Bone morphogenetic proteins (BMPs) are important regulators of embryonic development and stem cell fate decisions.

In human ESCs, BMP4 promotes cell differentiation, so that maintenance of human ESC self-renewal requires BMP signaling inhibition.

Once committed to differentiating, BMPs promote the commitment of ESCs to the mesendoderm germ layer. These BMP-induced mesendoderm cells can further differentiate into multiple cell lineages, including cardiac, hematopoietic, and hepatic cells.

Recently, several small molecules activate or synergize with the BMP pathway, such as SVAK-3, SVAK-12, KM11073, A1. They enhance BMP2-induced early osteoblast marker expression.

However, most of those compounds show relatively low activity and are not able to induce the generation of mature osteoblasts, which limits their application to modulate BMP signaling. that can be used in stem cell differentiation. Thus, It extremely urgent to identify efficient BMP activators or sensitizers.

In this article, we will introduce a potent dual checkpoint kinase Chk1 and WEE1 inhibitor as a chemical BMP sensitizer, PD407824.

In vitro, in C2C12 myoblasts, PD407824 can sensitize C2C12 myoblasts to BMP4-induced activation of BMP signaling. DMSO + BMP4 (10 ng/ml ) increases endogenous Id2 gene transcript levels, while PD407824 + BMP4 treatment increased the Id2 transcript levels more than 10 fold.

As we all know,  BMPs are key drivers of bone formation, and previous studies indicate that BMP treatment can reprogram C2C12 myoblasts to osteoblasts. In this article, BMP4 (10 ng/ml) shows strong induction of ALK expression but is not sufficient to block myogenesis.
PD407824 itself is not sufficient to induce ALK expression or block myogenesis. However,  PD407824 (1 μM)+BMP4 (3 ng/ml)  induces high levels of ALK and completely lost the capacity to form myotubes.

In conclusion, PD407824 sensitizes cells to BMP4-induced upregulation of BMP pathway target genes, including Id1 and Id2. More importantly, PD407824 cooperates with BMP4 protein when added to ESCs during differentiation towards mesoderm or cytotrophoblast stem cells.

Feng L, et al.Cell Rep. 2016 May 31;15(9):2063-75.