In vitro activity: PTC-209 inhibits both the UTR-mediated reporter expression and endogenous BMI-1 expression in human colorectal HCT116 and human fibrosarcoma HT1080 tumor cells. PTC-209 decreases colorectal tumor cell growth in a BMI-1-dependent way. In addition, PTC-209 impairs colorectal cancer-initiating cells (CICs) through irreversible growth inhibition.

Kinase Assay: HEK293 cells are transfected with a GEMS reporter vector that contains the luciferase open-reading frame flanked by and under post-transcriptional control of the BMI-1 5′ and 3′ UTRs. The resulting stable cells (F8) are treated with PTC-209 or vehicle control overnight, and then luciferase reporter activity is determined using Bright-Glo assays. The assays are run in triplicate for each point, and the percentage of inhibition was calculated against vehicle control.

Cell Assay: To determine whether pretreatment with the inhibitor affects tumor cell growth, cells are plated with the inhibitor for 4 d in vitro and plated in limiting doses in vitro without adding further inhibitor. Trypan blue exclusion is used to count viable cells. The in vitro sphere-initiating cell frequency is calculated after inhibitor treatment by evaluating the number of wells containing spheres. For the experiments where LDAs are set up following recovery of PTC-209 treated cells, 6-well plates were seeded with 1E6 cells per well and incubated overnight. Cells are subsequently treated for 4 d in triplicate with either DMSO vehicle or PTC-209 (0.01, 0.1, 1 and 10 μM). Drug treatments are washed off and 4 mL fresh suspension medium added to all wells. To assess cell viability following the 4 d treatment window, cells are trypsinized and counted at 0, 24, 72 and 120 h after removal of the drug. Long-lasting effects of the drug treatment on sphere-forming ability are assessed by plating LDAs (50,000, 10,000, 1,000,100, 10 and 1 cell per well) using the cells obtained 120 h after the 4-d drug treatment.

Nat Med. 2014 Jan;20(1):29-36.