Upstream signaling inhibition enhances rapamycin effect on growth of kidney cancer cells

Renal oncometabolite L-2-hydroxyglutarate imposes a block in kidney tubulogenesis: Evidence for an epigenetic basis for the L-2HG-induced impairment of differentiation

2-Hydroxyglutarate (2HG) overproducing tumors arise in a number of tissues, including the kidney. The tumorigenesis resulting from overproduced 2HG has been attributed to the ability of 2HG alter gene expression by inhibiting α-ketoglutarate (αKG)-dependent dioxygenases, including Ten-eleven-Translocation (TET) enzymes. Genes that regulate cellular differentiation are reportedly repressed, blocking differentiation of mesenchymal cells into myocytes, and adipocytes. In this report, the expression of the enzyme responsible for L2HG degradation, L-2HG dehydrogenase (L2HGDH), is knocked down, using lentiviral shRNA, as well as siRNA, in primary cultures of normal Renal Proximal Tubule (RPT) cells. The knockdown (KD) results in increased L-2HG levels, decreased demethylation of 5mC in genomic DNA, and increased methylation of H3 Histones. Consequences include reduced tubulogenesis by RPT cells in matrigel, and reduced expression of molecular markers of differentiation, including membrane transporters as well as HNF1α and HNF1β, which regulate their transcription. These results are consistent with the hypothesis that oncometabolite 2HG blocks RPT differentiation by altering the methylation status of chromatin in a manner that impedes the transcriptional events required for normal differentiation. Presumably, similar alterations are responsible for promoting the expansion of renal cancer stem-cells, increasing their propensity for malignant transformation.

The value of erlotinib related target molecules in kidney renal cell carcinoma via bioinformatics analysis

OBJECTIVE

Erlotinib was found to be an effective treatment for metastatic kidney renal cell carcinoma (KIRC). This study employed bioinformatics to explore the value of erlotinib's target molecules in KIRC.

METHODS

We screened GSE25698 dataset for differentially expressed genes (DEGs) following erlotinib treatment, followed by analyzing their underlying functional mechanisms. The value of DEGs was identified in TCGA database to construct risk model and nomogram, and possible mechanisms underlying model factors and their relationship with KIRC immune infiltration were analyzed.

RESULTS

Following erlotinib treatment, DEGs were involved in antigen binding, myeloid leukocyte activation, JAK-STAT signaling pathway, etc. COL11A1, EMCN, GLYATL1, HHLA2, IGFN1, LIPA, LRRC19, PANK1, PRAME, and TNFSF14 were independent factors influencing poor prognosis in KIRC patients. Age, grade, and risk score were independent risk factors influencing poor prognosis of KIRC patients. The risk score was associated with immune cells such as T cells regulatory, T cells follicular helper, macrophages M0, etc., and participated signaling mechanisms such as ERBB, insulin, mTOR, PPAR, apoptosis, MAPK, T cell receptor, etc. CONCLUSIONS: The expression levels of COL11A1, EMCN, GLYATL1, HHLA2, IGFN1 LIPA, LRRC19, PANK1, PRAME, and TNFSF14 were associated with KIRC prognosis and immune cell infiltration. The risk model and nomogram based on erlotinib's target molecules were expected to be a tool for evaluating the prognosis of KIRC patients.

Interferon-α enhances the susceptibility of renal cell carcinoma to rapamycin by suppressing mTOR activity

The aim of the present study was to investigate the antiproliferative effects of interferon (IFN)-α and rapamycin (RPM) on renal cell carcinoma (RCC) cells and examine the synergistic growth suppression conferred by IFN-α and RPM. The effects of IFN-α and/or RPM on RCC cells were determined using a WST-1 assay and the synergy of IFN-α and RPM against three RCC cell lines was analyzed with isobolographic analysis. The expression of mammalian target of rapamycin (mTOR) was downregulated by RNAi, and the expression and phosphorylation of proteins in the mTOR pathway following treatment with IFN-α and/or RPM was examined by western blot analysis. The observations indicated that IFN-α significantly increased the susceptibility of RCC cells to RPM and the synergistic effect of IFN-α and RPM against RCC cells was confirmed in all three RCC cell lines. The mTOR pathway was shown to be associated with the synergistic effect of IFN-α and RPM against RCC. IFN-α and RPM alone decreased the phosphorylation of mTOR, p70 S6 kinase, S6 and 4E binding protein 1, and IFN-α significantly enhanced the RPM-induced suppression of the mTOR pathway. However, in RCC cells with low mTOR activity, the synergy of IFN-α and RPM was eliminated. Therefore, the results of the present study indicate that the mTOR pathway plays an important role in the synergistic effect of IFN-α and RPM against RCC cells. Thus, mTOR may serve as an effective therapeutic target in the treatment of advanced RCC.

Emerging strategies to overcome the resistance to current mTOR inhibitors in renal cell carcinoma

The mammalian target of rapamycin (mTOR) has emerged as an attractive cancer therapeutic target. Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. Unfortunately, a number of potential mechanisms that may lead to resistance to mTOR inhibitors have been proposed. In this paper, we discuss the mechanisms underlying resistance to mTOR inhibitors, which include the downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway, the activation of hypoxia-inducible factor (HIF), the PIM kinase family, PTEN expression, elevated superoxide levels, stimulation of autophagy, immune cell response and ERK/MAPK, Notch and Aurora signaling pathways. Moreover, we present an updated analysis of clinical trials available on PubMed Central and www.clinicaltrials.gov, which were pertinent to the resistance to rapalogs. The new frontier of inhibiting the mTOR pathway is to identify agents targeting the feedback loops and cross talks with other pathways involved in the acquired resistance to mTOR inhibitors. The true goal will be to identify biomarkers predictive of sensitivity or resistance to efficiently develop novel agents with the aim to avoid toxicities and to better choose the active drug for the right patient.

Icotinib combined with rapamycin in a renal transplant recipient with epidermal growth factor receptor-mutated non-small cell lung cancer: A case report

As kidney transplant recipients are at increased risk of developing cancer, regular monitoring should be undertaken to monitor the balance between immunosuppression and graft function and to identify malignancy. The present study reports the outcome of the treatment of adenocarcinoma of the lung (T1aN0M1a, stage IV) using the molecular-targeted therapy, icotinib, in a 66-year-old male renal transplant patient receiving rapamycin and prednisolone as ongoing renal immunosuppressive therapy. An initial partial response to icotinib was achieved, and graft function remained good. However, the patient subsequently developed interstitial pneumonitis. The plasma concentrations of rapamycin and icotinib were within the normal ranges, which excluded the possibility of a pharmacokinetic drug interaction and indicated that the interstitial pneumonitis was likely to be associated with the side-effects of icotinib. Drug therapy was discontinued and the patient underwent a segmentectomy. Tacrolimus was administered for ongoing renal graft immunosuppression. To the best of our knowledge, this is the first report of the concomitant administration of icotinib and rapamycin in post-transplant de novo lung cancer. It is also the first report of interstitial pneumonitis associated with icotinib in a post-transplant patient.

AKT kinase pathway: a leading target in cancer research

AKT1, a serine/threonine-protein kinase also known as AKT kinase, is involved in the regulation of various signalling downstream pathways including metabolism, cell proliferation, survival, growth, and angiogenesis. The AKT kinases pathway stands among the most important components of cell proliferation mechanism. Several approaches have been implemented to design an efficient drug molecule to target AKT kinases, although the promising results have not been confirmed. In this paper we have documented the detailed molecular insight of AKT kinase protein and proposed a probable doxorubicin based approach in inhibiting miR-21 based cancer cell proliferation. Moreover, the inhibition of miR-21 activation by raising the FOXO3A concentration seems promising in reducing miR-21 mediated cancer activation in cell. Furthermore, the use of next generation sequencing and computational drug design approaches will greatly assist in designing a potent drug molecule against the associated cancer cases.

Present and Future of EGFR Inhibitors for Head and Neck Squamous Cell Cancer

Although EGFR is expressed at high levels in head and neck squamous cell carcinomas (HNSCCs) and mutations are extremely rare, monotherapy with EGFR inhibitors has shown limited success. The PI3kinase/Akt pathway is responsible for cellular survival, and inhibition of phosphatidylinositol (PI) synthesis has antiproliferative, anti-invasive, and antiangiogenesis effects on HNSCC. Molecular crosstalk has been observed between EGFR and IGF1R signaling through the PI3kinase/Akt pathway in HNSCC, as has molecular crosstalk between the NFκB and STAT3 signaling pathways. Therefore, the combination of an EGFR antagonist with an agent that inhibits the activation of both Akt and NFκB may overcome resistance to EGFR antagonists in HNSCC.

MicroRNA-1826 directly targets beta-catenin (CTNNB1) and MEK1 (MAP2K1) in VHL-inactivated renal cancer

The aim of this project is to identify new therapeutic microRNAs (miRNAs) for von Hippel-Lindau (VHL)-inactivated renal cancer cells. We initially identified several potential miRNAs targeting CTNNB1 and MEK1 using several targets scan algorithms. Only miR-1826 was found to target CTNNB1 and MEK1. Therefore, we focused on miRNA-1826 and performed 3' untranslated region (UTR) luciferase assay, functional analyses and association study between miR-1826 expression and renal cancer patient outcomes. miR-1826 expression was significantly lower in renal cancer tissues compared with non-neoplastic areas and lower expression was significantly associated with overall shorter survival and earlier recurrence after radical nephrectomy. Following miR-1826 transfection, 3' UTR luciferase activity and protein expression of beta-catenin and MEK1 were significantly downregulated in renal cancer cells. Introduction of miR-1826 also inhibited renal cancer cell proliferation, invasion and migration. Additionally, miR-1826 promoted apoptosis and G(1) arrest in VHL-inactivated renal cancer cells. Knockdowns of CTNNB1 and MEK1 by small interfering RNAs reproduced the tumor-suppressive effect of miR-1826. Our data suggest that the miR-1826 plays an important role as a tumor suppressor by downregulating beta-catenin and MEK1 in VHL-inactivated renal cancers.

Safety and efficacy of the combination of erlotinib and sirolimus for the treatment of metastatic renal cell carcinoma after failure of sunitinib or sorafenib

BACKGROUND

The mammalian target of rapamycin (mTOR) is an important therapeutic target in the treatment of renal cell carcinoma (RCC). Pre-clinical data indicate that the combined inhibition of both the epidermal growth factor receptor and mTOR results in enhanced anticancer activity.

METHODS

All patients had metastatic RCC with progression after treatment with sunitinib and/or sorafenib. Treatment consisted of erlotinib 150 mg orally once a day starting on day 1 and sirolimus 6 mg orally on day 8 followed by 2 mg daily, adjusted according to blood levels.

RESULTS

A total of 25 patients were enrolled between July 2006 and March 2008. The median progression-free survival (PFS) was 12 weeks (95% CI 5.9-18.1) and median overall survival (OS) 40 weeks (95% CI 0-85.7). No confirmed complete or partial responses were observed, but stable disease >6 months was noted in 21.8% (95% CI 4.9-38.6) of patients. The most common adverse events were rash and diarrhoea. There was no correlation between erlotinib, OSI-420 (days 8 and 15) or sirolimus (days 15 and 29) blood levels and PFS or OS.

CONCLUSIONS

The combination of sirolimus and erlotinib for RCC failed to demonstrate an advantage over available single-agent therapy in the second-line setting.

Effect of combination treatment of rapamycin and isoflavones on mTOR pathway in human glioblastoma (U87) cells

Glioblastoma Multiforme (GBM) is a malignant primary brain tumor associated with poor survival rate. PI3K/Akt pathway is highly upregulated in gliomas due to deletion or mutation of PTEN and its activation is associated with tumor grade. mTOR is downstream from PI3K/Akt pathway and it initiates translation through its action on S6K and 4E-BP1. mTOR is an important therapeutic target in many cancers, including glioblastomas. Rapamycin and its analogues are known to inhibit mTOR pathway; however, they also show simultaneous upregulation of Akt and eIF4E survival pathways on inhibition of mTOR, rendering cells more resistant to rapamycin treatment. In this study we investigated the effect of combination treatment of rapamycin with isoflavones such as genistein and biochanin A on mTOR pathway and activation of Akt and eIF4E in human glioblastoma (U87) cells. Our results show that combination treatment of rapamycin with isoflavones, especially biochanin A at 50 muM, decreased the phosphorylation of Akt and eIF4E proteins and rendered U87 cells more sensitive to rapamycin treatment when compared to cells treated with rapamycin alone. These results suggest the importance of combining chemopreventive with chemotherapeutic agents in order to increase the efficacy of chemotherapeutic drugs.

Temsirolimus in the treatment of renal cell carcinoma associated with Xp11.2 translocation/TFE gene fusion proteins: a case report and review of literature

Xp11.2 translocation renal cell carcinomas (TRCCs) are a rare family of tumors newly recognized by the World Health Organization (WHO) in 2004. These tumors result in the fusion of partner genes to the TFE3 gene located on Xp11.2. They are most common in the pediatric population, but have been recently implicated in adult renal cell carcinoma (RCC) presenting at an early age. TFE3-mediated direct transcriptional upregulation of the Met tyrosine kinase receptor triggers dramatic activation of downstream signaling pathways including the protein kinase B (Akt)/phosphatidylinositol-3 kinase (PI3K) and mammalian target of rapamycin (mTOR) pathways. Temsirolimus is an inhibitor of mammalian target of rapamycin (mTOR) kinase, a component of intracellular signaling pathways involved in the growth and proliferation of malignant cells. Here we present a case of a 22-year old female who has been treated with temsirolimus for her Xp11.2/TFE3 gene fusion RCC.

Factors underlying sensitivity of cancers to small-molecule kinase inhibitors

Selective small-molecule kinase inhibitors have emerged over the past decade as an important class of anti-cancer agents, and have demonstrated impressive clinical efficacy in several different diseases, including relatively common malignancies such as breast and lung cancer. However, clinical benefit is typically limited to a fraction of treated patients. Genomic features of individual tumours contribute significantly to such clinical responses, and these seem to vary tremendously across patients. Additional factors, including pharmacogenomics, the tumour microenvironment and rapidly acquired drug resistance, also contribute to the clinical sensitivity of various cancers, and should be considered and applied in the development and use of new kinase inhibitors.

Combined inhibition of MEK and mammalian target of rapamycin abolishes phosphorylation of cyclin-dependent kinase 4 in glioblastoma cell lines and prevents their proliferation

The Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) signaling pathways are aberrantly activated in many tumors, including highly proliferative glioblastomas, but how they are wired with the cell cycle remains imperfectly understood. Inhibitors of MEK/ERK and mTOR pathways are tested as anticancer agents. They are generally considered to induce a G(1) cell cycle arrest through down-regulation of D-type cyclins and up-regulation of p27(kip1). Here, we examined the effect of targeting mTOR by rapamycin and/or MEK by PD184352 in human glioblastoma cell lines. In combination, these drugs cooperatively and potently inhibited the G(1)-S transition and retinoblastoma protein phosphorylation. Their cooperation could not be explained by their partial and differential inhibitory effects on cyclin D1 or D3 but instead by their synergistic inhibition of the activating T172 phosphorylation of cyclin-dependent kinase (CDK) 4. This appeared independent of p27 and unrelated to weak modulations of the CDK-activating kinase activity. The T172 phosphorylation of CDK4 thus appears as a crucial node integrating the activity of both MEK/ERK and mTOR pathways. Combined inhibition of both pathways should be considered as a promising strategy for treatment of tumors harboring a deregulated CDK4 activity.

Rapamycin induces transactivation of the EGFR and increases cell survival

The mammalian target of rapamycin (mTOR) signaling network regulates cell growth, proliferation and cell survival. Deregulated activation of this pathway is a common event in diverse human diseases such as cancers, cardiac hypertrophy, vascular restenosis and nephrotic hypertrophy. Although mTOR inhibitor, rapamycin, has been widely used to inhibit the aberrant signaling due to mTOR activation that plays a major role in hyperproliferative diseases, in some cases rapamycin does not attenuate the cell proliferation and survival. Thus, we studied the mechanism(s) by which cells may confer resistance to rapamycin. Our data show that in a variety of cell types the mTOR inhibitor rapamycin activates extracellularly regulated kinases (Erk1/2) signaling. Rapamycin-mediated activation of the Erk1/2 signaling requires (a) the epidermal growth factor receptor (EGFR), (b) its tyrosine kinase activity and (c) intact autophosphorylation sites on the receptor. Rapamycin treatment increases tyrosine phosphorylation of EGFR without the addition of growth factor and this transactivation of receptor involves activation of c-Src. We also show that rapamycin treatment triggers activation of cell survival signaling pathway by activating the prosurvival kinases Erk1/2 and p90RSK. These studies provide a novel paradigm by which cells escape the apoptotic actions of rapamycin and its derivatives that inhibit the mTOR pathway.

Akt as a therapeutic target in cancer

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors.

OBJECTIVE

This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells.

METHODS

We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular.

RESULTS/CONCLUSIONS

The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.

Gene microarray analysis of human renal cell carcinoma: the effects of HDAC inhibition and retinoid treatment

Histone deacetylase (HDAC) inhibitor treatments can augment the anti-tumor effects of retinoids in renal cancer cells. We studied the effects of the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) and 13-cis retinoic acid (cRA) on two human renal cell carcinoma (RCC) lines. Cells were cultured in the presence of each drug for six days to determine the responses to monotherapy and to combination therapy. The proliferation of SKRC06 was inhibited with cRA treatment; the proliferation of SKRC39 was not. However, both RCC lines were sensitive to growth inhibition by dibutyryl cyclic AMP, with or without 13-cis RA. SAHA alone also reduced cell proliferation in both cell lines. To identify the alterations in gene expression that correlate with the responsiveness to treatment, gene microarray analyses were performed. Several retinoid-regulated genes exhibited much higher mRNA levels in SKRC06 than in SKRC39, even in the absence of drugs; these included crabp2, rargamma and cyp26A1. Combination treatment of cells with both SAHA and cRA induced several transcripts with known anti-cancer/immunomodulatory effects, including dhrs9, gata3, il1beta, phlda1, txk and vhl. Immunostaining confirmed the decreased expression of gata3 in human RCC specimens compared to normal kidney. Together, our results show that treatment of RCC with cRA and/or SAHA increases the expression of several genes and gene families that result in reduced cell proliferation.

Rapamycin treatment for a child with germline PTEN mutation

BACKGROUND

A 9-month-old boy with Proteus syndrome and a de novo germline mutation in the tumor suppressor PTEN was referred to a specialist centre for management. Over the first years of life, the patient developed life-threatening respiratory dysfunction and malnutrition because of progressive growth of hamartomas affecting the chest, mediastinum, abdomen and pelvis.

INVESTIGATIONS

Physical examination, CT scans of the mediastinum, pelvis and abdomen, measurement of serum insulin-like growth factor binding protein-2, and investigation of the effect of the PTEN mutation on phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling in an in vitro cell model.

DIAGNOSIS

PTEN hamartoma tumor syndrome, specifically Proteus syndrome.

MANAGEMENT

Oral rapamycin.

Combined expression of caveolin-1 and an activated AKT/mTOR pathway predicts reduced disease-free survival in clinically confined renal cell carcinoma

We previously reported that tumour-associated caveolin-1 is a potential biomarker in renal cell carcinoma (RCC), whose overexpression predicts metastasis following surgical resection for clinically confined disease. Much attention has recently focused on the AKT/mTOR pathway in a number of malignancies, including RCC. Since caveolin-1 and the AKT/mTOR signalling cascade are independently shown to be important regulators of tumour angiogenesis, we hypothesised that caveolin-1 interacts with the AKT/mTOR pathway to drive disease progression and metastasis in RCC. The aims of this study were to determine (i) the expression status of the activated AKT/mTOR pathway components (phosphorylated forms) in RCC and (ii) their prognostic value when combined with caveolin-1. Immunohistochemistry for caveolin-1, pAKT, pmTOR, pS6 and p4E-BP1 was performed on tissue microarrays from 174 clinically confined RCCs. Significantly decreased mean disease-free survival was observed when caveolin-1 was coexpressed with either pAKT (2.95 vs 6.14 years), pmTOR (3.17 vs 6.28 years), pS6 (1.45 vs 6.62 years) or p4E-BP1 (2.07 vs 6.09 years) than when neither or any one single biomarker was expressed alone. On multivariate analysis, the covariate of ‘caveolin-1/AKT’ (neither alone were influential covariates) was a significant influential indicator of poor disease-free survival with a hazard ratio of 2.13 (95% CI: 1.15–3.92), higher than that for vascular invasion. Tumours that coexpressed caveolin-1 and activated mTOR components were more likely to be larger, higher grade and to show vascular invasion. Our results provide the first clinical evidence that caveolin-1 cooperates with an activated AKT/mTOR pathway in cancer and may play an important role in disease progression. We conclude that evaluation of the ‘caveolin-1/AKT/mTOR axis’ in primary kidney tumours will identify subsets of RCC patients who require greater postoperative surveillance and more intensive treatment.

Targeting the PI3K/Akt/mTOR pathway: effective combinations and clinical considerations

The PI3K/Akt/mTOR pathway is a prototypic survival pathway that is constitutively activated in many types of cancer. Mechanisms for pathway activation include loss of tumor suppressor PTEN function, amplification or mutation of PI3K, amplification or mutation of Akt, activation of growth factor receptors, and exposure to carcinogens. Once activated, signaling through Akt can be propagated to a diverse array of substrates, including mTOR, a key regulator of protein translation. This pathway is an attractive therapeutic target in cancer because it serves as a convergence point for many growth stimuli, and through its downstream substrates, controls cellular processes that contribute to the initiation and maintenance of cancer. Moreover, activation of the Akt/mTOR pathway confers resistance to many types of cancer therapy, and is a poor prognostic factor for many types of cancers. This review will provide an update on the clinical progress of various agents that target the pathway, such as the Akt inhibitors perifosine and PX-866 and mTOR inhibitors (rapamycin, CCI-779, RAD-001) and discuss strategies to combine these pathway inhibitors with conventional chemotherapy, radiotherapy, as well as newer targeted agents. We will also discuss how the complex regulation of the PI3K/Akt/mTOR pathway poses practical issues concerning the design of clinical trials, potential toxicities and criteria for patient selection.

Von Hippel-Lindau tumor suppressor gene loss in renal cell carcinoma promotes oncogenic epidermal growth factor receptor signaling via Akt-1 and MEK-1

OBJECTIVES

Clear-cell renal cell carcinoma (RCC) is the most prevalent form of kidney cancer and is frequently associated with loss of von Hippel-Lindau (VHL) gene function, resulting in the aberrant transcriptional activation of genes that contribute to tumor growth and metastasis, including transforming growth factor-alpha (TGF-alpha), a ligand of the epidermal growth factor receptor (EGFR) tyrosine kinase. To determine the functional impact of EGFR activation on RCC, we suppressed critical components of this pathway: EGFR, Akt-1, and MEK-1.

METHODS

Stable transfection of RCC cells with plasmids bearing shRNA directed against each of these genes was used to individually suppress their expression. Transfectants were characterized for growth and invasiveness in vitro and tumorigenesis in vivo.

RESULTS

RCC cell transfectants displayed significantly reduced growth rate and matrix invasion in vitro and RCC tumor xenograft growth rate in vivo. Analysis of tumor cells that emerged after extended periods in each model showed that significant EGFR suppression was sustained, whereas Akt-1 and MEK-1 knock-down cells had escaped shRNA suppression.

CONCLUSIONS

EGFR, Akt-1, and MEK-1 are individually critical for RCC cell invasiveness in vitro and tumorigenicity in vivo, and even partial suppression of each can have a significant impact on tumor progression. The emergence of transfectants that had escaped Akt-1 and MEK-1 suppression during tumorigenicity experiments suggests that these effectors may each be more critical than EGFR for RCC tumorigenesis, consistent with results from clinical trials of EGFR inhibitors for RCC, where durable clinical responses have not been seen.

Synergic antiproliferative and antiangiogenic effects of EGFR and mTor inhibitors on pancreatic cancer cells

The in vitro efficacy of both EGFR inhibitor gefitinib and mTor inhibitor rapamycin, either administrated alone or in different combination schedules, was analysed in four pancreas cancer cell lines. Both drugs were found to induce cell growth inhibition, apoptosis as well as a slight but stable accumulation of cells in the G0/G1 phase. In all cell lines, neither gefitinib nor rapamycin affected EGFR and the expression of its downstream effectors. By contrast, gefitinib inhibited in a fast and completely way p-EGFR and partially p-Akt while a 3 days-rapamycin exposure resulted in the inhibition of the expression of both mTor and p70S6K. Moreover, after early stimulation, the mTor inhibitor produced a progressive, and almost complete inhibition of p-Akt. The analysis of combined gefitinib and rapamycin administration showed a clear schedule-dependent activity which turned out to be synergic only when gefitinib was given before rapamycin. This synergism seemed to depend on increase of both p-Akt and p70S6K inhibition, the greater the induction of apoptosis, the higher the decrease in cell cycle rate. Moreover, the antiangiogenic activity of the two drugs given in combination was demonstrated by a strong reduction of VEGF release which turned out to be more pronounced in the synergic schedule, and HIF-1alpha inhibition-independent. Our results suggest that the schedule of gefitinib followed by rapamycin, acting at different levels of the EGFR cellular pathway, could induce antitumor and antiangiogenic effects of clinical interest in the pancreas cancer model.