The Trypanocidal Drug Suramin and Other Trypan Blue Mimetics Are Inhibitors of Pyruvate Kinases and Bind to the Adenosine Site

Abstract

Therapies against trypanosomatid-borne diseases have evolved from the historic work of Paul Ehrlich (1), who was the first to provide a rationale for a chemotherapeutic approach in the treatment of infectious diseases. He used a series of naphthalene dyes related to trypan red and trypan blue (see Fig. 1a) and demonstrated that they had trypanocidal activity. Trypan blue successfully cleared trypanosomatid infections in mouse models but were not successful in other mammals. Ehrlich noted in his mouse trials where he tested over 50 related diazo dyes that mice treated with trypan red retained a red color for weeks and even months. This side effect was a significant drawback to its use in human therapy, and the search for a colorless analog was pursued by chemists at Bayer, who synthesized Bayer 205, now known as suramin (see Fig. 1c), which is still used in the treatment of human African trypanosomiasis (sleeping sickness) caused by the parasitic protist Trypanosoma brucei (2). Additional uses for suramin have been explored in the treatment of human cancers (3) and HIV infection (4), where it was the first drug to show antiviral activity (5). It is evident from the mass of literature that suramin is a promiscuous inhibitor of many enzymes and receptors and shows a range of interesting clinically relevant effects (6, 7). Despite following none of the currently accepted criteria for drug-likeness (8), suramin and a number of diverse analogues (9, 10) are still of clinical interest in an ever growing repertoire of diseases (11-13).Suramin has been characterized as an inhibitor of T. brucei and mammalian glycolytic enzymes (14 -16) and has been shown to inhibit all seven of the T. brucei glycolytic enzymes isolated from glycosomes (peroxisome-like organelles specific for kinetoplastid protists that harbor the first seven glycolytic enzymes converting glucose into 3-phosphoglycerate) with IC 50 values between 3 and 100 M (15). The three glycolytic enzymes found in the cytosol (phosphoglycerate mutase, enolase, and pyruvate kinase (PYK) 2 (17)) were not examined in these experiments. The importance of glycolytic enzymes for the viability of T. brucei has been confirmed by RNAi knockdown of glycosomal and cytosolic enzymes (including PYK) with consequent death of the parasite (18,19

Conformational Dynamics and Allostery in Pyruvate Kinase

“…This strongly suggests that it may play an important part in the transition between inactive and active state populations. This result is inconsistent with the L. mexicana and T. cruzi pyruvate kinase crystal structures (10,47), which show a rigid body rocking of the A/C-core domains, and temperature factor analysis of these structures does not suggest that fructose 1,6-bisphosphate binding affects the mobility of the A/C interdomain interface. Our result is, however, consistent with the model put forward by Mattevi et al (8), who reasoned that the A/C-domains were altered based on the nonallosteric rabbit M1 structure.…”

Small-Molecule Modulators of Methyl-Lysine Binding for the CBX7 Chromodomain

“…Given that suramin interacts with different proteins, including thrombin and pyruvate kinase (Lima et al, 2009; Morgan et al, 2011), we focused our study of small molecule modulation of CBX7ChD activity in transcriptional repression with MS37452. Prior research showed that mutation or deletion of CBX7ChD results in a decrease in binding of CBX7 to the INK4A/ARF (CDKN2A) locus at multiple sites (Figure 4A) (Bracken et al, 2007).…”

Exploiting the Achilles’ heel of membrane trafficking in trypanosomes

“…[32, 33, 34]). Although suramin inhibits all seven trypanosome glycolytic enzymes plus cytosolic pyruvate kinase (PYK) in the micromolar range [35], it inhibits bloodstream stage trypanosome proliferation at nanomolar concentrations [26 •• ], making it unlikely that glycolysis represents the primary target. However, endocytosis may accumulate the drug to higher intracellular levels than the external concentration; importantly the highly charged suramin molecule, once internalized, cannot easily escape from the cell.…”