Drug-induced ototoxicity: Mechanisms, Pharmacogenetics, and protective strategies

Interaction of the New Monofunctional Anticancer Agent Phenanthriplatin With Transporters for Organic Cations

Cancer treatment with platinum compounds is an important achievement of modern chemotherapy. However, despite the beneficial effects, the clinical impact of these agents is hampered by the development of drug resistance as well as dose-limiting side effects. The efficacy but also side effects of platinum complexes can be mediated by uptake through plasma membrane transporters. In the kidneys, plasma membrane transporters are involved in their secretion into the urine. Renal secretion is accomplished by uptake from the blood into the proximal tubules cells, followed by excretion into the urine. The uptake process is mediated mainly by organic cation transporters (OCT), which are expressed in the basolateral domain of the plasma membrane facing the blood. The excretion of platinum into the urine is mediated by exchange with protons via multidrug and toxin extrusion proteins (MATE) expressed in the apical domain of plasma membrane. Recently, the monofunctional, cationic platinum agent phenanthriplatin, which is able to escape common cellular resistance mechanisms, has been synthesized and investigated. In the present study, the interaction of phenanthriplatin with transporters for organic cations has been evaluated. Phenanthriplatin is a high affinity substrate for OCT2, but has a lower apparent affinity for MATEs. The presence of these transporters increased cytotoxicity of phenanthriplatin. Therefore, phenanthriplatin may be especially effective in the treatment of cancers that express OCTs, such as colon cancer cells. However, the interaction of phenanthriplatin with OCTs suggests that its use as chemotherapeutic agent may be complicated by OCT-mediated toxicity. Unlike cisplatin, phenanthriplatin interacts with high specificity with hMATE1 and hMATE2K in addition to hOCT2. This interaction may facilitate its efflux from the cells and thereby decrease overall efficacy and/or toxicity.

In vitro gentamicin exposure alters caveolae protein profile in cochlear spiral ligament pericytes

Background

The aminoglycoside antibiotic gentamicin is an ototoxic drug and has been used experimentally to investigate cochlear damage induced by noise.We have investigated the changes in the protein profile associated with caveolae in gentamicin treated and untreated spiral ligament (SL) pericytes, specialized cells in the blood labyrinth barrier of the inner ear microvasculature. Pericytes from various microvascular beds express caveolae, protein and cholesterol rich microdomains, which can undergo endocytosis and transcytosis to transport small molecules in and out the cells. A different protein profile in transport-specialized caveolae may induce pathological changes affecting the integrity of the blood labyrinth barrier and ultimately contributing to hearing loss.

Method

Caveolae isolation from treated and untreated cells is achieved through ultracentrifugation of the lysates in discontinuous gradients. Mass spectrometry (LC-MS/MS) analysis identifies the proteins in the two groups. Proteins segregating with caveolae isolated from untreated SL pericytes are then compared to caveolae isolated from SL pericytes treated with the gentamicin for 24 h. Data are analyzed using bioinformatic tools.

Results

The caveolae proteome in gentamicin treated cells shows that 40% of total proteins are uniquely associated with caveolae during the treatment, and 15% of the proteins normally associated with caveolae in untreated cell are suppressed. Bioinformatic analysis of the data shows a decreased expression of proteins involved in genetic information processing, and an increase in proteins involved in metabolism, vesicular transport and signal transduction in gentamicin treated cells. Several Rab GTPases proteins, ubiquitous transporters, uniquely segregate with caveolae and are significantly enriched in gentamicin treated cells.

Conclusion

We report that gentamicin exposure modifies protein profile of caveolae from SL pericytes. We identified a pool of proteins which are uniquely segregating with caveolae during the treatment, mainly participating in metabolic and biosynthetic pathways, in transport pathways and in genetic information processing. Finally, we show for the first time proteins associated with caveolae SL pericytes linked to nonsyndromic hearing loss.

Prevalence of ototoxic medication use among older adults in Beaver Dam, Wisconsin

BACKGROUND AND PURPOSE

Drug-related ototoxicity may exacerbate presbycusis (age-related hearing loss); yet, few data are available on the prevalence of ototoxic medication use by older adults. The purposes of this study were to assess the impact of aging and ototoxicity on hearing loss, the prevalence of ototoxic medication use, and select characteristics associated with ototoxic medication use among older adults.

METHODS

Cross-sectional analyses were conducted using select variables extracted from the baseline and 10-year follow-up assessments of the two population-based epidemiological studies to compare two points in time.

RESULTS

Ninety-one percent of the sample was taking a medication reported to be ototoxic. Nonsteroidal anti-inflammatory drugs were the most commonly used (75.2%), followed by acetaminophen (39.9%) and diuretics (35.6%). Hypertension, diabetes, cardiovascular disease, and history of smoking were associated with ototoxic medication use. Participants with hearing loss were taking a significantly greater number of ototoxic medications than those without hearing loss.

CONCLUSION

Known ototoxic medications are widely used. Any subsequent ototoxicity may interact with age changes and a more severe hearing loss than that associated with only age.

IMPLICATIONS FOR PRACTICE

Nurse practitioners should inform older adults about the possibility of drug-related ototoxicity and monitor hearing acuity of all older adults taking known ototoxic medications.

Neuronal erythropoietin overexpression is protective against kanamycin-induced hearing loss in mice

Aminoglycosides have detrimental effects on the hair cells of the inner ear, yet these agents indisputably are one of the cornerstones in antibiotic therapy. Hence, there is a demand for strategies to prevent aminoglycoside-induced ototoxicity, which are not available today. In vitro data suggests that the pleiotropic growth factor erythropoietin (EPO) is neuroprotective against aminoglycoside-induced hair cell loss. Here, we use a mouse model with EPO-overexpression in neuronal tissue to evaluate whether EPO could also in vivo protect from aminoglycoside-induced hearing loss. Auditory brainstem response (ABR) thresholds were measured in 12-weeks-old mice before and after treatment with kanamycin for 15 days, which resulted in both C57BL/6 and EPO-transgenic animals in a high-frequency hearing loss. However, ABR threshold shifts in EPO-transgenic mice were significantly lower than in C57BL/6 mice (mean difference in ABR threshold shift 13.6 dB at 32 kHz, 95% CI 3.8-23.4 dB, p = 0.003). Correspondingly, quantification of hair cells and spiral ganglion neurons by immunofluorescence revealed that EPO-transgenic mice had a significantly lower hair cell and spiral ganglion neuron loss than C57BL/6 mice. In conclusion, neuronal overexpression of EPO is protective against aminoglycoside-induce hearing loss, which is in accordance with its known neuroprotective effects in other organs, such as the eye or the brain.

Anti-cancer characteristics and ototoxicity of platinum(II) amine complexes with only one leaving ligand

Unlike cisplatin, which forms bifunctional DNA adducts, monofunctional platinum(II) complexes bind only one strand of DNA and might target cancer without causing auditory side-effects associated with cisplatin treatment. We synthesized the monofunctional triamine-ligated platinum(II) complexes, Pt(diethylenetriamine)Cl, [Pt(dien)Cl]+, and Pt(N,N-diethyldiethylenetriamine)Cl, [Pt(Et2dien)Cl]+, and the monofunctional heterocyclic-ligated platinum(II) complexes, pyriplatin and phenanthriplatin, and compared their 5'-GMP binding rates, cellular compartmental distribution and cellular viability effects. A zebrafish inner ear model was used to determine if the monofunctional complexes and cisplatin caused hearing threshold shifts and reduced auditory hair cell density. The four monofunctional complexes had varied relative GMP binding rates, but similar cytosolic and nuclear compartmental uptake in three cancer cell lines (A549, Caco2, HTB16) and a control cell line (IMR90). Phenanthriplatin had the strongest effect against cellular viability, comparable to cisplatin, followed by [Pt(Et2dien)Cl]+, pyriplatin and [Pt(dien)Cl]+. Phenanthriplatin also produced the highest hearing threshold shifts followed by [Pt(dien)Cl]+, [Pt(Et2dien)Cl]+, cisplatin and pyriplatin. Hair cell counts taken from four regions of the zebrafish saccule showed that cisplatin significantly reduced hair cell density in three regions and phenanthriplatin in only one region, with the other complexes having no significant effect. Utricular hair cell density was not reduced by any of the compounds. Our results suggest that placing greater steric hindrance cis to one side of the platinum coordinating center in monofunctional complexes promotes efficient targeting of the nuclear compartment and guanosine residues, and may be responsible for reducing cancer cell viability. Also, the monofunctional compounds caused hearing threshold shifts with minimal effect on hair cell density, which suggests that they may affect different pathways than cisplatin.

Further Investigation of the Role of ACYP2 and WFS1 Pharmacogenomic Variants in the Development of Cisplatin-Induced Ototoxicity in Testicular Cancer Patients

Purpose: Adverse drug reactions such as ototoxicity, which occurs in approximately one-fifth of adult patients who receive cisplatin treatment, can incur large socioeconomic burdens on patients with testicular cancer who develop this cancer during early adulthood. Recent genome-wide association studies have identified genetic variants in ACYP2 and WFS1 that are associated with cisplatin-induced ototoxicity. We sought to explore the role of these genetic susceptibility factors to cisplatin-induced ototoxicity in patients with testicular cancer.Experimental Design: Extensive clinical and demographic data were collected for 229 patients with testicular cancer treated with cisplatin. Patients were genotyped for two variants, ACYP2 rs1872328 and WFS1 rs62283056, that have previously been associated with hearing loss in cisplatin-treated patients. Analyses were performed to investigate the association of these variants with ototoxicity in this cohort of adult patients with testicular cancer.Results: Pharmacogenomic analyses revealed that ACYP2 rs1872328 was significantly associated with cisplatin-induced ototoxicity [P = 2.83 × 10^-3, OR (95% CI):14.7 (2.6-84.2)]. WFS1 rs62283056 was not significantly associated with ototoxicity caused by cisplatin (P = 0.39); however, this variant was associated with hearing loss attributable to any cause [P = 5.67 × 10^-3, OR (95% CI): 3.2 (1.4-7.7)].Conclusions: This study has provided the first evidence for the role of ACYP2 rs1872328 in cisplatin-induced ototoxicity in patients with testicular cancer. These results support the use of this information to guide the development of strategies to prevent cisplatin-induced ototoxicity across cancers. Further, this study has highlighted the importance of phenotypic differences in replication studies and has provided further evidence for the role of WFS1 rs62283056 in susceptibility to hearing loss, which may be worsened by cisplatin treatment. Clin Cancer Res; 24(8); 1866-71. ©2018 AACR.

Medicações ototóxicas utilizadas no tratamento oncológico pediátrico: uma revisão sistemática

RESUMO Objetivo Fazer um levantamento dos medicamentos ototóxicos utilizados no tratamento do câncer pediátrico, apontar os danos das drogas para o sistema auditivo e os métodos utilizados na identificação destes danos nessa população. Estratégia de pesquisa: Foram utilizados periódicos nacionais e internacionais pertinentes ao assunto, acessados eletronicamente em bases de dados da Biblioteca Virtual em Saúde - MS, PubMed, Biblioteca Digital Brasileira de Teses e Dissertações, que envolvessem a população pediátrica com histórico de tratamento oncológico, publicados entre 2007 e 2016, e no Banco de Teses e Dissertações da Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. Critérios de seleção Foram selecionados estudos que contemplassem os seguintes critérios: estudos observacionais nas línguas portuguesa, inglesa ou espanhola e resumos disponíveis que informassem o método de avaliação do dano auditivo. Resultados A amostra final resultou em 12 artigos. Destes, a audiometria tonal limiar foi o método de avaliação auditiva mais utilizado, estando presente em 10 (84,61%) dos estudos, seguido das emissões otoacústicas (46,15%). Todos os estudos foram desenvolvidos com pacientes que fizeram uso de cisplatina ou derivados da platina e, quanto ao dano auditivo, apenas 1 dos estudos incluídos não relatou presença de alteração na população estudada. Conclusão Os derivados da platina expressam papel importante no tratamento do câncer em diversos níveis e são os agentes ototóxicos mais citados em pesquisas. A cóclea é o local mais afetado, mais especificamente as células ciliadas externas. Os métodos de investigação da alteração auditiva mais utilizados são a audiometria tonal limiar e as emissões otoacústicas.

Novel SS-31 modified liposomes for improved protective efficacy of minocycline against drug-induced hearing loss

SS-31 modified, minocycline-loaded liposomes significantly increased hair cell survival against chronic exposure to gentamicin in a zebrafish model.

Using thermal scanning assays to test protein-protein interactions of inner-ear cadherins

Protein-protein interactions play a crucial role in biological processes such as cell-cell adhesion, immune system-pathogen interactions, and sensory perception. Understanding the structural determinants of protein-protein complex formation and obtaining quantitative estimates of their dissociation constant (KD) are essential for the study of these interactions and for the discovery of new therapeutics. At the same time, it is equally important to characterize protein-protein interactions in a high-throughput fashion. Here, we use a modified thermal scanning assay to test interactions of wild type (WT) and mutant variants of N-terminal fragments (EC1+2) of cadherin-23 and protocadherin-15, two proteins essential for inner-ear mechanotransduction. An environmentally sensitive fluorescent dye (SYPRO orange) is used to monitor melting temperature (Tm) shifts of protocadherin-15 EC1+2 (pcdh15) in the presence of increasing concentrations of cadherin-23 EC1+2 (cdh23). These Tm shifts are absent when we use proteins containing deafness-related missense mutations known to disrupt cdh23 binding to pcdh15, and are increased for some rationally designed mutants expected to enhance binding. In addition, surface plasmon resonance binding experiments were used to test if the Tm shifts correlated with changes in binding affinity. We used this approach to find a double mutation (cdh23(T15E)- pcdh15(G16D)) that enhances binding affinity of the cadherin complex by 1.98 kJ/mol, roughly two-fold that of the WT complex. We suggest that the thermal scanning methodology can be used in high-throughput format to quickly compare binding affinities (KD from nM up to 100 μM) for some heterodimeric protein complexes and to screen small molecule libraries to find protein-protein interaction inhibitors and enhancers.

Amikacin: Uses, Resistance, and Prospects for Inhibition

Aminoglycosides are a group of antibiotics used since the 1940s to primarily treat a broad spectrum of bacterial infections. The primary resistance mechanism against these antibiotics is enzymatic modification by aminoglycoside-modifying enzymes that are divided into acetyl-transferases, phosphotransferases, and nucleotidyltransferases. To overcome this problem, new semisynthetic aminoglycosides were developed in the 70s. The most widely used semisynthetic aminoglycoside is amikacin, which is refractory to most aminoglycoside modifying enzymes. Amikacin was synthesized by acylation with the l-(-)-γ-amino-α-hydroxybutyryl side chain at the C-1 amino group of the deoxystreptamine moiety of kanamycin A. The main amikacin resistance mechanism found in the clinics is acetylation by the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib], an enzyme coded for by a gene found in integrons, transposons, plasmids, and chromosomes of Gram-negative bacteria. Numerous efforts are focused on finding strategies to neutralize the action of AAC(6')-Ib and extend the useful life of amikacin. Small molecules as well as complexes ionophore-Zn⁺² or Cu⁺² were found to inhibit the acetylation reaction and induced phenotypic conversion to susceptibility in bacteria harboring the aac(6')-Ib gene. A new semisynthetic aminoglycoside, plazomicin, is in advance stage of development and will contribute to renewed interest in this kind of antibiotics.

Pharmacogenetics of drug-induced ototoxicity caused by aminoglycosides and cisplatin

Aminoglycosides and the anticancer drug cisplatin can cause permanent hearing loss, which impacts patients' quality of life and results in considerable subsequent costs. Since patients' individual susceptibility to aminoglycoside- and cisplatin-induced ototoxicity varies considerably, strategies are needed to identify patients at risk, who may require alternative treatments or specific protection strategies. For both drugs, various genetic variants were linked to an increased or decreased risk for ototoxicity. Except for the association between the A1555G mitochondrial DNA mutation and aminoglycoside ototoxicity, their evidence is considered low because study cohorts were often small and replication studies either missing or contradictory. This review summarizes the pharmacogenetic markers linked to aminoglycoside- or cisplatin-induced ototoxicity and discusses reasons for replication failure and future perspective.

A mitochondrial targeting tetrapeptide Bendavia protects lateral line hair cells from gentamicin exposure

The hearing loss induced by aminoglycosides is caused by the permanent loss of mechanosensory hair cells of the inner ear. The aim of the present study is therefore to evaluate the protective effect of Bendavia, a novel antioxidant, on gentamicin-induced hair cell damage in zebrafish lateral lines. The results demonstrated the pretreatment of Bendavia exhibited dose-dependent protection against gentamicin in both acute and chronic exposure. We found that Bendavia at 150 μm conferred optimal protection from either acute or chronic exposure with ototoxin. Bendavia reduced uptake of fluorescent-tagged gentamicin via mechanoelectrical transduction channels, suggesting its protective effects may be partially due to decreasing ototoxic molecule uptake. The intracellular death pathways inhibition triggered by gentamicin might be also included as no blockage of gentamicin was observed. Our data suggest that Bendavia represents a novel otoprotective drug that might provide a therapeutic alternative for patients receiving aminoglycoside treatment.

Non-autonomous Cellular Responses to Ototoxic Drug-Induced Stress and Death

The first major recognition of drug-induced hearing loss can be traced back more than seven decades to the development of streptomycin as an antimicrobial agent. Since then at least 130 therapeutic drugs have been recognized as having ototoxic side-effects. Two important classes of ototoxic drugs are the aminoglycoside antibiotics and the platinum-based antineoplastic agents. These drugs save the lives of millions of people worldwide, but they also cause irreparable hearing loss. In the inner ear, sensory hair cells (HCs) and spiral ganglion neurons (SGNs) are important cellular targets of these drugs, and most mechanistic studies have focused on the cell-autonomous responses of these cell types in response to ototoxic stress. Despite several decades of studies on ototoxicity, important unanswered questions remain, including the cellular and molecular mechanisms that determine whether HCs and SGNs will live or die when confronted with ototoxic challenge. Emerging evidence indicates that other cell types in the inner ear can act as mediators of survival or death of sensory cells and SGNs. For example, glia-like supporting cells (SCs) can promote survival of both HCs and SGNs. Alternatively, SCs can act to promote HC death and inhibit neural fiber expansion. Similarly, tissue resident macrophages activate either pro-survival or pro-death signaling that can influence HC survival after exposure to ototoxic agents. Together these data indicate that autonomous responses that occur within a stressed HC or SGN are not the only (and possibly not the primary) determinants of whether the stressed cell ultimately lives or dies. Instead non-cell-autonomous responses are emerging as significant determinants of HC and SGN survival vs. death in the face of ototoxic stress. The goal of this review is to summarize the current evidence on non-cell-autonomous responses to ototoxic stress and to discuss ways in which this knowledge may advance the development of therapies to reduce hearing loss caused by these drugs.