Background:  Mature  eukaryotic translation initiation factor 5A (eIF5A), involved in nucleocytoplasmic transport of certain mRNA, contains the functionally essential residue hypusine. The latter is formed by deoxyhypusine hydroxylase (DOHH), a 2-oxoacid utilizing non-heme iron dioxygenase whose catalysis follows the HAG mechanism. Mature eIF5A is a cellular cofactor of the viral Rev/Rex proteins, required for retroviral multiplication and suppression of host cell apoptosis. We hypothesized that HAG mechanism-based agents that target the ferrous ion of DOHH, but not metal chelators in general, deny mature eIF5A to HIV-1, causing a lack of retroviral anti-apoptotic proteins and thus releasing the self-destruction of HIV-infected lymphocytes. DOHH inhibition in human papillomavirus (HPV)-infected or normal cells should not trigger apoptosis.  

Methods:  The drugs deferiprone (DEF) and ciclopirox (CPX), known DOHH inhibitors, were compared to the chelators 2-imidazoyl-4-methylphenol (IMP) and desferal (DES). Apoptosis of HIV-1-infected H9 cells, HPV-16-infected SiHa cells, and uninfected lymphocytes was analyzed by TUNEL flow cytometry. DOHH activity was measured by metabolic labeling with ³H-spermidine.

Results:  In a dose-dependent manner, DEF and CPX inhibited DOHH in HIV⁺ H9 cells and in HPV⁺ SiHa cells. The chelator IMP was uniformly ineffective even at 400 µM. In the H9 cells, only the DOHH inhibitors DEF and CPX triggered dose-dependent apoptosis. The chelators IMP and DES failed to elicit apoptosis even at maximal concentrations (400 µM and 20 µM, respectively). With complete suppression of DOHH activity, i.e. at 200 µM DEF or 40 µM CPX, at least 30% of these H9 cells became apoptotic within 20 hours. By contrast, 40 µM CPX did not initiate apoptosis in the SiHa cells even after 120 hours, although CPX totally suppressed their DOHH activity. Likewise, lymphocytes harvested from healthy volunteers failed to respond with apoptosis when exposed for 20 hours to DEF, CPX, or DES. 

Conclusions:  The ability to chelate iron in solution is not sufficient for DOHH inhibition. The latter triggers apoptosis in HIV-infected, but not in HPV-infected or normal cells. Deferiprone is a clinical trial candidate for a novel treatment strategy:  Cycled, high-dose pulse therapy to achieve selective ablation of infected cells, bypassing all currently pursued and mutation-prone viral targets.

Keywords: Rational drug development; Eukaryotic initiation factor 5A; Hypusine