4687

The inhibition of CuZn superoxide dismutase (SOD1) by ATN-224, a second generation tetrathiomolybdate, interferes with multiple signaling pathways in tumor and endothelial cells in vitro

Tuesday, Apr 04, 2006, 1:00 PM - 5:00 PM

Exhibit Hall, Washington Convention Center

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Jose C. Juarez, Mari M. Manuia, Oscar Betancourt Jr., Andrew P. Mazar, Fernando Donate. Attenuon, LLC, San Diego, CA

Tetrathiomolybdate (TM) is a copper binding drug that has demonstrated anti-tumor and anti-angiogenic activity in a number of preclinical studies as well as preliminary evidence of anti-tumor activity in cancer patients. However, very little is understood about the mechanism of action of TM at the molecular level. ATN-224 is a second generation analogue of TM that is currently entering several Phase II cancer trials. ATN-224 inhibits CuZn superoxide dismutase (SOD1), which catalyzes the dismutation of superoxide anion (O₂^-) into H₂O₂ and O₂. In endothelial cells, SOD1 inhibition results in reduced phosphorylation of ERK1/2 mediated by FGF-2 and VEGF. This leads to suppression of proliferation in vitro and the inhibition of angiogenesis in vivo. In the present study, we demonstrate that ATN-224 inhibition of SOD1 also leads to the inhibition of EGF, IGF-1 and PDGF mediated ERK phosphorylation in a variety of tumor cell lines (A431, HT-29 and U87). This inhibition appears to occur at the level of the growth factor receptor, since (i) ATN-224 mediated SOD1 inhibition in A431 cells decreases EGF mediated phosphorylation of EGFR; and, (ii) ATN-224 treatment of U87 glioma cells stimulated with PDGF decreases levels of the PDGF receptor. In contrast to endothelial cells, where ATN-224 inhibits proliferation but does not cause cell death, the induction of apoptosis is observed in tumor cells treated with ATN-224. Further, EGF, PDGF and IGF-1 have been reported to elicit an increase in H₂O₂ by activating superoxide producing enzymes when bound to their receptors. Superoxide produced in this way is then converted into H₂O₂, which inactivates phosphatases by oxidizing an essential cysteine residue in the active site. SOD1 inhibition mediated by ATN-224 in A431 cells impedes the H₂O₂ mediated inactivation of PTEN and other phosphatases, suggesting that the preservation of phosphatase activity contributes to ATN-224 inhibition of growth factor mediated signaling. These results support the inhibition of SOD1 by ATN-224 as a novel therapeutic strategy for the inhibition of multiple signaling pathways implicated in tumor growth and angiogenesis.