Preclinical comparison of mTHPC and verteporfin for intracavitary photodynamic therapy of malignant pleural mesothelioma
Efficacy and tumour selectivity of photodynamic therapy with two clinically approved sensitizers (mTHPC, verteporfin) were assessed for focal intracavitary photodynamic therapy (PDT) in rodents with malignant pleural mesothelioma (MPM) at recommended drug-light conditions and at escalating sensitizer dosages. MPM tumours were generated in 15 Fischer rats by subpleural mediastinal tumour cell injection followed after 5 days by intracavitary PDT with light delivery monitored by in situ dosimetry. Animals were intravenously sensitized either with mTHPC (0.1 mg/kg, n = 3; 0.2 mg/kg, n = 3) followed after 4 days by illumination with 20 J/cm(2) at 652 nm, or with verteporfin (0.6 mg/kg, n = 3; 1.2 mg/kg, n = 3) followed after 20 min by illumination with 100 J/cm(2) at 689 nm. Three untreated tumour-bearing animals served as controls. Histological evaluation of the treated tumour and of adjacent normal organs was performed 10 days after tumour implantation. The extent of PDT-induced tumour necrosis was compared to the non-necrosed area and expressed in percentage. A locally invasive growing MPM tumour (3.1 +/- 1 mm diameter) without spontaneous necrosis diameter was found in all animals. For both sensitizers, focal intracavitary PDT was well tolerated at drug-light conditions recommended for clinical applications. Mediastinal organs were spared for both sensitizers but verteporfin resulted in a higher extent of tumour necrosis (80%) than mTHPC (50%). Drug dose escalation revealed a higher extent of PDT-related tumour necrosis for both sensitizers (mTHPC 55%, verteporfin 88%), however, verteporfin-PDT was associated with a higher toxicity than mTHPC-PDT.