P4B

The chemical probe is a PROTAC (PROteolysis Targeting Chimera) targeting BRAF. In addition to its key role in MAPK signalling and as a drug target, BRAF has interesting scaffolding functions. Therefore, there is a great need for agents that target both the enzymatic as well as the scaffold function of BRAF. Both the active PROTAC (P4B) and a negative control P4BMe have been developed. The negative control inactivates E3 binding (cereblon) through the well-established N-methylation of the gulteramide ring. The developed PROTAC degrades BRAF (Dmax = 76%; DC50 = 15 nM) and induces apoptosis more efficiently than the parent compound. Selectivity was assessed by proteomics using A375 melanoma cells after exposure to 200 µM P4B, P4BME or DMSO for 24 hours. Several targets were observed to be up- and down-regulated (Supplementary Data). I suspect that 200 µM is a typo, as it is unlikely that the PROTAC was soluble at such a high compound concentration. Also, the time point chosen (24h) is quite late, suggesting that toxicity may have contributed to the altered expression levels. P4B and the control P4BMe are well characterised. Several other BRAF PROTACs are now commercially available, including the VHL-based degrader SJF-0628. Therefore, due to the inherent context dependency of PROTACs, it would be advisable to also use an orthogonal PROTAC (such as SJF-0628) together with P4B/P4BMe to study the role of BRAF and its oncogenic mutants in cellular systems.

This is a compound I recommend as chemical probe. Degradation of BRAF was not complete at an early time point, but reached it's maximum over ~41 h .