Phenotype Screening for G2/M Checkpoint Abrogation
The unique dependency of most cancer cells on the G2/M checkpoint for survival after sustaining DNA damage makes it an attractive target for selectively killing cancer cells. Various cytotoxic drugs like Cisplatin and Bleomycin damage tumor-cell DNA and arrest the cells at the G2/M checkpoint.
CanBas has developed a proprietary phenotypic screen using tumor cells treated with Cisplatin. Tumor cells with an intact G2/M checkpoint will arrest and accumulate at the end of G2 just before mitosis. Using tumor cell-cycle distribution patterns, CanBas screens for compounds that abrogate the G2/M checkpoint, allowing tumor cells to pass through without accumulation in G2.
As shown in the figures below, treating MiaPaca2 cells (pancreatic cancer) with cisplatin increased number of cells in G2/M compared to untreated cells. The addition of CBP501, CanBas’ lead G2/M abrogator, allowed damaged tumor cells through the G2/M checkpoint without repairing damaged DNA Normal cells (HUVEC, human umbilical vein endothelial cells) treated with cisplatin were not affected because an intact G1 allowed repair damaged DNA before progressing into the S phase (DNA replication) of the cell cycle. By definition, compounds identified in this screen are specific for tumor cells, inasmuch as normal cells are able to repair damaged DNA at G1.
CanBas’ core technology includes its proprietary cell cycle phenotype-based screening platform (Issued Patent: US 6,881,575 B1; EP 1 218 494 B1) that efficiently identifies compounds with cancer cell-selective cytotoxicity when combined with DNA damaging treatment. This platform has been validated by the successful identification of CBP501, which has been shown in human clinical trials to enhance anti-tumor activity of cisplatin without increasing adverse effects. The small molecule CBS9106 in our pipeline was similarly identified and optimized through a modified version of this phenotype screening platform, as was our CBS2400 series.