Protein STK17A or DRAK1 is a serine/threonine kinase that belongs to the death-associated protein kinase family (DAPK). This family is comprised of five members: DAPK1, DAPK2, DAPK3, DRAK1 and DRAK2, being the last two the least studied. As part of our efforts to find inhibitors for understudied kinases, we recently disclosed a high quality chemical probe for DRAK2 (compound UNC-AP-194, smiles string O=C(O)CSC1=C2C(C=C(C3=CC(C=CC=C4)=C4S3)S2)=NC=N1). Following these lines, DRAK1 is our next target, for which non selective and potent inhibitors have been found yet. DRAK1 overexpression has been linked to head and neck squamous cell carcinoma and glioblastoma multiforme.1
The starting point to look for inhibitors was our very own Kinase Chemogenomic Set (KCGS). From here, compounds annotated as DRAK1 inhibitors with Kd <100 nM were screened for cell potency in a target engagement assay in HEK293 cells using NanoBRET technology, Table 1. This assay was performed by our colleague Julie Pickett.
Table 1. Selected DRAK1 inhibitors from KCGS.
| Entry | Compound ID | DRAK1 IC50 (uM) |
| 1 | GSK2250882 | 5.8 |
| 2 | GSK2283293 | 3.7 |
| 3 | GSK2283293-F1 | 1.0 |
| 4 | GSK2283293-F2 | >10.0 |
| 5 | GKS2298859 | 7.5 |
| 6 | GKS2298859-F1 | 5.4 |
| 7 | GKS2298859-F2 | >10.0 |
| 8 | JNK-IN-7 | 7.8 |
Most compounds shown cell potency greater than 1 uM and even two resulted inactive. But more interesting is to see the results for GSK2283293 and GKS2298859 (entries 2 & 5) which were screened as racemates showing IC50 of 3.7 and 7.5 uM respectively, then when their enantiomers were screened individually, one of them resulted completely inactive while the other one shown inhibition activity (e.g., GSK2283293-F1 vs GSK2283293-F2 and GKS2298859-F1 vs GKS2298859-F2).
GSK2250882, GSK2283293 and GKS2298859 belong to the family of 3-aminoindazoles, their chemical structures are shown in Figure 1.
Figure 1. Selected aminoindazoles from KCGS.
As mentioned, most compounds in Table 1 have Kd <100 nM for DRAK1, however this strong biding potency did not translate into a good cell potency and we do not know the reasons yet. On the other hand, it is clear that different stereoisomers have totally different activity against DRAK1 or in other words for compounds with stereocenters, one enantiomer is active and the other one is not. One of the next steps includes determination of the absolute stereochemistry for enantiomers of GSK2283293 and GKS2298859, then this information will be used as a starting point to synthesized other DRAK1 inhibitors with the right stereochemistry to improve cell potency in the aminoindazoles series.
References
- Farag, A. K.; Roh, E. J. Res. Rev. 2018, 1-37.