Resistance to receptor tyrosine kinase inhibition in cancer: molecular mechanisms and therapeutic strategies

From Tyrosine Kinases to Tyrosine Phosphatases: New Therapeutic Targets in Cancers and Beyond

Protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) regulate the level of tyrosine phosphorylation in proteins. PTKs are key enzymes that catalyze the transfer of an ATP phosphoric acid to a tyrosine residue on target protein substrates. Protein tyrosine phosphatases (PTPs) are responsible for the dephosphorylation of tyrosine residues and play a role in countering PTK overactivity. As widespread oncogenes, PTKs were once considered to be promising targets for therapy. However, tyrosine kinase inhibitors (TKIs) now face a number of challenges, including drug resistance and toxic side effects. Treatment strategies now need to be developed from a new perspective. In this review, we assess the current state of TKIs and highlight the role of PTPs in cancer and other diseases. With the advances of allosteric inhibition and the development of multiple alternative proprietary drug strategies, the reputation of PTPs as "undruggable" targets has been overturned, and they are now considered viable therapeutic targets. We also discuss the strategies and prospects of PTP-targeted therapy, as well as its future development.

Therapeutic targeting of the functionally elusive TAM receptor family

The TAM receptor family of TYRO3, AXL and MERTK regulates tissue and immune homeostasis. Aberrant TAM receptor signalling has been linked to a range of diseases, including cancer, fibrosis and viral infections. Specifically, the dysregulation of TAM receptors can enhance tumour growth and metastasis due to their involvement in multiple oncogenic pathways. For example, TAM receptors have been implicated in the epithelial-mesenchymal transition, maintaining the stem cell phenotype, immune modulation, proliferation, angiogenesis and resistance to conventional and targeted therapies. Therapeutically, multiple TAM receptor inhibitors are in preclinical and clinical development for cancers and other indications, with those targeting AXL being the most clinically advanced. Although there has been notable clinical advancement in recent years, challenges persist. This Review aims to provide both biological and clinical insights into the current therapeutic landscape of TAM receptor inhibitors, and evaluates their potential for the treatment of cancer and non-malignant diseases.

Galectin-1-mediated MET/AXL signaling enhances sorafenib resistance in hepatocellular carcinoma by escaping ferroptosis

Sorafenib, a small-molecule inhibitor targeting several tyrosine kinase pathways, is the standard treatment for advanced hepatocellular carcinoma (HCC). However, not all patients with HCC respond well to sorafenib, and 30% of patients develop resistance to sorafenib after short-term treatment. Galectin-1 modulates cell-cell and cell-matrix interactions and plays a crucial role in HCC progression. However, whether Galectin-1 regulates receptor tyrosine kinases by sensitizing HCC to sorafenib remains unclear. Herein, we established a sorafenib-resistant HCC cell line (Huh-7/SR) and determined that Galectin-1 expression was significantly higher in Huh-7/SR cells than in parent cells. Galectin-1 knockdown reduced sorafenib resistance in Huh-7/SR cells, whereas Galectin-1 overexpression in Huh-7 cells increased sorafenib resistance. Galectin-1 regulated ferroptosis by inhibiting excessive lipid peroxidation, protecting sorafenib-resistant HCC cells from sorafenib-mediated ferroptosis. Galectin-1 expression was positively correlated with poor prognostic outcomes for HCC patients. Galectin-1 overexpression promoted the phosphorylation of AXL receptor tyrosine kinase (AXL) and MET proto-oncogene, receptor tyrosine kinase (MET) signaling, which increased sorafenib resistance. MET and AXL were highly expressed in patients with HCC, and AXL expression was positively correlated with Galectin-1 expression. These findings indicate that Galectin-1 regulates sorafenib resistance in HCC cells through AXL and MET signaling. Consequently, Galectin-1 is a promising therapeutic target for reducing sorafenib resistance and sorafenib-mediated ferroptosis in patients with HCC.

Role and mechanistic actions of protein kinase inhibitors as an effective drug target for cancer and COVID

Kinases can be grouped into 20 families which play a vital role as a regulator of neoplasia, metastasis, and cytokine suppression. Human genome sequencing has discovered more than 500 kinases. Mutations of the kinase itself or the pathway regulated by kinases leads to the progression of diseases such as Alzheimer's, viral infections, and cancers. Cancer chemotherapy has made significant leaps in recent years. The utilization of chemotherapeutic agents for treating cancers has become difficult due to their unpredictable nature and their toxicity toward the host cells. Therefore, targeted therapy as a therapeutic option against cancer-specific cells and toward the signaling pathways is a valuable avenue of research. SARS-CoV-2 is a member of the Betacoronavirus genus that is responsible for causing the COVID pandemic. Kinase family provides a valuable source of biological targets against cancers and for recent COVID infections. Kinases such as tyrosine kinases, Rho kinase, Bruton tyrosine kinase, ABL kinases, and NAK kinases play an important role in the modulation of signaling pathways involved in both cancers and viral infections such as COVID. These kinase inhibitors consist of multiple protein targets such as the viral replication machinery and specific molecules targeting signaling pathways for cancer. Thus, kinase inhibitors can be used for their anti-inflammatory, anti-fibrotic activity along with cytokine suppression in cases of COVID. The main goal of this review is to focus on the pharmacology of kinase inhibitors for cancer and COVID, as well as ideas for future development.

Receptor tyrosine kinase inhibitors in cancer

Targeted therapy is a new cancer treatment approach, involving drugs that particularly target specific proteins in cancer cells, such as receptor tyrosine kinases (RTKs) which are involved in promoting growth and proliferation, Therefore inhibiting these proteins could impede cancer progression. An understanding of RTKs and the relevant signaling cascades, has enabled the development of many targeted drug therapies employing RTK inhibitors (RTKIs) some of which have entered clinical application. Here we discuss RTK structures, activation mechanisms and functions. Moreover, we cover the potential effects of combination drug therapy (including chemotherapy or immunotherapy agents with one RTKI or multiple RTKIs) especially for drug resistant cancers.

How cells sense and integrate information from different sources

Cell signaling is a fundamental cellular process that enables cells to sense and respond to information in their surroundings. At the molecular level, signaling is primarily carried out by transmembrane protein receptors that can initiate complex downstream signal transduction cascades to alter cellular behavior. In the human body, different cells can be exposed to a wide variety of environmental conditions, and cells express diverse classes of receptors capable of sensing and integrating different signals. Furthermore, different receptors and signaling pathways can crosstalk with each other to calibrate the cellular response. Crosstalk occurs through multiple mechanisms at different levels of signaling pathways. In this review, we discuss how cells sense and integrate different chemical, mechanical, and spatial signals as well as the mechanisms of crosstalk between pathways. To illustrate these concepts, we use a few well-studied signaling pathways, including receptor tyrosine kinases and integrin receptors. Finally, we discuss the implications of dysregulated cellular sensing on driving diseases such as cancer. This article is categorized under: Cancer > Molecular and Cellular Physiology Metabolic Diseases > Molecular and Cellular Physiology.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-022-01521-3.

Receptor-Tyrosine Kinase Inhibitor Ponatinib Inhibits Meningioma Growth In Vitro and In Vivo

To date, there is no standard-of-care systemic therapy for the treatment of aggressive meningiomas. Receptor tyrosine kinases (RTK) are frequently expressed in aggressive meningiomas and are associated with poor survival. Ponatinib is a FDA- and EMA-approved RTK inhibitor and its efficacy in meningioma has not been studied so far. Therefore, we investigated ponatinib as a potential drug candidate against meningioma. Cell viability and cell proliferation of ponatinib-treated meningioma cells were assessed using crystal violet assay, manual counting and BrdU assay. Treated meningioma cell lines were subjected to flow cytometry to evaluate the effects on cell cycle and apoptosis. Meningioma-bearing mice were treated with ponatinib to examine antitumor effects in vivo. qPCR was performed to assess the mRNA levels of tyrosine kinase receptors after ponatinib treatment. Full-length cDNA sequencing was carried out to assess differential gene expression. IC50 values of ponatinib were between 171.2 and 341.9 nM in three meningioma cell lines. Ponatinib induced G0/G1 cell cycle arrest and subsequently led to an accumulation of cells in the subG1-phase. A significant induction of apoptosis was observed in vitro. In vivo, ponatinib inhibited meningioma growth by 72.6%. Mechanistically, this was associated with downregulation of PDGFRA/B and FLT3 mRNA levels, and mitochondrial dysfunction. Taken together, ponatinib is a promising candidate for targeted therapy in the treatment of aggressive meningioma.

Targeted protein degraders from an oncologist point of view: The Holy Grail of cancer therapy?

In the era of precision medicine, monoclonal antibodies and small molecule inhibitors are the mainstays of the biological therapy in patients with solid tumors. However, resistance to treatment and the "undruggability" of certain key oncogenic proteins emerged as major limitations and jeopardize the clinical benefit of modern therapeutic approaches. Targeted protein degraders are novel molecules entering the early phase of clinical development that exploit the intracellular ubiquitine-proteasome system to promote a specific degradation of target proteins. Since the peculiar mechanism of action, targeted protein degraders have the potential to limit and overcome resistance to treatment and to allow a full actionability of certain cancer drivers that are actually elusive targets. Here, we discuss the state-of-the-art and the open issues in the development of these emerging biological agents from a clinical perspective and with a focus on solid tumors.

Higher cMET dependence of sacral compared to clival chordoma cells: contributing to a better understanding of cMET in chordoma

Chordomas are rare slow growing, malignant bone tumors of the axial skeleton with no approved medical treatment. As the majority of chordomas express cMET and its ligand, HGF, and crosstalks between EGFR and MET-signaling exist, we aimed to explore cMET activity in chordoma cell lines and clinical samples. We investigated nine chordoma patients and four chordoma cell lines for cMET expression. Two clival and two sacral chordoma cell lines were tested for chromosomal abnormalities of the MET gene locus; we studied the influence of HGF on the autocrine secretion and migration behavior, as well as protein expression and phosphorylation. Two MET/ALK inhibitors were investigated for their effects on cell viability, cell cycle, cyclin alterations, apoptosis, and downstream signaling pathways. Moderate and strong expression of membrane and cytoplasmic cMET in chordoma patients and cell lines used, as well as concentration-dependent increase in phospho cMET expression after HGF stimulation in all four chordoma cell lines was shown. U-CH2, MUG-Chor1, and UM-Chor1 are polysomic for MET. Chordoma cell lines secreted EGF, VEGF, IL-6, and MMP9 upon HGF-stimulation. Sacral cell lines showed a distinct HGF-induced migration. Both inhibitors dose-dependently inhibited cell growth, induce apoptosis and cell-cycle arrest, and suppress downstream pathways. Heterogeneous responses obtained in our in vitro setting indicate that cMET inhibitors alone or in combination with other drugs might particularly benefit patients with sacral chordomas.

A systematic analysis of signaling reactivation and drug resistance

Increasing evidence suggests that the reactivation of initially inhibited signaling pathways causes drug resistance. Here, we analyze how network topologies affect signaling responses to drug treatment. Network-dependent drug resistance is commonly attributed to negative and positive feedback loops. However, feedback loops by themselves cannot completely reactivate steady-state signaling. Newly synthesized negative feedback regulators can induce a transient overshoot but cannot fully restore output signaling. Complete signaling reactivation can only occur when at least two routes, an activating and inhibitory, connect an inhibited upstream protein to a downstream output. Irrespective of the network topology, drug-induced overexpression or increase in target dimerization can restore or even paradoxically increase downstream pathway activity. Kinase dimerization cooperates with inhibitor-mediated alleviation of negative feedback. Our findings inform drug development by considering network context and optimizing the design drug combinations. As an example, we predict and experimentally confirm specific combinations of RAF inhibitors that block mutant NRAS signaling.

Kholodenko et al. uncover signaling network circuitries and molecular mechanisms necessary and sufficient for complete reactivation or overshoot of steady-state signaling after kinase inhibitor treatment. The two means to revive signaling output fully are through network topology or reactivation of the kinase activity of the primary drug target. Blocking RAF dimer activity by a combination of type I½ and type II RAF inhibitors efficiently blocks mutant NRAS-driven ERK signaling.

Discovery of Aminopyrazole Derivatives as Potent Inhibitors of Wild-Type and Gatekeeper Mutant FGFR2 and 3

Fibroblast growth factor receptors (FGFR) 2 and 3 have been established as drivers of numerous types of cancer with multiple drugs approved or entering late stage clinical trials. A limitation of current inhibitors is vulnerability to gatekeeper resistance mutations. Using a combination of targeted high-throughput screening and structure-based drug design, we have developed a series of aminopyrazole based FGFR inhibitors that covalently target a cysteine residue on the P-loop of the kinase. The inhibitors show excellent activity against the wild-type and gatekeeper mutant versions of the enzymes. Further optimization using SAR analysis and structure-based drug design led to analogues with improved potency and drug metabolism and pharmacokinetics properties.

Tyrosine Kinase Inhibitors in Cancer: Breakthrough and Challenges of Targeted Therapy

Receptor tyrosine kinases (RTKs) are key regulatory signaling proteins governing cancer cell growth and metastasis. During the last two decades, several molecules targeting RTKs were used in oncology as a first or second line therapy in different types of cancer. However, their effectiveness is limited by the appearance of resistance or adverse effects. In this review, we summarize the main features of RTKs and their inhibitors (RTKIs), their current use in oncology, and mechanisms of resistance. We also describe the technological advances of artificial intelligence, chemoproteomics, and microfluidics in elaborating powerful strategies that could be used in providing more efficient and selective small molecules inhibitors of RTKs. Finally, we discuss the interest of therapeutic combination of different RTKIs or with other molecules for personalized treatments, and the challenge for effective combination with less toxic and off-target effects.

Analysis of the Effect of Increased α2,3-Sialylation on RTK Activation in MKN45 Gastric Cancer Spheroids Treated with Crizotinib

In the scenario of personalized medicine, targeted therapies are currently the focus of cancer drug development. These drugs can block the growth and spread of tumor cells by interfering with key molecules involved in malignancy, such as receptor tyrosine kinases (RTKs). MET and Recepteur d'Origine Nantais (RON), which are RTKs frequently overactivated in gastric cancer, are glycoprotein receptors whose activation have been shown to be modulated by the cellular glycosylation. In this work, we address the role of sialylation in gastric cancer therapy using an innovative 3D high-throughput cell culture methodology that mimics better the in vivo tumor features. We evaluate the response to targeted treatment of glycoengineered gastric cancer cell models overexpressing the sialyltransferases ST3GAL4 or ST3GAL6 by subjecting 3D spheroids to the tyrosine kinase inhibitor crizotinib. We show here that 3D spheroids of ST3GAL4 or ST3GAL6 overexpressing MKN45 gastric cancer cells are less affected by the inhibitor. In addition, we disclose a potential compensatory pathway via activation of the Insulin Receptor upon crizotinib treatment. Our results suggest that cell sialylation, in addition of being involved in tumor progression, could play a critical role in the response to tyrosine kinase inhibitors in gastric cancer.

Arginine–glycine–aspartate (RGD)-targeted positron-labeled dendritic polylysine nanoprobe for tumor PET imaging

This work investigated the optimization of the ⁶⁸Ga radiolabeling of the dendritic polylysine-1,4,7-triazacyclononane-1,4,7-triacetic acid conjugate (DGL-NOTA). Under pH = 4.0, reaction temperature of 70 °C, and incubation time of 10.0 min, the conjugate (DGL-NOTA) radiochemical yield was between 50% and 70%. After separation and purification, the radiochemical purity was greater than 98%. The radiolabeled formulation (⁶⁸Ga-NOTA-DGL-PEG-RGDyC) remained stable in both phosphate buffer and serum (all radiochemically greater than 95%) for up to 2 hours with a specific activity of 30 GBq/μmol. Cellular experimental studies have shown that radiolabeled preparations can rapidly enter U87MG cells, and after 2 hours, there was still retention of imaging agents in the cells. In vivo distribution studies had shown that the tracer is excreted by the kidneys. Two hours after injecting the imaging agent, the U87MG tumor tissue uptake value was (4.67 ± 0.09)% ID/g. Positron emission tomography (PET) imaging in animals showed that ⁶⁸Ga-NOTA-DGL-PEG-RGDyC had good targeting and can be enriched in tumor sites. Through hemolysis testing and morphological changes of red blood cells, it was proved that NOTA-DGL-PEG-RGDyC has good blood compatibility.

This work investigated the optimization of the ⁶⁸Ga radiolabeling of the dendritic polylysine-1,4,7-triazacyclononane-1,4,7-triacetic acid conjugate (DGL-NOTA).

BMSC-derived leptin and IGFBP2 promote erlotinib resistance in lung adenocarcinoma cells through IGF-1R activation in hypoxic environment

EGFR-TKIs such as erlotinib and gefitinib have been introduced into the first-line treatment for patients having a mutation of deletion in exon 19 or L858R missense mutations in exon 21. Almost all patients who respond to EGFR-TKIs at first place eventually develop acquired resistance after several months of therapy. The secondary mutations and bypass signaling activation are involved in the generation of the resistance. Hypoxia in non-small cell lung cancer (NSCLC) is an important factor in treatment resistance including radiotherapy, chemotherapy and EGFR-TKI therapy. In this study, the effect of hypoxic cancer microenvironment in the bypass signaling activation was investigated. We found that bone marrow-derived mesenchymal stem cells (BMSCs) residing in the hypoxic solid cancer microenvironment highly produced molecules associated with adipocytes including adipokine leptin and IGFBPs. Leptin could induce the resistance of lung cancer cells to erlotinib through activating IGF-1R signaling. IGFBP2 counteracted the activation role of IGF-1 and induced erlotinib resistance by activating IGF-1R signaling in an IGF-1 independent manner. IGFBP2 had synergistic effect with leptin to induce erlotinib resistance. Leptin and IGFBP2 may be predictive factors for acquired resistance for EGFR-TKIs.

A selective and robust UPLC-MS/MS method for the simultaneous quantitative determination of anlotinib, ceritinib and ibrutinib in rat plasma and its application to a pharmacokinetic study

A selective and robust UPLC-MS/MS method has been firstly developed for simultaneous determination of three anti-tumor tyrosine kinase inhibitors (anlotinib, ANL; ceritinib, CER; ibrutinib, IBR) in rat plasma using cost-effective protein precipitation extraction. LC separation was achieved on Waters XBrige C18 column (50 mm × 2.1 mm, 3.5 μm) under gradient conditions in a run time of 5 min. ESI⁺ was involved through mass spectrometry. Multiple reaction monitoring transitions were at m/z 408.2 → 339.2 for ANL, 558.2 → 433.2 for CER, 441.0 → 138.0 for IBR, 285.0 → 193.1 for diazepam (internal standard), respectively. The optimized method was validated based on US FDA guideline, EMEA guideline as well as Pharmacopoeia of the People's Republic of China. The assay was linear in the range of 0.1-20 ng mL^-1 for ANL, 2-1000 ng mL^-1 for CER, 1-500 ng mL^-1 for IBR. Intra- and inter-day accuracy and precision for all analytes were ≦13.84% and ≦12.56%, respectively. ANL, CER and IBR were sufficiently stable under most investigated conditions. The optimized method was successfully applied for a pharmacokinetic study after single oral gavage administration of mixture (ANL, CER and IBR) at dose of 6 mg kg^-1, 25 mg kg^-1 and 10 mg kg^-1.

Computational analysis of receptor tyrosine kinase inhibitors and cancer metabolism: implications for treatment and discovery of potential therapeutic signatures

BACKGROUND

Receptor tyrosine kinase (RTK) inhibitors are frequently used to treat cancers and the results have been mixed, some of these small molecule drugs are highly successful while others show a more modest response. A high number of studies have been conducted to investigate the signaling mechanisms and corresponding therapeutic influence of RTK inhibitors in order to explore the therapeutic potential of RTK inhibitors. However, most of these studies neglected the potential metabolic impact of RTK inhibitors, which could be highly associated with drug efficacy and adverse effects during treatment.

METHODS

In order to fill these knowledge gaps and improve the therapeutic utilization of RTK inhibitors a large-scale computational simulation/analysis over multiple types of cancers with the treatment responses of RTK inhibitors was performed. The pharmacological data of all eight RTK inhibitor and gene expression profiles of 479 cell lines from The Cancer Cell Line Encyclopedia were used.

RESULTS

The potential metabolic impact of RTK inhibitors on different types of cancers were analyzed resulting in cancer-specific (breast, liver, pancreas, central nervous system) metabolic signatures. Many of these are in line with results from different independent studies, thereby providing indirect verification of the obtained results.

CONCLUSIONS

Our study demonstrates the potential of using a computational approach on signature-based-analysis over multiple cancer types. The results reveal the strength of multiple-cancer analysis over conventional signature-based analysis on a single cancer type.

A multitargeted probe-based strategy to identify signaling vulnerabilities in cancers

Most cancer cells are dependent on a network of deregulated signaling pathways for survival and are insensitive, or rapidly evolve resistance, to selective inhibitors aimed at a single target. For these reasons, drugs that target more than one protein (polypharmacology) can be clinically advantageous. The discovery of useful polypharmacology remains serendipitous and is challenging to characterize and validate. In this study, we developed a non-genetic strategy for the identification of pathways that drive cancer cell proliferation and represent exploitable signaling vulnerabilities. Our approach is based on using a multitargeted kinase inhibitor, SM1-71, as a tool compound to identify combinations of targets whose simultaneous inhibition elicits a potent cytotoxic effect. As a proof of concept, we applied this approach to a KRAS-dependent non-small cell lung cancer (NSCLC) cell line, H23-KRAS^G12C Using a combination of phenotypic screens, signaling analyses, and kinase inhibitors, we found that dual inhibition of MEK1/2 and insulin-like growth factor 1 receptor (IGF1R)/insulin receptor (INSR) is critical for blocking proliferation in cells. Our work supports the value of multitargeted tool compounds with well-validated polypharmacology and target space as tools to discover kinase dependences in cancer. We propose that the strategy described here is complementary to existing genetics-based approaches, generalizable to other systems, and enabling for future mechanistic and translational studies of polypharmacology in the context of signaling vulnerabilities in cancers.

Targeted Therapies in Type II Endometrial Cancers: Too Little, but Not Too Late

Type II endometrial carcinomas (ECs) are responsible for most endometrial cancer-related deaths due to their aggressive nature, late stage detection and high tolerance for standard therapies. However, there are no targeted therapies for type II ECs, and they are still treated the same way as the clinically indolent and easily treatable type I ECs. Therefore, type II ECs are in need of new treatment options. More recently, molecular analysis of endometrial cancer revealed phosphorylation-dependent oncogenic signalling in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways to be most frequently altered in type II ECs. Consequently, clinical trials tested pharmacologic kinase inhibitors targeting these pathways, although mostly with rather disappointing results. In this review, we highlight the most common genetic alterations in type II ECs. Additionally, we reason why most clinical trials for ECs using targeted kinase inhibitors had unsatisfying results and what should be changed in future clinical trial setups. Furthermore, we argue that, besides kinases, phosphatases should no longer be ignored in clinical trials, particularly in type II ECs, where the tumour suppressive phosphatase protein phosphatase type 2A (PP2A) is frequently mutated. Lastly, we discuss the therapeutic potential of targeting PP2A for (re)activation, possibly in combination with pharmacologic kinase inhibitors.

MicroRNAs as Mediators of Resistance Mechanisms to Small-Molecule Tyrosine Kinase Inhibitors in Solid Tumours

Receptor tyrosine kinases (RTKs) are widely expressed transmembrane proteins that act as receptors for growth factors and other extracellular signalling molecules. Upon ligand binding, RTKs activate intracellular signalling cascades, and as such are involved in a broad variety of cellular functions including differentiation, proliferation, migration, invasion, angiogenesis, and survival under physiological as well as pathological conditions. Aberrant RTK activation can lead to benign proliferative conditions as well as to various forms of cancer. Indeed, more than 70% of the known oncogene and proto-oncogene transcripts involved in cancer code for RTKs. Consequently, these receptors are broadly studied as targets in the treatment of different tumours, and a large variety of small-molecule tyrosine kinase inhibitors (TKIs) are approved for therapy. In most cases, patients develop resistance to the TKIs within a short time. MicroRNAs are short (18-22 nucleotides) non-protein-coding RNAs that fine-tune cell homeostasis by controlling gene expression at the post-transcriptional level. Deregulation of microRNAs is common in many cancers, and increasing evidence exists for an important role of microRNAs in the development of resistance to therapies, including TKIs. In this review we focus on the role of microRNAs in mediating resistance to small-molecule TKIs in solid tumours.

Efficacy of pemetrexed-based regimens in advanced non-small cell lung cancer patients with activating epidermal growth factor receptor mutations after tyrosine kinase inhibitor failure: a systematic review

Pemetrexed-based chemotherapy regimens (pem regimens) are the standard first-line treatment option in patients with non-squamous non-small cell lung cancer (NSCLC). The objective of this systematic review was to assess the efficacy of pemetrexed in the context of epidermal growth factor receptor (EGFR) mutation-positive NSCLC following the failure of EGFR-tyrosine kinase inhibitor (TKI) treatment. We searched biomedical literature databases (PubMed, EMBASE, and the Cochrane library) and conference proceedings for studies evaluating the efficacy of pemetrexed monotherapy or pemetrexed combined with platinum or any other chemotherapeutic agent in EGFR-mutation-positive NSCLC after EGFR-TKI failure. We extracted data of primary outcomes of interest (progression-free survival [PFS], overall survival [OS], and overall response rate [ORR]). The weighted median PFS, OS, and ORR were then calculated. Of 83 potentially relevant studies, eight (three randomized studies and five retrospective studies) were identified (involving 1,193 patients) and included in this systematic review, with 640 patients receiving pem regimens. The weighted median PFS, median OS, and ORR for patients treated with pem regimens were 5.09 months, 15.91 months, and 30.19%, respectively. Our systematic review results showed a favorable efficacy profile of pem regimens in NSCLC patients with EGFR mutation after EGFR-TKI failure.

Store operated calcium entry is altered by the inhibition of receptors tyrosine kinase

SOCE (Store-Operated Calcium Entry) is the main mechanism by which external Ca²⁺ enters into non-excitable cells after endoplasmic reticulum emptying. It is implicated in several processes such as proliferation and migration. Alterations in SOCE could initiate or support the development of hallmarks of cancer. In this project, we showed that disruption of the EGFR/ErbB2-dependent signalling by lapatinib and CP-724714, two inhibitors of the receptor tyrosine kinase (RTK), dramatically reduced the amplitude of the SOCE in breast cancer cells. LY294002 and MK2206, two inhibitors of the PI3K/Akt pathway, mimicked the effect of the inhibition of EGFR/ErbB2. In contrast, inhibitors of the MAPK pathway had no effect on SOCE. The involvement of EGFR/ErbB2 receptors and the PI3K/Akt pathway in the regulation of SOCE was confirmed in other cell lines derived from various cancer types. All these results showed that SOCE is positively regulated by the PI3K/Akt pathway and that this effect may be suppressed by the inhibition of the upstream RTKs. Inhibition of SOCE might therefore contribute to the anticancer effects of RTK inhibitors.

Kinase inhibitors: the road ahead

Receptor tyrosine kinase signalling pathways have been successfully targeted to inhibit proliferation and angiogenesis for cancer therapy. However, kinase deregulation has been firmly demonstrated to play an essential role in virtually all major disease areas. Kinase inhibitor drug discovery programmes have recently broadened their focus to include an expanded range of kinase targets and therapeutic areas. In this Review, we provide an overview of the novel targets, biological processes and disease areas that kinase-targeting small molecules are being developed against, highlight the associated challenges and assess the strategies and technologies that are enabling efficient generation of highly optimized kinase inhibitors.

Recent development in clinical applications of PD-1 and PD-L1 antibodies for cancer immunotherapy

Antibodies against programmed death (PD) pathway are revolutionizing cancer immunotherapy. Currently five antibodies against PD-1/PD-L1 have been approved. The clinical use of these antibodies is rapidly expanding. Incorporation of PD antibodies into chemotherapy regimens is in active clinical investigations. The combination of pembrolizumab with carboplatin and pemetrexed has been approved for the first line therapy of metastatic non-squamous non-small cell lung cancer. Combination of PD-1/PD-L1 antibodies with small molecule inhibitors such as tyrosine kinase inhibitors and IDO inhibitors are in active clinical trials. This review summarized recent development in clinical trials of PD-1 and PD-L1 antibodies for cancer immunotherapy.

The afatinib resistance of in vivo generated H1975 lung cancer cell clones is mediated by SRC/ERBB3/c-KIT/c-MET compensatory survival signaling

We generated afatinib resistant clones of H1975 lung cancer cells by transient exposure of established tumors to the drug and collected the re-grown tumors. Afatinib resistant H1975 clones did not exhibit any additional mutations in proto-oncogenes when compared to control clones. Afatinib resistant H1975 tumor clones expressed less PTEN than control clones and in afatinib resistant clones this correlated with increased basal SRC Y416, ERBB3 Y1289, AKT T308 and mTOR S2448 phosphorylation, decreased expression of ERBB1, ERBB2 and ERBB3 and increased total expression of c-MET, c-KIT and PDGFRβ. Afatinib resistant clones were selectively killed by knock down of [ERBB3 + c-MET + c-KIT] but not by the individual or doublet knock down combinations. The combination of the ERBB1/2/4 inhibitor afatinib with the SRC family inhibitor dasatinib killed afatinib resistant H1975 cells in a greater than additive fashion; other drugs used in combination with dasatinib such as sunitinib, crizotinib and amufatinib were less effective. [Afatinib + dasatinib] treatment profoundly inactivated ERBB3, AKT and mTOR in the H1975 afatinib resistant clones and increased ATG13 S318 phosphorylation. Knock down of ATG13, Beclin1 or eIF2α strong suppressed killing by [ERBB3 + c-MET + c-KIT] knock down, but were only modestly protective against [afatinib + dasatinib] lethality. Thus afatinib resistant H1975 NSCLC cells rely on ERBB1- and SRC-dependent hyper-activation of residual ERBB3 and elevated signaling, due to elevated protein expression, from wild type c-MET and c-KIT to remain alive. Inhibition of ERBB3 signaling via both blockade of SRC and ERBB1 results in tumor cell death.

The equilibrium between antagonistic signaling pathways determines the number of synapses in Drosophila

The number of synapses is a major determinant of behavior and many neural diseases exhibit deviations in that number. However, how signaling pathways control this number is still poorly understood. Using the Drosophila larval neuromuscular junction, we show here a PI3K-dependent pathway for synaptogenesis which is functionally connected with other previously known elements including the Wit receptor, its ligand Gbb, and the MAPkinases cascade. Based on epistasis assays, we determined the functional hierarchy within the pathway. Wit seems to trigger signaling through PI3K, and Ras85D also contributes to the initiation of synaptogenesis. However, contrary to other signaling pathways, PI3K does not require Ras85D binding in the context of synaptogenesis. In addition to the MAPK cascade, Bsk/JNK undergoes regulation by Puc and Ras85D which results in a narrow range of activity of this kinase to determine normalcy of synapse number. The transcriptional readout of the synaptogenesis pathway involves the Fos/Jun complex and the repressor Cic. In addition, we identified an antagonistic pathway that uses the transcription factors Mad and Medea and the microRNA bantam to down-regulate key elements of the pro-synaptogenesis pathway. Like its counterpart, the anti-synaptogenesis signaling uses small GTPases and MAPKs including Ras64B, Ras-like-a, p38a and Licorne. Bantam downregulates the pro-synaptogenesis factors PI3K, Hiw, Ras85D and Bsk, but not AKT. AKT, however, can suppress Mad which, in conjunction with the reported suppression of Mad by Hiw, closes the mutual regulation between both pathways. Thus, the number of synapses seems to result from the balanced output from these two pathways.

Insulin-Mediated Signaling Facilitates Resistance to PDGFR Inhibition in Proneural hPDGFB-Driven Gliomas

Despite abundant evidence implicating receptor tyrosine kinases (RTK), including the platelet-derived growth factor receptor (PDGFR), in the pathogenesis of glioblastoma (GBM), the clinical use of RTK inhibitors in this disease has been greatly compromised by the rapid emergence of therapeutic resistance. To study the resistance of proneural gliomas that are driven by a PDGFR-regulated pathway to targeted tyrosine kinase inhibitors, we utilized a mouse model of proneural glioma in which mice develop tumors that become resistant to PDGFR inhibition. We found that tumors resistant to PDGFR inhibition required the expression and activation of the insulin receptor (IR)/insulin growth-like factor receptor (IGF1R) for tumor cell proliferation and survival. Cotargeting IR/IGF1R and PDGFR decreased the emergence of resistant clones in vitro Our findings characterize a novel model of glioma recurrence that implicates the IR/IGF1R signaling axis in mediating the development of resistance to PDGFR inhibition and provide evidence that IR/IGF1R signaling is important in the recurrence of the proneural subtype of glioma in which PDGF/PDGFR is most commonly expressed at a high level. Mol Cancer Ther; 16(4); 705-16. ©2017 AACR.

RON Signaling Is a Key Mediator of Tumor Progression in Many Human Cancers

With an increasing body of literature covering RON receptor tyrosine kinase function in different types of human cancers, it is becoming clear that RON has prominent roles in both cancer cells and in the tumor-associated microenvironment. RON not only activates several oncogenic signaling pathways in cancer cells, leading to more aggressive behavior, but also promotes an immunosuppressive, alternatively activated phenotype in macrophages and limits the antitumor immune response. These two unique functions of this oncogene, the strong correlation between RON expression and poor outcomes in cancer, and the high tolerability of a new RON inhibitor make it an exciting therapeutic target, the blocking of which offers an advantage toward improving the survival of cancer patients. Here, we discuss recent findings on the role of RON signaling in cancer progression and its potential in cancer therapy.

Distinct Receptor Tyrosine Kinase Subsets Mediate Anti-HER2 Drug Resistance in Breast Cancer

Targeted inhibitors of the human epidermal growth factor receptor 2 (HER2), such as trastuzumab and lapatinib, are among the first examples of molecularly targeted cancer therapy and have proven largely effective for the treatment of HER2-positive breast cancers. However, approximately half of those patients either do not respond to these therapies or develop secondary resistance. Although a few signaling pathways have been implicated, a comprehensive understanding of mechanisms underlying HER2 inhibitor drug resistance is still lacking. To address this critical question, we undertook a concerted approach using patient expression data sets, HER2-positive cell lines, and tumor samples biopsied both before and after trastuzumab treatment. Together, these methods revealed that high expression and activation of a specific subset of receptor tyrosine kinases (RTKs) was strongly associated with poor clinical prognosis and the development of resistance. Mechanistically, these RTKs are capable of maintaining downstream signal transduction to promote tumor growth via the suppression of cellular senescence. Consequently, these findings provide the rationale for the design of therapeutic strategies for overcoming drug resistance in breast cancer via combinational inhibition of the limited number of targets from this specific subset of RTKs.

EAI045: The fourth-generation EGFR inhibitor overcoming T790M and C797S resistance

The third-generation tyrosine kinase inhibitors (TKI), AZD9291 (osimertinib) and CO-1686 (rociletinib) of epidermal growth factor receptor (EGFR) are highly active against T790M positive non-small cell lung cancer (NSCLC). However, resistance develops rapidly. EGFR C797S mutation was reported to be a leading mechanism of resistance to the third-generation inhibitors. The C797S mutation appears to be an ideal target for overcoming the acquired resistance to the third-generation inhibitors. This review summarizes the latest development on the discovery of a fourth-generation EGFR TKI, EAI045.3.