Antero J. Abrunhosa

Therapeutic implications of an enriched cancer stem-like cell population in a human osteosarcoma cell line

BackgroundOsteosarcoma is a bone-forming tumor of mesenchymal origin that presents a clinical pattern that is consistent with the cancer stem cell model. Cells with stem-like properties (CSCs) have been identified in several tumors and hypothesized as the responsible for the relative resistance to therapy and tumor relapses. In this study, we aimed to identify and characterize CSCs populations in a human osteosarcoma cell line and to explore their role in the responsiveness to conventional therapies.MethodsCSCs were isolated from the human MNNG/HOS cell line using the sphere formation assay and characterized in terms of self-renewal, mesenchymal stem cell properties, expression of pluripotency markers and ABC transporters, metabolic activity and tumorigenicity. Cells sensitivity to conventional chemotherapeutic agents and to irradiation was analyzed and related with cell cycle-induced alterations and apoptosis.ResultsThe isolated CSCs were found to possess self-renewal and multipotential differentiation capabilities, express markers of pluripotent embryonic stem cells Oct4 and Nanog and the ABC transporters P-glycoprotein and BCRP, exhibit low metabolic activity and induce tumors in athymic mice. Compared with parental MNNG/HOS cells, CSCs were relatively more resistant to both chemotherapy and irradiation. None of the treatments have induced significant cell-cycle alterations and apoptosis in CSCs.ConclusionsMNNG/HOS osteosarcoma cells contain a stem-like cell population relatively resistant to conventional chemotherapeutic agents and irradiation. This resistant phenotype appears to be related with some stem features, namely the high expression of the drug efflux transporters P-glycoprotein and BCRP and their quiescent nature, which may provide a biological basis for resistance to therapy and recurrence commonly observed in osteosarcoma.

Molecular imaging with SPECT as a tool for drug development.

Molecular imaging techniques are increasingly being used as valuable tools in the drug development process. Radionuclide-based imaging modalities such as single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have proven to be useful in phases ranging from preclinical development to the initial stages of clinical testing. The high sensitivity of these imaging modalities makes them particularly suited for exploratory investigational new drug (IND) studies as they have the potential to characterize in vivo pharmacokinetics and biodistribution of the compounds using only a fraction of the intended therapeutic dose (microdosing). This information obtained at an early stage of clinical testing results in a better selection among promising drug candidates, thereby increasing the success rate of agents entering clinical trials and the overall efficiency of the process. In this article, we will review the potential applications of SPECT imaging in the drug development process with an emphasis on its applications in exploratory IND studies.

Chemotherapy induces stemness in osteosarcoma cells through activation of Wnt/β-catenin signaling

Development of resistance represents a major drawback in osteosarcoma treatment, despite improvements in overall survival. Treatment failure and tumor progression have been attributed to pre-existing drug-resistant clones commonly assigned to a cancer stem-like phenotype. Evidence suggests that non stem-like cells, when submitted to certain microenvironmental stimuli, can acquire a stemness phenotype thereby strengthening their capacity to handle with stressful conditions. Here, using osteosarcoma cell lines and a mouse xenograft model, we show that exposure to conventional chemotherapeutics induces a phenotypic cell transition toward a stem-like phenotype. This associates with activation of Wnt/β-catenin signaling, up-regulation of pluripotency factors and detoxification systems (ABC transporters and Aldefluor activity) that ultimately leads to chemotherapy failure. Wnt/β-catenin inhibition combined with doxorubicin, in the MNNG-HOS cells, prevented the up-regulation of factors linked to transition into a stem-like state and can be envisaged as a way to overcome adaptive resistance. Finally, the analysis of the public R2 database, containing microarray data information from diverse osteosarcoma tissues, revealed a correlation between expression of stemness markers and a worse response to chemotherapy, which provides evidence for drug-induced phenotypic stem cell state transitions in osteosarcoma.

Bursting electrical activity in pancreatic β-cells: evidence that the channel underlying the burst is sensitive to Ca2+ influx through L-type Ca2+ channels

In glucose-stimulated pancreatic β-cells, the membrane potential alternates between a hyperpolarized silent phase and a depolarized phase with Ca2+ action potentials. The molecular and ionic mechanisms underlying these bursts of electrical activity remain unknown. We have observed that 10.2–12.8 mM Ca2+, 1 μM Bay K 8644 and 2 mM tetraethylammonium (TEA) trigger bursts of electrical activity and oscillations of intracellular free Ca2+ concentration ([Ca2+]i) in the presence of 100 μM tolbutamide. The [Ca2+]i was monitored from single islets of Langerhans using fura-2 microfluorescence techniques. Both the high-Ca2+ and Bay-K-8644 evoked [Ca2+]i oscillations overshot the [Ca2+]i recorded in tolbutamide. Nifedipine (10–20 μM) caused an immediate membrane hyperpolarization, which was followed by a slow depolarization to a level close to the burst active phase potential. The latter depolarization was accompanied by suppression of spiking activity. Exposure to high Ca2+ in the presence of nifedipine caused a steady depolarization of approximately 8 mV. Ionomycin (10 μM) caused membrane hyperpolarization in the presence of 7.7 mM Ca2+, which was not abolished by nifedipine. Charybdotoxin (CTX, 40–80 nM), TEA (2 mM) and quinine (200 μM) did not suppress the high-Ca2+-evoked bursts. It is concluded that: (1) the channel underlying the burst is sensitive to [Ca2+]i rises mediated by Ca2+ influx through L-type Ca2+ channels, (2) both the ATP-dependent K+ channel and the CTX and TEA-sensitive Ca2+-dependent K+ channel are highly unlikely to provide the pacemaker current underlying the burst. We propose that the burst is mediated by a distinct Ca2+-dependent K+ channel and/or by [Ca2+]idependent slow processes of inactivation of Ca2+ currents.

The Warburg effect in mycobacterial granulomas is dependent on the recruitment and activation of macrophages by interferon-γ

Granulomas are the hallmark of mycobacterial disease. Here, we demonstrate that both the cell recruitment and the increased glucose consumption in granulomatous infiltrates during Mycobacterium avium infection are highly dependent on interferon‐γ (IFN‐γ). Mycobacterium avium‐infected mice lacking IFN‐γ signalling failed to developed significant inflammatory infiltrations and lacked the characteristic uptake of the glucose analogue fluorine‐18‐fluorodeoxyglucose (FDG). To assess the role of macrophages in glucose uptake we infected mice with a selective impairment of IFN‐γ signalling in the macrophage lineage (MIIG mice). Although only a partial reduction of the granulomatous areas was observed in infected MIIG mice, the insensitivity of macrophages to IFN‐γ reduced the accumulation of FDG. In vivo, ex vivo and in vitro assays showed that macrophage activated by IFN‐γ displayed increased rates of glucose uptake and in vitro studies showed also that they had increased lactate production and increased expression of key glycolytic enzymes. Overall, our results show that the activation of macrophages by IFN‐γ is responsible for the Warburg effect observed in organs infected with M. avium.

P-glycoprotein Versus MRP1 on Transport Kinetics of Cationic Lipophilic Substrates: A Comparative Study Using [99mTc]Sestamibi and [99mTc]Tetrofosmin

The multidrug resistance (MDR) phenotype in cancer is closely related with the overexpression of P-glycoprotein (Pgp) and multidrug resistance protein-1 (MRP1). Although conferring resistance to a similar spectrum of drugs, these proteins present distinct transport mechanisms and have their own substrates. In this work, we compared the functional properties of Pgp and MRP1 in the transport kinetics of two cationic lipophilic tracers, [(99m)Tc]sestamibi and [(99m)Tc]tetrofosmin, in cellular models of resistance. Cellular transport kinetics of both tracers was evaluated in Small-cell lung cancer cell line H69 and in its drug-resistant sublines, H69LX4 and H69AR, overexpressing Pgp and MRP1, respectively. Studies were performed in the absence and in the presence of MDR modulators. Kinetic parameters extracted from time-activity curves were analyzed through receiver-operating characteristics curve analysis. The uptake and the efflux rate of both radiotracers were significantly higher (p < 0.05) in sensitive cells. However, MRP1 was more effective than Pgp in removing tracers from the intracellular medium. The addition of verapamil and PSC833 significantly reduced the efflux rate and restored the accumulation of both tracers in H69LX4 cells. Only verapamil was effective in the inhibition of MRP1; however, the effects were more pronounced with [(99m)Tc]sestamibi, when compared to [(99m)Tc]tetrofosmin. Outward transport of radiotracers by MRP1 was dependent on the intracellular glutathione levels. We concluded that both tracers can detect Pgp- and MRP1-mediated drug resistance, based on transport kinetics; however, MRP1 is more effective than Pgp on outward transport of radiotracers. We postulate that this finding can be useful to distinguish between the two resistance mechanisms.

GABA deficiency in NF1 A multimodal [11C]-flumazenil and spectroscopy study

Objective: To provide a comprehensive investigation of the γ-aminobutyric acid (GABA) system in patients with neurofibromatosis type 1 (NF1) that allows understanding the nature of the GABA imbalance in humans at pre- and postsynaptic levels. Methods: In this cross-sectional study, we employed multimodal imaging and spectroscopy measures to investigate GABA type A (GABAA) receptor binding, using [11C]-flumazenil PET, and GABA concentration, using magnetic resonance spectroscopy (MRS). Fourteen adult patients with NF1 and 13 matched controls were included in the study. MRS was performed in the occipital cortex and in a frontal region centered in the functionally localized frontal eye fields. PET and MRS acquisitions were performed in the same day. Results: Patients with NF1 have reduced concentration of GABA+ in the occipital cortex (p = 0.004) and frontal eye fields (p = 0.026). PET results showed decreased binding of GABAA receptors in patients in the parieto-occipital cortex, midbrain, and thalamus, which are not explained by decreased gray matter levels. Conclusions: Abnormalities in the GABA system in NF1 involve both GABA concentration and GABAA receptor density suggestive of neurodevelopmental synaptopathy with both pre- and postsynaptic involvement.

Synthesis of a new 18F labeled porphyrin for potential application in positron emission tomography. In vivo imaging and cellular uptake

Herein we report, for the first time, the development, labeling optimization and preliminary biodistribution studies of an [18F] radiolabeled meso-tetraphenylporphyrin. After synthesis and characterization of the “cold” fluorinated porphyrin, the conditions have been transferred to an automated radiochemistry module and the desired 5-(2-[18F]fluoroethoxyphenyl)-10,15,20-triphenylporphyrin was prepared in a radiochemical purity >95%. Moreover, data regarding the uptake into human bladder tumor cells and the radiotracer biodistribution after C57BL/6 mice injection are also presented. The maximum cellular uptake was reached at 45 min and was of 2.5%.

Therapeutic potential of the metabolic modulator Metformin on osteosarcoma cancer stem-like cells

PurposeOsteosarcoma is the most common primary bone tumour appearing in children and adolescents. Recent studies demonstrate that osteosarcoma possesses a stem-like cell subset, so-called cancer stem-like cells, refractory to conventional chemotherapeutics and pointed out as responsible for relapses frequently observed in osteosarcoma patients. Here, we explored the therapeutic potential of Metformin on osteosarcoma stem-like cells, alone and as a chemosensitizer of doxorubicin.MethodsStem-like cells were isolated from human osteosarcoma cell lines, MNNG/HOS and MG-63, using the sphere-forming assay. Metformin cytotoxicity alone and combined with doxorubicin were evaluated using MTT/BrdU assays. Protein levels of AMPK and AKT were evaluated by Western Blot. Cellular metabolic status was assessed based on [18F]-FDG uptake and lactate production measurements. Sphere-forming efficiency and expression of pluripotency transcription factors analysed by qRT-PCR were tested as readout of Metformin effects on stemness features.ResultsMetformin induced a concentration-dependent decrease in the metabolic activity and proliferation of sphere-forming cells and improved doxorubicin-induced cytotoxicity. This drug also down-regulated the expression of master regulators of pluripotency (OCT4, SOX2, NANOG), and decreased spheres’ self-renewal ability. Metformin effects on mitochondria led to the activation and phosphorylation of the energetic sensor AMPK along with an upregulation of the pro-survival AKT pathway in both cell populations. Furthermore, Metformin-induced mitochondrial stress increased [18F]-FDG uptake and lactate production in parental cells but not in the quiescent stem-like cells, suggesting the inability of the latter to cope with the energy crisis induced by metformin.ConclusionsThis preclinical study suggests that Metformin may be a potentially useful therapeutic agent and chemosensitizer of osteosarcoma stem-like cells to doxorubicin.

Neuronal and developmental effects of high magnetic fields in the development of an intact living organism: Ceanorhabditis elegans

In this paper we report on the progress of our research regarding the effects of high magnetic fields in the development of an intact living organism, the nematode Ceanorhabditis elegans. The objective is to observe details of possible changes in morphology and neurobiology during the development process. Results obtained so far with fields up to 14 Tesla failed to show any statistically significant alterations.