Purpose: DNA damage repair can lead to epigenetic changes. DNA mismatch repair proteins bind to platinum DNA adducts and at sites of DNA damage can recruit the DNA methylating enzyme DNMT1, resulting in aberrant methylation. We hypothesised that DNA damage repair during platinum-based chemotherapy may cause aberrant DNA methylation in normal tissues of patients such as blood. Experimental Design: We used Illumina 450k methylation arrays and bisulphite pyrosequencing to investigate methylation at presentation and relapse in blood DNA from patients with ovarian cancer enrolled in the SCOTROC1 trial (n = 247) and in a cohort of ovarian tumor DNA samples collected at first relapse (n = 46). We used an ovarian cancer cell line model to investigate the role of the DNA mismatch repair gene MLH1 in platinum-induced methylation changes. Results: Specific CpG methylation changes in blood at relapse are observed following platinum-based chemotherapy and are associated with patient survival, independent of other clinical factors [hazard ratio, 3.7; 95% confidence interval, 1.8–7.6, P = 2.8 × 10⁻⁴]. Similar changes occur in ovarian tumors at relapse, also associated with patient survival (hazard ratio, 2.6; 95% confidence interval, 1.0–6.8, P = 0.048). Using an ovarian cancer cell line model, we demonstrate that functional mismatch repair increases the frequency of platinum-induced methylation. Conclusions: DNA methylation in blood at relapse following chemotherapy, and not at presentation, is informative regarding survival of patients with ovarian cancer. Functional DNA mismatch repair increases the frequency of DNA methylation changes induced by platinum. DNA methylation in blood following chemotherapy could provide a noninvasive means of monitoring patients' epigenetic responses to treatment without requiring a tumor biopsy. Clin Cancer Res; 23(9); 2213–22. ©2016 AACR.

Ototoxicity is an often-underestimated sequela for cancer patients undergoing chemotherapy, with an incidence rate exceeding 50%, affecting approximately 4 million individuals worldwide each year. Despite the nearly 2,000 publications on chemotherapy-related ototoxicity in the past decade, the understanding of its prevalence, mechanisms, and preventative or therapeutic measures remains ambiguous and subject to debate. To date, only one drug, sodium thiosulfate, has gained FDA approval for treating ototoxicity in chemotherapy. However, its utilization is restricted. This review aims to offer clinicians and researchers a comprehensive perspective by thoroughly and carefully reviewing available data and current evidence. Chemotherapy-induced ototoxicity is characterized by four primary symptoms: hearing loss, tinnitus, vertigo, and dizziness, originating from both auditory and vestibular systems. Hearing loss is the predominant symptom. Amongst over 700 chemotherapeutic agents documented in various databases, only seven are reported to induce hearing loss. While the molecular mechanisms of the hearing loss caused by the two platinum-based drugs are extensively explored, the pathways behind the action of the other five drugs are primarily speculative, rooted in their therapeutic properties and side effects. Cisplatin attracts the majority of attention among these drugs, encompassing around two-thirds of the literature regarding ototoxicity in chemotherapy. Cisplatin ototoxicity chiefly manifests through the loss of outer hair cells, possibly resulting from damages directly by cisplatin uptake or secondary effects on the stria vascularis. Both direct and indirect influences contribute to cisplatin ototoxicity, while it is still debated which path is dominant or where the primary target of cisplatin is located. Candidates for hearing protection against cisplatin ototoxicity are also discussed, with novel strategies and methods showing promise on the horizon.

Hearing loss is a health crisis that affects more than 60 million Americans. Currently, sodium thiosulfate is the only drug approved by the Food and Drug Administration (FDA) to counter hearing loss. Sirtuins were proposed as therapeutic targets in the search for new compounds or drugs to prevent or cure age-, noise-, or drug-induced hearing loss. Sirtuins are proteins involved in metabolic regulation with the potential to ameliorate sensorineural hearing loss. The mammalian sirtuin family includes seven members, SIRT1-7. This paper is a literature review on the sirtuins and their protective roles in sensorineural hearing loss. Literature search on the NCBI PubMed database and NUsearch included the keywords ‘sirtuin’ and ‘hearing’. Studies on sirtuins without relevance to hearing and studies on hearing without relevance to sirtuins were excluded. Only primary research articles with data on sirtuin expression and physiologic auditory tests were considered. The literature review identified 183 records on sirtuins and hearing. After removing duplicates, eighty-one records remained. After screening for eligibility criteria, there were forty-eight primary research articles with statistically significant data relevant to sirtuins and hearing. Overall, SIRT1 (n = 29) was the most studied sirtuin paralog. Over the last two decades, research on sirtuins and hearing has largely focused on age-, noise-, and drug-induced hearing loss. Past and current studies highlight the role of sirtuins as a mediator of redox homeostasis. However, more studies need to be conducted on the involvement of SIRT2 and SIRT4-7 in hearing protection.

Cisplatin-induced hearing loss (CIHL) affects half a million cancer patients annually, but treatment strategies are limited. We have previously shown that honokiol, an antioxidant and otoprotective compound, upregulates mitochondrial sirtuin 3 (SIRT3) and protects against CIHL. In the present study, we investigated the molecular requirements of this protection using a Sirt3 knockout (Sirt3^-/-) mouse model. Our results showed that honokiol pre-treatment ameliorated auditory threshold shifts in both wild-type and Sirt3^-/- mice. Quantitative histological analysis showed that honokiol pre-treatment protected against cisplatin-induced synaptopathy. To explore the underlying molecular mechanisms, we performed RNA-seq on wild-type outer hair cells (OHCs). Cisplatin treatment resulted in a global transcriptomic downregulation, which was biased towards longer genes. Differential expression analysis showed that cisplatin treatment resulted in the downregulation of mitochondrial redox genes, such as Idh2 and Aldh2, a pattern that was reversed by honokiol pre-treatment. Computational transcription factor binding site analysis predicted that honokiol rescues chromatin-modifying pathways, while suppressing the ternary complex factor subfamily. Lastly, honokiol-only treatment proactively reinforced antioxidant defenses via Sod2 upregulation. Together, these results provide a comprehensive transcriptomic map of OHCs in the cisplatin background and highlight the clinical potential of honokiol to protect against CIHL.

Background/Objectives: Cisplatin-induced hearing loss (CIHL) is a major global health sequela of chemotherapy, affecting over half a million cancer patients annually. We previously reported that honokiol, a multifunctional molecule compatible with cisplatin, protects against CIHL and upregulates sirtuin 3. The sirtuin family is composed of seven highly conserved yet differentially expressed members that are critical enzymes for oxidative stress regulation in different cellular compartments. Therefore, this study aims to further verify the expression and upregulation of the entire sirtuin family during honokiol-mediated hearing protection against CIHL in a tumor-bearing mouse model. Methods: Adult female mice carrying the mouse mammary tumor virus polyomavirus middle T agent oncogene were used. These mice developed palpable tumors spontaneously at the age of 70.8 ± 10.3 days. CIHL was induced using a three-cycle (14 days/cycle) low-dose (4 mg/kg/day for 4 days per cycle, intraperitoneal injection) cisplatin treatment mimicking chemotherapy regimens. Honokiol (5–20 mg/kg) was administered one hour before cisplatin. Cochlear function was evaluated by auditory brainstem response threshold shifts and synaptic changes. Immunostaining and RT-qPCR were performed to verify the upregulation of sirtuin family members (1, 2, 3, 5, and 7) during these processes. Results: CIHL was observed in the high-frequency range (24–32 kHz), which was mitigated by honokiol treatment. The optimal dose of honokiol for oto-protection and animal survival was 10 mg/kg. Fluorescence signals of sirtuins 1, 2, 3, 5, and 7 increased in cochleae from honokiol-treated mice. RT-qPCR confirmed a significant upregulation of sirtuin 3 mRNA with honokiol treatment. Conclusions: Sirtuin family upregulation was involved in honokiol-mediated hearing protection against CIHL. The dose–response curve of honokiol lays the foundation for potential translational applications for human studies.