BimEL is an important determinant for induction of anoikis sensitivity by mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitors

Kinase signalling adaptation supports dysfunctional mitochondria in disease

Mitochondria form a critical control nexus which are essential for maintaining correct tissue homeostasis. An increasing number of studies have identified dysregulation of mitochondria as a driver in cancer. However, which pathways support and promote this adapted mitochondrial function? A key hallmark of cancer is perturbation of kinase signalling pathways. These pathways include mitogen activated protein kinases (MAPK), lipid secondary messenger networks, cyclic-AMP-activated (cAMP)/AMP-activated kinases (AMPK), and Ca2+/calmodulin-dependent protein kinase (CaMK) networks. These signalling pathways have multiple substrates which support initiation and persistence of cancer. Many of these are involved in the regulation of mitochondrial morphology, mitochondrial apoptosis, mitochondrial calcium homeostasis, mitochondrial associated membranes (MAMs), and retrograde ROS signalling. This review will aim to both explore how kinase signalling integrates with these critical mitochondrial pathways and highlight how these systems can be usurped to support the development of disease. In addition, we will identify areas which require further investigation to fully understand the complexities of these regulatory interactions. Overall, this review will emphasize how studying the interaction between kinase signalling and mitochondria improves our understanding of mitochondrial homeostasis and can yield novel therapeutic targets to treat disease.

Loss of EGF receptor polarity enables homeostatic imbalance in epithelial-cell models

The polarized distribution of membrane proteins into apical and basolateral domains provides the basis for specialized functions of epithelial tissues. The EGF receptor (EGFR) plays important roles in embryonic development, adult-epithelial tissue homeostasis, and growth and survival of many carcinomas. Typically targeted to basolateral domains, there is also considerable evidence of EGFR sorting plasticity but very limited knowledge regarding domain-specific EGFR substrates. Here we have investigated effects of selective EGFR mistargeting because of inactive-basolateral sorting signals on epithelial-cell homeostatic responses to growth-induced stress in MDCK cell models. Aberrant EGFR localization was associated with multilayer formation, anchorage-independent growth, and upregulated expression of the intermediate filament-protein vimentin characteristically seen in cells undergoing epithelial-to-mesenchymal transition. EGFRs were selectively retained following their internalization from apical membranes, and a signaling pathway involving the signaling adaptor Gab1 protein and extracellular signal-regulated kinase ERK5 had an essential role integrating multiple responses to growth-induced stress. Our studies highlight the potential importance of cellular machinery specifying EGFR polarity in epithelial pathologies associated with homeostatic imbalance.

Acquired Secondary HER2 Mutations Enhance HER2/MAPK Signaling and Promote Resistance to HER2 Kinase Inhibition in Breast Cancer

HER2 mutations drive the growth of a subset of breast cancers and are targeted with HER2 tyrosine kinase inhibitors (TKI) such as neratinib. However, acquired resistance is common and limits the durability of clinical responses. Most HER2-mutant breast cancers progressing on neratinib-based therapy acquire secondary mutations in HER2. It is unknown whether these secondary HER2 mutations, other than the HER2T798I gatekeeper mutation, are causal to neratinib resistance. Herein, we show that secondary acquired HER2T862A and HER2L755S mutations promote resistance to HER2 TKIs via enhanced HER2 activation and impaired neratinib binding. While cells expressing each acquired HER2 mutation alone were sensitive to neratinib, expression of acquired double mutations enhanced HER2 signaling and reduced neratinib sensitivity. Computational structural modeling suggested that secondary HER2 mutations stabilize the HER2 active state and reduce neratinib binding affinity. Cells expressing double HER2 mutations exhibited resistance to most HER2 TKIs but retained sensitivity to mobocertinib and poziotinib. Double-mutant cells showed enhanced MEK/ERK signaling, which was blocked by combined inhibition of HER2 and MEK. Together, these findings reveal the driver function of secondary HER2 mutations in resistance to HER2 inhibition and provide a potential treatment strategy to overcome acquired resistance to HER2 TKIs in HER2-mutant breast cancer.

SIGNIFICANCE

HER2-mutant breast cancers acquire secondary HER2 mutations that drive resistance to HER2 tyrosine kinase inhibitors, which can be overcome by combined inhibition of HER2 and MEK.

Mechanisms of EGFR-TKI-Induced Apoptosis and Strategies Targeting Apoptosis in EGFR-Mutated Non-Small Cell Lung Cancer

Homeostasis is achieved by balancing cell survival and death. In cancer cells, especially those carrying driver mutations, the processes and signals that promote apoptosis are inhibited, facilitating the survival and proliferation of these dysregulated cells. Apoptosis induction is an important mechanism underlying the therapeutic efficacy of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) for EGFR-mutated non-small cell lung cancer (NSCLC). However, the mechanisms by which EGFR-TKIs induce apoptosis have not been fully elucidated. A deeper understanding of the apoptotic pathways induced by EGFR-TKIs is essential for the developing novel strategies to overcome resistance to EGFR-TKIs or to enhance the initial efficacy through therapeutic synergistic combinations. Recently, therapeutic strategies targeting apoptosis have been developed for cancer. Here, we review the state of knowledge on EGFR-TKI-induced apoptotic pathways and discuss the therapeutic strategies for enhancing EGFR-TKI efficiency. We highlight the great progress achieved with third-generation EGFR-TKIs. In particular, combination therapies of EGFR-TKIs with anti-vascular endothelial growth factor/receptor inhibitors or chemotherapy have emerged as promising therapeutic strategies for patients with EGFR-mutated NSCLC. Nevertheless, further breakthroughs are needed to yield an appropriate standard care for patients with EGFR-mutated NSCLC, which requires gaining a deeper understanding of cancer cell dynamics in response to EGFR-TKIs.

Clinical Implications of the BIM Deletion Polymorphism in Advanced Lung Adenocarcinoma Treated With Gefitinib

BACKGROUND

Proapoptotic protein Bcl-2-like 11 (BIM) is a crucial tumor suppressor gene in lung cancer development. A 2903-bp genomic deletion polymorphism is present in BIM intron 2, which alters RNA splicing and impairs the generation of the death-inducing isoform of BIM and resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). In the present study, we investigated the clinical implications of this genetic polymorphism in patients with advanced lung adenocarcinoma treated with gefitinib.

MATERIALS AND METHODS

After genotyping the BIM deletion polymorphism in 111 patients with stage IIIB or IV lung adenocarcinoma receiving gefitinib, the hazard ratio (HR) and 95% confidence interval (CI) for progression-free survival and overall survival were estimated using Cox proportional hazards models.

RESULTS

Possession of ≥ 1 deletion allele of the BIM polymorphism was observed in 18.02% of the patients. The BIM deletion polymorphism was an independent indicator of a shorter PFS (7.5 months vs. 11.3 months; HR, 2.38; 95% CI, 1.30-4.34; P = .005) and shorter OS (9.9 months vs. 27.5 months; HR, 2.53; 95% CI, 1.37-4.65; P = .003). Additionally, patients carrying the BIM deletion allele were more likely to experience acquired gefitinib-resistant disease.

CONCLUSION

Our results indicate that the BIM deletion polymorphism might be a promising germline biomarker for gefitinib treatment in Chinese patients with lung adenocarcinoma.

Determination of the Relative Efficacy of Eicosapentaenoic Acid and Docosahexaenoic Acid for Anti-Cancer Effects in Human Breast Cancer Models

Epidemiological studies have associated high fish oil consumption with decreased risk of breast cancer (BC). n-3 long chain polyunsaturated fatty acids (n-3 LCPUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish and fish oils exert anti-cancer effects. However, few studies have examined the relative efficacy of EPA and DHA alone and in mixtures on BC subtypes. This was the objective of the present review, as this research is a necessity for the translation of findings to human health and disease. The literature suggests that DHA has a greater anti-cancer effect in triple negative BC (TNBC). In estrogen positive (ER+) BC, DHA has a greater effect on cell viability, while both fatty acids have similar effects on apoptosis and proliferation. These effects are associated with preferential uptake of DHA into TNBC lipid rafts and EPA in ER+ BC. EPA:DHA mixtures have anti-cancer activity; however, the ratio of EPA:DHA does not predict the relative incorporation of these two fatty acids into membrane lipids as EPA appears to be preferentially incorporated. In summary, DHA and EPA should be considered separately in the context of BC prevention. The elucidation of optimal EPA:DHA ratios will be important for designing targeted n-3 LCPUFA treatments.

Cysteine-linked dimerization of BST-2 confers anoikis resistance to breast cancer cells by negating proapoptotic activities to promote tumor cell survival and growth

Almost all breast tumors express the antiviral protein BST-2 with 67%, 25% and 8.2% containing high, medium or low levels of BST-2, respectively. Breast tumor cells and tissues that contain elevated levels of BST-2 are highly aggressive. Suppression of BST-2 expression reprograms tumorigenic properties of cancer cells and diminishes cancer cell aggressiveness. Using structure/function studies, we report that dimerization of BST-2 through cysteine residues located in the BST-2 extracellular domain (ECD), leads to anoikis resistance and cell survival through proteasome-mediated degradation of BIM—a key proapoptotic factor. Importantly, BST-2 dimerization promotes tumor growth in preclinical breast cancer models in vitro and in vivo. Furthermore, we demonstrate that restoration of the ECD cysteine residues is sufficient to rescue cell survival and tumor growth via a previously unreported pathway—BST-2/GRB2/ERK/BIM/Cas3. These findings suggest that disruption of BST-2 dimerization offers a potential therapeutic approach for breast cancer.

Coadministration of the FNIII14 Peptide Synergistically Augments the Anti-Cancer Activity of Chemotherapeutic Drugs by Activating Pro-Apoptotic Bim

The acquisition of drug resistance mediated by the interaction of tumor cells with the extracellular matrix (ECM), commonly referred to as cell adhesion-mediated drug resistance (CAM-DR), has been observed not only in hematopoietic tumor cells but also in solid tumor cells. We have previously demonstrated that a 22-mer peptide derived from fibronectin, FNIII14, can inhibit cell adhesion through the inactivation of β1 integrin; when coadministered with cytarabine, FNIII14 completely eradicates acute myelogenous leukemia by suppressing CAM-DR. In this study, we show that our FNIII14 peptide also enhances chemotherapy efficacy in solid tumors. Coadministration of FNIII14 synergistically enhances the cytotoxicity of doxorubicin and aclarubicin in mammary tumor and melanoma cells, respectively. The solid tumor cell chemosensitization induced by FNIII14 is dependent upon the upregulation and activation of the pro-apoptotic protein, Bim. Furthermore, the metastasis of tumor cells derived from ventrally transplanted mammary tumor grafts is suppressed by the coadministration of FNIII14 and doxorubicin. These results suggest that the coadministration of our FNIII14 peptide with chemotherapy could achieve efficient solid tumor eradication by increasing chemosensitivity and decreasing metastasis. The major causes of tumor recurrence are the existence of chemotherapy-resistant primary tumor cells and the establishment of secondary metastatic lesions. As such, coadministering FNIII14 with anti-cancer drugs could provide a promising new approach to improve the prognosis of patients with solid tumors.

Targeting the mitogen-activated protein kinase pathway in low-grade serous carcinoma of the ovary

Until recently, there has been little change in the management of epithelial ovarian cancer with the majority of women receiving identical systemic therapy, regardless of histological subtype. The heterogeneity of epithelial ovarian cancer is now well established, with distinct subtypes characterized by specific molecular alterations and patterns of clinical behavior. Low-grade serous carcinoma is a rare subtype associated with an indolent biological behavior and inherent resistance to chemotherapy. The mitogen-activated protein kinase pathway plays a prominent role in the pathogenesis of low-grade serous carcinoma, and provides an attractive target for novel therapeutic agents. Selumetinib, a MEK1/2 inhibitor, demonstrates promising efficacy in women with relapsed low-grade serous carcinoma, and further trials of MEK-inhibition are underway. Translational research will be essential to identify predictive biomarkers for this treatment approach.

EGFR-TKI resistance due to BIM polymorphism can be circumvented in combination with HDAC inhibition

BIM (BCL2L11) is a BH3-only proapoptotic member of the Bcl-2 protein family. BIM upregulation is required for apoptosis induction by EGF receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKI) in EGFR-mutant forms of non-small cell lung cancer (NSCLC). Notably, a BIM deletion polymorphism occurs naturally in 12.9% of East Asian individuals, impairing the generation of the proapoptotic isoform required for the EGFR-TKIs gefitinib and erlotinib and therefore conferring an inherent drug-resistant phenotype. Indeed, patients with NSCLC, who harbored this host BIM polymorphism, exhibited significantly inferior responses to EGFR-TKI treatment than individuals lacking this polymorphism. In an attempt to correct this response defect in the resistant group, we investigated whether the histone deacetylase (HDAC) inhibitor vorinostat could circumvent EGFR-TKI resistance in EGFR-mutant NSCLC cell lines that also harbored the BIM polymorphism. Consistent with our clinical observations, we found that such cells were much less sensitive to gefitinib-induced apoptosis than EGFR-mutant cells, which did not harbor the polymorphism. Notably, vorinostat increased expression in a dose-dependent manner of the proapoptotic BH3 domain-containing isoform of BIM, which was sufficient to restore gefitinib death sensitivity in the EGFR mutant, EGFR-TKI-resistant cells. In xenograft models, while gefitinib induced marked regression via apoptosis of tumors without the BIM polymorphism, its combination with vorinostat was needed to induce marked regression of tumors with the BIM polymorphism in the same manner. Together, our results show how HDAC inhibition can epigenetically restore BIM function and death sensitivity of EGFR-TKI in cases of EGFR-mutant NSCLC where resistance to EGFR-TKI is associated with a common BIM polymorphism.

Anoikis, initiated by Mcl-1 degradation and Bim induction, is deregulated during oncogenesis

Anoikis, a Bax-dependent apoptosis triggered by detachment from the extracellular matrix, is often dysfunctional in metastatic cancer cells. Using wild-type and c-Src-transformed NIH3T3 cells as a model, we identified Mcl-1 degradation and Bim up-regulation as a critical determinant of anoikis initiation. Detachment rapidly degraded Mcl-1 via a GSK-3beta-dependent proteasomal pathway and transcriptionally up-regulated Bim expression. Mcl-1 degradation in the presence of Bim was sufficient to induce anoikis. By analyzing nonmetastatic Saos-2 and metastatic derivative LM7 cells, we confirmed that dysregulation of Mcl-1 degradation and Bim induction during detachment contributes to decreased anoikis sensitivity of metastatic cells. Furthermore, knockdown of Mcl-1 or pharmacologic inhibition of the phosphoinositide-3-kinase/Akt and mitogen-activated protein kinase pathways that suppress Mcl-1 degradation and Bim expression could markedly sensitize metastatic breast cancer cells to anoikis and prevent metastases in vivo. Therefore, Mcl-1 degradation primes the cell for Bax activation and anoikis, which can be blocked by oncogenic signaling in metastatic cells.