Establishment of a bone-infiltrating head and neck tumor model in rats for the further development of "laser-induced breakdown spectroscopy" (LIBS) as a bony frozen section method

• Applicant: Dr. Philipp Winnand
• Subject Area: Otolaryngology, Phoniatrics and Audiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549156247

The oncological safety of tumor surgery procedures depends on the possibility of securing tumor-free resection margins. Established frozen section techniques can ensure the intraoperative assessment of soft tissue. Since the histological assessment of bone is only possible after 8 days of decalcification, tumor-free resection margins in the bone cannot be secured intraoperatively. The absence of rapid bone analysis procedures is a fundamental problem in oncologic head and neck surgery. Experimental approaches to rapid bone analysis are limited due to low sensitivity and high subjectivity. Spectroscopic-optical methods can provide a direct and objective assessment of the bony resection margin status. Laser-induced breakdown spectroscopy (LIBS) makes it possible to examine a minimal tissue sample with a few pulses of an Nd:YAG laser by determining the electrolyte ratios based on the emissions of the laser-generated plasma. After optimizing the technical components of a LIBS-based experimental setup, we used LIBS for the first time in ex-vivo feasibility studies as a rapid bone analysis technique on native mandibular cross-sections from 15 patients. Tumor-induced small animal models are required for the further development of laser-assisted procedures. The recapitulation of bone-infiltrating head and neck tumors is mainly performed in mice, the use of which is a compromise due to the small facial skull. The aim of this study is to establish a syngeneic and orthotopic transplantation model for the recapitulation of a bone-infiltrating head and neck tumor model in immunocompetent Fischer-344 rats. For the purpose of tumor induction, cultured tumor cells will be injected once subperiosteally into the masseter muscle region. The bone invasive growth of three tumor cell lines (FAT-7, SCC-131 or SCC-158) in two different concentrations (low or high) and at three different time points (after one, two or three weeks) will be investigated in 5 animals per group and compared with healthy control animals. The behavior of the invasion into the bone will be examined image morphologically in the μCT and In Vivo Imaging System IVIS Lumina. After euthanizing the animals, the mandibles are examined natively within a few minutes using LIBS. The LIBS spectra are used to train tissue detection algorithms, which are tested on LIBS spectra with defined distances to the tumor boundary. The LIBS spectra and the measured electrolyte ratios are validated by histology and electron microscopy. This project aims to define the ideal tumor cell line, the optimal tumor cell concentration and the most appropriate time points for in vivo imaging, surgery, and euthanasia of the animals. The tumor model is intended to create the basis for follow-up projects for the further development of laser-assisted procedures in head and neck oncology.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Ali Modabber