The pharmacological effects of Oridonin: anti-inflammasome activity and anticancer activity

Introduction

Oridonin (Ori;Figure 1), a bioactive ent-kaurane diterpenoid, is the major active constituent of Rabdosia rubescens, which has been widely used in traditional Chinese medicine. Oridonin has shown considerable anticancer activities, which include cell cycle arrest, apoptosis induction, and angiogenesis suppression,but the relatively moderate potency and imprecise mechanisms of action have greatly hindered its clinical applications for the treatment of cancer. Besides their antitumor activity, Rabdosia rubescens and oridonin have also possessed anti-inflammatory activity. In China, Rabdosia rubescens is a commonly available over-the-counter (OTC) herbal medicine for the treatment of inflammatory diseases. Oridonin has been reported to inhibit NF-κB or MAPK activation to suppress the release of proinflammatory cytokines, such as tumor necrosis factor (TNF)-α and interleukin (IL)-6. Moreover, oridonin has also exhibited anti-inflammatory activity and protective role in colitis, sepsis, and neuroinflammation.[1]

1. anti-inflammasome activity

NLRP3 is a central component of NLRP3 inflammasome and has been involved in a widevariety of chronic inflammation-driven human diseases. Here, we show that oridonin is a specific and covalent inhibitor for NLRP3 inflammasome. Oridonin forms a covalent bond with the cysteine 279 of NLRP3 in NACHT domain to block the interaction between NLRP3 and NEK7, therebyinhibiting NLRP3 inflammasome assembly and activation. Importantly, oridonin has both preventive or therapeutic effects on mouse models of peritonitis, gouty arthritis and type 2 diabetes, via inhibition of NLRP3 activation. Our results thus identify NLRP3 as the direct target of oridonin for mediating oridonin's anti-inflammatory activity. Oridonin could serve as a lead for developing new therapeutics against NLRP3-driven diseases.[1]

Oridonin attenuates the progression of atherosclerosis by inhibiting NLRP3 and activating Nrf2 in apolipoprotein E-deficient mice.

This study focused on the effects of oridonin on oxidative stress and inflammation generated from atherosclerosis. The therapeutic effect on atherosclerosis was evaluated by intraperitoneal injection of oridonin in a high-fat fed ApoE-/- mouse model. The researchers isolated mouse peritoneal macrophages and detected the effect of oridonin on oxidized low-density lipoprotein-induced lipid deposition. Oil red O staining, Masson's staining, dihydroethidium fluorescence staining, immunohistochemical staining, western blotting analysis, immunofluorescence, enzyme-linked immunosorbent assay and quantitative real-time PCR were used to evaluate the effect on atherosclerosis and explore the mechanisms. Oridonin treatment significantly alleviated the progression of atherosclerosis, reduced macrophage infiltration and stabilized plaques. Oridonin could significantly inhibit inflammation associated with NLRP3 activation. Oridonin significantly reduced oxidative stress by blocking Nrf2 ubiquitination and degradation. We also found that oridonin could prevent the formation of foam cells by increasing lipid efflux protein and reducing lipid uptake protein in macrophages. Oridonin has a protective effect on atherosclerosis in ApoE^-/- mice, which may be related to the inhibition of NLRP3 and the stabilization of Nrf2. Therefore, oridonin may be a potential therapeutic agent for atherosclerosis.[2]

2.Anticancer activity

oridonin has been proved to be effective in the treatments of various cancer cells such as hepatic, colorectal, cervical, prostate, breast,hemalogical and lung cancer, mainly through the interference of carcinogen metabolism, induction of DNA repair and cell cycle arrest, inhibition of cell proliferation, antiangiogenesis, retarding metastasis, reversing drug resistance and enhancing chemotherapy by the combination use with other agents[3] 

Oridonin inhibits bladder cancer survival and immune escape by covalently targeting HK1

Hexokinase I (HK1) is highly expressed in a variety of malignancies, regulates glycolytic pathway in cancer cells, and thus considered to be one of the promising molecular targets for cancer therapy. Nonetheless, the development of a specific inhibitor against HK1 remains elusive. PURPOSE: This study aims to elucidate the mechanism by which oridonin inhibits the proliferation and immune evasion of bladder cancer cells, specifically through the suppression of HK1. To examine the mechanisms by which oridonin directly binds to cysteines of HK1 and inhibits bladder cancer growth, this study utilized a variety of methods. These included the Human Proteome Microarray, Streptavidin-agarose affinity assay, Biolayer Interferometry (BLI) ainding analysis, Mass Spectrometry, Cellular Thermal Shift Assay, Extracellular Acidification Rate measurement, and Xenotransplant mouse models. As indicated by our current findings, oridonin forms a covalent bond with Cys-813, located adjacently to glucose-binding domain of HK1. This suppresses the enzymatic activity of HK1, leading to an effective reduction of glycolysis, which triggers cell death via apoptosis in cells derived from human bladder cancer. Significantly, oridonin also inhibits lactate-induced PD-L1 expression in bladder cancer. Furthermore, pairing oridonin with a PD-L1 inhibitor amplifies the cytotoxicity of CD8⁺T cells against bladder cancer. This research strongly suggests that oridonin serves as a covalent inhibitor of HK1. Moreover, it indicates that functional cysteine residue of HK1 could operate as viable targets for selective inhibition. Consequently, oridonin exhibits substantial potential for the evolution of anti-cancer agents targeting the potential therapeutic target HK1 via metabolism immunomodulation.[4]

Oridonin and Its Derivatives for the Treatment of Acute Myelogenous Leukemia (AML)

Researchers began to investigate the effects of oridoninon AML about ten years ago. Zhou et al. studied the potency of oridonin on a group of leukemic cell lines including the t(8;21)-harboring Kasumi-1 cells and other primary leukemia cells acquired from patients with de novo or relapsed/refractory t(8;21) AML. The results showed that oridonin, at clinically available concentrations (0.5-5.0µM), hindered the growth and initiated programmed cell death of t(8;21) leukemic cells by damaging the mitochondria functions and unleashing the apoptosis machinery, down-regulating the apoptosis antagonist Bcl-2, and activating caspase-3 and -9. In addition, the researcher assessed the effects on the resultant AML1-ETO (AE) fusion protein and learned that oridonin could induce caspase-3 dependent decrease of AE, and theaspartic acid residue at position 188 of AE (D188) was identified as the site of cleavage. In t(8;21) AML murinemodels, apoptosis induced by oridonin significantly increased the life expectancy of mice. Furthermore, it could inhibit the growth of tumors in nude mice, meanwhile without inhibition of bone marrow or loss of body weight.[5] 

Oridonin exerts anticonvulsant profile and neuroprotective activity in epileptic mice by inhibiting NLRP3-mediated pyroptosis

Oridonin can inhibit the increased excitability of neurons caused by glutamate accumulation at the cellular level. However, whether oridonin affects neuronal excitability and whether it has antiepileptic potential has not been reported in animal models or clinical studies. Pentylenetetrazol was injected into mice to create a model of chronic epilepsy. Seizure severity was assessed using the Racine scale, and the duration and latency of seizures were observed. Abnormal neuronal discharge was detected using electroencephalography, and neuronal excitability was assessed using calcium imaging. Damage to hippocampal neurons was evaluated using Hematoxylin-Eosin and Nissl staining. The expression of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome and other pyroptosis-related proteins was determined using western blotting and immunofluorescence. A neuronal pyroptosis model was established using the supernatant of BV2 cells treated with lipopolysaccharide and adenosine triphosphate to stimulate hippocampal neurons. Oridonin (1 and 5 mg/kg) reduced neuronal damage, increased the latency of seizures, and shortened the duration of fully kindled seizures in chronic epilepsy model mice. Oridonin decreased abnormal discharge during epileptic episodes and suppressed increased neuronal excitability. In vitro experiments showed that oridonin alleviated pyroptosis in hippocampal HT22 neurons. Oridonin exerts neuroprotective effects by inhibiting pyroptosis through the NLRP3/caspase-1 pathway in chronic epilepsy model mice. It also reduces pyroptosis in hippocampal neurons in vitro, suggesting its potential as a therapy for epilepsy.[6]

References

[1] He H, Jiang H, Chen Y, et al. Oridonin is a covalent NLRP3 inhibitor with strong anti-inflammasome activity. Nat Commun. 2018;9(1):2550. Published 2018 Jun 29. doi:10.1038/s41467-018-04947-6

[2] Wang L, Zhao X, Ding J, et al. Oridonin attenuates the progression of atherosclerosis by inhibiting NLRP3 and activating Nrf2 in apolipoprotein E-deficient mice. Inflammopharmacology. 2023;31(4):1993-2005. doi:10.1007/s10787-023-01161-9

[3] Zhao Z, Chen Y. Oridonin, a promising antitumor natural product in the chemotherapy of hematological malignancies. Curr Pharm Biotechnol. 2014;15(11):1083-1092. doi:10.2174/1389201015666141111115608

[4] Liu S, Wang X, Sun X, et al. Oridonin inhibits bladder cancer survival and immune escape by covalently targeting HK1. Phytomedicine. 2024;126:155426. doi:10.1016/j.phymed.2024.155426

[5] Hu X, Wang Y, Gao X, et al. Recent Progress of Oridonin and Its Derivatives for the Treatment of Acute Myelogenous Leukemia. Mini Rev Med Chem. 2020;20(6):483-497. doi:10.2174/1389557519666191029121809

[6] Zhao T, Zhang X, Cui X, et al. Oridonin exerts anticonvulsant profile and neuroprotective activity in epileptic mice by inhibiting NLRP3-mediated pyroptosis. Int Immunopharmacol. 2024;134:112247. doi:10.1016/j.intimp.2024.112247