Porphyrin Based Nanotechnology: A Minimally Invasive Approach for Drug Delivery and Cholesteatoma Treatment

Dina Ashraf Mahmoud^1,2,3*Lili Ding⁴Zannatul Ferdous²Zhifen Zhang²Juan Chen⁴Jennifer Spiegel^2,5,6Edward Alexander Sykes^5,7Yumai Situ²Robert Harrison⁸Gang Zheng^10,11,4,9Trung Le^12,2,5

• ¹Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
• ²Biological Sciences Platform, Hurvitz Brain Sciences Program, Sunnybrook Research Institute, Toronto, Ontario, Canada, Toronto, Ontario, Canada
• ³Faculty of Pharmacy, Alexandria University, Alexandria, Alexandria, Egypt
• ⁴Princess Margaret Cancer Centre, University Health Network, 101 College Street, PMCRT 5-354, Toronto, ON M5G1L7 Canada, Toronto, Canada
• ⁵Department of Otolaryngology – Head and Neck Surgery, University of Toronto, Toronto, Ontario, Canada, Toronto, Ontario, Canada
• ⁶Department of Otorhinolaryngology, Faculty of Medicine, Ludwig Maximilians University Munich, Munich, Bavaria, Germany
• ⁷St. Joseph's health science center unity health, Toronto, Canada
• ⁸Department of Otolaryngology - Head & Neck Surgery, University of Toronto; Program in Neuroscience and Mental Health, Hospital for Sick Children, 555 Avenue Road, Toronto, M5G 1X8, Canada., Toronto, Canada
• ⁹Department of Pharmaceutical Sciences, University of Toronto, 144 College St. Toronto, Toronto, ON M5S 3M2 Canada, Toronto, Canada
• ¹⁰Institute of Biomedical Engineering, University of Toronto, 64 College St., Toronto, ON M5S 3G9 Canada, Toronto, Canada
• ¹¹Department of Medical Biophysics, University of Toronto, 101 College St., Toronto, ON M5G 1L7 Canada, Toronto, Canada
• ¹²Institute of Medical Science, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada

The treatment of inner and middle ear diseases remains a significant challenge, often requiring surgical intervention as the only option. In this study, we investigated porphysomes, self-assembled porphyrin-based nanoparticles, as a minimally invasive drug delivery platform for inner ear applications and as photothermal agents for cholesteatoma ablation. Three porphysome formulations were evaluated: parent porphysomes (PS), porphyrin-stabilized nano emulsions (nPS), and EDTA-lipid incorporated porphysomes (ePS). Rats received intratympanic injections of each formulation, and fluorescence imaging performed 1 hour post-injection demonstrated concentration-dependent inner ear penetration for all formulations. Notably, no signs of ototoxicity were observed based on histological and functional assessments of hearing and balance. Among ePS-treated rats, 250 μM and 1000 μM groups showed significantly higher inner ear fluorescence compared to the 50 μM group. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) tests were performed at baseline, 2-, and 6-weeks post-injection. No significant threshold shifts were detected in PS and ePS groups compared to controls. In contrast, nPS-treated rats exhibited a significant ABR threshold elevation at 6 weeks (p < 0.02). At 6 weeks, minor yet statistically significant DPOAE threshold differences were observed at 16 kHz (PS group) and 32 kHz (all porphysome groups); however, all shifts remained below 0 dB, indicating no functional hearing loss. Vestibular assessments, including swim and beam tests, revealed no significant impairments. Upon laser activation, all porphysome formulations induced substantial temperature elevation (ΔT = 31 ± 3.76 °C, p < 0.05) and histological burn effects in cholesteatoma tissues. These findings support the potential of porphysomes as safe, minimally invasive drug delivery system and photothermal agent for treatment of inner and middle ear disorders.