Early investigational drugs for hearing loss

2.1 Ebselen

Ebselen contains selenium and mimics GSH-Px activity. Thus, it selectively scavenges peroxides [13-15]. Ebselen has also been shown to inhibit cyclooxygenase and lipoxygenase enzymes thereby acting as an anti-inflammatory agent.

SPI-1005 is a proprietary preparation of ebselen prepared by Sound Pharmaceuticals that allows it to be effective orally. Phase I of clinical trials to determine the safety and pharmaco-kinetics of SPI-1005 have been completed (Study to Evaluate the Safety and Pharmacokinetics of SPI-1005: NCT 01452607). During this trial, a single dose of ebselen in increasing doses (200, 400, 800 and 1600 mg) was given to the subjects who were then monitored for the safety and pharmacokinetic properties of the drug. No clinical treatment data are available yet.

Phase II clinical trials of SPI-1005: Otoprotection with SPI-1005 for Prevention of Temporary Auditory Threshold Shift (NCT01444846) to evaluate potential prevention of temporary threshold shifts in hearing that may occur after listening to music through an iPod or personal music player has been completed. The sound level was established based on prior human studies where a slight temporary auditory threshold shift was safely induced in the subjects who were randomized to either placebo or SPI-1005 and treated before and after music exposure. All subjects and investigators were blinded to the intervention. Three different dosages of SPI-1005, 200, 400 and 600 mg, were used in this study and were administered in the form of oral capsules twice daily for 4 days. The level of temporary threshold shift was determined by pure-tone audiometry. Comparisons between the treatment and placebo groups were carried out at several time points after the music exposure. Clinical data are not yet available. This clinical trial is being sponsored by Sound Pharmaceuticals, Inc. in collaboration with University of Florida. This Phase II clinical trial is still active. The details of this study have not been disclosed; therefore, the sound exposure levels or the duration of exposure are unknown. Similarly, the treatment regimen does not specify the time of administration in relation to the sound exposure. Ebselen seems to be a strong candidate for NIHL if the clinical trial data show benefit.

Ebselen is also under clinical investigation for chemotherapy-induced ototoxicity in adult cancer patients, who can suffer both HL and tinnitus: SPI-1005 for Prevention and Treatment of Chemotherapy Induced Hearing Loss (NCT01451853). The objective of this trial is to evaluate the safety and efficacy of SPI-1005 at three dose levels when delivered orally twice daily for 3 days, surrounding each cycle of platinum chemotherapy for head and neck or non small cell lung cancer patients to prevent and treat chemotherapy-induced HL and tinnitus. This clinical trial is yet to open for recruiting.

In animal studies, ebselen was shown to improve GSH-Px levels within critical cochlear structures thereby reducing the temporary threshold shift induced by intense noise and cisplatin. Kil et al. reported that treatment with oral ebselen (4 mg/kg) in F-344 rat before and immediately after noise exposure reduced both outer hair cell loss and the acute swelling of stria vascularis by scavenging ROS and other free radicals and by stimulating glutathione peroxide expression and activity [16]. Another study by Lynch et al. showed that oral ebselen along with allopurinol, a xanthine oxidase inhibitor, significantly protected against HL in a rat model of acute cisplatin toxicity by preventing the loss of outer hair cells. A subsequent publication showed that the combination of ebselen with allopurinol does not affect the chemotherapeutic efficacy of cisplatin in the rat model [17].

2.2 N-acetylcysteine

N-acetylcysteine (NAC) is a derivative of cysteine in which an acetyl group is attached to the nitrogen atom. It is an antioxidant with liver protecting properties. NAC is commonly sold as a dietary supplement. It is also used to treat cough. It breaks disulfide bonds in mucus and liquefies it, making it easier to expectorate. Clinically, NAC is used: as a mucolytic agent; in the management of paracetamol (acetaminophen) overdose; and in carbon monoxide poisoning. Other uses of NAC include sulfate repletion in conditions such as autism, where cysteine and related sulfur amino acids may be depleted [18]. NAC is well tolerated by humans. The first use of NAC in protection from noise-induced ototoxicity was in combination with salicylic acid [19] in the chinchilla model of HL. Since then, NAC has been shown to be somewhat protective against cisplatin ototoxicity (about ∼ 20% of ears protected) in a pilot randomized study in head and neck cancer patients [20]. In this study, 2% l-NAC was administered transtympanically in one ear (the other ear served as a control) of 11 patients treated with cisplatin. Statistically significant hearing preservation was seen in two patients (18.2%), compared to the untreated control ear. However, as a group, hearing in the NAC-treated ears did not show statistically significant protection. Two per cent NAC was well-tolerated transtympanically. There is the possibility that the dose of NAC used in this study was lower than what was required to elicit a robust protective effect.

Another ongoing study that uses NAC in combination with magnesium against noise damage is reported on the clinical trials website: Prevention of Noise-induced Damage by Use of Antioxidants (NCT 01727492). The study is being conducted in Belgium, and the combination of NAC (600 mg) and magnesium (200 mg) is named Antioxidantia. This study will determine the ability of Antioxidantia to prevent NIHL and noise-induced tinnitus (NIT), when taken orally as prior to noise exposure. Antioxidantia will be given to young adults 1 h prior to leisure noise above 100 dB for at least 3 consecutive hours. Each participant will be exposed to this noise four times, with an interval of at least 4 days between each noise exposure and will be given either the antioxidant (twice) or the placebo (twice). NIT will be scored by a visual analogue scale, and tinnitus loudness will be assessed. This will be measured prior to noise exposure (at the time of antioxidant/placebo intake) and 1 h after noise exposure. The predicted outcome is a reduction of 50% of the tinnitus loudness in the antioxidant-treated group compared with the placebo group. The study participants will also undergo audiological testing (audiometry up to 16 kHz, distortion product as well as transient-evoked otoacoustic emissions and speech-in-noise tests), and the data generated will compare the placebo results to the antioxidant trials and will be performed prior to and within 7 h after noise exposure. The latest update on this study was published by Gilles et al., who reports that half of the participants has been recruited at the time of this article submission in November 2013. This is a well-designed study [21], but it has not been completed and there are no results posted as yet. We expect this study may have positive results. In the future, it will be very interesting to see whether Antioxidantia can rescue patients from NIHL and NIT when administered after noise insult.

In a different study: The Use of Anti-oxidants to Reduce Sequela of Mild Traumatic Brain Injury (mTBI) After Blast Exposure (NCT00822263), it was seen that NAC administration reduced the sequelae of mTBI in military personnel after blast exposure. The results of this study have been published [22]. Briefly, active duty military personnel diagnosed at the Al Taquaddum Level II Medical Facility (TQ), in Iraq for mTBI were administered 4-g loading dose of NAC or placebo either within 24 h or 26 – 72 h post-traumatic brain injury. The subsequent doses of 4 g daily for the next 3 days within 18 – 24 h after the first dose and then 3 g dose for the next 3 days were administered in a placebo-controlled double-blind randomized study. Eighty-one participants completed this study and were evaluated for HL and several other mTBI symptoms. The primary outcome measure for this study was the resolution of these symptoms 7 days after the blast exposure. It was reported that the outcome of ‘no day 7 symptoms’ by logistic regression analyses, indicated that NAC treatment was significantly better than placebo (OR = 3.6, p = 0.006). Secondary analysis also revealed that participants who received NAC within 24 h of blast had ∼ 86% chance of symptom resolution versus 42% for those seen early who received placebo. No adverse side effects from the drug were reported.

This study was conducted in an active war zone and demonstrates that NAC is a well-tolerated drug and has been shown to ameliorate the severity and resolution of the mTBI sequelae. This is an acute study, and the long-term benefits of NAC in war zone personnel suffering from mTBI needs to be documented to confirm and establish that significant resolution of symptoms with NAC is actually long lasting. It would be of immense help if these participants could be contacted for a follow-up, to ensure that the benefit seen by NAC use is actually permanent, because permanent HL cannot be evaluated within 7 days of injury.

NAC is also being evaluated for its protection against cisplatin-induced ototoxicity at the Children's Hospital in Los Angeles (NAC to Prevent Cisplatin-induced Hearing Loss: NCT 02094625). Specifically, this study is to evaluate the dosage required to protect from cisplatin ototoxicity and tolerability of NAC in the pediatric population in the traditional 3 + 3 dose-escalation scheme. The patients will be evaluated for NAC and glutathione serum levels at baseline prior to the start of chemotherapy (-6 h), immediately following cisplatin (prior to NAC) (0 h), immediately following NAC (0.5 h) and 4 h post-NAC infusion (4 h). This will also help establish intra-patient and inter-patient variability in achieved serum levels. Hearing assessment and renal toxicity will be assessed up to 40 weeks. Tumor response to treatment and effect of genotype on HL and protection will be assessed up to 15 weeks post-cisplatin chemotherapy. The data collected will be compared to the patient's baseline or to normal established levels. This is a Phase I clinical trial and has not started recruiting participants at this time. However, it will be critical to closely monitor pediatric patients as NAC seems to affect the rate of metalloprotein degradation in plasma and this would be in addition to myelosuppression seen by cisplatin, Sooriyaarachchi et al. [23].

NIHL is another condition for which NAC is being evaluated as an otoprotectant. In this clinical trial: Antioxidation Medication for NIHL (NCT00552786). This clinical trial recruited 53 noise-exposed workers from steel industries in Taiwan. In this randomized, double-blind, crossover Phase II study, 1200 mg NAC or placebo was administered orally to the noise-exposed workers for 2 weeks. Their temporary threshold shift in hearing was examined, and blood samples were collected to determine deletion polymorphisms in the glutathione S-transferase (GST) T1 and GSTM1 genes. The results published for this study show that NAC had a significant protective effect against temporary threshold shifts at high frequencies; however, NAC did not affect the temporary threshold shift at low frequencies. When workers were grouped by GSTT1 and GSTM-null genotypes (p = 0.004), NAC's otoptotective effect seemed more prominent [24].

NAC is also being used to determine whether it can effectively prevent aminoglycoside-induced ototoxicity in peritoneal dialysis patients. In this clinical trial: Prevention of Drug Induced Ototoxicity in Peritoneal Dialysis Patients by NAC (NCT01131468). In this Phase II clinical study, NAC was evaluated for protection against HL induced by amino-glycoside and/or vancomycin in peritoneal dialysis patients. Although no improvement in hearing of the patients after 1 week was observed, there was significant hearing improvement after 4 weeks of NAC treatment (p < 0.05).

Earlier studies have shown that NAC can significantly reduce cochlear cell apoptosis and the generation of ROS to mitigate radiation-induced ototoxicity in patients undergoing radiotherapy [25,26]. It was also reported that NAC had a protective effect against cisplatin-mediated ototoxicity as well [25,27]. NAC can mitigate the production of ROS, significantly reducing the cascade of ROS-mediated toxic events. NAC could be an effective drug against various ototoxic agents. Further clinical studies with cisplatin, aminoglycosides and noise exposure and NAC may confirm the effectiveness of prophylactic administration of NAC against HL.

2.3 Lactated Ringer's

Lactated Ringer's is isotonic with blood and is traditionally used to combat hypovolemia due to blood loss caused by trauma, surgery or burn injuries. It is also used to counteract liver acidosis and helps in the maintenance of stable blood pH. In ototoxicity studies, its success as a protective agent appears to be based on its ability to maintain pH balance.

Lactated Ringer's solution was serendipitously discovered to offer near complete preservation of distortion product of otoacoustic emission, when administered transtympanically, against cisplatin-induced ototoxicity by Choe et al. in guinea pigs [28]. These findings were confirmed and extended by Nader et al. and Sanli et al. using auditory brainstem responses in guinea pig and rats, respectively [29,30]. On the other hand, Munguia et al. have shown that intratympanic administration of Ringer's lactate solution through a tympanostomy tube failed to provide protection against cisplatin-induced HL in chinchillas [31].

Lactated Ringer's has been used in clinical trial: Protection from Cisplatin Ototoxicity by Lactated Ringers (NCT005 84155). This clinical trial, sponsored by University of Oklahoma, aimed to determine if the application of lactated Ringer's solution into the middle ear could prevent cisplatin-induced HL. Patients older than 18 years of age with head and neck cancer with no active external or middle ear disease were included in the study. The subjects were assigned to normal saline treated placebo comparator and lactated Ringer's treated experimental groups administered as ear drops into the external auditory canal 30 min after cisplatin chemotherapy (minimum dose of 70 mg/m²) was started and at hourly intervals for 4 h after infusion. The patients were assigned randomly as single blinded and single intervention group. Each participant received a hearing evaluation (audiogram) before each dose of cisplatin and another evaluation 2 – 4 weeks after the final treatment. This trial has been completed, but no results have been posted or published.

Another study in Phase I and Phase II clinical trial is: Trans-tympanic Ringer's Lactate for the Prevention of Cisplatin Ototoxicity (NCT01108601). In this study, a pressure-equalizing tube was inserted under local anesthesia to ensure adequate drug delivery to the middle ear, prior to chemotherapy treatment in the patients. For each patient, one ear would receive the Ringer's lactate solution (Ringer's lactate [0.03% ciprofloxacin]) and the contralateral ear will act as an untreated control. The patients were instructed to administer four drops of Ringer's lactate solution to the experimental ear twice a day during their chemotherapy treatment. Pre- and post-chemotherapy audiograms and distortion product otoacoustic emissions (DPOAEs) were to be compared to determine changes in hearing from baseline and between ears. To determine possible long-term effects hearing was to be assessed every 6 months after chemotherapy treatment for up to 4 years. This study was sponsored by McGill University Health Center, CA. The last verified information was in 2010, and the study was recruiting participants. This study may have a better chance for positive results compared to the previous study due to the insertion of ventilation tubes. Lactate is expected to provide an alternate source of bicarbonate and prevent cisplatin-induced acidosis in the cochlea. However, there are no results or updates available on this study.

2.4 Ginkgo biloba

Ginkgo biloba extract (GBE761) is a very potent superoxide and hydroxyl-free radical scavenger and can block apoptosis [32,33]. Previous animal (intraperitoneal) and clinical studies (per oral) have shown that concomitant or prior administration of GBE761 can significantly and effectively antagonize cisplatin-induced ototoxicity and unilateral idiopathic sudden SNHL in a prospective, randomized double-blind study of 106 patients [32-37]. In the Phase II clinical trial: The Protective Effect of Ginkgo Biloba Extract on Cisplatin-induced Ototoxicity in Humans (NCT01139281), patients were randomly assigned to drug (120 mg GBE761 twice a day along with maximal cumulative cisplatin dosage of 300 mg/m²) or placebo (maximal cumulative cisplatin dosage of 300 mg/m²) group Treatment was double blinded. Hearing was evaluated by distortion-product otoacoustic emissions assessed for 90 days. This study was sponsored by University of Brasilia and has been completed in 2010. No results or updates have been posted or published.

2. 5 Vitamins and micronutrients

Various antioxidants in the form of vitamins (β-carotene [metabolized to vitamin A in vivo], vitamin C, vitamin E [38-40], enzymes [manganese SOD] [41] and other dietary micronutrients [selenium and magnesium]) and NAC [37] have been successfully investigated in animals for the prevention of HL. Some of these antioxidants are currently being tested in clinical trials.

Dietary supplements and vitamins like A, C and E that scavenge ROS can act synergistically with minerals like magnesium to prevent ROS-induced damage to the inner ear. A combination of natural dietary supplements, which includes β-carotene (metabolized to vitamin A), vitamins C and E and magnesium, has shown promise for protection against NIHL in animal models [42]. The combination of these antioxidant vitamins (vitamins A, C and E) and mineral magnesium (acts in part as a vasodilator but also as an antioxidant) was evaluated for its efficacy to prevent NIHL in humans in the clinical trial: Micronutrients to Prevent Noise-induced Hearing Loss (NCT00808470). A randomized, double-blind, cross-over study was conducted in Swedish military personnel to evaluate potential protection against temporary changes in hearing induced by military weapons training, using this nutrient therapy. The study reported that the noise exposures did not result in any significant threshold shift either in the placebo or in the treatment group. No noise-induced changes were observed in any of the secondary functional test metrics [43]. However, analysis of the plasma samples after oral consumption for 2 days (short-term dosing) confirmed significant elevations of all the nutrients, except magnesium, in plasma 2 h after administration. The elevated plasma levels of the nutrients after a short-term dosing indicates that the nutrients have good bioavailability. This trial design and study protocol can be applied to other populations exposed to different noise insults.

A retrospective clinical study by Choi et al. also highlights the importance of antioxidant vitamins (daily β-carotene and vitamins C and E) in attenuating the risk of HL in the US general population. A cross-sectional data from 2592 participants of age group 20 – 69 years showed that higher intake of these micronutrients and magnesium lowered the risk of HL as inferred from the lower (better) pure-tone averages (PTAs) at both speech (0.5, 1, 2 and 4 kHz) and high frequencies (3, 4 and 6 kHz). Moreover, a comparative study of higher intake of β-carotene or vitamin C with high magnesium versus a lower intake of both nutrients demonstrated a significantly decreased risk of HL [44]. The investigators did not clarify which causes of HL are ameliorated by antioxidant vitamins. This study included a wide range of ages of subjects and most likely included various types of HL. Recently, in a population-based study, Kang et al. have also demonstrated a protective role of dietary vitamin intake against age-related HL. Statistical analysis from 1910 participants between age group 50 and 80 years showed that dietary supplement use of vitamin C significantly preserves hearing at all frequencies. Interestingly, though the same group reported that high serum concentration of vitamin D was correlated to HL instead of hearing protection [45]. Kang et al. [45] thus strongly recommend judicious intake of vitamins as a preventive measure for HL in the elderly population.

2.6 α-Lipoic acid

α-Lipoic acid, an essential cofactor for mitochondrial enzymes, has been demonstrated to exert a protective effect against cisplatin-induced HL in animal models [46,47]. A recent study by Kim et al. [47] reported that α-lipoic acid pre-treatment significantly reduced apoptotic cell death of the inner and outer hair cells in cisplatin-treated rat organ of Corti explants. This effect of α-lipoic acid was mediated via marked inhibition of the increase in the expression of IL-1β and IL-6, the phosphorylation of ERK and p38, the degradation of IκBα, the increase in intracellular levels of ROS and the activation of caspase-3 in cisplatin-treated HEI-OC1 cells. In another study, rats treated with α-lipoic acid plus cisplatin did not show significant elevation of hearing thresholds. Furthermore, α-lipoic acid acting as ROS scavenger prevented the depletion of glutathione as well as the decrease of SOD, CAT, GSH-Px and GSH-R activities in the cochlea [46]. α-Lipoic acid also showed beneficial effects against age-related HL. Administration of α-lipoic acid for 6 weeks in 24-month-old Fischer rats showed delay in the progression of age-induced HL. However, this delay was only seen to be significant at 3 kHz [48]. The authors concluded that as a mitochondrial metabolite, α-lipoic acid may reduce age-related worsening in auditory sensitivity and improve cochlear function by preventing the ROS-induced mtDNA4834bp deletion in inner ear of rats [49], thus protecting and repairing age-induced mitochondrial DNA damage.

A preliminary study conducted by Quaranta et al. evaluated the effect of α-lipoic acid on temporary threshold shift measured 2 min after the end of exposure induced by a 90 dB HL 3 kHz pure tone for 10 min in young normal hearing subjects (10/group). Group of subjects taking 600 mg of oral α-lipoic acid for 10 days prior to noise insult had significantly lower temporary threshold shift as compared with the control group (exposed to noise without α-lipoic acid) and the subjects who were exposed to noise 1 h after oral ingestion of α-lipoic acid. A single dose of α-lipoic acid did not induce any protection against noise-induced temporary threshold shift, whereas 10 days of treatment caused a significant lowering of the threshold, which indicates that single dosage is not sufficient to achieve the therapeutic concentration and a short course of α-lipoic acid treatment is required for necessary protection of HL [50]. Thus, multiple-dose lipoic acid appears very promising as a preventative agent against noise-induced temporary HL. Future studies are needed to determine whether this agent protects against permanent HL from noise.

3.1 Corticosteroids

Corticosteroids have been used in the treatment and prevention of cisplatin and aminoglycoside ototoxicity and SSHL based on their anti-inflammatory effects. Animal studies have shown that corticosteroids effectively attenuate the cisplatin- and aminoglycoside-induced HL by inhibition of the generation of ROS in the cochlea [52-54].

Recent studies by Filipo et al. [55] showed that intratympanic steroid therapy in moderate SSHL showed complete recovery in 76% of the patients, marked recovery (PTA improvement > 30 dB) in 8% of the patients, slight recovery (PTA improvement 10 – 30 dB) in 12% of the patients and no improvement in 4% of the patients. Control group was treated with saline intratympanic therapy and showed complete recovery in 20% of the patients. Total of 50 patients were recruited for this study. Intratympanic steroid treatment consisted of 0.3 ml of 62.5 mg/ml of predinosolone for 3 consecutive days. The control group was administered intratympanic saline for 3 consecutive days. Audiometric evaluations were performed at 7 days from the start of treatment. All patients not showing complete recovery were then administered oral prednisolone in a tapering dose for 8 days. The intratympanic steroid group did not show any further improvements with oral steroids. The control group on the other hand after oral steroid showed complete recovery in 72% of the patients and no recovery in 28% of the patients. This study underscores the importance of early treatment that was started as early as 3 – 13 days from the onset of idiopathic sudden sensorineural hearing loss (ISSHL) and that steroid therapy is effective in treatment of ISSHL. Filipo et al. [56] have further shown that oral steroid therapy versus short-term intratympanic steroid therapy for ISSHL showed no significant difference in PTA improvement; however, the intratympanic steroid groups showed better audiometric curves.

The use of intratympanic steroid injections as a rescue therapy in patients with SSHL who did not respond to systemic steroid therapy have been reported by several investigators [57,58]. Briefly, Ferri et al. [58] have reported that the patients showed full or partial recovery in hearing capability in 52.7% of the patients, 43.7% had no change in hearing and in 3.5% hearing worsened with IST. Patient profile for this study consisted of 55 patients with refractory ISSHL who had a PTA of 30 dB or more after 10 days of intravenous steroid treatment. These patients were then treated with 0.5 ml of methylprednisolone (40 mg/ml). IST was performed every 2 or 3 days up to a total of 7 injections. In this study, the authors further delineated that the recovery associated with IST was positively correlated with time of treatment and onset of HL, severity of HL, age of the patients, status of the contralateral ear and the frequencies of HL.

In a similar study by Raghunandhan et al. [59] showed that high-dose intravenous steroid therapy of 30 patients with ISSNHL, complete recovery occurred in 56.66% cases and marked improvement (> 30 dB) in 16.66% patients. However, the caveat is that the treatment had to begin within 6 h from the onset of HL in order to restore normal hearing. This study also assessed the various co-morbidities influencing the outcomes as well as improvement in associated symptoms such as vertigo and tinnitus [59].

Dexamethasone and Ginaton are also being evaluated for the treatment of acute sensorineural HL in the clinical trial: Sudden Hearing Loss Multi-center Clinical Trial (NCT0 2026479). This study will compare two doses of dexamethasone (5 and 10 mg) as postauricular treatment and Ginaton (40 mg, thrice a day, oral). Pure-tone audiometry will be measured for the three contiguous frequencies with the worst HL at baseline and at day 30 post-treatment. This study will also evaluate tinnitus and vertigo resolution in the patients by questionnaires at baseline, 14, 30 and 90 days. This study is sponsored by Peking University People's Hospital and is not open to recruitment as yet.

Another clinical trial is testing the efficacy of fludrocortisone in the amelioration of ISSNHL: Fludrocortisone for Sudden Hearing Loss (NCT01186185). The rationale behind this study is that mineralocorticoids regulate the balance of electrolytes and water. Fludrocortisone has been shown to be effective in combination with prednisolone at low doses in a mouse model of autoimmune HL [60]. Fludrocortisone is not approved for the treatment of SSNHL, and the purpose of this study was to test whether fludrocortisone can treat sudden HL. Fludrocortisone was to be administered 0.2 mg by mouth daily for 30 days for patients with ISSNHL within the last 3 months. HL was to be determined by pure-tone and speech audiometry on completion of a 1-month course of treatment and compared with pretreatment test results. This study was sponsored by Oregon Health and Science University. There are no updates available.

Dexamethasone has also been used in the prevention of cisplatin-induced HL. Several studies have shown that intratympanic administration of dexamethasone is protective against cisplatin ototoxicity [54,61-64]. However, recent studies did not demonstrate any protection with dexamethasone when administered either intratympanically or intraperitonially, against cisplatin-induced HL [61,62]. There is one clinical trial that is in Phase IV of clinical testing: Prevention of Cisplatin-Induced HL by Intratympanic Dexamethasone Treatment (NCT01372904).

4.1 Gevokizumab

Gevokizumab is a mAb raised against pro-inflammatory cytokine IL-1β [67]. It binds to IL-1β with a strong affinity and allosterically modulates its activity. Increase in IL-1β has been well documented in autoimmune inner ear disease (AIED) [68-70]. The clinical trial: The Effects of Gevokizumab in Corticosteroid-resistant Subjects with AIED (NCT01 950312) is a Phase II open-label clinical trial. The purpose of the study is to determine whether gevokizumab can be used as an alternative therapy for the corticosteroid-resistant patients with AIED. The primary outcome will be measured after 28 – 84 days of therapeutic interventions (gevokizumab as subcutaneous injections) by determining the improvement either at PTA of ≥ 5 dB or 12% of word recognition score. This is an ongoing trial and is recruiting participants at this point. It is being sponsored by XOMA (US) LLC in collaboration with Feinstein Institute for Medical Research and National Institute on Deafness and Other Communication Disorders (NIDCD). The details regarding the dosage and treatment time points have not been provided.

Gevokizumab has wide varieties of applications for different diseases. It is in Phase III trials for different indications like erosive osteoarthritis of the hand. There have been no reports of adverse side effects.

4.2 Anakinra

Anakinra is a recombinant, nonglycosylated human IL-1 receptor antagonist (IL-1Ra). Anakinra has an extra methionine residue at the amino terminus, compared to the native IL-1R antagonist. It works by competitively binding to IL-1R type I and therefore does not allow the IL-I to bind to its receptor. This prevents further responses to any inflammatory and immunological stimuli. Anakinra is generated using the Escherichia coli expression system.

IL-1β has been found to be crucial to the pathogenesis of autoimmune inner ear [69,71,72]. IL-1β antagonists, such as anakinra, rilonacept and canakinumab, have been found to be effective in mitigating autoimmune HL when treatment was initiated promptly [71-75]. Pathak et al. showed significant increase in the release of IL-1β from the peripheral blood mononuclear cells (PBMC) of patients with autoimmune inner ear disease (AIED) who did not respond to corticosteroid therapy [69] compared to responders. More interestingly, this study also showed that stimulation of cultured PBMCs isolated from the responders as well as non-responders for 16 h with 100 ng/ml of anakinra showed significant inhibition of IL-1β from the monocytes of both the responders and non-responders. These data strongly suggest that anakinra may be a good choice for the treatment of AIED, especially in those patients who have not responded to corticosteroid therapy. The clinical trial: A Clinical Trial of Anakinra for Steroid-Resistant AIED (NCT01267994) aims to do just that. This is an open-label Phase I and Phase II study to determine whether the use of anakinra in corticosteroid-resistant subjects with AIED show improvement in hearing thresholds. This study will evaluate whether treatment with anakinra for 84 days will demonstrate improved hearing threshold when compared with their baseline pre-anakinra-treatment threshold in corticosteroid-resistant patients with AIED. Audiometric thresholds will be compared to those treated with a prolonged corticosteroid taper and those that elect for no further treatment. The durability of the response will be measured over a total of 180 days. This is an ongoing study, sponsored by Dr. Andrea Vambutas, North Shore Long Island Jewish Health System and in collaboration with NIDCD.

4.3 Etanercept

Etanercept is a widely used biological agent in the treatment of autoimmune diseases such as rheumatoid arthritis, psoriasis and so on by targeting TNF-α. TNF-α is a pro-inflammatory cytokine that belongs to the TNF superfamily. TNF-α is a pro-inflammatory immune regulator that stimulates the acute phase reaction. Dysregulation in TNF-α signaling has been documented as one of the hallmarks of autoimmune diseases. There is increasing evidence to support the efficacy of TNF-α receptor antagonist, etanercept, against inflammatory disease. Etanercept can mitigate the inflammation and HL in labyrinthitis induced by keyhole limpet hemocyanin (KLH) in mice [76]. In a guinea pig model of immune-mediated HL, within 3 – 5 days of KLH insult, the labyrinth developed infiltration of inflammatory cells and HL occurred. Both the systemic treatment with etanercept (2.5 mg for 30 min) and long-term infusion of etanercept (5.0 μg/h for 7 days) into the scala tympani significantly protected the labyrinth against KLH-induced inflammation and the development of HL [76]. Etanercept prevents NIHL via improvement of cochlear blood flow in vivo [77]. TNF-α signaling is known to be activated upon noise exposure. Systemic administration of etanercept after loud noise exposure (106 dB SPL, 30 min) significantly attenuated NIHL. The microcirculatory analysis of cochlea showed significant increase in cochlear blood flow in strial capillary segments. Moreover, significant hearing improvement was observed in etanercept-treated groups versus controls. Hence, there appears to be a compelling rationale for conducting further research on etanercept as a treatment strategy against NIHL.

In Wistar rats, Kaur et al. have shown that etanercept can significantly ameliorate cisplatin ototoxicity significantly [78,79]. Etanercept (250 μg/50 μl per ear) was administered transtympanically prior to cisplatin (11 mg/kg intraperitoneal) treatment. Auditory thresholds were measured at baseline in the naive animals and again at 72-h post-cisplatin administration. Etanercept pretreatment provided almost complete protection from cisplatin-induced HL. Outer hair cell morphology was preserved as shown by scanning electron microscopy. These data provide a strong rationale for additional studies of etanercept for prevention of cisplatin ototoxicity.

4.4 Short inhibitory RNA

siRNA is double-stranded RNA of 20 – 30 nucleotides in length and among other properties interferes with specific gene expression [80-82]. siRNA silences by preventing mRNA from translation by binding and degradation of the specific mRNA. Several studies have shown siRNA to be very efficient in the inhibition of protein expression in animals. However, siRNA has a very short life span after systemic administration, as exo- and endonucleases in blood and serum degrade it [83]. Anatomical isolation of the cochlea helps avoid this drawback; additionally, the cochlea is sparsely populated with blood vessels. Another anatomically isolated organ is the eye, which is also a target organ for gene-specific treatment options. Localized delivery of drugs and siRNA by transtympanic route by our laboratory has helped to provide treatment options and route of delivery to the inner ear. One of the earliest gene silencing studies in which siRNA was delivered by round window application required surgery, drilling a hole in the bulla of the mouse and subsequent delivery of the siRNA for the gap junction protein, β-2 (GJB2) in the mouse [84]. Round window administration of siRNA against Transient Receptor Potential Vanilloid 1 (TRPV1) gene was reported to be otoprotective against cisplatin ototoxicity. The expression of that gene was shown to be upregulated following cisplatin administration [85]. Subsequently, Mukherjea et al. showed that siRNA against cochlear-specific NADPH oxidase 3 gene showed a dose-dependent protection from cisplatin ototoxicity when administered by single transtympanic injections 48 h prior to cisplatin administration [86]. More animal studies from the same group also showed that siRNA against signal transducer and activator of transcription 1, a transcription factor known to be critical in cisplatin-induced inflammation of the cochlea [87], showed amelioration of cisplatin-induced HL in the rat [78]. Localized molecular targets afford these siRNA molecules almost the ideal drug status for otoprotection. Additionally, since the siRNA has a short life span, is administered transtympanically to target the cochlea alone, and required a low dose for effective treatment, it is not likely to interfere with the chemotherapeutic efficacy of cisplatin.

4.5 CMV vaccine

CMV infection during pregnancy can result in SNHL in new-borns and infants. Four independent Towne/Toledo chimera vaccines were developed by genetic recombination of unattenutated human CMV Toledo strain and immunogenic Towne strains against human CMV [88], and it induces humoral immune response. Clinical trial: Safety Study of Four Chimera CMV Vaccines in Healthy Adult Males 30 – 50 Years of Age (NCT01195571). The purpose of this study is to assess the safety and tolerability of four new chimeric Towne/Toledo vaccines (Towne/Toledo 1, 2, 3, 4), which can be used to prevent congenital SNHL. The total number of participants will be 36 that will be allocated randomly in four different groups and will receive different types of vaccines. Vaccine will be administered at a dose of 103 p. f. u. (plaque forming unit) and for three addition individuals a dose of 102 p. f. u. will be given followed by 103 p. f. u. dose. The safety and tolerability of different doses will be followed for 12 weeks. At the end of the study, the presence of virus will be determined in different biological samples such as blood and urine of patients. However, the immune response profiles of the patients have to be carefully evaluated to determine the safety and tolerability.