Established roles for PI3K and MAPK signaling pathways in
tumorigenesis has prompted extensive research towards the discovery of small-molecule inhibitors as
cancer therapeutics. However, significant compensatory regulation exists between these two signaling cascades, leading to redundancy among survival pathways. Consequently, initial clinical trials aimed at either PI3K or
MEK inhibition alone have proven ineffective and highlight the need for development of targeted and innovative therapeutic combination strategies. We designed a series of PI3K inhibitor derivatives wherein a single
morpholine group of the PI3K inhibitor
ZSTK474 was substituted with a variety of 2-aminoethyl functional groups. Analogs with pendant
hydroxyl or methoxy groups maintained low nanomolar inhibition towards PI3Kα, PI3Kγ, and PI3Kδ
isoforms in contrast to those with pendant amino groups which were significantly less inhibitory. Synthesis of prototype PI3K/
MEK bifunctional inhibitors (6r, 6s) was guided by the structure-activity data, where a
MEK-targeting inhibitor was tethered directly via a short PEG linker to the
triazine core of the PI3K inhibitor analogs. These compounds (6r, 6s) displayed nanomolar inhibition towards PI3Kα, δ, and
MEK (IC50 ∼105-350 nM), and low micromolar inhibition for PI3Kβ and PI3Kγ (IC50 ∼1.5-3.9 μM) in enzymatic inhibition assays. Cell viability assays demonstrated superior anti-proliferative activity for 6s over 6r in three
tumor-derived cell lines (A375, D54, SET-2), which correlated with inhibition of downstream AKT and ERK1/2 phosphorylation. Compounds 6r and 6s also demonstrated in vivo tolerability with therapeutic efficacy through reduction of
kinase activation and amelioration of disease phenotypes in the JAK2V617F mutant
myelofibrosis mouse
cancer model. Taken together, these results support further structure optimization of 6r and 6s as promising leads for combination
therapy in human
cancer as a new class of PI3K/
MEK bifunctional inhibitors.