Visualizing photodynamic therapy response with time-lapse OCT in an in vitro model of metastatic ovarian cancer

Ovarian epithelial cancer has a high morbidity due to its propensity to metastasize onto surfaces in the abdomen. In order to effectively treat these metastatic lesions with photodynamic therapy (PDT), it is critical to understand the detailed dynamics of the PDT response. 3D in vitro models of ovarian cancer are a promising system for studying the response to PDT of these lesions, as they replicate the size, appearance, and characteristics of metastatic disease observed in the clinic. An ideal approach capable of non-purturbative, 3D imaging of this model is optical coherence tomography (OCT). An ultrahigh resolution time-lapse OCT (TL-OCT) system was used to visualize the photodynamic therapeutic response in the hours and days following treatment. Tumor nodules were observed to experience rapid cell death within the first 24 hours post-treatment using benzophorphyrin derivative monoacid A (BPD), characterized by structural breakdown of the model nodules. Highly scattering bodies were observed with OCT contrast to form at the periphery of the tumor nodules. These highly scattering moieties were identified as apoptotic bodies, indicating that OCT is capable of tracking the PDT-induced apoptosis in real-time without the need for labels.