Specific mTOR inhibitor rapamycin enhances cytotoxicity induced by alkylating agent 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU) in human U251 malignant glioma cells

Rapamycin Inhibits Glioma Cells Growth and Promotes Autophagy by miR-26a-5p/DAPK1 Axis

Background

Glioma is a common intracranial malignant tumor with high rates of invasiveness and mortality. This study aimed to investigate the mechanism of rapamycin in glioma.

Methods

U118-MG cells were treated with and without rapamycin in vivo and then collected for RNA sequencing. Differentially expressed miRNAs (DEMs) were screened and verified. MiR-26a-5p was selected for functional verification, and the target gene of miR-26a-5p was identified. The effects of miR-26a-5p on cell proliferation, cell cycle, apoptosis, and autophagy were also investigated.

Results

In total, 58 up-regulated and 41 down-regulated DEMs were identified between rapamycin-treated and untreated U118-MG cells. MiR-26-5p levels were up-regulated in U118-MG cells treated with 12.5 μM rapamycin, and death-associated protein kinase 1 (DAPK1) expression, a direct miR-26a-5p target gene, was down-regulated. Rapamycin substantially inhibited cell proliferation and cell percentage in the S phase and promoted cell apoptosis; miR-26a-5p inhibitor increased cell proliferation and cell cycle and decreased cell apoptosis; DAPK1 overexpression further induced cell proliferation, increased the cell number in the S phase, and inhibited apoptosis in glioma cells. Notably, rapamycin increased the autophagy-related Beclin1 protein expression levels and the LC3 II/I ratio.

Conclusion

Rapamycin exerts anti-tumor effects by promoting autophagy in glioma cells, which was dependent on the miR-26a-5p/DAPK1 pathway activation by rapamycin.

Inhibition of mTOR by Rapamycin Results in Auditory Hair Cell Damage and Decreased Spiral Ganglion Neuron Outgrowth and Neurite Formation In Vitro

Rapamycin is an antifungal agent with immunosuppressive properties. Rapamycin inhibits the mammalian target of rapamycin (mTOR) by blocking the mTOR complex 1 (mTORC1). mTOR is an atypical serine/threonine protein kinase, which controls cell growth, cell proliferation, and cell metabolism. However, less is known about the mTOR pathway in the inner ear. First, we evaluated whether or not the two mTOR complexes (mTORC1 and mTORC2, resp.) are present in the mammalian cochlea. Next, tissue explants of 5-day-old rats were treated with increasing concentrations of rapamycin to explore the effects of rapamycin on auditory hair cells and spiral ganglion neurons. Auditory hair cell survival, spiral ganglion neuron number, length of neurites, and neuronal survival were analyzed in vitro. Our data indicates that both mTOR complexes are expressed in the mammalian cochlea. We observed that inhibition of mTOR by rapamycin results in a dose dependent damage of auditory hair cells. Moreover, spiral ganglion neurite number and length of neurites were significantly decreased in all concentrations used compared to control in a dose dependent manner. Our data indicate that the mTOR may play a role in the survival of hair cells and modulates spiral ganglion neuronal outgrowth and neurite formation.

A phase II trial of everolimus, temozolomide, and radiotherapy in patients with newly diagnosed glioblastoma: NCCTG N057K

BACKGROUND

The mammalian target of rapamycin (mTOR) functions within the phosphatidylinositol-3 kinase (PI3K)/Akt pathway as a critical modulator of cell survival. This clinical trial evaluated the combination of the mTOR inhibitor everolimus with conventional temozolomide (TMZ)-based chemoradiotherapy.

METHODS

Newly diagnosed patients with glioblastoma multiforme were eligible for this single arm, phase II study. Everolimus (70 mg/wk) was started 1 week prior to radiation and TMZ, followed by adjuvant TMZ, and continued until disease progression. The primary endpoint was overall survival at 12 months, and secondary endpoints were toxicity and time to progression. Eleven patients were imaged with 3'-deoxy-3'-(18)F-fluorothymidine ((18)FLT)-PET/CT before and after the initial 2 doses of everolimus before initiating radiation/TMZ. Imaged patients with sufficient tumor samples also underwent immunohistochemical and focused exon sequencing analysis.

RESULTS

This study accrued 100 evaluable patients. Fourteen percent of patients had grade 4 hematologic toxicities. Twelve percent had at least one grade 4 nonhematologic toxicity, and there was one treatment-related death. Overall survival at 12 months was 64% and median time to progression was 6.4 months. Of the patients who had (18)FLT-PET data, 4/9 had a partial response after 2 doses of everolimus. Focused exon sequencing demonstrated that (18)FLT-PET responders were less likely to have alterations within the PI3K/Akt/mTOR or tuberous sclerosis complex/neurofibromatosis type 1 pathway compared with nonresponders.

CONCLUSION

Combining everolimus with conventional chemoradiation had moderate toxicity. (18)FLT-PET studies suggested an initial antiproliferative effect in a genetically distinct subset of tumors, but this did not translate into an appreciable survival benefit compared with historical controls treated with conventional therapy.

Co-delivery of cisplatin and rapamycin for enhanced anticancer therapy through synergistic effects and microenvironment modulation

The tumor microenvironment plays an important role in the tumor's progression and metastasis. Therefore, successful alteration of this delicate setting against the tumor's favor can open a window for therapeutic efficacy. We have developed a modality to bring about treatment-induced alterations in the tumor microenvironment by employing the synergistic effects between two drugs. Co-delivery of rapamycin (RAPA), an mTOR inhibitor that may offer notable therapy through antiangiogenic activity, alongside cisplatin can foster significant potency as RAPA sensitizes A375 melanoma cells to cisplatin therapy through microenvironment modulation. However, encapsulation of these drugs into poly(lactic-co-glycolic acid) (PLGA) NPs was inefficient due to the incompatibility between the two free drugs and the polymer matrix. Here, we show cisplatin can be made hydrophobic by coating a nanoprecipitate (cores) of the drug with dioleoylphosphatidic acid (DOPA). These DOPA coated cisplatin cores are compatible with PLGA and can be coencapsulated in PLGA NPs alongside RAPA at a molar ratio to promote synergistic antitumor activity. The presence of the cisplatin cores significantly improved the encapsulation of RAPA into PLGA NPs. Furthermore, PLGA NPs containing both cisplatin cores and RAPA induced significant apoptosis on A375-luc human melanoma cells in vitro. Additionally, they inhibited the growth of A375-luc melanoma in a xenograft tumor model through modulation of the tumor vasculature and permitted enhanced penetration of NPs into the tumor.

RTOG 0913: a phase 1 study of daily everolimus (RAD001) in combination with radiation therapy and temozolomide in patients with newly diagnosed glioblastoma

PURPOSE

To determine the safety of the mammalian target of rapamycin inhibitor everolimus (RAD001) administered daily with concurrent radiation and temozolomide in newly diagnosed glioblastoma patients.

METHODS AND MATERIALS

Everolimus was administered daily with concurrent radiation (60 Gy in 30 fractions) and temozolomide (75 mg/m(2) per day). Everolimus was escalated from 2.5 mg/d (dose level 1) to 5 mg/d (dose level 2) to 10 mg/d (dose level 3). Adjuvant temozolomide was delivered at 150 to 200 mg/m(2) on days 1 to 5, every 28 days, for up to 12 cycles, with concurrent everolimus at the previously established daily dose of 10 mg/d. Dose escalation continued if a dose level produced dose-limiting toxicities (DLTs) in fewer than 3 of the first 6 evaluable patients.

RESULTS

Between October 28, 2010, and July 2, 2012, the Radiation Therapy Oncology Group 0913 protocol initially registered a total of 35 patients, with 25 patients successfully meeting enrollment criteria receiving the drug and evaluable for toxicity. Everolimus was successfully escalated to the predetermined maximum tolerated dose of 10 mg/d. Two of the first 6 eligible patients had a DLT at each dose level. DLTs included gait disturbance, febrile neutropenia, rash, fatigue, thrombocytopenia, hypoxia, ear pain, headache, and mucositis. Other common toxicities were grade 1 or 2 hypercholesterolemia and hypertriglyceridemia. At the time of analysis, there was 1 death reported, which was attributed to tumor progression.

CONCLUSIONS

Daily oral everolimus (10 mg) combined with both concurrent radiation and temozolomide followed by adjuvant temozolomide is well tolerated, with an acceptable toxicity profile. A randomized phase 2 clinical trial with mandatory correlative biomarker analysis is currently under way, designed to both determine the efficacy of this regimen and identify molecular determinants of response.

De-repression of PDGFRβ transcription promotes acquired resistance to EGFR tyrosine kinase inhibitors in glioblastoma patients

Acquired resistance to tyrosine kinase inhibitors (TKI) represents a major challenge for personalized cancer therapy. Multiple genetic mechanisms of acquired TKI resistance have been identified in several types of human cancer. However, the possibility that cancer cells may also evade treatment by co-opting physiologically regulated receptors has not been addressed. Here, we show the first example of this alternate mechanism in brain tumors by showing that EGF receptor (EGFR)-mutant glioblastomas (GBMs) evade EGFR TKIs by transcriptionally de-repressing platelet-derived growth factor receptor β (PDGFRβ). Mechanistic studies show that EGFRvIII signaling actively suppresses PDGFRβ transcription in an mTORC1- and extracellular signal-regulated kinase-dependent manner. Genetic or pharmacologic inhibition of oncogenic EGFR renders GBMs dependent on the consequently de-repressed PDGFRβ signaling for growth and survival. Importantly, combined inhibition of EGFR and PDGFRβ signaling potently suppresses tumor growth in vivo. These data identify a novel, nongenetic TKI resistance mechanism in brain tumors and provide compelling rationale for combination therapy.

SIGNIFICANCE

These results provide the fi rst clinical and biologic evidence for receptor tyrosinekinase (RTK) "switching" as a mechanism of resistance to EGFR inhibitors in GBM and provide a molecular explanation of how tumors can become "addicted" to a non amplified, nonmutated, physiologically regulated RTK to evade targeted treatment.

A phase I study of temozolomide and everolimus (RAD001) in patients with newly diagnosed and progressive glioblastoma either receiving or not receiving enzyme-inducing anticonvulsants: an NCIC CTG study

PURPOSE

This phase I trial was designed to determine the recommended phase II dose(s) of everolimus (RAD001) with temozolomide (TMZ) in patients with glioblastoma (GBM). Patients receiving enzyme-inducing antiepileptic drugs (EIAEDs) and those not receiving EIAEDs (NEIAEDs) were studied separately.

PATIENTS AND METHODS

Enrollment was restricted to patients with proven GBM, either newly diagnosed or at first progression. Temozolomide was administered at a starting dose of 150 mg/m(2)/day for 5 days every 28 days, and everolimus was administered continuously at a starting dose of 2.5 mg orally on a daily schedule starting on day 2 of cycle 1 in 28-day cycles.

RESULTS

Thirteen patients receiving EIAEDs and 19 not receiving EIAEDs were enrolled and received 83 and 116 cycles respectively. Everolimus 10 mg daily plus TMZ 150 mg/m(2)/day for 5 days was declared the recommended phase II dose for the NEIAEDs cohort. In the EIAEDs group, doses were well tolerated without DLTs, and pharmacokinetic parameters indicated decreased everolimus exposure. Temozolomide pharmacokinetic parameters were unaffected by EIAEDs or everolimus. In the subset of 28 patients with measurable disease, 3 had partial responses (all NEIAEDs) and 16 had stable disease.

CONCLUSION

A dosage of 10 mg everolimus daily with TMZ 150 mg/m(2)/day for five consecutive days every 28 days in patients is the recommended dose for this regimen. Everolimus clearance is increased by EIAEDs, and patients receiving EIAEDs should be switched to NEIAEDs before starting this regimen.

Local delivery of rapamycin: a toxicity and efficacy study in an experimental malignant glioma model in rats

Rapamycin, an anti-proliferative agent, is effective in the treatment of renal cell carcinoma and recurrent breast cancers. We proposed that this potent mammalian target of rapamycin inhibitor may be useful for the treatment of gliomas as well. We examined the cytotoxicity of rapamycin against a rodent glioma cell line, determined the toxicity of rapamycin when delivered intracranially, and investigated the efficacy of local delivery of rapamycin for the treatment of experimental malignant glioma in vivo. We also examined the dose-dependent efficacy of rapamycin and the effect when locally delivered rapamycin was combined with radiation therapy. Rapamycin was cytotoxic to 9L cells, causing 34% growth inhibition at a concentration of 0.01 µg/mL. No in vivo toxicity was observed when rapamycin was incorporated into biodegradable caprolactone-glycolide (35:65) polymer beads at 0.3%, 3%, and 30% loading doses and implanted intracranially. Three separate efficacy studies were performed to test the reproducibility of the effect of the rapamycin beads as well as the validity of this treatment approach. Animals treated with the highest dose of rapamycin beads tested (30%) consistently demonstrated significantly longer survival durations than the control and placebo groups. All dose-escalating rapamycin bead treatment groups (0.3%, 3% and 30%), treated both concurrently with tumor and in a delayed manner after tumor placement, experienced a significant increase in survival, compared with controls. Radiation therapy in addition to the simultaneous treatment with 30% rapamycin beads led to significantly longer survival duration than either therapy alone. These results suggest that the local delivery of rapamycin for the treatment of gliomas should be further investigated.

Rapamycin-mediated mTOR inhibition attenuates survivin and sensitizes glioblastoma cells to radiation therapy

Survivin, an antiapoptotic protein, is elevated in most malignancies and attributes to radiation resistance in tumors including glioblastoma multiforme. The downregulation of survivin could sensitize glioblastoma cells to radiation therapy. In this study, we investigated the effect of rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), in attenuating survivin and enhancing the therapeutic efficacy for glioblastoma cells, and elucidated the underlying mechanisms. Here we tested various concentrations of rapamycin (1-8 nM) in combination with radiation dose 4 Gy. Rapamycin effectively modulated the protein kinase B (Akt)/mTOR pathway by inhibiting the phosphorylation of Akt and mTOR proteins, and this inhibition was further enhanced by radiation. The expression level of survivin was decreased in rapamycin pre-treatment glioblastoma cells followed by radiation; meanwhile, the phosphorylation of H2A histone family member X (H2AX) at serine-139 (γ-H2AX) was increased. p21 protein was also induced on radiation with rapamycin pre-treatment, which enhanced G1 arrest and the accumulation of cells at G0/subG1 phase. Furthermore, the clonogenic cell survival assay revealed a significant dose-dependent decrease in the surviving fraction for all three cell lines pre-treated with rapamycin. Our studies demonstrated that targeting survivin may be an effective approach for radiosensitization of malignant glioblastoma.

Antagonism of the mammalian target of rapamycin selectively mediates metabolic effects of epidermal growth factor receptor inhibition and protects human malignant glioma cells from hypoxia-induced cell death

Although inhibition of the epidermal growth factor receptor is a plausible therapy for malignant gliomas that, in vitro, enhances apoptosis, the results of clinical trials have been disappointing. The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that integrates starvation signals and generates adaptive responses that aim at the maintenance of energy homeostasis. Antagonism of mTOR has been suggested as a strategy to augment the efficacy of epidermal growth factor receptor inhibition by interfering with deregulated signalling cascades downstream of Akt. Here we compared effects of antagonism of mTOR utilizing rapamycin or a small hairpin RNA-mediated gene silencing to those of epidermal growth factor receptor inhibition or combined inhibition of epidermal growth factor receptor and mTOR in human malignant glioma cells. In contrast to epidermal growth factor receptor inhibition, mTOR antagonism neither induced cell death nor enhanced apoptosis induced by CD95 ligand or chemotherapeutic drugs. However, mTOR inhibition mimicked the hypoxia-protective effects of epidermal growth factor receptor inhibition by maintaining adenosine triphosphate levels. These in vitro experiments thus challenge the current view of mTOR as a downstream target of Akt that mediates antiapoptotic stimuli. Under the conditions of the tumour microenvironment, metabolic effects of inhibition of epidermal growth factor receptor, Akt and mTOR may adversely affect outcome by protecting the hypoxic tumour cell fraction.