Tumeurs endocrines : biologie et physiopathologie

Applications of spatially resolved omics in the field of endocrine tumors

Endocrine tumors derive from endocrine cells with high heterogeneity in function, structure and embryology, and are characteristic of a marked diversity and tissue heterogeneity. There are still challenges in analyzing the molecular alternations within the heterogeneous microenvironment for endocrine tumors. Recently, several proteomic, lipidomic and metabolomic platforms have been applied to the analysis of endocrine tumors to explore the cellular and molecular mechanisms of tumor genesis, progression and metastasis. In this review, we provide a comprehensive overview of spatially resolved proteomics, lipidomics and metabolomics guided by mass spectrometry imaging and spatially resolved microproteomics directed by microextraction and tandem mass spectrometry. In this regard, we will discuss different mass spectrometry imaging techniques, including secondary ion mass spectrometry, matrix-assisted laser desorption/ionization and desorption electrospray ionization. Additionally, we will highlight microextraction approaches such as laser capture microdissection and liquid microjunction extraction. With these methods, proteins can be extracted precisely from specific regions of the endocrine tumor. Finally, we compare applications of proteomic, lipidomic and metabolomic platforms in the field of endocrine tumors and outline their potentials in elucidating cellular and molecular processes involved in endocrine tumors.

Role of the tumor microenvironment in digestive neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a group of heterogeneous tumors whose incidence increased over the past few years. Around half of patients already present with metastatic disease at the initial diagnosis. Despite extensive efforts, cytotoxic and targeted therapies have provided only limited efficacy for patients with metastatic GEP-NETs, mainly due to the development of a certain state of resistance. One factor contributing to both the failure of systemic therapies and the emergence of an aggressive tumor phenotype may be the tumor microenvironment (TME), comprising dynamic and adaptative assortment of extracellular matrix components and non-neoplastic cells, which surround the tumor niche. Accumulating evidence shows that the TME can simultaneously support both tumor growth and metastasis and contribute to a certain state of resistance to treatment. In this review, we summarize the current knowledge of the TME of GEP-NETs and discuss the current therapeutic agents that target GEP-NETs and those that could be of interest in the (near) future.

Combined Treatments of Magnetic Intra-Lysosomal Hyperthermia with Doxorubicin Promotes Synergistic Anti-Tumoral Activity

Doxorubicin is a cytotoxic drug used for the treatment of many cancer types. However, its significant dose-related adverse effects including cardiotoxicity may hamper its efficiency. Moreover, the multidrug resistance that appears during treatments limits anti-cancer therapies. Hyperthermia has been introduced as an adjuvant anti-cancer therapy and presents promising opportunities especially in combination with chemotherapy. However, hyperthermia methods including standard magnetic hyperthermia do not discriminate between the target and the surrounding normal tissues and can lead to side effects. In this context, a Magnetic Intra-Lysosomal Hyperthermia (MILH) approach, which occurs without perceptible temperature rise, has been developed. We previously showed that minute amounts of iron oxide magnetic nanoparticles targeting the gastrin receptor (CCK2R) are internalized by cancer cells through a CCK2R-dependent physiological process, accumulated into their lysosomes and kill cancer cells upon high frequency alternating magnetic field (AMF) application through lysosomal cell death. Here, we show that the combination of MILH with doxorubicin increases the efficiency of the eradication of endocrine tumor cells with synergism. We also demonstrate that these two treatments activate two different cell death pathways that are respectively dependent on Caspase-1 and Caspase-3 activation. These findings will result in the development of new anti-tumoral, intra-lysosomal-thermo/chemotherapy with better curative effects than chemotherapy alone and that are devoid of adverse effects linked to standard hyperthermia approaches.

mTOR inhibitors activate PERK signaling and favor viability of gastrointestinal neuroendocrine cell lines

mTOR and Unfolded Protein Response (UPR) are two signaling pathways frequently activated in cancer cells. The mTOR pathway has been shown to be up-regulated in most gastroenteropancreatic neuroendocrine tumors. In contrast, little is known about the UPR status in neoplastic neuroendocrine cells. However, these hormone-producing cells are likely to present distinctive adaptations of this pathway, as other secretory cells. We therefore analyzed the status of the three axes of UPR and their relation to mTOR pathway in two gastrointestinal neuroendocrine tumors (GI-NET) cell lines STC-1 and GluTag. At baseline, pharmacological inducers activate the three arms of UPR: PERK, ATF6 and IRE1. Although hypoxia stimulates the PERK, ATF6 and IRE-1 pathways in both cell lines, glucose depletion activates UPR only in STC-1 cell line. Strikingly, P-p70S6K1 increases concomitantly to P-PERK and BiP in response to thapsigargin treatment, glucose depletion or hypoxia. We found that different mTOR inhibitors activate the PERK signaling pathway. To confirm that mTOR inhibition modulates PERK activation, we inhibited PERK and showed that it decreased cell viability when associated to mTOR inhibition, indicating that mTOR drives a PERK-dependent survival pathway. In conclusion, in GI-NET cell lines, UPR signaling is functional and PERK arm is induced by mTOR inhibition. These observations open up new perspectives for therapeutic strategies: the crosstalk between mTOR and UPR might contribute to the resistance to mTOR inhibitors and could be targeted by mTOR and PERK inhibitors in combination therapy.

Angiogenesis and tumor progression in neuroendocrine digestive tumors

BACKGROUND

Clinical observations suggest that in neuroendocrine digestive tumors a high intratumoral microvascular density is associated with good prognosis. We used an experimental orthotopic xenograft model to analyze the relations between angiogenic activity and tumor progression in this tumor subset.

MATERIAL AND METHODS

We compared 2 endocrine cell lines: STC-1, a low vascular endothelial growth factor (VEGF)-producing cell line, and INS-r3, a high VEGF-producing cell line. Tumor cells were grafted in the adventitial layer of the caecal wall of nude mice, sacrificed after 8 wk.

RESULTS

At 8 wk, "primary" tumors were present in all animals. STC-1 derived tumors were morphologically moderately differentiated, with high proliferative and apoptotic activities; in contrast, INS-r3 derived tumors were well differentiated, with low proliferative and apoptotic activities. VEGF was expressed in <50% grafted STC-1 cells but in >90% of grafted INS-r3 cells. Microvascular density was significantly higher in INS-r3 derived tumors than in STC-1 derived tumors. All STC-1 derived tumors (n = 8) have invaded the mucosa, in contrast to none of the INS-r3 derived tumors (n = 8); liver metastases were detected in 7/8 animals bearing STC-1 derived tumors and in 0/8 animals with INS-r3 derived tumors, despite the presence of lymph node metastases.

CONCLUSIONS

Our experimental data concur with clinical findings to suggest that in well differentiated digestive neuroendocrine tumors angiogenesis is disconnected from tumor progression: the development of a highly vascular tumor microenvironment is correlated with VEGF secretion but is not associated with invasive and metastatic properties; it must therefore be regarded as an indirect marker of differentiation.