Discovery of spiro amide SHR902275: A potent, selective, and efficacious RAF inhibitor targeting RAS mutant cancers

Spirocyclic compounds as innovative tools in drug discovery for medicinal chemists

The occurrence of spirocyclic motifs in clinical candidates and approved drugs is on the rise. This is related to the improvement of drug-like properties that can be achieved by introducing this sp3-rich system into bioactive compounds. Given the increasing number of synthetic methodologies and building blocks available, spirocycles are becoming widely accessible to medicinal chemists. From restricting conformation to induce a better fit with the target, to modulation of physicochemical and pharmacokinetic properties, spirocycles are being used to address several challenges in drug discovery. This review covers general aspects of the chemistry of spirocycles, highlighting some key strategies for their preparation. As reported in publications over the past five years, we demonstrate that, beyond the exploration of structure-activity relationships (SAR) in medicinal chemistry, the use of spirocycles is an attractive approach for enhancing properties such as potency, selectivity, physicochemistry, and pharmacokinetics.

Structural insights, regulation, and recent advances of RAS inhibitors in the MAPK signaling cascade: a medicinal chemistry perspective

The MAPK pathway has four main components: RAS, RAF, MEK, and ERK. Among these, RAS is the most frequently mutated protein and the leading cause of cancer. The three isoforms of the RAS gene are HRAS, NRAS, and KRAS. The KRAS gene is characterized by two splice variants, K-Ras4A and K-Ras4B. The occurrence of cancer often involves a mutation in both KRAS4A and KRAS4B. In this study, we have elucidated the mechanism of the RAS protein complex and the movement of switches I and II. Only two RAS inhibitors, sotorasib and adagrasib, have been approved by the FDA, and several are in clinical trials. This review comprises recent developments in synthetic RAS inhibitors, their unique properties, their importance in inhibiting RAS mutations, and the current challenges in developing new RAS inhibitors. This review will undoubtedly help researchers design novel RAS inhibitors.

An overview of RAF kinases and their inhibitors (2019-2023)

Protein kinases (PKs) including RAF, perform a principal role in regulating countless cellular events such as cell growth, differentiation, and angiogenesis. Overexpression and mutation of RAF kinases are significant contributors to the development and spread of cancer. Therefore, RAF kinase inhibitors show promising outcomes as anti-cancer small molecules by suppressing the expression of RAF protein, blocking RAS/RAF interaction, or inhibiting RAF enzymes. Currently, there are insufficient reports about approving drugs with minimal degree of toxicity. Therefore, it is an urgent need to develop new RAF kinase inhibitors correlated with increased anticancer activity and lower cytotoxicity. This review outlines reported RAF kinase inhibitors for cancer treatment in patents and literature from 2019 to 2023. It highlights the available inhibitors by shedding light on their chemical structures, biochemical profiles, and current status. Additionally, we highlighted the hinge region-binding moiety of the reported compounds by showing the hydrogen bond patterns of representative inhibitors with the hinge region for each class. In recent years, RAF kinase inhibitors have gained considerable attention in cancer research and drug development due to their potential to be studied under clinical trials and their demonstration of various degrees of efficacy and safety profiles across different cancer types. However, addressing challenges related to drug resistance and safety represents a major avenue for the optimization and enhancement of RAF kinase inhibitors. Strategies to overcome such obstacles were discussed such as developing novel pan-RAF inhibitors, RAF dimer inhibitors, and combination treatments.

Recent contributions of pyridazine as a privileged scaffold of anticancer agents in medicinal chemistry: An updated review

Pyridazine, as a privileged scaffold, has been extensively utilized in drug development due to its multiple biological activities. Especially around its distinctive anticancer property, a massive number of pyridazine-containing compounds have been synthesized and evaluated that target a diverse array of biological processes involved in cancer onset and progression. These include glutaminase 1 (GLS1) inhibitors, tropomyosin receptor kinase (TRK) inhibitors, and bromodomain containing protein (BRD) inhibitors, targeting aberrant tumor metabolism, cell signal transduction and epigenetic modifications, respectively. Pyridazine moieties functioned as either core frameworks or warheads in the above agents, exhibiting promising potential in cancer treatment. Therefore, the review aims to summarize the recent contributions of pyridazine derivatives as potent anticancer agents between 2020 and 2024, focusing mainly on their structure-activity relationships (SARs) and development strategies, with a view to show that the application of the pyridazine scaffold by different medicinal chemists provides new insights into the rational design of anticancer drugs.

Targeting CRAF kinase in anti-cancer therapy: progress and opportunities

The RAS/mitogen-activated protein kinase (MAPK) signaling cascade is commonly dysregulated in human malignancies by processes driven by RAS or RAF oncogenes. Among the members of the RAF kinase family, CRAF plays an important role in the RAS-MAPK signaling pathway, as well as in the progression of cancer. Recent research has provided evidence implicating the role of CRAF in the physiological regulation and the resistance to BRAF inhibitors through MAPK-dependent and MAPK-independent mechanisms. Nevertheless, the effectiveness of solely targeting CRAF kinase activity remains controversial. Moreover, the kinase-independent function of CRAF may be essential for lung cancers with KRAS mutations. It is imperative to develop strategies to enhance efficacy and minimize toxicity in tumors driven by RAS or RAF oncogenes. The review investigates CRAF alterations observed in cancers and unravels the distinct roles of CRAF in cancers propelled by diverse oncogenes. This review also seeks to summarize CRAF-interacting proteins and delineate CRAF's regulation across various cancer hallmarks. Additionally, we discuss recent advances in pan-RAF inhibitors and their combination with other therapeutic approaches to improve treatment outcomes and minimize adverse effects in patients with RAF/RAS-mutant tumors. By providing a comprehensive understanding of the multifaceted role of CRAF in cancers and highlighting the latest developments in RAF inhibitor therapies, we endeavor to identify synergistic targets and elucidate resistance pathways, setting the stage for more robust and safer combination strategies for cancer treatment.

Design, synthesis, and biological evaluation of novel spirocyclic compounds as potential anti-glioblastoma agents

Glioblastoma (GBM) is an aggressive brain tumor with extremely limited clinical treatment options. Because of the blood-brain barrier (BBB), it is difficult for anti-GBM drug candidates to enter the brain to exert their therapeutic effects. The spirocyclic skeleton structure exhibits good lipophilicity and permeability, enabling small-molecule compounds to cross the BBB. Herein, we designed and synthesized novel 3-oxetanone-derived spirocyclic compounds containing a spiro[3.4]octane ring and determined their structure-activity relationship for antiproliferation in GBM cells. Among these, the chalcone-spirocycle hybrid 10m/ZS44 exhibited high antiproliferative activity in U251 cells and permeability in vitro. Furthermore, 10m/ZS44 activated the SIRT1/p53-mediated apoptosis pathway to inhibit proliferation in U251 cells, whereas it minimally impaired other cell-death pathways, such as pyroptosis or necroptosis. In a mouse xenograft model, 10m/ZS44 exhibited a substantial inhibitory effect on GBM tumor growth without showing obvious toxicity. Overall, 10m/ZS44 represents a promising spirocyclic compound for the treatment of GBM.

The pyridazine heterocycle in molecular recognition and drug discovery

The pyridazine ring is endowed with unique physicochemical properties, characterized by weak basicity, a high dipole moment that subtends π-π stacking interactions and robust, dual hydrogen-bonding capacity that can be of importance in drug-target interactions. These properties contribute to unique applications in molecular recognition while the inherent polarity, low cytochrome P450 inhibitory effects and potential to reduce interaction of a molecule with the cardiac hERG potassium channel add additional value in drug discovery and development. The recent approvals of the gonadotropin-releasing hormone receptor antagonist relugolix (24) and the allosteric tyrosine kinase 2 inhibitor deucravacitinib (25) represent the first examples of FDA-approved drugs that incorporate a pyridazine ring. In this review, the properties of the pyridazine ring are summarized in comparison to the other azines and its potential in drug discovery is illustrated through vignettes that explore applications that take advantage of the inherent physicochemical properties as an approach to solving challenges associated with candidate optimization.

Graphical Abstract

Discovery of novel spiro compound as RAF kinase inhibitor with in vitro potency against KRAS mutant cancer

The development of RAF inhibitors targeting cancers with wild type RAF kinase and/or RAS mutation has been challenging due to the paradoxical activation of the RAS-RAF-MEK-ERK cascade following RAF inhibitor treatment. Herein is the discovery and optimization of a series of RAF inhibitors with a novel spiro structure. The most potent spiro molecule 9 showed excellent in vitro potency against b/c RAF enzymes and RAS mutant H358 cancer cells with minimal paradoxical RAF signaling activation. Compound 9 also exhibited good drug-like properties as demonstrated by in vitro cytochrome P450 (CYP), liver microsome stability (LMS) data and moderate oral pharmacokinetics (PK) profiles in rat and mouse.