Adaptation to an acid microenvironment promotes pancreatic cancer organoid growth and drug resistance.

Harsh environments in poorly perfused tumor regions may select for traits driving cancer aggressiveness. Here, we investigated whether tumor acidosis interacts with driver mutations to exacerbate cancer hallmarks. We adapted mouse organoids from normal pancreatic duct (mN10) and early pancreatic cancer (mP4, KRAS-G12D mutation, ± p53 knockout) from extracellular pH 7.4 to 6.7, representing acidic niches. Viability was increased by acid adaptation, a pattern most apparent in wild-type (WT) p53 organoids, and exacerbated upon return to pH 7.4. This led to increased survival of acid-adapted organoids treated with gemcitabine and/or erlotinib, and, in WT p53 organoids, acid-induced attenuation of drug effects. New genetic variants became dominant during adaptation, yet they were unlikely to be its main drivers. Transcriptional changes induced by acid and drug adaptation differed overall, but acid adaptation increased the expression of gemcitabine resistance genes. Thus, adaptation to acidosis increases cancer cell viability after chemotherapy.

Dynamic localization of the Na+-HCO3- co-transporter NBCn1 to the plasma membrane, centrosomes, spindle and primary cilia.

Finely tuned regulation of transport protein localization is vital for epithelial function. The Na+-HCO3- co-transporter NBCn1 (also known as SLC4A7) is a key contributor to epithelial pH homeostasis, yet the regulation of its subcellular localization is not understood. Here, we show that a predicted N-terminal ß-sheet and short C-terminal α-helical motif are essential for NBCn1 plasma membrane localization in epithelial cells. This localization was abolished by cell-cell contact disruption, and co-immunoprecipitation (co-IP) and proximity ligation (PLA) revealed NBCn1 interaction with E-cadherin and DLG1, linking it to adherens junctions and the Scribble complex. NBCn1 also interacted with RhoA and localized to lamellipodia and filopodia in migrating cells. Finally, analysis of native and GFP-tagged NBCn1 localization, subcellular fractionation, co-IP with Arl13B and CEP164, and PLA of NBCn1 and tubulin in mitotic spindles led to the surprising conclusion that NBCn1 additionally localizes to centrosomes and primary cilia in non-dividing, polarized epithelial cells, and to the spindle, centrosomes and midbodies during mitosis. We propose that NBCn1 traffics between lateral junctions, the leading edge and cell division machinery in Rab11 endosomes, adding new insight to the role of NBCn1 in cell cycle progression.

Crosstalk between tumor acidosis, p53 and extracellular matrix regulates pancreatic cancer aggressiveness.

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive malignancy with minimal treatment options and a global rise in prevalence. PDAC is characterized by frequent driver mutations including KRAS and TP53 (p53), and a dense, acidic tumor microenvironment (TME). The relation between genotype and TME in PDAC development is unknown. Strikingly, when wild type (WT) Panc02 PDAC cells were adapted to growth in an acidic TME and returned to normal pH to mimic invasive cells escaping acidic regions, they displayed a strong increase of aggressive traits such as increased growth in 3-dimensional (3D) culture, adhesion-independent colony formation and invasive outgrowth. This pattern of acidosis-induced aggressiveness was observed in 3D spheroid culture as well as upon organotypic growth in matrigel, collagen-I and combination thereof, mimicking early and later stages of PDAC development. Acid-adaptation-induced gain of cancerous traits was further increased by p53 knockout (KO), but only in specific extracellular matrix (ECM) compositions. Akt- and Transforming growth factor-ß (TGFß) signaling, as well as expression of the Na+ /H+ exchanger NHE1, were increased by acid adaptation. Whereas Akt inhibition decreased spheroid growth regardless of treatment and genotype, stimulation with TGFßI increased growth of WT control spheroids, and inhibition of TGFß signaling tended to limit growth under acidic conditions only. Our results indicate that a complex crosstalk between tumor acidosis, ECM composition and genotype contributes to PDAC development. The findings may guide future strategies for acidosis-targeted therapies.

Metabolic reprogramming by driver mutation-tumor microenvironment interplay in pancreatic cancer: new therapeutic targets.

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers globally with a mortality rate exceeding 95% and very limited therapeutic options. A hallmark of PDAC is its acidic tumor microenvironment, further characterized by excessive fibrosis and depletion of oxygen and nutrients due to poor vascularity. The combination of PDAC driver mutations and adaptation to this hostile environment drives extensive metabolic reprogramming of the cancer cells toward non-canonical metabolic pathways and increases reliance on scavenging mechanisms such as autophagy and macropinocytosis. In addition, the cancer cells benefit from metabolic crosstalk with nonmalignant cells within the tumor microenvironment, including pancreatic stellate cells, fibroblasts, and endothelial and immune cells. Increasing evidence shows that this metabolic rewiring is closely related to chemo- and radioresistance and immunosuppression, causing extensive treatment failure. Indeed, stratification of human PDAC tumors into subtypes based on their metabolic profiles was shown to predict disease outcome. Accordingly, an increasing number of clinical trials target pro-tumorigenic metabolic pathways, either as stand-alone treatment or in conjunction with chemotherapy. In this review, we highlight key findings and potential future directions of pancreatic cancer metabolism research, specifically focusing on novel therapeutic opportunities.

MET-Pyk2 Axis Mediates Acquired Resistance to FGFR Inhibition in Cancer Cells.

Deregulation of fibroblast growth factor receptors (FGFRs) signaling, as a result of FGFR amplification, chromosomal translocation, or mutations, is involved in both initiation and progression of a wide range of human cancers. Clinical data demonstrating the dependence of cancer cells on FGFRs signaling clearly indicate these receptors as the molecular targets of anti-cancer therapies. Despite the increasing number of tyrosine kinase inhibitors (TKIs) being investigated in clinical trials, acquired resistance to these drugs poses a serious therapeutic problem. In this study, we focused on a novel pan-FGFR inhibitor-CPL304110, currently being investigated in phase I clinical trials in adults with advanced solid malignancies. We analyzed the sensitivity of 17 cell lines derived from cancers with aberrant FGFR signaling, i.e. non-small cell lung cancer, gastric and bladder cancer to CPL304110. In order to explore the mechanism of acquired resistance to this FGFR inhibitor, we developed from sensitive cell lines their variants resistant to CPL304110. Herein, for the first time we revealed that the process of acquired resistance to the novel FGFR inhibitor was associated with increased expression of MET in lung, gastric, and bladder cancer cells. Overexpression of MET in NCI-H1703, SNU-16, RT-112 cells as well as treatment with HGF resulted in the impaired response to inhibition of FGFR activity. Moreover, we demonstrated that cells with acquired resistance to FGFR inhibitor as well as cells overexpressing MET displayed enhanced migratory abilities what was accompanied with increased levels of Pyk2 expression. Importantly, inhibition of both MET and Pyk2 activity restored sensitivity to FGFR inhibition in these cells. Our results demonstrate that the HGF/MET-Pyk2 signaling axis confers resistance to the novel FGFR inhibitor, and this mechanism is common for lung, gastric, and bladder cancer cells. Our study suggests that targeting of MET/Pyk2 could be an approach to overcome resistance to FGFR inhibition.

Cancer Cell Acid Adaptation Gene Expression Response Is Correlated to Tumor-Specific Tissue Expression Profiles and Patient Survival.

The acidic pH of the tumor microenvironment plays a critical role in driving cancer development toward a more aggressive phenotype, but the underlying mechanisms are unclear. To this end, phenotypic and genotypic changes induced by adaptation of cancer cells to chronic acidosis have been studied. However, the generality of acid adaptation patterns across cell models and their correlation to the molecular phenotypes and aggressiveness of human cancers are essentially unknown. Here, we define an acid adaptation expression response shared across three cancer cell models, dominated by metabolic rewiring, extracellular matrix remodeling, and altered cell cycle regulation and DNA damage response. We find that many genes which are upregulated by acid adaptation are significantly correlated to patient survival, and more generally, that there are clear correlations between acid adaptation expression response and gene expression change between normal and tumor tissues, for a large subset of cancer patients. Our data support the notion that tumor microenvironment acidity is one of the key factors driving the selection of aggressive cancer cells in human patient tumors, yet it also induces a growth-limiting genotype that likely limits cancer cell growth until the cells are released from acidosis, for instance during invasion.

3D multicellular models to study the regulation and roles of acid-base transporters in breast cancer.

As a result of elevated metabolic rates and net acid extrusion in the rapidly proliferating cancer cells, solid tumours are characterized by a highly acidic microenvironment, while cancer cell intracellular pH is normal or even alkaline. Two-dimensional (2D) cell monocultures, which have been used extensively in breast cancer research for decades, cannot precisely recapitulate the rich environment and complex processes occurring in tumours in vivo. The use of such models can consequently be misleading or non-predictive for clinical applications. Models mimicking the tumour microenvironment are particularly pivotal for studying tumour pH homeostasis, which is profoundly affected by the diffusion-limited conditions in the tumour. To advance the understanding of the mechanisms and consequences of dysregulated acid-base homeostasis in breast cancer, clinically relevant models that incorporate the unique microenvironment of these tumours are required. The development of three-dimensional (3D) cell cultures has provided new tools for basic research and pre-clinical approaches, allowing the culture of breast cancer cells under conditions that closely resemble tumour growth in a living organism. Here we provide an overview of the main 3D techniques relevant for breast cancer cell culture. We discuss the advantages and limitations of the classical 3D models as well as recent advances in 3D culture techniques, focusing on how these culture methods have been used to study acid-base transport in breast cancer. Finally, we outline future directions of 3D culture technology and their relevance for studies of acid-base transport.

RSK1 promotes murine breast cancer growth and metastasis.

INTRODUCTION: Triple-negative breast cancer (TNBC), representing over 15% of all breast cancers, has a poorer prognosis than other subtypes. There is no effective targeted treatment available for the TNBC sufferers. Ribosomal S6 kinases (RSKs) have been previously proposed as drug targets for TNBC based on observations that 85% of these tumors express activated RSKs. MATERIALS AND METHODS: Herein we examined an involvement of RSK1 (p90 ribosomal S6 kinase 1) in a regulation of TNBC growth and metastatic spread in an animal model, which closely imitates human disease. Mice were inoculated into mammary fat pad with 4T1 cells or their RSK1-depleted variant. We examined tumor growth and formation of pulmonary metastasis. Boyden chamber, wound healing and soft agarose assays were performed to evaluate cells invasion, migration and anchorage-independent growth. RESULTS: We found that RSK1 promoted tumor growth and metastasis in vivo. After 35 days all animals inoculated with control cells developed tumors while in the group injected with RSK1-negative cells, there were 75% tumor-bearing mice. Average tumor mass was estimated as 1.16 g and 0.37 g for RSK1-positive vs. -negative samples, respectively (p < 0.0001). Quantification of the macroscopic pulmonary metastases indicated that mice with RSK1-negative tumors developed approximately 85% less metastatic foci on the lung surface (p < 0.001). This has been supported by in vitro data presenting that RSK1 promoted anchorage-independent cell growth and migration. Moreover, RSK1 knock-down corresponded with decreased expression of cell cycle regulating proteins, i.e. cyclin D3, CDK6 and CDK4. CONCLUSIONS: We provide evidence that RSK1 supports tumor growth and metastatic spread in vivo as well as in vitro migration and survival in non-adherent conditions. Further studies of RSK1 involvement in TNBC progression may substantiate our findings, laying the foundations for development of anti-RSK1-based therapeutic strategies in the management of patients with TNBC.

FGFR2-Driven Signaling Counteracts Tamoxifen Effect on ERα-Positive Breast Cancer Cells.

Signaling mediated by growth factors receptors has long been suggested as one of the key factors responsible for failure of endocrine treatment in breast cancer (BCa). Herein we present that in the presence of tamoxifen, FGFs (Fibroblast Growth Factors) promote BCa cell growth with the strongest effect being produced by FGF7. FGFR2 was identified as a mediator of FGF7 action and the FGFR2-induced signaling was found to underlie cancer-associated fibroblasts-dependent resistance to tamoxifen. FGF7/FGFR2-triggered pathway was shown to induce ER phosphorylation, ubiquitination and subsequent ER proteasomal degradation which counteracted tamoxifen-promoted ER stabilization. We also identified activation of PI3K/AKT signaling targeting ER-Ser167 and regulation of Bcl-2 expression as a mediator of FGFR2-promoted resistance to tamoxifen. Analysis of tissue samples from patients with invasive ductal carcinoma revealed an inversed correlation between expression of FGFR2 and ER, thus supporting our in vitro data. These results unveil the complexity of ER regulation by FGFR2-mediated signaling likely to be associated with BCa resistance to endocrine therapy.

Tetraspanin CD151 mediates communication between PC3 prostate cancer cells and osteoblasts.

Invasion and migration of cancer cells are crucial for the formation of secondary lesions. These require activation of signalling cascades modulated by the number of regulatory molecules. One such molecule is CD151, a member of evolutionary conserved tetraspanin family. CD151 is involved in cell adhesion, motility and cancer progression due to formation of complexes with laminin-binding integrins and regulation of growth factor receptors function (e.g. HGFR, TGFßR, EGFR). Recent studies point to correlation between CD151 expression and high tumour grade in prostate cancer (PCa). Herein, we investigated a possible role of CD151 in communication between PC3 cancer cells and either cancer-associated fibroblasts (CAFs) or osteoblasts, an interplay which is significant for metastasis. The analysis showed that although CAFs strongly enhanced both migration and invasion of PC3 prostate cancer cells, the effect was not dependent on CD151. On the other hand, CD151 was found to promote 3D migration as well as invasive growth in response to osteoblasts-secreted growth factors. Obtained data revealed that knockdown of CD151 abolished activation of pro-migratory/pro-survival kinases (i.e FAK, Src, HSP27) triggered by osteoblasts, along with expression of matrix metalloproteinase-13. This suggests that CD151 participates in communication between PC3 cells and bone microenvironment and the process can be considered as a significant step of PCa progression and metastasis.

Simplified, serine-rich theta-defensin analogues as antitumour peptides.

θ-defensins belong to the family of host defence peptides. They are the only known example of cyclic polypeptides in animal proteomes. This study presents the synthesis of simplified θ-defensin analogues with pairs of cysteine replaced either by alanine, leucine or serine residues. Cytotoxicity tests were performed on human mammary epithelial (HB2) and breast cancer (SKBR3, MDA-MB-231) cell lines to determine whether peptides are selectively targeting cancer cells. The effect of these peptides was also evaluated in 3D Matrigel cultures, which are based on extracellular matrix components and therefore closely represent in vivo conditions. Finally, to determine whether analogues are able to sensitize MDA-MB-231 triple-negative breast cancer cells to chemotherapeutics, we co-administrated peptides with cisplatin or doxorubicin hydrochloride also in 3D Matrigel cultures. Additionally, cytotoxicity towards peripheral blood mononuclear cells and haemolytic effect were examined for a chosen representative of synthesized compounds. The results showed that positively charged serine-containing θ-defensin derivatives were more cytotoxic towards breast cancer cells (SKBR3, MDA-MB-231) than towards mammary epithelial cells (HB2). Analogues enhanced the effect of cisplatin and doxorubicin hydrochloride on triple-negative breast cancer cell line (MDA-MB-231).

Fibroblast growth factor signalling induces loss of progesterone receptor in breast cancer cells.

We have recently demonstrated that, fibroblast growth factor 2 (FGFR2), signalling via ribosomal S6 kinase 2 (RSK2), promotes progression of breast cancer (BCa). Loss of progesterone receptor (PR), whose activity in BCa cells can be stimulated by growth factor receptors (GFRs), is associated with poor patient outcome. Here we showed that FGF7/FGFR2 triggered phosphorylation of PR at Ser294, PR ubiquitination and subsequent receptor`s degradation via the 26S proteasome pathway in BCa cells. We further demonstrated that RSK2 mediated FGF7/FGFR2-induced PR downregulation. In addition, a strong synergistic effect of FGF7 and progesterone (Pg), reflected in the enhanced anchorage-independent growth and cell migration, was observed. Analysis of clinical material demonstrated that expression of PR inversely correlated with activated RSK (RSK-P) (p = 0.016). Patients with RSK-P(+)/PR(-) tumours had 3.629-fold higher risk of recurrence (p = 0.002), when compared with the rest of the cohort. Moreover, RSK-P(+)/PR(-) phenotype was shown as an independent prognostic factor (p = 0.006). These results indicate that the FGF7/FGFR2-RSK2 axis promotes PR turnover and activity, which may sensitize BCa cells to stromal stimuli and contribute to the progression toward steroid hormone negative BCa.

Interactions between FGFR2 and RSK2-implications for breast cancer prognosis.

We have previously demonstrated that fibroblast growth factor receptor 2 (FGFR2) activates ribosomal s6 kinase 2 (RSK2) in mammary epithelial cells and that this pathway promotes in vitro cell growth and migration. Potential clinical significance of FGFR2 and RSK2 association has never been investigated. Herein, we have undertaken an evaluation of a possible relationship between FGFR2/RSK2 interdependence and disease outcome in breast cancer (BCa) patients. The clinical analysis was complemented by an in vitro investigation of an involvement of RSK2 in the regulation of FGFR2 function. Primary tumour samples from 152 stage I-III BCa patients were examined for FGFR2 and RSK2 gene and protein expression. FGFR2 showed a positive correlation with RSK2 at both protein (p = 0.003) and messenger RNA (mRNA) (p = 0.001) levels. Lack of both FGFR2 and activated RSK (RSK-P) significantly correlated with better disease-free survival (DFS) (p = 0.01). Patients with tumours displaying immunoreactivity for either or both FGFR2 and RSK-P had 4.89-fold higher risk of recurrence when compared to the FGFR2/RSK-P-negative subgroup. FGFR2-RSK2 interactions were verified by co-immunoprecipitation and internalization assays in HB2 mammary epithelial cell line (characterized by high endogenous FGFR2 and RSK2 expression). In vitro analyses revealed that FGFR2 and RSK2 formed an indirect complex and that activated RSK exerted a significant impact on fibroblast growth factor 2 (FGF2)-triggered internalization of FGFR2. Our results suggest that the FGFR2-RSK2 signalling pathway is involved in pathophysiology of BCa and evaluation of FGFR2/RSK-P expression may be useful in disease prognostication.

Phosphorylation of RSK2 at Tyr529 by FGFR2-p38 enhances human mammary epithelial cells migration.

The members of p90 ribosomal S6 kinase (RSK) family of Ser/Thr kinases are downstream effectors of MAPK/ERK pathway that regulate diverse cellular processes including cell growth, proliferation and survival. In carcinogenesis, RSKs are thought to modulate cell motility, invasion and metastasis. Herein, we have studied an involvement of RSKs in FGF2/FGFR2-driven behaviours of mammary epithelial and breast cancer cells. We found that both silencing and inhibiting of FGFR2 attenuated phosphorylation of RSKs, whereas FGFR2 overexpression and/or its stimulation with FGF2 enhanced RSKs activity. Moreover, treatment with ERK, Src and p38 inhibitors revealed that p38 kinase acts as an upstream RSK2 regulator. We demonstrate for the first time that in FGF2/FGFR2 signalling, p38 but not MEK/ERK, indirectly activated RSK2 at Tyr529, which facilitated phosphorylation of its other residues (Thr359/Ser363, Thr573 and Ser380). In contrast to FGF2-triggered signalling, inhibition of p38 in the EGF pathway affected only RSK2-Tyr529, without any impact on the remaining RSK phosphorylation sites. p38-mediated phosphorylation of RSK2-Tyr529 was crucial for the transactivation of residues located at kinase C-terminal domain and linker-region, specifically, in the FGF2/FGFR2 signalling pathway. Furthermore, we show that FGF2 promoted anchorage-independent cell proliferation, formation of focal adhesions and cell migration, which was effectively abolished by treatment with RSKs inhibitor (FMK). These indicate that RSK2 activity is indispensable for FGF2/FGFR2-mediated cellular effects. Our findings identified a new FGF2/FGFR2-p38-RSK2 pathway, which may play a significant role in the pathogenesis and progression of breast cancer and, hence, may present a novel therapeutic target in the treatment of FGFR2-expressing tumours.