Systemic co-treatment with alpha-melanocyte stimulating hormone delays hearing loss caused by local cisplatin administration in guinea pigs

Platinum-Based Combination Therapy: Molecular Rationale, Current Clinical Uses, and Future Perspectives

Platinum drugs are common in chemotherapy, but their clinical applications have been limited due to drug resistance and severe toxic effects. The combination of platinum drugs with other drugs with different mechanisms of anticancer action, especially checkpoint inhibitors, is increasingly popular. This combination is the leading strategy to improve the therapeutic efficiency and minimize the side effects of platinum drugs. In this review, we focus on the mechanistic basis of the combinations of platinum-based drugs with other drugs to inspire the development of more promising platinum-based combination regimens in clinical trials as well as novel multitargeting platinum drugs overcoming drug resistance and toxicities resulting from current platinum drugs.

Current Strategies to Combat Cisplatin-Induced Ototoxicity

Cisplatin is widely used for the treatment of a number of solid malignant tumors. However, ototoxicity induced by cisplatin is an obstacle to effective treatment of tumors. The basis for this toxicity has not been fully elucidated. It is generally accepted that hearing loss is due to excessive production of reactive oxygen species by cells of the cochlea. In addition, recent data suggest that inflammation may trigger inner ear cell death through endoplasmic reticulum stress, autophagy, and necroptosis, which induce apoptosis. Strategies have been extensively explored by which to prevent, alleviate, and treat cisplatin-induced ototoxicity, which minimize interference with antitumor activity. Of these strategies, none have been approved by the Federal Drug Administration, although several preclinical studies have been promising. This review highlights recent strategies that reduce cisplatin-induced ototoxicity. The focus of this review is to identify candidate agents as novel molecular targets, drug administration routes, delivery systems, and dosage schedules. Animal models of cisplatin ototoxicity are described that have been used to evaluate drug efficacy and side effect prevention. Finally, clinical reports of otoprotection in patients treated with cisplatin are highlighted. For the future, high-quality studies are required to provide reliable data regarding the safety and effectiveness of pharmacological interventions that reduce cisplatin-induced ototoxicity.

Association of skin color, race/ethnicity, and hearing loss among adults in the USA

Epidemiologic studies of hearing loss in adults have demonstrated that the odds of hearing loss are substantially lower in black than in white individuals. The basis of this association is unknown. We hypothesized that skin pigmentation as a marker of melanocytic functioning mediates this observed association and that skin pigmentation is associated with hearing loss independent of race/ethnicity. We analyzed cross-sectional data from 1,258 adults (20-59 years) in the 2003-2004 cycle of the National Health and Nutritional Examination Survey who had assessment of Fitzpatrick skin type and pure-tone audiometric testing. Audiometric thresholds in the worse hearing ear were used to calculate speech- (0.5-4 kHz) and high-frequency (3-8 kHz) pure-tone averages (PTA). Regression models were stratified by Fitzpatrick skin type or race/ethnicity to examine the association of each factor with hearing loss independent of the other. Models were adjusted for potential confounders (demographic, medical, and noise exposure covariates). Among all participants, race/ethnicity was associated with hearing thresholds (black participants with the best hearing followed by Hispanics and then white individuals), but these associations were not significant in analyses stratified by skin color. In contrast, in race-stratified analyses, darker-skinned Hispanics had better hearing than lighter-skinned Hispanics by an average of -2.5 dB hearing level (HL; 95% CI, -4.8 to -0.2) and -3.1 dB HL (95% CI, -5.3 to -0.8) for speech and high-frequency PTA, respectively. Associations between skin color and hearing loss were not significant in white and black participants. Our results demonstrate that skin pigmentation is independently associated with hearing loss in Hispanics and suggest that skin pigmentation as a marker of melanocytic functioning may mediate the strong association observed between race/ethnicity and hearing loss.

Alpha-melanocyte-stimulating hormone and related tripeptides: biochemistry, antiinflammatory and protective effects in vitro and in vivo, and future perspectives for the treatment of immune-mediated inflammatory diseases

Alpha-MSH is a tridecapeptide derived from proopiomelanocortin. Many studies over the last few years have provided evidence that alpha-MSH has potent protective and antiinflammatory effects. These effects can be elicited via centrally expressed melanocortin receptors that orchestrate descending neurogenic antiinflammatory pathways. alpha-MSH can also exert antiinflammatory and protective effects on cells of the immune system and on peripheral nonimmune cell types expressing melanocortin receptors. At the molecular level, alpha-MSH affects various pathways implicated in regulation of inflammation and protection, i.e., nuclear factor-kappaB activation, expression of adhesion molecules and chemokine receptors, production of proinflammatory cytokines and mediators, IL-10 synthesis, T cell proliferation and activity, inflammatory cell migration, expression of antioxidative enzymes, and apoptosis. The antiinflammatory effects of alpha-MSH have been validated in animal models of experimentally induced fever; irritant and allergic contact dermatitis, vasculitis, and fibrosis; ocular, gastrointestinal, brain, and allergic airway inflammation; and arthritis, but also in models of organ injury. One obstacle limiting the use of alpha-MSH in inflammatory disorders is its pigmentary effect. Due to its preserved antiinflammatory effect but lack of pigmentary action, the C-terminal tripeptide of alpha-MSH, KPV, has been delineated as an alternative for antiinflammatory therapy. KdPT, a derivative of KPV corresponding to amino acids 193-195 of IL-1beta, is also emerging as a tripeptide with antiinflammatory effects. The physiochemical properties and expected low costs of production render both agents suitable for the future treatment of immune-mediated inflammatory skin and bowel disease, fibrosis, allergic and inflammatory lung disease, ocular inflammation, and arthritis.

AAV-mediated delivery of the caspase inhibitor XIAP protects against cisplatin ototoxicity

HYPOTHESIS

Delivery of the gene encoding X-linked inhibitor of apoptosis (XIAP) using an adeno-associated viral (AAV) vector can protect against cisplatin-mediated ototoxicity.

BACKGROUND

Cisplatin is a widely used chemotherapeutic agent with significant ototoxic side effects. One possible mechanism of toxicity is apoptotic death of many cochlear cell types. Acute treatment with inhibitors of caspases- enzymes critical for apoptosis- has been shown to prevent hearing loss in vivo, but is too short-acting for therapeutic use. Gene therapy provides a specific and chronic means of delivering potential therapeutic gents. Introducing an anti-apoptotic gene into the cochlea could provide long-term prophylaxis against the ototoxic effects of cisplatin.

METHOD

Two groups of rats were treated with unilateral injection into the round window of AAV harboring a gene encoding either XIAP or green fluorescent protein (GFP). After at least two months of gene expression, auditory-brainstem-response (ABR) threshold shifts and outer-hair-cell (OHC) number were measured in these two groups of animals after 72-hour treatment with cisplatin.

RESULTS

Consistent with previous reports, uninjected and AAV.GFP-injected ears displayed profound ABR threshold elevations and OHC loss after cisplatin treatment. Ears that had been injected with AAV encoding XIAP, however, were significantly protected from these effects: cisplatin-induced ABR-threshold shift and hair-cell loss were attenuated by as much as 78% and 45%, respectively, when compared with contralateral (untreated) ears.

CONCLUSION

XIAP delivery to the cochlea can protect against the audiometric changes and hair-cell loss associated with cisplatin ototoxicity. The efficacy, specificity, and duration of the protective effects make this a potentially attractive therapeutic paradigm.

Genetic dependence of cochlear cells and structures injured by noise

The acute and permanent effects of a single damaging noise exposure were compared in CBA/J, C57BL/6 (B6), and closely related strains of mice. Two hours of broadband noise (4-45 kHz) at 110 dB SPL led to temporary reduction in the endocochlear potential (EP) of CBA/J and CBA/CaJ (CBA) mice and acute cellular changes in cochlear stria vascularis and spiral ligament. For the same exposure, B6 mice showed no EP reduction and little of the pathology seen in CBA. Eight weeks after exposure, all mice showed a normal EP, but only CBA mice showed injury and cell loss in cochlear lateral wall, despite the fact that B6 sustained larger permanent threshold shifts. Examination of noise injury in B6 congenics carrying alternate alleles of genes encoding otocadherin (Cdh23), agouti protein, and tyrosinase (albinism) indicated that none of these loci can account for the strain differences observed. Examination of CBA x B6 F1 mice and N2 backcross mice to B6 further indicated that susceptibility to noise-related EP reduction and associated cell pathology are inherited in an autosomal dominant manner, and are established by one or a few large effect quantitative trait loci. Findings support a common genetic basis for an entire constellation of noise-related cochlear pathologies in cochlear lateral wall and spiral limbus. Even within species, cellular targets of acute and permanent cochlear noise injury may vary with genetic makeup.

Cellular correlates of age-related endocochlear potential reduction in a mouse model

Age-related degeneration of cochlear stria vascularis and resulting reduction in the endocochlear potential (EP) are the hallmark features of strial presbycusis, one of the major forms of presbycusis, or age-related hearing loss (ARHL) (Schuknecht, H.F., 1964. Further observations on the pathology of presbycusis. Archives of Otolaryngology 80, 369-382; Schuknecht, H.F., 1993. Pathology of the Ear. Lea and Febiger, Philadelphia; Schuknecht, H.F., Gacek, M.R., 1993. Cochlear pathology in presbycusis. Annals of Otology, Rhinology and Laryngology 102, 1-16). It is unclear whether there are multiple forms of strial ARHL having different sequences of degenerative events and different risk factors. Human temporal bone studies suggest that the initial pathology usually affects strial marginal cells, then spreads to other strial cell types. While inheritance studies support a moderate genetic influence, no contributing genes have been identified. Establishment of mouse models of strial ARHL may promote the identification of underlying genes and gene/environment interactions. We have found that BALB/cJ mice show significant EP reduction by 19 months of age. The reduction only occurs in a subset of animals. To identify key anatomical correlates of the EP reduction, we compared several cochlear lateral wall metrics in BALBs with those in C57BL/6J (B6) mice, which show little EP reduction for ages up to 26 months. Among the measures obtained, marginal cell density and spiral ligament thickness were the best predictors of both the EP decline in BALBs, and EP stability in B6. Our results indicate that the sequence of strial degeneration in BALBs is like that suggested for humans. Additional strain comparisons we have performed suggest that genes governing strial melanin production do not play a role.

Contributions of mouse models to understanding of age- and noise-related hearing loss

Once an oddity, mice have become the most widely used hearing research model. Their value for research in noise-induced hearing loss (NIHL) stems from their high vulnerability to noise and reduced variance of results, made possible by genetic standardization. To research in age-related hearing loss (ARHL), they offer economies of small size and a short lifespan, both of which reduce housing costs. Inbred mouse strains show a wide range of noise sensitivities and rates of hearing loss with age. These can be studied using classical genetic analysis, as well as hypothesis-driven experiments utilizing genetic engineering. Through such investigations, presently 3 loci have been identified to date that contribute to NIHL, 10 that promote ARHL, and at least 6 loci that promote both. The types of genes involved implicate homeostatic and protective mechanisms as key to the appearance of either type of pathology and support a causal link between injury and some apparent ARHL. While the majority of mouse ARHL models examined most closely resemble sensory ARHL, recent work has identified mice possessing the essential characteristics of neural and strial ARHL. Using these models, it should be possible to identify genes and alleles that promote the major forms of ARHL and their combinations.

Prevention of Cisplatin Ototoxicity Using Transtympanic N-Acetylcysteine and Lactate

HYPOTHESIS

Transtympanic administration of the antioxidant N-acetylcysteine or lactated Ringer's solution onto the round window membrane will prevent cisplatin ototoxicity in the guinea pig model.

BACKGROUND

Cochlear ototoxicity is a well-known side effect of cisplatin administration, with the mechanism of injury thought to rest in oxidative damage to the outer hair cells. However, previous attempts at transtympanic antioxidant delivery have met with varied success. We present an effective method of counteracting cisplatin ototoxicity via the transtympanic application of lactated Ringer's solution or N-acetylcysteine.

METHODS

Baseline distortion product otoacoustic emission measurements were obtained. Intraperitoneal cisplatin was administered to a cumulative dose of 20 mg/kg. The middle ears were either untreated (control) or filled with normal saline (negative control), 2%N-acetylcysteine diluted in normal saline (treatment), or lactated Ringer's solution (treatment) via anterosuperior quadrant myringotomies. Posttreatment distortion product otoacoustic emissions were obtained.

RESULTS

Animals in the untreated control group and the negative control normal saline group demonstrated consistent obliteration of distortion product otoacoustic emissions. However, those receiving either lactated Ringer's solution or 2%N-acetylcysteine diluted in normal saline demonstrated significant preservation of distortion product otoacoustic emissions. The treatment regimen was well tolerated, with minimal animal loss.

CONCLUSION

We have demonstrated the efficacy of transtympanic lactated Ringer's solution and N-acetylcysteine in the prevention of cisplatin ototoxicity using a guinea pig model. The possible mechanisms for the high efficacy of lactated Ringer's solution are discussed in detail.

Perilymphatic application of alpha-melanocyte stimulating hormone ameliorates hearing loss caused by systemic administration of cisplatin

It has previously been demonstrated that ototoxicity induced by systemic administration of cisplatin is reduced by concomitant systemic administration of alpha-melanocyte stimulating hormone (alpha-MSH). In this study we investigated the effects of cochlear, perilymphatic application of alpha-MSH during intraperitoneal administration of cisplatin. Guinea pigs, implanted with a round-window electrode, allowing daily monitoring of the compound action potential (CAP), and also implanted with a mini-osmotic pump, pumping at a rate of 0.25 microl/h either physiological saline or alpha-MSH solution (0.02, 2, and 20 microg/ml), were treated daily with a bolus injection of cisplatin (2 mg/kg) until the electrocochleogram showed a persistent decrease in CAP amplitude (> or = 40 dB threshold shift at 8 kHz). Then, cisplatin treatment was stopped, but intracochlear perfusion of alpha-MSH or physiological saline was continued for 10 days to evaluate possible effects of alpha-MSH on the expected recovery. On day 10, the animals were killed and the cochleas were fixed and processed for histological analysis. All groups required 6-7 days of cisplatin to reach the criterion CAP threshold shift. Ten days after cessation of the cisplatin treatment, recovery of the CAP was observed in all groups and at all frequencies, although it was more pronounced at the lower frequencies. With respect to recovery, small statistically significant differences were found between the saline and the alpha-MSH co-treated groups. Histological results showed significantly less outer hair cell (OHC) loss in the group co-treated with 2 microg/ml alpha-MSH as compared to the group co-treated with saline. Since alpha-MSH was directly delivered to the cochlea, the ameliorating effect of alpha-MSH on OHC survival is likely to involve a cochlear target.