Background:
The program’s objective was to identify up to three small molecule inhibitors against the Partner’s target for non-GLP studies within a span of 8-10 months. The key deliverable in the program was for the three inhibitors to demonstrate > 75% tumour growth inhibition (TGI) in a mouse efficacy study in any one of three models available.
The Problem:
Some early leads were available which showed low nM biochemical potency but with poor translation into the cellular potency. Additionally, compounds showed high in-vivo clearance and poor oral bioavailability. Key goals were, therefore, to achieve cellular potency < 250 nM and improved in-vivo PK properties.
Solution:
AIDD team first studied the gaps in the SAR around the molecule by synthesizing several modifications on different parts of the molecule. With the goal of filling in the SAR gaps the structural variations were made on LHS Q-substituted motif, A-ring, the linker and the terminal acid group (Figure). While the modifications on the linker and the acid did not show traction in cell-based assay, specific changes made in the A-ring and the LHS amine (Q = N), did show improved cellular potency. We discovered that “F”, when appropriately substituted on LHS amine, improves the cell potency. However, right balance between fluorine content and basicity of N is necessary, else cell potency is affected.
Furthermore, metabolic identification studies showed liabilities in different positions of the molecule (Figure) – over-oxidation, deamination and glucuronidation. Considering improved cell potencies on LHS portion of the molecule, optimization of substitutions on A-ring and LHS amine were both separately undertaken keeping in mind the basicity of the amine N that impacts the potency. Endocyclic amines shows the most promise in this effort. We tested the possibilities in which over-oxidation happened on the LHS by blocking potential metabolism sites, using bulky amines (bridgehead, spiro, 2-substd. etc) and by substituting A-ring (Figure). After testing 150+ analogues which included those that hybridized both features on A-ring and amine, a few compounds with good cell potency and PK profiles were eligible and selected to move forward into animal models.
Impact:
The team was able to progress four compounds through the mouse efficacy studies with > 75% TGI. Additionally, one of these molecules progressed towards a preclinical candidate nomination.
