MAP3K Family Review and Correlations with Patient Survival Outcomes in Various Cancer Types

The mitogen-activated protein kinase (MAPK) pathways are ubiquitous in cellular signaling and are essential for proper biological functions. Disruptions in this signaling axis can lead to diseases such as the development of cancer. In this review, we discuss members of the MAP3K family and correlate their mRNA expression levels to patient survival outcomes in different cancers. Furthermore, we highlight the importance of studying the MAP3K family due to their important roles in the larger, overall MAPK pathway, relationships with cancer progression, and the understudied status of these kinases.

Crystal structure of 4-bromo-N-(propylcarbamoyl)benzenesulfonamide

The X-ray crystal structure, and Hirshfeld surface analysis of a sulfonyl urea analogue, 4-bromo-N-(propyl­carbamo­yl)benzene­sulfonamide is reported.

The title compound, C₁₀H₁₃BrN₂O₃S, 1, contains a sulfonyl urea moiety, which possesses potential therapeutic functions (e.g., anti-diabetic and herbicidal). The geometry of 1 is similar to its closely related analogues, chlorpropamide and tolbutamide. This compound crystallizes in the monoclinic space group C2/c, having one mol­ecule in its asymmetric unit. The crystal structure of 1, recorded at 296 K, shows inter­molecular N—H⋯O and C—H⋯O-type infinite hydrogen-bonded chains involving the sulfonyl urea moiety. Hirshfeld surface analysis and the two-dimensional fingerprint plots confirmed hydrogen bonding as the dominant feature in the crystal packing.

Diverse and converging roles of ERK1/2 and ERK5 pathways on mesenchymal to epithelial transition in breast cancer

The epithelial to mesenchymal transition (EMT) is characterized by a loss of cell polarity, a decrease in the epithelial cell marker E-cadherin, and an increase in mesenchymal markers including the zinc-finger E-box binding homeobox (ZEB1). The EMT is also associated with an increase in cell migration and anchorage-independent growth. Induction of a reversal of the EMT, a mesenchymal to epithelial transition (MET), is an emerging strategy being explored to attenuate the metastatic potential of aggressive cancer types, such as triple-negative breast cancers (TNBCs) and tamoxifen-resistant (TAMR) ER-positive breast cancers, which have a mesenchymal phenotype. Patients with these aggressive cancers have poor prognoses, quick relapse, and resistance to most chemotherapeutic drugs. Overexpression of extracellular signal-regulated kinase (ERK) 1/2 and ERK5 is associated with poor patient survival in breast cancer. Moreover, TNBC and tamoxifen resistant cancers are unresponsive to most targeted clinical therapies and there is a dire need for alternative therapies. In the current study, we found that MAPK3, MAPK1, and MAPK7 gene expression correlated with EMT markers and poor overall survival in breast cancer patients using publicly available datasets. The effect of ERK1/2 and ERK5 pathway inhibition on MET was evaluated in MDA-MB-231, BT-549 TNBC cells, and tamoxifen-resistant MCF-7 breast cancer cells. Moreover, TU-BcX-4IC patient-derived primary TNBC cells were included to enhance the translational relevance of our study. We evaluated the effect of pharmacological inhibitors and lentivirus-induced activation or inhibition of the MEK1/2-ERK1/2 and MEK5-ERK5 pathways on cell morphology, E-cadherin, vimentin and ZEB1 expression. Additionally, the effects of pharmacological inhibition of trametinib and XMD8-92 on nuclear localization of ERK1/2 and ERK5, cell migration, proliferation, and spheroid formation were evaluated. Novel compounds that target the MEK1/2 and MEK5 pathways were used in combination with the AKT inhibitor ipatasertib to understand cell-specific responses to kinase inhibition. The results from this study will aid in the design of innovative therapeutic strategies that target cancer metastases.

Constitutive activation of MEK5 promotes a mesenchymal and migratory cell phenotype in triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited targeted therapeutic options. A defining feature of TNBC is the propensity to metastasize and acquire resistance to cytotoxic agents. Mitogen activated protein kinase (MAPK) and extracellular regulated kinase (ERK) signaling pathways have integral roles in cancer development and progression. While MEK5/ERK5 signaling drives mesenchymal and migratory cell phenotypes in breast cancer, the specific mechanisms underlying these actions remain under-characterized. To elucidate the mechanisms through which MEK5 regulates the mesenchymal and migratory phenotype, we generated stably transfected constitutively active MEK5 (MEK5-ca) TNBC cells. Downstream signaling pathways and candidate targets of MEK5-ca cells were based on RNA sequencing and confirmed using qPCR and Western blot analyses. MEK5 activation drove a mesenchymal cell phenotype independent of cell proliferation effects. Transwell migration assays demonstrated MEK5 activation significantly increased breast cancer cell migration. In this study, we provide supporting evidence that MEK5 functions through FRA-1 to regulate the mesenchymal and migratory phenotype in TNBC.

Dual inhibition of MEK1/2 and MEK5 suppresses the EMT/migration axis in triple-negative breast cancer through FRA-1 regulation

Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. Constitutive activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway has been linked to chemoresistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT) when cells adopt a motile and invasive phenotype through loss of epithelial markers (CDH1), and acquisition of mesenchymal markers (VIM, CDH2). Although MAPK/ERK1/2 kinase inhibitors (MEKi) are useful antitumor agents in a clinical setting, including the Food and Drug Administration (FDA)-approved MEK1,2 dual inhibitors cobimetinib and trametinib, there are limitations to their clinical utility, primarily adaptation of the BRAF pathway and ocular toxicities. The MEK5 (HGNC: MAP2K5) pathway has important roles in metastatic progression of various cancer types, including those of the prostate, colon, bone and breast, and elevated levels of ERK5 expression in breast carcinomas are linked to a worse prognoses in TNBC patients. The purpose of this study is to explore MEK5 regulation of the EMT axis and to evaluate a novel pan-MEK inhibitor on clinically aggressive TNBC cells. Our results show a distinction between the MEK1/2 and MEK5 cascades in maintenance of the mesenchymal phenotype, suggesting that the MEK5 pathway may be necessary and sufficient in EMT regulation while MEK1/2 signaling further sustains the mesenchymal state of TNBC cells. Furthermore, additive effects on MET induction are evident through the inhibition of both MEK1/2 and MEK5. Taken together, these data demonstrate the need for a better understanding of the individual roles of MEK1/2 and MEK5 signaling in breast cancer and provide a rationale for the combined targeting of these pathways to circumvent compensatory signaling and subsequent therapeutic resistance.

Crystal structure of tert-butyl 4-[4-(4-fluoro-phen-yl)-2-methyl-but-3-yn-2-yl]piperazine-1-carboxyl-ate

The title sterically congested piperazine derivative, C20H27FN2O2, was prepared using a modified Bruylants approach. A search of the Cambridge Structural Database identified 51 compounds possessing an N-tert-butyl piperazine substructure. Of these only 14 were asymmetrically substituted on the piperazine ring and none with a synthetically useful second nitro-gen. Given the novel chemistry generating a pharmacologically useful core, determination of the crystal structure for this compound was necessary. The piperazine ring is present in a chair conformation with di-equatorial substitution. Of the two N atoms, one is sp 3 hybridized while the other is sp 2 hybridized. Inter-molecular inter-actions resulting from the crystal packing patterns were investigated using Hirshfeld surface analysis and fingerprint analysis. Directional weak hydrogen-bond-like inter-actions (C-H⋯O) and C-H⋯π inter-actions with the dispersion inter-actions as the major source of attraction are present in the crystal packing.

Molecular Mechanisms of Epithelial to Mesenchymal Transition Regulated by ERK5 Signaling

Extracellular signal-regulated kinase (ERK5) is an essential regulator of cancer progression, tumor relapse, and poor patient survival. Epithelial to mesenchymal transition (EMT) is a complex oncogenic process, which drives cell invasion, stemness, and metastases. Activators of ERK5, including mitogen-activated protein kinase 5 (MEK5), tumor necrosis factor α (TNF-α), and transforming growth factor-β (TGF-β), are known to induce EMT and metastases in breast, lung, colorectal, and other cancers. Several downstream targets of the ERK5 pathway, such as myocyte-specific enhancer factor 2c (MEF2C), activator protein-1 (AP-1), focal adhesion kinase (FAK), and c-Myc, play a critical role in the regulation of EMT transcription factors SNAIL, SLUG, and β-catenin. Moreover, ERK5 activation increases the release of extracellular matrix metalloproteinases (MMPs), facilitating breakdown of the extracellular matrix (ECM) and local tumor invasion. Targeting the ERK5 signaling pathway using small molecule inhibitors, microRNAs, and knockdown approaches decreases EMT, cell invasion, and metastases via several mechanisms. The focus of the current review is to highlight the mechanisms which are known to mediate cancer EMT via ERK5 signaling. Several therapeutic approaches that can be undertaken to target the ERK5 pathway and inhibit or reverse EMT and metastases are discussed.

ERK5 Is Required for Tumor Growth and Maintenance Through Regulation of the Extracellular Matrix in Triple Negative Breast Cancer

Conventional mitogen-activated protein kinase (MAPK) family members regulate diverse cellular processes involved in tumor initiation and progression, yet the role of ERK5 in cancer biology is not fully understood. Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. ERK5 signaling contributes to drug resistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT). More recently a role for ERK5 in regulation of the extracellular matrix (ECM) has been proposed, and here we investigated the necessity of ERK5 in TNBC tumor formation. Depletion of ERK5 expression using the CRISPR/Cas9 system in MDA-MB-231 and Hs-578T cells resulted in loss of mesenchymal features, as observed through gene expression profile and cell morphology, and suppressed TNBC cell migration. In vivo xenograft experiments revealed ERK5 knockout disrupted tumor growth kinetics, which was restored using high concentration Matrigel™ and ERK5-ko reduced expression of the angiogenesis marker CD31. These findings implicated a role for ERK5 in the extracellular matrix (ECM) and matrix integrity. RNA-sequencing analyses demonstrated downregulation of matrix-associated genes, integrins, and pro-angiogenic factors in ERK5-ko cells. Tissue decellularization combined with cryo-SEM and interrogation of biomechanical properties revealed that ERK5-ko resulted in loss of key ECM fiber alignment and mechanosensing capabilities in breast cancer xenografts compared to parental wild-type cells. In this study, we identified a novel role for ERK5 in tumor growth kinetics through modulation of the ECM and angiogenesis axis in breast cancer.

Abstract B078: Inhibition of the MAPK pathways enhances the sensitivity of triple negative breast cancer cells to chemotherapeutic drugs

Triple negative breast cancer is characterized by the loss of hormone receptors and lack of targeted therapy. Most invasive cancers, including triple negative (TNBC) breast cancer have a mesenchymal phenotype, which is associated with increased chemoresistance. Activation of the MEK1/2 and MEK5 pathways plays a crucial role in the activation of the epithelial to mesenchymal transition program and increases the survival, proliferation, and migration of the cancer cells. Disruption of actin skeleton via ras and src mediated activation of extracellular regulated kinase 1/2 (ERK1/2) and ERK5 is reported, indicating their role in oncogenic transformation. Moreover, inhibition of either pathway results in a compensatory increase in the PI3K/AKT pathway. These crosstalk mechanisms are involved in mediating therapeutic drug resistance. MDA-MB-231, a BRAF and KRAS mutant TNBC cell line has more than 90% of high CD44+/CD24-/low stem cell population, and high ERK5 and ERK1/2 expression; hence it was used as the model for our experiments. Moreover, MDA-MB-231-ERK5-KO cells were utilized to confirm the mechanism of action. To target TNBC, known inhibitors of the MEK1/2 pathway: trametinib, an FDA approved drug for BRAF mutant melanoma, VX-11-e, an ERK2 inhibitor, and XMD-8-92, an ERK5 inhibitor were used in combination with the chemotherapeutic drugs paclitaxel and doxorubicin to examine cell viability. We have shown that dual inhibition of the ERK5 and AKT signaling pathways synergistically reduces TNBC cell viability and enhances sensitivity of the cells to paclitaxel. A series of novel quinazoline derivatives was generated to dually target the ERK5 and the AKT pathway. The effect of novel quinazolines on cell viability in combination with the chemotherapeutic agent paclitaxel was examined in the TNBC cells and some encouraging results were obtained. The overall significance of this research is to enhance the anti-cancer activity of chemotherapeutic agents and reduce off-target toxicity by dose-reduction strategy.

Citation Format: Akshita B. Bhatt, Thomas D. Wright, Saloni Patel, Suravi Chakrabarty, Van Barnes, Matthew Burow, Patrick T. Flaherty, Jane Cavanaugh. Inhibition of the MAPK pathways enhances the sensitivity of triple negative breast cancer cells to chemotherapeutic drugs [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B078. doi:10.1158/1535-7163.TARG-19-B078

Pharmacological inhibition of the MEK5/ERK5 and PI3K/Akt signaling pathways synergistically reduces viability in triple-negative breast cancer

Triple-negative breast cancers (TNBCs) represent 15% to 20% of all breast cancers and are often associated with poor prognosis. The lack of targeted therapies for TNBCs contributes to higher mortality rates. Aberrations in the phosphoinositide-3-kinase (PI3K) and mitogen-activated protein kinase pathways have been linked to increased breast cancer proliferation and survival. It has been proposed that these survival characteristics are enhanced through compensatory signaling and crosstalk mechanisms. While the crosstalk between PI3K and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways has been characterized in several systems, new evidence suggests that MEK5/ERK5 signaling is a key component in the proliferation and survival of several aggressive cancers. In this study, we examined the effects of dual inhibition of PI3K/protein kinase B (Akt) and MEK5/ERK5 in the MDA-MB-231, BT-549, and MDA-MB-468 TNBC cell lines. We used the Akt inhibitor ipatasertib, ERK5 inhibitors XMD8-92 and AX15836, and the novel MEK5 inhibitor SC-1-181 to investigate the effects of dual inhibition. Our results indicated that dual inhibition of PI3K/Akt and MEK5/ERK5 signaling was more effective at reducing the proliferation and survival of TNBCs than single inhibition of either pathway alone. In particular, a loss of Bad phosphorylation at two distinct sites was observed with dual inhibition. Furthermore, the inhibition of both pathways led to p21 restoration, decreased cell proliferation, and induced apoptosis. In addition, the dual inhibition strategy was determined to be synergistic in MDA-MB-231 and BT-549 cells and was relatively nontoxic in the nonneoplastic MCF-10 cell line. In summary, the results from this study provide a unique prospective into the utility of a novel dual inhibition strategy for targeting TNBCs.

Novel Diphenylamine Analogs Induce Mesenchymal to Epithelial Transition in Triple Negative Breast Cancer

Epithelial to mesenchymal transition (EMT) is a cellular program that converts non-motile epithelial cells into invasive mesenchymal cells. EMT is implicated in cancer metastasis, chemo-resistance, cancer progression, and generation of cancer stem cells (CSCs). Inducing mesenchymal to epithelial transition (MET), the reverse phenomenon of EMT, is proposed as a novel strategy to target triple negative and tamoxifen-resistant breast cancer. Triple negative breast cancer (TNBC) is characterized by the loss of hormone receptors, a highly invasive mesenchymal phenotype, and a lack of targeted therapy. Estrogen receptor-positive breast cancer can be targeted by tamoxifen, an ER antagonist. However, these cells undergo EMT over the course of treatment and develop resistance. Thus, there is an urgent need to develop therapeutic interventions to target these aggressive cancers. In this study, we examined the role of novel diphenylamine analogs in converting the mesenchymal phenotype of MDA-MB-231 TNBC cells to a lesser aggressive epithelial phenotype. Using analog-based drug design, a series of diphenylamine analogs were synthesized and initially evaluated for their effect on E-cadherin protein expression and changes incell morphology, which was quantified by measuring the spindle index (SI) value. Selected compound 1 from this series increases the expression of E-cadherin, a primary marker for epithelial cells, and decreases the mesenchymal markers SOX2, ZEB1, Snail, and vimentin. The increase in epithelial markers and the decrease in mesenchymal markers are consistent with a phenotypic switch from spindle-like morphology to cobblestone-like morphology. Furthermore, Compound 1 decreases spheroid viability, cell migration, and cell proliferation in triple negative BT-549 and tamoxifen-resistant MCF-7 breast cancer cells.

Abstract 1879: Novel diphenylamine analogs induce mesenchymal to epithelial transition and enhance the sensitivity of breast cancer cells to conventional chemotherapeutic agents

Epithelial to mesenchymal transition is an important cellular adaptation that helps cancer cells acquire a spindle-like phenotype from a cuboidal phenotype, degrade the extracellular matrix, invade the neighboring tissues, and metastasize to other organs and form secondary tumor. Cellular plasticity is governed by growth factors that act in a paracrine manner to activate downstream oncogenes and regulate the activity of epigenetic factors, which facilitate phenotypic switch from epithelial to mesenchymal, ultimately leading to increased cell migration and invasion. The intracellular phosphorylation cascade that is downstream of growth factor receptors plays an important role in transmitting the signal from the extracellular environment into the nucleus, thereby completing the loop required to elicit a cellular response. Triple negative breast cancer (TNBC), characterized by loss of hormone receptors is a highly aggressive form of cancer and patients show poor prognosis and disease-free survival due to lack of targeted therapy. In contrast, estrogen positive breast cancer can be targeted by estrogen receptor antagonists or CDK4/6 inhibitors, but drug resistance and relapse is often associated with epithelial to mesenchymal transition and poor patient outcome. Hence, targeting the mesenchymal phenotype with small molecule inhibitors is an emerging strategy to attenuate the invasive and aggressive nature of cancer cells. The MEK5-ERK5 pathway is understudied in triple negative breast cancer and there are few research tools available to selectively inhibit this pathway. Diphenylamine derivatives, synthesized as putative MEK5 inhibitors from parent MEK1/2 inhibitor trametinib, are effective in inducing mesenchymal to epithelial transition in MDA-MB-231 triple negative breast cancer cells, as indicated by an increase in E-cadherin expression, which is a marker of epithelial phenotype, and a decrease in spindle index, an important cell shape determinant. Compound 1, a dual MEK1/2 (98%) and MEK5 (59%) inhibitor was further characterized in functional assays; Compound 1 was found to significantly inhibit cell viability, proliferation, migration, spheroid viability, and colony formation in MDA-MB-231 cells. Compound 1 is effective in reversing the mesenchymal phenotype of MDA-MB-231, BT-549, and tamoxifen resistant-MCF-7 breast cancer cells. Signaling crosstalk and drug resistance in cancer limits the applicability of monotherapy. Our current work is focused on treating diverse breast cancer cells with combination of novel compound 1 and paclitaxel, ipatasertib, JQ-1, and LBH589 to induce synthetic lethality at lower concentration, restore drug sensitivity, and enhance selectivity.

Citation Format: Akshita B. Bhatt, Thomas D. Wright, Katie Anna, Mohit Gupta, Suravi Chakrabarty, Van Hoang, Matthew Burow, Patrick T. Flaherty, Jane E. Cavanaugh. Novel diphenylamine analogs induce mesenchymal to epithelial transition and enhance the sensitivity of breast cancer cells to conventional chemotherapeutic agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1879.

Abstract P5-08-07: Study of diphenylamine analogs as inducers of mesenchymal to epithelial transition in breast cancer

The organization of cell cytoskeleton is altered in events of epithelial to mesenchymal transition (EMT), promotion of cell motility, and cancer metastases. EMT is associated with decreased cell-cell adhesion, downregulation of epithelial markers like E-Cadherin, cytokeratins, and occludins, and upregulation of mesenchymal markers such as N-cadherin, vimentin, and various transcription factors such as slug and ZEB. Epithelial to mesenchymal transition is also a consequence of drug resistance and is responsible for cancer metastases. Triple negative breast cancer is highly aggressive cancer and patients show poor prognosis and disease-free survival due to the lack of targeted therapy. Mitogen activated protein kinase pathway, including extracellular activated kinase ERK1/2 and ERK5, and phosphoinositide 3-kinase (PI3K) pathway are known to alter the cytoskeleton through the downstream activation of oncogenes such as FRA-1 and loss of focal adhesions. Of these pathways, the MEK5-ERK5 pathway is understudied in triple negative breast cancer TNBC, and there are few research tools available to selectively inhibit this pathway. The diphenylamine analogs were derived from the parent molecule Mekinist, a FDA approved MEK1/2 inhibitor for melanoma, and modified to gain selectivity towards MEK5. SC-1-151, a type-III allosteric inhibitor of MEK5 is a dual MEK1/2 (98.6%) and MEK5 (59%) inhibitor; the molecule inhibits cell viability and colony formation, and attenuates tumor growth.

SC-1-151 was serendipitously identified as a mesenchymal to epithelial transition activator in TNBC cell line MDA-MB-231. E-cadherin protein expression and cell morphology were examined to study MET after the treatment of MDA-MB-231 cells with different structural analogs of SC-1-151 after treatment for 5 days. The compound was further found to induce E-cadherin expression and epithelial phenotype in tamoxifen resistant estrogen positive MCF-7 cell line that underwent EMT. The compound is identified to promote this activity by targeting at least the ERK-FRA1-ZEB1 axis. Alkyl or N-Methyl piperazine substituents on the amide of ring 1 produced similar result as SC-1-151, and substituting the amide group with acid or ester also induced MET. In contrast, ortho-fluoro, para-iodo functional groups of the arene ring 2, when replaced with a meta-bromo substituent did not induce MET. We aim to test the compounds on EGF treated MDA-MB-468 cells to observe the attenuation of EGF induced EMT. Future studies will be performed to determine the specific protein interactions of the promising compounds.

Citation Format: Bhatt AB, Wright TD, Anna K, Gupta M, Chakrabarty S, Flaherty PT, Hoang V, Burow M, Cavanaugh JE. Study of diphenylamine analogs as inducers of mesenchymal to epithelial transition in breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-08-07.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

Oncogenic signaling of MEK5-ERK5

Mitogen-activated protein kinases (MAPKs) regulate diverse cellular processes including proliferation, cell survival, differentiation, and apoptosis. While conventional MAPK constituents have well-defined roles in oncogenesis, the MEK5 pathway has only recently emerged in cancer research. In this review, we consider the MEK5 signaling cascade, focusing specifically on its involvement in drug resistance and regulation of aggressive cancer phenotypes. Moreover, we explore the role of MEK5/ERK5 in tumorigenesis and metastatic progression, discussing the discrepancies in preclinical studies and assessing its viability as a therapeutic target for anti-cancer agents.

Abstract 1596: Induction of mesenchymal-to-epithelial transition through pan-MEK inhibition in triple-negative breast cancer

Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. Constitutive activation of the MAPK/extracellular signal-regulated kinases (MEK) pathways has been linked to chemoresistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT). Here we proposed to investigate dual inhibition of MEK1/2 and MEK5 as a more efficacious method for intervention to target mesenchymal and highly metastatic breast cancer cells than MEK1/2 or MEK5 alone through the use of a novel pan-MEK inhibitor SC-151. Interestingly, TNBC cells demonstrated a change in cell morphology indicative of mesenchymal-to-epithelial transition (MET) and exhibited a significant decrease in migration potential following pan-MEK inhibition. Additionally, immuno-compromised mice inoculated with MDA-MB-231 cells and treated with SC-151 demonstrated decreased tumor volumes compared to vehicle-treated animals. To parse the roles of MEK1/2 and MEK5 in EMT and tumorigenesis, we used the CRISPR/Cas9 approach to knock out ERK5 expression in the TNBC cell line MDA-MB-231. Similar to biological changes induced by pan-MEK inhibition, loss of ERK5 promoted epithelial characteristics in TNBC cells at the morphological and molecular level and impaired tumor formation in vivo. Treatment of ERK5-ko cells with SC-151 further enhanced these effects in vitro, suggesting that MEK1/2 and MEK5 play distinct roles in maintaining the mesenchymal phenotype. Further analysis revealed that constitutive activation of MEK5 abrogated the effects of SC-151 on the reversal of EMT, highlighting the requirement for MEK5 inhibition in MET induction. Taken together, these findings show that while the MEK5-ERK5 pathway may be sufficient in EMT regulation, MEK1/2 signaling further sustains the mesenchymal state of TNBC cells. Thus, dual MEK inhibition exerts optimal effects in the reversal of EMT. These data present a novel compound and viable therapeutic strategy to target both MEK1/2 and MEK5 in phenotypically mesenchymal and clinically aggressive breast cancer cells, warranting further investigation into mechanisms by which MEK1/2 and MEK5 individually modulate the EMT axis. Additionally, as MEK inhibition has been shown to sensitize resistant cancer cells to targeted therapies, synergistic and sensitizing effects of SC-151 combined with inhibitors of alternative signaling pathways as well as kinases upstream of MEK will be examined.

Citation Format: Van T. Hoang, Steven Elliott, Elizabeth C. Martin, Lyndsay V. Rhodes, Hope E. Burks, Margarite Matossian, Suravi Chakrabarty, Darlene Monlish, Theresa B. Phamduy, Lowry Curley, Muralidharan Anbalagan, Brian G. Rowan, Doug Chrisey, Jane E. Cavanaugh, Patrick T. Flaherty, Bridgette M. Collins-Burow, Matthew E. Burow. Induction of mesenchymal-to-epithelial transition through pan-MEK inhibition in triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1596.

Abstract 1337: Exploration of 2-aryl fused thiophene analogs as selective inhibitors of MEK5

In several cancers intermediate enzymes in the MAPK cascades are up-regulated and may represent adaptive changes giving these cancers a competitive metabolic edge over normal cells. Additionally these alterations may induce resistance to previously useful chemotherapeutic agents. The enzyme MEK5, a component of the MEK5/ERK5 cascade, is up-regulated in several cancer types including triple negative breast cancer and prostrate cancers. Our group has previously described the synthesis and testing of anthranillic acid derived compounds and their ring constrained analogs. To explore chemical functional group tolerance and preference on the central arene ring by MEK5, a series of fused-thiophene ring variations, obtainable by the Gewald reaction were prepared and tested. These compounds were examined at 10 μM with MDA-MB-231 cells treated with EGF to induce MEK1/2 and MEK5 phosphorylation. Western blot analysis using IR-tagged antibodies against pERK1/2, pERK5, ERK1/2, or ERK5 was used to determine total and relative inhibition of MEK-mediated phosphorylation of respective pERK products. Incubation with PD0325901 resulted in full suppression of both pERK1/2 and pERK5. For the variations explored, several novel compounds were identified that resulted in no inhibition in the formation of pERK1/2 and 70% inhibition of pERK5. This establishes a new structural class of selective Type III inhibitors of MEK5 that are more amenable to structural variation, facilitating additional structure activity relationship studies.

Citation Format: Patrick T. Flaherty, Dhruv Shah, Mohit Gupta, Thomas Wright, Jane E. Cavanaugh, Matthew E. Burow. Exploration of 2-aryl fused thiophene analogs as selective inhibitors of MEK5. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1337.

Abstract 1963: Analysis of aryl substitution and intramolecular ligand H-bonding in selective inhibitors of the MEK5/ERK5 cascade

Mitogen Activated Protein Kinase (MAPK) pathways initiate with external signaling, proceed through a sequence of protein kinases, and alter cell proliferation, growth, and survival. MAPK pathways proceed through a well-ordered sequence but are interconnected and modified by the cell's internal needs. The MEK-catalyzed phosphorylation of its target ERK represents the most selective interaction of MAPK signaling cascades. The type III MEK1/2 inhibitor, Mekinist, was recently approved by the FDA for the treatment of unresectable or metastatic melanoma with BRAF V600E or V600K mutations. This success suggests inhibitors of other MEK/ERK cascades may be reasonable strategies for anti-cancer therapeutic strategies. Despite the likely involvement of MEK5 phosphorylation of ERK5 in early and triple negative breast cancers, prostate cancer, and renal cancer, little work has been focused on developing selective MEK5 inhibitors. We have previously described an initial series of anthranilic acid derivatives structurally derived from the known non-selective MEK inhibitor PD0325901. To explore structural requirements for selective inhibition of MEK5 versus MEK1/2, aryl substitution and the role of proposed internal hydrogen bonding of the ligand were examined with novel compounds. These were tested at 10 μM in MDB-MB-213 cells subsequently treated with EGF to induce MEK1/2 and MEK5 phosphorylation. Western blot analysis following electrophoresis using IR-tagged antibodies raised against pERK1/2, pERK5, ERK1/2, or ERK5 permitted determination of total and relative inhibition of MEK-mediated generation of pERK. Incubation with PD0325901 resulted in full suppression of both pERK1/2 and pERK5. For the aryl substitutions examined, omission of the halogens on the pendant phenyl group (SC-1-181) abolished MEK1/2 inhibition(0% decrease in pERK1/2) yet retained good MEK5 inhibition (82% decrease in pERK5). Disruption of an internal nitrogen-acyl hydrogen bond preferentially decreased MEK5 inhibition (SC-2-32: 40% and 16% decrease in pERK5 and pERK1/2 respectively). This establishes early evidence of significant variation in specificity of MEK type III binding sites that may be exploited as pharmacological tools and possibly as therapeutic agents for cancers overexpressing MEK5.

Citation Format: Patrick T. Flaherty, Jane C. Cavanaugh, Mohit Gupta, Colin Vechery, Suravi Chakrabarty, Darlene Monlish, Thomas Wright. Analysis of aryl substitution and intramolecular ligand H-bonding in selective inhibitors of the MEK5/ERK5 cascade. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1963. doi:10.1158/1538-7445.AM2015-1963

Abstract 929: Caboxylic acid esters as inhibitors of the MEK1/2 and MEK5 signaling cascades

The purpose of the current study is to examine how structural variation on methyl anthranilates can differentially affect specific branches of the MAPK signaling cascade. The specific goal is to correlate the role of MEK1/2 versus MEK5 in breast cancer proliferation and migration modeled by the profile of pERK isoforms in treated BT-474 (ER+/PR+/HER2high) and MDA-MB-231 (ER−/PR−/HER2low) human breast cancer cell lines. The MAPK signaling pathway is a complex interconnected signaling cascade activated by extracellular stimuli, including growth factors, cytokines, and mechanical and chemical stressors, to elicit appropriate cellular responses including cell survival, proliferation, differentiation, and apoptotic cell death. The interconnected nature of these pathways permits a single external stimulus to be interpreted in the context of the immediate metabolic demands of the cell. The singularly specific and parallel event is phosphorylation of ERK by its corresponding activating kinase or MEK. In the course of examining small molecules with the design goal of developing selective inhibitors of the MEK5 isoform, we identified a simple substituted methyl anthranilate derivative that unexpectedly and specifically inhibited ERK1/2 activation but had little effect on ERK5 activation. We subsequently explored structural variations and prepared structure assisted new compounds from this initial find. In the BT-474 and MDA-MB-231 cell lines, western blot analysis was performed to determine the expression and activation of ERK1/2 and ERK5 following treatment with the novel MEK-specific inhibitors. An MTT assay was used to assess changes in cell proliferation following kinase inhibition, while scratch and invasion assays were performed to assess the effect of the carboxylic acid esters on cell migration and invasion in these cell lines. The data obtained from these studies indicate methyl anthranilate derivatives warrant further investigation as potential inhibitors of tumor proliferation and migration in breast cancer.

Citation Format: Jane E. Cavanaugh, Darlene A. Monlish, Suravi Chakrabarty, Si Qin, Patrick T. Flaherty. Caboxylic acid esters as inhibitors of the MEK1/2 and MEK5 signaling cascades. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 929. doi:10.1158/1538-7445.AM2013-929

The effect of the steroid sulfatase inhibitor (p-O-sulfamoyl)-tetradecanoyl tyramine (DU-14) on learning and memory in rats with selective lesion of septal-hippocampal cholinergic tract

Dehydroepiandrosterone sulfate (DHEAS), is an excitatory neurosteroid synthesized within the CNS that modulates brain function. Effects associated with augmented DHEAS include learning and memory enhancement. Inhibitors of the steroid sulfatase enzyme increase brain DHEAS levels and can also facilitate learning and memory. This study investigated the effect of steroid sulfatase inhibition on learning and memory in rats with selective cholinergic lesion of the septo-hippocampal tract using passive avoidance and delayed matching to position T-maze (DMP) paradigms. The selective cholinergic immunotoxin 192 IgG-saporin (SAP) was infused into the medial septum of animals and then tested using a step-through passive avoidance paradigm or DMP paradigm. Peripheral administration of the steroid sulfatase inhibitor, DU-14, increased step-through latency following footshock in rats with SAP lesion compared to both vehicle treated control and lesioned animals (p<0.05). However, in the DMP task, steroid sulfatase inhibition impaired acquisition in lesioned rats while having no effect on intact animals. These results suggest that steroid sulfatase inhibition facilitates memory associated with contextual fear, but impairs acquisition of spatial memory tasks in rats with selective lesion of the septo-hippocampal tract.

Identification of HIV inhibitors guided by free energy perturbation calculations

Free energy perturbation (FEP) theory coupled to molecular dynamics (MD) or Monte Carlo (MC) statistical mechanics offers a theoretically precise method for determining the free energy differences of related biological inhibitors. Traditionally requiring extensive computational resources and expertise, it is only recently that its impact is being felt in drug discovery. A review of computer-aided anti-HIV efforts employing FEP calculations is provided here that describes early and recent successes in the design of human immunodeficiency virus type 1 (HIV-1) protease and non-nucleoside reverse transcriptase inhibitors. In addition, our ongoing work developing and optimizing leads for small molecule inhibitors of cyclophilin A (CypA) is highlighted as an update on the current capabilities of the field. CypA has been shown to aid HIV-1 replication by catalyzing the cis/trans isomerization of a conserved Gly-Pro motif in the Nterminal domain of HIV-1 capsid (CA) protein. In the absence of a functional CypA, e.g., by the addition of an inhibitor such as cyclosporine A (CsA), HIV-1 has reduced infectivity. Our simulations of acylurea-based and 1-indanylketone-based CypA inhibitors have determined that their nanomolar and micromolar binding affinities, respectively, are tied to their ability to stabilize Arg55 and Asn102. A structurally novel 1-(2,6-dichlorobenzamido) indole core was proposed to maximize these interactions. FEP-guided optimization, experimental synthesis, and biological testing of lead compounds for toxicity and inhibition of wild-type HIV-1 and CA mutants have demonstrated a dose-dependent inhibition of HIV-1 infection in two cell lines. While the inhibition is modest compared to CsA, the results are encouraging.

Structure-activity relationships of benzimidazole-based selective inhibitors of the mitogen activated kinase-5 signaling pathway

In a prior communication we identified a novel class of benzimidazole-based inhibitors of EGF-induced phosphorylation of ERK5. In this paper we examine the biological activity of several 1-isopropyl-4-amino-6-ether linked benzimidazole-based compounds for their ability to selectively inhibit EGF-mediated ERK5 phosphorylation; potential utility of variation at the 6-position was indicated by the initial structural feature survey. Modification of EGF-induced formation of pERK1/2 and pERK5 in HEK293 cells were analyzed by Western blot analysis. Subsequent analysis of selected compounds in a high-throughput multiple kinase scan and the NCI 60-cell-line screen is presented.

1-Isopropyl-4-nitro-6-meth-oxy-1H-benzimidazole

There are two independent mol­ecules in the asymmetric unit of the title compound, C₁₁H₁₃N₃O₃. The inter­planar angles for the two rings of the benzimidazole ring system is 2.21 (12)° in one mol­ecule and 0.72 (12)° in the other. The nitro group is twisted in the same direction relative to the least-squares plane through its attached benzene ring in both mol­ecules, with inter­planar angles of 15.22 (9) and 18.02 (8)°. In the crystal structure, mol­ecules are stacked along the a axis through π–π inter­actions (centroid–centroid distance 4.1954 Å). C—H⋯O hydrogen bonds are also present.

Synthesis and anti-tubulin activity of a 3'-(4-azidophenyl)-3'-dephenylpaclitaxel photoaffinity probe

The synthesis and biological evaluation of a novel paclitaxel photoaffinity probe is described. The synthesis involved the preparation of an azide-containing C13 side chain through a Staudinger cycloaddition followed by a lipase-mediated kinetic resolution to obtain the azetidinone in 99% ee. Coupling of the enantiopure side chain precursor to 7-TES-baccatin III and subsequent silyl ether deprotection afforded 3'-(4-azidophenyl)-3'-dephenylpaclitaxel, which was shown to be as active as paclitaxel in tubulin assembly and cytotoxicity assays.

Formal Total Synthesis of (+)-Salicylihalamides A and B: A Combined Chiral Pool and RCM Strategy

The formal total synthesis of the (+)-salicylihalamides A and B is detailed, utilizing a chiral pool approach to generate the three stereogenic centers and a ring-closing metathesis (RCM) for the formation of the macrocyclic ring structure. Starting from a known glucose-derived alcohol, the formal total synthesis was achieved in an efficient 13-step protocol in 26% overall yield. It was found that substitution at the remote phenolic group significantly influenced the ratio of the E- and Z-double bond products in the RCM step. The introduction of phenol protecting groups provided E-isomers preferentially and also enhanced the rates of the RCM reactions.

Synthesis and evaluation of N-(phenylacetyl)trifluoromethanesulfonamides as anticonvulsant agents

A series of N-(phenylacetyl)trifluoromethanesulfonamides (3a-g) was prepared according to the Topliss scheme in order to determine if aryl substituents would influence anticonvulsant activity. In initial (phase I) screening and quantitative (phase II) evaluation, all seven compounds exhibited significant activity against MES- and scMet-induced seizures. N-(Phenylacetyl)trifluoromethanesulfonamide (3a) was then advanced through five additional testing phases (phases III-VII). Compound 3a displayed good oral bioavailability, low toxicity, and a larger protective index in mice than the prototype drugs, phenytoin, phenobarbital, valproate, and ethosuximide. Additionally, 3a exhibited a longer time to peak effect in all tests and a greater 24-h margin of safety (HD(50)/ED(50)) than the prototypes. Compound 3a blocked picrotoxin-induced seizures but was ineffective against seizures induced by bicuculline or strychnine. In vitro receptor binding studies revealed that 3a did not displace [(3)H]-labeled gamma-aminobutyric acid or [(3)H]-labeled flunitrazepam, and tolerance did not develop during a 5-day chronic administration.

A-ring ortho-disubstituted aporphine derivatives as potential agonists or antagonists at serotonergic 5-HT1A receptors

(R)- And (S)-11-hydroxy-10-methylaporphine 1 and 2 are, respectively, a potent, highly specific serotonergic (5-HT1A) agonist and antagonist. In an ongoing structure-activity study, racemates of the positional isomers 8-hydroxy-9-methyl- and 8-methyl-9-hydroxyaporphine were prepared by modifications of literature methods and were resolved. The methyl ethers of the target compounds were also evaluated pharmacologically. All of the free phenolic derivatives [(+)- and (-)-8 and 10] were inert in an assay for 5-HT1A receptor activity. All of the methyl ethers [(+)- and (-)-9 and 11] demonstrated quantitatively similar low potency stimulant effect at 5-HT1A receptors. The agonist or antagonist activity exhibited by 1 and 2 reflects the high degree of structural specificity required of aporphine derivatives for action at 5-HT1A receptors.