Leptospermum extract (QV0) suppresses pleural mesothelioma tumour growth in vitro and in vivo by mitochondrial dysfunction associated apoptosis

Pleural mesothelioma (PM) is a highly aggressive, fast-growing asbestos-induced cancer with limited effective treatments. There has been an interest in using naturally occurring anticancer agents derived from plant materials for the treatment of PM. However, it is unclear if aqueous extract from the Leptospermum polygalifolium (QV0) has activity against PM. Here we investigated the anti-cancer property of QV0 in vitro and in vivo. Animals treated with Defender® (QV0 dietary supply) exhibited a reduced tumour size over 30 days, which was associated with an average extended of seven days mouse life. There was no liver toxicity, nor increased blood glucose post-treatment in animals treated with Defender®. Moreover, QV0 suppressed the growth of 13 cancer cell lines in a dose-dependent manner, effective at concentrations as low as 0.02% w/v. This response was found to be associated with inhibited cell migration, proliferation, and colony formation, but without evident cell cycle alteration. We observed mitochondrial dysfunction post QV0 treatment, as evidenced by significantly decreased basal and maximal oxygen consumption rates. Significantly enhanced tumour apoptosis was observed in the Defender®-treated animals, correlating with mitochondrial dysfunction. To the best of our knowledge, this study constitutes the first demonstration of an improved host survival (without adverse effects) response in a QV0-treated PM mouse model, associated with an evident inhibition of PM cell growth and mitochondrial dysfunction-related enhancement of tumour apoptosis. Importance A major problem with cancer chemotherapy or immunotherapy is the severe adverse effects associated with normal tissue damage. PM is known to be treatment resistant and has poor a prognosis, therefore new therapeutic treatment options are urgently needed. In the present study, we explored the potential utility of a Leptospermum extract (QV0) as a treatment option for mesothelioma. We demonstrated for the first time that QV0 exhibits an anti-tumour response in mesothelioma, without any associated adverse effects observed in the PM mouse model. These findings provide a rationale for early-stage clinical trials. We anticipate that prospective translational research will lead to the clinical implementation of a novel QV0-based treatment strategy that will ultimately benefit PM patients.