Lung cancer remains a major cause of cancer death in the United States and world-wide. Therapies targeted to tumor-specific genomic alterations may hold the most promise for the future, yet no one has successfully leveraged the most commonly mutated gene in lung cancer, TP53. We have taken a synthetic lethal approach, aiming to identify small molecules that are specifically lethal to TP53 mutant cancer cells. We screened a library of 2000 small molecules for cytotoxic effects in TP53 mutant and wild-type lung adenocarcinoma cell lines and identified one compound, CID 2874250, which selectively killed the TP53 mutant cell line. In a panel of thirty-two cancer cells lines CID 2874250 was very potent (EC50 < 20 nM) against a subset of TP53-mutant (or functionally inactive) cells, including the H1563, H2122, H1734, and HeLa cell lines. The compound was inactive against the remaining cell lines, including immortalized but nontumorigenic cell lines. Separation of enantiomers demonstrated that one enantiomer was responsible for the observed cellular activity. Commercially available analogs of CID 2874250 provided limited SAR.
Synthetic chemistry established the absolute stereochemistry of the active enantiomer of CID 2874250. Medicinal chemistry efforts created a library of approximately fifty analogs which were tested against sensitive HeLa cells (TP53 mutant) and insensitive A549 cells (TP53 wild type). Activity was improved with these highly soluble, low molecular weight compounds. Undesirable groups, e.g a nitro group, were removed, and metabolic stability was increased. The more active analogs, including the probe ML379, displayed low nM activity in a larger panel of TP53 mutant cell lines. Activity was observed in a murine xenograph experiment.
The initial lead, CID 2874250, significantly inhibited only PDE3 isoforms in a PDE panel. An affinity resin with an analog pulled down predominantly PDE3A from lysed HeLa cells. These results suggest a hitherto unknown role for PDE3 in certain cancer cells.