sirolimus and Peripheral-Nervous-System-Neoplasms

About one half of malignant peripheral nerve sheath tumors (MPNST) have Neurofibromin 1 (NF1) mutations. NF1 is a tumor suppressor gene essential for negative regulation of RAS signaling. Survival for MPNST patients is poor and we sought to identify an effective combination therapy. Starting with the mTOR inhibitors rapamycin and everolimus, we screened for synergy in 542 FDA approved compounds using MPNST cells with a native NF1 loss in both alleles. We further analyzed the cell cycle and signal transduction. In vivo growth effects of the drug combination with local radiation therapy (RT) were assessed in MPNST xenografts. The synergistic combination of mTOR inhibitors with bortezomib yielded a reduction in MPNST cell proliferation. The combination of mTOR inhibitors and bortezomib also enhanced the anti-proliferative effect of radiation in vitro. In vivo, the combination of mTOR inhibitor (everolimus) and bortezomib with RT decreased tumor growth and proliferation, and augmented apoptosis. The combination of approved mTOR and proteasome inhibitors with radiation showed a significant reduction of tumor growth in an animal model and should be investigated and optimized further for MPNST therapy.

Topics: Antineoplastic Agents; Caspase 3; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Dose-Response Relationship, Drug; Drug Synergism; Gene Expression Regulation, Neoplastic; Humans; Neurilemmoma; Peptides; Peripheral Nervous System Neoplasms; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Radiation, Ionizing; RNA, Small Interfering; Sirolimus; TOR Serine-Threonine Kinases; Transfection; Xenograft Model Antitumor Assays

Neurofibromatosis type 1 (NF1) patients are prone to the development of malignant tumors, the most common being Malignant Peripheral Nerve Sheath Tumor (MPNST). NF1-MPNST patients have an overall poor survival due to systemic metastasis. Currently, the management of MPNSTs includes surgery and radiation; however, conventional chemotherapy is not very effective, underscoring the need for effective biologically-targeted therapies. Recently, the NF1 gene product, neurofibromin, was shown to negatively regulate the phosphoinositide-3-kinase (PI3K)/Protein Kinase-B (Akt)/mammalian Target Of Rapamycin (mTOR) pathway, with loss of neurofibromin expression in established human MPNST cell lines associated with high levels of mTOR activity. We developed and characterized a human NF1-MPNST explant grown subcutaneously in NOD-SCID mice, to evaluate the effect of the mTOR inhibitor rapamycin. We demonstrate that rapamycin significantly inhibited human NF1-MPNST mTOR pathway activation and explant growth in vivo at doses as low as 1.0 mg/kg/day, without systemic toxicities. While rapamycin was effective at reducing NF1-MPNST proliferation and angiogenesis, with decreased CyclinD1 and VEGF respectively, there was no increase in tumor apoptosis. Rapamycin effectively decreased activation of S6 downstream of mTOR, but there was accompanied increased Akt activation. This study demonstrates the therapeutic potential and limitations of rapamycin in NF1-associated, and likely sporadic, MPNSTs.

Topics: Animals; Antibiotics, Antineoplastic; Apoptosis; Blotting, Western; Cyclin D1; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Humans; Immunohistochemistry; Male; Mice; Mice, Inbred NOD; Mice, SCID; Neurofibromatosis 1; Peripheral Nervous System Neoplasms; Protein Kinases; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Burden; Vascular Endothelial Growth Factor A; Xenograft Model Antitumor Assays; Young Adult