Cell experiment:

Cell line growth-death assays are performed with a few modifications. Briefly, cells are seeded into 384-well or 96-well plates at a density optimized for 6 days of growth. The following day, T0 measurements are taken using CellTiter-Glo, CellTiter-Fluor, or CyQuant Direct. Plates are read on an Envision, Safire 2, or SpectraMax Gemini EM plate reader. Remaining plates are treated with DMSO or a titration of GSK1324726A. Cells are incubated for 6 days and developed. Results are plotted as a percentage of the T0 value, normalized to 100%, versus concentration of compound. A 4-parameter equation is used to generate concentration response curves. Growth IC50 (gIC50) values are calculated at the mid-point of the growth window (between DMSO and T0 values). Ymin-T0 values are calculated by subtracting the T0 value (100%) from the Ymin value on the curve, and are a measure of net population cell growth or death[1].

Animal experiment:

Mice[1] CHP-212 (1×107) or SK-N-AS (5×106) cells in 100% matrigel are implanted subcutaneously into the right flank of approximately 9 week old female nude (Crl:CD-1-Foxn1 nu) mice. Tumors are measured with calipers and randomized using stratified sampling according to tumor size into treatment groups of 10 mice. GSK1324726A in vehicle or vehicle alone is administered orally by individual body weight at 10mls/kg. Mice are weighed and tumors are measured with calipers twice weekly, and mice are observed daily for any adverse treatment affects. Mice are euthanized using CO2 inhalation according to AVMA guidelines after two consecutive tumor measurements greater than 2500mm3, or if body weight loss greater than 20% is observed. For mouse pharmacodynamic studies, mice are euthanized as described above. Tumors are harvested from euthanized mice and placed in RNAlater for RNA isolation. Blood is collected after euthanasia via cardiac puncture.Rats[2] Male CD rats (253-283 g) are surgically prepared with implanted cannulae in the femoral vein (for GSK1324726A administration) and jugular vein (for blood sampling). Each rat receives Duphacillin (100 mg/kg s.c.) and Carprofen (7.5 mg/kg s.c.) as a pre-operative antibiotic and analgesic respectively. Each rat is allowed to recover for at least 2 days prior to dosing. Rats have free access to food and water throughout. Rat PK studies are conducted as a crossover design over 2 dosing occasions, with 3 days between dose administrations. Serial blood samples are taken (via indwelling jugular cannula) up to 26 h post dose administration on both dosing occasions. On study day 1, n=3 male rats each receives a 1 h intravenous infusion of GSK1324726A formulated in DMSO and 10% (w/v) KleptoseTM in saline (2%:98%) at a concentration of 0.2 mg/mL and the dose is filtered using a ca. 0.2 μm syringe filter unit. GSK1324726A is administered as a 1 h i.v. infusion at 5 mL/kg/h to achieve a target dose of 1 mg/kg. On study day 2, the same three rats each receives an oral administration of GSK1324726A suspended in 3% Pharmacoat 603/0.2% Sodium Lauryl Sulphate (w/v) aq. at a concentration of 0.6 mg/mL administered by gavage at 5 mL/kg to achieve a target dose of 3 mg/kg. At the end of the study the rats are euthanised by administration of sodium pentobarbital through the jugular vein cannula.

GSK1324726A is a selective small molecule inhibitor of BET proteins with IC50 values of 41nM, 31nM and 22nM, respectively for BRD2, BRD3 and BRD4 [1].

GSK1324726A competes with histone H4 peptides for binding to the bromodomains of the BET proteins. It notably inhibits cell growth in neuroblastoma cell lines with a median GI50 value of 75nM. And it is also found to cause some level of net cell death. The mechanism of this is that GSK1324726A induces cytotoxicity in these cell lines. Treatment of GSK1324726A results in an induction of G1 arrest in SK–N-AS, SK–N–SH and CHP-212 cell lines. Meanwhile, caspase 3/7 induction is observed in SK–N–SH and CHP-212 cell lines. In mice bearing the neuroblastoma xenografts, GSK1324726A also shows the potency of inhibiting tumor growth [1].

References:
[1] Wyce A, Ganji G, Smitheman KN, Chung CW, Korenchuk S, Bai Y, Barbash O, Le B, Craggs PD, McCabe MT, Kennedy-Wilson KM, Sanchez LV, Gosmini RL, Parr N, McHugh CF, Dhanak D, Prinjha RK, Auger KR, Tummino PJ. BET inhibition silences expression of MYCN and BCL2 and induces cytotoxicity in neuroblastoma tumor models. PLoS One. 2013 Aug 23;8(8):e72967.