Distortion Product Otoacoustic Emission Test is Not the Test to Use in Nonclinical Safety Assessment.

Ototoxicity and ocular toxicity screening are but two examples of specialty product lines that are often employed as Tier II or III nonclinical safety/hazard screening assessments. Compared to the regulatory guidelines that govern over standard toxicology or neurotoxicology programs, there is a paucity of regulatory strategies to address these specialized product lines. With respect to ototoxicity testing, we argue for the inclusion of the "least burdensome principles" adopted by the US FDA in providing the most pragmatic, efficient, and directed identification of potential harm to auditory function in the nonclinical safety arena. We argue for the exclusive use of the auditory brainstem response and the exclusion of the distortion product otoacoustic emissions (DPOAEs) in these Tiered II safety assessment programs. The inclusion of both are a burden on operational staff and, due to the extended episodes of anesthesia required to conduct both assays, this strategy poses a health and welfare concern for the selected animal species to be used. The DPOAE does not provide any sufficiently valid or reliable data above and beyond the gold standard ABR data, followed by complete oto-histopathology and cytocochleogram combination designs.

Predicting the Need for a Tier II Ototoxicity Study From Early Renal Function Data.

History has established that many drugs, such as the antibiotics, chemotherapies, and loop diuretics, are capable of inducing both nephrotoxicity and ototoxicity. The exact mechanisms by which cellular damage occurs remain to be fully elucidated. Monitoring the indices of renal function conducted in the Food and Drug Administration's prescribed set of early investigational new drug (IND)-enabling studies may be the first signs of ototoxicity properties of the new drug candidate. In developing improved and efficacious new molecular entities, it is critically necessary to understand the cellular and molecular mechanisms underlying the potential ototoxic effects as early in the drug development program as possible. Elucidation of these mechanisms will facilitate the development of safe and effective clinical approaches for the prevention and amelioration of drug-induced ototoxicity prior to the first dose in man. Biomarkers for nephrotoxicity in early tier I or tier II nonclinical IND-enabling studies should raise an inquiry as to the need to conduct a full auditory function assay early in the game to clear the pipeline with a safer candidate that has a higher probability of continued therapeutic compliance once approved for distribution.

Relative equivalence of CNS safety (FOB) assessment outcomes in male and female Wistar-Han and Sprague-Dawley rats.

In 2006 the National Toxicology Program (NTP) of the FDA shifted to the preferred use of Wistar-Han rats from the more commonly used Sprague-Dawley (SD) strain - and industry followed. While European laboratories preferred the Wistar-Han line, there was a paucity of relevant historical control data in many US research institutions for the new "industry standard" rat strain. In 2010 the NTP reversed its decision and shifted back to SD rats because of reproductive issues with the Wistar strain. For post hoc comparative analyses, we report minimal practical differences in Functional Observational Battery (FOB) data from a large sample of male and female Wistar-Han and SD rats. In summarizing data from the preclinical safety evaluations of the CNS effects of new drugs using the FOB, it is crucial to understand the value of not only how the functional expression of drug effects in the rat are predictive of the human response, but also how and why they differ. What we can predict from the behavioral and physiological response of the designated test system to drug administration is the foundation of "generalizability" to the human's response. Here, we conclude that the use of either SD or WH rat strains in standard CNS safety studies provide equivalent supportive data for CNS safety assessment required for IND approval under the harmonized guidelines.

Ototoxicity: The Radical Drum Beat and Rhythm of Cochlear Hair Cell Life and Death.

The function and structure of the auditory information processing system establishes a unique sensory environment for the "perfect storm." The battle between life and death pits the cascade of an apoptotic storm, programmed cell death cascades, against simple cell death (necrosis) pathways. Live or die, the free radical biology of oxygen and hydroxylation, and the destruction of transition metal migration through the mechanical gate sensory processes of the hair cell lead to direct access to the cytoplasm, cytoplasmic reticulum, and mitochondria of the inner workings of the hair cells. These lead to subsequent interactions with nuclear DNA resulting in permanent hearing loss. The yin and yang of pharmaceutical product development is to document what kills, why it kills, and how do we mitigate it. This review highlights the processes of cell death within the cochlea.

Down for the count: The critical endpoint in ototoxicity remains the cytocochleogram.

There are three major assays that must be conducted in standard investigational new drug (IND) -enabling ototoxicity study designs: 1) functional acoustic threshold measurements (Auditory Brainstem Respsonse, ABR); 2) otohistopathology and 3) cytocochleograms. We provide evidence to demonstrate the unreliability of auditory threshold shifts (ABRs) to predict cochlear cell death and build a case for conducting full cochlea processing and cell count measurements from the complete cochlea from apex to base.

Small Compartment Toxicity: CN VIII and Quality of Life: Hearing Loss, Tinnitus, and Balance Disorders.

Life experiences, industrial/environmental exposures, and administration of Food and Drug Administration (FDA)-approved drugs may have unintended but detrimental effects on peripheral and central auditory pathways. Most relevant to the readership of this journal is the role that drug treatments approved by the FDA as safe and effective appear to interact with 3 independent modes of toxicity within the small compartment of the ear. What may seem to be trivial drug-induced toxicity has the potential to change important measures of quality of life and functional capacity of mid- to late-life patients. Drugs meant to treat can become the source of interference in the activities of daily living, and as a result, treatment compliance may be jeopardized. Ototoxicity has been defined as the tendency of certain therapeutic agents and other chemical substances to cause functional impairments and cellular degeneration of the tissues of the inner ear resulting in hearing loss. However, one of the largest contributors to hospitalizations is fall-related injuries in the elderly patients associated with disorders of vestibular function linked to progressive and drug-induced toxicities. Tinnitus affects 35 to 50 million adults representing approximately 25% of the US population, with 12 million seeking medical care and 2 to 3 million reporting symptoms that were severely debilitating. This review is intended to highlight these targets of neurotoxicity that threaten the usefulness of drug treatments deemed safe and effective prior to access by the general public.

The failure to detect drug-induced sensory loss in standard preclinical studies.

Over the years a number of drugs have been approved for human use with limited signs of toxicity noted during preclinical risk assessment study designs but then show adverse events in compliant patients taking the drugs as prescribed within the first few years on the market. Loss or impairments in sensory systems, such as hearing, vision, taste, and smell have been reported to the FDA or have been described in the literature appearing in peer-reviewed scientific journals within the first five years of widespread use. This review highlights the interactive cross-modal compensation within sensory systems that can occur that reduces the likelihood of identifying these losses in less sentient animals used in standard preclinical toxicology and safety protocols. We provide some historical and experimental evidence to substantiate these sensory effects in and highlight the critical importance of detailed training of technicians on basic ethological, species-specific behaviors of all purpose-bred laboratory animals used in these study designs. We propose that the time, effort and cost of training technicians to be better able to identify and document very subtle changes in behavior will serve to increase the likelihood of early detection of biomarkers predictive of drug-induced sensory loss within current standard regulatory preclinical research protocols.

Utility of the auditory brainstem response evaluation in non-clinical drug safety evaluations.

INTRODUCTION: The Food and Drug Administration (FDA) requires thorough evaluation of the potential safety hazards of all new drugs, food additives, and therapeutic devices that are intended for human use. Drugs that are otically administered (i.e., ear drops), or are known to systemically distribute to the inner ear, require additional specialized safety testing to ensure that the drug does not permanently impair auditory function. METHODS: To properly determine a drug's impact on auditory function, the FDA's Center for Drug Evaluation and Research requires the use of the Auditory Brainstem Response (ABR) evaluation. The ABR evaluation uses auditory stimuli evoked potentials to assess function by establishing minimum intensity thresholds. These thresholds can be monitored following drug treatment to determine an impact on hearing loss. This review discusses methodical considerations for conducting ABR evaluations as they apply to specialized drug safety studies. Alternative assays are discussed and compared to the utility of the ABR evaluation. CONCLUSIONS: The ABR evaluation provides reliable and sensitive measures of hearing function that are suitable for definitive drug safety evaluations or hazardous risk assessments.

OTO-104: a sustained-release dexamethasone hydrogel for the treatment of otic disorders.

HYPOTHESIS: To investigate whether OTO-104, a poloxamer-based hydrogel containing micronized dexamethasone for intratympanic delivery, can provide long-lasting inner ear exposure and be well tolerated. METHODS: OTO-104 was administered intratympanically to guinea pigs and sheep, and its pharmacokinetic and toxicity profiles were examined. RESULTS: After a single intratympanic injection of OTO-104 (from 0.6% to 20%, w/w), significant and prolonged exposure to dexamethasone in the inner ear was observed. Increasing the concentration of OTO-104 resulted in higher perilymph drug levels as well as a more prolonged duration of exposure. At the highest dose, therapeutic perilymph levels of dexamethasone could be sustained over 3 months in guinea pigs and more than 1 month in sheep. A toxicologic evaluation was conducted, including assessments of middle and inner ear function and physiology, as well as appraisal of local and systemic toxicity. A small and transient shift in hearing threshold was observed, most probably conductive in nature. No significant histologic changes in middle or inner ear tissues were noted. Although macroscopically mild erythema/inflammation was documented in a subset of guinea pigs treated with 20% OTO-104, the nature and the severity of these changes were not different between the poloxamer vehicle, saline, and 20% OTO-104 groups. No evidence of acute dermal toxicity, delayed hypersensitivity, or systemic adverse effects was found. CONCLUSION: OTO-104 is a novel proprietary therapeutic delivery system that can achieve prolonged, sustained release of dexamethasone within the inner ear fluids. The administration of this clinical candidate formulation via intratympanic injection is expected to be well tolerated both locally and systemically.

Animal reuse: balancing scientific integrity and animal welfare.

Research scientists and IACUC members are faced with the difficult task of balancing the necessity of using animals for experimental research and their mandate to protect the welfare of those animals used in that research. One way to reduce the number of research animals would be to reuse them, but the regulations do not specifically address this topic. To learn more about the reuse of research animals, the authors conducted an online survey of animal facilities involved in preclinical studies. Their results suggest that animal reuse is a common practice in the field.