Molecular mechanisms for the activity of PX-478, an antitumor inhibitor of the hypoxia-inducible factor-1alpha.
Koh MY, Spivak-Kroizman T, Venturini S, Welsh S, Williams RR, Kirkpatrick DL, Powis G.
M. D. Anderson Cancer Center, University of Texas, FC-6.3044, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
We have reported previously that PX-478 (S-2-amino-3-[4'-N,N,-bis(chloroethyl)amino]phenyl propionic acid N-oxide dihydrochloride) has potent antitumor activity against a variety of human tumor xenografts associated with the levels of the hypoxia-inducible factor-1alpha (HIF-1alpha) within the tumor. We now report that PX-478 inhibits HIF-1alpha protein levels and transactivation in a variety of cancer cell lines. Hypoxia-induced vascular endothelial growth factor formation was inhibited by PX-478, whereas baseline levels of vascular endothelial growth factor in normoxia were unaffected. Studies of the mechanism of PX-478 action showed that HIF-1alpha inhibition occurs in both normoxia and hypoxia and does not require pVHL or p53. In addition, PX-478 decreases levels of HIF-1alpha mRNA and inhibits translation as determined by 35S labeling experiments and reporter assays using the 5' untranslated region of HIF-1alpha. Moreover, to a lesser extent, PX-478 also inhibits HIF-1alpha deubiquitination resulting in increased levels of polyubiquitinated HIF-1alpha. The inhibitory effect of PX-478 on HIF-1alpha levels is primarily due to its inhibition of translation because HIF-1alpha translation continues in hypoxia when translation of most proteins is decreased. We conclude that PX-478 inhibits HIF-1alpha at multiple levels that together or individually may contribute to its antitumor activity against HIF-1alpha-expressing tumors.
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PMID: 18202012 [PubMed - indexed for MEDLINE]