Uncovering cell cycle-dependent effects on cell survival in near-infrared photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT) is an innovative cancer treatment that selectively induces cell death in cancer cells. Cetuximab-IRdye700DX (Cmab-IR700) conjugate is commonly used in NIR-PIT for head and neck squamous cell carcinoma (HNSCC) because of the frequent overexpression of epidermal growth factor receptor (EGFR) in HNSCC cells. This study examined the influence of cell cycle phases on the response and sensitivity to NIR-PIT in cell lines expressing a fluorescent ubiquitination-based cell cycle indicator (Fucci). The timing of cell death was quantified using time-lapse imaging and a clonogenic assay was used to assess cell survival. The results indicated that the timing of cell death varied among cell lines, with G1-phase cells in HSC3 and CAL33 lines showing slower cell death than those in the S/G2/M phases, whereas HeLa cells exhibited no cell cycle phase-dependent correlation. Cell rupture was predominant in HSC3 and CAL33 cells, whereas HeLa cells exhibited a combination of cell rupture and swelling. Clonogenic survival differed among the cell lines, mirroring variations in the timing of cell death. Among CAL33 and HeLa cells, G1-phase cells demonstrated greater resistance to NIR-PIT. EGFR expression levels, which varied according to cell line and cell cycle phase, were associated with sensitivity to NIR-PIT. Additionally, L-ascorbic acid-treated HeLa cells exhibited increased time to cell death and reduced NIR-PIT sensitivity, which may be due to reactive oxygen species. These findings provide information for the development of NIR-PIT strategies based on cell cycle kinetics to enhance therapeutic outcomes.