The combination of brusatol and methionine restriction for treatment of lung cancer

Objective

Lung cancer is the leading cause of cancer deaths in the U.S. and has a 5-year survival rate of just 18.6%. There is a need for alternative or adjunctive therapies to treat cancer or enhance efficacy of standard treatments. Nutritional therapies such as methionine restriction (MR) are being explored because of the role of the essential amino acid in cancer metabolism. MR is effective at slowing growth of many types of cancer in preclinical models. Likewise, the novel compound, brusatol, inhibits cancer growth in preclinical models. Independently, MR and brusatol reduce cancer progression, likely through differing mechanisms. It is probable that a combination of MR and brusatol could synergistically inhibit cancer progression. However, the efficacy of this polytherapy has not been investigated. Therefore, the aim of this study was to determine if treatment with both MR and brusatol inhibits lung cancer growth and to determine the mechanism of action of this combination therapy. We focused on markers of oxidative stress and cell death since brusatol is a known inhibitor of the antioxidant transcription factor, NRF2. 

Methods

Approximately 85% of lung cancers are non-small cell lung cancer. For these studies, we utilized A549 cells, which are a model of human non-small cell lung cancer. A549 cells were treated with vehicle or brusatol (5 nM) in control or MR media. Cell proliferation was measured at days 0, 3, and 6. Protein was extracted from cells after 24 hours of treatment. Protein expression of NRF2 and its target protein, NQO1, were measured by western blot. 

Results

On days 3 and 6, MR and combination of MR + brusatol significantly reduced lung cancer proliferation compared to control, while brusatol alone had no significant effect. MR tended to reduce NRF2 expression (p=0.068). However, brusatol alone, and in combination with MR, significantly reduced NRF2 expression by 38% and 43%, respectively. NQO1 expression was not affected by any treatment.  

Conclusion

A combination of MR and brusatol may be an effective intervention for lung cancer that induces minimal adverse effects on noncancer cells. Our ongoing studies continue to explore the mechanism of action of MR + brusatol.