Targeting SHP2 phosphatase in breast cancer overcomes RTK-mediated resistance to PI3K inhibitors

BACKGROUND: PI3K signaling is frequently activated in breast cancer and is targeted by PI3K inhibitors. However, resistance of tumor cells to PI3K inhibition, often mediated by activated receptor tyrosine kinases, is commonly observed and reduces the potency of PI3K inhibitors. Therefore, new treatment strategies to overcome resistance to PI3K inhibitors are urgently needed to boost their efficacy. The phosphatase SHP2, which plays a crucial role in mediating signal transduction between receptor tyrosine kinases and both the PI3K and MAPK pathways, is a potential target for combination treatment. METHODS: We tested combinations of PI3K and SHP2 inhibitors in several experimental breast cancer models that are resistant to PI3K inhibition. Using cell culturing, biochemical and genetic approaches, we evaluated tumor cell proliferation and signaling output in cells treated with PI3K and SHP2 inhibitors. RESULTS: Combination treatment with PI3K and SHP2 inhibitors counteracted both acquired and intrinsic breast cancer cell resistance to PI3K inhibition that is mediated by activated receptor tyrosine kinases. Dual PI3K and SHP2 inhibition blocked proliferation and led to sustained inactivation of PI3K and MAPK signaling, where resistant cells rapidly re-activated these pathways upon PI3K inhibitor monotreatment. In addition, we demonstrate that overexpression of SHP2 induced resistance to PI3K inhibition, and that SHP2 was frequently activated during the development of PI3K inhibitor resistance after prolonged treatment of sensitive cells. CONCLUSIONS: Our results highlight the importance of SHP2 as a player in resistance to PI3K inhibitors. Combination treatment with PI3K and SHP2 inhibitors could pave the way for significant improvements in therapies for breast cancer

Using functional genetics to identify components of cancer relevant signaling pathways

The clinical introduction of the so-called ‘targeted therapies’ some 15 years ago has started a new era in the treatment of cancer patients. These drugs hugely increase the possibilities to treat patients based on the genetic mutations of their cancer and therefore hold the promise of ‘personalized medicine’. However, resistance to these drugs is a major problem. New strategies to combat drug resistance are therefore urgently needed and much effort is put into understanding and uncovering mechanisms of drug resistance. In this thesis, the use of functional genetics is employed to identify components of cancer relevant signaling pathways. Knowledge of the complex functioning of such pathways could lead to the identification of new drug targets and the design of improved treatment strategies, for instance by combining multiple drugs to prevent or delay the onset of drug resistance. Chapter 1 is an introduction of the subjects that are relevant to this thesis. In chapter 2 the role of the growth factor HGF and its receptor MET in relation to drug resistance are discussed. Chapter 3 describes that inhibition of the tyrosine phosphatase PTPN11 is an excellent strategy to battle resistance to BRAF inhibitors that is cause by activation of Receptor Tyrosine Kinases. In chapter 4 MAML3 is identified as a factor that promotes resistance to retinoic acid in neuroblastoma. Chapter 5 describes that CTBP2 is involved in retinoic acid resistance. Finally, chapter 6 puts these findings into a broader perspective and the possibilities and problems of treating cancer patients on the basis of ‘personalized medicine’ are discussed

Cancer stem cells regulate cancer-associated fibroblasts via activation of Hedgehog signaling in mammary gland tumors

Many tumors display intracellular heterogeneity, with subsets of cancer stem cells (CSC) that sustain tumor growth, recurrence, and therapy resistance. Cancer associated fibroblasts (CAF) have been shown to support and regulate CSC function. Here we investigated the interactions between CSCs and CAFs in mammary gland tumors driven by combined activation of Wnt/{beta}-catenin and Hgf/Met signaling in mouse mammary epithelial cells. In this setting, CSCs secreted the hedgehog ligand SHH, which regulated CAFs via paracrine activation of Hedgehog signaling. CAFs subsequently secreted factors that promoted expansion and self-renewal of CSCs. In vivo treatment of tumors with the Hedgehog inhibitor vismodegib reduced CAF and CSC expansion, resulting in an overall delay of tumor formation. Our results identify a novel intracellular signaling module that synergistically regulates CAFs and CSCs. Targeting CAFs with Hedgehog inhibitors may offer a novel therapeutic strategy against breast cancer

From pyrazolones to azaindoles: evolution of active-site SHP2 inhibitors based on scaffold hopping and bioisosteric replacement

The tyrosine phosphatase SHP2 controls the activity of pivotal signaling pathways, including MAPK, JAK-STAT, and PI3K-Akt. Aberrant SHP2 activity leads to uncontrolled cell proliferation, tumorigenesis, and metastasis. SHP2 signaling was recently linked to drug resistance against cancer medications such as MEK and BRAF inhibitors. In this work, we present the development of a novel class of azaindole SHP2 inhibitors. We applied scaffold hopping and bioisosteric replacement concepts to eliminate unwanted structural motifs and to improve the inhibitor characteristics of the previously reported pyrazolone SHP2 inhibitors. The most potent azaindole 45 inhibits SHP2 with an IC(50) = 0.031 μM in an enzymatic assay and with an IC(50) = 2.6 μM in human pancreas cells (HPAF-II). Evaluation in a series of cellular assays for metastasis and drug resistance demonstrated efficient SHP2 blockade. Finally, 45 inhibited proliferation of two cancer cell lines that are resistant to cancer drugs and diminished ERK signaling

SUMOylation inhibition overcomes proteasome inhibitor resistance in multiple myeloma

Proteasome inhibition is a highly effective treatment for multiple myeloma (MM). However, virtually all patients develop proteasome inhibitor resistance which is associated with a poor prognosis. Hyperactive SUMO signaling is involved in both cancer pathogenesis and cancer progression. A state of increased SUMOylation has been associated with aggressive cancer biology. We found that relapsed/refractory MM is characterized by a SUMO-high state, and high expression of the SUMO E1 activating enzyme (SAE1/UBA2) is associated with poor overall survival. Consistently, continuous treatment of MM cell lines with carfilzomib (CFZ) enhanced SUMO pathway activity. Treatment of MM cell lines with the SUMO E1 activating enzyme inhibitor subasumstat (TAK-981) showed synergy with CFZ in both CFZ-sensitive and CFZ-resistant MM cell lines, irrespective of the TP53 state. Combination therapy was effective in primary MM cells and in two murine MM xenograft models. Mechanistically, combination treatment with subasumstat and CFZ enhanced genotoxic and proteotoxic stress and induced apoptosis was associated with activity of the prolyl isomerase PIN1. In summary, our findings reveal activated SUMOylation as a therapeutic target in MM and point to combined SUMO/proteasome inhibition as a novel and potent strategy for the treatment of proteasome inhibitor-resistant MM