title: Molecular mechanisms for the activity of PX-478, an antitumor inhibitor of the hypoxia-inducible factor-1alpha.
abstract: 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.
authors.affiliation: M. D. Anderson Cancer Center, University of Texas, FC-6.3044, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Mei Y
authors.initials: MY
authors.lastname: Koh
authors.forename: Taly
authors.initials: T
authors.lastname: Spivak-Kroizman
authors.forename: Sara
authors.initials: S
authors.lastname: Venturini
authors.forename: Sarah
authors.initials: S
authors.lastname: Welsh
authors.forename: Ryan R
authors.initials: RR
authors.lastname: Williams
authors.forename: D Lynn
authors.initials: DL
authors.lastname: Kirkpatrick
authors.forename: Garth
authors.initials: G
authors.lastname: Powis
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D009150:Mustard Compounds / Q000737:chemistry / Q000494:pharmacology*; D010666:Phenylpropionates / Q000737:chemistry / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics; D012680:Sensitivity and Specificity; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination
chemical_list: C492908:2-amino-3-(4'-N,N-bis(2-chloroethyl)amino)phenylpropionic acid N-oxide; D000970:Antineoplastic Agents; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009150:Mustard Compounds; D010666:Phenylpropionates; D016159:Tumor Suppressor Protein p53