Src and ADAM-17-Mediated Shedding of Transforming Growth Factor-alpha Is a Mechanism of Acute Resistance to TRAIL

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L) has emerged as a promising anticancer agent. However, resistance to TRAIL is likely to be a major problem, and sensitization of cancer cells to TRAIL may therefore be an important anticancer strategy. In this study, we examined the effect of the epidermal growth factor receptor (EGFR)tyrosine kinase inhibitor (TKI) gefitinib and a human epidermal receptor 2 (HER2)-TKI (M578440) on the sensitivity of human colorectal cancer (CRC) cell lines to recombinant human TRAIL (rhTRAIL). A synergistic interaction between rhTRAIL and gefitinib and rhTRAIL and M578440 was observed in both rhTRAIL-sensitive and resistant CRC cells. This synergy correlated with an increase in EGFR and HER2 activation after rhTRAIL treatment. Furthermore, treatment of CRC cells with rhTRAIL resulted in activation of the Src family kinases (SFK). Importantly, we found that rhTRAIL treatment induced shedding of transforming growth factor-alpha (TGF-alpha) that was dependent on SFK activity and the protease ADAM-17. Moreover, this shedding of TGF-alpha was critical for rhTRAIL-induced activation of EGFR. In support of this, SFK inhibitors and small interfering RNAs targeting ADAM-17 and TGF-alpha also sensitized CRC cells to rhTRAIL-mediated apoptosis. Taken together, our findings indicate that both rhTRAIL-sensitive and resistant CRC cells respond to rhTRAIL treatment by activating an EGFR/HER2-mediated survival response and that these cells can be sensitized to rhTRAIL using EGFR/HER2-targeted therapies. Furthermore, this acute response to rhTRAIL is regulated by SFK-mediated and ADAM-17-mediated shedding of TGF-alpha, such that targeting SFKs or inhibiting ADAM-17, in combination with rhTRAIL, may enhance the response of CRC tumors to rhTRAIL. [Cancer Res 2008;68(20):8312-21]

ADAM17-Dependent c-MET-STAT3 Signaling Mediates Resistance to MEK Inhibitors in KRAS Mutant Colorectal Cancer

There are currently no approved targeted therapies for advanced KRAS mutant (KRASMT) colorectal cancer (CRC). Using a unique systems biology approach, we identified JAK1/2-dependent activation of STAT3 as the key mediator of resistance to MEK inhibitors in KRASMT CRC in vitro and in vivo. Further analyses identified acute increases in c-MET activity following treatment with MEK inhibitors in KRASMT CRC models, which was demonstrated to promote JAK1/2-STAT3-mediated resistance. Furthermore, activation of c-MET following MEK inhibition was found to be due to inhibition of the ERK-dependent metalloprotease ADAM17, which normally inhibits c-MET signaling by promoting shedding of its endogenous antagonist, soluble "decoy" MET. Most importantly, pharmacological blockade of this resistance pathway with either c-MET or JAK1/2 inhibitors synergistically increased MEK-inhibitor-induced apoptosis and growth inhibition in vitro and in vivo in KRASMT models, providing clear rationales for the clinical assessment of these combinations in KRASMT CRC patients.