Citation: Enzian, P.; Rahmanzadeh, R. Photochemical Internalization with Fimaporfin: Enhanced Bleomycin Treatment for Head and Neck Cancer. Pharmaceutics 2023, 15, 2040. https://doi.org/10.3390/ pharmaceutics15082040 Academic Editors: Wujun Xu and Juri M. Timonen Received: 25 May 2023 Revised: 25 July 2023 Accepted: 26 July 2023 Published: 28 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). pharmaceutics Article Photochemical Internalization with Fimaporfin: Enhanced Bleomycin Treatment for Head and Neck Cancer Paula Enzian and Ramtin Rahmanzadeh * Institute of Biomedical Optics, University of Lübeck, 23562 Lübeck, Germany; p.enzian@uni-luebeck.de * Correspondence: ramtin.rahmanzadeh@uni-luebeck.de; Tel.: +49-451-3101-3210 Abstract: Head and neck squamous cell carcinoma (HNSCC) still represents the world’s sixth most common tumor entity, with increasing incidence. The reachability of light makes HNSCC suitable for light-based therapies such as Photochemical Internalization (PCI). The drug Bleomycin is cytotoxic and used as an anti-tumor medication. Since Bleomycin is endocytosed as a relatively large molecule, part of it is degraded in lysosomes before reaching its intracellular target. The goal of our study was to improve the intracellular availability of Bleomycin with PCI. We investigate the intracellular delivery of Bleomycin after PCI with the photosensitizer Fimaporfin. A systematic variation of Bleomycin and Fimaporfin concentrations and light irradiation led to the pronounced cell death of HNSCC cells. After optimization, the same level of tumor cell death of 75% was reached with a 20-fold lower Bleomycin concentration. This would allow treatment of HNSCC with high local tumor cell death and reduce the side effects of Bleomycin, e.g., lung fibrosis, at the same time. This demonstrates the increased efficacy of the anti-tumor medication Bleomycin in combination with PCI. Keywords: photochemical internalization; HNSCC; drug delivery; fimaporfin; bleomycin 1. Introduction Head and neck squamous cell carcinoma (HNSCC) refers to a group of cancers that originate in the epithelium of the oral and nasal cavities, the pharynx, and the larynx [1]. HNSCC represents the world’s sixth most common tumor entity, with an incidence of about 500,000 new cases per year worldwide [2]. A total of 90% of head and neck cancers are squamous cell carcinomas. There has been an increase in the annual incidence of human papillomavirus (HPV)-related HNSCC, suggesting that a subset of HNSCC is a sexually transmitted disease with distinct clinical features. The prognosis, particularly in advanced tumor stages, is extremely poor. Unchanged during the past three decades, the overall 5-year survival rate is below 50% [3], since 50–60% of patients develop a recurrent disease [4]. Standard therapies are still surgery, radiotherapy, and chemotherapy. For many therapeutic approaches, the delivery of the drug to the site of action is of fundamental importance for the drug’s effect. Many macromolecules, like antibodies, show low tissue penetration or cellular uptake and therefore low activity in vivo [5]. And moreover, not only the transport of active substances into cells but also their intracellular release from endosomes is limiting many therapeutic interventions [5,6]. A technique to improve the delivery of macromolecules is photochemical internal- ization (PCI), which involves the use of light and a photosensitizing agent [7,8]. Many macromolecules are taken up by cells via endosomes and will be degraded in lysosomes before reaching their intracellular target. Better delivery can enhance the effectiveness of drugs or other therapeutic agents. PCI is already in clinical trials for the release of gemcitabine in patients with bile duct cancer. In earlier studies, we showed the delivery of monoclonal antibodies into cells with the lipophilic photosensitizer Benzoporphyrin (BPD) [9–11]. More recently, we demonstrated the potential for successful delivery with photoactive liposomes [12]. Pharmaceutics 2023, 15, 2040. https://doi.org/10.3390/pharmaceutics15082040 https://www.mdpi.com/journal/pharmaceutics