A novel drug discovery concept for tuberculosis: inhibition of bacterial and host cell signalling.
The Mycobacterium tuberculosis genome encodes for eleven eukaryotic-like Ser/Thr protein kinases. At least three of these (PknA, PknB and PknG) are essential for bacterial growth and survival. PknG is secreted by pathogenic mycobacteria, in macrophages to intervene with host cell signalling pathways and to block the fusion of the lysosomes with the phagosome by a still unknown mechanism. Based on our previously published results, we have initiated a drug discovery program, aiming to improve the potency against PknG and the physiochemical properties of the initially identified hit compound, AX20017, from the class of the tetrahydrobenzothiophenes. We have established a radioactive biochemical PknG kinase assay to test the novel analogues around AX20017. We have developed lead molecules with IC50 values in nanomolar range, and demonstrated their antituberculotic effects on human macrophages. Selected leads might ultimately serve the purpose of inducing phagosomal-lysosomal fusion and therefore destroy the residence of the intracellular mycobacteria. It is unclear at this time if these "homeless" mycobacteria are getting killed by the host, but they will be at least vulnerable to the activity of antimycobacterial agents. Released mycobacteria rely on the essential function of PknB for survival, which is our second molecular kinase target. PknB is a transmembrane protein, responsible for the cell growth and morphology. We have screened our library and synthesized novel compounds for the inhibition of PknB. A pharmacophore model was built and 70,000 molecules from our synthesizable virtual library have been screened to identify novel inhibitor scaffolds for the generation of templated compound libraries. Currently, we are using a radioactive kinase assay employing GarA as the putative, physiological substrate of PknB kinase. We have identified hits and generated optimised hit compounds with IC50 values for the inhibition of PknB in the nanomolar range. Yet those promising hits are not potent enough to yield meaningful "minimum inhibitory concentrations" in mycobacterial growth assays. In the course of our future work, we will increase the potency of the next generation of PknB inhibitors in order to improve their antibacterial activity.
Székely
Rita
R
Vichem Chemie Research Ltd., Herman Ottó. 15, H-1022 Budapest, Hungary. rszekely@vichem.hu
Wáczek
Frigyes
F
Szabadkai
István
I
Németh
Gábor
G
Hegymegi-Barakonyi
Bálint
B
Eros
Dániel
D
Szokol
Bálint
B
Pató
János
J
Hafenbradl
Doris
D
Satchell
Jacqueline
J
Saint-Joanis
Brigitte
B
Cole
Stewart T
ST
Orfi
László
L
Klebl
Bert M
BM
Kéri
György
G
D000577:Amides / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D002478:Cells, Cultured; D015195:Drug Design; D020128:Inhibitory Concentration 50; D008264:Macrophages / Q000187:drug effects; D051379:Mice; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013329:Structure-Activity Relationship; D013876:Thiophenes / Q000737:chemistry / Q000494:pharmacology; D014376:Tuberculosis / Q000188:drug therapy* / Q000201:enzymology / Q000382:microbiology*
C487783:AX 20017; D000577:Amides; D001426:Bacterial Proteins; D047428:Protein Kinase Inhibitors; D013876:Thiophenes; C475060:PknB protein, Mycobacterium tuberculosis; D017346:Protein Serine-Threonine Kinases