A more comprehensive understanding of how cells respond to
drug intervention, the likely immediate signalling responses and how resistance may develop within different microenvironments will help inform treatment regimes. The nonreceptor
tyrosine kinase SRC regulates many cellular signalling processes, and pharmacological inhibition has long been a target of
cancer drug discovery projects. Here, we describe the in vitro and in vivo characterisation of the small-molecule SRC inhibitor
AZD0424. We show that
AZD0424 potently inhibits the phosphorylation of tyrosine-419 of SRC (IC50 ~ 100 nm) in many
cancer cell lines; however, inhibition of cell viability, via a G1 cell cycle arrest, was observed only in a subset of
cancer cell lines in the low (on target) micromolar range. We profiled the changes in intracellular pathway signalling in
cancer cells following exposure to
AZD0424 and other targeted
therapies using reverse-phase
protein array (RPPA) analysis. We demonstrate that SRC is activated in response to treatment of KRAS-mutant colorectal cell lines with
MEK inhibitors (
trametinib or
AZD6244) and that
AZD0424 abrogates this. Cell lines treated with
trametinib or
AZD6244 in combination with
AZD0424 had reduced EGFR, FAK and SRC compensatory activation, and cell viability was synergistically inhibited. In vivo,
trametinib treatment of mice-bearing HCT116 tumours increased phosphorylation of SRC on Tyr419, and, when combined with
AZD0424, inhibition of tumour growth was greater than with
trametinib alone. We also demonstrate that
drug-induced resistance to
trametinib is not re-sensitised by
AZD0424 treatment in vitro, likely as a result of multiple compensatory signalling mechanisms; however, inhibition of SRC remains an effective way to block invasion of
trametinib-resistant tumour cells. These data imply that SRC inhibition may offer a useful addition to
MEK inhibitor combination strategies.