Mechanisms of acquired resistance to ERK1/2 pathway inhibitors

Novel Biological Strategies for Melanoma Therapy: A Focus on lncRNAs and Their Targeting

Increasing evidence revealed that restoring the correct expression of lncRNAs could have implications in the management of melanoma patients. In this context, here, we aim to dissect the main characteristics of lncRNAs altered in melanoma and their crosstalk with the signaling pathways involved in the progression of this disease. We also highlight the role of nucleic acid-based techniques and natural compounds (i.e., phytochemicals) as a therapeutic tool to increase or silence their expression in cancer cells. Finally, we explore the advances in nanotechnologies as delivery systems to efficiently carry these chemicals into cancer cells, thus limiting their potential off-target effects. The analysis of the literature showed that HOTAIR, MALAT1, and H19 are the oncogenic lncRNAs most studied in melanoma, while MEG3 is an important tumor suppressor decreased in this cancer. The aberrant expression of these lncRNAs affects several hallmarks of cancer, e.g., proliferation, motility, and epithelial to mesenchymal transition, promoting the melanoma plasticity and drug resistance. In this frame, siRNA, antisense oligonucleotide, and CRISPR-Cas9 genome editing appear to be the most effective nucleic acid strategies to restore the physiologic expression of lncRNA, while curcumin, resveratrol, and quercetin are the main phytochemicals able to target and influence the expression of lncRNAs altered in cancer. Overall, this study provides a comprehensive overview regarding the role of lncRNAs in the phenotype plasticity of melanoma cells and their potential targeting using RNA-based therapy and natural products.

Targeting the RAS upstream and downstream signaling pathway for cancer treatment

Cancer often involves the overactivation of RAS/RAF/MEK/ERK (MAPK) and PI3K-Akt-mTOR pathways due to mutations in genes like RAS, RAF, PTEN, and PIK3CA. Various strategies are employed to address the overactivation of these pathways, among which targeted therapy emerges as a promising approach. Directly targeting specific proteins, leads to encouraging results in cancer treatment. For instance, RTK inhibitors such as imatinib and afatinib selectively target these receptors, hindering ligand binding and reducing signaling initiation. These inhibitors have shown potent efficacy against Non-Small Cell Lung Cancer. Other inhibitors, like lonafarnib targeting Farnesyltransferase and GGTI 2418 targeting geranylgeranyl Transferase, disrupt post-translational modifications of proteins. Additionally, inhibition of proteins like SOS, SH2 domain, and Ras demonstrate promising anti-tumor activity both in vivo and in vitro. Targeting downstream components with RAF inhibitors such as vemurafenib, dabrafenib, and sorafenib, along with MEK inhibitors like trametinib and binimetinib, has shown promising outcomes in treating cancers with BRAF-V600E mutations, including myeloma, colorectal, and thyroid cancers. Furthermore, inhibitors of PI3K (e.g., apitolisib, copanlisib), AKT (e.g., ipatasertib, perifosine), and mTOR (e.g., sirolimus, temsirolimus) exhibit promising efficacy against various cancers such as Invasive Breast Cancer, Lymphoma, Neoplasms, and Hematological malignancies. This review offers an overview of small molecule inhibitors targeting specific proteins within the RAS upstream and downstream signaling pathways in cancer.

Advances in research on autophagy mechanisms in resistance to endometrial cancer treatment

Administering medication is a crucial strategy in improving the prognosis for advanced endometrial cancer. However, the rise of drug resistance often leads to the resurgence of cancer or less-than-ideal treatment outcomes. Prior studies have shown that autophagy plays a dual role in the development and progression of endometrial cancer, closely associated with drug resistance. As a result, concentrating on autophagy and its combination with medical treatments might be a novel approach to improve the prognosis for endometrial cancer. This study explores the impact of autophagy on drug resistance in endometrial cancer, investigates its core mechanisms, and scrutinizes relevant treatments aimed at autophagy, aiming to illuminate the issue of treatment resistance in advanced endometrial cancer.

1,3-Dichloroadamantyl-Containing Ureas as Potential Triple Inhibitors of Soluble Epoxide Hydrolase, p38 MAPK and c-Raf

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of bioactive lipid signaling molecules. sEH converts epoxyeicosatrienoic acids (EET) to virtually inactive dihydroxyeicosatrienoic acids (DHET). The first acids are "medicinal" molecules, the second increase the inflammatory infiltration of cells. Mitogen-activated protein kinases (p38 MAPKs) are key protein kinases involved in the production of inflammatory mediators, including tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). p38 MAPK signaling plays an important role in the regulation of cellular processes, especially inflammation. The proto-oncogenic serine/threonine protein kinase Raf (c-Raf) is a major component of the mitogen-activated protein kinase (MAPK) pathway: ERK1/2 signaling. Normal cellular Raf genes can also mutate and become oncogenes, overloading the activity of MEK1/2 and ERK1/2. The development of multitarget inhibitors is a promising strategy for the treatment of socially dangerous diseases. We synthesized 1,3-disubstituted ureas and diureas containing a dichloroadamantyl moiety. The results of computational methods show that soluble epoxide hydrolase inhibitors can act on two more targets in different signaling pathways of mitogen-activated protein kinases p38 MAPK and c-Raf. The two chlorine atoms in the adamantyl moiety may provide additional Cl-π interactions in the active site of human sEH. Molecular dynamics studies have shown that the stability of ligand-protein complexes largely depends on the "spacer effect." The compound containing a bridge between the chloroadamantyl fragment and the ureide group forms more stable ligand-protein complexes with sEH and p38 MAPK, which indicates a better conformational ability of the molecule in the active sites of these targets. In turn, a compound containing two chlorine atoms forms a more stable complex with c-Raf, probably due to the presence of additional halogen bonds of chlorine atoms with amino acid residues.

Oncogenic KRASG12D Reprograms Lipid Metabolism by Upregulating SLC25A1 to Drive Pancreatic Tumorigenesis

Pancreatic cancer is a highly lethal disease with obesity as one of the risk factors. Oncogenic KRAS mutations are prevalent in pancreatic cancer and can rewire lipid metabolism by altering fatty acid (FA) uptake, FA oxidation (FAO), and lipogenesis. Identification of the underlying mechanisms could lead to improved therapeutic strategies for treating KRAS-mutant pancreatic cancer. Here, we observed that KRASG12D upregulated the expression of SLC25A1, a citrate transporter that is a key metabolic switch to mediate FAO, fatty acid synthesis, glycolysis, and gluconeogenesis. In genetically engineered mouse models and human pancreatic cancer cells, KRASG12D induced SLC25A1 upregulation via GLI1, which directly stimulated SLC25A1 transcription by binding its promoter. The enhanced expression of SLC25A1 increased levels of cytosolic citrate, FAs, and key enzymes in lipid metabolism. In addition, a high-fat diet (HFD) further stimulated the KRASG12D-GLI1-SLC25A1 axis and the associated increase in citrate and FAs. Pharmacologic inhibition of SLC25A1 and upstream GLI1 significantly suppressed pancreatic tumorigenesis in KrasG12D/+ mice on a HFD. These results reveal a KRASG12D-GLI1-SLC25A1 regulatory axis, with SLC25A1 as an important node that regulates lipid metabolism during pancreatic tumorigenesis, thus indicating an intervention strategy for oncogenic KRAS-driven pancreatic cancer.

SIGNIFICANCE

Upregulation of SLC25A1 induced by KRASG12D-GLI1 signaling rewires lipid metabolism and is exacerbated by HFD to drive the development of pancreatic cancer, representing a targetable metabolic axis to suppress pancreatic tumorigenesis.

Design, Synthesis, and Antitumor Activity Evaluation of Proteolysis-Targeting Chimeras as Degraders of Extracellular Signal-Regulated Kinases 1/2

Inhibition of the extracellular signal-regulated kinases 1/2 (ERK1/2) alone or in combination with other targets has emerged as a promising treatment strategy for a variety of human tumors. In addition to the development of inhibitors, the development of ERK1/2 degraders is an alternative approach to decrease its activity. We synthesized proteolysis-targeting chimeras (PROTACs) as effective ERK1/2 degraders, among which B1-10J showed high degradative activity, with DC50 of 102 nM and cytotoxic IC50 of 2.2 μM against HCT116 cells. Moreover, B1-10J dose-dependently inhibited tumor cell migration. Xenograft experiments in nude mice demonstrated that B1-10J inhibited HCT116 tumor cell growth and achieved significant regression of tumors at a daily dose of 25 mg/kg.

PLX4032 resistance of patient-derived melanoma cells: crucial role of oxidative metabolism

Background

Malignant melanoma is the most lethal form of skin cancer which shows BRAF mutation in 50% of patients. In this context, the identification of BRAFV600E mutation led to the development of specific inhibitors like PLX4032. Nevertheless, although its initial success, its clinical efficacy is reduced after six-months of therapy leading to cancer relapse due to the onset of drug resistance. Therefore, investigating the mechanisms underlying PLX4032 resistance is fundamental to improve therapy efficacy. In this context, several models of PLX4032 resistance have been developed, but the discrepancy between in vitro and in vivo results often limits their clinical translation.

Methods

The herein reported model has been realized by treating with PLX4032, for six months, patient-derived BRAF-mutated melanoma cells in order to obtain a reliable model of acquired PLX4032 resistance that could be predictive of patient's treatment responses. Metabolic analyses were performed by evaluating glucose consumption, ATP synthesis, oxygen consumption rate, P/O ratio, ATP/AMP ratio, lactate release, lactate dehydrogenase activity, NAD+/NADH ratio and pyruvate dehydrogenase activity in parental and drug resistant melanoma cells. The intracellular oxidative state was analyzed in terms of reactive oxygen species production, glutathione levels and NADPH/NADP+ ratio. In addition, a principal component analysis was conducted in order to identify the variables responsible for the acquisition of targeted therapy resistance.

Results

Collectively, our results demonstrate, for the first time in patient-derived melanoma cells, that the rewiring of oxidative phosphorylation and the maintenance of pyruvate dehydrogenase activity and of high glutathione levels contribute to trigger the onset of PLX4032 resistance.

Conclusion

Therefore, it is possible to hypothesize that inhibitors of glutathione biosynthesis and/or pyruvate dehydrogenase activity could be used in combination with PLX4032 to overcome drug resistance of BRAF-mutated melanoma patients. However, the identification of new adjuvant targets related to drug-induced metabolic reprogramming could be crucial to counteract the failure of targeted therapy in metastatic melanoma.

Targeting KRAS-mutant stomach/colorectal tumors by disrupting the ERK2-p53 complex

KRAS is widely mutated in human cancers, resulting in unchecked tumor proliferation and metastasis, which makes identifying KRAS-targeting therapies a priority. Herein, we observe that mutant KRAS specifically promotes the formation of the ERK2-p53 complex in stomach/colorectal tumor cells. Disruption of this complex by applying MEK1/2 and ERK2 inhibitors elicits strong apoptotic responses in a p53-dependent manner, validated by genome-wide knockout screening. Mechanistically, p53 physically associates with phosphorylated ERK2 through a hydrophobic interaction in the presence of mutant KRAS, which suppresses p53 activation by preventing the recruitment of p300/CBP; trametinib disrupts the ERK2-p53 complex by reducing ERK2 phosphorylation, allowing the acetylation of p53 protein by recruiting p300/CBP; acetylated p53 activates PUMA transcription and thereby kills KRAS-mutant tumors. Our study shows an important role for the ERK2-p53 complex and provides a potential therapeutic strategy for treating KRAS-mutant cancer.

Discovery of Coumarin-Based MEK1/2 PROTAC Effective in Human Cancer Cells

The RAF/MEK/ERK pathway is a crucial signal path which is closely associated with the proliferation, differentiation, and apoptosis of tumors. MEK1/2 is a key kinase target in the pathway, with ERK1/2 acting as the main substrate of it. Despite the rapid development of MEK1/2 inhibitors, acquired resistance still happens and remains a significant problem. Most of the inhibitors possess a similar diarylamine scaffold. Here we designed and synthesized a series of MEK1/2 degraders based on a coumarin derivative which was a potent non-diarylamine allosteric MEK1/2 inhibitor. P6b among them showed the most potent degradation effect, with DC50 values of 0.3 μM and 0.2 μM in MEK1 and MEK2 degradation, respectively. An antiproliferation assay showed that it more significantly inhibits the growth of A375 cells (IC50= 2.8 μM) compared to A549 cells (IC50 = 27.3 μM). To sum up, we discovered P6b with a non-diarylamine scaffold for the first time as a potent MEK PROTAC effective in human cancer cells.

The Agonist of Adenosine A1 Receptor Induced Desensitization of delta Opioid receptor-mediated Raf-1/MEK/ERK Signaling by Feedback Phosphorylation of Raf-1-Ser289/296/301

Our previous study found that activation of adenosine A1 receptor (A₁R) induced phosphorylation of delta opioid receptor (DOR) and desensitization of its downstream signaling molecules, cAMP and Akt. To further investigate the effect of A₁R agonist on DOR signaling and the underlying mechanism, we examined the effect of A₁R activation upon binding of its agonist N6-cyclohexyl-adenosine (CHA) on DOR-mediated Raf-1/MEK/ERK activation, and found that prolonged CHA exposure resulted in downregulation of DOR-mediated Raf-1/MEK/ERK signaling pathway. CHA-treatment time dependently attenuated Raf-1-Ser338 phosphorylation induced by [D-Pen2,5] enkephalin (DPDPE), a specific agonist of DOR, and further caused downregulation of the Raf-1/MEK/ERK signaling pathway activated by DOR agonist. Moreover, CHA exposure time-dependently induced the phosphorylation of Raf-1-Ser289/296/301, the inhibitory phosphorylation sites that were regulated by negative feedback, thereby inhibiting activation of the MEK/ERK pathway, and this effect could be blocked by MEK inhibitor U0126. Finally, we proved that the heterologous desensitization of the Raf-1/MEK/ERK cascade was essential in the regulation of anti-nociceptive effect of DOR agonists by confirming that such effect was inhibited by pretreatment of CHA. Therefore, we conclude that the activation of A₁R inhibits DOR-mediated MAPK signaling pathway via heterologous desensitization of the Raf-1/MEK/ERK cascade, which is a result of ERK-mediated Raf-1-Ser289/296/301 phosphorylation mediated by activation of A₁R.

Immune Checkpoint Inhibitors and RAS-ERK Pathway-Targeted Drugs as Combined Therapy for the Treatment of Melanoma

Metastatic melanoma is a highly immunogenic tumor with very poor survival rates due to immune system escape-mechanisms. Immune checkpoint inhibitors (ICIs) targeting the cytotoxic T-lymphocyte-associated protein 4 (CTLA4) and the programmed death-1 (PD1) receptors, are being used to impede immune evasion. This immunotherapy entails an increment in the overall survival rates. However, melanoma cells respond with evasive molecular mechanisms. ERK cascade inhibitors are also used in metastatic melanoma treatment, with the RAF activity blockade being the main therapeutic approach for such purpose, and in combination with MEK inhibitors improves many parameters of clinical efficacy. Despite their efficacy in inhibiting ERK signaling, the rewiring of the melanoma cell-signaling results in disease relapse, constituting the reinstatement of ERK activation, which is a common cause of some resistance mechanisms. Recent studies revealed that the combination of RAS-ERK pathway inhibitors and ICI therapy present promising advantages for metastatic melanoma treatment. Here, we present a recompilation of the combined therapies clinically evaluated in patients.

ERK5 Signalling and Resistance to ERK1/2 Pathway Therapeutics: The Path Less Travelled?

The RAS-regulated RAF-MEK1/2-ERK1/2 signalling pathway is frequently de-regulated in human cancer. Melanoma in particular exhibits a high incidence of activating BRAFV600E/K and NRASQ61L/K mutations and such cells are addicted to the activity of these mutant oncoproteins. As a result three different BRAF inhibitors (BRAFi) have now been approved for BRAFV600E/K- mutant melanoma and have transformed the treatment of this disease. Despite this, clinical responses are typically transient as tumour cells develop resistance. These resistance mechanisms frequently involve reinstatement of ERK1/2 signalling and BRAFi are now deployed in combination with one of three approved MEK1/2 inhibitors (MEKi) to provide more durable, but still transient, clinical responses. Furthermore, inhibitors to ERK1/2 (ERK1/2i) have also been developed to counteract ERK1/2 signalling. However, recent studies have suggested that BRAFi/MEKi and ERK1/2i resistance can arise through activation of a parallel signalling pathway leading to activation of ERK5, an unusual protein kinase that contains both a kinase domain and a transcriptional transactivation domain. Here we review the evidence supporting ERK5 as a mediator of BRAFi/MEKi and ERK1/2i resistance. We also review the challenges in targeting ERK5 signalling with small molecules, including paradoxical activation of the transcriptional transactivation domain, and discuss new therapeutic modalities that could be employed to target ERK5.

Identification of a Novel Inhibitor of TfR1 from Designed and Synthesized Muriceidine A Derivatives

The transferrin receptor 1 (TfR1) plays a key role in cellular iron uptake through its interaction with iron-bound Tf. TfR1 is often reported to be overexpressed in malignant cells, and this increase may be associated with poor prognosis in different types of cancer, which makes it an attractive target for antitumor therapy. The marine natural product Muriceidine A is a potent anticancer agent reported in our previous work. In this study, we designed and synthesized a series of Muriceidine A derivatives and described the systematic investigation into their cytotoxic activities against four tumor cells. Most of the derivatives showed stronger antitumor activity and we found that the introduction of electron-donating groups at position C-2 of unsaturated piperidine was beneficial to anticancer activity and unsaturated piperidine was responsible for the antiproliferative activity. Among these compounds, 12b (methyl at position C-2 of unsaturated piperidine) exhibited the strongest cytotoxicity against MDA-MB-231 cells. Further pharmacological research showed that 12b bound to Transferrin receptor 1 (TfR1) directly caused iron deprivation and ROS imbalance along with the degradations of several oncoproteins, especially FGFR1, through the proteasome pathway; thus, inducing cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells. Our findings indicate that 12b is a promising lead compound targeting TfR1 for triple negative breast cancer.

Discovery of SHR2415, a Novel Pyrrole-Fused Urea Scaffold ERK1/2 Inhibitor

ERK1/2 kinase is a key downstream node of the RAS-RAF-MEK-ERK signaling pathway. A highly potent and selective ERK1/2 inhibitor is a promising option for cancer treatment that will provide a potential solution for overcoming drug resistance. Herein we designed and synthesized a novel scaffold featuring a pyrrole-fused urea template. The lead compound, SHR2415, was shown to be a highly potent ERK1/2 inhibitor that exhibited high cell potency based on the Colo205 assay. In addition, SHR2415 displayed favorable PK profiles across species as well as robust in vivo efficacy in a mouse Colo205 xenograft model.

Revealing molecular pathways for cancer cell fitness through a genetic screen of the cancer translatome

The major cap-binding protein eukaryotic translation initiation factor 4E (eIF4E), an ancient protein required for translation of all eukaryotic genomes, is a surprising yet potent oncogenic driver. The genetic interactions that maintain the oncogenic activity of this key translation factor remain unknown. In this study, we carry out a genome-wide CRISPRi screen wherein we identify more than 600 genetic interactions that sustain eIF4E oncogenic activity. Our data show that eIF4E controls the translation of Tfeb, a key executer of the autophagy response. This autophagy survival response is triggered by mitochondrial proteotoxic stress, which allows cancer cell survival. Our screen also reveals a functional interaction between eIF4E and a single anti-apoptotic factor, Bcl-xL, in tumor growth. Furthermore, we show that eIF4E and the exon-junction complex (EJC), which is involved in many steps of RNA metabolism, interact to control the migratory properties of cancer cells. Overall, we uncover several cancer-specific vulnerabilities that provide further resolution of the cancer translatome.

Research progress of MEK1/2 inhibitors and degraders in the treatment of cancer

Mitogen-activated protein kinase kinases 1 and 2 (MEK1/2) are the crucial part of the RAS-RAF-MEK-ERK pathway (or ERK pathway), which is involved in the regulation of various cellular processes including proliferation, survival, and differentiation et al. Targeting MEK has become an important strategy for cancer therapy, and 4 MEK inhibitors (MEKis) have been approved by FDA to date. However, the application of MEKis is limited due to acquired resistance under long-term treatment. Fortunately, an emerging technology, named proteolysis targeting chimera (PROTAC), could break through this limitation by inducing MEK1/2 degradation. Compared to MEKis, MEK1/2 PROTAC is rarely studied and only three MEK1/2 PROTAC molecules, have been reported until now. This paper will outline the ERK pathway and the mechanism and research progress of MEK1/2 inhibitors, but focus on the development of MEK degraders and their optimization strategies. PAC-1 strategy which can induce MEK degradation indirectly, other PROTACs on ERK pathway, the advantages and challenges of PROTAC technology will be subsequently discussed.

Playing the Whack-A-Mole Game: ERK5 Activation Emerges Among the Resistance Mechanisms to RAF-MEK1/2-ERK1/2- Targeted Therapy

Molecularly tailored therapies have opened a new era, chronic myeloid leukemia being the ideal example, in the treatment of cancer. However, available therapeutic options are still unsatisfactory in many types of cancer, and often fail due to the occurrence of resistance mechanisms. With regard to small-molecule compounds targeting the components of the Mitogen-Activated Protein Kinase (MAPK) cascade RAF-MEK1/2-ERK1/2, these drugs may result ineffective as a consequence of the activation of compensatory pro-survival/proliferative signals, including receptor tyrosine kinases, PI3K, as well as other components of the MAPK family such as TPL2/COT. The MAPK ERK5 has been identified as a key signaling molecule in the biology of several types of cancer. In this review, we report pieces of evidence regarding the activation of the MEK5-ERK5 pathway as a resistance mechanism to RAF-MEK1/2-ERK1/2 inhibitors. We also highlight the known and possible mechanisms underlying the cross-talks between the ERK1/2 and the ERK5 pathways, the characterization of which is of great importance to maximize, in the future, the impact of RAF-MEK1/2-ERK1/2 targeting. Finally, we emphasize the need of developing additional therapeutically relevant MEK5-ERK5 inhibitors to be used for combined treatments, thus preventing the onset of resistance to cancer therapies relying on RAF-MEK1/2-ERK1/2 inhibitors.

The effects of mutant Ras proteins on the cell signalome

The genetic alterations in cancer cells are tightly linked to signaling pathway dysregulation. Ras is a key molecule that controls several tumorigenesis-related processes, and mutations in RAS genes often lead to unbiased intensification of signaling networks that fuel cancer progression. In this article, we review recent studies that describe mutant Ras-regulated signaling routes and their cross-talk. In addition to the two main Ras-driven signaling pathways, i.e., the RAF/MEK/ERK and PI3K/AKT/mTOR pathways, we have also collected emerging data showing the importance of Ras in other signaling pathways, including the RAC/PAK, RalGDS/Ral, and PKC/PLC signaling pathways. Moreover, microRNA-regulated Ras-associated signaling pathways are also discussed to highlight the importance of Ras regulation in cancer. Finally, emerging data show that the signal alterations in specific cell types, such as cancer stem cells, could promote cancer development. Therefore, we also cover the up-to-date findings related to Ras-regulated signal transduction in cancer stem cells.

Design, Synthesis, and In Vitro/In Vivo Anti-Cancer Activities of Novel (20S)-10,11-Methylenedioxy-Camptothecin Heterocyclic Derivatives

A novel camptothecin analogue, (20S)-10,11-methylenedioxy-camptothecin (FL118), has been proven to show significant antitumor efficacy for a wide variety of solid tumors. However, the further development of FL118 is severely hindered due to its extremely poor water solubility and adverse side effects. Here, two series of novel 20-substituted (20S)-10,11-methylenedioxy-camptothecin coupled with 5-substituted uracils and other heterocyclic rings through glycine were synthesized. All the derivatives showed superior cytotoxic activities in vitro with IC50 values in the nanomolar range. Among them, 12e displayed higher cytotoxic activities in several cancer cell lines with better water solubility than FL118. Our results further showed that, like FL118, 12e inhibited cell proliferation resulting from cell cycle arrest and apoptosis by blocking the anti-apoptotic gene transcription of survivin, Mcl-1, Bcl-2, and XIAP in both A549 cells and NCI-H446 cells. Furthermore, 12e did not show any inhibitory activity on Topo I, which is involved in hematopoietic toxicity. In vivo, 12e showed similar antitumor efficacy to FL118 but lower toxicity. Our findings indicate that 12e is a promising therapeutic agent for cancer treatment, and the core structure of FL118 represents a promising platform to generate novel FL118-based antitumor drugs.

Discoidin Domain Receptors in Melanoma: Potential Therapeutic Targets to Overcome MAPK Inhibitor Resistance

Melanoma is a highly malignant skin cancer with high propensity to metastasize and develop drug resistance, making it a difficult cancer to treat. Current therapies targeting BRAF (V600) mutations are initially effective, but eventually tumors overcome drug sensitivity and reoccur. This process is accomplished in part by reactivating alternate signaling networks that reinstate melanoma proliferative and survival capacity, mostly through reprogramming of receptor tyrosine kinase (RTK) signaling. Evidence indicates that the discoidin domain receptors (DDRs), a set of RTKs that signal in response to collagen, are part of the kinome network that confer drug resistance. We previously reported that DDR1 is expressed in melanomas, where it can promote tumor malignancy in mouse models of melanoma, and thus, DDR1 could be a promising target to overcome drug resistance. In this review, we summarize the current knowledge on DDRs in melanoma and their implication for therapy, with emphasis in resistance to MAPK inhibitors.

Tissue dynamics spectroscopic imaging: functional imaging of heterogeneous cancer tissue

SIGNIFICANCE

Tumor heterogeneity poses a challenge for the chemotherapeutic treatment of cancer. Tissue dynamics spectroscopy captures dynamic contrast and can capture the response of living tissue to applied therapeutics, but the current analysis averages over the complicated spatial response of living biopsy samples.

AIM

To develop tissue dynamics spectroscopic imaging (TDSI) to map the heterogeneous spatial response of tumor tissue to anticancer drugs.

APPROACH

TDSI is applied to tumor spheroids grown from cell lines and to ex vivo living esophageal biopsy samples. Doppler fluctuation spectroscopy is performed on a voxel basis to extract spatial maps of biodynamic biomarkers. Functional images and bivariate spatial maps are produced using a bivariate color merge to represent the spatial distribution of pairs of signed drug-response biodynamic biomarkers.

RESULTS

We have mapped the spatial variability of drug responses within biopsies and have tracked sample-to-sample variability. Sample heterogeneity observed in the biodynamic maps is associated with histological heterogeneity observed using inverted selective-plane illumination microscopy.

CONCLUSION

We have demonstrated the utility of TDSI as a functional imaging method to measure tumor heterogeneity and its potential for use in drug-response profiling.

RAF kinase dimerization: implications for drug discovery and clinical outcomes

The RAF kinases activated by RAS GTPases regulate cell growth and division by signal transduction through the ERK cascade and mutations leading to constitutive activity are key drivers of human tumors, as are upstream activators including RAS and receptor tyrosine kinases. The development of first-generation RAF inhibitors, including vemurafenib (VEM) and dabrafenib led to initial excitement due to high response rates and profound regression of malignant melanomas carrying BRAF^V600E mutations. The excitement about these unprecedented response rates, however, was tempered by tumor unresponsiveness through both intrinsic and acquired drug-resistance mechanisms. In recent years much insight into the complexity of the RAS-RAF axis has been obtained and inactivation and signal transduction mechanisms indicate that RAF dimerization is a critical step in multiple cellular contexts and plays a key role in resistance. Both homo- and hetero-dimerization of BRAF and CRAF can modulate therapeutic response and disease progression in patients treated with ATP-competitive inhibitors and are therefore highly clinically significant. Ten years after the definition of the RAF dimer interface (DIF) by crystallography, this review focuses on the implications of RAF kinase dimerization in signal transduction and for drug development, both from a classical ATP-competitive standpoint and from the perspective of new therapeutic strategies including inhibiting dimer formation. A structural perspective of the DIF, how dimerization impacts inhibitor activation and the structure-based design of next-generation RAF kinase inhibitors with unique mechanisms of action is presented. We also discuss potential fields of application for DIF inhibitors, ranging from non-V600E oncoproteins and BRAF fusions to tumors driven by aberrant receptor tyrosine kinase or RAS signaling.

Protein Expression in Metastatic Melanoma and the Link to Disease Presentation in a Range of Tumor Phenotypes

Malignant melanoma is among the most aggressive skin cancers and it has among the highest metastatic potentials. Although surgery to remove the primary tumor is the gold standard treatment, once melanoma progresses and metastasizes to the lymph nodes and distal organs, i.e., metastatic melanoma (MM), the usual outcome is decreased survival. To improve survival rates and life span, advanced treatments have focused on the success of targeted therapies in the MAPK pathway that are based on BRAF (BRAF V600E) and MEK. The majority of patients with tumors that have higher expression of BRAF V600E show poorer prognosis than patients with a lower level of the mutated protein. Based on the molecular basis of melanoma, these findings are supported by distinct tumor phenotypes determined from differences in tumor heterogeneity and protein expression profiles. With these aspects in mind, continued challenges are to: (1) deconvolute the complexity and heterogeneity of MM; (2) identify the signaling pathways involved; and (3) determine protein expression to develop targeted therapies. Here, we provide an overview of the results from protein expression in MM and the link to disease presentation in a variety of tumor phenotypes and how these will overcome the challenges of clinical problems and suggest new promising approaches in metastatic melanoma and cancer therapy.

Discovery of a First-in-Class Mitogen-Activated Protein Kinase Kinase 1/2 Degrader

MEK1 and MEK2 (also known as MAP2K1 and MAP2K2) are the "gatekeepers" of the ERK signaling output with redundant roles in controlling ERK activity. Numerous inhibitors targeting MEK1/2 have been developed including three FDA-approved drugs. However, acquired resistance to MEK1/2 inhibitors has been observed in patients, and new therapeutic strategies are needed to overcome the resistance. Here, we report a first-in-class degrader of MEK1/2, MS432 (23), which potently and selectively degraded MEK1 and MEK2 in a VHL E3 ligase- and proteasome-dependent manner and suppressed ERK phosphorylation in cells. It inhibited colorectal cancer and melanoma cell proliferation much more effectively than its negative control MS432N (24), and its effect was phenocopied by MEK1/2 knockdown. Compound 23 was highly selective for MEK1/2 in global proteomic profiling studies. It was also bioavailable in mice and can be used for in vivo efficacy studies. We provide two well-characterized chemical tools to the biomedical community.

Mitotic checkpoint kinase Mps1/TTK predicts prognosis of colon cancer patients and regulates tumor proliferation and differentiation via PKCα/ERK1/2 and PI3K/Akt pathway

Mps1/TTK plays an important role in development of many tumors. The purpose of the present study was designed to investigate the role of TTK in colon cancer. We analyzed TTK and colon cancer in the GEO database, colon cancer tissues and normal tissues were collected to verify the results by immunohistochemistry. We detected the TTK expression in the colon cancer cell lines, and overexpressed or silenced TTK expression in colon cancer cell lines. GEO database showed that the expression of TTK was higher in the colon cancer tissues than normal tissues, higher level of TTK shows unfavourable prognosis in colon patients. Furthermore, high differentiation of colon shows the lower expression of TTK. The higher expression of TTK links with the high microsatellite status. However, the expression of TTK has no significant difference among the different stages of colon cancer patients, and has no significant relationship with recurrence or relapse. Here, we also report that the differential expression of TTK in colon cancer cells alters the intrinsic negative regulation of cell proliferation and differentiation, resulting in the difference of proliferation and differentiation capacity. TTK could activate the PKCα/ERK1/2 to influence the proliferation and inactivate the PI3K/AKT pathway to inhibition the expression of MUC2 and TFF3 that related to the differentiation of colon cells. In conclusions, TTK promote the colon cancer cell proliferation via activation of PKCα/ERK1/2 and inhibit the differentiation via inactivation of PI3K/Akt pathway. TTK inhibition may be the potential therapeutic pathway for the treatment of colon cancer.

Development of ERK1/2 inhibitors as a therapeutic strategy for tumour with MAPK upstream target mutations

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylate a variety of substrates that play key roles in promoting cell survival and proliferation. Many inhibitors, acting on upstream of the ERK pathway, exhibit excellent antitumor activity. However, drug-resistant tumour cells invariably emerge after their use due to the reactivation of ERK1/2 signalling. ERK1/2 inhibitors have shown clinical efficacy as a therapeutic strategy for the treatment of tumours with mitogen-activated protein kinase (MAPK) upstream target mutations. These inhibitors may be effective against cancers with altered MAPK upstream pathway and may be used as a possible strategy to overcome acquired resistance to MAPK inhibitors. In this review, we describe the mechanism and types of ERK1/2 inhibitors, summarise the current development status of small-molecule ERK1/2 inhibitors, including the preclinical data and clinical study progress, and discuss the future research directions for the application of ERK1/2 inhibitors.

Selective ERK1/2 agonists isolated from Melia azedarach with potent anti-leukemic activity

BACKGROUND

MAPK/ERK kinases transmit signals from many growth factors/kinase receptors during normal cell growth/differentiation, and their dysregulation is a hallmark of diverse types of cancers. A plethora of drugs were developed to block this kinase pathway for clinical application. With the exception of a recently identified agent, EQW, most of these inhibitors target upstream factors but not ERK1/2; no activator of ERK1/2 is currently available.

METHOD

A library of compounds isolated from medicinal plants of China was screened for anti-cancer activities. Three limonoid compounds, termed A1541-43, originally isolated from the plant Melia azedarach, exhibiting strong anti-leukemic activity. The anti-neoplastic activity and the biological target of these compounds were explored using various methods, including western blotting, flow cytometry, molecular docking and animal model for leukemia.

RESULTS

Compounds A1541-43, exhibiting potent anti-leukemic activity, was shown to induce ERK1/2 phosphorylation. In contrast, the natural product Cedrelone, which shares structural similarities with A1541-43, functions as a potent inhibitor of ERK1/2. We provided evidence that A1541-43 and Cedrelone specifically target ERK1/2, but not the upstream MAPK/ERK pathway. Computational docking analysis predicts that compounds A1541-43 bind a region in ERK1/2 that is distinct from that to which Cedrelone and EQW bind. Interestingly, both A1541-43, which act as ERK1/2 agonists, and Cedrelone, which inhibit these kinases, exerted strong anti-proliferative activity against multiple leukemic cell lines, and induced robust apoptosis as well as erythroid and megakaryocytic differentiation in erythroleukemic cell lines. These compounds also suppressed tumor progression in a mouse model of erythroleukemia.

CONCLUSIONS

This study identifies for the first time activators of ERK1/2 with therapeutic potential for the treatment of cancers driven by dysregulation of the MAPK/ERK pathway and possibly for other disorders.

Extracellular-Signal Regulated Kinase: A Central Molecule Driving Epithelial-Mesenchymal Transition in Cancer

Epithelial-mesenchymal transition (EMT) is a reversible cellular process, characterized by changes in gene expression and activation of proteins, favoring the trans-differentiation of the epithelial phenotype to a mesenchymal phenotype. This process increases cell migration and invasion of tumor cells, progression of the cell cycle, and resistance to apoptosis and chemotherapy, all of which support tumor progression. One of the signaling pathways involved in tumor progression is the MAPK pathway. Within this family, the ERK subfamily of proteins is known for its contributions to EMT. The ERK subfamily is divided into typical (ERK 1/2/5), and atypical (ERK 3/4/7/8) members. These kinases are overexpressed and hyperactive in various types of cancer. They regulate diverse cellular processes such as proliferation, migration, metastasis, resistance to chemotherapy, and EMT. In this context, in vitro and in vivo assays, as well as studies in human patients, have shown that ERK favors the expression, function, and subcellular relocalization of various proteins that regulate EMT, thus promoting tumor progression. In this review, we discuss the mechanistic roles of the ERK subfamily members in EMT and tumor progression in diverse biological systems.

Targeting ERK beyond the boundaries of the kinase active site in melanoma

Extracellular signal-regulated kinase 1/2 (ERK1/2) constitute a point of convergence for complex signaling events that regulate essential cellular processes, including proliferation and survival. As such, dysregulation of the ERK signaling pathway is prevalent in many cancers. In the case of BRAF-V600E mutant melanoma, ERK inhibition has emerged as a viable clinical approach to abrogate signaling through the ERK pathway, even in cases where MEK and Raf inhibitor treatments fail to induce tumor regression due to resistance mechanisms. Several ERK inhibitors that target the active site of ERK have reached clinical trials, however, many critical ERK interactions occur at other potentially druggable sites on the protein. Here we discuss the role of ERK signaling in cell fate, in driving melanoma, and in resistance mechanisms to current BRAF-V600E melanoma treatments. We explore targeting ERK via a distinct site of protein-protein interaction, known as the D-recruitment site (DRS), as an alternative or supplementary mode of ERK pathway inhibition in BRAF-V600E melanoma. Targeting the DRS with inhibitors in melanoma has the potential to not only disrupt the catalytic apparatus of ERK but also its noncatalytic functions, which have significant impacts on spatiotemporal signaling dynamics and cell fate.

AKT and ERK dual inhibitors: The way forward?

Phosphatidylinositol 3-kinase (PI3K)/AKT pathway regulates cell growth, proliferation, survival, mobility and invasion. Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway is also an important mitogenic signaling pathway involved in various cellular progresses. AKT, also named protein kinase B (PKB), is a primary mediator of the PI3K signaling pathway; and ERK at the end of MAPK signaling is the unique substrate and downstream effector of mitogen-activated protein/extracellular signal-regulated kinase (MEK). The AKT and ERK signaling are both aberrantly activated in a wide range of human cancers and have long been targeted for cancer therapy, but the clinical benefits of these targeted therapies have been limited due to complex cross-talk. Novel strategies, such as AKT/ERK dual inhibitors, may be needed.

MEK1/2 inhibitor withdrawal reverses acquired resistance driven by BRAFV600E amplification whereas KRASG13D amplification promotes EMT-chemoresistance

Acquired resistance to MEK1/2 inhibitors (MEKi) arises through amplification of BRAFV600E or KRASG13D to reinstate ERK1/2 signalling. Here we show that BRAFV600E amplification and MEKi resistance are reversible following drug withdrawal. Cells with BRAFV600E amplification are addicted to MEKi to maintain a precise level of ERK1/2 signalling that is optimal for cell proliferation and survival, and tumour growth in vivo. Robust ERK1/2 activation following MEKi withdrawal drives a p57KIP2-dependent G1 cell cycle arrest and senescence or expression of NOXA and cell death, selecting against those cells with amplified BRAFV600E. p57KIP2 expression is required for loss of BRAFV600E amplification and reversal of MEKi resistance. Thus, BRAFV600E amplification confers a selective disadvantage during drug withdrawal, validating intermittent dosing to forestall resistance. In contrast, resistance driven by KRASG13D amplification is not reversible; rather ERK1/2 hyperactivation drives ZEB1-dependent epithelial-to-mesenchymal transition and chemoresistance, arguing strongly against the use of drug holidays in cases of KRASG13D amplification.

Quercetin preferentially induces apoptosis in KRAS-mutant colorectal cancer cells via JNK signaling pathways

Colorectal cancer (CRC) is the third most common type of cancer, and its incidence and mortality are markedly increasing worldwide. Oncogenic mutations of KRAS occur in up to 40% of CRC cases and pose a great challenge in the treatment of the disease. Quercetin is a dietary flavonoid that exerts anti-oxidant, anti-inflammatory, and anti-cancer properties. The current study investigated the anti-proliferative effect of quercetin on CRC cells harboring mutant or wild-type KRAS. The effect of quercetin on cell viability was investigated by MTT and colony formation assays, and apoptosis was detected using flow cytometry by labeling cells with Annexin V-FITC. The expression of the relevant proteins was examined by Western blotting. The data revealed that KRAS-mutant cells were more sensitive to quercetin-induced apoptosis than wild-type cells. Caspase activation was involved in quercetin-induced apoptosis. In addition, quercetin selectively activated the c-Jun N-terminal kinase (JNK) pathway in KRAS-mutant cells, while inhibition of phospho-JNK by SP600125 blocked quercetin-induced apoptosis. The results of the present study suggest that treatment with quercetin, a common flavonoid in plants, is potentially a useful strategy for the treatment of CRCs carrying KRAS mutations.

Plumbagin Increases Paclitaxel-Induced Cell Death and Overcomes Paclitaxel Resistance in Breast Cancer Cells through ERK-Mediated Apoptosis Induction

ERK is a component of mitogen-activated protein kinases that controls a range of cellular processes including cell proliferation and survival. The upregulation of ERK has been associated with apoptosis inhibition in response to various stimuli including chemotherapeutic agents. Research has suggested that the upregulation of ERK signaling by the anticancer agent paclitaxel leads to acquired resistance of cells to this compound. The presented research focused on determining the role of plumbagin, a naturally derived naphthoquinone, in the sensitization of breast cancer cells to paclitaxel-induced cell death and the involvement of ERK signaling in this process. The results of the study indicated that plumbagin increases the sensitivity of breast cancer cells to paclitaxel. Moreover, a synergistic effect between plumbagin and paclitaxel was observed. Plumbagin was shown to decrease levels of phosphorylated ERK in breast cancer cells and abrogated paclitaxel-induced ERK phosphorylation. The role of ERK in plumbagin-mediated sensitization of breast cancer cells to paclitaxel was shown through the enhancement of the synergistic effect between compounds in cells with decreased ERK expression. Furthermore, plumbagin reduced p-ERK levels in paclitaxel-resistant breast cancer cells and resensitized paclitaxel-resistant cells to this compound. These results imply that plumbagin inhibits ERK activation in breast cancer cells, which plays a role in the sensitization of cells to paclitaxel-induced cell death.

A Novel Naphthyridine Derivative, 3u, Induces Necroptosis at Low Concentrations and Apoptosis at High Concentrations in Human Melanoma A375 Cells

Naphthyridine derivatives are a widely-used class of heterocycles due to their pharmacological activities. A novel compound (10-Methoxy-1,2,3,4-tetrahydrobenzo(g)(1,3) diazepino(1,2-a)-(1,8)naphthyridin-6-yl)(phenyl) methanone (named 3u), showed good anticancer activity in the human malignant melanoma cell line A375 via Thiazolyl Blue Tetrazolium Bromide (MTT) assay. After Western blotting confirmed, we found that 3u induces necroptosis at low concentrations and apoptosis at high concentrations via the upregulation of death receptors and scaffold protein in A375 cells. Furthermore, by combining 3u with the caspase inhibitor zVAD-fmk or Receptor Interacting Serine/Threonine Kinase 1 (RIP1) kinase inhibitor Necrostatin-1 (Nec-1), we found that the activity of caspase-8 was the crucial factor that determined whether either apoptosis or necroptosis occurred. The results indicate that 3u should be considered as a potential chemical substance for melanoma treatment.

Frequent functional activation of RAS signalling not explained by RAS/RAF mutations in relapsed/refractory multiple myeloma

RAS mutations are frequent in relapsed/refractory multiple myeloma (RRMM) but functional study in primary samples is scanty. Herein, in primary myeloma plasma cells of 17 suspected RRMM, functional activation of RAS signalling was studied by Western blot of phosphorylated ERK1/2 (phospho-ERK1/2). Moreover, activating mutations in KRAS, NRAS, BRAF, and ALK were studied by PCR and bidirectional direct sequencing. Furthermore, methylation of negative RAS signalling regulator genes, RASSF1A and RASD1, were analyzed by methylation-specific PCR. As evidenced by phospho-ERK1/2 over-expression, functional RAS activation was detected in 12 (75.0%) RRMM. Of patients with functional RAS activation, sequencing data showed only seven (58.3%) patients with one each had NRAS Q61H, NRAS Q61K, KRAS G12D, KRAS G12V, KRAS G13D, KRAS Q61P, or BRAF V600E mutation, whereas five (41.7%) patients had no RAS/RAF mutation. Conversely, patients without functional RAS activation had no RAS/RAF mutation. Moreover, none of the patients with functional RAS activation had ALK mutations, or methylation of RASSF1A and RASD1. Collectively, functional activation of RAS signalling was present in majority of RRMM but only about half (58.3%) accountable by RAS/RAF mutations. If verified in larger studies, clinical investigations of MEK inhibitors are warranted regardless of RAS/RAF mutations.

Protein-Protein Interactions: Emerging Oncotargets in the RAS-ERK Pathway

Given the implication of aberrant RAS-extracellular signal-regulated kinase (ERK) signaling in the development of a large number of tumor types, this route is under intense scrutiny to identify new anticancer drugs. Most avenues in that direction have been primarily focused on the inhibition of the catalytic activity of the kinases that participate in this pathway. Although promising, the efficacy of these therapies is short lived due to undesired toxicity and/or drug resistance problems. As an alternative path, new efforts are now being devoted to the targeting of protein-protein interactions (PPIs) involved in the flow of RAS-ERK signals. Many of these efforts have shown promising results in preclinical models. In this review, we summarize recent progress made in this area.

ERK1/2 inhibitors: New weapons to inhibit the RAS-regulated RAF-MEK1/2-ERK1/2 pathway

The RAS-regulated RAF-MEK1/2-ERK1/2 signalling pathway is de-regulated in a variety of cancers due to mutations in receptor tyrosine kinases (RTKs), negative regulators of RAS (such as NF1) and core pathway components themselves (RAS, BRAF, CRAF, MEK1 or MEK2). This has driven the development of a variety of pharmaceutical agents to inhibit RAF-MEK1/2-ERK1/2 signalling in cancer and both RAF and MEK inhibitors are now approved and used in the clinic. There is now much interest in targeting at the level of ERK1/2 for a variety of reasons. First, since the pathway is linear from RAF-to-MEK-to-ERK then ERK1/2 are validated as targets per se. Second, innate resistance to RAF or MEK inhibitors involves relief of negative feedback and pathway re-activation with all signalling going through ERK1/2, validating the use of ERK inhibitors with RAF or MEK inhibitors as an up-front combination. Third, long-term acquired resistance to RAF or MEK inhibitors involves a variety of mechanisms (KRAS or BRAF amplification, MEK mutation, etc.) which re-instate ERK activity, validating the use of ERK inhibitors to forestall acquired resistance to RAF or MEK inhibitors. The first potent highly selective ERK1/2 inhibitors have now been developed and are entering clinical trials. They have one of three discrete mechanisms of action - catalytic, "dual mechanism" or covalent - which could have profound consequences for how cells respond and adapt. In this review we describe the validation of ERK1/2 as anti-cancer drug targets, consider the mechanism of action of new ERK1/2 inhibitors and how this may impact on their efficacy, anticipate factors that will determine how tumour cells respond and adapt to ERK1/2 inhibitors and consider ERK1/2 inhibitor drug combinations.

Targeting ERK, an Achilles' Heel of the MAPK pathway, in cancer therapy

The mitogen-activated protein kinases (MAPK) pathway, often known as the RAS-RAF-MEK-ERK signal cascade, functions to transmit upstream signals to its downstream effectors to regulate physiological process such as cell proliferation, differentiation, survival and death. As the most frequently mutated signaling pathway in human cancer, targeting the MAPK pathway has long been considered a promising strategy for cancer therapy. Substantial efforts in the past decades have led to the clinical success of BRAF and MEK inhibitors. However, the clinical benefits of these inhibitors are compromised by the frequently occurring acquired resistance due to cancer heterogeneity and genomic instability. This review briefly introduces the key protein kinases involved in this pathway as well as their activation mechanisms. We also generalize the correlations between mutations of MAPK members and human cancers, followed by a summarization of progress made on the development of small molecule MAPK kinases inhibitors. In particular, this review highlights the potential advantages of ERK inhibitors in overcoming resistance to upstream targets and proposes that targeting ERK kinase may hold a promising prospect for cancer therapy.

Cell death-based treatments of melanoma:conventional treatments and new therapeutic strategies

The incidence of malignant melanoma has continued to rise during the past decades. However, in the last few years, treatment protocols have significantly been improved thanks to a better understanding of the key oncogenes and signaling pathways involved in its pathogenesis and progression. Anticancer therapy would either kill tumor cells by triggering apoptosis or permanently arrest them in the G1 phase of the cell cycle. Unfortunately, melanoma is often refractory to commonly used anticancer drugs. More recently, however, some new anticancer strategies have been developed that are “external” to cancer cells, for example stimulating the immune system’s response or inhibiting angiogenesis. In fact, the increasing knowledge of melanoma pathogenetic mechanisms, in particular the discovery of genetic mutations activating specific oncogenes, stimulated the development of molecularly targeted therapies, a form of treatment in which a drug (chemical or biological) is developed with the goal of exclusively destroying cancer cells by interfering with specific molecules that drive growth and spreading of the tumor. Again, after the initial exciting results associated with targeted therapy, tumor resistance and/or relapse of the melanoma lesion have been observed. Hence, very recently, new therapeutic strategies based on the modulation of the immune system function have been developed. Since cancer cells are known to be capable of evading immune-mediated surveillance, i.e., to block the immune system cell activity, a series of molecular strategies, including monoclonal antibodies, have been developed in order to “release the brakes” on the immune system igniting immune reactivation and hindering metastatic melanoma cell growth. In this review we analyze the various biological strategies underlying conventional chemotherapy as well as the most recently developed targeted therapies and immunotherapies, pointing at the molecular mechanisms of cell injury and death engaged by the different classes of therapeutic agents.

Integration analysis of microRNA and mRNA paired expression profiling identifies deregulated microRNA-transcription factor-gene regulatory networks in ovarian endometriosis

BACKGROUND

The etiology and pathophysiology of endometriosis remain unclear. Accumulating evidence suggests that aberrant microRNA (miRNA) and transcription factor (TF) expression may be involved in the pathogenesis and development of endometriosis. This study therefore aims to survey the key miRNAs, TFs and genes and further understand the mechanism of endometriosis.

METHODS

Paired expression profiling of miRNA and mRNA in ectopic endometria compared with eutopic endometria were determined by high-throughput sequencing techniques in eight patients with ovarian endometriosis. Binary interactions and circuits among the miRNAs, TFs, and corresponding genes were identified by the Pearson correlation coefficients. miRNA-TF-gene regulatory networks were constructed using bioinformatic methods. Eleven selected miRNAs and TFs were validated by quantitative reverse transcription-polymerase chain reaction in 22 patients.

RESULTS

Overall, 107 differentially expressed miRNAs and 6112 differentially expressed mRNAs were identified by comparing the sequencing of the ectopic endometrium group and the eutopic endometrium group. The miRNA-TF-gene regulatory network consists of 22 miRNAs, 12 TFs and 430 corresponding genes. Specifically, some key regulators from the miR-449 and miR-34b/c cluster, miR-200 family, miR-106a-363 cluster, miR-182/183, FOX family, GATA family, and E2F family as well as CEBPA, SOX9 and HNF4A were suggested to play vital regulatory roles in the pathogenesis of endometriosis.

CONCLUSION

Integration analysis of the miRNA and mRNA expression profiles presents a unique insight into the regulatory network of this enigmatic disorder and possibly provides clues regarding replacement therapy for endometriosis.

BRAF inhibition upregulates a variety of receptor tyrosine kinases and their downstream effector Gab2 in colorectal cancer cell lines

BRAF mutations occur in ~10% of colorectal cancer (CRC) and are associated with poor prognosis. Inhibitors selective for the BRAF^V600E oncoprotein, the most common BRAF mutant, elicit only poor response rates in BRAF-mutant CRC as single agents. This unresponsiveness was mechanistically attributed to the loss of negative feedbacks on the epidermal growth factor receptor (EGFR) and initiated clinical trials that combine BRAF (and MEK) inhibitors, either singly or in combination, with the anti-EGFR antibodies cetuximab or panitumumab. First results of these combinatorial studies demonstrated improved efficacy, however, the response rates still were heterogeneous. Here, we show that BRAF inhibition leads to the upregulation of a variety of receptor tyrosine kinases (RTKs) in CRC cell lines, including not only the EGFR, but also human epidermal growth factor receptor (HER) 2 and HER3. Importantly, combination of the BRAF inhibitors (BRAFi) vemurafenib (PLX4032), dabrafenib, or encorafenib with inhibitors dually targeting the EGFR and HER2 (such as lapatinib, canertinib, and afatinib) significantly reduced the metabolic activity and proliferative potential of CRC cells. This re-sensitization was also observed after genetic depletion of HER2 or HER3. Interestingly, BRAF inhibitors did not only upregulate RTKs, but also increased the abundance of the GRB2-associated binders (Gab) 1 and Gab2, two important amplifiers of RTK signaling. An allele-specific shRNA-mediated knockdown of BRAF^V600E revealed that Gab2 upregulation was directly dependent on the loss of the oncoprotein and was not caused by an "off-target" effect of these kinase inhibitors. Furthermore, Gab2 and Gab2-mediated Shp2 signaling were shown to be functionally important in BRAFi resistance. These findings highlight potential new escape mechanisms to these targeted therapies and indicate that a broad suppression of RTK signaling might be beneficial and should be taken into account in future research addressing targeted therapy in BRAF-mutant CRC.

Future perspectives in melanoma research "Melanoma Bridge", Napoli, November 30th-3rd December 2016

Major advances have been made in the treatment of cancer with targeted therapy and immunotherapy; several FDA-approved agents with associated improvement of 1-year survival rates became available for stage IV melanoma patients. Before 2010, the 1-year survival were quite low, at 30%; in 2011, the rise to nearly 50% in the setting of treatment with Ipilimumab, and rise to 70% with BRAF inhibitor monotherapy in 2013 was observed. Even more impressive are 1-year survival rates considering combination strategies with both targeted therapy and immunotherapy, now exceeding 80%. Can we improve response rates even further, and bring these therapies to more patients? In fact, despite these advances, responses are heterogeneous and are not always durable. There is a critical need to better understand who will benefit from therapy, as well as proper timing, sequence and combination of different therapeutic agents. How can we better understand responses to therapy and optimize treatment regimens? The key to better understanding therapy and to optimizing responses is with insights gained from responses to targeted therapy and immunotherapy through translational research in human samples. Combination therapies including chemotherapy, radiotherapy, targeted therapy, electrochemotherapy with immunotherapy agents such as Immune Checkpoint Blockers are under investigation but there is much room for improvement. Adoptive T cell therapy including tumor infiltrating lymphocytes and chimeric antigen receptor modified T cells therapy is also efficacious in metastatic melanoma and outcome enhancement seem likely by improved homing capacity of chemokine receptor transduced T cells. Tumor infiltrating lymphocytes therapy is also efficacious in metastatic melanoma and outcome enhancement seem likely by improved homing capacity of chemokine receptor transduced T cells. Understanding the mechanisms behind the development of acquired resistance and tests for biomarkers for treatment decisions are also under study and will offer new opportunities for more efficient combination therapies. Knowledge of immunologic features of the tumor microenvironment associated with response and resistance will improve the identification of patients who will derive the most benefit from monotherapy and might reveal additional immunologic determinants that could be targeted in combination with checkpoint blockade. The future of advanced melanoma needs to involve education and trials, biobanks with a focus on primary tumors, bioinformatics and empowerment of patients and clinicians.

MicroRNAs in melanoma development and resistance to target therapy

microRNAs constitute a complex class of pleiotropic post-transcriptional regulators of gene expression involved in the control of several physiologic and pathologic processes. Their mechanism of action is primarily based on the imperfect matching of a seed region located at the 5′ end of a 21-23 nt sequence with a partially complementary sequence located in the 3′ untranslated region of target mRNAs. This leads to inhibition of mRNA translation and eventually to its degradation. Individual miRNAs are capable of binding to several mRNAs and several miRNAs are capable of influencing the function of the same mRNAs. In recent years networks of miRNAs are emerging as capable of controlling key signaling pathways responsible for the growth and propagation of cancer cells. Furthermore several examples have been provided which highlight the involvement of miRNAs in the development of resistance to targeted drug therapies. In this review we provide an updated overview of the role of miRNAs in the development of melanoma and the identification of the main downstream pathways controlled by these miRNAs. Furthermore we discuss a group of miRNAs capable to influence through their respective up- or down-modulation the development of resistance to BRAF and MEK inhibitors.

Endometrial Carcinoma: Specific Targeted Pathways

Endometrial cancer (EC) is the most common gynecologic malignancy in the western world with more than 280,000 cases per year worldwide. Prognosis for EC at early stages, when primary surgical resection is the most common initial treatment, is excellent. Five-year survival rate is around 70 %.Several molecular alterations have been described in the different types of EC. They occur in genes involved in important signaling pathways. In this chapter, we will review the most relevant altered pathways in EC, including PI3K/AKT/mTOR, RAS-RAF-MEK-ERK, Tyrosine kinase, WNT/β-Catenin, cell cycle, and TGF-β signaling pathways. At the end of the chapter, the most significant clinical trials will be briefly discussed.This information is important to identify specific targets for therapy.

Future perspectives in melanoma research : Meeting report from the "Melanoma Bridge". Napoli, December 1st-4th 2015

The sixth "Melanoma Bridge Meeting" took place in Naples, Italy, December 1st-4th, 2015. The four sessions at this meeting were focused on: (1) molecular and immune advances; (2) combination therapies; (3) news in immunotherapy; and 4) tumor microenvironment and biomarkers. Recent advances in tumor biology and immunology has led to the development of new targeted and immunotherapeutic agents that prolong progression-free survival (PFS) and overall survival (OS) of cancer patients. Immunotherapies in particular have emerged as highly successful approaches to treat patients with cancer including melanoma, non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), bladder cancer, and Hodgkin's disease. Specifically, many clinical successes have been using checkpoint receptor blockade, including T cell inhibitory receptors such as cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and the programmed cell death-1 (PD-1) and its ligand PD-L1. Despite demonstrated successes, responses to immunotherapy interventions occur only in a minority of patients. Attempts are being made to improve responses to immunotherapy by developing biomarkers. Optimizing biomarkers for immunotherapy could help properly select patients for treatment and help to monitor response, progression and resistance that are critical challenges for the immuno-oncology (IO) field. Importantly, biomarkers could help to design rational combination therapies. In addition, biomarkers may help to define mechanism of action of different agents, dose selection and to sequence drug combinations. However, biomarkers and assays development to guide cancer immunotherapy is highly challenging for several reasons: (i) multiplicity of immunotherapy agents with different mechanisms of action including immunotherapies that target activating and inhibitory T cell receptors (e.g., CTLA-4, PD-1, etc.); adoptive T cell therapies that include tissue infiltrating lymphocytes (TILs), chimeric antigen receptors (CARs), and T cell receptor (TCR) modified T cells; (ii) tumor heterogeneity including changes in antigenic profiles over time and location in individual patient; and (iii) a variety of immune-suppressive mechanisms in the tumor microenvironment (TME) including T regulatory cells (Treg), myeloid derived suppressor cells (MDSC) and immunosuppressive cytokines. In addition, complex interaction of tumor-immune system further increases the level of difficulties in the process of biomarkers development and their validation for clinical use. Recent clinical trial results have highlighted the potential for combination therapies that include immunomodulating agents such as anti-PD-1 and anti-CTLA-4. Agents targeting other immune inhibitory (e.g., Tim-3) or immune stimulating (e.g., CD137) receptors on T cells and other approaches such as adoptive cell transfer are tested for clinical efficacy in melanoma as well. These agents are also being tested in combination with targeted therapies to improve upon shorter-term responses thus far seen with targeted therapy. Various locoregional interventions that demonstrate promising results in treatment of advanced melanoma are also integrated with immunotherapy agents and the combinations with cytotoxic chemotherapy and inhibitors of angiogenesis are changing the evolving landscape of therapeutic options and are being evaluated to prevent or delay resistance and to further improve survival rates for melanoma patients' population. This meeting's specific focus was on advances in immunotherapy and combination therapy for melanoma. The importance of understanding of melanoma genomic background for development of novel therapies and biomarkers for clinical application to predict the treatment response was an integral part of the meeting. The overall emphasis on biomarkers supports novel concepts toward integrating biomarkers into personalized-medicine approach for treatment of patients with melanoma across the entire spectrum of disease stage. Translation of the knowledge gained from the biology of tumor microenvironment across different tumors represents a bridge to impact on prognosis and response to therapy in melanoma. We also discussed the requirements for pre-analytical and analytical as well as clinical validation process as applied to biomarkers for cancer immunotherapy. The concept of the fit-for-purpose marker validation has been introduced to address the challenges and strategies for analytical and clinical validation design for specific assays.

The lack of Raf-1 kinase feedback regulation enhances antiapoptosis in cancer cells

Raf-1 has an important role in cellular antiapoptosis. So far, there is no solid evidence that shows that Raf-1 mutation is associated with cancer development. In the course of further study of Raf-1 signaling, we have reported that Raf-1 hyperphosphorylation inhibits its kinase activity toward its downstream mitogen-activated protein kinase kinase 1/2 (MEK1/2) and proposed a model for negative feedback regulation of Raf-1. Here, we show that there is no hyperphosphorylation in some cancer cells, which results in increased kinase activity and enhances the antiapoptotic ability. Inhibition of either Raf-1 or ALG-2 (apoptosis-linked gene 2) expression results in apoptosis signal-regulating kinase 1/c-Jun N-terminal kinase (ASK1/JNK) signaling activation, and cell sensitivity to chemotherapeutic reagents, indicating that inhibition of ASK1/JNK apoptotic signaling by Raf-1 is mediated by ALG-2. A previous report indicated that extracellular signal-regulated kinase 1/2 (ERK1/2) were responsible for Raf-1 hyperphosphorylation. However, our evidence shows that when ERK1/2 are activated and the Raf-1 gene is not mutated, Raf-1 is not hyperphosphorylated in these cells, indicating that ERK1/2 are not responsible for the Raf-1 hyperphosphorylation in these cancer cell lines. Surprisingly, we also found that Raf-1 is not a necessary kinase for MEK1/2 activation under normal tissue culture conditions, but is required for MEK1/2 activation under apoptosis-inducing conditions. Our research demonstrates that although Raf-1 gene is not mutated, an abnormality of Raf-1 kinase feedback regulation enhances its antiapoptotic function, and Raf-1 can still be a pharmaceutical target to increase chemotherapy or radiotherapy sensitivity in these cancer cells.

Grifolin directly targets ERK1/2 to epigenetically suppress cancer cell metastasis

Grifolin, a secondary metabolite isolated from the fresh fruiting bodies of the mushroom Albatrellus confluens, has been reported by us and others to display potent antitumor effects. However, the molecular target of grifolin has not been identified and the underlying mechanism of action is not fully understood. Here, we report that the ERK1/2 protein kinases are direct molecular targets of grifolin. Molecular modeling, affinity chromatography and fluorescence quenching analyses showed that grifolin directly binds to ERK1/2. And in vitro and ex vivo kinase assay data further demonstrated that grifolin inhibited the kinase activities of ERK1/2. We found that grifolin suppressed adhesion, migration and invasion of high-metastatic cancer cells. The inhibitory effect of grifolin against tumor metastasis was further confirmed in a metastatic mouse model. We found that grifolin decreased phosphorylation of Elk1 at Ser383, and the protein as well as the mRNA level of DNMT1 was also down-regulated. By luciferase reporter and ChIP assay analyses, we confirmed that grifolin inhibited the transcription activity of Elk1 as well as its binding to the dnmt1 promoter region. Moreover, we report that significant increases in the mRNA levels of Timp2 and pten were induced by grifolin. Thus, our data suggest that grifolin exerts its anti-tumor activity by epigenetic reactivation of metastasis inhibitory-related genes through ERK1/2-Elk1-DNMT1 signaling. Grifolin may represent a promising therapeutic lead compound for intervention of cancer metastasis, and it may also be useful as an ERK1/2 kinase inhibitor as well as an epigenetic agent to further our understanding of DNMT1 function.

miR-579-3p controls melanoma progression and resistance to target therapy

Therapy of melanoma patients harboring activating mutations in the BRAF (V-raf murine sarcoma viral oncogene homolog B1) oncogene with a combination of BRAF and MEK inhibitors is plagued by the development of drug resistance. Mutational events, as well as adaptive mechanisms, contribute to the development of drug resistance. In this context we uncover here the role of a miRNA, miR-579-3p. We first show that low expression of miR-579-3p is a negative prognostic factor correlating with poor survival. Expression levels of miR-579-3p decrease from nevi to stage III/IV melanoma samples and even further in cell lines resistant to BRAF/MEK inhibitors. Mechanistically, we demonstrate that miR-579-3p acts as an oncosuppressor by targeting the 3'UTR of two oncoproteins: BRAF and an E3 ubiquitin protein ligase, MDM2. Moreover miR-579-3p ectopic expression impairs the establishment of drug resistance in human melanoma cells. Finally, miR-579-3p is strongly down-regulated in matched tumor samples from patients before and after the development of resistance to targeted therapies.