Selective targeting of the inactive state of hematopoietic cell kinase (Hck) with a stable curcumin derivative.

Hck, a Src family nonreceptor tyrosine kinase (SFK), has recently been established as an attractive pharmacological target to improve pulmonary function in COVID-19 patients (Treon et al., Blood, 2020). Hck inhibitors are also well known for their regulatory role in various malignancies and autoimmune diseases (Ashleigh et al., Oncotarget,2015). Previous report shows that binding of curcumin to active conformation of DYRK2 at sub nanomolar range makes it an excellent DYRK-2 inhibitor(Banerjee et al., PNAS,2018), but curcumin's fate is tainted by its instability in the cellular environment and its nonspecific binding nature(Kathryn et al., J. Med. Chem.,2017). Besides, the planar symmetry makes curcumin less druggable toward asymmetric binding pockets such as kinases (Knight et al., Chem. Biol. 2005). small molecules targeting the inactive states of a kinase are desirable to reduce promiscuity (Hanson et al., Chembiol., 2019). Here, we show that functionalization of the 4-arylidene position of the fluorescent curcumin scaffold with an aryl nitrogen mustard provides a stable Hck inhibitor which binds specifically to the inactive conformation of Hck, similar to type-II kinase inhibitors that are less promiscuous. Moreover, the lead compound showed no inhibitory effect on two other kinases (DYRK2 and Abl) which can be explained by difference in p-loop dynamics between Abl and src family kinases. We demonstrate that the cytotoxicity may be mediated via inhibition of the SFK signalling pathway in triple-negative breast cancer and murine macrophage cells. Our data suggest that curcumin is a modifiable fluorescent scaffold to develop selective kinase inhibitors by remodelling its target affinity and cellular stability.