MPS1-IN-1

While MPS1-IN-1 is a relatively selective kinase inhibitor, it displays only moderate biochemical (~0.5 uM) and cellular (3-10 uM) potency. The original study does provide evidence of the engagement of MPS1 in cells using a wild-type vs M602Q-mutant cell system. Nonetheless, when used at the high concentrations (10 uM) in cells, interaction with additional (nonkinase) targets may occur. Additionally, no ADME, PK or in vivo data are available from the primary reference. Accordingly, MPS1-IN-1 should be used with caution in cellular assays (preferably in conjunction with additional MPS1 inhibitors based on alternative chemical scaffolds), and its use is not recommended for in vivo experiments. Multiple recent publications describe the identification and characterization of more advanced MPS1 inhibitors, likely better suited for interrogation of MPS1 function in cells and in vivo. For example, compound 27b from PMID 25625617 displays a biochemical IC50 of 2.7 nM and a cellular IC50 for pMPS1 of 0.7 nM. Its utility in vivo may be limited by toxicity at higher doses. Similarly, NMS-P715 (PMID 21723120), MPI-0479605 (PMID 22632936) and 34h (PMID 27055065) all provide good MPS1 potency and kinome selectivity while having been used in vivo.

MPS1-IN-1 is only a moderately potent kinase inhibitor. In vitro IC₅₀ = 350-650 nM for enzyme inhibition. Doses of 2-10 uM are required to inhibit MPS1-dependent activities in cells. The probe needs to be more potent and is only useful in cells at micromolar concentrations. Kinase inhibition profile and potency would need to determined on the kinases from the model organism for use in vivo. Additional controls are required to ensure that phenotypic activity is not due to off targets - examples include an inactive analog or another inhibitor from a different chemotype.

MPS1-IN-1 shows cellular activity in the range of 1-10 µM. Ideally the potency would be well below micromolar, but the compound is still useful for interrogating cellular biology. However, given the tight binding of ATP to MPS1 (Km < 1 µM), further potency optimization may be challenging. I suggest that 10 µM is not exceeded. If possible, a minimal dose response experiment would be useful (e.g., 0.3, 1.0, 3.0, and 10 µM). There is no available pharmacokinetic data for this compound. The utility of MPS1-IN-1 to probe MPS1 function is enhanced by the availability of the dual MPS1/PLK1 inhibitor MPS1-IN-2. Both compounds are known to inhibit other kinases, and their concurrent usage will help to increase confidence in MPS1 as the molecular target if they phenocopy.