Molecular biology of neuroendocrine tumors: from pathways to biomarkers and targets.

Neuroendocrine tumors (NETs) represent a heterogeneous group of diseases with varied natural history and prognosis depending upon the organ of origin and grade of aggressiveness. The most widely used biomarker to determine disease burden and monitor response to treatment is chromogranin A (CgA), but it is far from being the optimal predictive and prognostic biomarker in NETs. Biological understanding and derived treatment options for NETs have changed markedly in recent years. Over the last decade, the genomic landscape of these tumors has been extensively investigated. This has resulted in the discovery of mutations and expression anomalies in genes and pathways such as the PI3K/Akt/mTOR, DAXX/ATRX, and MEN1, which are promising predictive and prognostic biomarkers and future candidates for targeted therapies. Additionally, the study of tumor stroma and environment are one of the most promising fields for discovery of potential new targets and biomarkers.

Pazopanib in pretreated advanced neuroendocrine tumors: a phase II, open-label trial of the Spanish Task Force Group for Neuroendocrine Tumors (GETNE).

BACKGROUND: The management of advanced neuroendocrine tumors (NETs) has recently changed. We assessed the activity of pazopanib after failure of other systemic treatments in advanced NETs. METHODS: This was a multicenter, open-label, phase II study evaluating pazopanib as a single agent in advanced NETs (PAZONET study). The clinical benefit rate (CBR) at 6 months was the primary end point. Translational correlation of radiological response and progression-free survival (PFS) with circulating and tissue biomarkers was also evaluated. RESULTS: A total of 44 patients were enrolled. Twenty-five patients (59.5%) were progression-free at 6 months (4 partial responses, 21 stable diseases) with a median PFS of 9.5 months [95% confidence interval (CI) 4.8-14.1]. The CBR varied according to prior therapy received, with 73%, 60% and 25% in patients treated with prior multitarget inhibitors, prior mTOR inhibitors and both agents, respectively. A nonsignificant increase in PFS was observed in patients presenting lower baseline circulating tumor cell (CTC) counts (9.1 versus 5.8 months; P = 0.22) and in those with decreased levels of soluble-vascular endothelial growth factor receptor-2 (sVEGFR-2) (12.6 versus 9.1 months; P = 0.067). A trend toward reduced survival was documented in patients with VEGFR3 rs307821 and rs307826 missense polymorphisms [hazard ratio (HR): 12.3; 95% CI 1.09-139.2; P = 0.042 and HR: 6.9; 95% CI 0.96-49.9; P = 0.055, respectively]. CONCLUSIONS: Pazopanib showed clinical activity in patients with advanced NETs regardless of previous treatments. Additionally, CTCs, soluble-s VEFGR-2 and VEGFR3 gene polymorphisms constitute potential biomarkers for selecting patients for pazopanib (NCT01280201). CLINICAL TRIAL NUMBER: NCT01280201.

ErbBs inhibition by lapatinib blocks tumor growth in an orthotopic model of human testicular germ cell tumor.

In this work, we have analyzed the expression of different members of the ErbB family in human samples of testicular germ cell tumors (GCTs). We observed expression of ErbB1 or ErbB2 in different tumor subtypes, but we also found high expression of ErbB3 in all GCTs tested. This pattern of expression was maintained when primary tumors were orthotopically implanted in nude mice. We have chosen a choriocarcinoma model characterized by high levels of ErbB1, but also of ErbB2 and ErbB3, to assay the in vivo effect of ErbB inhibitors on tumoral growth. Our results showed a complete lack of effect (refractoriness) to the pure ErbB1 receptor inhibitors cetuximab and gefitinib. While these inhibitors blocked ErbB1 phosphorylation, ErbB2 phosphorylation was not affected, suggesting an ErbB1-independent activation of this receptor. To confirm the importance of ErbB2 activation, animals were treated with lapatinib, a dual ErbB1 and ErbB2 inhibitor. Lapatinib treatment caused a 50% inhibition in tumor growth, an effect correlated with a blockade of both ErbB1 and ErbB2 phosphorylation levels, and of downstream signaling pathways (Akt, ERKs and Stat3). ErbB2 activation could still occur due to the formation of ErbB2/ErbB3 heterodimers, and ErbB3 activation was completely inhibited by lapatinib. Finally, combined inhibition of ErbB1 (gefitinib) and ErbB3 activities (knockdown expression by shRNA) inhibited tumoral testicular cells proliferation in a similar way to lapatinib. Our results explain why lapatinib but not anti-ErbB1 agents might be effective for treatment of testicular GCT patients.

Anti-angiogenesis and metastasis: a tumour and stromal cell alliance.

Tumour progression requires the activation of a tumour and stromal cell-driven angiogenic programme, and the targeting of this process demonstrates an impact on tumour growth and progression. The results of preclinical studies have demonstrated a proinvasive/metastatic effect of antiangiogenic treatments with recent evidence supporting a contribution of the stroma to tumour aggressiveness and the short-term effects of antivascular endothelial growth factor therapy. Furthermore, hypoxia-dependent and -independent factors are considered as driving forces for tumour cell escape by altering both the tumour cells themselves and the stroma. This tumour-stromal cell alliance should be taken into consideration for the development of innovative therapeutic options targeting both tumour components to improve clinical benefits for cancer patients.

Use of a mouse model of pancreatic neuroendocrine tumors to find pericyte biomarkers of resistance to anti-angiogenic therapy.

The successful introduction of rationally targeted agents into standard cancer care is a testimony of the vast knowledge base in tumor biology. However, in order to provide individually tailored therapy to patients and to identify small subsets of patients with a high likelihood to benefit from treatment, the identification of biomarkers for response or resistance to a particular therapeutic regimen is imperative. Herein, by the use of a genetically engineered mouse model of pancreatic neuroendocrine tumors, we have assessed the utility of pericyte characteristics in terms of differential marker expression to serve as surrogate markers for response or evasive resistance to anti-angiogenic therapy. We found that tumors refractory to therapy following long-term treatment with a vascular endothelial growth factor receptor-2 blocking antibody contained blood vessels with a prolific investment of pericytes expressing α-smooth muscle actin. Further analysis by simultaneous immunostaining for different pericyte markers led to the conclusion that the increased abundance of this particular subtype of blood vessels most likely occurred by co-option of vessels from the surrounding exocrine pancreas. Our findings may form the basis for retrospective analysis of pancreatic neuroendocrine tumors from patients having undergone treatment with anti-angiogenic agents in order to validate the occurrence of pericytes expressing α-smooth muscle actin as a biomarker for tumors refractory to therapy.

Translational research in neuroendocrine tumors: pitfalls and opportunities.

Interest in research on neuroendocrine tumors (NETs) has grown in the past 10 years, coinciding with improvements in our understanding of the molecular pathogenesis of NETs. In addition, NETs have become one of the most exciting settings for drug development. Two targeted agents for the management of advanced pancreatic NETs have been approved, but the development of targeted agents for NETs is limited by problems with both patient selection and demonstration of activity. In this review, we analyze these limitations and discuss ways to increase the predictive value of preclinical models for target discovery and drug development. The role of translational research and 'omics' methodologies is emphasized, with the final aim of developing personalized medicine. Because NETs usually grow slowly and metastatic tumors are found at easily accessible locations, and owing to improvements in techniques for liquid biopsies, NETs provide a unique opportunity to obtain tumor samples at all stages of the evolution of the disease and to adapt treatment to changes in tumor biology. Combining clinical and translational research is essential to achieve progress in the NET field. Slow growth and genetic stability limit and challenge both the availability and further development of preclinical models of NETs, one of the most crucial unmet research needs in the field. Finally, we suggest some useful approaches for improving clinical drug development for NETs: moving from classical RECIST-based response end points to survival parameters; searching for different criteria to define response rates (for example, antiangiogenic effects and metabolic responses); implementing randomized phase II studies to avoid single-arm phase II studies that produce limited data on drug efficacy; and using predictive biomarkers for patient selection.

Resistance to Targeted Therapies in Renal Cancer: The Importance of Changing the Mechanism of Action.

Renal cell carcinoma (RCC) is a complex disease characterized by mutations in several genes. Loss of function of the von Hippel-Lindau (VHL) tumour suppressor gene is a very common finding in RCC and leads to up-regulation of hypoxia-inducible factor (HIF)-responsive genes accountable for angiogenesis and cell growth, such as platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). Binding of these proteins to their cognate tyrosine kinase receptors on endothelial cells promotes angiogenesis. Promotion of angiogenesis is in part due to the activation of the phosphatidylinositol-3-kinase (PI3K)/AKT/mechanistic target of rapamycin (mTOR) pathway. Inhibition of this pathway decreases protein translation and inhibits both angiogenesis and tumour cell proliferation. Although tyrosine kinase inhibitors (TKIs) stand as the main first-line treatment option for advanced RCC, eventually all patients will become resistant to TKIs. Resistance can be overcome by using second-line treatments with different mechanisms of action, such as inhibitors of mTOR, c-MET, programmed death 1 (PD-1) receptor, or the combination of an mTOR inhibitor (mTORi) with a TKI. In this article, we briefly review current evidence regarding mechanisms of resistance in RCC and treatment strategies to overcome resistance with a special focus on the PI3K/AKT/mTOR pathway.

The PDGFRß-AKT pathway contributes to CDDP-acquired resistance in testicular germ cell tumors.

PURPOSE: We examined whether PI3K-AKT or extracellular signal-regulated kinase (ERK) signaling pathways could play a role in the development of cisplatin (CDDP) resistance in testicular germ cell tumor (TGT) cells. EXPERIMENTAL DESIGN: We compared AKT and ERK activation levels in CDDP-sensitive testicular tumor cells and in their corresponding CDDP-resistant-derived cells. We also analyzed these pathways in orthotopic testicular tumors and human patient samples. RESULTS: Our results indicated that there was overactivation of AKT in CDDP-resistant cells compared with sensitive cells, but no effect on activated ERK levels. We observed an increase in mRNA and protein levels for platelet-derived growth factor (PDGF) receptor ß and PDGF-B ligand. These were responsible for AKT overactivation in CDDP-resistant cells. When PDGFRß levels were decreased by short hairpin RNA (shRNA) treatment or its activation was blocked by pazopanib, CDDP-resistant cells behaved like sensitive cells. Moreover, CDDP-resistant cells were more sensitive to incubation with PDGFRß inhibitors such as pazopanib or sunitinib than sensitive cells, a finding consistent with these cells being dependent on this signaling pathway. We also found overexpression of PDGFRß and pAKT in CDDP-resistant choriocarcinoma orthotopic tumor versus their CDDP-sensitive counterparts. Finally, we found high PDGFRß levels in human testicular tumors, and overexpression in CDDP-resistant testicular choriocarcinomas compared with the CDDP-sensitive and nontreated tumors. CONCLUSIONS: The PDGFRß-AKT pathway plays a critical role in the development of CDDP resistance in testicular tumoral cells.

Progeny of Lgr5-expressing hair follicle stem cell contributes to papillomavirus-induced tumor development in epidermis.

Epidermal keratinocytes and hair follicle (HF) stem cells (SCs) expressing oncogenes are competent at developing squamous cell carcinomas (SCCs) in epidermis and HFs, respectively. To determine whether bulge and hair germ (HG) SCs from HF contribute to SCC generation at distant epidermis, the most frequent epidermal region where these lesions arise in human skin, we used a skin cancer mouse model expressing E6 and E7 oncoproteins from Human papillomavirus (HPV) 16 in SCs and basal keratinocytes. This previously described mouse model recapitulates the human skin papillomavirus-induced SCC pathology. We show that E6 and E7 expression promote the expansion of keratin 15 (K15)-expressing cells. These K15(+) aberrant cells exhibit some HGSC markers and diminished expression of Tcf3 and Sox9 hair SC specification genes, which are accumulated in HFs and mislocalized to interfollicular epidermis. Leucine-rich G-protein-coupled receptor 5 (Lgr5)-expressing SCs, localized in the bulge and HG, are the origin of the expanded K15(+) cell population. A large subset of the Lgr5(+) SC progeny, expressing K15 and P-cadherin, is aberrantly mobilized to the upper region of HFs and the epidermis, and accumulates at E6/E7-induced pre-neoplastic lesions and epidermal tumors. These findings indicate that aberrant accumulation of altered SCs in HFs and their subsequent migration to the epidermis contribute to HPV-induced tumor development.

Non-invasive monitoring of hypoxia-inducible factor activation by optical imaging during antiangiogenic treatment in a xenograft model of ovarian carcinoma.

Targeting the hypoxia response pathway and angiogenesis are two promising therapeutic strategies for cancer treatment. Their use as single strategies has important limitations. Thus, development of combined regimens has become an important step toward improving therapeutic efficacy. Also, non-invasive monitoring of the response to targeted biological therapies, as well as determination of the optimal schedule for combination regimens has become an active field of research over the last five years, with relevance for both preclinical and clinical settings. Here, we used an optical imaging method to non-invasively monitor the functional changes in HIF activity in response to antiangiogenic treatment in a xenograft model of human ovarian carcinoma. A bioluminescent reporter construct containing nine copies of the hypoxia response element upstream of the luciferase gene (9xHRE-luciferase) was characterized in vitro in a panel of tumor cell lines and in vivo in a subcutaneous xenograft model of ovarian carcinoma by means of optical imaging. We showed that in OVCAR-3 subcutaneous xenografts, the most abrupt change in the HIF functional reporter occurs before the onset of massive tumor growth. However, this system failed to detect hypoxia induced upon antiangiogenic treatment due to the compensating effects of increased hypoxia and decreased tumor cell viability caused by imbalanced neovascularization vs. tumor expansion. Therefore, the readout based on HIF functional reporter could be conditioned by the dynamics of tumor growth and angiogenesis, which is highly variable depending on the tumor type, tumor model and stage of progression.

New drug development in digestive neuroendocrine tumors.

The traditional cytotoxic agents are of limited efficacy in the treatment of neuroendocrine tumors of the gastrointestinal tract (NETs). Recent investigations have brought up a number of biological features in this family of neoplasms that could represent targets for anticancer treatment. NETs seem to have an extraordinary tumor vascularization with high expression of proangiogenic molecules such as the vascular endothelial growth factor along with overexpression of certain tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR), the insulin growth factor receptor (IGFR) and their downstream signaling pathway components (PI3K-AKT-mTOR). The rationale of an antiangiogenic approach in the treatment of NETs and the use of other pharmacological strategies such as EGFR, IGFR and mammalian target of rapamycin inhibitors are discussed. Additionally, the emerging results of recent clinical trials with these targeted drugs are presented.

How to define intermediate stage in Hodgkin's lymphoma?

BACKGROUND: Intermediate or unfavourable stage Hodgkin's lymphoma (HL) definition relies upon at least three different scoring systems defined by cooperative groups (EORTC, GHSG and Canadian-ECOG). We aimed to investigate their efficacy and their correlation with International Prognostic Score (IPS) for advanced HL. PATIENTS AND METHODS: We studied a population of 1156 patients with localized stage HL treated prospectively within GELA centres in H8 (518 patients) and H9 (638 patients) protocols. Median age: 30 yr, 18%, Female 50%; stage I: 25%; stage II: 75%. According to scoring systems 70% had 0-1 EORTC factors; 60% 0-1 GHSG factors and 82% 0-1 Canadian factors. The IPS for advanced stages was available only in H9 study with 64% 0-1 factor. RESULTS: Survival curves according to each of the different scoring systems could significantly discriminate the subgroup populations. When a multivariate Cox analysis was performed for overall survival (OS) including all the scoring system variables: age > 45 yr, sex male, Haemoglobin < 10.5 g/dL, lymphocytes < 600/microL, B symptoms with elevated ESR, extra nodal sites did retain an independent significant value. Probability of OS was 99%, 98%, 92%, 82% and 73% for patients with 1-5 factors, respectively P < 0.0001. CONCLUSION: These factors are similar for most of them with those described in the IPS when stages III and IV are replaced by extra nodal localization. This new score should be validated in other prospective trials, as it will simplify the Hodgkin prognostic scoring systems for localized and advanced stages.

Osmotic stress regulates the stability of cyclin D1 in a p38SAPK2-dependent manner.

We report here that different cell stresses regulate the stability of cyclin D1 protein. Exposition of Granta 519 cells to osmotic shock, oxidative stress, and arsenite induced the post-transcriptional down-regulation of cyclin D1. In the case of osmotic shock, this effect was completely reversed by the addition of p38(SAPK2)-specific inhibitors (SB203580 or SB220025), indicating that this effect is dependent on p38(SAPK2) activity. Moreover, the use of proteasome inhibitors prevented this down-regulation. Thus, osmotic shock induces proteasomal degradation of cyclin D1 protein by a p38(SAPK2)-dependent pathway. The effect of p38(SAPK2) on cyclin D1 stability might be mediated by direct phosphorylation at specific sites. We found that p38(SAPK2) phosphorylates cyclin D1 in vitro at Thr(286) and that this phosphorylation triggers the ubiquitination of cyclin D1. These results link for the first time a stress-induced MAP kinase pathway to cyclin D1 protein stability, and they will help to understand the molecular mechanisms by which stress transduction pathways regulate the cell cycle machinery and take control over cell proliferation.

The protein SET regulates the inhibitory effect of p21(Cip1) on cyclin E-cyclin-dependent kinase 2 activity.

The cyclin-dependent kinase (CDK) inhibitor p21(Cip1) has a dual role in the regulation of the cell cycle; it is an activator of cyclin D1-CDK4 complexes and an inhibitor of cyclins E/A-CDK2 activity. By affinity chromatography with p21(Cip1)-Sepharose 4B columns, we purified a 39-kDa protein, which was identified by microsequence analysis as the oncoprotein SET. Complexes containing SET and p21(Cip1) were detected in vivo by immunoprecipitation of Namalwa cell extracts using specific anti-p21(Cip1) antibodies. We found that SET bound directly to p21(Cip1) in vitro by the carboxyl-terminal region of p21(Cip1). SET had no direct effect on cyclin E/A-CDK2 activity, although it reversed the inhibition of cyclin E-CDK2, but not of cyclin A-CDK2, induced by p21(Cip1). This result is specific for p21(Cip1), since SET neither bound to p27(Kip1) nor reversed its inhibitory effect on cyclin E-CDK2 or cyclin A-CDK2. Thus, SET appears to be a modulator of p21(Cip1) inhibitory function. These results suggest that SET can regulate G(1)/S transition by modulating the activity of cyclin E-CDK2.

The cell cycle inhibitor p21CIP is phosphorylated by cyclin A-CDK2 complexes.

We report here experimental evidence indicating that the p21CIP, the universal inhibitor of cyclin-dependent protein kinases, general inhibitor CDKs is a substrate oof cyclin A-cdk2. The evidence comes from phosphorylation experiments in which the endogenous p21CIP present in using the original cyclin A-cdk2 complexes immunoprecipitated from HeLa cells extracts can be phosphorylated by the cdk2 of the same complexes. In vitro experiments showing that reconstituted GSTcyclin A-GSTcdk2 complexes from phosphorylate recombinant GSTp21CIP confirms that p21CIP is a cyclin A-cdk2 substrate.

Calmodulin binds to p21(Cip1) and is involved in the regulation of its nuclear localization.

p21(Cip1), first described as an inhibitor of cyclin-dependent kinases, has recently been shown to have a function in the formation of cyclin D-Cdk4 complexes and in their nuclear translocation. The dual behavior of p21(Cip1) may be due to its association with other proteins. Different evidence presented here indicate an in vitro and in vivo interaction of p21(Cip1) with calmodulin: 1) purified p21(Cip1) is able to bind to calmodulin-Sepharose in a Ca(2+)-dependent manner, and this binding is inhibited by the calmodulin-binding domain of calmodulin-dependent kinase II; 2) both molecules coimmunoprecipitate when extracted from cellular lysates; and 3) colocalization of calmodulin and p21(Cip1) can be detected in vivo by electron microscopy immunogold analysis. The carboxyl-terminal domain of p21(Cip1) is responsible for the calmodulin interaction, since p21(145-164) peptide is also able to bind calmodulin and to compete with full-length p21(Cip1) for the calmodulin binding. Because treatment of cells with anti-calmodulin drugs decreases the nuclear accumulation of p21(Cip1), we hypothesize that calmodulin interaction with p21(Cip1) is important for p21(Cip1), and in consequence for cyclin D-Cdk4, translocation into the cell nucleus.