Tumor regression induced by photodynamic treatment with chlorin p6 in hamster cheek pouch model of oral carcinogenesis: Dependence of mode of tumor cell death on the applied drug dose

SummaryWe investigated tumor regression and the mode of tumor cell death induced by photodynamic treatment (PDT) with chlorin p6 (Cp6) in hamster cheek pouch model of oral squamous cell carcinoma. Cp6 was administered systemically through intraperitoneal injection and after 4 h the tumors were subjected to photodynamic treatment using red light (660 ± 25 nm, fluence ∼100 J/cm2). Tumor response to PDT was monitored by measuring the tumor volume before PDT and 1 week after. Results show that smaller tumors (⩽80 mm3) regressed completely after PDT with Cp6 dose of 2.0 mg/kg body weight and for the bigger tumors (∼180 mm3) higher dose of Cp6 (4.0 mg/kg) was more effective. Tumors treated with lower Cp6 dose showed infiltration of immune cells, absence of TUNEL labeling, smeared pattern of DNA fragmentation and no significant increase in caspase-3 activity suggestive of necrotic cell death and inflammation. In tumors treated with higher Cp6 dose, features characteristic of apoptotic cell death such as extensive TUNEL positive labeling, increase in caspase-3 activity and laddered pattern of DNA fragmentation were observed and there was no infiltration of immune cells. PDT with Cp6 was also found to lead to expression of matrix metalloprotease-9 (MMP-9) which was greater at lower drug dose PDT as compared to higher drug dose PDT. These results suggest that drug dose plays an important role in determining the mechanism of tumor cell death and effectiveness of PDT.