Combating drug resistance in Chronic Myeloid Leukemia and HIV-1 infection. An academic consortium for the preclinic development of drugs

SEBASTIÁN KLINKE; POORNIMA PRISHADARSHINI; ZHENGGANG HAN; TIM BRUEMMENDORF; STEFAN BALABANOV; JAN VAN LUNZEN; MATTHIAS RAREY; CHRIS MEIER; JOACHIM HAUBER; ROLF HILGENFELD

Luebeck

Simposio; ICAV-9 Symposium; 2010

International Consortium on Anti-Virals (ICAV)

Resistance to drugs is a major problem on several therapeutic approaches. For example, patients suffering from Chronic Myeloid Leukemia (CML) develop resistance against Imatinib at late stages of the disease, as HIV-1 infected people do under Highly Active Antiretroviral Therapy (HAART). For this reason, the development of new therapeutic strategies that circumvent this drawback is of great medical importance. The project we present here targets a series of human proteins giving rise to a key advantage in comparison to classical antiviral treatments, in that drug resistance is unlikely to develop since the target are host proteins. Hypusine is a basic amino acid that occurs in a single protein, the so-called eukaryotic translation initiation factor 5A (eIF-5A)1. It is formed by two consecutive posttranslational reactions on a particular lysine residue, which are catalyzed by deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH). The first step involves the incorporation of a butylamino moiety coming from the substrate spermidine, whereas the second step corresponds to a hydroxylation of the intermediate deoxyhypusine residue. Hypusine-containing eIF-5A is essential for eukaryotic cell proliferation. It is known that this protein is involved in the Rev-mediated mRNA nuclear export in HIV-1 infection, and that it is down-regulated in CML. Targeting this unique posttranslational modification by inhibition of either the DHS or DOHH catalytic activities corresponds to a new treatment strategy for these two diseases, due to the fact that targeting host proteins lowers the chance of observing resistance, as mentioned before. To date, the Phase-II drug CNI-1493 (a tetraguanylhydrazone also known as semapimod) has been shown to be a potent inhibitor of the human DHS. The project focuses on a comprehensive study of CNI-1493 in the treatment of CML and HIV-1, as well as on the development of novel DHS and DOHH inhibitors based on bioinformatic analysis. The latter compounds are synthesized and subjected to clinical and inhibitory trials to test their efficiencies. Additionally, the project focuses on the structural basis of the inhibitory activity of CNI-1493 on DHS. In this sense, we have recently determined the crystal structure of DHS in complex with CNI-1493 at 1.85 Å resolution. Interestingly, the ligand binds to the outer surface of the enzyme in a shallow cavity that does not correspond to its described active site, but that is located next to the entry of the binding pocket of spermidine. This observation might indicate that CNI-1493 blocks the entrance of eIF-5A to the active site of DHS. To corroborate this theory, point mutants on some critical DHS residues were prepared to study their influence on deoxyhypusine formation and drug binding. The present crystal structure will also be used as a starting point for the development of more potent DHS inhibitors.