Enhancing the therapeutic responsiveness of photodynamic therapy with the antiangiogenic agents SU5416 and SU6668 in murine nasopharyngeal carcinoma models
Background: Photodynamic therapy (PDT) is a promising therapeutic modality using a tumor localizing photosensitizer and light to destroy tumor cells. A major limitation of PDT is tumor recurrence, which is partly due to neovascularization. Purpose: The objective of the present study was to determine whether combination therapy with PDT and antiangiogenic agents (i.e. SU5416 and SU6668) would be more effective in controlling tumor recurrence in a mouse model of human CNE2 poorly differentiated nasopharyngeal carcinoma compared with PDT or antiangiogenic agents administered alone. Methods: Athymic mice bearing CNE2 tumor xenografts received daily i.p. injections of 20 mg/kg SU5416 or 100 mg/kg SU6668 for 28 consecutive days either alone or following a single hypericin-PDT treatment. Results: Significant inhibition of CNE2 tumor growth was observed in all treatment groups. Differences in 4× tumor growth time, the number of mice with 4× tumor growth, tumor growth inhibition as well as the percent of mice surviving were not statistically significant among individual treatment groups. However, the number of mice with 4× tumor growth observed in SU6668 monotherapy and combined PDT and SU6668 treatment groups was significantly less than that in the control group (P<0.05 and 0.01, respectively). Moreover, compared with the control group, only the combined PDT and SU6668 treatment significantly extended survival of tumor-bearing host mice (P<0.05). The semiquantitative RT-PCR results showed that the expression of HIF-1α, VEGF, COX-2 and bFGF were increased in PDT-treated tumor samples collected 24 h post-PDT, suggesting that PDT-induced damage to tumor microvasculature and the resultant hypoxia upregulate the expression of certain proangiogenic factors. Conclusions: The effectiveness of PDT can be enhanced by antiangiogenic treatment with the synthetic RTK inhibitors. Of the two synthetic RTK inhibitors tested, SU6668 was more effective than SU5416 in enhancing tumor responsiveness to PDT.