Suillus luteus methanolic extract inhibits cell growth and proliferation of a colon cancer cell line

Several edible mushrooms extracts are known to have tumor cell growth inhibitory potential. The objective of this work was to study this potential in extracts of Suillus luteus collected from the Northeast of Portugal. Various extracts were prepared and their effect on tumor cell growth was studied with the SRB assay in four human tumor cell lines: MCF-7 (breast), NCI-H460 (non-small cell lung cancer), AGS (gastric) and HCT-15 (colon). The methanolic extract of S. luteus was the most potent extract. This extract was slightly more potent in the HCT-15 cells (with mutant p53, GI₅₀=17.8±1.6μg/mL) than in the other cell lines tested, which suggested that its effect was not p53-dependent. Indeed, in HCT-15 cells, an increase in the levels of p53 was detected but no alterations in some of the proteins transactivated by p53 (e.g. p21 or Bax) were found. The extract caused an increase in the cellular levels of p-H2A.X, which is suggestive of DNA damage. Growth inhibition in these cells was mostly due to inhibition of cell proliferation and an increase in the % of cell in the G1 phase of the cell cycle. An increase in cell death was also found, even though to very low levels. In addition, this extract was not cytotoxic to primary cultures of porcine hepatocytes (GI₅₀>400μg/mL). Together, these results indicate that the S. luteus methanolic extract may be an interesting source of compounds that inhibit the proliferation of tumor cells but further studies should be carried out in order to understand its potential.