Current trends in the management of malignant pleural mesothelioma

Epigallocatechin-3-gallate induces mesothelioma cell death via H2 O2 -dependent T-type Ca2+ channel opening

Malignant mesothelioma (MMe) is a highly aggressive, lethal tumour requiring the development of more effective therapies. The green tea polyphenol epigallocathechin-3-gallate (EGCG) inhibits the growth of many types of cancer cells. We found that EGCG is selectively cytotoxic to MMe cells with respect to normal mesothelial cells. MMe cell viability was inhibited by predominant induction of apoptosis at lower doses and necrosis at higher doses. EGCG elicited H₂O₂ release in cell cultures, and exogenous catalase (CAT) abrogated EGCG-induced cytotoxicity, apoptosis and necrosis. Confocal imaging of fluo 3-loaded, EGCG-exposed MMe cells showed significant [Ca²⁺]_i rise, prevented by CAT, dithiothreitol or the T-type Ca²⁺ channel blockers mibefradil and NiCl₂. Cell loading with dihydrorhodamine 123 revealed EGCG-induced ROS production, prevented by CAT, mibefradil or the Ca²⁺ chelator BAPTA-AM. Direct exposure of cells to H₂O₂ produced similar effects on Ca²⁺ and ROS, and these effects were prevented by the same inhibitors. Sensitivity of REN cells to EGCG was correlated with higher expression of Ca_v3.2 T-type Ca²⁺ channels in these cells, compared to normal mesothelium. Also, Ca_v3.2 siRNA on MMe cells reduced in vitro EGCG cytotoxicity and abated apoptosis and necrosis. Intriguingly, Ca_v3.2 expression was observed in malignant pleural mesothelioma biopsies from patients, but not in normal pleura. In conclusion, data showed the expression of T-type Ca²⁺ channels in MMe tissue and their role in EGCG selective cytotoxicity to MMe cells, suggesting the possible use of these channels as a novel MMe pharmacological target.

Malignant pleural mesothelioma: current concepts in treatment

Malignant pleural mesothelioma (MPM) is a primary and locally aggressive tumor of the pleura. A well defined causal relationship with asbestos exposure, and an overwhelming media interest in the use of asbestos in industrialized countries after World War II, has produced a high level of awareness of this disease. With a peak incidence of MPM expected in Europe, Australia, and the US within the next 15 years, and the failure of current treatment approaches to offer long-term survival and improve quality of life, new therapeutic regimens are warranted. The effects of surgery in terms of survival and symptomatic relief have yet to be defined because of a lack of randomized trials. The role of radiotherapy in the treatment of MPM remains controversial, as the radiosensitivity of malignant mesothelial cells is modest. MPM response to chemotherapy is comparatively poor. The combination of pemetrexed and cisplatin chemotherapy has achieved the best objective responses. Presently, a multimodal approach is considered to be the cornerstone of treatment of MPM. Important ongoing international and national trials are addressing the roles of chemotherapy (e.g. the EAP and MS01 trial), radical surgery (e.g. the MARS trial) and radiotherapy (e.g. the SAKK group phase III study).