Rigosertib sodium

Rigosertib sodium (ON-01910 sodium) is a non-ATP-competitive inhibitor of PLK1 with IC50 of 9 nM. It shows 30-fold greater selectivity against PLK2 and no activity to PLK3.Rigosertib has been used in trials studying the treatment and basic science of MDS, RAEB, Cancer, Hepatoma, and Neoplasms, among others

Rigosertib (ON-01910,Estybon) is a potent, specific PLK1 inhibitor with IC50 value of 9nM. Rigosertib strongly inhibited the proliferation of cancer cell lines, with observed IC50?values in the nanomolar range for both HeLa (115?nM) and C33A (45?nM) cells. In contrast, rigosertib had a minimal effect on normal cell lines, BJ and Ect1/E6E7 (IC50?>?0.1?mM) [1]

HeLa and C33A cells demonstrated a complete (>95%) G2/M arrest at concentrations of rigosertib >0.5?μM, whereas at <0.2?μM no clear perturbation of the cell cycle was evident. Normal cells were less affected by rigosertib [1].

Rigosertib has been reported to be a more potent radiosensitizer than cisplatin in?vivo [1].

References:
[1] Agoni L1,?Basu I2,?Gupta S3,?Alfieri A2,?Gambino A4,?Goldberg GL5,?Reddy EP6,?Guha C7. Rigosertib is a more effective radiosensitizer than cisplatin in concurrent chemoradiation treatment of cervical carcinoma, in vitro and in vivo. Int J Radiat Oncol Biol Phys.?2014 Apr 1;88(5):1180-7.

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Determination of intestinal permeability of rigosertib (ON 01910.Na, Estybon): correlation with systemic exposure.[Pubmed:23738723]

J Pharm Pharmacol. 2013 Jul;65(7):960-9.

OBJECTIVES: Rigosertib (ON 01910.Na, Estybon) is a novel, anticancer agent undergoing phase 3 clinical trials for a lead indication against myelodysplastic syndromes (MDS). In this research, the permeability of rigosertib was evaluated using the in-situ perfused rat intestine (IPRI) model to support development of an oral formulation for rigosertib for treating cancer patients. METHODS: Experiments (n = 6 per group) were conducted using male Sprague-Dawley rats. Studies evaluated permeability across various intestinal segments and assessed the dose-linearity of absorption over the entire intestinal length. Drug concentrations in the portal and jugular vein were collected to correlate permeability parameters with presystemic and systemic exposure. KEY FINDINGS: Rigosertib permeability was highest in the jejunum, although parameter estimates indicated that rigosertib was a medium permeability compound. The compound displayed nonlinear absorption in the IPRI model, suggesting a saturable transport process. Transport inhibition studies using Caco-2 cells demonstrated that rigosertib was a P-glycoprotein (P-gp) substrate. Absolute bioavailability of rigosertib (10 and 20 mg/kg, 1-h infusion) in rats was estimated to be 10-15%. However, the fraction absorbed in humans predicted from IPRI data (52%) was consistent with published clinical data for rigosertib (35% oral bioavailability). CONCLUSIONS: The results of this research indicated that rigosertib is a promising candidate for oral delivery. Further studies are needed to evaluate the potential impact of P-gp and other intestinal transporters on the oral absorption of this promising anticancer agent.

ON 01910.Na (rigosertib) inhibits PI3K/Akt pathway and activates oxidative stress signals in head and neck cancer cell lines.[Pubmed:27764820]

Oncotarget. 2016 Nov 29;7(48):79388-79400.

Squamous cell carcinoma of the head and neck (HNSCC) is characterized by high morbidity and mortality. Treatment failure, drug resistance and chemoradiation toxicity have necessitated the development of alternative treatment strategies. Styryl benzyl sulfones, a family of novel small molecule inhibitors, are being evaluated as anti-neoplastic agents in multiple clinical trials. The activity of these compounds has been well characterized in several preclinical tumor studies, but their activity has yet to be fully examined in HNSCC. We tested ON 01910.Na (rigosertib), a styryl benzyl sulfone in late-stage development, in HNSCC preclinical models. Rigosertib induced cytotoxicity in both HPV(+) and HPV(-) HNSCC cells in a dose-dependent manner. Characterization of the underlying molecular mechanism indicated that rigosertib induced inhibition of the PI3K/Akt/mTOR pathway, induced oxidative stress resulting in increased generation of reactive oxygen species (ROS), and activated extracellular signal-regulated kinases (ERK1/2) and c-Jun NH2-terminal kinase (JNK). Increased phosphorylation and cytoplasmic translocation of ATF-2 were also observed following rigosertib treatment. These changes in cell signaling led us to consider combining rigosertib with HNSCC standard-of-care therapies, such as cisplatin and radiation. Our study highlights the promising preclinical activity of rigosertib in HNSCC irrespective of HPV status and provides a molecular basis for rigosertib in combination with standard of care agents for HNSCC.

The safety and efficacy of rigosertib in the treatment of myelodysplastic syndromes.[Pubmed:27400247]

Expert Rev Anticancer Ther. 2016 Aug;16(8):805-10.

INTRODUCTION: Hypomethylating agents (HMAs) are the standard of care for patients with higher-risk myelodysplastic syndromes (MDS), but patients who relapse or are refractory have a poor prognosis with an estimated survival of 4-6 months. Rigosertib, a Ras mimetic that inhibits the phophoinositide 3-kinase and polo-like kinase pathways, has been tested in patients with higher-risk MDS following treatment with HMAs, where there are no approved second-line therapies. AREAS COVERED: This review will provide an overview of rigosertib, including safety and efficacy demonstrated in clinical trials. Expert commentary: There is an urgent need for new treatment options for patients who have failed or progressed on HMAs. Rigosertib is currently undergoing testing as a single agent in certain subsets of higher-risk MDS patients as well as in combination with azacitidine, where preliminary data show efficacy in patients with de novo MDS as well as HMA failures.

ON 01910.Na inhibits growth of diffuse large B-cell lymphoma by cytoplasmic sequestration of sumoylated C-MYB/TRAF6 complex.[Pubmed:27150054]

Transl Res. 2016 Sep;175:129-143.e13.

Diffuse large B-cell lymphoma (DLBCL), the most common lymphoma, shows either no response or development of resistance to further treatment in 30% of the patients that warrants the development of novel drugs. We have reported that ON 01910.Na (rigosertib), a multikinase inhibitor, is selectively cytotoxic for DLBCL and induces more hyperphosphorylation and sumoylation of Ran GTPase-activating protein 1 (RanGAP1) in DLBCL cells than in non-neoplastic lymphoblastoid cell line. However, the exact mechanism of rigosertib-induced cell death in DLBCL remains to be clarified. Here, we analyzed the efficacy of rigosertib against DLBCL cells in vitro and in vivo and its molecular effects on tumor biology. We found for the first time that rigosertib attenuated expression of unmodified and sumoylated tumor necrosis factor receptor-associated factor 6 (TRAF6) and c-Myb and inhibited nuclear entry of sumoylated RanGAP1, TRAF6, and c-Myb that was confirmed by immunofluorescence. Moreover, co-immunoprecipitation showed that rigosertib induced sequestration of c-Myb and TRAF6 in the cytoplasm by stimulating their sumoylation through the RanGAP1*SUMO1/Ubc9 pathway. Specific knockdown of c-Myb and TRAF6 induced tumor cell apoptosis and cell cycle arrest at G1 phase. Xenograft mice bearing lymphoma cells also exhibited effective tumor regression on rigosertib treatment along with cytoplasmic expression of c-Myb and TRAF6. Nuclear expression of c-Myb in clinical cases of DLBCL correlated with a poor prognosis. Thus, suppression of c-Myb and TRAF6 activity may have therapeutic implication in DLBCL. These data support the clinical development of rigosertib in DLBCL.

Blockade of RAS-Binding Domain Interactions Inhibits RAS Signaling.[Pubmed:27150538]

Cancer Discov. 2016 Jun;6(6):573.

Rigosertib acts as a RAS mimetic, binding to the RAS-binding domain of multiple RAS effector proteins.

Inhibition of Ras/Raf/MEK/ERK Pathway Signaling by a Stress-Induced Phospho-Regulatory Circuit.[Pubmed:27889448]

Mol Cell. 2016 Dec 1;64(5):875-887.

Ras pathway signaling plays a critical role in cell growth control and is often upregulated in human cancer. The Raf kinases selectively interact with GTP-bound Ras and are important effectors of Ras signaling, functioning as the initiating kinases in the ERK cascade. Here, we identify a route for the phospho-inhibition of Ras/Raf/MEK/ERK pathway signaling that is mediated by the stress-activated JNK cascade. We find that key Ras pathway components, the RasGEF Sos1 and the Rafs, are phosphorylated on multiple S/TP sites in response to JNK activation and that the hyperphosphorylation of these sites renders the Rafs and Sos1 unresponsive to upstream signals. This phospho-regulatory circuit is engaged by cancer therapeutics, such as rigosertib and paclitaxel/Taxol, that activate JNK through mitotic and oxidative stress as well as by physiological regulators of the JNK cascade and may function as a signaling checkpoint to suppress the Ras pathway during conditions of cellular stress.

Rigosertib sodium (ON-01910 sodium) is a multi-kinase inhibitor and a selective anti-cancer agent, which induces apoptosis by inhibition the PI3K/Akt pathway, promotes the phosphorylation of histone H2AX and induces G2/M arrest in cell cycle. Rigosertib sodium is a selective and non-ATP-competitive inhibitor of PLK1 with an IC50 of 9 nM.

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