The program also includes novel antibacterial agents against drug-resistant tuberculosis, MRSA, VRE and other pathogens. Despite extensive research in the last 40 years, the drugs used to treat these infections are still limited to rather classical antibacterial drugs that target cell wall biosynthesis, nucleic acid synthesis, protein synthesis, etc. Furthermore, the widespread misuse of drugs and poor patient compliance have allowed bacteria to become resistant to drugs by means of their adaptive genetic machinery, leading to multi-drug resistant (MDR) strains of bacteria. Widespread bacterial resistance to existing therapeutics for bacterial infections mentioned above has been a key hurdle for the complete treatment. Therefore, in order to counter attack the adaptive genetic machinery of bacteria, there is a dire need for the identification of novel therapeutic targets. In this context, filamentous temperature sensitive protein Z (FtsZ), an essential bacterial cytokinesis protein, is a highly promising therapeutic target since the disruption of cell division would lead to the inhibition/arrest of bacterial infection. The Ojima Laboratory has discovered novel taxanes and benzimidazoles exhibit high potency against drug-sensitive and drug-resistant tuberculosis through efficient inhibition of FtsZ polymerization, which is crucial for bacterial cell division. The drug discovery efforts have been supported by design and synthesis of novel libraries of compounds and moderately high throughput (HTP) screening as well as rational optimization of the hit compounds.
In order to counter attack the adaptive genetic machinery of bacteria, there is a dire need for the identification of novel therapeutic targets. In this context, FtsZ, an essential, most abundant and highly conserved bacterial cytokinesis protein, holds great potential as a novel therapeutic target. Inhibition of FtsZ assembly interferes with the formation and functioning of the Z-ring leading to the absence of septation, contributing to arrested bacterial growth. Therefore, we hypothesize that FtsZ-inhibitors can be developed into broad-spectrum antibacterial agents possessing novel mechanism of action.
Known Tubulin Inhibitors Provide a Good Starting Point
As FtsZ and tubulin have extensive structural and functional homology, a library of tubulin targeting taxanes, designed in our lab was screened to identify compounds which specifically target FtsZ. Several taxanes were found to exhibit MIC values of 1.25 - 2.5 uM with limited cytotoxicity. Optimization is currently in progress.
Novel Benzimidazoles Targeting FtsZ
Based on the similarity of the benzimidazole moiety to the pyridopyrazine and pteridine pharamacophores identified by White, Reynolds and others as FtsZ inhibitors, we hypothesized that the benzimidazole framework might be a promising starting point for the development of novel FtsZ inhibitors.
As FtsZ is highly conserved in a range of bacterial strains, we screened our benzimidazole library against other bacterial strans such as F. tularensis, Y. pestis, B. thailandensis etc. as well and identified several lead compounds with MIC values in the range of 1 - 5 ug / mL.
Kumar, Kunal; Awasthi, Divya; Lee, Seung-Yub; Zanardi, Ilaria; Ruzsicska, Bela; Knudson, Susan; Tonge, Peter J; Slayden, Richard A,; Ojima, Iwao. Novel trisubstituted benzimidazoles, targeting Mtb FtsZ, as a new class of antitubercular agents. J. Med. Chem., 2010, 54, 374-381
- Several lead benzimidazoles inhibited FtsZ polymerizaiton in a dose dependent manner.
- These compounds enhanced the GTPase activity by 3 - 4 folds.
- Scanning electron microscopy (SEM) images of Mtb cells treated with SB-P3G2 showed an absence of septum formation and slight cell elongation, indicative of FtsZ assembly inhibition.
- The drastic reduction in the mass of FtsZ polymer and bundling of FtsZ protofilaments was observed by transmission electrong microscopy (TEM) analysis of Mtb FtsZ treated with SB-P3G2.
On-going Research Efforts
- Extensive optimization of taxane-based and benzimidazole-based leads and screening of these libraries against other bacterial strains of interest.
- Focus on understanding the binding site of lead compounds:
- Photoaffinity labeling of FtsZ
- Co-crystallization of FtsZ with lead compounds
- In-silico docking
- ADMET and SAR study of lead compounds
- In-vivo assays to evaluate the metabolic and plasma stability of lead compounds