Establishing Drug Discovery and Identification of Hit Series for the Anti-apoptotic Proteins, Bcl‑2 and Mcl‑1

We describe our work to establish
structure- and fragment-based
drug discovery to identify small molecules that inhibit the anti-apoptotic
activity of the proteins Mcl-1 and Bcl-2. This identified hit series
of compounds, some of which were subsequently optimized to clinical
candidates in trials for treating various cancers. Many protein constructs
were designed to identify protein with suitable properties for different
biophysical assays and structural methods. Fragment screening using
ligand-observed NMR experiments identified several series of compounds
for each protein. The series were assessed for their potential for
subsequent optimization using 1H and 15N heteronuclear
single-quantum correlation NMR, surface plasmon resonance, and isothermal
titration calorimetry measurements to characterize and validate binding.
Crystal structures could not be determined for the early hits, so
NMR methods were developed to provide models of compound binding to
guide compound optimization. For Mcl-1, a benzodioxane/benzoxazine
series was optimized to a Kd of 40 μM
before a thienopyrimidine hit series was identified which subsequently
led to the lead series from which the clinical candidate S 64315 (MIK
665) was identified. For Bcl-2, the fragment-derived series were difficult
to progress, and a compound derived from a published tetrahydroquinone
compound was taken forward as the hit from which the clinical candidate
(S 55746) was obtained. For both the proteins, the work to establish
a portfolio of assays gave confidence for identification of compounds
suitable for optimization.