Acquired resistance to temsirolimus in human renal cell carcinoma cells is mediated by the constitutive activation of signal transduction pathways through mTORC2

Advances in Renal Cell Carcinoma Drug Resistance Models

Renal cell carcinoma (RCC) is the most common form of kidney cancer. Systemic therapy is the preferred method to eliminate residual cancer cells after surgery and prolong the survival of patients with inoperable RCC. A variety of molecular targeted and immunological therapies have been developed to improve the survival rate and prognosis of RCC patients based on their chemotherapy-resistant properties. However, owing to tumor heterogeneity and drug resistance, targeted and immunological therapies lack complete and durable anti-tumor responses; therefore, understanding the mechanisms of systemic therapy resistance and improving clinical curative effects in the treatment of RCC remain challenging. In vitro models with traditional RCC cell lines or primary cell culture, as well as in vivo models with cell or patient-derived xenografts, are used to explore the drug resistance mechanisms of RCC and screen new targeted therapeutic drugs. Here, we review the established methods and applications of in vivo and in vitro RCC drug resistance models, with the aim of improving our understanding of its resistance mechanisms, increasing the efficacy of combination medications, and providing a theoretical foundation for the development and application of new drugs, drug screening, and treatment guidelines for RCC patients.

Expression of TXNIP is associated with angiogenesis and postoperative relapse of conventional renal cell carcinoma

One of the common mediator of tumour progression is the oxidative stress induced by inflammatory tumour microenvironment (TME). Activated fibroblasts, local and immune cells produce reactive oxygen species (ROS) supporting tumour cell proliferation and pave the way for metastatic tumour growth. TXNIP regulates ROS generation by inhibiting the antioxidative function of thioredoxin (TXN). The shift of TXNIP/TXN balance towards overexpression of TXNIP is associated with proliferation of endothelial cells during tumor angiogenesis. The oxidative stress activates the hypoxia inducible factor-1 (HIF-1), which plays an important role in the biology of conventional RCC (cRCC). Under oxydative stress TXNIP interacts with NLRP3 inflammasome leading to maturation and secretion of inflammatory cytokine IL1β. To establish the role of TXNIP and downstream genes HIF1α and IL1β in the biology of cRCC, we have applied immunohistochemistry to multi-tissue arrays containing tumours of 691 patients without detectable metastases at the time of operation. We found that cRCC displaying a fine organised capillary network with nuclear translocation of TXNIP and expressing IL1β have a good prognosis. In contrary, we showed a significant correlation between cytoplasmic TXNIP expression, inefficient vascularisation by unorganized and tortuous vessels causing tumour cell necrosis and postoperative tumour relapse of cRCC.

Drug resistance in papillary RCC: from putative mechanisms to clinical practicalities

Papillary renal cell carcinoma (pRCC) is the second most common renal cell carcinoma (RCC) subtype and accounts for 10-15% of all RCCs. Despite clinical need, few pharmacogenomics studies in pRCC have been performed. Moreover, current research fails to adequately include pRCC laboratory models, such as the ACHN or Caki-2 pRCC cell lines. The molecular mechanisms involved in pRCC development and drug resistance are more diverse than in clear-cell RCC, in which inactivation of VHL occurs in the majority of tumours. Drug resistance to multiple therapies in pRCC occurs via genetic alteration (such as mutations resulting in abnormal receptor tyrosine kinase activation or RALBP1 inhibition), dysregulation of signalling pathways (such as GSK3β-EIF4EBP1, PI3K-AKT and the MAPK or interleukin signalling pathways), deregulation of cellular processes (such as resistance to apoptosis or epithelial-to-mesenchymal transition) and interactions between the cell and its environment (for example, through activation of matrix metalloproteinases). Improved understanding of resistance mechanisms will facilitate drug discovery and provide new effective therapies. Further studies on novel resistance biomarkers are needed to improve patient prognosis and stratification as well as drug development.

Everolimus resistance in clear cell renal cell carcinoma: miRNA-101 and HIF-2α as molecular triggers?

Aim: The majority of clear cell renal cell carcinoma patients develop resistance to mTOR inhibitors. Materials & methods: As an in vitro model four cell lines were used: HKC-8, 786- O, RCC-FG-2 and an everolimus-resistant cell line (786-OR) established during this study. The quantification of miRNA-101 and HIF-2α mRNA levels was assessed by real-time PCR. Results: We observed a significant decrease of miRNA-101 intracellular levels in 786-OR. However, this miRNA presented higher extracellular levels. Additionally, we found a significant increase of HIF-2α in 786-OR. Conclusion: The circulating levels of miRNA-101 may be a potential biomarker of anti-mTOR therapy response and resistance prediction. Moreover, the resistance to mTOR inhibitors seems to be related with the overexpression of HIF-2α.

The Effects of Different mTOR Inhibitors in EGFR Inhibitor Resistant Colon Carcinoma Cells

Several monoclonal antibodies and inhibitors targeting signalling pathways are being used in personalised medicine. Anti-EGFR antibodies seem to be effective, however, therapy resistance often occurs in colon carcinoma cases. mTOR inhibitors (mTORIs) could have a potential role in the breakthrough of therapy resistance. The mTOR activity related protein expression patterns and the in vitro effects of EGFR inhibitors (EGFRIs), mTORIs and their combinations were studied in different colon carcinoma cell lines (with different genetic backgrounds). Alamar Blue test and flow cytometry were used to analyse the in vitro proliferation and apoptotic effects of cetuximab, gefitinib, cisplatin, rapamycin, PP242 and NVP-BEZ235. The expressions of mTOR activity related proteins (p-70S6K, p-S6, Rictor, p-mTOR, Raptor) were studied by Western blot, immunocytochemistry and Duolink staining. The EGFRI resistance of the studied colon carcinoma cell lines related to their known mutations were confirmed, neither gefitinib nor cetuximab inhibited the proliferation or induced apoptosis in vitro. Individual differences in Rictor and Raptor expressions were detected by Western blot and immunocytochemistry beside elevated mTOR activity of these different colon carcinoma cell lines. These expression patterns correlated to the mTORIs sensitivity differences, moreover, mTORIs could enhance the effects of EGFRIs and other in vitro treatments. Our results suggest that mTORI combinations could be helpful in both EGFRI and platinum-based therapy of colon carcinomas. Moreover, we suggest determining both mTOR complex activity and mutations in Akt/mTOR signalling pathways for selecting the appropriate mTORIs and patients in potential future combination treatments.

Pan-class I PI3-kinase inhibitor BKM120 induces MEK1/2-dependent mitotic catastrophe in non-Hodgkin lymphoma leading to apoptosis or polyploidy determined by Bax/Bak and p53

Constitutive signaling of PI3K/Akt/mTOR plays a prominent role in malignant transformation and progression of B-cell non-Hodgkin lymphomas (B-NHL) underscoring the need for PI3K targeted therapies. The pan-class I PI3-kinase inhibitor BKM120 has shown preclinical activity in distinct malignancies and is currently tested in clinical trials. Intratumor heterogeneity is an intrinsic property of cancers that contributes to drug resistance and tumor recurrence. Here, we demonstrate that inhibition of PI3-kinases by BKM120 attenuates growth and survival of B-NHL cell lines by inducing mitotic arrest with subsequent induction of intrinsic apoptosis. BKM120-mediated downregulation of Cyclin A and activation of the CDK1/Cyclin B1 complex facilitates mitotic entry. In addition, concomitant BKM120-mediated upregulation of Cyclin B1 expression attenuates completion of mitosis, which results in mitotic catastrophe and apoptotic cell death. In Bax and Bak deficient B-NHL, which are resistant to BKM120-induced apoptosis, BKM120-induced mitotic catastrophe results in polyploidy. Upon re-expression of wt p53 in these p53 mutated cells, BKM120-induced polyploidy is strongly reduced demonstrating that the genetic status of the cells determines the outcome of a BKM120-mediated pathway inhibition. Mitotic catastrophe and unfavorable induction of polyploidy can be prevented in this setting by additional inhibition of MEK1/2 signaling. Combining MEK1/2 inhibitors with BKM120 enhances the anti-tumor effects of BKM120, prevents prognostic unfavorable polyploidy and might be a potential strategy for the treatment of B-NHL.

Phase I study of the investigational oral mTORC1/2 inhibitor sapanisertib (TAK-228): tolerability and food effects of a milled formulation in patients with advanced solid tumours

Background

Sapanisertib (TAK-228) is an investigational, orally available, potent and highly selective mTORC1/2 inhibitor demonstrating promise in numerous malignancies. This phase I study (NCT02412722) evaluated the safety, tolerability, pharmacokinetics and antitumour activity of single-agent TAK-228 (milled capsules), administered daily (QD) or weekly (QW) and in combination with paclitaxel in patients with advanced solid tumours. Pharmacokinetic comparisons of milled versus unmilled TAK-228 and the impact of food were also investigated.

Methods

Patients were enrolled to receive: TAK-228 QD, TAK-228 3 days/week plus paclitaxel 80 mg/m² days 1, 8, 15 (TAK-228+P) or TAK-228 QW (all 28-day cycles); starting TAK‑228 doses were 4, 6 and 20 mg, respectively.

Results

Sixty-one adults were enrolled. Maximum tolerated doses for milled TAK-228 were 3 mg (TAK-228 QD), 6 mg (TAK-228+P) and 30 mg (TAK-228 QW). Most patients reported ≥1 adverse event (AE); there were no meaningful differences in drug-related AEs across regimens or doses. Three on-study deaths occurred, all considered unrelated to study drugs. TAK-228 pharmacokinetics did not differ between unmilled/milled capsules or with/without paclitaxel. However, TAK-228 C_max decreased by ~40% in fed versus fasted patients. Objective response rates were 12% (TAK-228 QD), 18% (TAK-228+P) and 0% (TAK-228 QW). One patient receiving TAK-228+P had a complete response; three patients receiving TAK-228+P and two patients receiving TAK-228 QD had partial responses.

Conclusions

Milled TAK-228 was well tolerated with signs of antitumour activity; administration did not reduce overall exposure (area under the plasma concentration–time curve) but reduced C_max, which is expected when dosed in the fed state. These promising findings warrant further investigation.

Trial registration number

NCT02412722.

Morphoproteomics and biomedical analytics confirm the mTORC2/Akt pathway as a resistance signature and activated ERK and STAT3 as concomitant prosurvival/antiapoptotic pathways in metastatic renal cell carcinoma (RCC) progressing on rapalogs: pathogenesis and therapeutic options

Background

It has been proposed that resistance to rapalog therapies in renal cell carcinoma (RCC) is due to adaptive switching from mammalian target of rapamycin complex 1 (mTORC1) to mTORC2.

Objective

To combine phosphoprotein staining and applied biomedical analytics to investigate resistance signatures in patients with metastatic RCC progressing on rapalog therapies.

Design

We applied morphoproteomic analysis to biopsy specimens from nine patients with metastatic RCC who continued to show clinical progression of their tumors while being treated with a rapalog.

Results

In patients who were on temsirolimus or everolimus at the time of biopsy, a moderate to strong expression of phosphorylated (p)-mTOR (Ser 2448) in the nuclear compartment with concomitant expression of p-Akt (Ser 473) confirmed the mTORC2 pathway. Concomitant moderate to strong nuclear expression of p-ERK 1/2 (Thr202/Tyr204) and p-STAT3 (Tyr705) was confirmed. Histopathologic changes of hypoxic-type coagulative necrosis in 5 cases as well as identification of insulin-like growth factor-1 receptor (IGF-1R) expression and histone methyltransferase EZH2 in all tumors studied suggested that hypoxia also contributed to the resistance signature. Biomedical analytics provided insight into therapeutic options that could target such adaptive and pathogenetic mechanisms.

Conclusions

Morphoproteomics and biomedical analytics confirm mTORC2/Akt as a resistance signature to rapalog therapy in metastatic RCC and demonstrate activation of the prosurvival ERK and STAT3 pathways and involvement of hypoxic pathways that contribute to pathogenesis of such adaptive resistance. These results highlight the need for a novel combinatorial therapeutic approach in metastatic RCC progressing on rapalogs.

Dual targeting of mitochondrial function and mTOR pathway as a therapeutic strategy for diffuse intrinsic pontine glioma

Diffuse Intrinsic Pontine Gliomas (DIPG) are the most devastating of all pediatric brain tumors. They mostly affect young children and, as there are no effective treatments, almost all patients with DIPG will die of their tumor within 12 months of diagnosis. A key feature of this devastating tumor is its intrinsic resistance to all clinically available therapies. It has been shown that glioma development is associated with metabolic reprogramming, redox state disruption and resistance to apoptotic pathways. The mitochondrion is an attractive target as a key organelle that facilitates these critical processes. PENAO is a novel anti-cancer compound that targets mitochondrial function by inhibiting adenine nucleotide translocase (ANT). Here we found that DIPG neurosphere cultures express high levels of ANT2 protein and are sensitive to the mitochondrial inhibitor PENAO through oxidative stress, while its apoptotic effects were found to be further enhanced upon co-treatment with mTOR inhibitor temsirolimus. This combination therapy was found to act through inhibition of PI3K/AKT/mTOR pathway, HSP90 and activation of AMPK. In vivo experiments employing an orthotopic model of DIPG showed a marginal anti-tumour effect likely due to poor penetration of the inhibitors into the brain. Further testing of this anti-DIPG strategy with compounds that penetrate the BBB is warranted.

Promising response to axitinib rechallenge for metastatic renal cell carcinoma after progression on prior axitinib: report of two cases

With the marked improvement in the prognosis of patients with metastatic renal cell carcinoma (mRCC) in the era of molecularly targeted therapy, sequential therapies using multiple targeted agents have been intensively performed for these patients. Despite being conducted targeting small cohorts, several studies showed efficacious findings on rechallenge with some targeted agents, such as sunitinib and sorafenib; however, there has not been any report describing axitinib rechallenge for patients with mRCC. Here, we report two cases of mRCC showing a significant response to axitinib rechallenge after progression on prior systemic treatment with multiple agents, including axitinib. These findings suggest that mRCC, once refractory to axitinib, can still show favorable disease control on rechallenge with this agent during sequential treatment with targeted agents.

Resistance to Targeted Therapies in Renal Cancer: The Importance of Changing the Mechanism of Action

Renal cell carcinoma (RCC) is a complex disease characterized by mutations in several genes. Loss of function of the von Hippel-Lindau (VHL) tumour suppressor gene is a very common finding in RCC and leads to up-regulation of hypoxia-inducible factor (HIF)-responsive genes accountable for angiogenesis and cell growth, such as platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). Binding of these proteins to their cognate tyrosine kinase receptors on endothelial cells promotes angiogenesis. Promotion of angiogenesis is in part due to the activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mechanistic target of rapamycin (mTOR) pathway. Inhibition of this pathway decreases protein translation and inhibits both angiogenesis and tumour cell proliferation. Although tyrosine kinase inhibitors (TKIs) stand as the main first-line treatment option for advanced RCC, eventually all patients will become resistant to TKIs. Resistance can be overcome by using second-line treatments with different mechanisms of action, such as inhibitors of mTOR, c-MET, programmed death 1 (PD-1) receptor, or the combination of an mTOR inhibitor (mTORi) with a TKI. In this article, we briefly review current evidence regarding mechanisms of resistance in RCC and treatment strategies to overcome resistance with a special focus on the PI3K/AKT/mTOR pathway.

mTOR activity and its prognostic significance in human colorectal carcinoma depending on C1 and C2 complex-related protein expression

AIMS

Tumour heterogeneity and altered activation of signalling pathways play important roles in therapy resistance. The PI3K/Akt/mTOR signalling network is a well-known regulator of several functions that contribute to tumour growth. mTOR exists in two functionally different multiprotein complexes. We aimed to determine mTOR activity-related proteins in clinically followed, conventionally treated colon carcinomas and to analyse the correlation between clinical data and mTORC1 and mTORC2 activity.

METHODS

Immunohistochemistry was performed with different antibodies on tissue microarray blocks from 103 patients with human colorectal adenocarcinoma. mTORC1- and mTORC2-related activity were scored on different stainings including analysis of the expression of Raptor and Rictor-specific elements of mTORC1 and C2 complexes. The staining scores and clinical/survival data were compared and analysed.

RESULTS

Detailed characterisation showed stage and grade independent high mTOR activity in 74% of cases. High mTOR activity was present in mTORC1 and/or mTORC2 complexes; >60% of cases had mTORC2-related high mTOR activity. Based on our analysis, high mTOR activity and Rictor overexpression could be markers of a bad prognosis. Combined phosphoprotein and Rictor/Raptor expression evaluation revealed even stronger statistical correlation with prognosis.

CONCLUSIONS

The presented staining panel could be appropriate and highly recommended for the accurate specification of mTORC1 and C2 activity of tumour tissues. This could help in the selection of mTOR inhibitors and can provide information about prognosis, which may guide decisions about the intensity of therapy.

Inpp5e suppresses polycystic kidney disease via inhibition of PI3K/Akt-dependent mTORC1 signaling

Polycystic kidney disease (PKD) is a common cause of renal failure with few effective treatments. INPP5E is an inositol polyphosphate 5-phosphatase that dephosphorylates phosphoinositide 3-kinase (PI3K)-generated PI(3,4,5)P₃ and is mutated in ciliopathy syndromes. Germline Inpp5e deletion is embryonically lethal, attributed to cilia stability defects, and is associated with polycystic kidneys. However, the molecular mechanisms responsible for PKD development upon Inpp5e loss remain unknown. Here, we show conditional inactivation of Inpp5e in mouse kidney epithelium results in severe PKD and renal failure, associated with a partial reduction in cilia number and hyperactivation of PI3K/Akt and downstream mammalian target of rapamycin complex 1 (mTORC1) signaling. Treatment with an mTORC1 inhibitor improved kidney morphology and function, but did not affect cilia number or length. Therefore, we identify Inpp5e as an essential inhibitor of the PI3K/Akt/mTORC1 signaling axis in renal epithelial cells, and demonstrate a critical role for Inpp5e-dependent mTORC1 regulation in PKD suppression.

mTOR inhibitor temsirolimus and MEK1/2 inhibitor U0126 promote chromosomal instability and cell type-dependent phenotype changes of glioblastoma cells

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) and the RAF/mitogen-activated and extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are frequently deregulated in cancer. Temsirolimus (TEM) and its primary active metabolite rapamycin allosterically block mTOR complex 1 substrate recruitment. The context-/experimental setup-dependent opposite effects of rapamycin on the multiple centrosome formation, aneuploidy, DNA damage/repair, proliferation, and invasion were reported. Similarly, the context-dependent either tumor-promoting or suppressing effects of RAF-MEK-ERK pathway and its inhibitors were demonstrated. Drug treatment-mediated stress may promote chromosomal instability (CIN), accelerating changes in the genomic landscape and phenotype diversity. Here, we characterized the genomic and phenotypic changes of U251 and T98G glioblastoma cell lines long-term treated with TEM or U0126, an inhibitor of MEK1/2. TEM significantly increased clonal and non-clonal chromosome aberrations. Both TEM and U0126 affected copy number alterations (CNAs) pattern. A proliferation rate of U251TEM and U251U0126 cells was lower and higher, respectively, than control cells. Colony formation efficiency of U251TEM significantly decreased, whereas U251U0126 did not change. U251TEM and U251U0126 cells decreased migration. In contrast, T98GTEM and T98GU0126 cells did not change proliferation, colony formation efficiency, and migration. Changes in the sensitivity of inhibitor-treated cells to the reduction of the glucose concentration were observed. Our results suggest that CIN and adaptive reprogramming of signal transduction pathways may be responsible for the cell type-dependent phenotype changes of long-term TEM- or U0126-treated tumor cells.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin's lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.

Molecular mechanism mediating cytotoxic activity of axitinib in sunitinib-resistant human renal cell carcinoma cells

PURPOSE

This study aimed to clarify the molecular mechanism mediating the cytotoxicity of axitinib, a selective inhibitor of the vascular endothelial growth factor receptor (VEGFR), in sunitinib-resistant renal cell carcinoma (RCC).

METHODS

In our previous study (Sakai et al. in BJU Int 112:E211-E220, 2013), a human RCC cell line, ACHN, resistant to sunitinib (ACHN/R), was developed from a parental cell line (ACHN/P). Differences in molecular phenotypes following treatment with sunitinib or axitinib between these two cell lines were compared.

RESULTS

ACHN/R showed an approximately fivefold higher IC50 of sunitinib than ACHN/P; however, there was no significant difference in the sensitivity to axitinib between these two cell lines. In ACHN/R, despite the lack of a difference in the phosphorylated (p)-Akt or STAT-3 expression between treatment with sunitinib and axitinib, the expression of p-p44/42 mitogen-activated protein kinase (MAPK) and p-VEGFR-2 after treatment with axitinib was markedly down-regulated compared with those after treatment with sunitinib. Furthermore, additional treatment of ACHN/R with an inhibitor of MAPK kinase significantly enhanced the cytotoxic activity of sunitinib, but not that of axitinib. In vivo growth of ACHN/R in nude mice after treatment with axitinib was significantly inhibited compared with that following treatment with sunitinib, accompanying the marked inhibition of angiogenesis.

CONCLUSIONS

Antitumor activity of axitinib in RCC cells even after the acquisition of resistance to sunitinib could be explained, at least in part, by the inactivation of p44/42 MAPK and VEGFR-2, which were persistently phosphorylated in sunitinib-resistant RCC cells under treatment with sunitinib.

UNC-51-like kinase 1 expression in radical nephrectomy specimens as a predicting factor of progression-free survival in patients with metastatic renal cell carcinoma treated with mammalian target of rapamycin inhibitors

BACKGROUND

To analyze basal expression levels of multiple components in the autophagy pathway in radical nephrectomy specimens from patients with metastatic renal cell carcinoma (mRCC) treated with mammalian target of rapamycin (mTOR) inhibitors, to identify factors predicting susceptibility to these agents.

METHODS

This study included 48 consecutive patients undergoing radical nephrectomy, who were diagnosed with mRCC and subsequently treated with either everolimus or temsirolimus. Expression levels of 5 major molecular markers involved in the signaling pathway associated with autophagy, including autophagy-related protein (Atg)5, Atg9, Beclin1, microtubule-associated protein light chain 3, and UNC-51-like kinase 1 (ULK1), were measured by immunohistochemical staining of primary renal cell carcinoma specimens.

RESULTS

During the observation period of this study (median = 16.2 mo), 36 patients developed disease progression, with a median progression-free survival (PFS) period of 7.6 months. Of several factors examined, bone metastasis, liver metastasis, and ULK1 expression were shown to have significant effects on the response to mTOR inhibitors. PFS was significantly correlated with the expression level of ULK1 in addition to bone and liver metastases on univariate analysis. Of these significant factors, ULK1 expression and liver metastasis were independently associated with PFS on multivariate analysis.

CONCLUSIONS

It may be useful to consider expression levels of potential molecular markers in the autophagy pathway, particularly ULK1, in addition to conventional parameters, when selecting patients with mRCC who are likely to benefit from treatment with mTOR inhibitors.

Axl receptor tyrosine kinase is a potential therapeutic target in renal cell carcinoma

Background:

Axl plays multiple roles in tumourigenesis in several cancers. Here we evaluated the expression and biological function of Axl in renal cell carcinoma (RCC).

Methods:

Axl expression was analysed in a tissue microarray of 174 RCC samples by immunostaining and a panel of 11 normal tumour pairs of human RCC tissues by western blot, as well as in RCC cell lines by both western blot and quantitative PCR. The effects of Axl knockdown in RCC cells on cell growth and signalling were investigated. The efficacy of a humanised Axl targeting monoclonal antibody hMAb173 was tested in histoculture and tumour xenograft.

Results:

We have determined by immunohistochemistry (IHC) that Axl is expressed in 59% of RCC array samples with moderate to high in 20% but not expressed in normal kidney tissue. Western blot analysis of 11 pairs of tumour and adjacent normal tissue show high Axl expression in 73% of the tumours but not normal tissue. Axl is also expressed in RCC cell lines in which Axl knockdown reduces cell viability and PI3K/Akt signalling. The Axl antibody hMAb173 significantly induced RCC cell apoptosis in histoculture and inhibited the growth of RCC tumour in vivo by 78%. The hMAb173-treated tumours also had significantly reduced Axl protein levels, inhibited PI3K signalling, decreased proliferation, and induced apoptosis.

Conclusions:

Axl is highly expressed in RCC and critical for RCC cell survival. Targeting Axl is a potential approach for RCC treatment.

Dual Targeting of mTOR Activity with Torin2 Potentiates Anticancer Effects of Cisplatin in Epithelial Ovarian Cancer

Mammalian target of rapamycin (mTOR) and phosphatidylinositol 3-kinase (PI3K) are two key components of PI3K/Akt/mTOR signaling pathway. Dysregulation of these pathways have been found in many cancers, including epithelial ovarian cancer (EOC), however, the role of mTOR has not been fully elucidated in Middle Eastern EOC. Therefore, we investigated the activation of mTOR complexes (mTORC1 and mTORC2) in a cohort of 156 EOC from Saudi Arabia by immunohistochemistry in a tissue microarray format. mTORC1 and mTORC2 were found to be activated in 55 of 146 (37.7%) and 63 of 140 (45%) of EOC samples, respectively. mTORC1 was significantly associated with mTORC2 (p < 0.0001) activation and both mTOR complexes were significantly associated with p-AKT (p = 0.0205 and 0.0298) and p-P70S6 (p < 0.0001 and 0.0035), respectively. Interestingly, mTOR activation incurred a poor progression-free survival (PFS) (p = 0.0188) in EOC. Next, the in vitro effect of inactivation of mTOR complexes was evaluated using a second-generation mTOR inhibitor, Torin2, on a panel of EOC cell lines. Torin2 treatment decreased cell viability and induced apoptosis in a dose-dependent manner via inactivation of mTORC1 and mTORC2 and their downstream targets in EOC cell lines. Furthermore, treatment of EOC cells with a subtoxic dose of Torin2 potentiated a cisplatin-induced apoptotic response in EOC cell lines. Finally, we studied the in vivo effect of a combination of Torin2 and cisplatin and found that this combination synergistically inhibited tumor growth in nude mice. These studies highlight the importance of targeting the mTOR survival pathway and suggest that cotreatment with cisplatin and Torin2 may be beneficial for the management of EOC.

Enhanced sensitivity to sorafenib by inhibition of Akt1 expression in human renal cell carcinoma ACHN cells both in vitro and in vivo

To investigate whether antitumor activity of sorafenib, a potential molecular-targeted agent against RCC is enhanced by silencing Akt1 in a human RCC ACHN model. We established ACHN in which the expression vector containing short hairpin RNA targeting Akt1 was introduced (ACHN/sh-Akt1). Changes in several phenotypes of ACHN/sh-Akt1 following treatment with sorafenib were compared with those of ACHN transfected with control vector alone (ACHN/C) both in vitro and in vivo. When cultured in the standard medium, there was no significant difference in the in vitro growth pattern between ACHN/sh-Akt1 and ACHN/C; however, compared with ACHN/C, ACHN/sh-Akt1 showed a significantly higher sensitivity to sorafenib. Furthermore, treatment with Akt1 inhibitor, A-674563 also resulted in the significantly enhanced sensitivity of parental ACHN to sorafenib. Treatment of ACHN/sh-Akt1 with sorafenib, but not that of ACHN/C, induced marked downregulation of antiapoptotic proteins, including Bcl-2, Bcl-xL, and c-Myc. In vivo administration of sorafenib resulted in the significant growth inhibition of ACHN/sh-Akt1 tumor compared with that of ACHN/C tumor, and despite the lack of Ki-67 labeling index between ACHN/sh-Akt1 and ACHN/C tumors, apoptotic index in ACHN/sh-Akt1 tumor in mice treated with sorafenib was significantly greater than that in ACHN/C tumor. These findings suggest that combined treatment with Akt1 inhibitor and sorafenib could be a promising therapeutic approach for patients with advanced RCC.

Resistance to the mTOR inhibitor temsirolimus alters adhesion and migration behavior of renal cell carcinoma cells through an integrin α5- and integrin β3-dependent mechanism

Inhibitors of the mammalian target of rapamycin (mTOR) have improved the treatment of renal cell carcinoma (RCC). However, chronic drug exposure may trigger resistance, limiting the utility of these agents. The metastatic behavior of RCC cells, susceptible (RCC(par)) or resistant (RCC(res)) to the mTOR inhibitor temsirolimus, was investigated. Adhesion to vascular endothelium or immobilized collagen and fibronectin was quantified. Chemotactic motility was evaluated with a modified Boyden chamber assay. Integrin α and β subtype receptors were analyzed by flow cytometry and Western blot analysis. The physiological relevance of the integrins was then determined by blocking studies and small interfering RNA knockdown. Adhesion to endothelial cells and to fibronectin (not to collagen) and chemotaxis were enhanced in RCC(res) compared to RCC(par). RCC(res) detached from fibronectin and motile activity further increased under retreatment with low-dosed temsirolimus. α5 integrin was diminished inside the cell and at the cell surface, whereas the β3 subtype was reduced intracellularly but elevated at the plasma membrane. In RCC(par), blocking α5 surface receptors enhanced RCC-collagen but reduced RCC-fibronectin interaction, whereas the opposite was true for RCC(res). Chemotaxis of RCC(par) but not of RCC(res) was strongly diminished by the α5 antibody. Blocking β3 significantly lowered chemotaxis with stronger effects on RCC(res), compared to RCC(par). Importantly, β3 knockdown reduced chemotaxis of RCC(par) but upregulated the motile behavior of RCC(res). Temsirolimus resistance is characterized by quantitative alterations of integrin α5 and β3 expression, coupled to functional changes of the integrin molecules, and forces a switch from RCC adhesion to RCC migration.

Significance of 4E-binding protein 1 as a therapeutic target for invasive urothelial carcinoma of the bladder

BACKGROUND

To evaluate the expression of multiple molecular markers involved in the mammalian target of rapamycin (mTOR) signaling pathway in human muscle-invasive bladder cancer (BC) and to assess the therapeutic efficacies of mTOR inhibitors in human BC KoTCC-1 cells.

METHODS

Expression levels of 5 markers, including PTEN, phosphorylated (p)-Akt, p-mTOR, p-p70 ribosomal S6 kinase, and p-4E-binding protein 1 (4E-BP1), were measured in radical cystectomy specimens from 49 patients with muscle-invasive BC by immunohistochemical staining. We then analyzed the effects of treatment with temsirolimus or Ku-0063794, a dual inhibitor of mTOR complex 1 (C1) and mTOR complex 2 (C2), on changes in the growth and expression profiles of 5 mTOR-associated markers in KoTCC-1 cells.

RESULTS

During the follow-up period of this study, disease recurred in 27 patients (55.1%), and of several factors examined, the expression level of p-4E-BP1 in addition to the pathological T stage was independently related to recurrence-free survival on multivariate analysis. Although the growth of KoTCC-1 cells was inhibited by both temsirolimus and Ku-0063794 in dose-dependent manners, treatment with Ku-0063794 resulted in a marked decrease in the expression of p-4E-BP1 in KoTCC-1 cells compared with that with temsirolimus. Furthermore, the growth-inhibitory effect of both mTOR inhibitors was shown to be proportional to the expression levels of p-4E-BP1.

CONCLUSIONS

The phosphorylation status of 4E-BP1 appeared to be correlated with the prognosis of patients with muscle-invasive BC following radical cystectomy as well as the sensitivities of BC cells to mTOR inhibitors; therefore, the inactivation of 4E-BP1 using Ku-0063794 may be a promising novel approach for muscle-invasive BC.

Mammalian Target of Rapamycin Inhibitors Resistance Mechanisms in Clear Cell Renal Cell Carcinoma

Mammalian target of rapamycin (mTOR) is a kinase protein involved in PI3K/AKT signaling with a central role in the processes of cell growth, survival and angiogenesis. Frequent mutations of this pathway make upstream and downstream components novel targets for tailored therapy design. Two mTOR inhibitors - everolimus and temsirolimus - enable an increase in overall survival (OS) or progression-free survival (PFS) time in a treatment of renal cancer. Despite recent advances in renal cancer treatment, resistance to targeted therapy is common. Understanding of molecular mechanisms is the basis of drug resistance which can facilitate prediction of success or failure in combinational or sequential targeted therapy. The article provides current knowledge on the mTOR signaling network and gives insight into the mechanisms of resistance to mTOR inhibitors from the complex perspective of RCC biology. The mechanisms of resistance developed not only by cancer cells, but also by interactions with tumor microenvironment are analyzed to emphasize the role of angiogenesis in ccRCC pathogenesis. As recent studies have shown the role of PI3K/AKT-mTOR pathway in proliferation and differentiation of cancer stem cells, we discuss cancer stem cell hypothesis and its possible contribution to ccRCC resistance. In the context of drug resistance, we also elaborate on a new approach considering ccRCC as a metabolic disease. In conclusion we speculate on future developments in agents targeting the mTOR pathway taking into consideration the singular biology of ccRCC.

HDAC-inhibition counteracts everolimus resistance in renal cell carcinoma in vitro by diminishing cdk2 and cyclin A

Background

Targeted therapies have improved therapeutic options of treating renal cell carcinoma (RCC). However, drug response is temporary due to resistance development.

Methods

Functional and molecular changes in RCC Caki-1 cells, after acquired resistance to the mammalian target of rapamycin (mTOR)-inhibitor everolimus (Caki^res), were investigated with and without additional application of the histone deacetylase (HDAC)-inhibitor valproic acid (VPA). Cell growth was evaluated by MTT assay, cell cycle progression and apoptosis by flow cytometry. Target molecules of everolimus and VPA, apoptotic and cell cycle regulating proteins were investigated by western blotting. siRNA blockade was performed to evaluate the functional relevance of the proteins.

Results

Everolimus resistance was accompanied by significant increases in the percentage of G2/M-phase cells and in the IC₅₀. Akt and p70S6K, targets of everolimus, were activated in Caki^res compared to drug sensitive cells. The most prominent change in Caki^res cells was an increase in the cell cycle activating proteins cdk2 and cyclin A. Knock-down of cdk2 and cyclin A caused significant growth inhibition in the Caki^res cells. The HDAC-inhibitor, VPA, counteracted everolimus resistance in Caki^res, evidenced by a significant decrease in tumor growth and cdk2/cyclin A.

Conclusion

It is concluded that non-response to everolimus is characterized by increased cdk2/cyclin A, driving RCC cells into the G2/M-phase. VPA hinders everolimus non-response by diminishing cdk2/cyclin A. Therefore, treatment with HDAC-inhibitors might be an option for patients with advanced renal cell carcinoma and acquired everolimus resistance.

Cross-communication between histone H3 and H4 acetylation and Akt-mTOR signalling in prostate cancer cells

Molecular tumour targeting has significantly improved anti-cancer protocols. Still, the addition of molecular targeting to the treatment regime has not led to a curative breakthrough. Combined mammalian target of Rapamycin (mTOR) and histone deacetylase (HDAC) inhibition has been shown not only to enhance anti-tumour potential, but also to prevent resistance development seen under mono-drug therapy. This investigation was designed to evaluate whether cross-communication exists between mTOR signalling and epigenetic events regulated by HDAC. DU-145 prostate cancer cells were treated with insulin-like growth factor (IGF) to activate the Akt-mTOR cascade or with the HDAC-inhibitor valproic acid (VPA) to induce histone H3 and H4 acetylation (aH3, aH4). Subsequently, mTOR, Rictor, Raptor, p70s6k, Akt (all: total and phosphorylated), H3 and H4 (total and acetylated) were analysed by western blotting. Both techniques revealed a link between mTOR and the epigenetic machinery. IGF activated mTOR, Rictor, Raptor, p70s6k and Akt, but also enhanced aH3 and aH4. Inversely, IGFr blockade and knock-down blocked the Akt-mTOR axis, but simultaneously diminished aH3 and aH4. VPA treatment up-regulated histone acetylation, but also activated mTOR-Akt signalling. HDAC1 and 2 knock-down revealed that the interaction with the mTOR system is initiated by histone H3 acetylation. HDAC-mTOR communication, therefore, is apparent whereby tumour-promoting (Akt/mTOR^high, aH3/aH4^low) and tumour-suppressing signals (Akt/mTOR^low, aH3/aH4^high) are activated in parallel. Combined use of an HDAC- and mTOR inhibitor might then diminish pro-tumour effects triggered by the HDAC- (Akt/mTOR^high) or mTOR inhibitor (aH3/aH4^low) alone.

Renal cell carcinoma: how to hit the targets?

INTRODUCTION

Renal cell carcinoma (RCC) is a widespread oncourological disease with a tendency towards a slow increase of incidence. In the recent decade, there has been development of numerous effective drugs targeted at different molecules that play a dominant role in RCC carcinogenesis. Understanding of RCC carcinogenesis confirms the key role of angiogenesis in maintaining the viability of renal tumours and their metastases.

MATERIAL AND METHODS

We aimed to systemize numerous medicines, used to inhibit the angiogenesis in patients with advanced RCC according to their targets, and to analyze their efficacy.

RESULTS

There are roughly four main mechanisms of action of the targeted drugs:Blockade of circulating extracellular VEGF molecules.The selective blockade of tyrosine kinase receptors' domains.The simultaneous blockage of the tyrosine kinase receptors' domains and intracellular tyrosine kinases.The blockade of mammalian target of rapamycin (mTOR) which is responsible for support of vital functions of cancer cells. In addition to FDA officially approved drugs, numerous experimental agents have been synthesized, which are currently on initial stages of clinical studies in RCC treatment.

CONCLUSIONS

The results of the currently used targeted drugs demonstrate perspectives of metastatic RCC conservative treatment, that are able to prolong cancer-specific survival in previously doomed patients for up to 29 months. The development of schedules for sequential treatment or combination targeted therapy remains a current challenge. The quality of life is an important factor that influences remedy choice. The advantages and disadvantages of neoadjuvant and adjuvant targeted therapy are currently being intensively discussed.