A-485

This molecule showed good effect to block H3K27Ac in cells. The compound works well in cell and showed great potency in multiple cell lines. This probe is a great chemical tool to study biological function of EP300 and CBP.

Since the block of both EP300 and CBP function, this probe might introduce some toxicity in in vivo study. The dosage will need to be tuned down for the in vivo study. The overall toxicity profiling in mouse is not fully established.

Attention should be paid to the difference between the cellular activity (H3K27Ac) EC50 of 73 nM and the recommended cell assay use concentration of 800 nM. This difference of approximately 10-fold indicates that there is a high risk of non-target related activity at concentrations beyond 800 nM. As a result, cell viability and related read-outs at concentrations beyond 1 uM should not be interpreted as target mediated events without validation using an orthogonal inhibitor.

Further understanding of the in vivo PK/PD relationship is important to enhance confidence in this probe as a reliable tool for in vivo studies.

A-485 is a well optimized inhibitor of the acetyltransferase EP300/CREBBP.  Its on-target activity is well verified in several peer-reviewed manuscripts. Its cell-based activity versus its target occurs at reasonable ranges. It elicits various phenotypes at similar concentrations.  To establish an in vivo response (decrease in tumour volume) A-485 must be dosed at a relatively high concentration (100 mg/kg) daily for 21 days. There are other reported EP300/CREBBP inhibitors including CPI-703 and CPI-637. Another EP300/CREBBP inhibitor (CCS-1477) has entered clinical evaluation and has been reported on at several conferences but, to date (July 2020), no peer-reviewed publication is available to allow for comparison with A-485.  Therefore, A-485 remains the best-in-class agent for interrogation of this target.