Inducing the Degradation of Disease-Related Proteins Using Heterobifunctional Molecules

Advancing brain tumor therapy: unveiling the potential of PROTACs for targeted protein degradation

The long-term treatment of malignancies, particularly brain tumors, is challenged by abnormal protein expression and drug resistance. In terms of potency, selectivity, and overcoming drug resistance, Proteolysis Targeting Chimeras (PROTACs), a cutting-edge method used to selectively degrade target proteins, beats traditional inhibitors. This review summarizes recent research on using PROTACs as a therapeutic strategy for brain tumors, focusing on their mechanism, benefits, limitations, and the need for optimization. The review draws from a comprehensive search of peer-reviewed literature, scientific databases, and clinical trial databases. Articles published up to the knowledge cutoff date up to 14 April 2023 were included. Inclusion criteria covered PROTAC-based brain tumor therapies, including preclinical and early clinical studies, with no restrictions on design or publication type. We included studies using in vitro, in vivo brain tumor models, and human subjects. Eligible treatments involved PROTACs targeting proteins linked to brain tumor progression. We evaluated the selected studies for methodology, including design, sample size, and data analysis techniques. A narrative synthesis summarized key outcomes and trends in PROTAC-based brain tumor therapy. Recent research shows PROTACs selectively degrade brain tumor-related proteins with minimal off-target effects. They offer enhanced potency, selectivity, and the ability to combat resistance compared to traditional inhibitors. PROTACs hold promise for brain tumor treatment offering advantages over traditional inhibitors, but more research is needed to refine their mechanisms, efficacy, and safety. Larger-scale trials and translational studies are essential for assessing their clinical utility.

Novel Developments to Enable Treatment of CNS Diseases with Targeted Drug Delivery

The blood-brain barrier (BBB) is a major hurdle for the development of systemically delivered drugs against diseases of the central nervous system (CNS). Because of this barrier there is still a huge unmet need for the treatment of these diseases, despite years of research efforts across the pharmaceutical industry. Novel therapeutic entities, such as gene therapy and degradomers, have become increasingly popular in recent years, but have not been the focus for CNS indications so far. To unfold their full potential for the treatment of CNS diseases, these therapeutic entities will most likely have to rely on innovative delivery technologies. Here we will describe and assess approaches, both invasive and non-invasive, that can enable, or at least increase, the probability of a successful drug development of such novel therapeutics for CNS indications.

Is PROTAC technology really a game changer for central nervous system drug discovery?

Introduction: Central nervous system (CNS) diseases affect a large portion of the population, however, few therapeutic options are available. Furthermore, to date, clinical trials have been largely unsuccessful due to difficulty in targeting the undruggable, toxic proteins that underly many CNS disorders. PROteolysis Targeting Chimeras (PROTACs) are a rapidly emerging technology that has been proposed as a potential treatment option for various CNS diseases by hijacking the endogenous protein degradation process.Areas Covered: Herein, the authors discuss how the application of PROTACs may be beneficial in the treatment of major CNS diseases. They further discuss the main advantages and disadvantages of using PROTACs in the CNS, focusing on potential limitations such as their transient nature, localization, blood-brain barrier permeability and proteasome dysfunction.Expert opinion: It is evident that PROTACs have significant potential as a therapeutic tool for the treatment of CNS diseases and there is preliminary evidence suggesting that PROTACs could be successful in a clinical setting. Nevertheless, numerous limitations exist that must be overcome before this technology can be applied as a successful therapeutic for CNS disorders. Importantly, more in vivo studies are needed to determine the feasibility and effectiveness of using PROTACs in the brain.

Into the Fray! A Beginner's Guide to Medicinal Chemistry

Modern medicinal chemistry is a complex, multidimensional discipline that operates at the interface of the chemical and biological sciences. The medicinal chemistry contribution to drug discovery is typically described in the context of the well-recited linear progression of the drug discovery pipeline. However, compound optimization is idiosyncratic to each project, and clear definitions of hit and lead molecules and the subsequent progress along the pipeline becomes easily blurred. In addition, this description lacks insight into the entangled relationship between chemical and pharmacological properties, and thus provides limited guidance on how innovative medicinal chemistry strategies can be applied to solve optimization problems, regardless of the stage in the pipeline. Through discussion and illustrative examples, this article seeks to provide insights into the finesse of medicinal chemistry and the subtlety of balancing chemical properties pharmacology. In so doing, it aims to serve as an accessible and simple-to-digest guide for anyone who wishes to learn about the underlying principles of medicinal chemistry, in a context that has been decoupled from the pipeline description.

Targeted degradation of immune checkpoint proteins: emerging strategies for cancer immunotherapy

Cancer immunotherapy using immune-checkpoint blockade has displayed promising clinical effects, but prevalent antibody-based inhibitors face multiple challenges such as low response rate, acquired resistance, and adverse effects. The intracellular expression of PD-1/PD-L1 in recycling endosomes and their active trafficking to membrane highlight the importance of depleting rather than interfering with checkpoint proteins. Preclinical investigations on the therapeutic effects of lead compounds that function by degrading immune checkpoint ligands and receptors have reported highly promising results. By harnessing the degradation capabilities of the lysosome, proteasome and autophagosomes, different small molecules and peptides potently induced degradation of checkpoint proteins and enhanced anti-tumor immunity. Both in vitro and in vivo experiments support the therapeutic efficacy of these molecules. Thus, targeted degradation through endo-lysosomal, autophagic, proteasomal, or endoplasmic reticulum-related pathways may provide promising strategies for tackling the challenges in cancer immunotherapy.

Two-Stage Strategy for Development of Proteolysis Targeting Chimeras and its Application for Estrogen Receptor Degraders

Proteolysis targeting chimeras (PROTACs) have emerged as useful chemical probes and potential therapeutics by taking advantage of the ubiquitin-proteasome system to degrade intracellular disease-associated proteins. PROTACs are heterobifunctional molecules composed of a target protein ligand, E3 ubiquitin ligase ligand, and a linker between them. The generation of efficient PROTACs requires screening of many parameters, especially the lengths and types of the linkers. We report our proof-of-concept study using a two-stage strategy to facilitate the development of PROTACs against the estrogen receptor (ER). In stage one, a library of close to 100 PROTACs was synthesized by simply mixing a library of ERα ligands containing a hydrazide functional group at different positions with a preassembled library of E3 ligase ligands bearing different types and lengths of linkers with a terminal aldehyde group in a 1:1 ratio. Cell-based screening occurred without further purification, because the formation of the acylhydrazone linkage is highly efficient and produces water as the only byproduct. Compound A3 was the most potent ER degrader in two ER+ cell lines (DC₅₀= ∼ 10 nM, D_max= ≥ 95%). Stage two involved transformation to a more stable amide linker to generate a more drug-like molecule. The new compound, AM-A3, showed comparable biological activity (DC₅₀ = 1.1 nM, D_max = 98%) and induced potent antiproliferation (IC₅₀= 13.2 nM, I_max= 69%) in MCF-7. This proof-of -concept study demonstrates that the two-stage strategy can significantly facilitate the development of PROTACs against ER without the tedious process of making large numbers of PROTACs one by one. It has the potential to be expanded to many other targets.

Degraders early developability assessment: face-to-face with molecular properties

Pharmaceutical scientists have huge expectations from heterobifunctional small molecule degraders to treat diseases with an unmet medical need. However, degraders are large and flexible and pose significant challenges in terms of cellular uptake and bioavailability. An efficient property-based design is therefore required to discover new oral degrader medicines. Here, we show the non‑transferability to degraders of in silico tools routinely implemented in small molecule drug discovery programs; and provide ionization, lipophilicity, polarity and chameleonicity data for a series of seven degraders. We also reveal that permeability can be modeled by Δlog k_W^IAM - an experimental polarity descriptor. Overall, the paper is a proof-of-concept that shows to discover new oral degrader drugs ad hoc property-based design strategies are required.

Selective Degradation of Target Proteins by Chimeric Small-Molecular Drugs, PROTACs and SNIPERs

New therapeutic modalities are needed to address the problem of pathological but undruggable proteins. One possible approach is the induction of protein degradation by chimeric drugs composed of a ubiquitin ligase (E3) ligand coupled to a ligand for the target protein. This article reviews chimeric drugs that decrease the level of specific proteins such as proteolysis targeting chimeric molecules (PROTACs) and specific and nongenetic inhibitor of apoptosis protein (IAP)-dependent protein erasers (SNIPERs), which target proteins for proteasome-mediated degradation. We cover strategies for increasing the degradation activity induced by small molecules, and their scope for application to undruggable proteins.