Preferential Cochleotoxicity of Cisplatin

Comprehensive Audiologic Analyses After Cisplatin-Based Chemotherapy

Importance

Cisplatin is highly ototoxic but widely used. Evidence is lacking regarding cisplatin-related hearing loss (CRHL) in adult-onset cancer survivors with comprehensive audiologic assessments (eg, Words-in-Noise [WIN] tests, full-spectrum audiometry, and additional otologic measures), as well as the progression of CRHL considering comorbidities, modifiable factors associated with risk, and cumulative cisplatin dose.

Objective

To assess CRHL with comprehensive audiologic assessments, including the WIN, evaluate the longitudinal progression of CRHL, and identify factors associated with risk.

Design, Setting, and Participants

The Platinum Study is a longitudinal study of cisplatin-treated testicular cancer survivors (TCS) enrolled from 2012 to 2018 with follow-up ongoing. Longitudinal comprehensive audiologic assessments at Indiana University and Memorial Sloan Kettering Cancer Center included 100 participants without audiometrically defined profound hearing loss (HL) at baseline and at least 3.5 years from their first audiologic assessment. Data were analyzed from December 2013 to December 2022.

Exposures

Factors associated with risk included cumulative cisplatin dose, hypertension, hypercholesterolemia, diabetes, tobacco use, physical inactivity, body mass index, family history of HL, cognitive dysfunction, psychosocial symptoms, and tinnitus.

Main Outcomes and Measures

Main outcomes were audiometrically measured HL defined as combined-ears high-frequency pure-tone average (4-12 kHz) and speech-recognition in noise performance measured with WIN. Multivariable analyses evaluated factors associated with risk for WIN scores and progression of audiometrically defined HL.

Results

Median (range) age of 100 participants at evaluation was 48 (25-67) years; median (range) time since chemotherapy: 14 (4-31) years. At follow-up, 78 (78%) TCS had audiometrically defined HL; those self-reporting HL had 2-fold worse hearing than TCS without self-reported HL (48 vs 24 dB HL; P < .001). A total of 54 (54%) patients with self-reported HL showed clinically significant functional impairment on WIN testing. Poorer WIN performance was associated with hypercholesterolemia (β = 0.88; 95% CI, 0.08 to 1.69; P = .03), lower-education (F1 = 5.95; P = .004), and severity of audiometrically defined HL (β̂ = 0.07; 95% CI, 0.06 to 0.09; P < .001). CRHL progression was associated with hypercholesterolemia (β̂ = -4.38; 95% CI, -7.42 to -1.34; P = .01) and increasing age (β̂ = 0.33; 95% CI, 0.15 to 0.50; P < .001). Importantly, relative to age-matched male normative data, audiometrically defined CRHL progression significantly interacted with cumulative cisplatin dose (F1 = 5.98; P = .02); patients given 300 mg/m2 or less experienced significantly less progression, whereas greater temporal progression followed doses greater than 300 mg/m2.

Conclusions and Relevance

Follow-up of cisplatin-treated cancer survivors should include strict hypercholesterolemia control and regular audiological assessments. Risk stratification through validated instruments should include querying hearing concerns. CRHL progression relative to age-matched norms is likely associated with cumulative cisplatin dose; investigation over longer follow-up is warranted.

LRRC8/VRAC volume-regulated anion channels are crucial for hearing

Hearing crucially depends on cochlear ion homeostasis as evident from deafness elicited by mutations in various genes encoding cation or anion channels and transporters. Ablation of ClC-K/barttin chloride channels causes deafness by interfering with the positive electrical potential of the endolymph, but roles of other anion channels in the inner ear have not been studied. Here we report the intracochlear distribution of all five LRRC8 subunits of VRAC, a volume-regulated anion channel that transports chloride, metabolites and drugs such as the ototoxic anti-cancer drug cisplatin, and explore its physiological role by ablating its subunits. Sensory hair cells express all LRRC8 isoforms, whereas only LRRC8A, D and E were found in the potassium-secreting epithelium of the stria vascularis. Cochlear disruption of the essential LRRC8A subunit, or combined ablation of LRRC8D and E, resulted in cochlear degeneration and congenital deafness of Lrrc8a-/- mice. It was associated with a progressive degeneration of the organ of Corti and its innervating spiral ganglion. Like disruption of ClC-K/barttin, loss of VRAC severely reduced the endocochlear potential. However, the mechanism underlying this reduction seems different. Disruption of VRAC, but not ClC-K/barttin, led to an almost complete loss of Kir4.1 (KCNJ10), a strial K+ channel crucial for the generation of the endocochlear potential. The strong downregulation of Kir4.1 might be secondary to a loss of VRAC-mediated transport of metabolites regulating inner ear redox potential such as glutathione. Our study extends the knowledge of the role of cochlear ion transport in hearing and ototoxicity.

Murine cochlear damage models in the context of hair cell regeneration research

Understanding the complex pathologies associated with hearing loss is a significant motivation for conducting inner ear research. Lifelong exposure to loud noise, ototoxic drugs, genetic diversity, sex, and aging collectively contribute to human hearing loss. Replicating this pathology in research animals is challenging because hearing impairment has varied causes and different manifestations. A central aspect, however, is the loss of sensory hair cells and the inability of the mammalian cochlea to replace them. Researching therapeutic strategies to rekindle regenerative cochlear capacity, therefore, requires the generation of animal models in which cochlear hair cells are eliminated. This review discusses different approaches to ablate cochlear hair cells in adult mice. We inventoried the cochlear cyto- and histo-pathology caused by acoustic overstimulation, systemic and locally applied drugs, and various genetic tools. The focus is not to prescribe a perfect damage model but to highlight the limitations and advantages of existing approaches and identify areas for further refinement of damage models for use in regenerative studies.

FDA-Approved MEK1/2 Inhibitor, Trametinib, Protects Mice from Cisplatin and Noise-Induced Hearing Loss

Hearing loss is one of the most common types of disability; however, there is only one FDA-approved drug to prevent any type of hearing loss. Treatment with the highly effective chemotherapy agent, cisplatin, and exposure to high decibel noises are two of the most common causes of hearing loss. The mitogen activated protein kinase (MAPK) pathway, a phosphorylation cascade consisting of RAF, MEK1/2, and ERK1/2, has been implicated in both types of hearing loss. Pharmacologically inhibiting BRAF or ERK1/2 is protective from noise and cisplatin-induced hearing loss in multiple mouse models. Trametinib, a MEK1/2 inhibitor, protects from cisplatin induced outer hair cell death in mouse cochlear explants; however, to the best of our knowledge, inhibiting MEK1/2 has not yet been shown to be protective from hearing loss in vivo. In this study, we demonstrate that trametinib protects from cisplatin-induced hearing loss in a translationally relevant mouse model and does not interfere with cisplatin's tumor killing efficacy in cancer cell lines. Higher doses of trametinib were toxic to mice when combined with cisplatin but lower doses of the drug were protective from hearing loss without any known toxicity. Trametinib also protected mice from noise-induced hearing loss and synaptic damage. This study shows that MEK1/2 inhibition protects from both insults of hearing loss and that targeting all three kinases in the MAPK pathway protect from cisplatin and noise-induced hearing loss in mice.

Combined genetic polymorphisms of the GSTT1 and NRF2 genes increase susceptibility to cisplatin-induced ototoxicity: A preliminary study

OBJECTIVE

The genotype-phenotype relationship in cisplatin-induced ototoxicity remains unclear. By assessing early shifts in distortion product otoacoustic emission (DPOAE) levels after initial cisplatin administration, we aimed to discriminate patients' susceptibility to cisplatin-induced ototoxicity and elucidate their genetic background.

STUDY DESIGN

A prospective cross-sectional study.

SETTING

Tertiary referral hospital in Japan.

PATIENTS

Twenty-six patients with head and neck cancer were undergoing chemoradiotherapy with three cycles of 100 mg/m2 cisplatin.

INTERVENTIONS

Repetitive pure-tone audiometry and DPOAE measurements, and blood sampling for DNA extraction were performed. Patients were grouped into early ototoxicity presence or absence based on whether DPOAE level shifts exceeded the corresponding reference limits of the 21-day test interval.

MAIN OUTCOME MEASURES

Hearing thresholds after each cisplatin cycle, severity of other adverse events, and polymorphisms in cisplatin-induced ototoxicity-associated genes were compared.

RESULTS

Early ototoxicity was present in 14 and absent in 12 patients. Ototoxicity presence on DPOAEs was associated with greater progression of hearing loss in frequencies ≥2 kHz throughout therapy and with higher ototoxicity grades compared with ototoxicity absence. Ototoxicity was further associated with grade ≥2 nausea. Ototoxicity presence was genetically associated with the GSTT1 null genotype and G-allele of NFE2L2 rs6721961, whereas ototoxicity absence was associated with the GSTM1 null genotype. Dose-dependent progression of hearing loss was the greatest in the combined genotype pattern of GSTT1 null and the T/G or G/G variants of rs6721961.

CONCLUSION

Early DPOAE changes reflected genetic vulnerability to cisplatin-induced ototoxicity. Hereditary insufficiency of the antioxidant defense system causes severe cisplatin-induced hearing loss and nausea.

Copper Chaperone Atox1 Protected the Cochlea From Cisplatin by Regulating the Copper Transport Family and Cell Cycle

Antioxidant 1 copper chaperone (Atox1) may contribute to preventing DDP cochlear damage by regulating copper transport family and cell cycle proteins. A rat model of cochlear damage was developed by placing gelatin sponges treated with DDP in the cochlea. HEI-OC1 cells were treated with 133 μM DDP as a cell model. DDP-induced ototoxicity in rats was confirmed by immunofluorescence (IF) imaging. The damage of DDP to HEI-OC1 cells was assessed by using CCK-8, TUNEL, and flow cytometry. The relationship between Atox1, a member of the copper transport protein family, and the damage to in vivo/vitro models was explored by qRT-PCR, western blot, CCK-8, TUNEL, and flow cytometry. DDP had toxic and other side effects causing cochlear damage and promoted HEI-OC1 cell apoptosis and cell cycle arrest. The over-expression of Atox1 (oe-Atox1) was accomplished by transfecting lentiviral vectors into in vitro/vivo models. We found that oe-Atox1 increased the levels of Atox1, copper transporter 1 (CTR1), and SOD3 in HEI-OC1 cells and decreased the expression levels of ATPase copper transporting α (ATP7A) and ATPase copper transporting β (ATP7B). In addition, the transfection of oe-Atox1 decreased cell apoptosis rate and the number of G2/M stage cells. Similarly, the expression of myosin VI and phalloidin of cochlea cells in vivo decreased. Atox1 ameliorated DDP-induced damage to HEI-OC1 cells or rats' cochlea by regulating the levels of members of the copper transport family.

Mechanisms underlying dose-limiting toxicities of conventional chemotherapeutic agents

Dose-limiting toxicities (DLTs) are severe adverse effects that define the maximum tolerated dose of a cancer drug. In addition to the specific mechanisms of each drug, common contributing factors include inflammation, apoptosis, ion imbalances, and tissue-specific enzyme deficiencies. Among various DLTs are bleomycin-induced pulmonary fibrosis, doxorubicin-induced cardiomyopathy, cisplatin-induced nephrotoxicity, methotrexate-induced hepatotoxicity, vincristine-induced neurotoxicity, paclitaxel-induced peripheral neuropathy, and irinotecan, which elicits severe diarrhea. Currently, specific treatments beyond dose reduction are lacking for most toxicities. Further research on cellular and molecular pathways is imperative to improve their management. This review synthesizes preclinical and clinical data on the pharmacological mechanisms underlying DLTs and explores possible treatment approaches. A comprehensive perspective reveals knowledge gaps and emphasizes the need for future studies to develop more targeted strategies for mitigating these dose-dependent adverse effects. This could allow the safer administration of fully efficacious doses to maximize patient survival.

Molecular Characteristics of Cisplatin-Induced Ototoxicity and Therapeutic Interventions

Cisplatin is a commonly used chemotherapeutic agent with proven efficacy in treating various malignancies, including testicular, ovarian, cervical, breast, bladder, head and neck, and lung cancer. Cisplatin is also used to treat tumors in children, such as neuroblastoma, osteosarcoma, and hepatoblastoma. However, its clinical use is limited by severe side effects, including ototoxicity, nephrotoxicity, neurotoxicity, hepatotoxicity, gastrointestinal toxicity, and retinal toxicity. Cisplatin-induced ototoxicity manifests as irreversible, bilateral, high-frequency sensorineural hearing loss in 40-60% of adults and in up to 60% of children. Hearing loss can lead to social isolation, depression, and cognitive decline in adults, and speech and language developmental delays in children. Cisplatin causes hair cell death by forming DNA adducts, mitochondrial dysfunction, oxidative stress, and inflammation, culminating in programmed cell death by apoptosis, necroptosis, pyroptosis, or ferroptosis. Contemporary medical interventions for cisplatin ototoxicity are limited to prosthetic devices, such as hearing aids, but these have significant limitations because the cochlea remains damaged. Recently, the U.S. Food and Drug Administration (FDA) approved the first therapy, sodium thiosulfate, to prevent cisplatin-induced hearing loss in pediatric patients with localized, non-metastatic solid tumors. Other pharmacological treatments for cisplatin ototoxicity are in various stages of preclinical and clinical development. This narrative review aims to highlight the molecular mechanisms involved in cisplatin-induced ototoxicity, focusing on cochlear inflammation, and shed light on potential antioxidant and anti-inflammatory therapeutic interventions to prevent or mitigate the ototoxic effects of cisplatin. We conducted a comprehensive literature search (Google Scholar, PubMed) focusing on publications in the last five years.

Macrophage Depletion Protects Against Cisplatin-Induced Ototoxicity and Nephrotoxicity

Cisplatin is a widely used and highly effective anti-cancer drug with significant side effects including ototoxicity and nephrotoxicity. Macrophages, the major resident immune cells in the cochlea and kidney, are important drivers of both inflammatory and tissue repair responses. To investigate the roles of macrophages in cisplatin-induced ototoxicity and nephrotoxicity, we used PLX3397, an FDA-approved inhibitor of the colony-stimulating factor 1 receptor (CSF1R), to eliminate tissue-resident macrophages during the course of cisplatin administration. Mice treated with cisplatin alone (cisplatin/vehicle) had significant hearing loss (ototoxicity) as well as kidney injury (nephrotoxicity). Macrophage ablation using PLX3397 resulted in significantly reduced hearing loss measured by auditory brainstem responses (ABR) and distortion-product otoacoustic emissions (DPOAE). Sensory hair cells in the cochlea were protected against cisplatin-induced death in mice treated with PLX3397. Macrophage ablation also protected against cisplatin-induced nephrotoxicity, as evidenced by markedly reduced tubular injury and fibrosis as well as reduced plasma blood urea nitrogen (BUN) and neutrophil gelatinase-associated lipocalin (NGAL) levels. Mechanistically, our data suggest that the protective effect of macrophage ablation against cisplatin-induced ototoxicity and nephrotoxicity is mediated by reduced platinum accumulation in both the inner ear and the kidney. Together our data indicate that ablation of tissue-resident macrophages represents a novel strategy for mitigating cisplatin-induced ototoxicity and nephrotoxicity.

Brief summary

Macrophage ablation using PLX3397 was protective against cisplatin-induced ototoxicity and nephrotoxicity by limiting platinum accumulation in the inner ear and kidney.

Experimental drugs for the prevention or treatment of sensorineural hearing loss

INTRODUCTION

Sensorineural hearing loss results in irreversible loss of inner ear hair cells and spiral ganglion neurons. Reduced sound detection and speech discrimination can span all ages, and sensorineural hearing rehabilitation is limited to amplification with hearing aids or cochlear implants. Recent insights into experimental drug treatments for inner ear regeneration and otoprotection have paved the way for clinical trials in order to restore a more physiological hearing experience. Paired with the development of innovative minimally invasive approaches for drug delivery to the inner ear, new, emerging treatments for hearing protection and restoration are within reach.

AREAS COVERED

This expert opinion provides an overview of the latest experimental drug therapies to protect from and to restore sensorineural hearing loss.

EXPERT OPINION

The degree and type of cellular damage to the cochlea, the responsiveness of remaining, endogenous cells to regenerative treatments, and the duration of drug availability within cochlear fluids will determine the success of hearing protection or restoration.

Cisplatin ototoxicity mechanism and antagonistic intervention strategy: a scope review

Cisplatin is a first-line chemotherapeutic agent in the treatment of malignant tumors with remarkable clinical effects and low cost. However, the ototoxicity and neurotoxicity of cisplatin greatly limit its clinical application. This article reviews the possible pathways and molecular mechanisms of cisplatin trafficking from peripheral blood into the inner ear, the toxic response of cisplatin to inner ear cells, as well as the cascade reactions leading to cell death. Moreover, this article highlights the latest research progress in cisplatin resistance mechanism and cisplatin ototoxicity. Two effective protective mechanisms, anti-apoptosis and mitophagy activation, and their interaction in the inner ear are discussed. Additionally, the current clinical preventive measures and novel therapeutic agents for cisplatin ototoxicity are described. Finally, this article also forecasts the prospect of possible drug targets for mitigating cisplatin-induced ototoxicity. These include the use of antioxidants, inhibitors of transporter proteins, inhibitors of cellular pathways, combination drug delivery methods, and other mechanisms that have shown promise in preclinical studies. Further research is needed to evaluate the efficacy and safety of these approaches.

Hearing Outcomes in a Deintensification Trial of Adjuvant Therapy for HPV-Related Oropharyngeal Squamous Cell Carcinoma

OBJECTIVE

To explore whether deintensification of adjuvant therapy reduces ototoxicity among patients with human papillomavirus (HPV)-related oropharyngeal squamous cell carcinoma (OPSCC).

STUDY DESIGN

Retrospective cohort study.

SETTING

Single academic center.

METHODS

The ototoxicity rate among adult patients with HPV-related OPSCC enrolled in the Minimalist Trial (MINT), a prospective phase 2 trial of surgery followed by risk-adjusted deintensified adjuvant therapy (42 Gy radiation given alone or with a single 100 mg/m² dose of cisplatin), was compared to that among a historical cohort treated with standard adjuvant therapy (60-66 Gy radiation with up to three 100 mg/m² doses of cisplatin). Ototoxicity was defined as Common Terminology Criteria for Adverse Events v5.0 ≥ Grade 2. Mixed model analysis was performed to investigate the association between deintensified adjuvant therapy and treatment-related hearing loss.

RESULTS

A total of 29 patients (58 ears) were analyzed in the MINT cohort, and 27 patients (54 ears) in the historical cohort. The ototoxicity rate was 5% (n = 3/58 ears) in the MINT cohort and 46% (n = 25/54 ears) in the historical cohort (difference, 41%; 95% confidence interval [CI] = 27%-56%). Patients in the MINT cohort demonstrated a 95% decrease in risk of ototoxicity compared to those in the historical cohort (adjusted odds ratio: 0.05, 95% CI = 0.01-0.31). Differences in estimated marginal mean threshold shifts were statistically and clinically significant at frequencies ≥ 3 kHz.

CONCLUSION

The deintensified adjuvant therapy given in MINT led to less ototoxicity than standard adjuvant therapy among patients with HPV-related OPSCC.

Cisplatin-induced ototoxicity: From signaling network to therapeutic targets

Administration of cisplatin, a common chemotherapeutic drug, has an inevitable side effect of sensorineural hearing loss. The main etiologies are stria vascularis injury, spiral ganglion degeneration, and hair cell death. Over several decades, the research scope of cisplatin-induced ototoxicity has expanded with the discovery of the molecular mechanism mediating inner ear cell death, highlighting the roles of reactive oxygen species and transport channels for cisplatin uptake into inner ear cells. Upon entering hair cells, cisplatin disrupts organelle metabolism, induces oxidative stress, and targets DNA to cause intracellular damage. Recent studies have also reported the role of inflammation in cisplatin-induced ototoxicity. In this article, we preform a narrative review of the latest reported molecular mechanisms of cisplatin-induced ototoxicity, from extracellular to intracellular. We build up a signaling network starting with cisplatin entering into the inner ear through the blood labyrinth barrier, disrupting cochlear endolymph homeostasis, and activating inflammatory responses of the outer hair cells. After entering the hair cells, cisplatin causes hair cell death via DNA damage, redox system imbalance, and mitochondrial and endoplasmic reticulum dysfunction, culminating in programmed cell death including apoptosis, necroptosis, autophagic death, pyroptosis, and ferroptosis. Based on the mentioned mechanisms, prominent therapeutic targets, such as channel-blocking drugs of cisplatin transporter, construction of cisplatin structural analogues, anti-inflammatory drugs, antioxidants, cell death inhibitors, and others, were collated. Considering the recent research efforts, we have analyzed the feasibility of the aforementioned therapeutic strategies and proposed our otoprotective approaches to overcome cisplatin-induced ototoxicity.

Hair cell toxicology: With the help of a little fish

Hearing or balance loss are disabling conditions that have a serious impact in those suffering them, especially when they appear in children. Their ultimate cause is frequently the loss of function of mechanosensory hair cells in the inner ear. Hair cells can be damaged by environmental insults, like noise or chemical agents, known as ototoxins. Two of the most common ototoxins are life-saving medications: cisplatin against solid tumors, and aminoglycoside antibiotics to treat infections. However, due to their localization inside the temporal bone, hair cells are difficult to study in mammals. As an alternative animal model, zebrafish larvae have hair cells similar to those in mammals, some of which are located in a fish specific organ on the surface of the skin, the lateral line. This makes them easy to observe in vivo and readily accessible for ototoxins or otoprotective substances. These features have made possible advances in the study of the mechanisms mediating ototoxicity or identifying new potential ototoxins. Most importantly, the small size of the zebrafish larvae has allowed screening thousands of molecules searching for otoprotective agents in a scale that would be highly impractical in rodent models. The positive hits found can then start the long road to reach clinical settings to prevent hearing or balance loss.

Acetophenone protection against cisplatin-induced end-organ damage

Cisplatin is a widely used and efficacious chemotherapeutic agent for treating solid tumors, yet it causes systemic end-organ damage that is often irreversible and detrimental to quality of life. This includes severe sensorineural hearing loss, hepatotoxicity, and renal injury. Based on the hard-soft acid-base theory, we recently developed two acetophenone-derived, enol-based compounds that directly interfere with the side effects of cisplatin. We investigated organ-specific and generalized toxicity in order to define dose-dependent responses in rodents injected with cisplatin with or without the protective compounds. All metrics that were used as indicators of toxicity showed retention of baseline or control measurements when animals were pre-treated with acetophenones prior to cisplatin administration, while animals injected with no protective compounds showed expected elevations in toxicity measurements or depressions in measurements of organ function. These data support the further investigation of novel acetophenone compounds for the prevention of cisplatin-induced end-organ toxicity.

Cisplatin exposure acutely disrupts mitochondrial bioenergetics in the zebrafish lateral-line organ

Cisplatin is a commonly used chemotherapeutic agent that causes debilitating high-frequency hearing loss. No targeted therapies currently exist to treat cisplatin ototoxicity, partly because the underlying mechanisms of cisplatin-induced hair cell damage are not completely defined. Zebrafish may offer key insights to cisplatin ototoxicity because their lateral-line organ contains hair cells that are remarkably similar to those within the cochlea but are optically accessible, permitting observation of cisplatin injury in live intact hair cells. In this study, we used a combination of genetically encoded biosensors in zebrafish larvae and fluorescent indicators to characterize changes in mitochondrial bioenergetics in response to cisplatin. Following exposure to cisplatin, confocal imaging of live intact neuromasts demonstrated increased mitochondrial activity. Staining with fixable fluorescent dyes that accumulate in active mitochondria similarly showed hyperpolarized mitochondrial membrane potential. Zebrafish expressing a calcium indicator within their hair cells revealed elevated levels of mitochondrial calcium immediately following completion of cisplatin treatment. A fluorescent ROS indicator demonstrated that these changes in mitochondrial function were associated with increased oxidative stress. After a period of recovery, cisplatin-exposed zebrafish demonstrated caspase-3-mediated apoptosis. Altogether, these findings suggest that cisplatin acutely disrupts mitochondrial bioenergetics and may play a key role in initiating cisplatin ototoxicity.

Changes in vestibular and cochlear function following platinum-based chemotherapy: A preliminary report

OBJECTIVES

This study investigated the changes in vestibular and cochlear function in patients receiving platinum-based chemotherapy.

METHODS

A longitudinal study of 32 participants (10-70 years) receiving chemotherapy participated in the study. Baseline and exit vestibular and hearing assessments that included video head impulse (VHIT) testing, cervical and ocular vestibular evoked myogenic potentials (VEMP), dynamic visual acuity (DVA) and pure-tone audiometry were performed at the patient's treatment venue.

RESULTS

Half (50%) of the participants showed cochleotoxicity from baseline to exit testing, with left ears significantly more affected than right ears. There was no consistent relationship between hearing loss and vestibular dysfunction. DVA yielded normal results at baseline and exit testing in all participants. VEMP responses were absent in 28.1% of participants at baseline, reflecting the challenges of using VEMP for monitoring. VEMP and VHIT results showed a statistically significant (p < 0.05) decline in results from baseline to exit testing; however, participants did not report symptoms related to vestibular dysfunction. VHIT also showed left ears significantly (p < 0.05) more affected than right ears.

CONCLUSION

VHIT proved to be a valuable measure of changes in vestibular function secondary to ototoxicity. Future investigations should determine vestibulotoxicity criteria and optimal protocols for vestibulotoxicity monitoring at the patient's treatment venue.

Cochlear Marginal Cell Pyroptosis Is Induced by Cisplatin via NLRP3 Inflammasome Activation

Better understanding the mechanism of cisplatin-induced ototoxicity is of great significance for clinical prevention and treatment of cisplatin-related hearing loss. However, the mechanism of cisplatin-induced inflammatory response in cochlear stria vascularis and the mechanism of marginal cell (MC) damage have not been fully clarified. In this study, a stable model of cisplatin-induced MC damage was established in vitro, and the results of PCR and Western blotting showed increased expressions of NLRP3, Caspase-1, IL-1β, and GSDMD in MCs. Incomplete cell membranes including many small pores appearing on the membrane were also observed under transmission electron microscopy and scanning electron microscopy. In addition, downregulation of NLRP3 by small interfering RNA can alleviate cisplatin-induced MC pyroptosis, and reducing the expression level of TXNIP possesses the inhibition effect on NLRP3 inflammasome activation and its mediated pyroptosis. Taken together, our results suggest that NLRP3 inflammasome activation may mediate cisplatin-induced MC pyroptosis in cochlear stria vascularis, and TXNIP is a possible upstream regulator, which may be a promising therapeutic target for alleviating cisplatin-induced hearing loss.

Supporting Cells and Their Potential Roles in Cisplatin-Induced Ototoxicity

Cisplatin is a known ototoxic chemotherapy drug, causing irreversible hearing loss. Evidence has shown that cisplatin causes inner ear damage as a result of adduct formation, a proinflammatory environment and the generation of reactive oxygen species within the inner ear. The main cochlear targets for cisplatin are commonly known to be the outer hair cells, the stria vascularis and the spiral ganglion neurons. Further evidence has shown that certain transporters can mediate cisplatin influx into the inner ear cells including organic cation transporter 2 (OCT2) and the copper transporter Ctr1. However, the expression profiles for these transporters within inner ear cells are not consistent in the literature, and expression of OCT2 and Ctr1 has also been observed in supporting cells. Organ of Corti supporting cells are essential for hair cell activity and survival. Special interest has been devoted to gap junction expression by these cells as certain mutations have been linked to hearing loss. Interestingly, cisplatin appears to affect connexin expression in the inner ear. While investigations regarding cisplatin-induced hearing loss have been focused mainly on the known targets previously mentioned, the role of supporting cells for cisplatin-induced ototoxicity has been overlooked. In this mini review, we discuss the implications of supporting cells expressing OCT2 and Ctr1 as well as the potential role of gap junctions in cisplatin-induced cytotoxicity.

The Mechanotransduction Channel and Organic Cation Transporter Are Critical for Cisplatin Ototoxicity in Murine Hair Cells

Cisplatin is one of the most widely used chemotherapeutic drugs across the world. However, the serious ototoxic effects, leading to permanent hair cell death and hearing loss, significantly limit the utility of cisplatin. In zebrafish, the functional mechanotransduction channel is required for cisplatin ototoxicity. However, it is still unclear the extent to which the mechanotransduction channel is involved in cisplatin uptake and ototoxicity in mammalian hair cells. Herein, we show that genetically disrupting mechanotransduction in mouse partially protects hair cells from cisplatin-induced hair cell death. Using a fluorescent-dye conjugated cisplatin, we monitored cisplatin uptake in cochlear explants and found that functional mechanotransduction is required for the uptake of cisplatin in murine hair cells. In addition, cimetidine, an inhibitor of the organic cation transporter, also partially protects hair cells from cisplatin ototoxicity. Notably, the otoprotective effects of cimetidine do not require mechanotransduction. These findings suggest that both the mechanotransduction channel and the organic cation transporter are critical for cisplatin ototoxicity in murine hair cells.

Tetramethylpyrazine: A Review of Its Antitumor Potential and Mechanisms

Cancer remains a major public health threat. The mitigation of the associated morbidity and mortality remains a major research focus. From a molecular biological perspective, cancer is defined as uncontrolled cell division and abnormal cell growth caused by various gene mutations. Therefore, there remains an urgent need to develop safe and effective antitumor drugs. The antitumor effect of plant extracts, which are characterized by relatively low toxicity and adverse effect, has attracted significant attention. For example, increasing attention has been paid to the antitumor effects of tetramethylpyrazine (TMP), the active component of the Chinese medicine Chuanqiong, which can affect tumor cell proliferation, apoptosis, invasion, metastasis, and angiogenesis, as well as reverse chemotherapeutic resistance in neoplasms, thereby triggering antitumor effects. Moreover, TMP can be used in combination with chemotherapeutic agents to enhance their effects and reduce the side effect associated with chemotherapy. Herein, we review the antitumor effects of TMP to provide a theoretical basis and foundation for the further exploration of its underlying antitumor mechanisms and promoting its clinical application.

Mechanisms of Ototoxicity and Otoprotection

Ototoxicity refers to damage to the inner ear that leads to functional hearing loss or vestibular disorders by selected pharmacotherapeutics as well as a variety of environmental exposures (eg, lead, cadmium, solvents). This article reviews the fundamental mechanisms underlying ototoxicity by clinically relevant, hospital-prescribed medications (ie, aminoglycoside antibiotics or cisplatin, as illustrative examples). Also reviewed are current strategies to prevent prescribed medication-induced ototoxicity, with several clinical or candidate interventional strategies being discussed.