Open Lab as a source of hits and leads against tuberculosis, malaria and kinetoplastid diseases

The repurposing of Tebipenem pivoxil as alternative therapy for severe gastrointestinal infections caused by extensively drug resistant Shigella spp

Background:

Diarrhoea remains one of the leading causes of childhood mortality globally. Recent epidemiological studies conducted in low-middle income countries (LMICs) identified Shigella spp. as the first and second most predominant agent of dysentery and moderate diarrhoea, respectively. Antimicrobial therapy is often necessary for Shigella infections; however, we are reaching a crisis point with efficacious antimicrobials. The rapid emergence of resistance against existing antimicrobials in Shigella spp. poses a serious global health problem.

Methods:

Aiming to identify alternative antimicrobial chemicals with activity against antimicrobial resistant Shigella, we initiated a collaborative academia-industry drug discovery project, applying high-throughput phenotypic screening across broad chemical diversity and followed a lead compound through in vitro and in vivo characterisation.

Results:

We identified several known antimicrobial compound classes with antibacterial activity against Shigella. These compounds included the oral carbapenem Tebipenem, which was found to be highly potent against broadly susceptible Shigella and contemporary MDR variants for which we perform detailed pre-clinical testing. Additional in vitro screening demonstrated that Tebipenem had activity against a wide range of other non-Shigella enteric bacteria. Cognisant of the risk for the development of resistance against monotherapy, we identified synergistic behaviour of two different drug combinations incorporating Tebipenem. We found the orally bioavailable prodrug (Tebipenem pivoxil) had ideal pharmacokinetic properties for treating enteric pathogens and was effective in clearing the gut of infecting organisms when administered to Shigella-infected mice and gnotobiotic piglets.

Conclusions:

Our data highlight the emerging antimicrobial resistance crisis and shows that Tebipenem pivoxil (licenced for paediatric respiratory tract infections in Japan) should be accelerated into human trials and could be repurposed as an effective treatment for severe diarrhoea caused by MDR Shigella and other enteric pathogens in LMICs.

Funding:

Tres Cantos Open Lab Foundation (projects TC239 and TC246), the Bill and Melinda Gates Foundation (grant OPP1172483) and Wellcome (215515/Z/19/Z).

New Drugs for Human African Trypanosomiasis: A Twenty First Century Success Story

The twentieth century ended with human African trypanosomiasis (HAT) epidemics raging across many parts of Africa. Resistance to existing drugs was emerging, and many programs aiming to contain the disease had ground to a halt, given previous success against HAT and the competing priorities associated with other medical crises ravaging the continent. A series of dedicated interventions and the introduction of innovative routes to develop drugs, involving Product Development Partnerships, has led to a dramatic turnaround in the fight against HAT caused by Trypanosoma brucei gambiense. The World Health Organization have been able to optimize the use of existing tools to monitor and intervene in the disease. A promising new oral medication for stage 1 HAT, pafuramidine maleate, ultimately failed due to unforeseen toxicity issues. However, the clinical trials for this compound demonstrated the possibility of conducting such trials in the resource-poor settings of rural Africa. The Drugs for Neglected Disease initiative (DNDi), founded in 2003, has developed the first all oral therapy for both stage 1 and stage 2 HAT in fexinidazole. DNDi has also brought forward another oral therapy, acoziborole, potentially capable of curing both stage 1 and stage 2 disease in a single dosing. In this review article, we describe the remarkable successes in combating HAT through the twenty first century, bringing the prospect of the elimination of this disease into sight.

Evaluation of Novel Chalcone-Thiosemicarbazones Derivatives as Potential Anti-Leishmania amazonensis Agents and Its HSA Binding Studies

A series of seven chalcone-thiosemicarbazones (5a-5g) were synthesized and evaluated as potential new drugs (anti-leishmanial effect). Although four of the chalcone-thiosemicarbazones are already known, none of them or any compound in this class has been previously investigated for their effects on parasites of the Leishmania genus. The compounds were prepared in satisfactory yields (40-75%) and these compounds were evaluated against promastigotes, axenic amastigotes and intracellular amastigotes of L. amazonensis after 48 h of culture. The half maximal inhibitory concentration (IC₅₀) values of the intracellular amastigotes were determined to be in the range of 3.40 to 5.95 µM for all compounds assayed. The selectivity index showed value of 15.05 for 5a, whereas pentamidine (reference drug) was more toxic in our model (SI = 2.32). Furthermore, to understand the preliminary relationship between the anti-leishmanial activity of the chalcone-thiosemicarbazones, their electronic (σ), steric (MR) and lipophilicity (π) properties were correlated, and the results indicated that moieties with electronic withdrawing effects increase the anti-leishmanial activity. The preliminary pharmacokinetic evaluation of one of the most active compound (5e) was studied via interaction to human serum albumin (HSA) using multiple spectroscopic techniques combined with molecular docking. The results of antiparasitic effects against L. amazonensis revealed the chalcone-thiosemicarbazone class to be novel prototypes for drug development against leishmaniasis.

Novel chemical starting points for drug discovery in leishmaniasis and Chagas disease

Visceral leishmaniasis (VL) and Chagas disease (CD) are caused by kinetoplastid parasites that affect millions of people worldwide and impart a heavy burden against human health. Due to the partial efficacy and toxicity-related limitations of the existing treatments, there is an urgent need to develop novel therapies with superior efficacy and safety profiles to successfully treat these diseases. Herein we report the application of whole-cell phenotypic assays to screen a set of 150,000 compounds against Leishmania donovani, a causative agent of VL, and Trypanosoma cruzi, the causative agent of CD, with the objective of finding new starting points to develop novel drugs to effectively treat and control these diseases. The screening campaign, conducted with the purpose of global open access, identified twelve novel chemotypes with low to sub-micromolar activity against T. cruzi and/or L. donovani. We disclose these hit structures and associated activity with the goal to contribute to the drug discovery community by providing unique chemical tools to probe kinetoplastid biology and as hit-to-lead candidates for drug discovery.

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An open source drug discovery screen between The Tres Cantos Open Lab Foundation and Calibr at Scripps Research.

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High-throughput phenotypic screen of a 150,000-compound library against T. cruzi and L. donovani.

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Identification and characterization of 12 novel chemical series.

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7 of those 12 chemical series are active against both T. cruzi and L. donovani.

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These chemical series may be valuable tools to identify new drug targets.

Collaborative drug discovery and the Tres Cantos Antimalarial Set (TCAMS)

Malaria affects a population of over 200 million people worldwide. New drugs are needed because of widespread resistance, and the hunt for such drugs involves a coordinated research effort from the scientific community. The release of the Tres Cantos Antimalarial Set (TCAMS) in 2010 represented a landmark in the field of collaborative drug discovery for malaria. This set of >13 000 molecules with confirmed activity against several strains of Plasmodium falciparum was publicly released with the goal of fostering additional research beyond the GlaxoSmithKline (GSK) network of collaborators. Here, we examine the outcomes realized from TCAMS over the past 8 years and whether the expectations surrounding this initiative have become a reality.

Innovation in neglected tropical disease drug discovery and development

BACKGROUND

Neglected tropical diseases (NTDs) are closely related to poverty and affect over a billion people in developing countries. The unmet treatment needs cause high mortality and disability thereby imposing a huge burden with severe social and economic consequences. Although coordinated by the World Health Organization, various philanthropic organizations, national governments and the pharmaceutical industry have been making efforts in improving the situation, the control of NTDs is still inadequate and extremely difficult today. The lack of safe, effective and affordable medicines is a key contributing factor. This paper reviews the recent advances and some of the challenges that we are facing in the fight against NTDs.

MAIN BODY

In recent years, a number of innovations have demonstrated propensity to promote drug discovery and development for NTDs. Implementation of multilateral collaborations leads to continued efforts and plays a crucial role in drug discovery. Proactive approaches and advanced technologies are urgently needed in drug innovation for NTDs. However, the control and elimination of NTDs remain a formidable task as it requires persistent international cooperation to make sustainable progresses for a long period of time. Some currently employed strategies were proposed and verified to be successful, which involve both mechanisms of 'Push' which aims at cutting the cost of research and development for industry and 'Pull' which aims at increasing market attractiveness. Coupled to this effort should be the exercise of shared responsibility globally to reduce risks, overcome obstacles and maximize benefits. Since NTDs are closely associated with poverty, it is absolutely essential that the stakeholders take concerted and long-term measures to meet multifaceted challenges by alleviating extreme poverty, strengthening social intervention, adapting climate changes, providing effective monitoring and ensuring timely delivery.

CONCLUSIONS

The ongoing endeavor at the global scale will ultimately benefit the patients, the countries they are living and, hopefully, the manufacturers who provide new preventive, diagnostic and therapeutic products.

Repurposing clinically approved cephalosporins for tuberculosis therapy

While modern cephalosporins developed for broad spectrum antibacterial activities have never been pursued for tuberculosis (TB) therapy, we identified first generation cephalosporins having clinically relevant inhibitory concentrations, both alone and in synergistic drug combinations. Common chemical patterns required for activity against Mycobacterium tuberculosis were identified using structure-activity relationships (SAR) studies. Numerous cephalosporins were synergistic with rifampicin, the cornerstone drug for TB therapy, and ethambutol, a first-line anti-TB drug. Synergy was observed even under intracellular growth conditions where beta-lactams typically have limited activities. Cephalosporins and rifampicin were 4- to 64-fold more active in combination than either drug alone; however, limited synergy was observed with rifapentine or rifabutin. Clavulanate was a key synergistic partner in triple combinations. Cephalosporins (and other beta-lactams) together with clavulanate rescued the activity of rifampicin against a rifampicin resistant strain. Synergy was not due exclusively to increased rifampicin accumulation within the mycobacterial cells. Cephalosporins were also synergistic with new anti-TB drugs such as bedaquiline and delamanid. Studies will be needed to validate their in vivo activities. However, the fact that cephalosporins are orally bioavailable with good safety profiles, together with their anti-mycobacterial activities reported here, suggest that they could be repurposed within new combinatorial TB therapies.

A new 'golden age' for the antitubercular target InhA

The increasing prevalence of multidrug-resistant strains of Mycobacterium tuberculosis is the main contributing factor in unfavorable outcomes in the treatment of tuberculosis. Studies suggest that direct inhibitors of InhA, an enoyl-ACP-reductase, might yield promising clinical candidates that can be developed into new antitubercular drugs. In this review, we describe the application of different hit-identification strategies to InhA, which clearly illustrate the druggability of its active site through distinct binding mechanisms. We further characterize four classes of InhA inhibitors that show novel binding modes, and provide evidence of their successful target engagement as well as their in vivo activity.