Medical treatment of neuroendocrine tumours

Radiolabeled Somatostatin Analogue Therapy Of Gastroenteropancreatic Cancer

Peptide receptor radionuclide therapy (PRRT) has been utilized for more than two decades and has been accepted as an effective therapeutic modality in the treatment of inoperable or metastatic gastroenteropancreatic neuroendocrine neoplasms (NENs) or neuroendocrine tumors (NETs). The two most commonly used radiopeptides for PRRT, (90)Y-octreotide and (177)Lu-octreotate, produce disease-control rates of 68%-94%, with progression-free survival rates that compare favorably with chemotherapy, somatostatin analogues, and newer targeted therapies. In addition, biochemical and symptomatic responses are commonly observed. In general, PRRT is well tolerated with only low to moderate toxicity in most individuals. In line with the need to place PRRT in the therapeutic sequence of gastroenteropancreatic NENs, a recently sponsored phase III randomized trial in small intestine NENs treated with (177)Lu-octreotate vs high-dose octreotide long-acting release demonstrated that (177)Lu-octreotate significantly improved progression-free survival. Other strategies that are presently being developed include combinations with targeted therapies or chemotherapy, intra-arterial PRRT, and salvage treatments. Sophisticated molecular tools need to be incorporated into the management strategy to more effectively define therapeutic efficacy and for an early identification of adverse events. The strategy of randomized controlled trials is a key issue to standardize the treatment and establish the position of PRRT in the therapeutic algorithm of NENs.

New perspectives on the use of mTOR inhibitors in allogeneic haematopoietic stem cell transplantation and graft-versus-host disease

Inhibition of the mechanistic target of rapamycin (mTOR) has been exploited largely both in solid tumour oncology and solid organ transplantation. More recently mTOR inhibitors such as sirolimus and everolimus have been introduced to the field of allogeneic haematopoietic stem cell transplantation where their unique combination of immunosuppressive purposes offering reduced nephrotoxicity and potential antimalignant effects reflect a unique drug profile that has led to their widespread use in both prophylaxis and therapy of graft-versus-host disease (GVHD). On the other hand haematological insufficiency, infectious complications as well as vasculopathies, have been frequently reported as limiting toxicities. Here, we review both the retrospective and prospective experience available to date and stress the need for prospective registration trials to reduce off label use and improve patient safety by optimizing dosing and enhancing pharmacovigilance. Furthermore, we speculate on the future role of mTOR inhibitors in allogeneic haematopoietic stem cell transplantation.

New horizons for targeted treatment of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare and heterogeneous tumors and there is a paucity of randomized clinical trials evaluating the different therapeutic strategies. Over recent years, some important molecular aspects have been investigated and multiple targeted therapies are currently available. One of the most promising targets for the therapy of NETs are the mTOR and angiogenic growth factor receptors. The advent of the inhibitors of the mTOR pathway, tyrosine kinase inhibitors and of somatostatin analogs have shown their efficacy in randomized clinical trials in terms of implementing clinical hormone-induced syndromes and progression-free survival of advanced NETs. This article summarizes the standard therapies and new perspectives in NET's treatment, which remains still very heterogeneous and little known entity.

Mid-gut ACTH-secreting neuroendocrine tumor unmasked with (18)F-dihydroxyphenylalanine-positron emission tomography

Ectopic ACTH Cushing's syndrome (EAS) is often caused by neuroendocrine tumors (NETs) of lungs, pancreas, thymus, and other less frequent locations. Localizing the source of ACTH can be challenging. A 64-year-old man presented with rapidly progressing fatigue, muscular weakness, and dyspnea. He was in poor condition and showed facial redness, proximal amyotrophy, and bruises. Laboratory disclosed hypokalemia, metabolic alkalosis, and markedly elevated ACTH and cortisol levels. Pituitary was normal on magnetic resonance imaging (MRI), and bilateral inferior petrosal sinus blood sampling with corticotropin-releasing hormone stimulation showed no significant central-to-periphery gradient of ACTH. Head and neck, thoracic and abdominal computerized tomography (CT), MRI, somatostatin receptor scintigraphy (SSRS), and ¹⁸F-deoxyglucose-positron emission tomography (FDG-PET) failed to identify the primary tumor. ¹⁸F-dihydroxyphenylalanine (F-DOPA)-PET/CT unveiled a 20-mm nodule in the jejunum and a metastatic lymph node. Segmental jejunum resection showed two adjacent NETs, measuring 2.0 and 0.5 cm with a peritoneal metastasis. The largest tumor expressed ACTH in 30% of cells. Following surgery, after a transient adrenal insufficiency, ACTH and cortisol levels returned to normal values and remain normal over a follow-up of 26 months. Small mid-gut NETs are difficult to localize on CT or MRI, and require metabolic imaging. Owing to low mitotic activity, NETs are generally poor candidates for FDG-PET, whereas SSRS shows poor sensitivity in EAS due to intrinsically low tumor concentration of type-2 somatostatin receptors (SST2) or to receptor down regulation by excess cortisol. However, F-DOPA-PET, which is related to amine precursor uptake by NETs, has been reported to have high positive predictive value for occult EAS despite low sensitivity, and constitutes a useful alternative to more conventional methods of tumor localization.

Aspirin inhibits cell viability and mTOR downstream signaling in gastroenteropancreatic and bronchopulmonary neuroendocrine tumor cells

AIM: To investigate the effect of aspirin on neuroendocrine tumor (NET) cell growth and signaling in vitro.

METHODS: Human pancreatic BON1, bronchopulmonary NCI-H727 and midgut GOT1 neuroendocrine tumor cells were treated with different concentrations of aspirin (from 0.001 to 5 mmol/L), and the resulting effects on metabolic activity/cell proliferation were measured using cell proliferation assays and SYBR-DNA-labeling after 72, 144 and 216 h of incubation. The effects of aspirin on the expression and phosphorylation of several critical proteins that are involved in the most common intracellular growth factor signaling pathways (especially Akt protein kinase B) and mammalian target of rapamycin (mTOR) were determined by Western blot analyses. Propidium iodide staining and flow cytometry were used to evaluate changes in cell cycle distribution and apoptosis. Statistical analysis was performed using a 2-tailed Student’s t-test to evaluate the proliferation assays and cell cycle analyses. The results are expressed as the mean ± SD of 3 or 4 independently performed experiments. Statistical significance was set at P < 0.05.

RESULTS: Treatment with aspirin suppressed the viability/proliferation of BON1, NCI-H727 and GOT1 cells in a time- and dose-dependent manner. Significant effects were observed at starting doses of 0.5-1 mmol/L and peaked at 5 mmol/L. For instance, after treatment with 1 mmol/L aspirin for 144 h, the viability of pancreatic BON1 cells decreased to 66% ± 13% (P < 0.05), the viability of bronchopulmonary NCI-H727 cells decreased to 53% ± 8% (P < 0.01) and the viability of midgut GOT1 cells decreased to 89% ± 6% (P < 0.01). These effects were associated with a decreased entry into the S phase, the induction of the cyclin-dependent kinase inhibitor p21 and reduced expression of cyclin-dependent kinase 4 and cyclin D3. Aspirin suppressed mTOR downstream signaling, evidenced by the reduced phosphorylation of the mTOR substrates 4E binding protein 1, serine/threonine kinase P70S6K and S6 ribosomal protein and inhibited glycogen synthase kinase 3 activity. We observed the (compensatory) activation of tuberous sclerosis 2, the serine/threonine specific protein kinase AKT and extracellular signal-regulated kinases.

CONCLUSION: Aspirin demonstrates promising anticancer properties for NETs in vitro. Further preclinical and clinical studies are needed.

Peptide receptor radionuclide therapy for advanced neuroendocrine tumors

Peptide receptor radionuclide therapy (PRRT) consists of the systemic administration of a synthetic peptide, labeled with a suitable β-emitting radionuclide, able to irradiate tumors and their metastases via internalization through a specific receptor (usually somatostatin S2), over-expressed on the cell membrane. After almost 2 decades of experience, PRRT, with either (90)Y-octreotide or (177)Lu-octreotate, has established itself to be an efficient and effective therapeutic modality. As a treatment, it is relatively safe up to the known thresholds of absorbed and bio-effective isotope dosages and the renal and hematological toxicity profiles are acceptable if adequate protective measures are undertaken.

New insights into the role of chronic inflammation and cytokines in the etiopathogenesis of gastroenteropancreatic neuroendocrine tumors

Although previously considered rare, recent epidemiological studies have revealed that the incidence (3.6/100,000) and prevalence (35/100,000) of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) has increased over the past few decades. Despite the progress in the understanding of GEP-NET molecular biology, there is still little advance in the early diagnosis due to lack of specific tumor markers. As the tumors are mostly detected in their late stage, they are not well controlled by either biotherapy or conventional chemotherapy, and thus represent a significant clinical issue. Chronic inflammation has been implicated in the development of GEP-NETs. This review presents recent findings that link pro-inflammatory cytokines to the molecular basis of GEP-NET tumorigenesis, leading to a more personalized approach to disease management and therapy.

Everolimus in the treatment of patients with advanced pancreatic neuroendocrine tumors: latest findings and interpretations

Pancreatic neuroendocrine tumors (pNETs) are a heterogeneous group of neoplasms with various clinical presentations. More than half of patients present with so-called nonfunctioning tumors with no hormone-related symptoms, whereas other tumors produce symptoms like gastric problems, ulcers, hypoglycemia, skin rash and diarrhea related to hormone production. The traditional treatment for pNETs over the last three decades has been cytotoxic agents, mainly streptozotocin plus 5-fluorouracil or doxorubicin. Most recently two new compounds have been registered worldwide for the treatment of pNETs, the mammalian target of rapamycin (mTOR) inhibitor everolimus and the tyrosine kinase inhibitor sunitinib. This paper concentrates on the use of mTOR inhibitors and the mechanisms of action. The mTOR pathway is altered in a number of pNETs. Everolimus (RAD001) is an orally active rapamycin analog and mTOR inhibitor. It blocks activity of the mTOR pathway by binding with high affinity to the cytoplasmic protein FKBP-12. The efficacy of everolimus in pNETs has been demonstrated in two multicenter studies (RADIANT 1 and 3). The RADIANT 3 study was a randomized controlled study in pNETs of everolimus 10 mg/day versus placebo, showing an increased progression-free survival (11.7 months versus 4.6 months) and hazard ratio of 0.35 (p < 0.001). Current studies indicate that there is strong evidence to support the antitumor effect of rapalogs in pNETs. However, significant tumor reduction is very rarely obtained, usually in less than 10% of treated patients. Therefore, these drugs may be more effective in combination with other anticancer agents, including chemotherapy, targeted therapies as well as peptide receptor radiotherapy.