p110α (Ki = 0.019 nM); p110α-E545K (Ki = 0.008 nM); p110α-E542K (Ki = 0.008 nM); p110α-H1047R (Ki = 0.009 nM); p110β (Ki = 0.13 nM); p110δ (Ki = 0.024 nM); p110γ (Ki = 0.06 nM); mTORC1 (Ki = 0.18 nM); mTORC2 (Ki = 0.3 nM)

GSK2126458 potently inhibits the activity of common activating mutants of p110α (E542K, E545K, and H1047R) found in human cancer with Ki of 8 pM, 8 pM and 9 pM, respectively.[1] GSK2126458 significantly lowers the levels of pAkt-S473 in T47D and BT474 cells with a remarkable potency, with IC50 values of 0.41 nM and 0.18 nM, respectively. Additionally, GSK2126458 causes a G1 cell cycle arrest and has an inhibitory effect on cell proliferation in a variety of cell lines, including the T47D and BT474 breast cancer lines with IC50 values of 3 nM and 2.4 nM, respectively.[1]

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These studies eventually led to the identification of Omipalisib/1, an extraordinarily potent inhibitor of PI3Kα (p110α/p85α) with low picomolar activity (PI3Kα IC50 = 0.04 nM). In biochemical assays, compound 1 is significantly more potent than 2 (PI3Kα IC50 = 2 nM) and is the most potent PI3Kα inhibitor reported to date. In comparison with other clinical PI3K inhibitors, 1 is ∼100-fold more potent than BEZ235 (IC50 = 6 nM) and GDC-0941 (IC50 = 9 nM) and ∼1000-fold more active than XL-765 (IC50 = 39 nM). Importantly, 1 is also a low picomolar inhibitor of the common activating mutants of p110α (E542K, E545K, and H1047R) found in human cancer (Table 3). Similar to the other reported PI3K inhibitors, 1 is also active against the other class I PI3K isoforms (β, γ, and δ). [1]

Compound 1/Omipalisib shows excellent selectivity over protein kinases (>10,000-fold vs >240 kinases evaluated) with the notable exception of the class IV PI3K family. mTOR, a class IV PI3K protein kinase, is a central regulator of cell growth and exists in two functional complexes, mTORC1 and mTORC2. (25) mTORC2 is proposed to regulate AKT S473 phosphorylation, and its inhibition is believed to augment the antiproliferative efficacy of a PI3K inhibitor by dual inhibition of the PI3K/AKT pathway. The kinase domain of mTOR is homologous to the p110α catalytic subunit of the class I PI3Ks, and 1 is a potent inhibitor of both mTOR complexes with subnanomolar activity (Table 4). Compound 1 is also a potent inhibitor of the class IV PI3 kinase, DNA-PK (IC50 = 0.28 nM).[1]

A cocrystal structure of PI3Kγ in complex with 1/Omipalisib shows the inhibitor bound in the ATP-binding site of the enzyme (Figure 3). The structure was determined to 2.7 Å resolution and shows, like 6e, that the pyridyl nitrogen forms a key hydrogen bond with the conserved water molecule. The sulfonamide interacts with Lys833, making a strong charged interaction. On the basis of the pKa of the sulfonamide-NH (6.56), ∼87% of the moiety exists in its deprotonated form at physiological pH. This charged interaction may help to explain the superior potency of 1 as compared to the other reported PI3K inhibitors. In addition, the difluorophenyl group fills a hydrophobic region in the back pocket of the enzyme, while the quinoline nitrogen forms an interaction with the hinge (Val882).[1]

In mechanistic cellular assays, 1/Omipalisib caused a significant reduction in the levels of pAKT-S473 with remarkable potency (Table 5). Consistent with its activity against both PI3Kα and mTOR, 1 also inhibits phosphorylation of AKT-T308 and p70S6K at low nanomolar concentrations (data not shown). Compound 1 induces a G1 cell cycle arrest and inhibits cell proliferation in a large panel of cell lines, including T47D and BT474 breast cancer lines. [1]

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Inhibition of MAPK and PI3K/mTOR pathways enhances cell growth inhibition in the acquired resistant clones [2]
Although the combination of GSK2118436 and GSK1120212 profoundly inhibited proliferation of the resistant clones, phosphorylation of S6P was not inhibited completely. Because S6P phosphorylation can be induced by activation of the PI3K/mTOR pathway, we evaluated the combination of GSK2118436 or GSK1120212 with Omipalisib/GSK2126458 (PI3K/mTOR inhibitor). All clones displayed modest sensitivity cell growth inhibition by GSK2126458 (Table 1). GSK2126458 treatment of representative resistant clones decreased AKT phosphorylation and had minimal effect on S6P phosphorylation (Fig. 5A). Omipalisib/GSK2126458 in combination with GSK2118436 or GSK1120212 reduced S6P phosphorylation in the resistant clones, whereas GSK2118436 or GSK1120212 alone was sufficient to reduce S6P phosphorylation in A375. The reduction in pS6P with either GSK2118436 or GSK1120212 in combination with GSK2126458 was greater than the reduction observed with the GSK2118436 and GSK1120212 combination. MEK and ERK phosphorylation was similar to treatment with GSK2118436 or GSK1120212 alone. Cleaved PARP and caspase-3/7 activity, indicators of apoptosis, were increased slightly by GSK2126458 in combination with either GSK2118436 or GSK1120212 in clones 16R6-4 and 16R6-2, although basal apoptosis levels were higher in all of the resistant clones compared with A375 (Fig. 5A and data not shown). The addition of GSK2118436 to GSK2126458 enhanced cell growth inhibition (EOSHA >10 ppts) in 5/7 clones with NRAS mutations and the 2 clones harboring MEK1K59del (Table 1). The combination of GSK1120212 and GSK2126458 was synergistic (CI <0.8) in 8/9 clones and enhanced cell growth inhibition (EOSHA >20 ppts) in all 9 clones regardless of NRAS or MEK1 mutation (Table 1). Long-term proliferation assays confirmed the enhancement of growth inhibition by the combination of GSK2118436 or GSK1120212 with GSK2126458 (Fig. 5B). In general, the resistant clones were more sensitive to cell growth inhibition with the combination of GSK2126458 and GSK1120212 at the concentrations used; however, appreciable activity was also observed with 1 μmol/L GSK2118436 and 0.03 μmol/L Omipalisib/GSK2126458. The antiproliferative effect of GSK2118436 in combination with GSK2126458 was not as potent as that observed with the GSK2118436 and GSK1120212 combination, or the GSK1120212 and GSK2126458 combination. Benefits were observed for these combinations in the YUSIT1 GSK2118436–resistant clones, although the combination of GSK2126458 with GSK2118436 or GSK1120212 was moderately synergistic to nearly additive in these clones (Supplementary Table S1).

In a BT474 human tumor xenograft model, Omipalisib/GSK2126458 treatment reduces pAkt-S473 levels in a dose-dependent manner and inhibits tumor growth in a dose-dependent manner at a low dose of 300 μg/kg. The oral bioavailability of GSK2126458 is also good in four preclinical species (mouse, rat, dog, and monkey), and its blood clearance is low.[1]

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In an in vivo setting, Omipalisib/1 exhibited a dose-dependent reduction in pAKT-S473 levels in human BT474 tumors implanted in mice. In the study, designed to measure the magnitude and duration of the pharmacodynamic (PD) response, mice were treated orally with drug, and pAKT levels were determined over the course of 24 h. Following a single 300 μg/kg dose, 1 showed a profound and sustained PD response over the 10 h observation period with pAKT levels returning to those of control by 24 h (Figure 4). Remarkably, the sustained PD response was achieved with very low circulating levels of drug, consistent with the high in vitro potency of 1.[1]

Compound 1/Omipalisib was also evaluated in a BT474 human tumor xenograft growth efficacy model where mice were administered a single oral dose five times per week for 3 weeks. Consistent with inhibition of the PI3K/AKT/mTOR pathway, the drug exhibited dose-dependent tumor growth inhibition (Figure 5). The top dose (3 mg kg−1) was well-tolerated in the study. As reported previously, compound 2 exhibited efficacy in BT474 xenografts following twice daily dosing at 25 mg kg−1. In comparison, compound 1 exhibited similar efficacy at a much lower dose and less frequent administration. [1]

HTRF In vitro Profiling Assays for PI3K Inhibition [1]
The PI3-Kinase profiling assays were developed to measure the compound-dependent inhibition of the alpha, beta, delta, and gamma isoforms of PI3Kin an in vitro catalytic assay. This assay was developed and optimized from a kit produced by Upstate. Briefly, this procedure utilizes a pre-formed HTRF (Homogeneous Time-Resolved Fluorescence energy transfer) complex between four binding partners: 1) biotinylated PIP3, 2) GST tagged pleckstrin homology (PH) domain, 3) Europium labeled anti-GST monoclonal antibody, and 4) StreptavidinAllophycocyanin (APC). The native PIP3 produced by PI 3-Kinase activity displaces biotin-PIP3 from the PH domain, resulting in the dissociation of the HTRF complex and a decrease in the fluorescence signal. The format of this assay is the same for all 4 isoforms of PI3K; the differences lie in the concentration of enzyme used to achieve the most robust signal. The alpha and delta assays are run at 400pM enzyme; the beta assay is at 200pM enzyme and the gamma assay is run at 1nM enzyme. In addition, the alpha, beta and delta assays are run with 150mM NaCl while the gamma assay is run in the absence of NaCl. The ATP concentration is 100uM in the alpha, beta, and delta assays and 15uM ATP in the gamma assay. All reactions are run at 10uM PIP2.

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The Multidrop Combi is used to add 2.5 μL of stop solution (Stop A and Stop B pre-mixed at a ratio of 5:1, respectively) to all wells in order to quench reactions. The quenched reactions are then processed to identify product formation by adding 2.5 μL of detection solution using the Multidrop Combi (Detection mix C, Detection mix A, and Detection mix B combined together in an 18:1:1 ratio, i.e., for a 6000 μL total volume, mix 5400 μL Detection mix C, 300 μL Detection mix A, and 300 μL Detection mix B). Please take note that this solution needs to be prepared two hours before use. The HTRF signal is measured on the Envision plate reader set for 330nm excitation after an hour of dark incubation.

BT474, HCC1954 and T-47D (human breast) are cultured in RPMI-1640 containing 10% fetal bovine serum at 37 °C in 5% CO2 incubator. Prior to assay setup, cells are divided into T75 flasks at a density that results in 70–80% confluence at the time of assay harvest. Trypsin-EDTA 0.25% is used to harvest cells. Utilizing Trypan Blue exclusion staining, cell counts are carried out on cell suspension. Then, cells are plated in 384-well black flat-bottom polystyrene dishes with 1,000 cells per well and 48 μL of culture medium per dish. GSK2126458 is added the following day after all plates have been overnighted at 5% CO2, 37 °C. One plate is given a CellTiter-Glo treatment for a day 0 (t=0) measurement and read as per the instructions below. GSK2126458 is made in 384 well clear bottom polypropylene plates using successive two fold dilutions. 2 μL of these dilutions are added to each well of the cell plates after 4 μL of these dilutions are added to 105 μL of culture media and the solution is mixed. The final DMSO concentration in each well is 0.15%. 72 hours are spent incubating the cells at 37 °C and 5% CO2. Each plate is developed and read 72 hours after being incubated with GSK2126458. Using a volume equal to the cell culture volume in the wells, CellTiter-Glo reagent is added to assay plates. After about 30 minutes of incubation at room temperature and two minutes of shaking, the plates are read using the Analyst GT reader for the chemiluminescent signal. Results are plotted against the concentration of GSK2126458 and expressed as a percentage of the t=0. For GSK2126458, the concentration (gIC50) that inhibits 50% of the cell growth with Y min as the t=0 and Y max as the DMSO control is determined by fitting the dose response with a 4 or 6 parameter curve fit using the XLfit software. For background correction, the value from wells without cells is subtracted from all samples.

Human BT474 tumors implanted in mice.
≤300 μg /kg
Administered via p.o.

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The pharmacokinetics of 1 (free base) were studied following single intravenous and/or oral administration to the male mouse, rat, dog and monkey. The IV and PO solution formulations contained 40% (v/v) PEG-400, 16% (w/v) encapsin in saline and water, respectively. The pH was adjusted to within 3.0-4.0 for the mouse, rat, dog and monkey solutions. Oral bioavailability was estimated using a cross-over study design for the dog and monkey (n = 3). Oral bioavailability in the rat was estimated using crossover (n = 1) and non-crossover (n = 2) designs and a non-crossover serial design was employed in the mouse (n = 2 IV and n = 3 PO). Blood samples were assayed for Omipalisib (GSK2126458, GSK458) using protein precipitation with acetonitrile followed by HPLC/MS/MS analysis employing positive-ion Turbo IonSpray ionization. Blood concentration-time data were analyzed by non-compartmental methods. Mouse and rat data reported as mean ± range. Dog and monkey data reported as mean ± standard deviation. [1]

The pharmacokinetic profile of compound 1/omepalisib was investigated in four preclinical animal models (mice, rats, dogs, and monkeys). The compound showed low plasma clearance and good oral bioavailability (Table 6). In addition, compound 1 showed minimal inhibition of human cytochrome P450 isoenzymes (IC50 > 25 μM for CYP 3A4, 1A2, 2C9, 2C19, and 2D6). [1] Pharmacokinetic analysis of omepalisib [3] The median time to peak concentration (tmax) after a single daily dose ranged from 1 to 4 hours. The mean AUC0-24 hours and Cmax increased substantially proportionally with increasing daily dose from 0.1 mg to 0.4 mg and from 0.75 mg to 3.0 mg, but not across the entire dose range (Supplementary Table S1 and Figure 1A). As expected, due to the accumulation of Omipalisib GSK458, the mean AUC0–12 hours and Cmax after the second dose were generally higher with the twice-daily dosing regimen than with the first dose. The mean duration of drug concentrations >20 ng/mL (target dose level based on preclinical data) was longer with the twice-daily dosing regimen than with the once-daily dosing regimen (21.2 hours with the twice-daily 2 mg regimen versus 14.5 hours with the once-daily 2.5 mg maximum tolerated dose regimen; Figure 1B). Terminal T1/2 and AUC0–>∞ could not be determined due to large AUC extrapolations in over 20% of patients. Pharmacokinetic parameters overlapped between dose groups due to inter-subject variability. These results also highlight the importance of pharmacokinetic/pharmacodynamic data for determining the optimal biological dose in first-in-human trials of targeted anticancer therapies. Pharmacokinetic/pharmacodynamic modeling using mouse BT474 xenografts showed that the mean target serum concentration corresponding to the expected IC67 value of AKT phosphorylation was maintained at >20 ng/mL, ranging from 6.6 to 60 ng/mL, to account for potential conversion differences between mice and humans. Pharmacokinetic data from the daily dosing regimen showed that the target serum concentration >20 ng/mL could not be maintained over 24 hours. Furthermore, significant differences in drug exposure were observed among patients with the once-daily dosing regimen. These two factors may have contributed to the absence of dose- and exposure-dependent effects of Omipalisib/GSK458 in pharmacodynamic analyses under the daily dosing regimen and may have affected the observed antitumor activity. The twice-daily dosing regimen achieved more stable serum concentrations above the target exposure. Whether twice-daily GSK458 can more effectively inhibit the target and enhance antitumor activity requires further clinical evaluation, as pharmacodynamic analyses were almost entirely limited to the once-daily dosing group, and the twice-daily dosing group did not reach the maximum tolerated dose (MTD). [3] GSK458/omepalizib was well tolerated. The incidence of adverse events appeared to be similar in the once-daily and twice-daily dosing groups. Diarrhea was a common clinical event; however, most patients experienced grade 1-2 diarrhea, with only 8% of enrolled patients experiencing grade 3 diarrhea (more than 7 bowel movements per day from baseline). Diarrhea appeared to be self-limiting and could be relieved by temporary discontinuation of the drug; at the time of the last study report, diarrhea had resolved in more than 80% of patients. Hyperglycemia was a class effect of PI3K pathway inhibitors (and a potential pharmacodynamic biomarker), observed in 18% of patients in the study, and was mostly grade 1-2. Hyperglycemia was usually controlled with oral medications (e.g., metformin); initiation of insulin therapy during the regimen was rare. Other class effects of PI3K pathway inhibitors were also observed, including rash and mucositis, both of which were effectively controlled by temporary discontinuation of the drug and/or initiation of topical steroid therapy. It is noteworthy that the effect on mood in this study was not common compared to other PI3K inhibitors (such as BKM120), suggesting that the drug in this study may have differences in blood-brain barrier penetration or off-target differences in other receptor inhibition. [3]

Determining the maximum tolerated dose (MTD) of omepalizib: In the once-daily dose escalation study, a total of 8 dose levels were explored (Table 3). The first dose-limiting toxicity (DLT) (grade 3 diarrhea) occurred in the once-daily 1.5 mg dose group. This group was expanded without further dose-limiting events. Three DLTs (all grade 3 diarrhea) occurred in the once-daily 3 mg dose group, therefore this dose was determined to be the intolerable dose (NTD). Subsequently, patients were treated with once-daily 2 mg and 2.5 mg doses, respectively, without any DLTs observed, thus determining the MTD of the once-daily dosing regimen to be 2.5 mg. Because the duration of omepalizib/GSK458 drug concentrations above the target range was observed under the daily dosing regimen, a twice-daily dose escalation study was initiated with an initial dose of 0.75 mg twice daily, and 5 dose levels were studied (Table 3). No dose-limiting toxicities (DLTs) were observed at the twice-daily 2 mg dose level. One of three patients experienced DLT (grade 3 fatigue + grade 3 rash) at the twice-daily 2.5 mg dose level; however, no further patients received treatment at this dose level due to the decision to discontinue the GSK458 monotherapy trial; therefore, the maximum tolerated dose (MTD) for twice-daily administration could not be determined. Omipalizib Safety Results The most common adverse events (of any severity) in the study were fatigue (45%), diarrhea (45%), nausea (42%), decreased appetite (30%), and vomiting (26%) (Table 4). The most common ≥ grade 3 adverse events included diarrhea (8%), hyperglycemia (>250 mg/dL; 6%), and rash (5%). Nine patients (5%) experienced treatment-related serious adverse events, including four patients with diarrhea. Diarrhea appeared to be an intermittent, self-limiting event for most patients, with symptom relief in 82% of patients. Rash occurred in 21 patients (12%), with most experiencing only one rash (81%). The most common rash type was maculopapular; acne-like rash was rare (2 cases). Hyperglycemia occurred in 37 patients (22%), mostly grade 1 or 2, and most patients (92%) did not require dose adjustment. Cardiotoxicity was mild, with only 2 patients (1%) experiencing a post-baseline decrease in ejection fraction to below the lower limit of normal and a decrease of more than 10% from baseline. No significant effect on mood was observed. No treatment-related grade 5 adverse events occurred.

[1]. Discovery of GSK2126458, a Highly Potent Inhibitor of PI3K and the Mammalian Target of Rapamycin. ACS Med. Chem. Lett. 2010, 1, 1, 39–43

[2]. Combinations of BRAF, MEK, and PI3K/mTOR inhibitors overcome acquired resistance to the BRAF inhibitor GSK2118436 dabrafenib, mediated by NRAS or MEK mutations. Mol Cancer Ther. 2012 Apr;11(4):909-20.

[3]. First-in-Human Phase I Study of GSK2126458, an Oral Pan-Class I Phosphatidylinositol-3-Kinase Inhibitor, in Patients with Advanced Solid Tumor Malignancies. Clin Cancer Res. 2016 Apr 15;22(8):1932-9.

Omipalisib belongs to the quinoline class of compounds, with its quinoline ring substituted at positions 4 and 6 by pyridin-4-yl and 5-[(2,4-difluorophenyl-1-sulfonyl)amino]-6-methoxypyridin-3-yl, respectively. It is a highly potent PI3K and mTOR inhibitor developed by GlaxoSmithKline and has previously undergone Phase I human clinical trials for the treatment of idiopathic pulmonary fibrosis and solid tumors. Omipalisib has multiple functions, including autophagy induction, EC 2.7.1.137 (phosphatidylinositol 3-kinase) inhibition, mTOR inhibition, antitumor drug, radiosensitizer, and anticoronavirus drug. It belongs to the quinoline, difluorobenzene, sulfonamide, aromatic ether, pyridine, and pyridazine classes of compounds. Omipalisib has been used in clinical trials for the treatment of cancer, solid tumors, and idiopathic pulmonary fibrosis. Omepaliximab is a small-molecule pyridine sulfonamide phosphatidylinositol 3-kinase (PI3K) inhibitor with potential antitumor activity. Omepaliximab binds to and inhibits PI3K in the PI3K/mTOR signaling pathway, which may trigger the translocation of cytoplasmic Bax to the outer mitochondrial membrane, increasing mitochondrial membrane permeability and inducing apoptosis. Bax is a member of the pro-apoptotic protein Bcl2 family. PI3K is often overexpressed in cancer cells and plays a crucial role in tumor cell regulation and survival. Phosphatidylinositol 3-kinase α (PI3Kα) is a key regulator of cell growth and transformation, and its signaling pathway is the most commonly mutated pathway in human cancers. Mammalian target of rapamycin (mTOR) is a class IV PI3K protein kinase and a core regulator of cell growth; mTOR inhibitors are believed to enhance the antiproliferative effect of PI3K/AKT pathway inhibition. 2,4-Difluoro-N-{2-(methoxy)-5-[4-(4-pyridazinyl)-6-quinolinyl]-3-pyridyl}benzenesulfonamide (Omipalisib/GSK2126458, 1) has been identified as a highly potent, orally bioavailable PI3Kα and mTOR inhibitor, demonstrating in vivo activity in both pharmacodynamic and tumor growth efficacy models. Compound 1 is currently undergoing human clinical trials for the treatment of cancer. [1]

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In summary, we report the discovery of compound 1/Omipalisib, a novel PI3K/AKT/mTOR signaling pathway inhibitor with picomolar activity against PI3Kα and mTOR. Compound 1 has demonstrated significant efficacy in both mechanistic and antiproliferative cell assays. Compound 1 also exhibits excellent in vivo activity, particularly in maintaining pharmacodynamic effects at very low circulating drug concentrations. Inhibition of the PI3K/AKT/mTOR pathway is expected to have beneficial effects on cancer treatment, and compound 1 has entered a phase I open-label dose-escalation study for patients with solid tumors or lymphomas. [1]

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Recent clinical trial results of the BRAF inhibitors GSK2118436 (dabrafenib) and PLX4032 (vemurafenib) have shown encouraging response rates; however, the duration of response is limited. In order to determine the determinants of acquired resistance to GSK2118436 and strategies to overcome resistance, we isolated GSK2118436-resistant clones from the A375 BRAF (V600E) and YUSIT1 BRAF (V600K) melanoma cell lines. These clones also showed reduced sensitivity to the allosteric mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitor GSK1120212 (trametinib). Genetic characterization of these clones revealed in-frame deletions of MEK1 (MEK1(K59del)) or NRAS mutations (NRAS(Q61K) and/or NRAS(A146T)), with or without MEK1 (P387S), in the BRAF(V600E) background; and NRAS(Q61K) in the BRAF(V600K) background. Stable knockdown of NRAS using short hairpin RNA partially restored the sensitivity of mutant NRAS clones to GSK2118436, while expression of NRAS(Q61K) or NRAS(A146T) in A375 parental cells decreased their sensitivity to GSK2118436. Similarly, expression of MEK1(K59del) (but not MEK1(P387S)) decreased the sensitivity of A375 cells to GSK2118436. The combination of GSK2118436 and GSK1120212 effectively inhibited the cell growth of drug-resistant clones, reduced ERK phosphorylation levels, decreased cyclin D1 expression, and increased p27(kip1) protein expression. Furthermore, the combination of GSK2118436 or GSK1120212 with the phosphatidylinositol 3-kinase/mTOR inhibitor Omipalisib/GSK2126458 enhanced the inhibitory effect on the cell growth of these clones and reduced S6 ribosomal protein phosphorylation levels. Our results indicate that NRAS and/or MEK mutations are pathogenic factors for BRAF inhibitor resistance in vitro, and that the combination of GSK2118436 and GSK1120212 can overcome this resistance. Moreover, these drug-resistant clones responded to the combination of GSK2126458 with GSK2118436 or GSK1120212. Clinical trials are currently underway or planned to test these combination therapy regimens. [2] Objective: Omipalizib/GSK2126458 (GSK458) is a potent PI3K (α, β, γ, and δ) inhibitor with broad antitumor activity as demonstrated in preclinical studies. We conducted a first-in-human Phase I study in patients with advanced solid tumors. Materials and Methods: Patients were given GSK458 orally once or twice daily in a dose-escalation design to determine the maximum tolerated dose (MTD). An extended cohort study evaluated pharmacodynamics, pharmacokinetics, and clinical activity in a histologically and molecularly defined cohort. Results: 170 patients received doses ranging from 0.1 to 3 mg once or twice daily. Five patients experienced dose-limiting toxicities (grade 3 diarrhea, n=4; fatigue and rash, n=1) (3 of whom were in the 3 mg/day dose group). The maximum tolerated dose (MTD) was 2.5 mg/day (the MTD for twice-daily dosing is undefined). The most common ≥ grade 3 treatment-related adverse events included diarrhea (8%) and rash (5%). Pharmacokinetic analysis showed that twice-daily dosing prolonged the duration of drug exposure above the target level. Fasting insulin and glucose levels increased with increasing dose and exposure to Omipalisib/GSK458. Durable objective response rates (ORs) were observed in multiple tumor types (sarcoma, renal cell carcinoma, breast cancer, endometrial cancer, oropharyngeal cancer, and bladder cancer). Response rates were not associated with PIK3CA mutations (OR rate: wild-type 5% vs. mutant 6%). Conclusion: Although the maximum tolerated dose (MTD) of GSK458 is 2.5 mg once daily, twice-daily dosing may prolong the duration of target inhibition. Fasting insulin and glucose levels can serve as pharmacodynamic biomarkers of drug exposure. Some patients achieved durable remission; however, PIK3CA mutation is neither a necessary condition nor a predictor of remission. Combination therapy strategies and novel biomarkers may be needed to optimize PI3K targeted therapy. [3]

C25H17F2N5O3S

505.4960

505.102

C, 59.40; H, 3.39; F, 7.52; N, 13.85; O, 9.50; S, 6.34

1086062-66-9

1086062-66-9

25167777

light yellow solid powder

1.5±0.1 g/cm3

715.6±70.0 °C at 760 mmHg

187-189℃

386.6±35.7 °C

0.0±2.3 mmHg at 25°C

1.660

3.81

1

10

6

36

833

0

S(C1C([H])=C([H])C(=C([H])C=1F)F)(N([H])C1=C(N=C([H])C(=C1[H])C1C([H])=C([H])C2C(=C(C([H])=C([H])N=2)C2=C([H])N=NC([H])=C2[H])C=1[H])OC([H])([H])[H])(=O)=O

CGBJSGAELGCMKE-UHFFFAOYSA-N

InChI=1S/C25H17F2N5O3S/c1-35-25-23(32-36(33,34)24-5-3-18(26)12-21(24)27)11-17(13-29-25)15-2-4-22-20(10-15)19(7-8-28-22)16-6-9-30-31-14-16/h2-14,32H,1H3

2,4-difluoro-N-[2-methoxy-5-(4-pyridazin-4-ylquinolin-6-yl)pyridin-3-yl]benzenesulfonamide

Omipalisib; GSK2126458; GSK 2126458; 2,4-difluoro-N-(2-methoxy-5-(4-(pyridazin-4-yl)quinolin-6-yl)pyridin-3-yl)benzenesulfonamide; 2,4-difluoro-N-[2-methoxy-5-(4-pyridazin-4-ylquinolin-6-yl)pyridin-3-yl]benzenesulfonamide; GSK-212; GSK-2126458

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ~100 mg/mL (~197.8 mM)
Water: <1 mg/mL
Ethanol: <1 mg/mL

Solubility in Formulation 1: ≥ 2.5 mg/mL (4.95 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 1%DMSO+30% polyethylene glycol+1%Tween 80: 18mg/mL

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 (Please use freshly prepared in vivo formulations for optimal results.)