Hit-to-Lead Development of Hits Identified in the Phenotypic Screening against Mycobacterium tuberculosis (Mtb)
Project Completed
Please click to see the final report.
  • RFP Year
  • Awarded Amount
  • Disease
  • Intervention
  • Development Stage
    Lead Identification
  • Collaboration Partners
    Astellas Pharma Inc. ,  The Global Alliance for TB Drug Development
  • Past Project

Introduction and Background of the Project


The Hit-to-Lead collaboration between Astellas and TB Alliance is a continuation of an earlier screening project between the two organizations. The screening project, which involved screening Astella’s selected compound library, yielded promising hits resulting in the selection of series for further evaluation. This project extends the collaboration between Astellas, TB Alliance, and GHIT to develop a hit-to-lead phase for identifying potential candidates for the subsequent lead optimization phase.


Project objective

Astellas in collaboration with TB Alliance have identified two chemical series in our screen of the 20,000-compound library offered by Astellas.  We intend to develop them in a hit-to-lead phase by preparing a set of analogues for each to finetune their structure-activity relationships (SAR) and to acquire data on their pharmacokinetic (PK) properties and safety profiles. Consolidating the cumulative data, we aim to identify candidate compounds, ideally from both series, to test in a mouse acute infection model of TB. If successful, this project will provide a candidate for the lead optimization (LO) phase. 


Project design

New analogues in the two series will be synthesized and tested for the in vitro activity against Mtb and any promising analogues will be evaluated for PK and toxicity. Analogues selected after the PK and toxicity studies will be scaled up to test them in a mouse acute infection model.

How can your partnership (project) address global health challenges?

Tuberculosis (TB) is a global disease, found in every country in the world. It is the leading infectious cause of death worldwide. The World Health Organization estimates that 1.8 billion people—close to one quarter of the world's population—are infected with Mycobacterium tuberculosis (Mtb), the bacteria that causes TB. Last year, 10 million fell ill from TB and 1.4 million died. TB is an airborne disease that can be spread by coughing or sneezing and is the leading cause of infectious disease worldwide. It is responsible for economic devastation and the cycle of poverty and illness that entraps families, communities and even entire countries. Among the most vulnerable are women, children, and those with HIV/AIDS. There is growing resistance to available drugs, which means the disease is becoming more deadly and difficult to treat. There were more than half a million cases of drug resistant TB last year.

New TB drug candidates are urgently needed to treat patients around the world and eliminate the global TB pandemic. Our project aims to identify novel compounds, which show promise and can be further developed as effective TB drugs.

What sort of innovation are you bringing in your project?

The two series on hand appear to be unique in their structures compared with any TB drugs in use or under development. They also appear not to share the mechanism of action with any of the standard TB drugs, which is important for the prospect of discovering new drugs active against drug-resistant strains of Mtb.  We will investigate the mechanism of action of the two series potentially to identify new targets for drug discovery. 

Role and Responsibility of Each Partner

TB Alliance will coordinate synthesis of analogues, testing against Mtb, and generating ADMET data while Astellas will contribute to the design of new analogues and interpretation of the data.

Decisions on the direction of the project will be made jointly between TB Alliance and Astellas.

Final Report

1. Project objective

Two separate chemical series (A and B) were identified as hits in a phenotypic screening of a compound library provided by Astellas Pharma Inc., and their development in a hit-to-lead phase was started on April 1, 2021.  The main object was to select one series to focus on after a reasonable amount of time.  The main challenge in series A was to separate its anti-Mycobacterium tuberculosis (Mtb) activity from its original therapeutic target while the main challenge in series B was to broaden its structure-activity relationship.


2. Project design

Analogues of the two series were synthesized at a CRO and the resulting analogues were tested for activity against Mtb.  Selected analogues in series A were tested for activity in the original non-Mtb target.  Representative analogues were submitted for mechanism of action studies.  Yet other selected analogues were tested for in vitro ADME and mouse PK to select analogues for in vivo proof of concept.


3. Results, lessons learned

Approximately 100 analogues in each series were prepared.  It turned out it was relatively straightforward to separate the anti-Mtb activity from the original therapeutic objectives of series A.  For series B the structure-activity relationships were not very clear, and it was difficult to increase the potency of new analogues.  Therefore, we decided to focus on series A.  Some of the analogues in series A appeared to have reasonable in vitro potency against Mtb and appeared to possess reasonable PK properties.  We tested two analogues in mice for in vivo proof of concept, but it could not be demonstrated under the conditions we tried.  Its mechanism of action was most likely a well-known target and this was shown by whole genome sequencing of the new strains generated by exposing the wild-type strain of Mtb to a representative compound of series A.

Based on the above results, it was concluded that the target of the series A derivatives are likely to be a target with many previous studies and development of lead compounds, so lack of attraction to pursue optimization research from this point forward. Furthermore, considering that in vivo efficacy of the lead candidate compound could not be confirmed in mice model for proof of concept (POC) confirmation, this study has been deemed appropriate to terminate at current research stage.