Target Modulation by a Kinase Inhibitor Engineered to Induce a TandemBlockade of the Epidermal Growth Factor Receptor (EGFR) and c-Src: The Conceptof Type III Combi-Targeting

摘要

Cancer cells are characterized by a complex network of interrelated and compensatory signaling driven by multiple kinases that reduce their sensitivity to targeted therapy. Therefore, strategies directed at inhibiting two or more kinases are required to robustly block the growth of refractory tumour cells. Here we report on a novel strategy to promote sustained inhibition of two oncogenic kinases (Kin-1 and Kin-2) by designing a molecule K1-K2, termed “combi-molecule”, to induce a tandem blockade of Kin-1 and Kin-2, as an intact structure and to be further hydrolyzed to two inhibitors K1 and K2 directed at Kin-1 and Kin-2, respectively. We chose to target EGFR (Kin-1) and c-Src (Kin-2), two tyrosine kinases known to synergize to promote tumour growth and progression. Variation of K1-K2 linkers led to AL776, our first optimized EGFR-c-Src targeting prototype. Here we showed that: (a) AL776 blocked EGFR and c-Src as an intact structure using an in vitro kinase assay (IC50 EGFR = 0.12 μM and IC50 c-Src = 3 nM), (b) it could release K1 (AL621, a nanomolar EGFR inhibitor) and K2 (dasatinib, a clinically approved Abl/c-Src inhibitor) by hydrolytic cleavage both in vitro and in vivo, (c) it could robustly inhibit phosphorylation ofEGFR and c-Src (0.25–1 μM) in cells, (d) it induced 2–4fold stronger growth inhibition than gefitinib or dasatinib and apoptosis atconcentrations as low as 1 μM, and, (e) blocked motility and invasion atsub-micromolar doses in the highly invasive 4T1 and MDA-MB-231 cells. Despiteits size (MW = 1032), AL776 blocked phosphorylation of EGFR and c-Src in 4T1tumours in vivo. We now term this new targeting modelconsisting of designing a kinase inhibitor K1-K2 to target Kin-1 and Kin-2, andto further release two inhibitors K1 and K2 of the latter kinases, “typeIII combi-targeting”.