommendations are presented that standardize patient selection, adverse event reporting, posttreatment follow-up, and audiologic testing for potentially ototoxic investigational agents.

CONCLUSION

These recommendations are applicable to trials of investigational agents as well as various classes of drugs used in routine clinical care.

Effect of alpha-difluoromethylornithine on rectal mucosal levels of polyamines in a randomized, double-blinded trial for colon cancer prevention

BACKGROUND

Polyamines (e.g., putrescine, spermidine, and spermine) are required for optimal cell growth. Inhibition of polyamine synthesis suppresses carcinogen-induced epithelial cancers, including colon cancer, in animal models. In a short-term phase IIa trial, we determined that low doses of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (an enzyme involved in polyamine synthesis), reduced the polyamine content of normal-appearing rectal mucosa of subjects with a prior history of resected colon polyps. In a follow-up study, we have attempted to determine the lowest dose of DFMO that can suppress the polyamine content of rectal mucosa over a course of 1 year with no or minimal side effects.

METHODS

Participants were randomly assigned to daily oral treatment with a placebo or one of three doses (0.075, 0.20, or 0.40 g/m2) of DFMO. Baseline and serial determinations of polyamine levels in rectal mucosa and extensive symptom monitoring (including audiometric measurements, since DFMO causes some reversible hearing loss at higher doses) were performed over a 15-month period.

RESULTS

DFMO treatment reduced putrescine levels in a dose-dependent manner. Following 6 months of treatment, doses of 0.20 and 0.40 g/m2 per day reduced putrescine levels to approximately 34% and 10%, respectively, of those observed in the placebo group. Smaller decreases were seen in spermidine levels and spermidine:spermine ratios. Polyamine levels increased toward baseline values after discontinuation of DFMO. Although there were no statistically significant differences among the dose groups with respect to clinically important shifts in audiometric thresholds and nonaudiologic side effects, statistically significant higher dropout and discontinuation rates were observed in the highest dose group.

CONCLUSIONS

Polyamine levels in rectal mucosa can be continuously suppressed by daily oral doses of DFMO that produce few or no side effects. A dose of 0.20 g/m2 can be used safely in combination phase IIb or single-agent phase III chemoprevention trials.