Promising targetable biomarkers in pancreatic neuroendocrine tumours

INTRODUCTION

In the treatment scenario of PanNETs-targeted therapies are desired but limited, as rarity and heterogeneity on PanNETs pose limitations to their development.

AREAS COVERED

We performed a literature review searching for promising druggable biomarkers and potential treatments to be implemented in the next future. We focused on treatments which have already reached clinical experimentation, although in early phases. Six targets were identified, namely Hsp90, HIFa, HDACs, CDKs, uPAR, and DDR. Even though biological rational is strong, so far reported efficacy outcomes are quite disappointing. The reason of that should be searched in the patients' heterogeneity, lack of biomarker selection, poor knowledge of interfering mechanisms as well as difficulties in patients accrual. Moreover, different ways to assess treatment efficacy should be considered, other than response rate, in light of the more indolent nature of NETs.

EXPERT OPINION

Development of targeted treatments in PanNETs is still an uncovered area, far behind other more frequent cancers. Rarity of NETs led to accrual of unselected populations, possibly jeopardizing the drug efficacy. Better patients' selection, both in terms of topography, grading and biomarkers is crucial and will help understanding which role targeted therapies can really play in these tumors.

The amyloid precursor protein interacts with Go heterotrimeric protein within a cell compartment specialized in signal transduction

The function of the beta-amyloid protein precursor (betaAPP), a transmembrane molecule involved in Alzheimer pathologies, is poorly understood. We recently reported the presence of a fraction of betaAPP in cholesterol and sphingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether betaAPP actually interferes with cell signaling, we reexamined the interaction between betaAPP and Go GTPase. In strong contrast with results obtained with reconstituted phospholipid vesicles (Okamoto et al., 1995), we find that incubating total neuronal membranes with 22C11, an antibody that recognizes an N-terminal betaAPP epitope, reduces high-affinity Go GTPase activity. This inhibition is specific of Galphao and is reproduced, in the absence of 22C11, by the addition of the betaAPP C-terminal domain but not by two distinct mutated betaAPP C-terminal domains that do not bind Galphao. This inhibition of Galphao GTPase activity by either 22C11 or wild-type betaAPP cytoplasmic domain suggests that intracellular interactions between betaAPP and Galphao could be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, immunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of Galphao and betaAPP in CSEM. We show that inhibition of basal Galphao GTPase activity also occurs within CSEM and correlates with the coimmunoprecipitation of Galphao and betaAPP. The regulation of Galphao GTPase activity by betaAPP in a compartment specialized in signaling may have important consequences for our understanding of the physiopathological functions of betaAPP.

Defined glycosaminoglycan motifs have opposite effects on neuronal polarity in vitro

We previously reported that heparan sulfates enhance axonal outgrowth and inhibit dendrite elongation, whereas dermatan sulfates favor the development of both axons and dendrites. The present study focuses on the activity of small synthetic heparan or dermatan sulfate-like compounds. We found three heparan sulfate-like and three dermatan sulfate-like sugars that mimic the morphological effects of the high-molecular-weight natural glycosaminoglycans. Indeed, heparan sulfate-like compounds enhance axonal maturation and inhibit dendrite growth whereas the active sugars from the dermatan sulfate series act primarily on the elongation of cortical dendrites. The effect of dermatan sulfate-like sugars on cortical dendrite growth is only observed on the subpopulation of neurons with an established axon. We also studied the effects of the synthetic sugars on motoneurons. We found that the response of motoneurons to heparan sulfate-like compounds is indistinguishable from that of cortical neurons but that dermatan sulfate-like sugars do not enhance the development of motoneuron dendrites. The distinct effects of the two types of sugars and the fact that their activity only requires a short period of contact with the cells suggest the existence of specific binding sites for dermatan-like and heparan-like compounds. This possibility is reinforced by the fact that the binding and internalization of natural heparin fragments by neurons in culture is competitively inhibited by synthetic heparan sulfate-like derivatives, but not by dermatan sulfate-like derivatives.

Specific responses of axons and dendrites to cytoskeleton perturbations: an in vitro study

Several factors can influence the development of axons and dendrites in vitro. Some of these factors modify the adhesion of neurons to their substratum. We have previously shown that the threshold of neuron-substratum adhesion necessary for initiation and elongation of dendrites is higher than that required for axonal growth. To explain this difference we propose that, in order to antagonize actin-driven surface tension, axons primarily rely on the compression forces of microtubules whereas dendrites rely on adhesion. This model was tested by seeding the cells in conditions allowing the development either of axons or of axons and dendrites, then adding cytochalasin B or nocodazole 1 hour or 24 hours after plating. The addition of cytochalasin B, which depolymerizes actin filaments and thus reduces actin-tensile forces, increases the length of both axons and dendrites, indicating that both axons and dendrites have to antagonize surface tension in order to elongate. The addition of nocodazole, which acts primarily on microtubules, slightly reduces dendrite elongation and totally abolishes axonal growth. Similar results are obtained when the drugs are added 1 or 24 hours after plating, suggesting that the same mechanisms are at work both in initiation and in elongation. Finally, we find that in the presence of cytochalasin B axons adopt a curly morphology, a fact that could be explained by the importance of tensile forces in antagonizing the asymmetry created by polarized microtubules presenting a uniform minus/plus orientation.

Culture of fetal alveolar epithelial type II cells in serum-free medium

A serum-free culture medium (defined medium = DM) was elaborated by adding to Eagle's minimum essential medium (MEM), non-essential amino acids, transferrin, putrescine, tripeptide glycyl-histidyl-lysine, somatostatin, sodium selenite, ethanolamine, phosphoethanolamine, sodium pyruvate, and metal trace elements. This medium was tested for its ability to support sustained surfactant biosynthesis in fetal alveolar epithelial type II cells. For up to 8 days, ultrastructure was maintained with persistence of lamellar inclusion bodies. Thymidine incorporation into DNA was enhanced about 50% in DM as compared with MEM, whereas it was enhanced 300% in 10% fetal bovine serum. With DM, the incorporation of tritiated choline into phosphatidylcholine (PC) of isolated surfactant material was about twice that with MEM. Deletion experiments evidenced the prominent role of pyruvate, transferrin, and selenium in the stimulation of surfactant PC biosynthesis. The addition of biotin to DM enhanced surfactant PC biosynthesis slightly and nonsurfactant PC biosynthesis markedly. The presence of nucleosides seemed unfavorable to the synthesis of surfactant PC. Type II cells responded to the addition of epidermal growth factor and insulinlike growth factor-I both by increased thymidine incorporation into DNA and choline incorporation into PC. It is concluded that DM represents a useful tool for cultivating type II cells without loss of their specialized properties and for studying the regulation of cell proliferation and surfactant biosynthesis in a controlled environment.

Biochemical maturation of fetal rat lung: a comprehensive study including surfactant determination

The paper describes a comprehensive assessment of lung growth and biochemical maturation in the fetal and early postnatal rat. Fetal lung grew faster than whole body between gestational day 16.5 and term. Cell number increased quasi-exponentially, except for a slowing of cell growth between days 19.5 and 20.5 of gestation. By contrast, growth was limited during the two first postnatal days. Percentage of dry tissue and protein concentration increased in parallel during the whole period. Increases in whole lung tissue phosphatidylcholine were greatest between 20.5 and 21.5 days of gestation, whereas in isolated surfactant fraction, changes were most marked between 19.5 and 20.5 days. The most striking changes were a 19-fold increase in phosphatidylcholine and a 12.5-fold increase in the total phospholipid concentrations in the surfactant fraction between gestational day 19.5 and 1 day postpartum. Similar changes occurred in disaturated phosphatidylcholine (DSPC) concentration. During the same period, phospholipids of the residual (nonsurfactant) fraction increased only about 2-fold. These data indicate that analysis of an isolated surfactant fraction is advantageous in providing a very sensitive index of augmented phospholipid production during the process of fetal lung maturation. Evidence of biochemical maturation was detected earlier in females than in males, as indicated by a significantly larger surfactant fraction DSPC concentration in 19.5-day-old females; however, this difference was modest in degree and very transient, since it was no longer demonstrable in later stages.