PTGS2 and hepatocellular carcinoma: Using the MTS assay we first assessed the effects of sorafenib (SOR) and celecoxib (CLX) on the viability of two human HCC cell lines, HepG2 and Huh7, which display different characteristics including differentiation, biological behavior and genetic defects, COX-2 expression levels [21], as well as Raf/MEK/ERK pathway activities [23].