The potential role of mTOR inhibitors in the treatment of endocrine tumors

Mammalian target of rapamycin (mTOR), a main protein kinase in the phosphoinositide 3-kinase/Akt/p70S6K signaling pathway, is an important intracellular mediator involved in multiple cellular functions including proliferation, differentiation, apoptosis, longevity, tumorigenesis, and angiogenesis. Alterations of the normal activity of mTOR and of mTOR-related kinases in this pathway have been found in a diversity of human tumors, suggesting that mTOR may be an attractive target for the development of new anti-cancer therapies. The main objective of this article is to summarize the available pre-clinical and clinical data regarding a possible role of mTOR inhibitors in the treatment of different endocrine cancers.

RAD001 offers a therapeutic intervention through inhibition of mTOR as a potential strategy for esophageal cancer

Esophageal cancer is one of the most frequently occurring cancers in the world. Targeting therapy strategy of cancer with specific inhibitors is developing and has showed promising antitumor efficacy. It is known that mTOR is an important controller of cell growth. RAD001 (everolimus) is a specific inhibitor of mTOR that can block the mTOR signaling pathway. The purposes of this study was to explore the inhibitory effects of RAD001 on mTOR signaling and the mechanism of cell growth suppression by RAD001. We examined both the expression of mTOR, p70S6K and S6 in SEG-1 esophageal cancer cells and KOB-13 normal esophageal epithelial cells and the efficacy of RAD001 against SEG-1 esophageal cancer cells. mTOR, p70S6K and S6 were overexpressed in SEG-1 esophageal cancer cells compared with KOB-13 normal esophageal epithelial cells. SEG-1 esophageal cancer cells were sensitive to RAD001. The survival rate of the cells treated with RAD001 over 0.33 microM was significantly different compared with that of control (P<0.01). RAD001 inhibited the phosphorylation of mTOR (Ser2448) and S6 (Ser240/244) in different grades and the expressions of mTOR, p70S6K and S6. As a result, RAD001 induced a dose-dependent decrease in cell proliferation, G1/S arrest and damage of cell shape. Taken together, these data showed that RAD001 can inhibit mTOR signaling and proliferation in SEG-1 esophageal cancer cells in vitro. It offers a therapeutic intervention through inhibition of mTOR as a potential strategy for esophageal cancer.

Recent advances in the treatment of mantle cell lymphoma: a post-ASH 2009 discussion

Mantle cell lymphoma (MCL) is a rare subtype of non-Hodgkin lymphoma characterized by CD5 expression and a t(11;14) cytogenetic translocation that results in overexpression of the cyclin D1 gene. Currently, there is no standard of care for the treatment of MCL, and patient prognosis is poor. Traditional treatments for MCLrely on conventional chemotherapy agents, including cyclophosphamide, doxorubicin, vincristine, and prednisone(CHOP). The addition of the immunotherapeutic agent rituximab to this regimen (CHOP-R) has helped to improve patient response to treatment. These treatments often provide good initial responses that are difficult to sustain. Therefore, a number of newer agents and combinations have been investigated to produce more durable benefit. Several of these advances were reported at the 51st American Society of Hematology (ASH)Annual Meeting and Exposition, held December 5-8, 2009 in New Orleans, Louisiana. In this clinical roundtable monograph, new strategies in the treatment of MCL are discussed. Some of the drug classes examined here are proteasome inhibitors, inhibitors of the protein mammalian target of rapamycin (mTOR), the unique alkylating agent bendamustine, and immunomodulatory agents.

Genetic dissection of the oncogenic mTOR pathway reveals druggable addiction to translational control via 4EBP-eIF4E

We genetically dissect the contribution of the most prominent downstream translational components of mTOR signaling toward Akt-driven lymphomagenesis. While phosphorylation of rpS6 is dispensable for cancer formation, 4EBP-eIF4E exerts significant control over cap-dependent translation, cell growth, cancer initiation, and progression. This effect is mediated at least in part through 4EBP-dependent control of Mcl-1 expression, a key antiapoptotic protein. By using an active site inhibitor of mTOR, PP242, we show a marked therapeutic response in rapamycin-resistant tumors. The therapeutic benefit of PP242 is mediated through inhibition of mTORC1-dependent 4EBP-eIF4E hyperactivation. Thus, the 4EBP-eIF4E axis downstream of mTOR is a druggable mediator of translational control and Akt-mediated tumorigenesis that has important implications for the treatment of human cancers.

Role of the Akt/mTOR survival pathway in cisplatin resistance in ovarian cancer cells

The mechanism of cisplatin resistance in cancer cells is not fully understood. Here, we show that the Akt/mTOR survival pathway plays an important role in cisplatin resistance in human ovarian cancer cells. Specifically, we found that cisplatin treatment activates the Akt/mTOR survival pathway and that inhibition of this pathway by the PI3K inhibitor LY294002 or knockdown of Akt sensitizes ovarian cancer cells to cisplatin. Furthermore, we generated cisplatin-resistant cells and found that resistant cells express a higher level of activated Akt as compared to their cisplatin sensitive counterparts. Importantly, inhibition of Akt or mTOR sensitized resistant cells to cisplatin-induced apoptosis. Taken together, our data indicate that activation of the Akt/mTOR pathway prevents cisplatin-induced apoptosis, leading to cisplatin resistance. Therefore, our study suggests that cisplatin resistance can be overcome by targeting the Akt/mTOR survival pathway in human ovarian cancer cells.

Inhibition of myristoylated alanine-rich C kinase substrate (MARCKS) protein inhibits ozone-induced airway neutrophilia and inflammation

Evidence suggests inhibition of leukocyte trafficking mitigates, in part, ozone-induced inflammation. In the present study, the authors postulated that inhibition of myristoylated alanine-rich C kinase substrate (MARCKS), an 82-kDa protein with multiple biological roles, could inhibit ozone-induced leukocyte trafficking and cytokine secretions. BALB/c mice (n = 5/cohort) were exposed to ozone (100 ppb) or forced air (FA) for 4 hours. MARCKS-inhibiting peptides, MANS, BIO-11000, BIO-11006, or scrambled control peptide RNS, were intratracheally administered prior to ozone exposure. Ozone selectively enhanced bronchoalveolar lavage (BAL) levels of killer cells (KCs; 6 +/- 0.9-fold), interleukin-6 (IL-6; 12.7 +/- 1.9-fold), and tumor necrosis factor (TNF; 2.1 +/- 0.5-fold) as compared to cohorts exposed to FA. Additionally, ozone increased BAL neutrophils by 21% +/- 2% with no significant (P > .05) changes in other cell types. MANS, BIO-11000, and BIO-11006 significantly reduced ozone-induced KC secretion by 66% +/- 14%, 47% +/- 15%, and 71.1% +/- 14%, and IL-6 secretion by 69% +/- 12%, 40% +/- 7%, and 86.1% +/- 11%, respectively. Ozone-mediated increases in BAL neutrophils were reduced by MANS (86% +/- 7%) and BIO-11006 (84% +/- 2.5%), but not BIO-11000. These studies identify for the first time the novel potential of MARCKS protein inhibitors in abrogating ozone-induced increases in neutrophils, cytokines, and chemokines in BAL fluid. BIO-11006 is being developed as a treatment for chronic obstructive pulmonary disorder (COPD) and is currently being evaluated in a phase 2 clinical study.

mTOR inhibitor/proliferation signal inhibitors: entering or leaving the field?

BACKGROUND

The mammalian target of rapamycin (mTOR) is a highly conserved serine/threonine kinase that controls cell growth and metabolism in response to nutrients, growth factors, cellular energy and stress, and has pleiotropic effects. Its blockade, by mTOR inhibitors (mTOR-Is), such as sirolimus or everolimus, leads to antiproliferative effects.

METHODS

We have reviewed the major studies that deal with the utilization of mTOR-Is after kidney transplant and the outcomes.

RESULTS

Calcineurin-inhibitor (CNI) avoidance, under the umbrella of sirolimus-based immunosuppression in de novo kidney-transplant (KT) patients, is associated with worse results compared with those observed in patients receiving CNI-based immunosuppression. Conversely, using mTOR-Is in the context of CNI minimization and CNI-free protocols is safe and efficient when used after 3 months post-transplant. If cyclosporin A (CsA) is used in combination with mTOR-I, considerable dose reduction of both drugs is required. A better choice may be withdrawal of CsA from this combination after 3-12 months. Later withdrawal or conversion to an mTOR-I may not be beneficial. Kidney transplant recipients given mTOR-Is have reduced incidence of de novo posttransplant malignancies. Posttransplant Kaposi's sarcoma and nonmelanotic skin malignancies frequently undergo remission/regression after conversion to mTOR-I immunosuppression. The associated side effects of mTOR-Is are numerous and may lead to significant drug cessation.

CONCLUSION

mTOR-Is could be more widely used in kidney transplant patients due to reduced nephrotoxicity and de novo cancer compared with CNIs.

Synthetic triterpenoids inhibit growth, induce apoptosis and suppress pro-survival Akt, mTOR and NF-{kappa}B signaling proteins in colorectal cancer cells

Lack of apoptotic cell death has been implicated in malignant transformation and resistance to anticancer therapies. The promotion of apoptosis in cancer cells could potentially lead to the regression and improved prognosis of refractory colorectal cancer. Synthetic triterpenoids have shown strong antitumorigenic activity towards diverse cancer cell types, but have not been investigated for colorectal cancer. In the present study, we tested the apoptosis-inducing activity of oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its C-28 methyl ester (CDDO-Me) and C-28 imidazole (CDDO-Im) derivatives in colorectal cancer cells lines. Cell growth/viability assay (MTS) demonstrated that colorectal cancer cells are highly sensitive to CDDO-Me at concentrations of 1.25 to 10 microM. The primary mode of tumor cell destruction was apoptosis as demonstrated by the cleavage of PARP-1, activation of procaspases -3, -8, and -9 and mitochondrial depolarization. Induction of apoptosis by CDDO-Me was associated with the inhibition of pro-survival Akt, NF-kappaB and mTOR signaling proteins and NF-kappaB-regulated anti-apoptotic Bcl-2, Bcl-xL, Bad and survivin. These studies provide rationale for clinical evaluation of CDDO-Me for the treatment of advanced chemotherapy refractory colorectal cancer.

Orexin receptor subtype activation and locomotor behaviour in the rat

AIM

Orexin-producing neurones, located primarily in the perifornical region of the lateral hypothalamus, project to a wide spectrum of brain sites where they influence numerous behaviours as well as modulating the neuroendocrine and autonomic responses to stress. While some of the actions of orexin appear to be mediated via the type 1 receptor, some are not, including its action on the release of one stress hormone, prolactin. We describe here the ability of orexin to increase locomotor behaviours and identify the importance of both receptor subtypes in these actions.

METHODS

Rats were tested for their behavioural responses to the central activation of both the type 1 (OX(1)R) and type 2 (OX(2)R) receptor (ICV orexin A), compared to OX(2)R activation using a relatively selective OX(2)R agonist in the absence or presence of an orexin receptor antagonist that possesses highest affinity for OX(1)R.

RESULTS

Increases in locomotor activity were observed, effects which were expressed by not only orexin A, which binds to both the OX(1)R and the OX(2)R receptors, but also by the relatively selective OX(2)R agonist [(Ala(11), Leu(15))-orexin B]. Furthermore, the OX(1)R selective antagonist only partially blocked the action of orexin A on most locomotor behaviours and did not block the actions of [(Ala(11), Leu(15))-orexin B].

CONCLUSION

We conclude that orexin A exerts its effects on locomotor behaviour via both the OX(1)R and OX(2)R and that agonism or antagonism of only one of these receptors for therapeutic purposes (i.e. sleep disorders) would not provide selectivity in terms of associated behavioural side effects.

Map4k4 negatively regulates peroxisome proliferator-activated receptor (PPAR) gamma protein translation by suppressing the mammalian target of rapamycin (mTOR) signaling pathway in cultured adipocytes

The receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is considered a master regulator of adipocyte differentiation and promotes glucose and lipid metabolism in mature adipocytes. We recently identified the yeast Sterile 20 (Ste20) protein kinase ortholog, Map4k4, in an RNA interference-based screen as an inhibitor of PPARgamma expression in cultured adipocytes. Here, we show that RNA interference-mediated silencing of Map4k4 elevates the levels of both PPARgamma1 and PPARgamma2 proteins in 3T3-L1 adipocytes without affecting PPARgamma mRNA levels, suggesting that Map4k4 regulates PPARgamma at a post-transcriptional step. PPARgamma degradation rates are remarkably rapid as measured in the presence of cycloheximide (t(1/2) = 2 h), but silencing Map4k4 had no effect on PPARgamma degradation. However, depletion of Map4k4 significantly enhances [(35)S]methionine/cysteine incorporation into proteins, suggesting that Map4k4 signaling decreases protein translation. We show a function of Map4k4 is to inhibit rapamycin-sensitive mammalian target of rapamycin (mTOR) activity, decreasing 4E-BP1 phosphorylation. In addition, our results show mTOR and 4E-BP1 are required for the increased PPARgamma protein expression upon Map4k4 knockdown. Consistent with this concept, adenovirus-mediated expression of Map4k4 decreased PPARgamma protein levels and mTOR phosphorylation. These data show that Map4k4 negatively regulates PPARgamma post-transcriptionally, by attenuating mTOR signaling and a 4E-BP1-dependent mechanism.

Rubiae Radix suppresses the activation of mast cells through the inhibition of Syk kinase for anti-allergic activity

The effect of extracts from various Oriental medicinal herbs on mast-cell-mediated allergic reactions was investigated in this study. Of these extracts, the medicinal herb Rubiae Radix exhibited the most potent activity in the cells, with an IC50 value (concentration necessary to obtain 50% inhibition of the response) of approximately 35±2.1 μg mL−1, and its inhibition of compound-48/80-induced systemic anaphylaxis by 48.6±8.5% at 300 mg kg−1 in mice. It also inhibited the expression of the pro-inflammatory mediator tumour necrosis factor-α (TNF-α). As for its mechanism of action, Rubiae Radix suppressed the activating phosphorylation of Syk, a key enzyme in mast-cell signalling processes, and that of Akt in a dose-dependent manner. It also inhibited the MAP kinase ERK1/2, which is critical for the production of inflammatory cytokines in mast cells, as indicated by the suppression of the activating phosphorylation of ERK1/2. These results suggest that Rubiae Radix suppresses the activation of mast cells through the inhibition of Syk for antiallergic activity.

Discovery of 2-ureidophenyltriazines bearing bridged morpholines as potent and selective ATP-competitive mTOR inhibitors

Incorporation of bridged morpholines in monocyclic triazine PI3K/mTOR inhibitors gave compounds with increased mTOR selectivity relative to the corresponding morpholine analogs. Compounds with ureidophenyl groups gave highly potent and selective mTOR inhibitors. Potency and selectivity was demonstrated both in vitro and in vivo through biomarker suppression studies. Select compounds exhibited potent inhibition of tumor growth in nude mouse xenograft assays upon PO and IV administration.

[Treatment of locally advanced renal tumors]

INTRODUCTION

Locally advanced renal tumors show a high progression rate after surgery. Surgical treatment of renal tumors has some unique characteristics related to involvement of the adrenal gland, vena cava, or regional lymph nodes.

OBJECTIVE

To review the current treatment of locally advanced renal tumors.

MATERIALS AND METHODS

A review is made of both the different drugs used and the different therapeutic possibilities in these tumors.

RESULTS

Systemic treatment with angiogenesis inhibitors may improve the natural history of these patients. Systemic treatment may be administered before surgery or as an adjuvant to surgical treatment. Early studies showed a decrease in tumor mass when treatment is administered before surgery, but no prospective randomized studies providing adequate evidence for recommending neoadjuvant treatment are available.

CONCLUSIONS

Availability of systemic treatment with angiogenesis inhibitors may open an important field in the treatment of these tumors in both the neoadjuvant setting and as adjuvants to surgery, but no sufficiently solid scientific evidence as to recommend their use is currently available. Randomized studies with sunitinib and sorafenib will probably suggest the adequate approach to be used when their final results are reported.

A link between mir-100 and FRAP1/mTOR in clear cell ovarian cancer

MicroRNAs (miRNAs) are small noncoding RNAs that direct gene regulation through translational repression and degradation of complementary mRNA. Although miRNAs have been implicated as oncogenes and tumor suppressors in a variety of human cancers, functional roles for individual miRNAs have not been described in clear cell ovarian carcinoma, an aggressive and chemoresistant subtype of ovarian cancer. We performed deep sequencing to comprehensively profile miRNA expression in 10 human clear cell ovarian cancer cell lines compared with normal ovarian surface epithelial cultures and discovered 54 miRNAs that were aberrantly expressed. Because of the critical roles of the phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene homolog 1/mammalian target of rapamycin (mTOR) pathway in clear cell ovarian cancer, we focused on mir-100, a putative tumor suppressor that was the most down-regulated miRNA in our cancer cell lines, and its up-regulated target, FRAP1/mTOR. Overexpression of mir-100 inhibited mTOR signaling and enhanced sensitivity to the rapamycin analog RAD001 (everolimus), confirming the key relationship between mir-100 and the mTOR pathway. Furthermore, overexpression of the putative tumor suppressor mir-22 repressed the EVI1 oncogene, which is known to suppress apoptosis by stimulating phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene homolog 1 signaling. In addition to these specific effects, reversing the expression of mir-22 and the putative oncogene mir-182 had widespread effects on target and nontarget gene populations that ultimately caused a global shift in the cancer gene signature toward a more normal state. Our experiments have revealed strong candidate miRNAs and their target genes that may contribute to the pathogenesis of clear cell ovarian cancer, thereby highlighting alternative therapeutic strategies for the treatment of this deadly cancer.

Dual targeting of the PI3K/Akt/mTOR pathway as an antitumor strategy in Waldenstrom macroglobulinemia

We have previously shown clinical activity of a mammalian target of rapamycin (mTOR) complex 1 inhibitor in Waldenstrom macroglobulinemia (WM). However, 50% of patients did not respond to therapy. We therefore examined mechanisms of activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR in WM, and mechanisms of overcoming resistance to therapy. We first demonstrated that primary WM cells show constitutive activation of the PI3K/Akt pathway, supported by decreased expression of phosphate and tensin homolog tumor suppressor gene (PTEN) at the gene and protein levels, together with constitutive activation of Akt and mTOR. We illustrated that dual targeting of the PI3K/mTOR pathway by the novel inhibitor NVP-BEZ235 showed higher cytotoxicity on WM cells compared with inhibition of the PI3K or mTOR pathways alone. In addition, NVP-BEZ235 inhibited both rictor and raptor, thus abrogating the rictor-induced Akt phosphorylation. NVP-BEZ235 also induced significant cytotoxicity in WM cells in a caspase-dependent and -independent manner, through targeting the Forkhead box transcription factors. In addition, NVP-BEZ235 targeted WM cells in the context of bone marrow microenvironment, leading to significant inhibition of migration, adhesion in vitro, and homing in vivo. These studies therefore show that dual targeting of the PI3K/mTOR pathway is a better modality of targeted therapy for tumors that harbor activation of the PI3K/mTOR signaling cascade, such as WM.

Identifying the functional part of heparin-binding protein (HBP) as a monocyte stimulator and the novel role of monocytes as HBP producers

Heparin-binding protein (HBP), an evolutionary ancient and biologically highly important molecule in inflammation, is an inactive serine protease due to mutations in the catalytic triad. The histidine (position 41) in the conserved sequence TAAHC is mutated to serine and this sequence (TAASC) plays a crucial role when HBP binds to monocytes. We synthesized a 20-44 HBP peptide, cyclicized by a sulphur bridge, which encompasses this amino acid and functions as full-length HBP. Using a human monocyte cell line, we have shown that lipopolysaccharide (LPS)-triggered secretion of IL-6 is enhanced up to 10-fold when full-length HBP or the peptide are present in low-to-moderate concentrations. A monoclonal antibody neutralizing HBP also neutralizes the peptide, indicating that the ligand for the HBP receptor is located near serine in position 41 on the HBP surface. A 'back mutated' 20-44 peptide (serine→histidine) has some, but not significant, stimulatory effect on monocytes. Normally, HBP production and release is ascribed to neutrophil granulocytes, but here we find that also monocytes secrete HBP when stimulated with LPS. Furthermore, a small amount of HBP can be demonstrated when monocytes are incubated in medium alone. Our efforts to identify a suggested HBP receptor on monocytes has failed so far.

Functional consequences of mTOR inhibition

TOR (target of rapamycin) is a serine-threonine protein kinase that is conserved across a diverse range of species from fungi to mammals. The signaling pathway that is anchored by TOR is also conserved across species. In mammals, mTOR integrates growth factor, amino acid, nutrient and energy sensing signals, and thus plays a major role in cell growth and proliferation, protein synthesis and autophagy. As a result of the pivotal role of mTOR in signaling, the aberrant regulation of mTOR has been implicated in several disease processes, including cancer, diabetes, ocular diseases and neurodegenerative disorders, as well as in lifespan extension. More recently, rapamycin (sirolimus) analogs that antagonize the mTOR signaling pathway have been approved for the treatment of several cancers. This review describes some recent advances in the understanding of mTOR signaling, with an emphasis on the functional consequences of mTOR inhibition and therapeutic intervention strategies.

Rapamycin and CCI-779 inhibit the mammalian target of rapamycin signalling in hepatocellular carcinoma

BACKGROUND

The mammalian target of rapamycin (mTOR), which phosphorylates p70S6K and 4EBP1 and activates the protein translation process, is upregulated in cancers and its activation may be involved in cancer development.

AIMS

In this study, we investigated the tumour-suppressive effects of rapamycin and its new analogue CCI-779 on hepatocellular carcinoma (HCC).

METHODS

Rapamycin and its new analogue CCI-779 were applied to treat HCC cells. Cell proliferation, cell cycle profile and tumorigenicity were analysed.

RESULTS

In human HCCs, we observed frequent (67%, 37/55) overexpression of mTOR transcripts using real-time reverse transcriptase-polymerase chain reaction. Upon drug treatment, PLC/PRF/5 showed the greatest reduction in cell proliferation using the colony formation assay, as compared with HepG2, Hep3B and HLE. Rapamycin was a more potent antiproliferative agent than CCI-779 in HCC cell lines. Proliferation assays by cell counting showed that the IC(50) value of rapamycin was lower than that of CCI-779 in PLC/PRF/5 cells. Furthermore, flow cytometric analysis showed that both drugs could arrest HCC cells in the G(1) phase but did not induce apoptosis of these cells, suggesting that these mTOR inhibitors are cytostatic rather than cytotoxic. Upon rapamycin and CCI-779 treatment, the phosphorylation level of mTOR and p70S6K in HCC cell lines was significantly reduced, indicating that both drugs can suppress mTOR activity in HCC cells. In addition, both drugs significantly inhibited the growth of xenografts of PLC/PRF/5 cells in nude mice.

CONCLUSIONS

Our findings indicate that rapamycin and its clinical analogue CCI-779 possess tumour-suppressive functions towards HCC cells.

The role of the Akt/mTOR pathway in tobacco carcinogen-induced lung tumorigenesis

Lung cancer is the leading cause of cancer-related death in the United States, and 85 to 90% of lung cancer cases are associated with tobacco use. Tobacco components promote lung tumorigenesis through genotoxic effects, as well as through biochemical modulation of signaling pathways such as the Akt/mammalian target of rapamycin (mTOR) pathway that regulates cell proliferation and survival. This review will describe cell surface receptors and other upstream components required for tobacco carcinogen-induced activation of Akt and mTOR. Preclinical studies show that inhibitors of the Akt/mTOR pathway inhibit tumor formation in mouse models of carcinogen-induced lung tumorigenesis. Some of these inhibitors will be highlighted, and their clinical potential for the treatment and prevention of lung cancer will be discussed.

VEGF secretion by neuroendocrine tumor cells is inhibited by octreotide and by inhibitors of the PI3K/AKT/mTOR pathway

Gastroenteropancreatic (GEP) endocrine tumors are hypervascular tumors able to synthesize and secrete high amounts of VEGF. We aimed to study the regulation of VEGF production in GEP endocrine tumors and to test whether some of the drugs currently used in their treatment, such as somatostatin analogues and mTOR inhibitors, may interfere with VEGF secretion. We therefore analyzed the effects of the somatostatin analogue octreotide, the mTOR inhibitor rapamycin, the PI3K inhibitor LY294002, the MEK1 inhibitor PD98059 and the p38 inhibitor SB203850 on VEGF secretion, assessed by ELISA and Western blotting, in three murine endocrine cell lines, STC-1, INS-r3 and INS-r9. Octreotide and rapamycin induced a significant decrease in VEGF production by all three cell lines; LY294002 significantly inhibited VEGF production by STC-1 and INS-r3 only. We detected no effect of PD98059 whereas SB203850 significantly inhibited VEGF secretion in INS-r3 and INS-r9 cells only. By Western blotting analysis, we observed decreased intracellular levels of VEGF and HIF-1alpha under octreotide, rapamycin and LY294002. For rapamycin and LY294002, this effect was likely mediated by the inhibition of the mTOR/HIF-1/VEGF pathway. In addition to its well-known anti-secretory effects, octreotide may also act through the inhibition of the PI3K/Akt pathway, as suggested by the decrease in Akt phosphorylation detected in all three cell lines. In conclusion, our study points out to the complex regulation of VEGF synthesis and secretion in neoplastic GEP endocrine cells and suggests that the inhibition of VEGF production by octreotide and rapamycin may contribute to their therapeutic effects.

L-type amino acid transporter 1 inhibitors inhibit tumor cell growth

Most tumor cell membranes overexpress L-type amino acid transporter 1, while normal cell membranes contain l-type amino acid transporter 2; both are Na(+)-independent amino acid transporters. Therefore, compounds that selectively inhibit L-type amino acid transporter 1 offer researchers with a novel cancer molecular target. Synthetic chemistry efforts and in vitro screening have produced a variety of novel compounds possessing high in vitrol-type amino acid transporter 1 selectivity; KYT-0353 was one such compound. The present studies illustrate that KYT-0353 inhibited (14)C-leucine uptake and cell growth in human colon cancer-derived HT-29 cells; IC(50)s were 0.06 microm and 4.1 microm, respectively. KYT-0353 also inhibited (14)C-leucine uptake in mouse renal proximal tubule cells expressing l-type amino acid transporter 1, and inhibited cell growth; IC(50)s were 0.14 microm and 16.4 microm, respectively. Compared to control animals, intravenously administered KYT-0353 (12.5 mg/kg and 25.0 mg/kg) showed statistically significant growth inhibition against HT-29 tumors transplanted to nude mice with maximal inhibition ratios of 65.9% and 77.2%, respectively. Body weight increase with time--a safety indicator--was slightly depressed at 12.5 mg/kg and 25.0 mg/kg with maximal ratios of 3.7% (day 2) and 6.3% (day 11), respectively. Thus, KYT-0353 showed significant growth inhibitory effects on HT-29 cells both in vitro and in vivo, whereas it only caused a slight body weight depression. Therefore, KYT-0353 appears to have potential as a novel anti-tumor agent, presumably via selective in vivol-type amino acid transporter 1 inhibition.

Temsirolimus

Temsirolimus, an ester of sirolimus (rapamycin), selectively inhibits the kinase mammalian target of rapamycin and consequently blocks the translation of cell cycle regulatory proteins and prevents overexpression of angiogenic growth factors. Patients with advanced renal cell carcinoma (RCC) and a poor prognosis who received a once-weekly intravenous (IV) infusion of temsirolimus 25 mg, experienced significant survival benefits when compared with patients receiving standard interferon-alpha (IFNalpha) therapy in a large phase III clinical study. In this study, median overall survival was 10.9 vs. 7.3 months and objective response rates were 8.6% in temsirolimus recipients vs. 4.8% IFNalpha recipient group.Temsirolimus monotherapy recipients experienced significantly fewer grade 3 or 4 adverse events and had fewer withdrawals for adverse events than patients receiving IFNalpha.