Targeting orexin receptors: Recent advances in the development of subtype selective or dual ligands for the treatment of neuropsychiatric disorders

Orexin-A and orexin-B, also named hypocretin-1 and hypocretin-2, are two hypothalamic neuropeptides highly conserved across mammalian species. Their effects are mediated by two distinct G protein-coupled receptors, namely orexin receptor type 1 (OX1-R) and type 2 (OX2-R), which share 64% amino acid identity. Given the wide expression of OX-Rs in different central nervous system and peripheral areas and the several pathophysiological functions in which they are involved, including sleep-wake cycle regulation (mainly mediated by OX2-R), emotion, panic-like behaviors, anxiety/stress, food intake, and energy homeostasis (mainly mediated by OX1-R), both subtypes represent targets of interest for many structure-activity relationship (SAR) campaigns carried out by pharmaceutical companies and academies. However, before 2017 the research was predominantly directed towards dual-orexin ligands, and limited chemotypes were investigated. Analytical characterizations, including resolved structures for both OX1-R and OX2-R in complex with agonists and antagonists, have improved the understanding of the molecular basis of receptor recognition and are assets for medicinal chemists in the design of subtype-selective ligands. This review is focused on the medicinal chemistry aspects of small molecules acting as dual or subtype selective OX1-R/OX2-R agonists and antagonists belonging to different chemotypes and developed in the last years, including radiolabeled OX-R ligands for molecular imaging. Moreover, the pharmacological effects of the most studied ligands in different neuropsychiatric diseases, such as sleep, mood, substance use, and eating disorders, as well as pain, have been discussed. Poly-pharmacology applications and multitarget ligands have also been considered.

Lead Drug Discover Strategies from Natural Medicines Based on Network Pharmacology

The need for therapeutics to overcome development of existing diseases research to discover new lead agents. In the face of public health challenges worldwide, natural medicines play a pivotal role in innovative lead drug discovery. Network pharmacology can easily construct complicated poly-pharmacology network based on lead compound, biological function, and bioactive target proteins, which meets the overall feature of natural medicines, and enable to elucidate the action mechanism at molecule-protein level with systematic view. In this work, we first summarized the recent progress delineating lead drug development and its interaction with natural medicines. Second, we focused on the relationship between natural medicines and network pharmacology. Additionally, we discussed current issues and potential prospects for the lead drug discover from natural medicines by network pharmacology. Further investigations should be focus on relevant structural analysis for biological experiment, also the dynamic and quantitative network development. In summary, it is a rational approach for innovative lead drug discovery, and with the development of structure and biology research, this approach makes it a very powerful method for the lead molecules in a high-throughput manner from a comprehensive and powerful special multi-compound to target protein/disease poly pharmacology network.

First-in-Human Study of AT13148, a Dual ROCK-AKT Inhibitor in Patients with Solid Tumors

PURPOSE

AT13148 is an oral AGC kinase inhibitor, which potently inhibits ROCK and AKT kinases. In preclinical models, AT13148 has been shown to have antimetastatic and antiproliferative activity.

PATIENTS AND METHODS

The trial followed a rolling six design during dose escalation. An intrapatient dose escalation arm to evaluate tolerability and a biopsy cohort to study pharmacodynamic effects were later added. AT13148 was administered orally three days a week (Mon-Wed-Fri) in 28-day cycles. Pharmacokinetic profiles were assessed using mass spectrometry and pharmacodynamic studies included quantifying p-GSK3β levels in platelet-rich plasma (PRP) and p-cofilin and p-MLC2 levels in tumor biopsies.

RESULTS

Fifty-one patients were treated on study. The safety of 5-300 mg of AT13148 was studied. Further, the doses of 120-180-240 mg were studied in an intrapatient dose escalation cohort. The dose-limiting toxicities included hypotension (300 mg), pneumonitis, and elevated liver enzymes (240 mg), and skin rash (180 mg). The most common side effects were fatigue, nausea, headaches, and hypotension. On the basis of tolerability, 180 mg was considered the maximally tolerated dose. At 180 mg, mean C max and AUC were 400 nmol/L and 13,000 nmol/L/hour, respectively. At 180 mg, ≥50% reduction of p-cofilin was observed in 3 of 8 posttreatment biopsies.

CONCLUSIONS

AT13148 was the first dual potent ROCK-AKT inhibitor to be investigated for the treatment of solid tumors. The narrow therapeutic index and the pharmacokinetic profile led to recommend not developing this compound further. There are significant lessons learned in designing and testing agents that simultaneously inhibit multiple kinases including AGC kinases in cancer.

The inadequacy of the reductionist approach in discovering new therapeutic agents against complex diseases

For more than 20 years, drug discovery has relied on two assumptions, i.e. (i) a therapeutic response can be triggered by modulating the activity of a single gene product, and (ii) a compound uncovered by its activity on a recombinant protein in vitro can perform its activity in vivo. Drug discovery operates accordingly by using the concepts of targets and pipelines. The target, such as a gene product, is the intended point of therapeutic intervention, and compounds that modulate its activity in vitro follow a series of downstream developments. This reductionist approach has developed due to advances in combinatorial chemistry, robotics, molecular biology, and genomics. The expectation of this approach is that the frequency of drug discovery will dramatically increase, while its associated cost would decrease. However, the frequency of new drug discovery has decreased, while the associated costs have surged. We performed a retrospective study that examined how successful development programs have led to marketed drugs for all indications except anti-infective and anti-neoplastic agents. We concluded that the target and pipeline paradigms are limited and are actually causing the drug development industry to collectively fail to meet the critical medical needs. Impact statement The initial scope of this investigation was to build the set of human genes that are presumed to be the therapeutic intervention points of US FDA-approved drugs, in all therapeutics areas but oncology. The prerequisite for this study was the establishment of the non-redundant set of all active pharmaceutical ingredients for these disease areas. Pertaining to complex diseases, the main observation was that there is not a single instance in the history of drug discovery, where a compound, initially selected by means of a biochemical assay, achieved a significant therapeutic response. The whole field of Drug R&D faces an unacceptable lack of new treatments to address unmet medical needs. The conclusion is that complex biological assays have to be designed for the primary selection of candidate therapeutics.

Fragment-Based Whole Cell Screen Delivers Hits against M. tuberculosis and Non-tuberculous Mycobacteria

Reactive multi-target 'fragment drugs' represent critical components of current tuberculosis regimens. These compounds, such as pyrazinamide, are old synthetic antimycobacterials that are activated inside Mycobacterium tuberculosis bacilli and are smaller than the usual drug-like, single-target molecules. Based on the success of small 'dirty' drugs in the chemotherapy of tuberculosis, we suggested previously that fragment-based whole cell screens should be introduced in our current antimycobacterial drug discovery efforts. Here, we carried out such a screen and characterized bactericidal activity, selectivity and spectrum of hits we obtained. A library of 1725 fragments was tested at a single concentration for growth inhibitory activity against M. bovis BCG as screening strain and 38 of 116 primary hits were confirmed in dose response analyses to be active against virulent M. tuberculosis. Bacterial kill experiments showed that most hits displayed bactericidal activity at their minimal inhibitory concentration. Cytotoxicity assays established that a large proportion of hits displayed a favorable selectivity index for mammalian cells. Importantly, one third of M. tuberculosis active fragments were also active against M. abscessus and M. avium, two emerging non-tuberculous mycobacterial (NTM) pathogens, opening the opportunity to develop broad spectrum antimycobacterials. Activity determination against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa) bacteria, as well as fungi (Candida albicans, Cryptococcus neoformans) showed only a small overlap indicating a generally narrow spectrum of these novel antimicrobial hits for mycobacteria. In conclusion, we carried out the first fragment-based whole cell screen against bacteria and identified a substantial number of hits with excellent physicochemical properties and dual activity against M. tuberculosis and NTM pathogens. These hits will now be evaluated in animal models of mycobacterial infection to determine whether any of them can be moved forward as a new antimycobacterial fragment drug candidate.