Benzimidazole inhibitors of protein kinase CK2 potently inhibit the activity of atypical protein kinase Rio1

Two splice forms of OsbZIP1, a homolog of AtHY5, function to regulate skotomorphogenesis and photomorphogenesis in rice

Plants possess well-developed light sensing mechanisms and signal transduction systems for regulating photomorphogenesis. ELONGATED HYPOCOTYL5 (HY5), a basic leucine zipper (bZIP) transcription factor, has been extensively characterized in dicots. In this study, we show that OsbZIP1 is a functional homolog of Arabidopsis (Arabidopsis thaliana) HY5 (AtHY5) and is important for light-mediated regulation of seedling and mature plant development in rice (Oryza sativa). Ectopic expression of OsbZIP1 in rice reduced plant height and leaf length without affecting plant fertility, which contrasts with OsbZIP48, a previously characterized HY5 homolog. OsbZIP1 is alternatively spliced, and the OsbZIP1.2 isoform lacking the CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)-binding domain regulated seedling development in the dark. Rice seedlings overexpressing OsbZIP1 were shorter than the vector control under white and monochromatic light conditions, whereas RNAi knockdown seedlings displayed the opposite phenotype. While OsbZIP1.1 was light-regulated, OsbZIP1.2 showed a similar expression profile in both light and dark conditions. Due to its interaction with OsCOP1, OsbZIP1.1 undergoes 26S proteasome-mediated degradation under dark conditions. Also, OsbZIP1.1 interacted with and was phosphorylated by CASEIN KINASE2 (OsCK2α3). In contrast, OsbZIP1.2 did not show any interaction with OsCOP1 or OsCK2α3. We propose that OsbZIP1.1 likely regulates seedling development in the light, while OsbZIP1.2 is the dominant player under dark conditions. The data presented in this study reveal that AtHY5 homologs in rice have undergone neofunctionalization, and alternative splicing of OsbZIP1 has increased the repertoire of its functions.

Structure-guided discovery of adenosine triphosphate-competitive casein kinase 2 inhibitors

Casein kinase 2 (CK2) is a ubiquitous, highly pleiotropic serine-threonine kinase. CK2 has been identified as a potential drug target for the treatment of cancer and related disorders. Several adenosine triphosphate-competitive CK2 inhibitors have been identified and have progressed at different levels of clinical trials. This review presents details of CK2 protein, structural insights into adenosine triphosphate binding pocket, current clinical trial candidates and their analogues. Further, it includes the emerging structure-based drug design approaches, chemistry, structure-activity relationship and biological screening of potent and selective CK2 inhibitors. The authors tabulated the details of CK2 co-crystal structures because these co-crystal structures facilitated the structure-guided discovery of CK2 inhibitors. The narrow hinge pocket compared with related kinases provides useful insights into the discovery of CK2 inhibitors.

Benzimidazole and its derivatives as cancer therapeutics: The potential role from traditional to precision medicine

Cancer is the second leading cause of mortality globally which remains a continuing threat to human health today. Drug insensitivity and resistance are critical hurdles in cancer treatment; therefore, the development of new entities targeting malignant cells is considered a high priority. Targeted therapy is the cornerstone of precision medicine. The synthesis of benzimidazole has garnered the attention of medicinal chemists and biologists due to its remarkable medicinal and pharmacological properties. Benzimidazole has a heterocyclic pharmacophore, which is an essential scaffold in drug and pharmaceutical development. Multiple studies have demonstrated the bioactivities of benzimidazole and its derivatives as potential anticancer therapeutics, either through targeting specific molecules or non-gene-specific strategies. This review provides an update on the mechanism of actions of various benzimidazole derivatives and the structure‒activity relationship from conventional anticancer to precision healthcare and from bench to clinics.

Inhibiting CK2 among Promising Therapeutic Strategies for Gliomas and Several Other Neoplasms

In gliomas, casein kinase 2 (CK2) plays a dominant role in cell survival and tumour invasiveness and is upregulated in many brain tumours. Among CK2 inhibitors, benzimidazole and isothiourea derivatives hold a dominant position. While targeting glioma tumour cells, they show limited toxicity towards normal cells. Research in recent years has shown that these compounds can be suitable as components of combined therapies with hyperbaric oxygenation. Such a combination increases the susceptibility of glioma tumour cells to cell death via apoptosis. Moreover, researchers planning on using any other antiglioma investigational pharmaceutics may want to consider using these agents in combination with CK2 inhibitors. However, different compounds are not equally effective when in such combination. More research is needed to elucidate the mechanism of treatment and optimize the treatment regimen. In addition, the role of CK2 in gliomagenesis and maintenance seems to have been challenged recently, as some compounds structurally similar to CK2 inhibitors do not inhibit CK2 while still being effective at reducing glioma viability and invasion. Furthermore, some newly developed inhibitors specific for CK2 do not appear to have strong anticancer properties. Further experimental and clinical studies of these inhibitors and combined therapies are warranted.

A kinase-dependent checkpoint prevents escape of immature ribosomes into the translating pool

Premature release of nascent ribosomes into the translating pool must be prevented because these do not support viability and may be prone to mistakes. Here, we show that the kinase Rio1, the nuclease Nob1, and its binding partner Pno1 cooperate to establish a checkpoint that prevents the escape of immature ribosomes into polysomes. Nob1 blocks mRNA recruitment, and rRNA cleavage is required for its dissociation from nascent 40S subunits, thereby setting up a checkpoint for maturation. Rio1 releases Nob1 and Pno1 from pre-40S ribosomes to discharge nascent 40S into the translating pool. Weak-binding Nob1 and Pno1 mutants can bypass the requirement for Rio1, and Pno1 mutants rescue cell viability. In these strains, immature ribosomes escape into the translating pool, where they cause fidelity defects and perturb protein homeostasis. Thus, the Rio1–Nob1–Pno1 network establishes a checkpoint that safeguards against the release of immature ribosomes into the translating pool.

Here we show that the kinase Rio1, the nuclease Nob1, and its partner Pno1 establish a checkpoint that prevents the escape of immature ribosomes into polysomes. Bypass of this checkpoint perturbs ribosome fidelity, and mRNA specificity, and can be caused by cancer-associated mutations.

Integrating Rio1 activities discloses its nutrient-activated network in Saccharomyces cerevisiae

The Saccharomyces cerevisiae kinase/adenosine triphosphatase Rio1 regulates rDNA transcription and segregation, pre-rRNA processing and small ribosomal subunit maturation. Other roles are unknown. When overexpressed, human ortholog RIOK1 drives tumor growth and metastasis. Likewise, RIOK1 promotes 40S ribosomal subunit biogenesis and has not been characterized globally. We show that Rio1 manages directly and via a series of regulators, an essential signaling network at the protein, chromatin and RNA levels. Rio1 orchestrates growth and division depending on resource availability, in parallel to the nutrient-activated Tor1 kinase. To define the Rio1 network, we identified its physical interactors, profiled its target genes/transcripts, mapped its chromatin-binding sites and integrated our data with yeast’s protein–protein and protein–DNA interaction catalogs using network computation. We experimentally confirmed network components and localized Rio1 also to mitochondria and vacuoles. Via its network, Rio1 commands protein synthesis (ribosomal gene expression, assembly and activity) and turnover (26S proteasome expression), and impinges on metabolic, energy-production and cell-cycle programs. We find that Rio1 activity is conserved to humans and propose that pathological RIOK1 may fuel promiscuous transcription, ribosome production, chromosomal instability, unrestrained metabolism and proliferation; established contributors to cancer. Our study will advance the understanding of numerous processes, here revealed to depend on Rio1 activity.

Drug library screen reveals benzimidazole derivatives as selective cytotoxic agents for KRAS-mutant lung cancer

KRAS is one of the most frequently mutated oncogenes in human non-small cell lung cancer (NSCLC). Mutations in KRAS are detected in 30% of NSCLC cases, with most of them occurring in codons 12 and 13 and less commonly in others. Despite intense efforts to develop drugs targeting mutant KRAS, no effective therapeutic strategies have been successfully tested in clinical trials. Here, we investigated molecular targets for KRAS-activated lung cancer cells using a drug library. A total of 1271 small molecules were screened in KRAS-mutant and wild-type lung cancer cell lines. The screening identified the cytotoxic effects of benzimidazole derivatives on KRAS-mutant lung cancer cells. Treatments with two benzimidazole derivatives, methiazole and fenbendazole-both of which are structurally specific-yielded significant suppression of the RAS-related signaling pathways in KRAS-mutated cells. Moreover, combinatorial therapy with methiazole and trametinib, a MEK inhibitor, induced synergistic effects in KRAS-mutant lung cancer cells. Our study demonstrates that these benzimidazole derivatives play an important role in suppressing KRAS-mutant lung cancer cells, thus offering a novel combinatorial therapeutic approach against such cancer cells.

Design, synthesis and biological evaluation of novel benzimidazole amidines as potent multi-target inhibitors for the treatment of non-small cell lung cancer

A series of novel amidino 2-substituted benzimidazoles linked to 1,4-disubstituted 1,2,3-triazoles were synthesized by implementation of microwave and ultrasound irradiation in click reaction and subsequent condensation of thus obtained 4-(1,2,3-triazol-1-yl)benzaldehyde with o-phenylenediamines. In vitro antiproliferative screening of compounds performed on human cancer cell lines revealed that p-chlorophenyl-substituted 1,2,3-triazolyl N-isopropylamidine 10c and benzyl-substituted 1,2,3-triazolyl imidazoline 11f benzimidazoles had selective and potent cytostatic activities in the low nM range against non-small cell lung cancer cell line A549, which could be attributed to induction of apoptosis and primary necrosis. Additional Western blot analyses showed different mechanisms of cytostatic activity between compounds 10c and 11f that could be associated with the nature of aromatic substituent at 1-(1,2,3-triazolyl) and amidino moiety at C-5 position of benzimidazole ring. Specifically, compound 11f abrogated the activity of several protein kinases including TGM2, CDK9, SK1 and p38 MAPK, whereas compound 10c did not have profound effect on the activities of CDK9 and TGM2, but instead showed moderate downregulation of SK1 activity concomitant with a significant reduction in p38 MAPK. Further in silico structural analysis demonstrated that compound 11f bound slightly better to the ATP binding site of p38 MAPK compared to 10c, which correlated well with observed stronger decrement in the expression level of phospho-p38 MAPK elicited by 11f in comparison with 10c.

The Link between Protein Kinase CK2 and Atypical Kinase Rio1

The atypical kinase Rio1 is widespread in many organisms, ranging from Archaebacteria to humans, and is an essential factor in ribosome biogenesis. Little is known about the protein substrates of the enzyme and small-molecule inhibitors of the kinase. Protein kinase CK2 was the first interaction partner of Rio1, identified in yeast cells. The enzyme from various sources undergoes CK2-mediated phosphorylation at several sites and this modification regulates the activity of Rio1. The aim of this review is to present studies of the relationship between the two different kinases, with respect to CK2-mediated phosphorylation of Rio1, regulation of Rio1 activity, and similar susceptibility of the kinases to benzimidazole inhibitors.