Inhibition of c-Met downregulates TIGAR expression and reduces NADPH production leading to cell death

c-Met represents an important emerging therapeutic target in cancer. In this study, we demonstrate the mechanism by which c-Met tyrosine kinase inhibition inhibits tumor growth in a highly invasive Asian-prevalent head and neck cancer, nasopharyngeal cancer (NPC). c-Met tyrosine kinase inhibitors (TKIs; AM7 and c-Met TKI tool compound SU11274) downregulated c-Met phosphorylation, resulting in marked inhibition of NPC cell growth and invasion. Strikingly, inhibition of c-Met resulted in significant downregulation of TP53-induced Glycolysis and Apoptosis Regulator (TIGAR) and subsequent depletion of intracellular NADPH. Importantly, overexpression of TIGAR ameliorated the effects of c-Met kinase inhibition, confirming the importance of TIGAR downregulation in the growth inhibitory activity of c-Met TKI. The effects of c-Met inhibition on TIGAR and NADPH levels were observed with two different c-Met TKIs (AM7 and SU11274) and with multiple cell lines. As NADPH provides a crucial reducing power required for cell survival and proliferation, our findings reveal a novel mechanistic action of c-Met TKI, which may represent a key effect of c-Met kinase inhibition. Our data provide the first evidence linking c-Met, TIGAR and NADPH regulation in human cancer cells suggesting that inhibition of a tyrosine kinase/TIGAR/NADPH cascade may have therapeutic applicability in human cancers.     

XAV939对肝癌细胞增殖及糖酵解的影响

目的：探讨 Wnt／β－catenin 信号通路特异性抑制剂 XAV939对肝癌细胞增殖及糖酵解过程的影响。方法：MTT 方法检测不同浓度 XAV939对肝癌细胞 Bel －7402、HCCLM3增殖能力的影响;Western blot 方法检测 XAV939对肝癌 Bel －7402、HCCLM3细胞 Wnt／β－catenin 信号通路关键基因和其下游靶基因表达的影响,以及对糖酵解过程中关键调控基因表达的影响。运用 SPSS 19．0统计软件分析各组间的差异。结果：MTT 结果表明不同浓度的 XAV939能够不同程度的抑制 Bel －7402、HCCLM3细胞增殖能力,XAV939对两种细胞的抑制率接近50％时,浓度分别为：30μmol／L、20μmol／L。Western blot 结果显示,XAV939可以显著抑制 Wnt／β－catenin 及其下游基因 c －myc、Cyclin D1的表达,有效抑制β－catenin 信号通路活性;同时,XAV939可以通过抑制 HK －2、LDHA 而非 Glut －1的蛋白表达水平来抑制肝癌细胞的糖酵解过程。结论：XAV939在体外能够有效抑制肝癌细胞 Wnt／β－catenin 信号通路及其依赖性细胞增殖和糖酵解过程。     

SU11274逆转肝细胞生长因子诱导不同EGFR基因型非小细胞肺癌细胞株对吉非替尼耐药

背景与目的：肝细胞生长因子(hepatocyte growth factor,HGF)诱导敏感非小细胞肺癌(nonsmall cell lung cancer,NSCLC)细胞对表皮生长因子受体酪氨酸激酶抑制剂(epidermal growth factor receptor-tyrosine kinase inhibitor,EGFR-TKI)耐药,其机制与c-Met激活有关。本研究探讨c-Met抑制剂SU11274逆转HGF诱导的不同EGFR基因型NSCLC细胞株对吉非替尼耐药及逆转耐药机制。方法：选择人NSCLC细胞株PC9(EGFR突变型)、H292(EGFR野生型)和A549(EGFR野生型),应用吉非替尼和SU11274单独或联合作用于HGF诱导的细胞株。实验分为6组：C组(不加药对照组)、H组(HGF处理组)、G组(吉非替尼处理组)、S(SU11274处理组)、HG组(HGF+吉非替尼处理组)和HGS组(HGF+吉非替尼+SU11274处理组)。MTT法检测对细胞增殖的影响,流式细胞术检测细胞凋亡的影响;应用蛋白质印迹法(Western blot)检测细胞中c-Met及其下游通道Stat3、Akt和Erk1/2蛋白表达水平。结果：吉非替尼对3种细胞的生长抑制作用均呈浓度依赖性,HGF处理能够缓解吉非替尼的增殖抑制作用(P<0.05);不同浓度吉非替尼联合SU11274作用于HGF诱导细胞时,3种细胞株存活率比吉非替尼单独作用于HGF诱导细胞时明显降低(P<0.05);HGS组的细胞凋亡比HG组明显增加(P<0.05);HGS组的c-Met、Stat3、Akt和Erk1/2活化蛋白量比HG组明显减少。结论：c-Met抑制剂SU11274可逆转HGF诱导的不同EGFR基因型NSCLC细胞株对吉非替尼耐药,其机制可能与抑制HGF活化的c-Met及其下游通道蛋白表达有关。     

Co-expression of hepatocyte growth factor and c-Met predicts peritoneal dissemination established by autocrine hepatocyte growth factor/c-Met signaling in gastric cancer

Epithelial-mesenchymal transition (EMT) promotes and facilitates migration and invasion of epithelial tumor cells. EMT is induced by factors such as hepatocyte growth factor (HGF). This study aimed to establish whether the HGF/c-Met pathway is associated with gastric cancer metastasis; especially peritoneal dissemination. HGF and c-Met expression and EMT-related molecules were evaluated using real-time PCR and immunohistochemistry. The role of the HGF/c-Met pathway in EMT and anoikis was determined, and kinase inhibitor SU11274 was tested for its ability to block HGF-induced biological effects. In HGF(-) /c-Met(+) gastric cancer cells, recombinant HGF promoted an EMT phenotype that was characterized by morphology, impaired E-cadherin and induction of vimentin. HGF promoted cell growth, invasiveness and migration and inhibition of anoikis. SU11274 blocked HGF-induced EMT and biological effects in vitro. In HGF(+) /c-Met(+) gastric cancer cells, HGF did not affect the biological outcome of EMT and anoikis, but SU11274 exerted the same inhibitory effects as in HGF(-) /c-Met(+) cells. In vivo, HGF(+) /c-Met(+) gastric cancer cells only established peritoneal dissemination and SU11274 inhibited tumor growth. Clinically, HGF expression was significantly correlated with c-Met expression in gastric cancer. Increased HGF and c-Met had a significant association with poor prognosis and predicted peritoneal dissemination. We demonstrated that the HGF/c-Met pathway induces EMT and inhibition of anoikis in gastric cancer cells. Co-expression of HGF and c-Met has the potential to promote peritoneal dissemination in gastric cancer. Blockade of the autocrine HGF/c-Met pathway could be clinically useful for the treatment of peritoneal dissemination in gastric cancer.     

Functional analysis of c-Met/hepatocyte growth factor pathway in malignant pleural mesothelioma

c-Met receptor tyrosine kinase (RTK) has not been extensively studied in malignant pleural mesothelioma (MPM). In this study, c-Met was overexpressed and activated in most of the mesothelioma cell lines tested. Expression in MPM tissues by immunohistochemistry was increased (82%) in MPM in general compared with normal. c-Met was internalized with its ligand hepatocyte growth factor (HGF) in H28 MPM cells, with robust expression of c-Met. Serum circulating HGF was twice as high in mesothelioma patients as in healthy controls. There was a differential growth response and activation of AKT and extracellular signal-regulated kinase 1/2 in response to HGF for the various cell lines. Dose-dependent inhibition (IC50 < 2.5 micromol/L) of cell growth in mesothelioma cell lines, but not in H2052, H2452, and nonmalignant MeT-5A (IC50 > 10 micromol/L), was observed with the small-molecule c-Met inhibitor SU11274. Furthermore, migration of H28 cells was blocked with both SU11274 and c-Met small interfering RNA. Abrogation of HGF-induced c-Met and downstream signaling was seen in mesothelioma cells. Of the 43 MPM tissues and 7 cell lines, we have identified mutations within the semaphorin domain (N375S, M431V, and N454I), the juxtamembrane domain (T1010I and G1085X), and an alternative spliced product with deletion of the exon 10 of c-Met in some of the samples. Interestingly, we observed that the cell lines H513 and H2596 harboring the T1010I mutation exhibited the most dramatic reduction of cell growth with SU11274 when compared with wild-type H28 and nonmalignant MeT-5A cells. Ultimately, c-Met would be an important target for therapy against MPM.     

Does c-Met remain a rational target for therapy in patients with EGFR TKI-resistant non-small cell lung cancer?

Non-small cell lung cancer (NSCLC) inevitably develops resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) treatment. In 5–20% of cases, this can be attributed to aberrant c-Met activity, providing a clear rationale for the use of c-Met inhibitors in these patients. EGFR TKI-resistant tumors often remain sensitive to EGFR signaling, such that c-Met inhibitors are likely to be most effective when combined with continued EGFR TKI therapy. The phase III trials of the c–Met inhibitors onartuzumab and tivantinib, which failed to demonstrate significant benefit in patients with NSCLC but excluded patients with EGFR TKI-resistant disease, do not allow c-Met to be dismissed as a rational target in EGFR TKI-resistant NSCLC. Selective c-Met TKIs exhibit more favorable properties, targeting both hepatocyte growth factor (HGF)-dependent and -independent c-Met activity, with a reduced risk of toxicity compared to non-selective c-Met TKIs. Phase Ib/II trials of the selective c-Met TKIs capmatinib and tepotinib have shown encouraging signs of efficacy. Factors affecting the success of ongoing and future trials of c-Met inhibitors in patients with EGFR TKI-resistant, c-Met-positive NSCLC are considered.     

Differential activity of MEK and ERK inhibitors in BRAF inhibitor resistant melanoma

Acquired resistance to BRAF inhibitors often involves MAPK re‐activation, yet the MEK inhibitor trametinib showed minimal clinical activity in melanoma patients that had progressed on BRAF‐inhibitor therapy. Selective ERK inhibitors have been proposed as alternative salvage therapies. We show that ERK inhibition is more potent than MEK inhibition at suppressing MAPK activity and inhibiting the proliferation of multiple BRAF inhibitor resistant melanoma cell models. Nevertheless, melanoma cells often failed to undergo apoptosis in response to ERK inhibition, because the relief of ERK‐dependent negative feedback activated RAS and PI3K signalling. Consequently, the combination of ERK and PI3K/mTOR inhibition was effective at promoting cell death in all resistant melanoma cell models, and was substantially more potent than the MEK/PI3K/mTOR inhibitor combination. Our data indicate that a broader targeting strategy concurrently inhibiting ERK, rather than MEK, and PI3K/mTOR may circumvent BRAF inhibitor resistance, and should be considered during the clinical development of ERK inhibitors.     

Functional expression and mutations of c-Met and its therapeutic inhibition with SU11274 and small interfering RNA in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a difficult disease to treat. The c-Met receptor is an attractive potential target for novel therapeutic inhibition in human cancers. We provide strong evidence that c-Met is overexpressed, activated, and sometimes mutated in NSCLC cell lines and tumor tissues. Expression of c-Met was found in all (100%) of the NSCLC tumor tissues examined (n = 23) and most (89%) of the cell lines (n = 9). Sixty-one percent of tumor tissues strongly expressed total c-Met, especially adenocarcinoma (67%). Specific expression of phospho-Met (p-Met) [Y1003] and [Y1230/1234/1235] was seen by immunohistochemistry. p-Met expression was preferentially observed at the NSCLC tumor invasive fronts. c-Met alterations were identified within the semaphorin domain (E168D, L299F, S323G, and N375S) and the juxtamembrane domain (R988C, R988C + T1010I, S1058P, and alternative splice product skipping entire juxtamembrane domain) of a NSCLC cell line and adenocarcinoma tissues. We validated c-Met as potential therapeutic target using small interfering RNA down-regulation of the receptor expression by 50% to 60% in NSCLC cells. This led to inhibition of p-Met and phospho-AKT and up to 57.1 +/- 7.2% cell viability inhibition at 72 hours. The selective small molecule inhibitor of c-Met SU11274 inhibited cell viability in c-Met-expressing NSCLC cells. SU11274 also abrogated hepatocyte growth factor-induced phosphorylation of c-Met and its downstream signaling. Here, we provide first direct evidence by small interfering RNA targeting and small molecule inhibitor that c-Met is important in NSCLC biology and biochemistry. These results indicate that c-Met inhibition will be an important therapeutic strategy against NSCLC to improve its clinical outcome.     

Cabozantinib: an Active Novel Multikinase Inhibitor in Renal Cell Carcinoma

Clear cell renal cell carcinoma (RCC) is characterized by inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. VHL loss drives tumor angiogenesis and accounts for the clinical activity of VEGF receptor (VEGFR) tyrosine kinase inhibitors (TKIs), the first-line standard of care for advanced RCC. Within the last year, three new second-line treatments have received FDA approval for use after anti-angiogenic therapy: the immune checkpoint inhibitor nivolumab, the TKI cabozantinib, and the combination of the TKI lenvatinib and the mTOR inhibitor everolimus. Cabozantinib inhibits VEGFRs, MET, and AXL, kinases that promote tumorigenesis, angiogenesis, metastasis, and drug resistance. Compared with everolimus, cabozantinib has shown statistically significant improvements in the three key efficacy endpoints of overall survival, progression-free survival, and objective response rate in patients with RCC who were previously treated with a VEGFR TKI. Herein, we summarize the translational research and clinical development that led to approval of cabozantinib as second-line therapy in RCC.     

The Met kinase inhibitor SU11274 exhibits a selective inhibition pattern toward different receptor mutated variants

Point mutations constitute a major mode of oncogenic activation of the Met receptor tyrosine kinase. Met is aberrantly activated in many types of human malignancies and its deregulated activity is correlated with aggressive tumor traits such as abnormal proliferation and survival, leading to tumor growth, local invasion and metastasis. Here we report that the Met kinase inhibitor SU11274 differentially affects the kinase activity and subsequent signaling of various mutant forms of Met. Two Met variants tested, M1268T and H1112Y, were potently inhibited by 2 microM SU11274, while two other variants, L1213V and Y1248H, remained resistant under similar experimental conditions. Inhibition of the kinase altered cell proliferation, morphology and motility, while cells containing resistant mutants appeared unaffected by the compound. The basis for the sensitivity or resistance to SU11274 is discussed in terms of the position of the mutations predicted from a homology model.     

Collagen type I induces EGFR‐TKI resistance in EGFR‐mutated cancer cells by mTOR activation through Akt‐independent pathway

Primary resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR‐TKIs) is a serious problem in lung adenocarcinoma patients harboring EGFR mutations. The aim of this study was to examine whether and how collagen type I (Col I), the most abundantly deposited matrix in tumor stroma, affects EGFR‐TKI sensitivity in EGFR‐mutant cells. We evaluated the EGFR‐TKI sensitivity of EGFR‐mutated cancer cells cultured with Col I. Changes in the activation of downstream signaling molecules of EGFR were analyzed. We also examined the association between the Col I expression in tumor stroma in surgical specimens and EGFR‐TKI response of postoperative recurrence patients with EGFR mutations. Compared to cancer cells without Col I, the survival rate of cancer cells cultured with Col I was significantly higher after EGFR‐TKI treatment. In cancer cells cultured with and without Col I, EGFR‐TKI suppressed the levels of phosphorylated (p‐)EGFR, p‐ERK1/2, and p‐Akt. When compared to cancer cells without Col I, expression of p‐P70S6K, a hallmark of mTOR activation, was dramatically upregulated in cancer cells with Col I. This activation was maintained even after EGFR‐TKI treatment. Simultaneous treatment with EGFR‐TKI and mTOR inhibitor abrogated Col I‐induced resistance to EGFR‐TKI. Patients with Col I‐rich stroma had a significantly shorter progression‐free survival time after EGFR‐TKI therapy (238 days vs 404 days; P < .05). Collagen type I induces mTOR activation through an Akt‐independent pathway, which results in EGFR‐TKI resistance. Combination therapy using EGFR‐TKI and mTOR inhibitor could be a possible strategy to combat this resistance.     

A c-Met inhibitor increases the chemosensitivity of cancer stem cells to the irinotecan in gastric carcinoma

Background:

Cancer stem cells (CSCs) may be postulated mediators of the chemoresistance. This study aimed to determine an effective signal inhibitor with effects on the proliferation of CSCs in combination with anticancer drugs.

Methods:

We used three gastric cancer cell lines and three side population (SP)-enriched CSC cell lines. We examined the combined effects of inhibitors against stemness signals, including c-Met inhibitor SU11274, and five anticancer drugs on the CSC proliferation and mRNA expression of chemoresistance-associated genes.

Results:

The IC₅₀ of irinotecan in SP-enriched CSC was 10.5 times higher than parent OCUM-2M cells, whereas that of oxaliplatin, taxol, gemcitabine, and 5-fluorouracil was 2.0, 2.8, 2.0, and 1.2, respectively. The SP cell lines had higher expression levels of UGT1A1, ABCG2, and ABCB1 than their parent cell lines. There was a synergistic antiproliferative effect with a combination of SU11274 and SN38 in SP cells, but not other inhibitors. The SU11274 significantly decreased the expression of UGT1A1, but not ABCG2 and ABCB1. The SN38 plus SU11274 group more effectively suppressed in vivo tumour growth by OCUM-2M/SP cells than either group alone.

Conclusion:

Cancer stem cells have chemoresistance to irinotecan. The c-Met inhibitor may be a promising target molecule for irinotecan-based chemotherapy of gastric cancer.     

Stromal niche cells protect early leukemic FLT3-ITD+ progenitor cells against first-generation FLT3 tyrosine kinase inhibitors

Targeting constitutively activated FMS-like tyrosine kinase 3 [(FLT3); FLT3-ITD] with tyrosine kinase inhibitor (TKI) in acute myeloid leukemia (AML) leads to clearance of blasts in the periphery but not in the bone marrow, suggesting a protective effect of the marrow niche on leukemic stem cells. In this study, we examined the effect of stromal niche cells on CD34(+) progenitors from patients with FLT3-ITD(+) or wild-type FLT3 (FLT3-WT) AML treated with the TKIs SU5614 or sorafenib. TKIs effectively and specifically inhibited FLT3 and increased the fraction of undivided progenitors in both FLT3-ITD(+) and FLT3-WT samples. Treatment with SU5614 and sorafenib also reduced the number of mature leukemic progenitors, whereas contact with stroma protected against this cell loss. In contrast, primitive long-term progenitors from both FLT3-ITD(+) and FLT3-WT AML were resistant to TKIs. Additional contact with niche cells significantly expanded long-term FLT3-ITD(+) but not FLT3-WT progenitors in the presence of SU5614 but not that of sorafenib. Thus, TKIs with first-generation inhibitors fail to eradicate early leukemic stem/progenitor cells in FLT3-ITD(+) AML. Further, we defined a specific interaction between FLT3-ITD(+) progenitors and niche cells that enables the maintenance of leukemic progenitors in the presence of TKI. Collectively, our findings suggest that molecular therapy may have unpredicted effects on leukemic progenitors, underscoring the necessity of developing strategies to selectively eliminate the malignant stem cell clone.     

Antitumor activity of pimasertib,a selective MEK 1/2 inhibitor,in combination with PI3K/mTOR inhibitors or with multi‐targeted kinase inhibitors in pimasertib‐resistant human lung and colorectal cancer cells

The RAS/RAF/MEK/MAPK and the PTEN/PI3K/AKT/mTOR pathways are key regulators of proliferation and survival in human cancer cells. Selective inhibitors of different transducer molecules in these pathways have been developed as molecular targeted anti‐cancer therapies. The in vitro and in vivo anti‐tumor activity of pimasertib, a selective MEK 1/2 inhibitor, alone or in combination with a PI3K inhibitor (PI3Ki), a mTOR inhibitor (everolimus), or with multi‐targeted kinase inhibitors (sorafenib and regorafenib), that block also BRAF and CRAF, were tested in a panel of eight human lung and colon cancer cell lines. Following pimasertib treatment, cancer cell lines were classified as pimasertib‐sensitive (IC₅₀ for cell growth inhibition of 0.001 µM) or pimasertib‐resistant. Evaluation of basal gene expression profiles by microarrays identified several genes that were up‐regulated in pimasertib‐resistant cancer cells and that were involved in both RAS/RAF/MEK/MAPK and PTEN/PI3K/AKT/mTOR pathways. Therefore, a series of combination experiments with pimasertib and either PI3Ki, everolimus, sorafenib or regorafenib were conducted, demonstrating a synergistic effect in cell growth inhibition and induction of apoptosis with sustained blockade in MAPK‐ and AKT‐dependent signaling pathways in pimasertib‐resistant human colon carcinoma (HCT15) and lung adenocarcinoma (H1975) cells. Finally, in nude mice bearing established HCT15 and H1975 subcutaneous tumor xenografts, the combined treatment with pimasertib and BEZ235 (a dual PI3K/mTOR inhibitor) or with sorafenib caused significant tumor growth delays and increase in mice survival as compared to single agent treatment. These results suggest that dual blockade of MAPK and PI3K pathways could overcome intrinsic resistance to MEK inhibition.     

解整合素金属蛋白酶10通过介导Wnt/β-catenin信号通路促进子宫内膜癌细胞上皮-间质转化

目的:探讨解整合素金属蛋白酶10（ADAM10）对子宫内膜癌（EC）细胞上皮-间质转化（EMT）的影响及其作用机制。方法:收集84例EC患者的新鲜癌组织及癌旁组织标本,采用qRT-PCR检测癌组织及其癌旁组织中ADAM10 mRNA表达水平。以人EC细胞株HEC-1B作为研究对象,采用ADAM10过表达慢病毒感染HEC-1B细胞,并联合Wnt/β-catenin信号通路特异性抑制剂XAV939进行干预,再将细胞分为空白对照组（blank）、慢病毒阴性对照组（Lv-NC）、ADAM10过表达慢病毒组（Lv-ADAM10）和Lv-ADAM10+XAV939组。采用qRT-PCR检测感染后各组细胞中ADAM10 mRNA表达水平;划痕和Transwell实验检测各组细胞的迁移和侵袭能力;Western blot法分析各组细胞中ADAM10及EMT相关蛋白和Wnt/β-catenin信号通路相关蛋白表达水平。结果:EC患者癌组织中ADAM10 mRNA表达水平显著高于癌旁组织（P＜0.05）。与blank组或Lv-NC组比较,Lv-ADAM10组细胞中ADAM10 mRNA和蛋白表达水平以及N-cadherin、Vimentin、β-catenin、Snail、MMP2和MMP9等蛋白表达水平均显著升高（均P＜0.05）,而E-cadherin蛋白表达水平明显降低（P＜0.05）,同时细胞迁移和侵袭能力显著增强（均P＜0.05）。与Lv-ADAM10组比较,Lv-ADAM10+XAV939组细胞中N-cadherin、Vimentin、β-catenin、Snail、MMP2和MMP9等蛋白表达水平显著降低（均P＜0.05）,E-cadherin蛋白表达水平明显升高（P＜0.05）,且细胞迁移和侵袭能力明显降低（均P＜0.05）。结论:ADAM10在EC组织中高表达,其过表达可促进HEC-1B细胞的EMT进程,其作用机制可能与激活Wnt/β-catenin信号通路有关。     

Malignant gliomas induce and exploit astrocytic mesenchymal-like transition by activating canonical Wnt/β-catenin signaling

The complex microenvironment of malignant gliomas plays a dynamic and usually cancer-promoting role in glioma progression. Astrocytes, the major stromal cells in the brain, can be activated by glioma microenvironment, resulting in a layer of reactive astrocytes surrounding the gliomas. Reactive astrocytes are universally characterized with the upregulation of glial fibrillary protein and glycoprotein podoplanin. In this work, we investigated the role of reactive astrocytes on malignant glioma microenvironment and the potential mechanism by which glioma cells activated the tumor-associated astrocytes (TAAs). The reactive astrocytes were observed around gliomas in the intracranial syngeneic implantation of rat C6 and mouse GL261 glioma cells in vivo, as well as primary astrocytes cultured with glioma cells condition medium in vitro. Besides, reactive astrocytes exhibited distinct epithelial-to-mesenchymal (-like) transition and enhanced migration and invasion activity, with the decrease of E-cadherin and concomitant increase of vimentin and matrix metalloproteinases. Furthermore, canonical Wnt/β-catenin signaling was activated in TAAs. The Wnt/β-catenin pathway inhibitor XAV939 and β-catenin plasmid were used to verify the regulation of Wnt/β-catenin signaling on TAAs and their invasion ability. Taken together, our findings established that glioma cells remarkably activated astrocytes via upregulating Wnt/β-catenin signaling, with obviously mesenchymal-like transition and increased migration and invasion ability, indicating that glioma cells may stimulate adjacent astrocytes to degrade extracellular matrix and thereby promoting tumor invasiveness.     

Dual inhibition of (V600E)BRAF and the PI3K/AKT/mTOR pathway cooperates to induce apoptosis in melanoma cells through a MEK-independent mechanism

BRAF is a main oncogene in human melanomas. Here, we show that BRAF depletion by siRNA or inhibition of its activity by treatment with RAF inhibitor Sorafenib induces apoptosis in NPA melanoma cells expressing oncogenic ^V600EBRAF. This effect is mediated through a MEK/ERK-independent mechanism, since treatment with the MEK inhibitor U0126 does not exert any effect. Moreover, we demonstrate that inhibition of the PI3K/AKT/mTOR cascade alone does not increase apoptosis in these cells. However, the blockage of this pathway in cells lacking either BRAF expression or activity cooperates to induce higher levels of apoptosis than those achieved by inhibition of BRAF alone. Consistently, we demonstrate that abrogation of BRAF expression increases AKT and mTOR phosphorylation, suggesting the existence of a compensatory pro-survival mechanism after BRAF depletion. Together, our data provide a rationale for dual targeting of BRAF and PI3K/AKT/mTOR signalling to effectively control melanoma disease.     

Second-line systemic therapy for the treatment of metastatic renal cell cancer

The discovery of molecular mechanisms driving the progression of renal cell carcinoma (RCC) has led to the development of drugs that target RCC at the molecular level. Inhibition of VEGF-targeting pathways is successful as a front-line treatment in patients with metastatic RCC. In addition, bevacizumab/IFN-α, sunitinib and pazopanib are recommended for first-line use in good- or intermediate-risk patients, whereas temsirolimus is approved for poor-risk patients. Second-line options are valuable as these patients eventually progress. The present review addresses which drug is best in this second-line setting. Options for sequential therapy include tyrosine kinase inhibitor (TKI)–mTOR inhibitor or TKI–TKI sequences. We also address the question of whether sequential therapy with TKIs or the combination of VEGF followed by mTOR inhibition is the best choice for specific patients, and which sequence of TKIs is most beneficial.