Filanesib (ARRY 520) is a selective inhibitor of kinesin spindle protein (KSP, IC50 = 6 nM) with potent anti-proliferative activity.

KSP:6 nM

Filanesib shows anti-proliferative activity in multidrug-resistant cell lines including HCT-15, NCI/ADR-RES and K562/ADR with EC50 values of 3.7, 14 and 4.2 nM respectively. Filanesib (10 nM) blocks mitosis with the monopolar spindle structure typical of KSP inhibition as judged by both increased phosphorylation of histone H3 and the accumulation of cyclin B1 in four cells [2]. Filanesib (1 nM) induces a significant G2M cell cycle block in OCI-AML3 cells at 24 hours [4].

Filanesib (10, 15, 20, 30 mg/kg, i.p.) is active in UISO-BCA-1 xenograft, and also superior to paclitaxel in mice bearing subcutaneous HT-29, HCT-116, MDA-MB-231 and A2780 xenografts. Filanesib is superior to docetaxel in the androgen receptor-negative prostate cancer xenograft model PC-3 [1]. RPMI 8226 tumor xenografts are particularly sensitive to low doses of Filanesib (12.5 mg/kg, i.p.) [2]. Filanesib significantly inhibits tumor growth in HL60 and MV4-11 xenografts of SCID mice at concentrations of 27 mg/kg and 20 mg/kg, respectively [4].

Exponentially growing cells (0.4×10^6/mL) are treated with ARRY-520 for up to 48 hours. For combination, HL-60 and HL-60Bcl-2 cells (0.4×10^6/mL) are incubated with ARRY-520, ABT-737, or both for up to 96 hours. DMSO is used as the control agent. Apoptosis is estimated by flow cytometry measurements of phosphatidylserine with the Annexin-V-FLUOS Staining Kit. Membrane integrity is simultaneously assessed by 7-amino-actinomycin D (7-AAD). To measure changes in the mitochondrial membrane potential (MMP), cells are loaded with CMXRos (300 nM) and MitoTracker Green (500 nM) for 1 hour at 37°C. The loss of MMP is then assessed by measuring CMXRos retention while simultaneously adjusting for mitochondrial mass [4].

Subcutaneous tumor xenografts are allowed to grow to a volume of 250-350 mm3. The mice are randomized into groups of 3-4 based on tumor size and are given a single dose of ARRY-520 i.p. At various time-points after administration of the drug, the mice are euthanized by CO2 inhalation and the tumors excised and placed in 10% neutral buffered formalin. The formalin-fixed tumors are processed and paraffin-embedded by standard procedures. Spindle morphology is analyzed by staining tumor sections for α-tubulin, and apoptosis is analyzed by TUNEL stain. Monopolar/abnormal spindles and TUNEL positive (apoptotic) cells are counted in three ×40 fields from each sample, analyzed using algorithms developed in software [1].