Selective Inhibition of STAT3 Phosphorylation Using a Nuclear-Targeted Kinase Inhibitor

Abstract

The discovery of compounds that selectively modulate signaling and effector proteins downstream of EGFR could have important implications for understanding specific roles for pathway activation. A complicating factor for receptor tyrosine kinases is their capacity to be translocated to the nucleus upon ligand engagement. Once localized in subcellular compartments like the nucleus, the roles for EGFR take on additional features, many of which are still being revealed. Additionally, nuclear localization of EGFR has been implicated in downstream events that have significance for therapy resistance and disease progression. The challenges to addressing the differential roles for EGFR in the nucleus motivated experimental approaches that can selectively modulate its subcellular function. By adding modifications to the established EGFR kinase inhibitor gefitinib, an approach to small molecule conjugates with a unique nuclear-targeting peptoid sequence was tested in both human and murine breast tumor cell models for their capacity to inhibit EGF-stimulated activation of ERK1/2 and STAT3. While gefitinib alone inhibits both of these downstream effectors, data acquired here indicate that compartmentalization of the gefitinib conjugates allows for pathway specific inhibition of STAT3 while not affecting ERK1/2 signaling. The inhibitor conjugates offered a more direct route to evaluate the role of EGF-stimulated epithelial-to-mesenchymal transition in these breast cancer cell models. These conjugates revealed that STAT3 activation is not involved in EGF-induced EMT, and instead utilization of the cytoplasmic MAP kinase signaling pathway is critical to this process. This is the first example of a conjugate kinase inhibitor capable of partitioning to the nucleus and offers a new approach to enhancing kinase inhibitor specificity.

Biased signaling downstream of epidermal growth factor receptor regulates proliferative versus apoptotic response to ligand

“…Our recent studies demonstrate an enhanced localization of EGFR in the nucleus of metastatic breast cancer cells as compared to primary tumor cells 32 . Given the role of STAT1 in facilitating EGF-induced apoptosis in metastatic cells, we next sought to investigate the subcellular localization of STAT1 under nonstimulated and EGF-stimulated conditions.…”

Biased signaling downstream of epidermal growth factor receptor regulates proliferative versus apoptotic response to ligand

“…Our recent studies demonstrate an enhanced localization of EGFR in the nucleus of metastatic breast cancer cells as compared to primary tumor cells 35 . Given the role of STAT1 in facilitating EGF-induced apoptosis in metastatic cells we next sought to investigate the subcellular localization of STAT1 under nonstimulated and EGF-stimulated conditions.…”

“…To specifically target the function of the subpopulation of EGF receptors that reach the nuclear compartment, we utilized our recently reported novel EGFR inhibitor 35 . This chemical construct contains the EGFR tyrosine kinase inhibitor gefitinib linked to a peptoid moiety encoding the SV40 nuclear localization sequence (NLS-gefitinib).…”

“…This chemical construct contains the EGFR tyrosine kinase inhibitor gefitinib linked to a peptoid moiety encoding the SV40 nuclear localization sequence (NLS-gefitinib). This approach leads to robust accumulation of geftinib in the nucleus 35 . Consistent with the notion that only endocytosed EGFR molecules have access to the nuclear pool of STAT1, pretreatment of NME-LM1 cells with this chimeric NLS-gefitinib molecule led to potent blockade of EGF-induced STAT1 phosphorylation without affecting phosphorylation of ERK1/2 ( fig.…”

STAT3 signaling in ovarian cancer: a potential therapeutic target

“…Beside JAK inhibitors, the EGFR inhibitor is another way to inactivate STAT3 indirectly. Preclinical evidence reveals that EGFR inhibitors, such as Erlotinib, Cetuximab, Gefitinib and lapatinib, decrease the expression of STAT3 [157][158][159][160] . Nevertheless, such inhibitors have minimal clinical activity or do not improve progression-free or overall survival in the treatment of patients with ovarian cancer [161][162][163][164] .…”