Overcoming barriers: a review on innovations in drug delivery to the middle and inner ear

Despite significant advances in the development of therapeutics for hearing loss, drug delivery to the middle and inner ear remains a challenge. As conventional oral or intravascular administration are ineffective due to poor bioavailability and impermeability of the blood-labyrinth-barrier, localized delivery is becoming a preferable approach for certain drugs. Even then, localized delivery to the ear precludes continual drug delivery due to the invasive and potentially traumatic procedures required to access the middle and inner ear. To address this, the preclinical development of controlled release therapeutics and drug delivery devices have greatly advanced, with some now showing promise clinically. This review will discuss the existing challenges in drug development for treating the most prevalent and damaging hearing disorders, in particular otitis media, perforation of the tympanic membrane, cholesteatoma and sensorineural hearing loss. We will then address novel developments in drug delivery that address these including novel controlled release therapeutics such as hydrogel and nanotechnology and finally, novel device delivery approaches such as microfluidic systems and cochlear prosthesis-mediated delivery. The aim of this review is to investigate how drugs can reach the middle and inner ear more efficiently and how recent innovations could be applied in aiding drug delivery in certain pathologic contexts.

Prospective Observational Study of Evaluating Cisplatin-Induced Ototoxicity in Patients

Introduction Platinum-based chemotherapeutic agents cisplatin and carboplatin are two of the most widely used drugs in cancer today. They display wide range of adverse reactions; among them, ototoxicity is an important cumulative toxicity that more commonly observed with cisplatin. At a later stage, it can affect speech of individual and lead to communication problem with decreased cognitive function and depression in cancer survivors. Periodic monitoring of hearing loss with pure-tone audiometry (PTA) provides early evidence of ototoxicity which may decrease debilitating effect of the same in a patient.

Objective The primary objective of this study was to assess cisplatin-induced ototoxicity. We also investigated its severity, reversibility, and other modifying risk factors.

Materials and Methods We conducted a prospective observational descriptive type of epidemiological study. The study was conducted over 80 randomly selected cancer patients (for estimation of sample size, the following formula was used n = [Zα 2 PQ] / d 2), who were starting with their first cycle of cisplatin from August 2018 to July 2020. This study was conducted at tertiary cancer care center in western Gujarat which caters patients from all over India. We performed PTA in all randomized patients at baseline and periodically. We classified hearing loss according to the World Health Organization (WHO) criteria.

Results A total of 30% (n = 24) patients developed cisplatin-induced ototoxicity according to WHO criteria at end of 3 months after starting the first cycle of cisplatin. It was sensory neuronal, affecting both the ears equally, and was seen predominantly at high frequency. We observed hearing loss at 3 months to be significantly more common in the 301 to 400 mg/m2 cumulative dose group (47%), as compared with the other two groups (0–200 mg/m2 and 201–300 mg/m2; p < 0.05). It showed dose dependency with cisplatin. In the multivariate step-wise regression model, baseline hearing loss (odds ratio [OR] = 17.71, 95% confidence interval [CI]: 6.57–118.91, p < 0.05) and cumulative cisplatin dose of more than 300 mg/m2 were significantly associated with hearing loss at 3 months (OR = 6.62, 95% CI: 2.33–18.74, p < 0.05).

Conclusion Cisplatin-induced ototoxicity manifests as a bilateral high frequency sensorineural hearing loss. Cumulative dose of cisplatin is an important predictor of development of ototoxicity. Baseline and periodic audiometric monitoring could detect ototoxicity early which leads to possible limitation on the severity of ototoxicity.

Baseline audiological profiling of South African females with cervical cancer: an important attribute for assessing cisplatin-associated ototoxicity

BACKGROUND

Cisplatin is a popular antineoplastic agent used to treat cervical cancer in women from low and middle-income countries. Cisplatin treatment is associated with ototoxicity, often resulting in hearing loss. In light of this, it is crucial to conduct baseline audiological assessments prior to treatment initiation in order to evaluate the extent of cisplatin-associated-ototoxicity. Additionally, the identification of inherent risk factors and hearing patterns in specific patient cohorts is needed, especially in South Africa, a middle-income country characterized by the quadruple burden of disease (Human Immunodeficiency Virus (HIV), Tuberculosis (TB), Diabetes and Hypertension).

METHODS

This study aimed to describe a profile of risk factors and hearing in a cohort of females with cervical cancer before cisplatin treatment commenced. A descriptive study design that included 82 cervical cancer patients, who underwent audiological evaluation prescribed for ototoxicity monitoring was conducted.

RESULTS

All participants (n = 82) presented with risk factors (diabetes, hypertension, HIV, and antiretroviral therapy) for cisplatin ototoxicity and/or pre-existing sensorineural hearing loss. High-frequency tinnitus was the most common otological symptom experienced by 25 (31%) participants. Fifty-nine (72%) participants presented with normal hearing, twenty-two (27%) with a sensorineural hearing loss, and 36% were diagnosed with mild hearing loss. Abnormal Distortion Product Otoacoustic Emissions (DPOAE) findings were obtained bilaterally in two participants (2.4%), in the right ear only of another two (2.4%) participants and the left ear of three participants (3.7%). Most participants (94%) had excellent word recognition scores, demonstrating an excellent ability to recognize words within normal conversational levels under optimal listening conditions. Age was significantly associated with hearing loss at all thresholds. Among the co-morbidities, an HIV positive status significantly triggered hearing loss, especially at higher frequencies.

CONCLUSION

This study demonstrated that South African females with cervical cancer present with various co-morbidities, which may predispose them to develop cisplatin-associated -ototoxic hearing loss. Identification of these co-morbidities and hearing loss is essential for the accurate monitoring of cisplatin toxicities. Appropriate management of these patients is pivotal to reduce the adverse effects that hearing impairment can have on an individual's quality of life and to facilitate informed decision-making regarding the commencement of cisplatin chemotherapy.

Toll-like Receptor 4 Signaling and Downstream Neutrophilic Inflammation Mediate Endotoxemia-Enhanced Blood-Labyrinth Barrier Trafficking

HYPOTHESIS

Both toll-like receptor 4 (TLR4) and downstream neutrophil activity are required for endotoxemia-enhanced blood-labyrinth barrier (BLB) trafficking.

BACKGROUND

Aminoglycoside and cisplatin are valuable clinical therapies; however, these drugs often cause life-long hearing loss. Endotoxemia enhances the ototoxicity of aminoglycosides and cisplatin in a TLR4 dependent mechanism for which downstream proinflammatory signaling orchestrates effector immune cells including neutrophils. Neutrophil-mediated vascular injury (NMVI) can enhance molecular trafficking across endothelial barriers and may contribute to endotoxemia-enhanced drug-induced ototoxicity.

METHODS

Lipopolysaccharide (LPS) hypo-responsive TLR4-KO mice and congenitally neutropenic granulocyte colony-stimulating factor (GCSF) GCSF-KO mice were studied to investigate the relative contributions of TLR4 signaling and downstream neutrophil activity to endotoxemia-enhanced BLB trafficking. C57Bl/6 wild-type mice were used as a positive control. Mice were treated with LPS and 24 hours later cochleae were analyzed for gene transcription of innate inflammatory cytokine/chemokine signaling molecules, neutrophil recruitment, and vascular trafficking of the paracellular tracer biocytin-TMR.

RESULTS

Cochlear transcription of innate proinflammatory cytokines/chemokines was increased in endotoxemic C57Bl/6 and GCSF-KO, but not in TLR4-KO mice. More neutrophils were recruited to endotoxemic C57Bl/6 cochleae compared with both TLR4 and GCSF-KO cochleae. Endotoxemia enhanced BLB trafficking of biocytin-TMR in endotoxemic C57Bl/6 cochleae and this was attenuated in both TLR4 and GCSF-KO mice.

CONCLUSION

Together these results suggest that TLR4-mediated innate immunity cytokine/chemokine signaling alone is not sufficient for endotoxemia-enhanced trafficking of biocytin-TMR and that downstream neutrophil activity is required to enhance BLB trafficking. Clinically, targeting neutrophilic inflammation could protect hearing during aminoglycoside, cisplatin, or other ototoxic drug therapies.

Exploring the Experiences of Cancer Patients With Chemotherapy-Induced Ototoxicity: Qualitative Study Using Online Health Care Forums

BACKGROUND

Many cancer patients and survivors experience permanent and life-debilitating effects, such as ototoxicity, from treatment. Ototoxicity manifests as high-frequency hearing loss and tinnitus, which can have a detrimental effect on the quality of life (QoL) of those affected. Currently, there is little information and support offered to these patients who experience ototoxicity, potentially leading to many being undiagnosed and untreated.

OBJECTIVE

The aim of this study was to explore the extent of ototoxic side effects, such as hearing loss and tinnitus, and their impact on cancer patients following chemotherapy treatment. Secondary objectives included detecting the time periods of onset and duration of the ototoxicity and identifying what support was available to this population.

METHODS

Posts from publicly available online forums were thematically analyzed using the guidelines by Braun and Clarke. A coding manual was iteratively developed to create a framework for the analysis of the ototoxicity experience among the cancer population.

RESULTS

A total of 9 relevant online forums were identified, consisting of 86 threads and 570 posts from 377 members. Following the bottom-up thematic analysis, 6 major themes were identified: nature of ototoxicity, time of experienced ototoxicity, information on ototoxicity, quality of life, therapies, and online social support.

CONCLUSIONS

There was a significant number of reports expressing concerns about the lack of information on the risk of ototoxicity. More support for those suffering is needed; for example, improved interdepartmental communication between oncology and audiology services could optimize patient care. Patients should also be encouraged to communicate with their health care professionals about their ototoxicity and relay how their QoL is impacted by ototoxicity when accessing support. Tinnitus was the most common concern and was associated with distress. Hearing loss was less common; however, it was associated with fear and employment issues. Those who reported preexisting conditions were fearful about worsening their condition as their QoL was already impacted.

Development of Second-Generation CDK2 Inhibitors for the Prevention of Cisplatin-Induced Hearing Loss

There are currently no FDA-approved therapies to prevent the hearing loss associated with the usage of cisplatin in chemotherapeutic regimens. We recently demonstrated that the pharmacologic inhibition with kenpaullone or genetic deletion of CDK2 preserved hearing function in animal models treated with cisplatin, which suggests that CDK2 is a promising therapeutic target to prevent cisplatin-induced ototoxicity. In this study, we identified two lead compounds, AT7519 and AZD5438, from a focused library screen of 187 CDK2 inhibitors, performed in an immortalized cell line derived from neonatal mouse cochleae treated with cisplatin. Moreover, we screened 36 analogues of AT7519 and identified analogue 7, which exhibited an improved therapeutic index. When delivered locally, analogue 7 and AZD5438 both provided significant protection against cisplatin-induced ototoxicity in mice. Thus, we have identified two additional compounds that prevent cisplatin-induced ototoxicity in vivo and provided further evidence that CDK2 is a druggable target for treating cisplatin-induced ototoxicity.

Progress in the Development of Preventative Drugs for Cisplatin-Induced Hearing Loss

Cisplatin is a highly effective treatment for malignant cancers and has become a cornerstone in chemotherapeutic regimens. Unfortunately, its use in the clinic is often coupled with a high incidence of severe hearing loss. Over the past few decades, enormous effort has been put forth to find protective agents that selectively protect against the ototoxic side effects of cisplatin and do not interfere with its antitumoral activity. Many therapies have been successful in preclinical work, but only a few have shown any protection in the clinic, and none have been approved by the FDA. This review summarizes the clinical and preclinical studies of the most effective small-molecule candidates currently in clinical trials, while also detailing their molecular mechanisms of action, to gain insight for future drug development in the field.