Rac inhibition as a novel therapeutic strategy for EGFR/HER2 targeted therapy resistant breast cancer.

BACKGROUND: Even though targeted therapies are available for cancers expressing oncogenic epidermal growth receptor (EGFR) and (or) human EGFR2 (HER2), acquired or intrinsic resistance often confounds therapy success. Common mechanisms of therapy resistance involve activating receptor point mutations and (or) upregulation of signaling downstream of EGFR/HER2 to Akt and (or) mitogen activated protein kinase (MAPK) pathways. However, additional pathways of resistance may exist thus, confounding successful therapy. METHODS: To determine novel mechanisms of EGFR/HER2 therapy resistance in breast cancer, gefitinib or lapatinib resistant variants were created from SKBR3 breast cancer cells. Syngenic therapy sensitive and resistant SKBR3 variants were characterized for mechanisms of resistance by mammosphere assays, viability assays, and western blotting for total and phospho proteins. RESULTS: Gefitinib and lapatinib treatments reduced mammosphere formation in the sensitive cells, but not in the therapy resistant variants, indicating enhanced mesenchymal and cancer stem cell-like characteristics in therapy resistant cells. The therapy resistant variants did not show significant changes in known therapy resistant pathways of AKT and MAPK activities downstream of EGFR/HER2. However, these cells exhibited elevated expression and activation of the small GTPase Rac, which is a pivotal intermediate of GFR signaling in EMT and metastasis. Therefore, the potential of the Rac inhibitors EHop-016 and MBQ-167 to overcome therapy resistance was tested, and found to inhibit viability and induce apoptosis of therapy resistant cells. CONCLUSIONS: Rac inhibition may represent a viable strategy for treatment of EGFR/HER2 targeted therapy resistant breast cancer.

Targeting Rac and Cdc42 GTPases in Cancer.

Rac and Cdc42 are small GTPases that have been linked to multiple human cancers and are implicated in epithelial to mesenchymal transition, cell-cycle progression, migration/invasion, tumor growth, angiogenesis, and oncogenic transformation. With the exception of the P29S driver mutation in melanoma, Rac and Cdc42 are not generally mutated in cancer, but are overexpressed (gene amplification and mRNA upregulation) or hyperactivated. Rac and Cdc42 are hyperactivated via signaling through oncogenic cell surface receptors, such as growth factor receptors, which converge on the guanine nucleotide exchange factors that regulate their GDP/GTP exchange. Hence, targeting Rac and Cdc42 represents a promising strategy for precise cancer therapy, as well as for inhibition of bypass signaling that promotes resistance to cell surface receptor-targeted therapies. Therefore, an understanding of the regulatory mechanisms of these pivotal signaling intermediates is key for the development of effective inhibitors. In this review, we focus on the role of Rac and Cdc42 in cancer and summarize the regulatory mechanisms, inhibitory efficacy, and the anticancer potential of Rac- and Cdc42-targeting agents. Cancer Res; 78(12); 3101-11. ©2018 AACR.

Inhibition of Rac1 decreases the severity of pancreatitis and pancreatitis-associated lung injury in mice.

Pancreatitis is a disease with high morbidity and mortality. In vitro experiments on pancreatic acini showed that supramaximal but not submaximal cholecystokinin (CCK) stimulation induces effects in the acinar cell that can be correlated with acinar morphological changes observed in the in vivo experimental model of cerulein-induced pancreatitis. The GTPase Rac1 was previously reported to be involved in CCK-evoked amylase release from pancreatic acinar cells. Here, we demonstrate that pretreatment with the Rac1 inhibitor NSC23766 (100 microM, 2 h) effectively blocked Rac1 translocation and activation in CCK-stimulated pancreatic acini, without affecting activation of its closely related GTPase, RhoA. This specific Rac1 inhibition decreased supramaximal (10 nM) CCK-stimulated acinar amylase release (27.% reduction), which seems to be connected to the reduction observed in serum amylase (46.6% reduction) and lipase levels (46.1% reduction) from cerulein-treated mice receiving NSC23766 (100 nmol h(-1)). The lack of Rac1 activation also reduced formation of reactive oxygen species (ROS; 20.8% reduction) and lactate dehydrogenase release (LDH; 24.3% reduction), but did not alter calcium signaling or trypsinogen activation in 10 nM CCK-stimulated acini. In the in vivo model, the cerulein-treated mice receiving NSC23766 also presented a decrease in both pancreatic and lung histopathological scores (reduction in oedema, 32.4 and 66.4%; haemorrhage, 48.3 and 60.2%; and leukocyte infiltrate, 53.5 and 43.6%, respectively; reduction in pancreatic necrosis, 65.6%) and inflammatory parameters [reduction in myeloperoxidase, 52.2 and 38.9%; nuclear factor kappaB (p65), 61.3 and 48.6%; and nuclear factor kappaB (p50), 46.9 and 44.9%, respectively], together with lower serum levels for inflammatory (TNF-alpha, 40.4% reduction) and cellular damage metabolites (LDH, 52.7% reduction). Collectively, these results suggest that pharmacological Rac1 inhibition ameliorates the severity of pancreatitis and pancreatitis-associated lung injury through the reduction of pancreatic acinar damage induced by pathological digestive enzyme secretion and overproduction of ROS.