Serum microRNA profile of rhesus macaques following ionizing radiation exposure and treatment with a medical countermeasure, Ex-Rad.

Exposure to ionizing radiation (IR) presents a formidable clinical challenge. Total-body or significant partial-body exposure at a high dose and dose rate leads to acute radiation syndrome (ARS), the complex pathologic effects that arise following IR exposure over a short period of time. Early and accurate diagnosis of ARS is critical for assessing the exposure dose and determining the proper treatment. Serum microRNAs (miRNAs) may effectively predict the impact of irradiation and assess cell viability/senescence changes and inflammation. We used a nonhuman primate (NHP) model-rhesus macaques (Macaca mulatta)-to identify the serum miRNA landscape 96 h prior to and following 7.2 Gy total-body irradiation (TBI) at four timepoints: 24, 36, 48, and 96 h. To assess whether the miRNA profile reflects the therapeutic effect of a small molecule ON01210, commonly known as Ex-Rad, that has demonstrated radioprotective efficacy in a rodent model, we administered Ex-Rad at two different schedules of NHPs; either 36 and 48 h post-irradiation or 48 and 60 h post-irradiation. Results of this study corroborated our previous findings obtained using a qPCR array for several miRNAs and their modulation in response to irradiation: some miRNAs demonstrated a temporary increased serum concentration within the first 24-36 h (miR-375, miR-185-5p), whereas others displayed either a prolonged decline (miR-423-5p) or a long-term increase (miR-30a-5p, miR-27b-3p). In agreement with these time-dependent changes, hierarchical clustering of differentially expressed miRNAs showed that the profiles of the top six miRNA that most strongly correlated with radiation exposure were inconsistent between the 24 and 96 h timepoints following exposure, suggesting that different biodosimetry miRNA markers might be required depending on the time that has elapsed. Finally, Ex-Rad treatment restored the level of several miRNAs whose expression was significantly changed after radiation exposure, including miR-16-2, an miRNA previously associated with radiation survival. Taken together, our findings support the use of miRNA expression as an indicator of radiation exposure and the use of Ex-Rad as a potential radioprotectant.

Analysis of the Proteomic Profile in Serum of Irradiated Nonhuman Primates Treated with Ex-Rad, a Radiation Medical Countermeasure.

There are currently four radiation medical countermeasures that have been approved by the United States Food and Drug Administration to mitigate hematopoietic acute radiation syndrome, all of which are repurposed radiomitigators. The evaluation of additional candidate drugs that may also be helpful for use during a radiological/nuclear emergency is ongoing. A chlorobenzyl sulfone derivative (organosulfur compound) known as Ex-Rad, or ON01210, is one such candidate medical countermeasure, being a novel, small-molecule kinase inhibitor that has demonstrated efficacy in the murine model. In this study, nonhuman primates exposed to ionizing radiation were subsequently administered Ex-Rad as two treatment schedules (Ex-Rad I administered 24 and 36 h post-irradiation, and Ex-Rad II administered 48 and 60 h post-irradiation) and the proteomic profiles of serum using a global molecular profiling approach were assessed. We observed that administration of Ex-Rad post-irradiation is capable of mitigating radiation-induced perturbations in protein abundance, particularly in restoring protein homeostasis, immune response, and mitigating hematopoietic damage, at least in part after acute exposure. Taken together, restoration of functionally significant pathway perturbations may serve to protect damage to vital organs and provide long-term survival benefits to the afflicted population.

Analysis of the metabolomic profile in serum of irradiated nonhuman primates treated with Ex-Rad, a radiation countermeasure.

To date, the United States Food and Drug Administration (FDA) has approved four drugs to mitigate hematopoietic acute radiation syndrome and all four are repurposed radiomitigators. There are several additional drug candidates currently under evaluation that may also be helpful for use during a widespread emergency. One possible candidate is Ex-Rad, also known as ON01210, a chlorobenzyl sulfone derivative (organosulfur compound), which is a novel, small-molecule kinase inhibitor with demonstrated efficacy in the murine model. In this study, we have evaluated the metabolomic and lipidomic profiles in serum samples of nonhuman primates (NHPs) treated with Ex-Rad after exposure to ionizing radiation. Two different dose administration schedules (Ex-Rad I administered 24 and 36 h post-irradiation, and Ex-Rad II administered 48 and 60 h post-irradiation), were used and evaluated using a global molecular profiling approach. We observed alterations in biochemical pathways relating to inflammation and oxidative stress after radiation exposure that were alleviated in animals that received Ex-Rad I or Ex-Rad II. The results from this study lend credence to the possible radiomitigative effects of this drug possibly via a dampening of metabolism-based tissue injury, thus aiding in recovery of vital, radiation-injured organ systems.

Rigosertib in combination with azacitidine in patients with myelodysplastic syndromes or acute myeloid leukemia: Results of a phase 1 study.

Phase 1 results from a Phase 1/2 study comprise 18 patients with myelodysplastic syndromes (MDS; n = 9), acute myeloid leukemia (AML; n = 8), and chronic myelomonocytic leukemia (CMML; n = 1) who were either hypomethylating agent naïve (n = 10) or relapsed/refractory following prior hypomethylating agent therapy (n = 8) (NCT01926587). Patients received oral rigosertib, an inhibitor of Ras-effector pathways, in 3 successive cohorts (140 mg twice daily, 280 mg twice daily, or 840 mg/day [560 mg morning/280 mg evening]) for 3 weeks of a 4-week cycle. Patients received parenteral azacitidine (75 mg/m2/day × 7 days) during the second week; the cycle repeated every 4 weeks. The combination was well tolerated for a median of 4 (range 1-41) cycles, with 72% of patients experiencing ≥1 serious adverse events. No dose-limiting toxicities were observed. Thus, no maximum tolerated dose was reached. The most frequently reported adverse events were diarrhea (50%), constipation, fatigue, and nausea (each 44%), and pneumonia and back pain (each 33%). Sequential administration demonstrated an overall response rate of 56% in evaluable patients, with responses observed in 7/9 MDS/CMML patients (78%) and 2/7 AML patients (29%). Further clinical studies are warranted to investigate this doublet therapy in patients with myeloid malignancies.

Effect of Gender on the Pharmacokinetics of ON 123300, A Dual Inhibitor of ARK5 and CDK4/6 for the Treatment of Cancer, in Rats.

BACKGROUND AND OBJECTIVES: ON 123300, a small molecule dual inhibitor of the c-MYC activated kinases ARK5 and CDK4/6, is being developed as a novel drug candidate for the treatment of cancer. The objective of this research was to evaluate gender differences in the in vitro metabolism and in vivo systemic exposure of ON 123300 in rats. METHODS: In vitro metabolism experiments (n = 2/group) were performed in rat liver microsomes from male and female donors. ON 123300 bislactate (final concentration 10 µM) was incubated with 0.5 mg/mL microsomes, and samples (100 µL) were withdrawn at specified incubation times over a period of 60 min, and immediately quenched and centrifuged. The supernatant was analyzed for ON 123300 and its metabolites by HPLC. ON 123300 (bislactate salt) pharmacokinetics were evaluated following intravenous (i.v.) (30 s infusion, 5 and 10 mg/kg) or oral administration (25 and 100 mg/kg) to male and female Sprague-Dawley rats (250-300 g). Following dosing, blood samples were collected over a time period up to 24 h. ON 123300 plasma concentrations were measured by LC-MS/MS. Pharmacokinetic parameters were estimated by non-compartmental analysis. Plasma and microsomal binding of ON 123300 and blood:plasma ratio were also determined. RESULTS: ON 123300 displayed more rapid microsomal degradation in vitro in males compared to females, as reflected in intrinsic clearance (181 vs 53.1 µL/min/mg). This translated into a significantly higher exposure of ON 123300 following oral administration to female rats, with the area under the curve (AUC) increasing nearly 3-fold (5617 ± 1914 ng·h/mL) compared to males (AUC = 1965 ± 749 ng·h/mL). This gender effect was less pronounced following i.v. dosing, where the AUC was ~ 2-fold higher in females. Based on these results, the higher plasma exposure observed in females can be primarily attributed to reductions in both hepatic clearance and presystemic metabolism compared to males. CONCLUSIONS: This investigation demonstrated a significantly lower metabolism of ON 123300 in female rats, which resulted in high systemic exposure. Additional testing is warranted to assess the potential clinical implications of these findings.

Determination of Degradation Kinetics and Effect of Anion Exchange Resin on Dissolution of Novel Anticancer Drug Rigosertib in Acidic Conditions.

Rigosertib is a novel anticancer drug in clinical development by Onconova therapeutics, Inc. Currently, it is in pivotal phase III clinical trials for myelodysplastic syndrome (MDS) patients. Chemically, it is a sodium salt of weak acid with low solubility in lower pH solutions. In the preliminary studies, it was found that rigosertib is unstable in acidic conditions and forms multiple degradation products. In this research, drug degradation kinetics of rigosertib were studied in acidic conditions. Rigosertib follows pseudo-first-order general acid catalysis reaction. Cholestyramine, which is a strong anion exchange resin, was used to form complex with drug to improve stability and dissolution in acidic conditions. Drug complex with cholestyramine showed better dissolution profile compared to drug alone. Effect of polyethylene glycol was investigated on the release of drug from the drug resin complex. Polyethylene glycol further improved dissolution profile by improving drug solubility in acidic medium.

Clinical activity and safety of the dual pathway inhibitor rigosertib for higher risk myelodysplastic syndromes following DNA methyltransferase inhibitor therapy.

Rigosertib (ON 01910.Na) is an inhibitor of the phosphoinositide 3-kinase and polo-like kinase pathways that induces mitotic arrest and apoptosis in neoplastic cells, while sparing normal cells. Our purpose is to summarize the clinical activity and safety of intravenous (IV) rigosertib delivered by an external ambulatory infusion pump in patients with refractory anemia with excess blasts-1, -2, or, -t myelodysplastic syndromes (MDS) following prior treatment with DNA methyltransferase (DNMT) inhibitors. A total of 39 patients with MDS who fulfilled these criteria were enrolled in four phase 1-2 clinical trials of IV rigosertib. Thirty five (88%) had higher risk disease according to the Revised International Prognostic Scoring System. Median overall survival for this group of 39 patients was 35 weeks. Of 30 evaluable patients with follow-up bone marrow biopsies, 12 (40%) achieved complete (n = 5) or partial (n = 7) bone marrow blast responses. In addition, 15 patients achieved stabilization of bone marrow blasts. One patient with a complete bone marrow response also achieved a complete cytogenetic response. A second patient with stable bone marrow blasts achieved a partial cytogenetic response. Two of the responding patients and three patients with stable disease had hematological improvements. Rigosertib-induced bone marrow blast decreases and stability appeared to be predictive of prolonged survival. IV rigosertib had a favorable safety profile without significant myelosuppression. Most common drug-related toxicities included fatigue, diarrhea, nausea, dysuria, and hematuria. In summary, IV rigosertib is well tolerated and has clinical activity in patients with higher risk MDS following DNMT inhibitor treatment. A multinational pivotal phase 3 randomized clinical trial of rigosertib versus best supportive care for patients with MDS with excess blasts following prior treatment with DNMT inhibitors (ONTIME: ON 01910.Na Trial In Myelodysplastic SyndromE) has recently completed enrollment.

Phase I study of oral rigosertib (ON 01910.Na), a dual inhibitor of the PI3K and Plk1 pathways, in adult patients with advanced solid malignancies.

PURPOSE: To determine the pharmacokinetics (PK), maximum tolerated dose (MTD), safety, and antitumor activity of an oral formulation of rigosertib, a dual phosphoinositide 3-kinase (PI3K) and polo-like kinase 1 (Plk1) pathway inhibitor, in patients with advanced solid malignancies. EXPERIMENTAL DESIGN: Patients with advanced solid malignancies received rigosertib twice daily continuously in 21-day cycles. Doses were escalated until intolerable grade ≥2 toxicities, at which point the previous dose level was expanded to define the MTD. All patients were assessed for safety, PK, and response. Urinary PK were performed at the MTD. Archival tumors were assessed for potential molecular biomarkers with multiplex mutation testing. A subset of squamous cell carcinomas (SCC) underwent exome sequencing. RESULTS: Forty-eight patients received a median of 2 cycles of therapy at 5 dose levels. Rigosertib exposure increased with escalating doses. Dose-limiting toxicities were hematuria and dysuria. The most common grade ≥2 drug-related toxicities involved urothelial irritation. The MTD is 560 mg twice daily. Activity was seen in head and neck SCCs (1 complete response, 1 partial response) and stable disease for ≥12 weeks was observed in 8 additional patients. Tumors experiencing ≥partial response had PI3K pathway activation, inactivated p53, and unique variants in ROBO3 and FAT1, two genes interacting with the Wnt/ß-catenin pathway. CONCLUSIONS: The recommended phase II dose of oral rigosertib is 560 mg twice daily given continuously. Urinary toxicity is the dose-limiting and most common toxicity. Alterations in PI3K, p53, and Wnt/ß-catenin pathway signaling should be investigated as potential biomarkers of response in future trials.

Phase 1 study of intravenous rigosertib (ON 01910.Na), a novel benzyl styryl sulfone structure producing G2/M arrest and apoptosis, in adult patients with advanced cancer.

Rigosertib (ON 01910.Na), a synthetic novel benzyl styryl sulfone, was administered to 28 patients with advanced cancer in a Phase I trial in order to characterize its pharmacokinetic profile, determine the dose-limiting toxicities (DLT), define the recommended phase II dose (RPTD) and to document any antitumor activity. Patients with advanced malignant neoplasms refractory to standard therapy were given escalating doses of rigosertib (50, 100, 150, 250, 325, 400, 650, 850, 1,050, 1,375, 1,700 mg/m(2)/24h) as a 3-day continuous infusion (CI) every 2 weeks. An accelerated Fibonacci titration schedule with specified decreases for toxicities was used for escalation until grade ≥2 toxicity occurred. Intrapatient dose escalation was allowed if toxicity was grade ≤2 and the disease remained stable. Plasma pharmacokinetics (PK) and urinary PK assessments were studied in the 1st and 4th cycles. Twenty-nine patients (12 men and 17 women; age 36-87 y with a median of 63 y) were registered, but one died before study drug was given. Twenty-eight patients received a median of 3 cycles of therapy. Most common grade ≥2 toxicities attributable to rigosertib included fatigue, anorexia, vomiting and constipation. DLTs included muscular weakness, hyponatremia, neutropenia, delirium and confusional state. Risk factors for severe toxicities include pre-existing neurological dysfunction or advanced gynecologic cancer after pelvic surgery. Rigosertib pharmacokinetics showed rapid plasma distribution phases and urinary excretion. Elevations in plasma Cmax and AUC due to decreases in plasma clearance were associated with acute grade ≥3 toxicities. Of 22 evaluable patients, 9 (41%) achieved a best overall response of stable disease; all other patients (n=13; 59%) progressed. The median progression-free survival time was 50 days (95% confidence interval [CI]: 37-80 days). Nine (41%) patients survived for over 1 y. In summary, prolonged IV infusions of rigosertib were generally well tolerated. Nine (41%) patients achieved stable disease and 9 (41%) patients survived for over 1 year. The RPTD appears to be 850 mg/m(2)/24hr CI x 3 days. (ClinicalTrials.gov identifier: NCT01538537).

Phase I clinical trial of oral rigosertib in patients with myelodysplastic syndromes.

The multi-kinase inhibitor rigosertib (ON 01910.Na) induces mitotic arrest and apoptosis in myeloblasts, while sparing normal cells. The purpose of this study was to determine the pharmacokinetic profile, maximum-tolerated dose (MTD), safety, and clinical activity of an oral formulation of rigosertib in patients with myelodysplastic syndromes (MDS). For pharmacokinetic studies, patients received rigosertib in single escalating weekly doses. To determine the MTD, patient cohorts received escalating doses of rigosertib twice daily for 14 d of a 21-d cycle. Overall, 37 patients were treated. Rigosertib exposure increased with escalating oral doses. Mean absolute oral bioavailability ranged from 13·9% (fed) to 34·8% (fasting) in 12 patients treated at the 560 mg b.i.d. dose level. Dose-limiting toxicity (grade 3 dysuria and shortness of breath) occurred at the 700 mg b.i.d. dose. Five patients experienced grade 3 non-haematological toxicity, including symptoms of urothelial inflammation, hypotension and syncope, fatigue and abdominal pain. Encouraging signs of clinical activity included two bone marrow complete remissions in refractory anaemia with excess blasts type 1 patients previously treated with azacitidine. In addition, four patients each achieved transfusion independence and haematological improvements. In conclusion, oral rigosertib is bioavailable and well tolerated, and has clinical activity in patients with MDS.

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

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.

Disposition of ON 01210.Na (Ex-RAD(R)), a novel radioprotectant, in the isolated perfused rat liver: probing metabolic inhibition to increase systemic exposure.

ON 01210.Na (Ex-RAD) is a novel benzyl styryl sulfone analog, developed as a radioprotectant by Onconova Therapeutics Inc. The objectives of this research were to evaluate the hepatobiliary disposition of ON 01210.Na in the isolated perfused rat liver (IPRL) and to determine the effect of coadministration of ethacrynic acid (EA) on the pharmacokinetic profile of ON 01210.Na. EA acid was used as a prototypical inhibitor of glutathione-S-transferase inhibitor. ON 01210.Na was highly bound in IPRL perfusate proteins, and binding was significantly lower in the presence of EA. Dose-escalation studies (bolus dose, target concentrations 10-250 µg/mL) showed that ON 01210.Na followed nonlinear pharmacokinetics with hepatic clearance decreasing from 3.14 to 1.99 mL/min with increasing dose. ON 01210.Na underwent extensive metabolic degradation to its glutathione (GSH) adduct in liver. The GSH metabolite was mainly excreted into the bile. Coadministration of EA (1 mM) significantly inhibited the conversion of ON 01210.Na to its GSH conjugate, resulting in decreased clearance (approx. fivefold lower), and prolonged elimination from the perfusate. These preclinical studies suggest that EA is a potential pharmacoenhancer that can reduce the metabolism of ON 01210.Na in vivo, thereby increasing drug exposure and boosting radioprotective activity.

Amelioration of radiation-induced hematopoietic and gastrointestinal damage by Ex-RAD(R) in mice.

The aim of the present study was to assess recovery from hematopoietic and gastrointestinal damage by Ex-RAD(®), also known as ON01210.Na (4-carboxystyryl-4-chlorobenzylsulfone, sodium salt), after total body radiation. In our previous study, we reported that Ex-RAD, a small-molecule radioprotectant, enhances survival of mice exposed to gamma radiation, and prevents radiation-induced apoptosis as measured by the inhibition of radiation-induced protein 53 (p53) expression in cultured cells. We have expanded this study to determine best effective dose, dose-reduction factor (DRF), hematological and gastrointestinal protection, and in vivo inhibition of p53 signaling. A total of 500 mg/kg of Ex-RAD administered at 24 h and 15 min before radiation resulted in a DRF of 1.16. Ex-RAD ameliorated radiation-induced hematopoietic damage as monitored by the accelerated recovery of peripheral blood cells, and protection of granulocyte macrophage colony-forming units (GM-CFU) in bone marrow. Western blot analysis on spleen indicated that Ex-RAD treatment inhibited p53 phosphorylation. Ex-RAD treatment reduces terminal deoxynucleotidyl transferase mediated dUTP nick end labeling assay (TUNEL)-positive cells in jejunum compared with vehicle-treated mice after radiation injury. Finally, Ex-RAD preserved intestinal crypt cells compared with the vehicle control at 13 and 14 Gy. The results demonstrated that Ex-RAD ameliorates radiation-induced peripheral blood cell depletion, promotes bone marrow recovery, reduces p53 signaling in spleen and protects intestine from radiation injury.

Radioprotective effects of ON 01210.Na upon oral administration.

ON 01210.Na (Ex-RAD), a chlorobenzylsulfone derivative was investigated for its pharmacologic and radioprotective properties when administered via oral and subcutaneous (SC) routes. The goals of the study were to assess the comparative bioavailability of ON 01210.Na when administered by oral versus SC routes and to demonstrate that the oral drug delivery of ON 01210.Na afforded survival advantage similar to SC dosing. Pharmacokinetics was studied after two doses, 24 h apart, of ON 01210.Na (500 mg/kg) administered to male C3H/Hen mice (7-9 weeks) via SC injection or oral route. The dose response (100 to 750 mg/kg) and survival advantage of ON 01210.Na administered at 24 h and 15 min prior to 7.5 or 8 Gy whole body irradiation from a ¹³7Cs source (dose rate 1 Gy/min) were studied in these mice. Effects on the hematopoietic system were investigated by complete blood count and granulocyte-macrophage colony forming unit assay. A significant survival advantage and hematopoietic protection were observed after prophylactic oral ON 01210.Na and results were comparable to SC administration. These findings correlated well with pharmacokinetic data. Both SC and oral ON 01210.Na showed significant survival advantage against radiation toxicity and ON 01210.Na mediated hematopoietic protection plays key role in enhanced survival of mice. Oral administration holds better clinical promise as an effective countermeasure not only for early-responders in a nuclear accident, but also for the at-risk civilian population.

Directed therapy for patients with myelodysplastic syndromes (MDS) by suppression of cyclin D1 with ON 01910.Na.

BACKGROUND: We previously demonstrated upregulation of c-myc, survivin, and cyclin D1 in CD34+ bone marrow mononuclear cells (BMMNCs) of patients with trisomy 8 and monosomy 7 myelodysplastic syndromes (MDS). "Knockdown" of cyclin D1 by RNA interference decreased trisomy 8 cell growth, suggesting that this might be a therapeutic target in MDS. EXPERIMENTAL DESIGN: We performed preclinical studies using BMMNCs from patients with MDS and AML to examine the effects of the styryl sulfone ON 01910.Na on cyclin D1 accumulation, aneuploidy, and CD34+ blast percentage. We next treated twelve patients with higher risk MDS and two trisomy 8 AML patients with ON 01910.Na on a phase I clinical protocol (NCT00533416). RESULTS: ON 01910.Na inhibited cyclin D1 expression, and was selectively toxic to trisomy 8 cells in vitro. Flow cytometry studies demonstrated increased mature CD15+ myeloid cells and decreased CD34+ blasts. Three patients treated with ON 01910.Na on a clinical had decreased bone marrow blasts by ≥ 50%, and three patients had hematologic improvements, one of which was sustained for 33 months. Patients with hematologic responses to ON 01910.Na had decreased cyclin D1 expression in their CD34+ cells. CONCLUSIONS: The preclinical results and responses of patients on a clinical trial warrant further investigation of ON 01910.Na as a potential novel targeted therapy for higher risk MDS patients.

Phase I study of Rigosertib, an inhibitor of the phosphatidylinositol 3-kinase and Polo-like kinase 1 pathways, combined with gemcitabine in patients with solid tumors and pancreatic cancer.

PURPOSE: Rigosertib, a dual non-ATP inhibitor of polo-like kinase 1 (Plk1) and phosphoinositide 3-kinase pathways (PI3K), and gemcitabine have synergistic antitumor activity when combined in preclinical studies. This phase I study aimed to determine the recommended phase II dose (RPTD) of the combination of rigosertib and gemcitabine in patients with cancer. EXPERIMENTAL DESIGN: Patients with solid tumors who failed standard therapy or were candidates for gemcitabine-based therapy were eligible. Gemcitabine was administered on days 1, 8, and 15 on a 28-day cycle and rigosertib on days 1, 4, 8, 11, 15, and 18. Pharmacokinetic studies were conducted during an expansion cohort of patients with advanced pancreatic ductal adenocarcinoma (PDA). RESULTS: Forty patients were treated, 19 in the dose-escalation phase and 21 in the expansion cohort. Dose levels evaluated were (gemcitabine/rigosertib mg/m(2)): 750/600 (n = 4), 750/1,200 (n = 3), 1,000/600 (n = 3), 1,000/1,200 (n = 3), and 1,000/1,800 (n = 6 + 21). One dose-limiting toxicity (death) occurred at the highest dose level (1,000/1,800) tested. Non-dose-limiting ≥grade II/III toxicities included neutropenia, lymphopenia, thrombocytopenia, fatigue, and nausea. Grade III/IV neutropenia, thrombocytopenia, and fatigue were seen in two, one, and two patients in the expansion cohort. Partial responses were observed in PDA, thymic cancer, and Hodgkin lymphoma, including gemcitabine-pretreated PDA. The pharmacokinetic profile of rigosertib was not affected by gemcitabine. CONCLUSION: The RPTD established in this study is rigosertib 1,800 mg/m(2) and gemcitabine 1,000 mg/m(2). This regimen is well tolerated with a toxicity profile of the combination similar to the profile of gemcitabine alone. Antitumor efficacy was observed in patients who previously progressed on gemcitabine-based therapy.

Administration of ON 01210.Na after exposure to ionizing radiation protects bone marrow cells by attenuating DNA damage response.

BACKGROUND: Ionizing radiation-induced hematopoietic injury could occur either due to accidental exposure or due to diagnostic and therapeutic interventions. Currently there is no approved drug to mitigate radiation toxicity in hematopoietic cells. This study investigates the potential of ON 01210.Na, a chlorobenzylsulfone derivative, in ameliorating radiation-induced hematopoietic toxicity when administered after exposure to radiation. We also investigate the molecular mechanisms underlying this activity. METHODS: Male C3H/HeN mice (n = 5 mice per group; 6-8 weeks old) were exposed to a sub-lethal dose (5 Gy) of γ radiation using a ¹³7Cs source at a dose rate of 0.77 Gy/min. Two doses of ON 01210.Na (500 mg/kg body weight) were administered subcutaneously at 24 h and 36 h after radiation exposure. Mitigation of hematopoietic toxicity by ON 01210.Na was investigated by peripheral white blood cell (WBC) and platelet counts at 3, 7, 21, and 28 d after radiation exposure. Granulocyte macrophage colony forming unit (GM-CFU) assay was done using isolated bone marrow cells, and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) was performed on bone marrow sections at 7 d post-exposure. The DNA damage response pathway involving ataxia telangiectasia mutated (ATM) and p53 was investigated by Western blot in bone marrow cells at 7 d post-exposure. RESULTS: Compared to the vehicle, ON 01210.Na treated mice showed accelerated recovery of peripheral WBC and platelet counts. Post-irradiation treatment of mice with ON 01210.Na also resulted in higher GM-CFU counts. The mitigation effects were accompanied by attenuation of ATM-p53-dependent DNA damage response in the bone marrow cells of ON 01210.Na treated mice. Both phospho-ATM and phospho-p53 were significantly lower in the bone marrow cells of ON 01210.Na treated than in vehicle treated mice. Furthermore, the Bcl2:Bax ratio was higher in the drug treated mice than the vehicle treated groups. CONCLUSIONS: ON 01210.Na treatment significantly mitigated the hematopoietic toxicity induced by a sub-lethal radiation dose. Mechanistically, attenuation of ATM-p53 mediated DNA damage response by ON 01210.Na is contributing to the mitigation of radiation-induced hematopoietic toxicity.

Effects of formulation and route of administration on the systemic availability of Ex-RAD®, a new radioprotectant, in preclinical species.

ON 01210.Na (Ex-RAD®) is a novel small molecule under development by Onconova Therapeutics, Inc. as a radiation protection agent. The purpose of this investigation was to evaluate the effect of various formulation approaches on the systemic exposure of ON 01210.Na. In vitro experiments were used to characterize the plasma binding and metabolic stability of ON 01210.Na using hepatocytes from several animal species (mouse, rat, rabbit, dog, monkey and human). In vivo studies were performed in rats, rabbits, dogs and monkeys, and involved several routes of administration (intravenous, subcutaneous, oral). Plasma protein binding was high across species (>83%), and the rate of ON 01210.Na metabolism was highest in rat and mouse hepatocytes. After intravenous administration, ON 01210.Na demonstrated biphasic elimination from the plasma. Systemic exposure parameters (Cmax, AUC) were dose-proportional up to 100 mg/kg. Following subcutaneous dosing, ON 01210.Na showed relatively low bioavailability upon administration of the suspension formulation. Developing a solution formulation significantly increased the bioavailability of the drug. This solution formulation demonstrated significant oral bioavailability in rabbit (70%) and monkey (30%). The findings from these preclinical studies provide an overview of the systemic disposition of ON 01210.Na, aiding in the development of optimal formulations and routes of administration for pivotal animal efficacy and clinical safety studies. A solution formulation of ON 01210.Na for s.c. administration is being developed, in addition to an oral dosage form for potential use of the compound as a radioprotectant and a radiation-mitigating agent in wider military and civilian populations.

Preclinical pharmacokinetics and in vitro activity of ON 01910.Na, a novel anti-cancer agent.

PURPOSE: ON 01910.Na is a novel targeted anti-cancer agent under clinical investigation in Phase I and II trials. The purpose of this research was to evaluate the pharmacokinetic profile of ON 01910.Na across several species, and to evaluate the effects of protein binding and duration of exposure on its in vitro cytotoxic activity. METHODS: Data were collated from several preclinical investigations, where the plasma disposition and tissue distribution of ON 01910.Na were assessed after administration (10-150 mg/kg, IP or IV) to several species (mouse, rat, and dog). Plasma protein binding was assessed using ultrafiltration. Cytotoxic activity of ON 01910.Na was determined in DU145 cells, and activity was correlated to unbound drug concentration and the duration of exposure. RESULTS: ON 01910.Na exhibits extensive plasma protein binding and the compound displays rapid elimination from the circulation in all three animal species (t(1/2) range 0.404-0.870 h). Tissue distribution studies in mice revealed highest drug accumulation in the liver, followed by the kidneys. ON 01910.Na is not extensively metabolized in vivo and urinary excretion is predominant at higher doses. ON 01910.Na cytotoxicity in DU145 cells was adversely affected by protein binding in the incubation medium. Drug cytotoxicity was greatly enhanced upon extending the duration of exposure at reduced drug concentrations. CONCLUSIONS: Due to the short half-life and rapid clearance of the drug, administration of ON 01910.Na by continuous IV infusion is a likely treatment option for cancer patients.

Radiation protection by a new chemical entity, Ex-Rad: efficacy and mechanisms.

Ex-Rad is among a series of small molecule kinase inhibitors developed for modifying cell cycle distribution patterns in cancer cells subjected to radiation therapy, and it has been identified as a potential candidate for radiation protection studies. We have investigated its radioprotective efficacy using mouse and in vitro models. Thirty-day survival studies with C3H/HeN male mice revealed 88% survival when 500 mg/kg of Ex-Rad was injected subcutaneously 24 h and 15 min before gamma irradiation with 8.0 Gy. To understand Ex-Rad's mechanism of action, we also studied its radioprotective efficacy in lung fibroblast (HFL-1), skin fibroblast (AG1522) and human umbilical vein endothelial cells (HUVECs). Colony-forming assays indicated that Ex-Rad protected cells from radiation damage after exposure to (60)Co gamma radiation. A study using single-cell gel electrophoresis (SCGE; also known as the alkaline comet assay) showed that Ex-Rad protected cells from radiation-induced DNA damage. Western blot analyses indicated that the radiation protection provided by Ex-Rad resulted in reduced levels of pro-apoptosis proteins such as p53 as well as its downstream regulators p21, Bax, c-Abl and p73, indicating that Ex-Rad could rescue cells from ionizing radiation-induced p53-dependent apoptosis. In conclusion, it appears that Ex-Rad's radioprotective mechanisms involve prevention of p53-dependent and independent radiation-induced apoptosis.