Laryngeal cancer is expected to account for 184,615 new cases and 99,840 deaths in the world in 2020 [1]. About 1.0% of all new cancer cases and 1.0% of all cancer deaths occur in patients with laryngeal cancer [1]. Although the 5-year survival rate of laryngeal cancer is relatively high among all malignant tumors, traditional treatment strategies such as surgery, radiotherapy, and chemotherapy may add to the implications of difficulties with speaking, breathing, swallowing, and even psychosocial problems. Nowadays, the treatment strategy for laryngeal cancer is more inclined to multimodal therapy, striving for cure while maintaining the best quality of life possible for the patient.

As an emerging and promising cancer therapy, photodynamic therapy (PDT) destroys photosensitizer accumulated tumor cells by utilizing wavelength‑matched visible light irradiation [2]. Previous studies have shown that PDT in combination with chemotherapy can enhance tumor destruction and reduce toxicity compared with chemotherapy alone. Imran Rizvi et al. found that the combination treatment of BPD-PDT and low-dose carboplatin (CBDCA) produced a significant synergistic cytotoxic effect on ovarian cancer cells [3]. Raktim Biswas et al. also found that combination of PDT and CBDCA induced apoptosis in anaplastic thyroid cancer cells by synergistically generating reactive oxygen species (ROS) and disrupting mitochondrial membranes [4]. To overcome the limitations of light penetration and long-lasting cutaneous photosensitivity, various types of photosensitizers have been studied over the last 30 years, such as 5-aminolevulinic acid, hematoporphyrin and chlorin derivatives [5], [6], [7]. As a novel chlorophyll derived photosensitizer, 9‑hydroxypheophorbide α (9‑HPbD) has a relatively longer absorption wavelength (670 nm) and a shorter half‑life in the body compared with other photosensitizers [8]. Our previous study demonstrated that 9‑HPbD-PDT triggered apoptosis in vitro through the ROS-mediated mitochondrial pathway and endoplasmic reticulum stress in AMC-HN-3 human laryngeal cancer cells [9,10]. A similar pathway was also found in the treatment of HN-3 cells by CBDCA. The involvement of mitochondria at the initiation of apoptosis induced by CBDCA for HN-3 cells was triggered by excessive intracellular Ca2+ [11]. In addition, a previous study concerning combination treatment with 9-HPbD-PDT and CBDCA resulted in an enhanced photocytotoxicity and apoptosis induction in HN-3 cancer cells [12]. It is well known that some of these PDT effects are generated by ROS-mediated adaptive or cell death responses following the activation of photosensitizer by light irradiation [13]. But in the combined modality of 9-HPbD-PDT and CBDCA, the role of ROS remains to be examined.

In the present study, we investigated the role of ROS in apoptotic mechanisms induced by 9-HPbD-PDT and CBDCA in AMC-HN-3 cells. In vivo efficacy of 9-HPbD-PDT combined with CBDCA was also investigated.