In vitro activity: AZD6738 is an orally available morpholino-pyrimidine-based, and selective inhibitor of the ATR (ataxia telangiectasia and rad3 related) kinase with IC50 of 1 nM. ATR is a serine/threonine protein kinase that is upregulated in various cancer cells, it plays a key role in DNA repair, cell cycle progression, and survival; it is activated by DNA damage caused during DNA replication-associated stress. AZD6738 has potential antineoplastic activity. Upon administration by oral route, AZD6738 selectively inhibits ATR activity by blocking the downstream phosphorylation of the serine/threonine protein kinase CHK1, which prevents ATR-mediated signaling, and results in the inhibition of DNA damage checkpoint activation, disruption of DNA damage repair, and the induction of tumor cell apoptosis. In an in vitro model capable of reproducing, over 70 hours after the initiation of the treatment with AZD6738, the γH2AX signal was sustained. Stalled replication forks may collapse the formation of DNA double stranded breaks and the activation of the ataxia telangiectasia mutated (ATM) kinase. As a single agent across cancer cell line panels, AZD6738 is active. In cell lines lacking ATM-pathway, the sensitivity of AZD6738 was enhanced.

Kinase Assay: AZD6738 is a potent inhibitor of ATR kinase activity with an IC50 of 0.001 μM against the isolated enzyme and 0.074 μM against ATR kinase-dependent CHK1 phosphorylation in cells.

Cell Assay: AZD6738 is dissolved in DMSO at 30 mM and diluted in DMSO to desired working concentrations. The final DMSO concentration in media for all conditions and controls is 0.1% for AZD6738 dose response experiments, 0.05% for AZD6738 + chemotherapy viability experiments, and 0.025% for all experiments involving 0.3 μM and 1.0 μM doses of AZD6738.