These enzymes are most potently inhibited by MTX-polyglutamates, an important fact, given that MTX is rapidly converted to MTX-polyglutamates, the erythrocyte concentrations of which are more closely associated with clinical responses than MTX plasma levels.11 MTX is known to increase AICAR levels in HUVECs after a 48 h treatment12 and can enhance activation of AMPK by AICAR in cancer cell lines.35 While this manuscript was under review, Pirkmajer et al have shown that MTX and AICAR together increase ZMP in cultured myotubes, supporting our hypothesis as to how MTX activates AMPK.36 Here, PRKAA2 is linked to cancer.