Bortezomib Could Reduce Cell Viability by Activation of Heme Oxygenase 1 in Multiple Myeloma Cells

Abstract 5005

Bortezomib (PS-341, Velcade^®) specifically targeting the ubiquitin-proteosome pathway, is the first defined therapeutic proteosoma inhibitor approved by FDA for treatment of Multiple Myeloma (MM). We explored the hypothesis that the activity of Bortezomib in MM cells may involve the heme oxygenase 1 (HMOX1), a enzyme with pleiotropic effects, catalysing the degradation of heme to carbon monoxide, biliverdin and ferrous iron.

After 24h of treatment with Bortezomib at 10nM, the U266 and SKM-M1 MM cell lines showed a decrease of cell viability around 50% and an increase of HMOX1 protein and mRNA expression of 40 fold (p<0. 001). Using a colorimetric assay we observed that Bortezomib increased also the HMOX1enzymatic activity (p<0. 03). To elucidate the significance of the HMOX1 increase after bortezomib treatment, we treated myeloma cells with Bortezomib plus an inducer (Hemin 10uM) or an inhibitor (Tin, Sn-Mesoprotoporphyrin, 10uM) of the enzyme activity. Treatment with Hemin and Tin alone not changed the cell viability. Cell viability was reduced (p<0. 003) by addition of Hemin and was increased (p<0. 002) by Tin addiction with respect to Bortezomib alone.