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At clinically relevant concentrations, two widely used drugs blocked HIV-1 replication ex vivo. They specifically inhibited expression from the HIV-1 promoter at the level of transcription initiation. Both drugs interfered with the hydroxylation step in the hypusine modification of eIF5A. These results have profound implications for the potential therapeutic use of these drugs as antiretrovirals and for the development of optimized analogs.

The hypusine biosynthetic steps represent novel targets for intervention in cell proliferation. Hypusine is a rare amino acid, formed posttranslationally in one cellular protein, eIF5A, and is essential for cell proliferation. Deoxyhypusine hydroxylase, the metalloenzyme catalyzing the final step in hypusine biosynthesis, and prolyl 4-hydroxylase, a non-heme iron enzyme critical for collagen processing, can be inhibited by small chelating molecules that target their essential metal atom. We examined the effects of 5 compounds (ciclopirox, deferiprone, deferoxamine, mimosine and 2,2-dipyridyl) on these protein hydroxylases in HUVECs, on cell proliferation and on angiogenesis using 2 model assays: tube-like vessel formation on Matrigel and the chick aortic arch sprouting assay. These compounds inhibited cellular deoxyhypusine hydroxylase in a concentration-dependent manner, but their efficacy varied widely in the following order: ciclopirox3 deferoxamine32

The structure and function of the 2-oxoglutarate binding site of prolyl4-hydroxylase was studied by assaying the inhibitory potential of 24 selected aliphatic or aromatic compounds. All except one of them inhibited the enzyme competitively with respect to 2-oxoglutarate and noncompetitively with respect to Fez+, the Ki values ranging from 0.8 pM to over 15 mM. The Ki values for the two most effective inhibitors, pyridine 2,5-dicarboxylate and 2,4-dicarboxylate, were about 0.8 pM and 2 pM, these compounds being the most potent inhibitors of prolyl 4-hydroxylase with respect to 2-oxoglutarate known so far. Only one of the compounds tested, 2-oxoadipinate, was able to support hydroxylation by replacing 2-oxoglutarate as a cosubstrate. The data suggest that the 2-oxoglutarate binding site can be divided into three distinct subsites. Subsite I is probably a positively charged side chain of the enzyme that ionically binds the C5 carboxyl group of the 2-oxoglutarate, subsite I1 consists of two cis-positioned equatorial coordination sites of the enzyme-bound ferrous ion and is chelated by the C1-C2 moiety, while subsite I11 involves a hydrophobic binding site in the C3 -C4 region of the cosubstrate. The sp3 rehybridization of C2 within the chelating moiety of the cosubstrate appears to be a crucial event during decarboxylation that proceeds in the form of a ligand reaction inside the Fe2+ coordination sphere.Prolyl 4-hydroxylase catalyzes the formation of 4-hydroxyproline in collagens and other proteins with collagen-like amino acid sequences by the hydroxylation of certain proline residues in peptide linkages (for reviews, see [l-31). The minimum sequence requirement for hydroxylation is fulfilled by an -Xaa-Pro-Gly-triplet, and the reaction requires ferrous ions, 2-oxoglutarate, molecular oxygen and ascorbate. The 2-oxoglutarate is stoichiometrically decarboxylated, one atom of the O2 molecule being incorporated into the succinate while the other is incorporated into the hydroxyl group [l -31. The results of extensive kinetic studies [4-61 and other data [7, 81 are consistent with an ordered binding of Fe2 +, 2-oxoglutarate, O2 and the peptide substrate to the enzyme in this order, and an ordered release of the hydroxylated peptide, C02, succinate, and Fez+, in which Fe2 + does not leave the enzyme between the majority of the catalytic cycles and in which the order of release of the hydroxylated peptide and CO, is uncertain. Ascorbate is not consumed stoichiometrically [5, 91, and pure enzyme preparations can catalyze hydroxylation for a number of catalytic cycles in the complete absence of this vitamin [6, 81. These findings, together with the kinetic [6,10) and other data [S], suggest that ascorbate is required to prevent oxidation of the enzyme-bound iron and possibly some other groups on the enzyme molecule between some catalytic cycles, but not the majority.A detailed stereochemical mechanism has recently been suggested for prolyl4-hydroxylase [ll], in which it is proposed that binding of 2-oxoglutarate (compound...

HIV-1 blocks apoptosis, programmed cell death, an innate defense of cells against viral invasion. However, apoptosis can be selectively reactivated in HIV-infected cells by chemical agents that interfere with HIV-1 gene expression. We studied two globally used medicines, the topical antifungal ciclopirox and the iron chelator deferiprone, for their effect on apoptosis in HIV-infected H9 cells and in peripheral blood mononuclear cells infected with clinical HIV-1 isolates. Both medicines activated apoptosis preferentially in HIV-infected cells, suggesting that the drugs mediate escape from the viral suppression of defensive apoptosis. In infected H9 cells, ciclopirox and deferiprone enhanced mitochondrial membrane depolarization, initiating the intrinsic pathway of apoptosis to execution, as evidenced by caspase-3 activation, poly(ADP-ribose) polymerase proteolysis, DNA degradation, and apoptotic cell morphology. In isolate-infected peripheral blood mononuclear cells, ciclopirox collapsed HIV-1 production to the limit of viral protein and RNA detection. Despite prolonged monotherapy, ciclopirox did not elicit breakthrough. No viral re-emergence was observed even 12 weeks after drug cessation, suggesting elimination of the proviral reservoir. Tests in mice predictive for cytotoxicity to human epithelia did not detect tissue damage or activation of apoptosis at a ciclopirox concentration that exceeded by orders of magnitude the concentration causing death of infected cells. We infer that ciclopirox and deferiprone act via therapeutic reclamation of apoptotic proficiency (TRAP) in HIV-infected cells and trigger their preferential elimination. Perturbations in viral protein expression suggest that the antiretroviral activity of both drugs stems from their ability to inhibit hydroxylation of cellular proteins essential for apoptosis and for viral infection, exemplified by eIF5A. Our findings identify ciclopirox and deferiprone as prototypes of selectively cytocidal antivirals that eliminate viral infection by destroying infected cells. A drug-based drug discovery program, based on these compounds, is warranted to determine the potential of such agents in clinical trials of HIV-infected patients.

Cancer etiology is influenced by alterations in protein synthesis that are not fully understood. In this study, we took a novel approach to investigate the role of the eukaryotic translation initiation factor eIF5A in human cervical cancers, where it is widely overexpressed. eIF5A contains the distinctive amino acid hypusine, which is formed by a posttranslational modification event requiring deoxyhypusine hydroxylase (DOHH), an enzyme that can be inhibited by the drugs ciclopirox and deferiprone. We found that proliferation of cervical cancer cells can be blocked by DOHH inhibition with either of these pharmacologic agents, as well as by RNA interference–mediated silencing of eIF5A, DOHH, or another enzyme in the hypusine pathway. Proteomic and RNA analyses in HeLa cervical cancer cells identified two groups of proteins in addition to eIF5A that were coordinately affected by ciclopirox and deferiprone. Group 1 proteins (Hsp27, NM23, and DJ-1) were downregulated at the translational level, whereas group 2 proteins (TrpRS and PRDX2) were upregulated at the mRNA level. Further investigations confirmed that eIF5A and DOHH are required for Hsp27 expression in cervical cancer cells and for regulation of its key target IκB and hence NF-κB. Our results argue that mature eIF5A controls a translational network of cancer-driving genes, termed the eIF5A regulon, at the levels of mRNA abundance and translation. In coordinating cell proliferation, the eIF5A regulon can be modulated by drugs such as ciclopirox or deferiprone, which might be repositioned to control cancer cell growth.

S phase entry, I.e. start of DNA replication, Is a crucial step in proliferation. Inhibition of S phase entry correlates with Inbibition of hypusine formation, an event affecting only the eukaryotie Initiation factor $A (elF4A), Its hypuslnecontalning sequence wus postulated to authorize polysomal utilization of specific trauscripts for proteins necessary to enable DNA replication. Using ndmodne to reversibly suppress the hyposinc-forming deoxyhypusyi hydmxylase (E.C. 1.1¢99.29) in cells while differentially displaying their polysomal versus non-polysemal mRNA popolations, we report the detection and cla~!fleation of several mRNA species that indeed disappear from and reappear at !lo1-ysomes in con~rt with inhibition and d_!s!nhibition, respectively, of hypusine formation. Based on initial sequence data, two trauslationally controlled enzymes, both critical for proliferation, are identified us candicate wodncts of such mRNAs, methionine adenosyitrausferuse (E.C 2.$.1.6) and cytochrome-c oxiduse 0gC 1.9.3.1) subunit 1. The existence of such potative hyposinedependent messenger nnclde adds (/O, mas) prevides the basis for a proposal on their molecular function in onset of multiplication.Key words: Post-translational modification; eIF-5A; Hypusine; Cell cycle control; Translational control; mRNA I, IntroductionThe unique amino acid hypusine [~-(4-amino-2(R).hydroxybutyl)-t.-lysine] is formed post-translationally by the sequential action of deoxyhypusyl synthase (DOHS) and deoxyhypusyl hydroxylase (DOHH) on a single lysyl residue in only one cellular protein, the eukaryotic initiation factor 5A (elF-SA) [I-3]. The hypusine-containing domain shows remarkable interspecies conservation, and a sequence of 12 amino acids containing the hypusine residue has been strictly conserved throughout eukaryotic evolution, from fungi to plants, insects, and mammals [3]. Hypusine formation, which has not been demonstrated in prokaryotes [2], is an absolute requirement for growth of $. cerevesiae [4], and a number of *Correspondin8 authors, Fax: (I) (212) 746 0300 and Fax: (I) (212) 746 6382, respectively.'For Stephen Biko (December 18, 1944.-September 12, 1977.reports have established correlations between hypusine formation and the proliferation of eukaryotic cells (see [2,3]). However, the exact physiological function of this presumed translation initiatic~n factor is unknown, and at present it even is unclear whether elF-SA functions at the pretranslational and/ or the translational level [3].Deoxyhypusyl hydroxylase (E.C. 1.14.99.29), which catalyses the final step of hypusine biosynthesis, is apparently related [5,6] to other protein hydroxy]ating enzymes such as prolyl 4-hydroxylase (E.C 1.14.11.2) [7] and is effectively inhibited by mimosine (3-(N-(3-hydroxypyridin-4-one))-2[S]-aminopropionic acid), both in vitro and in culture [3]. This coincides with proliferative arrest in the late GI phase ofthe cell cycle [3,[8][9][10][11]. Fast recovery ofcellular DOHH activity occurs upon mimo,,;ine removal, an effect parallele...