Antitumor efficacy of intermittent treatment schedules with the rapamycin derivative RAD001 correlates with prolonged inactivation of ribosomal protein S6 kinase 1 in peripheral blood mononuclear cells

Everolimus restores gefitinib sensitivity in resistant non-small cell lung cancer cell lines

The epidermal growth factor receptor (EGFR) is a validated target for therapy in non-small cell lung cancer (NSCLC). Most patients, however, either do not benefit or develop resistance to specific inhibitors of the EGFR tyrosine kinase activity, such as gefitinib or erlotinib. The mammalian target of rapamycin (mTOR) is a key intracellular kinase integrating proliferation and survival pathways and has been associated with resistance to EGFR tyrosine kinase inhibitors. In this study, we assessed the effects of combining the mTOR inhibitor everolimus (RAD001) with gefitinib on a panel of NSCLC cell lines characterized by gefitinib resistance and able to maintain S6K phosphorylation after gefitinib treatment. Everolimus plus gefitinib induced a significant decrease in the activation of MAPK and mTOR signaling pathways downstream of EGFR and resulted in a growth-inhibitory effect rather than in an enhancement of cell death. A synergistic effect was observed in those cell lines characterized by high proliferative index and low doubling time. These data suggest that treatment with everolimus and gefitinib might be of value in the treatment of selected NSCLC patients that exhibit high tumor proliferative activity.

Targeting the mTOR signaling network for cancer therapy

The serine-threonine kinase mammalian target of rapamycin (mTOR) plays a major role in the regulation of protein translation, cell growth, and metabolism. Alterations of the mTOR signaling pathway are common in cancer, and thus mTOR is being actively pursued as a therapeutic target. Rapamycin and its analogs (rapalogs) have proven effective as anticancer agents in a broad range of preclinical models. Clinical trials using rapalogs have demonstrated important clinical benefits in several cancer types; however, objective response rates achieved with single-agent therapy have been modest. Rapalogs may be more effective in combination with other anticancer agents, including chemotherapy and targeted therapies. It is increasingly apparent that the mTOR signaling network is quite complex, and rapamycin treatment leads to different signaling responses in different cell types. A better understanding of mTOR signaling, the mechanism of action of rapamycin, and the identification of biomarkers of response will lead to more optimal targeting of this pathway for cancer therapy.

Novel therapeutic strategy for breast cancer: mammalian target of rapamycin inhibition

BACKGROUND

Mammalian target of rapamycin (mTOR) plays a central role in regulating cellular protein synthesis. Dysregulation of mTOR signaling pathway is strongly associated with tumorigenesis, angiogenesis, tumor progression and drug resistance. Inhibition of mTOR might not only promote cell cycle arrest, but also sensitize resistant cancer cells to chemotherapeutic and other targeted agents.

OBJECTIVE

To review and summarize the mechanism of mTOR on regulation of protein synthesis and latest clinical data, and to discuss the novel therapeutic strategy for the use of mTOR inhibitors in the treatment of breast cancer.

METHODS

A review of published literatures and conference abstracts obtained from MEDLINE, American Society of Clinical Oncology Meeting and San Antonio Breast Cancer Symposia proceedings for results of previous preclinical and latest clinical studies of mTOR inhibition in breast cancer was performed.

CONCLUSIONS

mTOR inhibitors seemed to be potentially useful for the treatment of breast cancer with acceptable safety profile. The challenge remains the identification of suitable candidates with different phenotypes. More structured studies incorporating molecular, clinical and translational research need to be initiated. Future research on mTOR inhibitors for breast cancer should focus on the evaluation of optimal schedule, patient selection and combination strategies to maximize the use of this new class of targeted agents.

Increased AKT S473 phosphorylation after mTORC1 inhibition is rictor dependent and does not predict tumor cell response to PI3K/mTOR inhibition

Mammalian target of rapamycin (mTOR) regulates cellular processes important for progression of human cancer. RAD001 (everolimus), an mTORC1 (mTOR/raptor) inhibitor, has broad antitumor activity in preclinical models and cancer patients. Although most tumor lines are RAD001 sensitive, some are not. Selective mTORC1 inhibition can elicit increased AKT S473 phosphorylation, involving insulin receptor substrate 1, which is suggested to potentially attenuate effects on tumor cell proliferation and viability. Rictor may also play a role because rictor kinase complexes (including mTOR/rictor) regulate AKT S473 phosphorylation. The role of raptor and rictor in the in vitro response of human cancer cells to RAD001 was investigated. Using a large panel of cell lines representing different tumor histotypes, the basal phosphorylation of AKT S473 and some AKT substrates was found to correlate with the antiproliferative response to RAD001. In contrast, increased AKT S473 phosphorylation induced by RAD001 did not correlate. Similar increases in AKT phosphorylation occurred following raptor depletion using siRNA. Strikingly, rictor down-regulation attenuated AKT S473 phosphorylation induced by mTORC1 inhibition. Further analyses showed no relationship between modulation of AKT phosphorylation on S473 and T308 and AKT substrate phosphorylation patterns. Using a dual pan-class I phosphatidylinositol 3-kinase/mTOR catalytic inhibitor (NVP-BEZ235), currently in phase I trials, concomitant targeting of these kinases inhibited AKT S473 phosphorylation, eliciting more profound cellular responses than mTORC1 inhibition alone. However, reduced cell viability could not be predicted from biochemical or cellular responses to mTORC1 inhibitors. These data could have implications for the clinical application of phosphatidylinositol 3-kinase/mTOR inhibitors.

S9, a novel anticancer agent, exerts its anti-proliferative activity by interfering with both PI3K-Akt-mTOR signaling and microtubule cytoskeleton

BACKGROUND

Deregulation of the phosphatidylinositol 3-kinases (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway plays a central role in tumor formation and progression, providing validated targets for cancer therapy. S9, a hybrid of alpha-methylene-gamma-lactone and 2-phenyl indole compound, possessed potent activity against this pathway.

METHODOLOGY/PRINCIPAL FINDINGS

Effects of S9 on PI3K-Akt-mTOR pathway were determined by Western blot, immunofluorescence staining and in vitro kinas assay. The interactions between tubulin and S9 were investigated by polymerization assay, CD, and SPR assay. The potential binding modes between S9 and PI3K, mTOR or tubulin were analyzed by molecular modeling. Anti-tumor activity of S9 was evaluated in tumor cells and in nude mice bearing human cancer xenografts. S9 abrogated EGF-activated PI3K-Akt-mTOR signaling cascade and Akt translocation to cellular membrane in human tumor cells. S9 possessed inhibitory activity against both PI3K and mTOR with little effect on other tested 30 kinases. S9 also completely impeded hyper-phosphorylation of Akt as a feedback of inhibition of mTOR by rapamycin. S9 unexpectedly arrested cells in M phase other than G1 phase, which was distinct from compounds targeting PI3K-Akt-mTOR pathway. Further study revealed that S9 inhibited tubulin polymerization via binding to colchicine-binding site of tubulin and resulted in microtubule disturbance. Molecular modeling indicated that S9 could potentially bind to the kinase domains of PI3K p110alpha subunit and mTOR, and shared similar hydrophobic interactions with colchicines in the complex with tubulin. Moreover, S9 induced rapid apoptosis in tumor cell, which might reflect a synergistic cooperation between blockade of both PI3-Akt-mTOR signaling and tubulin cytoskeleton. Finally, S9 displayed potent antiproliferative activity in a panel of tumor cells originated from different tissue types including drug-resistant cells and in nude mice bearing human tumor xenografts.

CONCLUSIONS/SIGNIFICANCE

Taken together, S9 targets both PI3K-Akt-mTOR signaling and microtubule cytoskeleton, which combinatorially contributes its antitumor activity and provides new clues for anticancer drug design and development.

Phase II trial of temsirolimus in patients with relapsed or refractory multiple myeloma

In a phase II trial, 16 patients with relapsed refractory multiple myeloma received temsirolimus 25mg I.V. weekly until progression. One partial response and 5 minor responses were observed for a total response rate of 38%. The median time to progression was 138 days. Grade 3-4 toxicity included fatigue (n=3), neutropenia (n=2), thrombocytopenia (n=2), interstitial pneumonitis (n=1), stomatitis (n=1) and diarrhea (n=1). Clinical activity was associated with a higher area under the curve (AUC) and maximal reduction in phosphorylated p70(S6)K and 4EBP1 in peripheral blood mononuclear cells. At the dose and schedule used, temsirolimus had low single agent activity. Investigation of alternate dosing schedules and use in combinations is indicated.

PI3K inhibitors for cancer treatment: where do we stand?

In contrast with cytotoxic agents that do not differentiate between normal proliferating and tumour cells, targeted therapies primarily exert their actions in cancer cells. Initiation and maintenance of tumours are due to genetic alterations in specific loci. The identification of the genes in which these alterations occur has opened new opportunities for cancer treatment. The PI3K (phosphoinositide 3-kinase) pathway is often overactive in human cancers, and various genetic alterations have been found to cause this. In all cases, PI3K inhibition is considered to be one of the most promising targeted therapies for cancer treatment. The present mini-review provides an update on new PI3K inhibitors currently in or entering clinical development. Recent discoveries, challenges and future prospects will be discussed.

Safety and pharmacokinetics of paclitaxel and the oral mTOR inhibitor everolimus in advanced solid tumours

Everolimus displays antiproliferative effects on cancer cells, yields antiangiogenic activity in established tumours, and shows synergistic activity with paclitaxel in preclinical models. This study assessed the safety and the pharmacokinetic interactions of everolimus and paclitaxel in patients with advanced malignancies. Everolimus was dose escalated from 15 to 30 mg and administered with paclitaxel 80 mg m⁻² on days 1, 8, and 15 every 28 days. Safety was assessed weekly, and dose-limiting toxicity (DLT) was evaluated in cycle 1. A total of 16 patients (median age 54.5 years, range 33–69) were entered; 11 had prior taxane therapy for breast (n=5), ovarian (n=3), and vaginal cancer (n=1) or angiosarcoma (n=2). Grade 3 neutropenia in six patients met the criteria for DLT in two patients receiving everolimus 30 mg weekly. Other drug-related grade 3 toxicities were leucopenia, anaemia, thrombocytopenia, stomatitis, asthenia, and increased liver enzymes. Tumour stabilisation reported in 11 patients exceeded 6 months in 2 patients with breast cancer. Everolimus showed an acceptable safety profile at the dose of 30 mg when combined with weekly paclitaxel 80 mg m⁻², warranting further clinical investigation.

The von Hippel-Lindau gene: turning discovery into therapy

Mutations or aberrations of the von Hippel-Lindau gene are responsible for the hereditary neoplastic syndrome that bears the same name, as well as for the majority of sporadic clear cell renal cell carcinomas. The discovery of this gene and subsequent clarification of its mechanism of action have led to a series of targeted treatments for advanced kidney cancer and have dramatically changed how we manage this disease. The discovery of the VHL gene is a prime example of how discoveries at the bench can inform and revolutionize therapeutics at the bedside. In this review, the authors trace this illuminating tale, from the cloning of the VHL gene, to elucidating its biologic function, to the development of novel therapeutics that have dramatically changed the paradigm of managing advanced renal cell carcinoma.

Effects of the dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 on the tumor vasculature: implications for clinical imaging

Dysregulated angiogenesis and high tumor vasculature permeability, two vascular endothelial growth factor (VEGF)-mediated processes and hallmarks of human tumors, are in part phosphatidylinositol 3-kinase (PI3K) dependent. NVP-BEZ235, a dual PI3K/mammalian target of rapamycin (mTOR) inhibitor, was found to potently inhibit VEGF-induced cell proliferation and survival in vitro and VEGF-induced angiogenesis in vivo as shown with s.c. VEGF-impregnated agar chambers. Moreover, the compound strongly inhibited microvessel permeability both in normal tissue and in BN472 mammary carcinoma grown orthotopically in syngeneic rats. Similarly, tumor interstitial fluid pressure, a phenomenon that is also dependent of tumor permeability, was significantly reduced by NVP-BEZ235 in a dose-dependent manner on p.o. administration. Because RAD001, a specific mTOR allosteric inhibitor, was ineffective in the preceding experiments, we concluded that the effects observed for NVP-BEZ235 are in part driven by PI3K target modulation. Hence, tumor vasculature reduction was correlated with full blockade of endothelial nitric oxide (NO) synthase, a PI3K/Akt-dependent but mTORC1-independent effector involved in tumor permeability through NO production. In the BN472 tumor model, early reduction of permeability, as detected by K(trans) quantification using the dynamic contrast-enhanced magnetic resonance imaging contrasting agent P792 (Vistarem), was found to be a predictive marker for late-stage antitumor activity by NVP-BEZ235.

RAD001 (Everolimus) inhibits growth of prostate cancer in the bone and the inhibitory effects are increased by combination with docetaxel and zoledronic acid

INTRODUCTION

mTOR activity is increased in advanced prostate cancer (CaP) as a result of a high rate of PTEN mutations. RAD001 (Everolimus) is a new orally available mTOR inhibitor. The objective of our study was to evaluate the effects of RAD001 on the growth of CaP in the bone, both alone and in combination with docetaxel and zoledronic acid.

METHODS

C4-2 CaP cells were injected into tibiae of mice and the animals were treated with RAD001, docetaxel, and zoledronic acid alone or in combination. Histomorphometrical analysis, serum PSA measurements, bone mineral density (BMD), and microCT were used to determine the effects of treatment on tumor and bone.

RESULTS

All three agents alone decreased tumor volume, and RAD001 and docetaxel also decreased levels of serum PSA by 68% and 65%, respectively (both P < 0.01). Combinations of the agents were more effective in decreasing tumor volume than single agents. Three-drug treatment showed the greatest effect: 64% inhibition versus control (P < 0.01). Treatment with RAD001 interfered with the weight loss associated with growth of this tumor in the bone (non-RAD001 groups: 4.0% decrease in body weight, P = 0.0014; RAD001 groups: increase of 3.6% in body weight, P = 0.0037).

CONCLUSIONS

RAD001 inhibited growth of C4-2 cells in bone, an effect augmented by addition of docetaxel and zoledronic acid. Moreover RAD001 had a significant impact on maintenance of body weight. RAD001 may hold promise for its effects on both metastatic CaP and the important syndrome of tumor cachexia.

The potential role of mTOR inhibitors in non-small cell lung cancer

The mammalian target of rapamycin (mTOR), a serine/threonine kinase, is a downstream mediator in the phosphatidylinositol 3-kinase/Akt signaling pathway, which plays a critical role in regulating basic cellular functions including cellular growth and proliferation. Currently, the mTOR inhibitor rapamycin and its analogues (CCI-779, RAD001, AP23573), which induce cell-cycle arrest in the G(1) phase, are being evaluated in cancer clinical trials. The mTOR inhibitors appear to be well tolerated, with skin reactions, stomatitis, myelosuppression, and metabolic abnormalities the most common toxicities seen. These adverse events are transient and reversible with interruption of dosing. Several pieces of evidence suggest a certain antitumor activity, including tumor regressions and prolonged stable disease, which has been reported among patients with a variety of malignancies, including non-small cell lung cancer (NSCLC). These promising preliminary clinical data have stimulated further research in this setting. Here, we review the basic structure of the pathway together with current results and future developments of mTOR inhibitors in the treatment of NSCLC patients.

Rapamycin and mTOR kinase inhibitors

Mammalian target of rapamycin (mTOR) is a protein kinase that controls cell growth, proliferation, and survival. mTOR signaling is often upregulated in cancer and there is great interest in developing drugs that target this enzyme. Rapamycin and its analogs bind to a domain separate from the catalytic site to block a subset of mTOR functions. These drugs are extremely selective for mTOR and are already in clinical use for treating cancers, but they could potentially activate an mTOR-dependent survival pathway that could lead to treatment failure. By contrast, small molecules that compete with ATP in the catalytic site would inhibit all of the kinase-dependent functions of mTOR without activating the survival pathway. Several non-selective mTOR kinase inhibitors have been described and here we review their chemical and cellular properties. Further development of selective mTOR kinase inhibitors holds the promise of yielding potent anticancer drugs with a novel mechanism of action.

RAD001 (everolimus) inhibits tumour growth in xenograft models of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common malignancy worldwide and highly resistant to available chemotherapies. Mammalian target of rapamycin (mTOR) functions to regulate protein translation, angiogenesis and cell cycle progression in many cancers including HCC. In the present study, subcutaneous patient-derived HCC xenografts were used to study the effects of an mTOR inhibitor, RAD001 (everolimus), on tumour growth, apoptosis and angiogenesis. We report that oral administration of RAD001 to mice bearing patient-derived HCC xenografts resulted in a dose-dependent inhibition of tumour growth. RAD001-induced growth suppression was associated with inactivation of downstream targets of mTOR, reduction in VEGF expression and microvessel density, inhibition of cell proliferation, up-regulation of p27(Kip1) and down-regulation of p21(Cip1/Waf1), Cdk-6, Cdk-2, Cdk-4, cdc-25C, cyclin B1 and c-Myc. Our data indicate that the mTOR pathway plays an important role in angiogenesis, cell cycle progression and proliferation of liver cancer cells. Our study provides a strong rationale for clinical investigation of mTOR inhibitor RAD001 in patients with HCC.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

Molecular target therapies in endometrial cancer: from the basic research to the clinic

Molecular targeted therapies represent an interesting field of pharmacological research in endometrial cancer. The loss of PTEN (phosphatase and tensin homolog deleted on chromosome 10) function, with consequent activation of the PI3K (phosphatidylinositol-3-kinase)-AKT (serine/threonine-specific protein kinase)-mTOR (mammalian target of rapamycin) signaling pathway, occurs in 32-83% of endometrioid-type endometrial carcinomas, thus suggesting a role for mTOR inhibition in this malignancy. Some analogues of rapamycin (CCI-799, RAD-001, AP-23573) have been developed and tested in different tumors including endometrioid-type endometrial carcinoma. For example, AP-23573 achieved a clinical benefit response in 33% of 27 heavily pretreated patients, and CCI-799 obtained a 26% partial response rate and a 63% stable disease rate in 19 patients. Overexpression of ErbB-2 (epidermal growth factor type II receptor) has been detected in 18-80% of uterine papillary serous carcinomas (UPSCs), thus providing a biological rationale for the use of trastuzumab in these aggressive tumors. UPSC often overexpresses claudin-3 and claudin-4, which represent the epithelial receptors for Clostridium perfringens enterotoxin (CPE). CPE-mediated therapy might be a novel treatment modality for UPSC resistant to chemotherapy. A better understanding of the signaling transduction pathways that are dysregulated in endometrioid-type endometrial carcinoma and UPSC will allow the development of novel molecular targeted therapies.

TGF-beta signalling-related markers in cancer patients with bone metastasis

We measured transforming growth factor (TGF)-beta-dependent biomarkers in plasma and in peripheral blood mononuclear cells (PBMCs) to identify suitable pharmacodynamic markers for future clinical trials with TGF-beta inhibitors. Forty-nine patients with bone metastasis were enrolled in the study, including patients with breast (n=23) and prostate cancer (n=15). Plasma TGF-beta1 levels were elevated in more than half of the cancer patients (geometric mean 2.63 ng ml(-1)) and positively correlated with increased platelet factor 4 (PF4) levels, parathyroid-related protein (PTHrP), von Willebrand Factor (vWF) and interleukin (IL)-10. PBMC were stimulated ex vivo to determine the individual biological variability of an ex vivo assay measuring pSMAD expression. This assay performed sufficiently well to allow its future use in a clinical trial of a TGF-beta inhibitor.

Phase I pharmacokinetic and pharmacodynamic study of the oral mammalian target of rapamycin inhibitor everolimus in patients with advanced solid tumors

PURPOSE

To identify the optimal regimen and dosage of the oral mammalian target of rapamycin inhibitor everolimus (RAD001).

METHODS

We performed a dose-escalation study in advanced cancer patients administering oral everolimus 5 to 30 mg/wk, with pharmacokinetic (PK) and pharmacodynamic (PD) studies. PD data prompted investigation of 50 and 70 mg weekly and daily dosing at 5 and 10 mg.

RESULTS

Ninety-two patients were treated. Dose-limiting toxicity was seen in one patient each at 50 mg/wk (stomatitis and fatigue) and 10 mg/d (hyperglycemia); hence, the maximum-tolerated dose was not reached. S6 kinase 1 activity in peripheral-blood mononuclear cells was inhibited for at least 7 days at doses >or= 20 mg/wk. Area under the curve increased proportional to dose, but maximum serum concentration increased less than proportionally at doses >or= 20 mg/wk. Terminal half-life was 30 hours (range, 26 to 38 hours). Partial responses were observed in four patients, and 12 patients remained progression free for >or= 6 months, including five of 10 patients with renal cell carcinoma.

CONCLUSION

Everolimus was satisfactorily tolerated at dosages up to 70 mg/wk and 10 mg/d with predictable PK. Antitumor activity and PD in tumors require further clinical investigation. Doses of 20 mg/wk and 5 mg/d are recommended as appropriate starting doses for these studies.

Identifying optimal biologic doses of everolimus (RAD001) in patients with cancer based on the modeling of preclinical and clinical pharmacokinetic and pharmacodynamic data

PURPOSE

To use preclinical and clinical pharmacokinetic (PK)/pharmacodynamic (PD) modeling to predict optimal clinical regimens of everolimus, a novel oral mammalian target of rapamycin (mTOR) inhibitor, to carry forward to expanded phase I with tumor biopsy studies in cancer patients.

PATIENTS AND METHODS

Inhibition of S6 kinase 1 (S6K1), a molecular marker of mTOR signaling, was selected for PD analysis in peripheral blood mononuclear cells (PBMCs) in a phase I clinical trial. PK and PD were measured up to 11 days after the fourth weekly dose. A PK/PD model was used to describe the relationship between everolimus concentrations and S6K1 inhibition in PBMCs of cancer patients and in PBMCs and tumors of everolimus-treated CA20948 pancreatic tumor-bearing rats.

RESULTS

Time- and dose-dependent S6K1 inhibition was demonstrated in human PBMCs. In the rat model, a relationship was shown between S6K1 inhibition in tumors or PBMCs and antitumor effect. This allowed development of a direct-link PK/PD model that predicted PBMC S6K1 inhibition-time profiles in patients. Comparison of rat and human profiles simulated by the model suggested that a weekly 20- to 30-mg dose of everolimus would be associated with an antitumor effect in an everolimus-sensitive tumor and that daily administration would exert a greater effect than weekly administration at higher doses.

CONCLUSION

A direct-link PK/PD model predicting the time course of S6K1 inhibition during weekly and daily everolimus administration allowed extrapolation from preclinical studies and first clinical results to select optimal doses and regimens of everolimus to explore in future clinical trials.

Dose- and schedule-dependent inhibition of the mammalian target of rapamycin pathway with everolimus: a phase I tumor pharmacodynamic study in patients with advanced solid tumors

PURPOSE

Everolimus is a selective mammalian target of rapamycin (mTOR) inhibitor with promising anticancer activity. In order to identify a rationally based dose and schedule for cancer treatment, we have conducted a tumor pharmacodynamic phase I study in patients with advanced solid tumors.

PATIENTS AND METHODS

Fifty-five patients were treated with everolimus in cohorts of 20, 50, and 70 mg weekly or 5 and 10 mg daily. Dose escalation depended on dose limiting toxicity (DLT) rate during the first 4-week period. Pre- and on-treatment steady-state tumor and skin biopsies were evaluated for total and phosphorylated (p) protein S6 kinase 1, eukaryotic initiation factor 4E (elF-4E) binding protein 1 (4E-BP1), eukaryotic initiation factor 4G (eIF-4G), AKT, and Ki-67 expression. Plasma trough levels of everolimus were determined on a weekly basis before dosing during the first 4 weeks.

RESULTS

We observed a dose- and schedule-dependent inhibition of the mTOR pathway with a near complete inhibition of pS6 and peIF-4G at 10 mg/d and >or= 50 mg/wk. In addition, pAKT was upregulated in 50% of the treated tumors. In the daily schedule, there was a correlation between everolimus plasma trough concentrations and inhibition of peIF4G and p4E-BP1. There was good concordance of mTOR pathway inhibition between skin and tumor. Clinical benefit was observed in four patients including one patient with advanced colorectal cancer achieving a partial response. DLTs occurred in five patients: one patient at 10 mg/d (grade 3 stomatitis) and four patients at 70 mg/wk (two with grade 3 stomatitis, one with grade 3 neutropenia, and one with grade 3 hyperglycemia).

CONCLUSION

Everolimus achieved mTOR signaling inhibition at doses below the DLT. A dosage of 10 mg/d or 50 mg/wk is recommended for further development.

Inhibition of mTOR pathway by everolimus cooperates with EGFR inhibitors in human tumours sensitive and resistant to anti-EGFR drugs

Inhibition of a single transduction pathway is often inefficient due to activation of alternative signalling. The mammalian target of rapamycin (mTOR) is a key intracellular kinase integrating proliferation, survival and angiogenic pathways and has been implicated in the resistance to EGFR inhibitors. Thus, mTOR blockade is pursued to interfere at multiple levels with tumour growth. We used everolimus (RAD001) to inhibit mTOR, alone or in combination with anti-EGFR drugs gefitinib or cetuximab, on human cancer cell lines sensitive and resistant to EGFR inhibitors, both in vitro and in vivo. We demonstrated that everolimus is active against EGFR-resistant cancer cell lines and partially restores the ability of EGFR inhibitors to inhibit growth and survival. Everolimus reduces the expression of EGFR-related signalling effectors and VEGF production, inhibiting proliferation and capillary tube formation of endothelial cells, both alone and in combination with gefitinib. Finally, combination of everolimus and gefitinib inhibits growth of GEO and GEO-GR (gefitinib resistant) colon cancer xenografts, activation of signalling proteins and VEGF secretion. Targeting mTOR pathway with everolimus overcomes resistance to EGFR inhibitors and produces a cooperative effect with EGFR inhibitors, providing a valid therapeutic strategy to be tested in a clinical setting.

Pharmacokinetic profile of the microtubule stabilizer patupilone in tumor-bearing rodents and comparison of anti-cancer activity with other MTS in vitro and in vivo

INTRODUCTION

Patupilone is a microtubule stabilizer (MTS) currently in clinical development. Here, we evaluate the anti-cancer activity in vitro and in vivo in comparison to paclitaxel and describe the pharmacokinetics (PK) of patupilone in tumor-bearing nude mice and rats.

METHODS

The potency in vitro of patupilone and two other MTS, paclitaxel and ixabepilone, was determined using human colon carcinoma cell lines with low (HCT-116, HT-29, RKO) and high (HCT-15) P-glycoprotein expression (P-gp), as well as two multi-drug resistance (MDR) model cell pairs, MCF7/ADR and KB-8511 cells and their respective drug-sensitive parental counterparts. The PK of patupilone was investigated in nude mice bearing HCT-15 or HT-29 xenografts and in rats bearing s.c. pancreatic CA20498 tumors or A15 glioma tumors. Anti-cancer activity in vivo was compared to that of paclitaxel using three different human tumor colon models. The retention and efficacy of patupilone was compared in small and large HT-29 xenografts whose vascularity was determined by non-invasive magnetic resonance imaging.

RESULTS

Patupilone was highly potent in vitro against four different colon carcinoma cell lines including those showing multi-drug-resistance. In contrast, paclitaxel and ixabepilone displayed significantly reduced activity with markedly increased resistance factors. In both rats and mice, a single i.v. bolus injection of patupilone (1.5-4 mg/kg) rapidly distributed from plasma to all tissues and was slowly eliminated from muscle, liver and small intestine, but showed longer retention in tumor and brain with no apparent elimination over 24 h. Patupilone showed significant activity against three human colon tumor models in vivo, unlike paclitaxel, which only had activity against low P-gp expressing tumors. In HT-29 tumors, patupilone activity and retention were independent of tumor size, blood volume and flow.

CONCLUSIONS

The high potency of patupilone, which is not affected by P-gp expression either in vitro or in vivo, and favorable PK, independent of tumor vascularity, suggest that it should show significant activity in colorectal cancer and in other indications where high P-gp expression may compromise taxane activity.

Low-scale phosphoproteome analyses identify the mTOR effector p70 S6 kinase 1 as a specific biomarker of the dual-HER1/HER2 tyrosine kinase inhibitor lapatinib (Tykerb) in human breast carcinoma cells

BACKGROUND

Discovery of key proliferative and/or survival cascades closely linked to the biological effects of human epidermal growth factor receptor (HER) 1 (erbB-1) and/or HER2 (erbB-2) inhibitors may identify a priori mechanisms responsible for the development of acquired resistance in breast cancer disease. Here, we took advantage of a semiquantitative protein array technology to identify intracellular oncogenic kinases that distinctively correlate with breast cancer cell sensitivity/resistance to the dual-HER1/HER2 tyrosine kinase inhibitor lapatinib (Tykerb(R)).

MATERIALS AND METHODS

MCF-7 cells were forced to overexpress HER2 following stable transduction with pBABE-HER2 retroviruses. The Human Phospho-MAPK Array Proteome Profilertrade mark (R&D Systems) was used to molecularly assess the effects of both the mono-HER2 inhibitor trastuzumab (Herceptintrade mark) and the dual-HER1/HER2 inhibitor lapatinib on 21 different oncogenic kinases. A model of acquired resistance to lapatinib (MCF-7/HER2-Lap10 cells) was established by chronically exposing MCF-7/HER2 cells to increasing concentrations of lapatinib for >10 months.

RESULTS

Treatment of MCF-7/HER2 cells with either trastuzumab or lapatinib similarly impaired HER2-enhanced activation status (i.e. phosphorylation) of the mitogen-activated protein kinases, c-Jun N-terminal kinases 1-3 and p38alpha/beta/gamma/delta and of the serine/threonine kinases AKT, glycogen synthase kinase-3, p90 ribosomal s6 kinase1/2, and mitogen- and stress-activated protein kinase1/2. Trastuzumab was less effective than lapatinib at blocking extracellular-signal regulated kinase (ERK) 1/2 and, notably, it failed to deactivate the mammalian target of rapamycin (mTOR) effector p70S6K1. Conversely, lapatinib treatment caused a drastic decrease in the phosphorylation of p70S6K1 at ERK1/2-regulated sites (Thr(421)/Ser(424)) and, as a consequence, p70S6K1 activity measured by its phospho-Thr(389) levels was abolished. The mTOR inhibitor rapamycin was found to supraadditively increase lapatinib efficacy in MCF-7/HER2 cells [ approximately 10-fold enhancement; combination index (CI(50)) = 0.243 < 1.0 = additivity, P < 0.001] but not in p70S6K1 gene-amplified MCF-7 parental cells ( approximately 1.3-fold enhancement; CI(50) = 0.920 congruent with 1.0 = additivity). Lapatinib-resistant MCF-7/HER2-Lap10 cells, which are capable of growing in the continuous presence of 10 microM lapatinib without significant effects on cell viability, notably exhibited a lapatinib-insensitive hyperphosphorylation of p70S6K1. Rapamycin cotreatment suppressed p70S6K1 hyperactivation and synergistically resensitized MCF-7/HER2-Lap10 cells to lapatinib (>20-fold increase in lapatinib-induced cytotoxicity; CI(50) = 0.175 < 1.0 = additivity).

CONCLUSIONS

Serine-threonine kinase p70S6K1, a marker for mTOR activity that regulates protein translation, constitutes a specific biomarker for the biological effects of the dual-HER1/HER2 inhibitor lapatinib. The clinical implications of our data are that the efficacy of lapatinib might be enhanced with therapies that target the mTOR pathway. Rapamycin analogues such as CCI-779 (Temsirolimus) and RAD001 (Everolimus) may warrant further clinical evaluation to effectively delay or prevent the development of acquired resistance to lapatinib in HER2-positive breast cancer patients.

mTOR signalling in human cancer

Inhibitors of mTOR, the mammalian target of rapamycin, have been extensively studied in clinical trials for cancer treatment. Results have been promising, mostly in certain lymphomas, but in solid tumours the results have been generally less encouraging. However, recent results, particularly in renal cell carcinoma, have provided renewed interest in the role of mTOR inhibitors in solid tumours. A rational, and potentially more successful, development of these agents (i.e., RAD001, temsirolimus and AP23573) likely relies in a deeper knowledge of mTOR signalling in cancer, both at the preclinical and clinical levels. These would allow a better selection of patients more likely to respond to the use of biologically active doses of the agents and the development of mechanistically based combinations with other agents. The goal of this review is to provide an update on the complex signalling of mTOR in cancer and on the biological effects of mTOR inhibitors in cancer cells.

Tumour suppressors in liver carcinogenesis

The circuitous cell signalling pathways of hepatocytes comprise several factors that operate to downgrade or even interrupt the transmission of a given signal. These down-regulating influences are essential to keep cell proliferation and cell survival in check and if impaired, can alter a delicate balance in favour of cell proliferation. Each signalling pathway that has been implicated in carcinogenesis is influenced by both oncogenic factors that promote tumour growth when activated as well as tumour suppressor proteins that have to be impaired to favour tumour growth. This summary of the Tumour Suppressors in Liver Carcinogenesis Symposium held at the 2007 EASL Annual Meeting discusses four pathways with pre-eminent tumour suppressor activity, each involved in hepatocarcinogenesis: p53, mTOR, beta-catenin and hedgehog.

Phase I/II study of the mammalian target of rapamycin inhibitor everolimus (RAD001) in patients with relapsed or refractory hematologic malignancies

PURPOSE

Everolimus (RAD001, Novartis), an oral derivative of rapamycin, inhibits the mammalian target of rapamycin (mTOR), which regulates many aspects of cell growth and division. A phase I/II study was done to determine safety and efficacy of everolimus in patients with relapsed or refractory hematologic malignancies.

EXPERIMENTAL DESIGN

Two dose levels (5 and 10 mg orally once daily continuously) were evaluated in the phase I portion of this study to determine the maximum tolerated dose of everolimus to be used in the phase II study.

RESULTS

Twenty-seven patients (9 acute myelogenous leukemia, 5 myelodysplastic syndrome, 6 B-chronic lymphocytic leukemia, 4 mantle cell lymphoma, 1 myelofibrosis, 1 natural killer cell/T-cell leukemia, and 1 T-cell prolymphocytic leukemia) received everolimus. No dose-limiting toxicities were observed. Grade 3 potentially drug-related toxicities included hyperglycemia (22%), hypophosphatemia (7%), fatigue (7%), anorexia (4%), and diarrhea (4%). One patient developed a cutaneous leukocytoclastic vasculitis requiring a skin graft. One patient with refractory anemia with excess blasts achieved a major platelet response of over 3-month duration. A second patient with refractory anemia with excess blasts showed a minor platelet response of 25-day duration. Phosphorylation of downstream targets of mTOR, eukaryotic initiation factor 4E-binding protein 1, and/or, p70 S6 kinase, was inhibited in six of nine patient samples, including those from the patient with a major platelet response.

CONCLUSIONS

Everolimus is well tolerated at a daily dose of 10 mg daily and may have activity in patients with myelodysplastic syndrome. Studies of everolimus in combination with therapeutic agents directed against other components of the phosphatidylinositol 3-kinase/Akt/mTOR pathway are warranted.

Exploiting novel molecular targets in gastrointestinal cancers

Novel molecular targets are being discovered as we learn more about the aberrant processes underlying various cancers. Efforts to translate this knowledge are starting to impact on the care of patients with gastrointestinal cancers. The epidermal growth factor receptor (EGFR) pathway and angiogenesis have been targeted successfully in colorectal cancer with cetuximab, panitunumab and bevacizumab. Similarly, EGFR-targeting with erlotinib yielded significant survival benefit in pancreatic cancer when combined with gemcitabine. The multi-targeting approach with sorafenib has made it the first agent to achieve significant survival benefit in hepatocellular carcinoma. Efforts to exploit the dysregulated Akt/mTOR pathway in GI cancer therapy are ongoing. These molecular targets can be disrupted by various approaches, including the use of monoclonal antibody to intercept extracellular ligands and disrupt receptor-ligand binding, and small molecule inhibitors that interrupt the activation of intracellular kinases.

Phase I study of everolimus in pediatric patients with refractory solid tumors

PURPOSE

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities (DLTs), and pharmacokinetic and pharmacodynamic properties of the mammalian target of rapamycin (mTOR) inhibitor, everolimus, in children with refractory or recurrent solid tumors.

PATIENTS AND METHODS

Everolimus was administered orally at a daily dose of 2.1, 3, 5, or 6.5 mg/m2 in cohorts of three to six patients per dosage level. Pharmacokinetic and pharmacodynamic studies were performed during the first course. The phosphorylation status of various components of the mTOR signal pathway was assessed in peripheral-blood mononuclear cells (PBMCs) isolated from treated patients.

RESULTS

There were 26 patients enrolled; 18 were assessable. DLTs included diarrhea (n = 1), mucositis (n = 1), and elevation of ALT (n = 1) at 6.5 mg/m2. At the MTD of 5 mg/m2, the median everolimus clearance was 15.2 L/h/m2, with a plasma everolimus concentration-time area under the curve (AUC) from 0 to infinity of 239.6 ng/mL x h. Significant inhibition of mTOR pathway signaling was observed in PBMCs from patients achieving AUCs 200 ng/mL x h, equivalent to dosages of 3 to 5 mg/m2 of everolimus. No objective tumor responses were observed.

CONCLUSION

Continuous, orally administered everolimus is well tolerated in children with recurrent or refractory solid tumors and demonstrates similar pharmacokinetic properties to those observed in adults. Everolimus significantly inhibits the mTOR signaling pathway in children at the MTD. The recommended phase II dose in children with solid tumors is 5 mg/m2.

Phase I trial of sirolimus combined with radiation and cisplatin in non-small cell lung cancer

PURPOSE

The safety and tolerability of sirolimus combined with thoracic radiation and cisplatin was evaluated in patients with lung cancer. In parallel, the effects of sirolimus were studied in a murine model of radiation pneumonitis.

MATERIALS AND METHODS

The phase I trial evaluated standard three-dimensional conformal thoracic radiation therapy (60 Gy) and weekly cisplatin (25 mg/m2 i.v.) in combination with escalating doses of oral sirolimus. Sirolimus drug levels and inhibition of mTOR signaling to ribosomal S6 protein were assessed in blood. The effects of sirolimus administered during and after whole thoracic radiation of C57BL6/J mice were evaluated by monitoring mouse breathing rates and survival.

RESULTS

Seven patients with stage III lung cancer were accrued to the clinical study. None of the four patients treated with 2 mg/day sirolimus developed dose-limiting toxicities. Three patients were treated with 5 mg/day sirolimus, and one patient at this dose level had dose-limiting toxicity of grade 3 dysphagia. However, the maximally tolerated dose of sirolimus in this regimen was not defined because the study was terminated prematurely because of loss of funding. In the mouse experiments, concomitant sirolimus treatment was not associated with an increase in radiation-associated morbidity or mortality.

CONCLUSIONS

Combination therapy with sirolimus, radiation, and cisplatin was well tolerated in patients.

Use of Everolimus as a Rescue Immunosuppressive Therapy in Liver Transplant Patients With Neoplasms

Everolimus is a new immunosuppressant with antitumoral properties and few side effects, but limited use in liver transplantation. The aim of the present study was to evaluate the effect on survival and safety of everolimus in post liver transplantation neoplasms in a single center. Ten liver transplant recipients with a posttransplant diagnosis of neoplasm received everolimus during a median of 12.7 (5.5-27.5) months; median survival was 21.3 (7.5-40.5) months. The probability of survival of everolimus group was significantly greater than the observed in a historical cohort of 14 liver recipients with comparable tumors who did not receive everolimus (100%, 90%, 72% vs. 50%, 29%, 14%) at 6, 12, and 24 months, respectively (HR=4.6, 95% confidence interval: 1.3-16.4; P=0.008). During everolimus therapy no patients showed rejection. Renal function improved in three patients. Furthermore, severe adverse effects and infections were infrequent. In summary, everolimus seems safe for liver transplant recipients with cancer and may improve short-term survival, but further studies are needed to determine long-term benefits and safety.

Recent advances in targeted therapy for renal cell carcinoma

PURPOSE OF REVIEW

To provide an overview and summary of the recent developments in the use of targeted therapy in the management of advanced kidney cancer. The focus is on publications within the last year.

RECENT FINDINGS

The last year has seen several exciting developments in the targeted approach to managing advanced renal cell carcinoma. The benefits of small-molecule tyrosine kinase inhibitors have been demonstrated in two large-scale, phase III prospective, randomized controlled trials. There is growing evidence, some not yet published, that mammalian target of rapamycin inhibitors are effective in this disease and the roles of therapies directed at the receptor for vascular endothelial growth factor continue to be refined.

SUMMARY

Recent published trials offer substantial hope for those patients with advanced kidney cancer, where before the outlook was often bleak. There is an expanding menu of potential agents in this disease, so-called targeted therapies, that are grounded in a growing understanding of the biology of kidney cancer. Many challenges and questions still remain, but there are encouraging signs of progress and hope for the future.

Everolimus and mycophenolate mofetil sensitize human pancreatic cancer cells to gemcitabine in vitro: a novel adjunct to standard chemotherapy?

BACKGROUND/AIMS

Gemcitabine improves survival in pancreatic adenocarcinoma. A variety of drugs have been tested to potentiate gemcitabine treatment for pancreatic cancer cells. Two major immunosuppressive drugs, mycophenolate mofetil (MMF) and everolimus (RAD001) have been shown to exert an anti-tumoral effect, but their ability to sensitize human pancreatic cell lines during gemcitabine treatment remains unclear. We examined the effects of everolimus and MMF on gemcitabine-treated MiaPaCa and Panc-1 cell lines.

METHODS

MiaPaCa and Panc-1 human pancreatic tumor cell lines were subjected to everolimus (0.001-1 microg/ml) or MMF (0.1-100 microg/ml) treatment in combination with gemcitabine (1-10(6) nM). Western blot analysis was performed for Panc-1 cells in the presence or absence of TGF-beta1 and different treatments: 0.1-100 muicro/ml MMF and 0.1-100 microg/ml everolimus. The antiproliferative effect of the treatment was assessed by BrdU test. The results were evaluated by two-way analysis of variance followed by post-hoc tests, and nonlinear regression analysis for dose-response rates.

RESULTS

As expected, standard treatment doses of gemcitabine decreased proliferation dose-dependently. Everolimus increased the actual EC(50) response to gemcitabine treatment (1-10(3) nM) to as much as 83.1 and 82.1% in MiaPaCa and Panc-1 cell lines, respectively. Likewise, concomitant administration with MMF altered the EC(50) of gemcitabine treatment in MiaPaCa cell lines to values between 76.8 and 85.2% for doses of >or=1 microg/ml. Even the minor dose of MMF (0.1 microg/ml) increased the antiproliferative effect of gemcitabine by 43.5% for MiaPaCa and 42.4% for Panc-1 cells. In addition, treatment of Panc-1 cells with MMF (0.1-100 microg/ml) dose-dependently inhibited TGF-beta1-induced collagen expression.

CONCLUSION

We found an overadditive antiproliferative effect of both MMF and everolimus in gemcitabine-treated MiaPaCa and Panc-1 cells in vitro, and an additional inhibitory effect of MMF on TGF-beta1-induced collagen type I expression. Interestingly, both the sensitizing effect of pancreatic cancer cells to gemcitabine treatment and the inhibition of collagen type I expression could be achieved by clinically feasible doses of everolimus and MMF. The use of these drugs is promising as a novel adjunct to standard chemotherapy.

Protein kinases as targets for cancer treatment

In various types of malignancies, conventional forms of therapy (surgery, radiation and chemotherapy) are often ineffective, as well as harmful. In the last few years, a convergence of scientific advances has enabled the identification of molecular targets and signaling pathways specific to cancer cells, resulting in therapies with enhanced selectivity and efficacy and reduced toxicity. Compound validation has relied on target validation first, although some of the most successful drugs often have effects outside of their postulated mechanism. Protein kinases represent such molecular targets; considerable research effort has been devoted to the development of targeted drugs that inhibit the action of pathogenic kinases, and clinical studies performed so far have validated the positive effects of kinase inhibitors for cancer treatment. In this review, the specificity, mechanism of action and antitumor activity of several new small-molecule inhibitors of tyrosine and serine/threonine kinases are discussed.

Monitoring Biological Action of Rapamycin in Renal Transplantation

BACKGROUND

Inhibition of P70S6 kinase (P70(S6K)) phosphorylation in activated T cells is 1 of the major mechanisms by which rapamycin exerts its immunosuppressive action.

STUDY DESIGN

Observational cohort study.

SETTINGS & PARTICIPANTS

2 different groups of kidney transplant recipients at a single center: 30 transplant recipients converted from mycophenolic acid and low-dose prednisone plus cyclosporine A to mycophenolic acid and low-dose prednisone plus rapamycin therapy for chronic allograft nephropathy (group 1) and 16 recipients of suboptimal organs converted from tacrolimus plus rapamycin to rapamycin therapy alone after 3 months (group 2).

PREDICTOR

Exposure to rapamycin therapy and rapamycin trough levels.

OUTCOMES & MEASUREMENTS

Basal and stimulated phosphorylation of P70(S6K) was measured by using Western blotting in patients' peripheral-blood mononuclear cells before and 6 to 11 months after conversion to rapamycin-based therapy. Kinase activation was attained in vivo by means of intravenous insulin injection.

RESULTS

The potency of rapamycin inhibition of P70(S6K) phosphorylation varied among patients (RAPA blood concentration required to achieve 50% inhibition of P70(S6K) activation for mitogen-activated kinase, 3.14 to 12.14 ng/mL) and failed to correlate with drug trough levels. The combination of tacrolimus and rapamycin limited the inhibitory effect of the latter drug on P70(S6K) activation.

LIMITATIONS

Need for additional studies exploring the relationship between P70(S6K) activity and kidney graft outcome. Exclusion of patients with diabetes.

CONCLUSIONS

Long-term rapamycin treatment inhibits P70(S6K) phosphorylation in peripheral-blood mononuclear cells without significant correlation with rapamycin trough levels. By measuring in vivo the biological action of rapamycin, the assay may provide potentially relevant information for the clinical management of rapamycin-treated patients.