The second generation mixed lineage kinase-3 (MLK3) inhibitor CLFB-1134 protects against neurotoxin-induced nigral dopaminergic neuron loss

Design, synthesis of new 3H-imidazo[4,5-b]pyridine derivatives and evaluation of their inhibitory properties as mixed lineage kinase 3 inhibitors

Mixed-lineage protein kinase 3 (MLK3) is implicated in several human cancers and neurodegenerative diseases. A series of 3H-imidazo[4,5-b]pyridine derivatives were designed, synthesized and evaluated as novel MLK3 inhibitors. A homology model of MLK3 was developed and all designed compounds were docked to assess their binding pattern and affinity toward the MLK3 active site. Based on this knowledge, we synthesized and experimentally evaluated the designed compounds. Majority of the compounds showed significant inhibition of MLK3 in the enzymatic assay. In particular, compounds 9a, 9e, 9j, 9 k, 12b and 12d exhibited IC50 values of 6, 6, 8, 11, 14 and 14 nM, respectively. Furthermore, compounds 9a, 9e, 9 k and 12b exhibited favorable physicochemical properties among these compounds.

The emerging role of mixed lineage kinase 3 (MLK3) and its potential as a target for neurodegenerative diseases therapies

Selective and brain-permeable protein kinase inhibitors are in preclinical development for treating neurodegenerative diseases. Among them, MLK3 inhibitors, with a potent neuroprotective biological action have emerged as valuable agents for the treatment of pathologies such as Alzheimer's, Parkinson's disease and amyotrophic lateral sclerosis. In fact, one MLK3 inhibitor, CEP-1347, reached clinical trials for Parkinson's disease. Additionally, another compound called prostetin/12k, a potent and rather selective MLK3 inhibitor has started clinical development for ALS based on its motor neuron protection in both in vitro and in vivo models. In this review, we will focus on the role of MLK3 in neuron-related cell death processes, neurodegenerative diseases, and the potential advantages of targeting this kinase through pharmacological modulation for neuroprotective treatment.

Kinases control of regulated cell death revealing druggable targets for Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder in the world. Motor impairment seen in PD is associated with dopaminergic neurotoxicity in the striatum, and dopaminergic neuronal death in the substantia nigra pars compacta. Cell death has a significant effect on the development and progression of PD. Extensive research over the last few decades has unveiled new regulated cell death (RCD) mechanisms that are not dependent on apoptosis such as necroptosis, ferroptosis, and others. In this review, we will overview the mechanistic pathways of different types of RCD. Unlike accidental cell death, RCD subroutines can be regulated and the RCD-associated kinases are potential druggable targets. Hence, we will address an overview and analysis of different kinases regulating apoptosis such as receptor-interacting protein kinase 1 (RIPK-1), RIPK3, mixed lineage kinase (MLK), Ataxia telangiectasia muted (ATM), cyclin-dependent kinase (CDK), death-associated protein kinase 1 (DAPK1), Apoptosis-signaling kinase-1 (ASK-1), and Leucine-rich repeat kinase-2 (LRRK2). In addition to the role of RIPK1, RIPK3, and Mixed Lineage Kinase Domain like Pseudokinase (MLKL) in necroptosis. We also overview functions of AMP-kinase (AMPK), protein kinase C (PKC), RIPK3, and ATM in ferroptosis. We will recap the anti-apoptotic, anti-necroptotic, and anti-ferroptotic effects of different kinase inhibitors in different models of PD. Finally, we will discuss future challenges in the repositioning of kinase inhibitors in PD. In conclusion, this review kicks-start targeting RCD from a kinases perspective, opening novel therapeutic disease-modifying therapeutic avenues for PD.

TrkA expression directs the anti-neoplastic activity of MLK3 inhibitors in triple-negative breast cancer

Mixed Lineage Kinase 3 (MLK3) is a viable target for neoplastic diseases; however, it is unclear whether its activators or inhibitors can act as anti-neoplastic agents. We reported that the MLK3 kinase activity was higher in triple-negative (TNBC) than in hormone receptor-positive human breast tumors, where estrogen inhibited MLK3 kinase activity and provided a survival advantage to ER⁺ breast cancer cells. Herein, we show that in TNBC, the higher MLK3 kinase activity paradoxically promotes cancer cell survival. Knockdown of MLK3 or MLK3 inhibitors, CEP-1347 and URMC-099, attenuated tumorigenesis of TNBC cell line and Patient-Derived (PDX) xenografts. The MLK3 kinase inhibitors decreased both the expression and activation of MLK3, PAK1, and NF-kB protein and caused cell death in TNBC breast xenografts. RNA-seq analysis identified several genes downregulated by MLK3 inhibition, and the NGF/TrkA MAPK pathway was significantly enriched in tumors sensitive to growth inhibition by MLK3 inhibitors. The TNBC cell line unresponsive to kinase inhibitor had substantially lower TrkA, and overexpression of TrkA restored the sensitivity to MLK3 inhibition. These results suggest that the functions of MLK3 in breast cancer cells depend on downstream targets in TNBC tumors expressing TrkA, and MLK3 kinase inhibition may provide a novel targeted therapy.

The regulatory function of mixed lineage kinase 3 in tumor and host immunity

Protein kinases are the second most sought-after G-protein coupled receptors as drug targets because of their overexpression, mutations, and dysregulated catalytic activities in various pathological conditions. Till 2019, 48 protein kinase inhibitors have received FDA approval for the treatment of multiple illnesses, of which the majority of them are indicated for different malignancies. One of the attractive sub-group of protein kinases that has attracted attention for drug development is the family members of MAPKs that are recognized to play significant roles in different cancers. Several inhibitors have been developed against various MAPK members; however, none of them as monotherapy has shown sustainable efficacy. One of the MAPK members, called Mixed Lineage Kinase 3 (MLK3), has attracted considerable attention due to its role in inflammation and neurodegenerative diseases; however, its role in cancer is an emerging area that needs more investigation. Recent advances have shown that MLK3 plays a role in cancer cell survival, migration, drug resistance, cell death, and tumor immunity. This review describes how MLK3 regulates different MAPK pathways, cancer cell growth and survival, apoptosis, and host's immunity. We also discuss how MLK3 inhibitors can potentially be used along with immunotherapy for different malignancies.

Therapeutic innovation in Parkinson's disease: a 2020 update on disease-modifying approaches

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting more than 10 million patients worldwide. Despite increasing improvements in disease management, a huge medical need still exists as its relentless progression cannot be delayed by current treatments. Therefore, scientists, clinicians, and pharmaceutical companies are hunting new drugs with 'disease-modifying' properties.

AREAS COVERED

This review concentrates on new therapeutics - excluding cell and gene therapies - under investigation for PD with 'disease-modifying' potential. This is a global, comprehensive picture of the current innovative drug pipeline, where the main preclinical and clinical data available are provided. Drug candidates presented include α-synuclein modulating agents, neuroprotective agents and neuroinflammation modulators, kinase modulators, neurotrophic factors, and drugs acting on emerging targets.

EXPERT OPINION

There is excitement for agents with 'disease-modifying' properties and the authors found more than 130 assets, not including cell and gene therapies under investigation - most of them still in preclinical development - meaning that the science is progressing multiple, diverse new opportunities. Many limitations hamper the successful development of these drug candidates such as the translational accuracy of preclinical models, the current clinical development paradigm as well as the lack of biomarkers to be used in diagnosis and therapy management.

Therapeutic potential of targeting mixed lineage kinases in cancer and inflammation

Dysregulation of intracellular signaling pathways is a key attribute of diseases associated with chronic inflammation, including cancer. Mitogen activated protein kinases have emerged as critical conduits of intracellular signal transmission, yet due to their ubiquitous roles in cellular processes, their direct inhibition may lead to undesired effects, thus limiting their usefulness as therapeutic targets. Mixed lineage kinases (MLKs) are mitogen-activated protein kinase kinase kinases (MAP3Ks) that interact with scaffolding proteins and function upstream of p38, JNK, ERK, and NF-kappaB to mediate diverse cellular signals. Studies involving gene silencing, genetically engineered mouse models, and small molecule inhibitors suggest that MLKs are critical in tumor progression as well as in inflammatory processes. Recent advances indicate that they may be useful targets in some types of cancer and in diseases driven by chronic inflammation including neurodegenerative diseases and metabolic diseases such as nonalcoholic steatohepatitis. This review describes existing MLK inhibitors, the roles of MLKs in various aspects of tumor progression and in the control of inflammatory processes, and the potential for therapeutic targeting of MLKs.