Prexasertib HCl (LY2606368)

In nonclinical studies, LY2606368 induced DNA damage as measured by replication catastrophe and increases in pH2A.X, a marker of double-stranded DNA breaks^[1]. Treatment of cells with LY2606368 results in the rapid appearance of TUNEL and pH2AX-positive double-stranded DNA breaks in the S-phase cell population. In a functional assay, LY2606368 potently abrogated the G2–M checkpoint activated by doxorubicin in p53-deficient HeLa cells with an EC50 of 9 nmol/L. LY2606368 was broadly antiproliferative with IC50 values typically <50 nmol/L in the most sensitive cell lines with a minority of cell lines showing considerable resistance with IC50's >1,000 nmol/L. LY2606368 requires CDC25A and CDK2 to cause DNA damage^[2].

HeLa cells were plated onto T25 flasks and allowed to recover for 24 hours. LY2606368 was then added to give final concentrations of 33 or 100 nmol/L. In some experiments, 20μmol/L Z-VAD-FMK was included during the drug treatment. Cells were treated for 12 hours, and during the last 2 hours, colchicine was added to 1 μg/mL. Fixation of nuclei for metaphase spreads was done following the method of Bayani and Squire. Chromosome spreads were done. A 12-μL volume of cell suspension in 3:1 methanol/acetic acid fixative was dropped from a height of 3 cm onto dry glass slides or coverslips. The slides were then heated for 45 seconds on a 43°C metal block, before being removed to allow drying to complete at room temperature. Coverslips were mounted on slides with Vectashield Hard Set mounting medium with DAPI. Slides were examined with a Leica DMR fluorescence microscope and images were captured using a SPOT RT3 Slider camera.

LY2606368 inhibited tumor growth in cancer xenografts as monotherapy and in combination with other agents^[1]. In an orthotopic SKOV3 ovarian cancer model, LY2606368 was shown to inhibit the growth of primary tumors and significantly reduce the incidence of metastases and ascites accumulation. LY2606368 also demonstrated efficacy in an SW1990 orthotopic pancreatic cancer model resulting in a 92% inhibition of primary tumor growth and the elimination of metastases to the lymphnode, spleen, and intestine^[3].