The Discovery of OSI-906, a Small-molecule Inhibitor of the Insulin-like Growth Factor-1 and Insulin Receptors - Accounts in Drug Discovery Case Studies in Medicinal Chemistry - page 89

LISN Cells (0.5% FCS starved) GEO Cells (10% FCS)

DMSO 0.01 0.1 1 OSI-906 ( µ M) DMSO 0.01 0.1 1 OSI-906 ( µ M)

- + + + + - + + + +

IGF-1 IGF-1

pY-IGF-1R pY-IGF-1R

total-IGF-1R

total-IGF-1R

p-AKT(T308) p-AKT(T308)

p-AKT(S473) p-AKT(S473)

p-ERK1/2

p-ERK1/2

total-ERK1/2 total-ERK1/2

p-p70S6K

p-p70S6K

Figure 4.8

Inhibition of IGF-1R and cellular signaling pathways by OSI-906 in LISN
and GEO cells.

in vivo and were therefore used as proof-of-concept models for tumor growth
inhibition (TGI) studies where the degree and duration of in vivo inhibition of
tumor IGF-1R phosphorylation could be correlated to in vivo e cacy. This
allowed for a critical in vivo correlation to be established between drug exposure
(PK), inhibition of pIGF-1R (PD), and overall tumor growth inhibition.
OSI-906 is a potent inhibitor of the tyrosine kinase activity of IGF-1R. In
biochemical assays of enzyme activity using poly(Glu:4Tyr) as the substrate,
recombinant human IGF-1R kinase domain was inhibited by OSI-906 with an
IC 50 value of 35 nM. In both LISN and GEO cell lines, OSI-906 fully blocked
IGF-1-stimulated receptor phosphorylation (Figure 4.8). To note, the GEO
line, because of its IGF2 autocrine loop, displays high levels of p-IGF-1R prior
to stimulation with exogenous IGF1. In contrast, the LISN line displays high
levels of total IGF-1R which requires ligand stimulation for IGF-1R activa-
tion. Immunoprecipitation and immunoblotting analysis of cell lysates also
demonstrated that IGF-1-stimulated phospho-AKT, phospho-ERK, and
phospho-p70S6K signaling pathways are inhibited as a result of IGF-1R
inhibition by OSI-906 in the LISN cells. In the GEO cells, OSI-906 effectively
inhibited AKT activation in the presence of 10% FCS, suggesting that survival
signaling is mediated predominantly by IGF-1R in this background. IC 50
values for the cellular inhibition in each respective cell line of IGF-1R auto-
phosphorylation and activation of the downstream signaling proteins AKT,
ERK1/2, and S6 kinase are shown in Table 4.11. We assessed the influence of
plasma protein binding for varied species on the biological activity of OSI-906
in order to allow for the prediction of ecacious in vivo plasma levels across
species. Whole plasma (90%) from mouse, rat, dog, monkey, or human was
included in the IGF-1R cellular autophosphorylation assay. Table 4.11 sum-
marizes the mouse and human plasma protein binding effects on OSI-906 in
this mechanistic assay. The greatest protein binding potency shift was seen in