Vinata Vedam-Mai

The Cancer Stem Cell Hypothesis: Failures and Pitfalls

Based on the clonal evolution model and the assumption that the vast majority of tumor cells are able to propagate and drive tumor growth, the goal of cancer treatment has traditionally been to kill all cancerous cells. This theory has been challenged recently by the cancer stem cell (CSC) hypothesis, that a rare population of tumor cells, with stem cell characteristics, is responsible for tumor growth, resistance, and recurrence. Evidence for putative CSCs has been described in blood, breast, lung, prostate, colon, liver, pancreas, and brain. This new hypothesis would propose that indiscriminate killing of cancer cells would not be as effective as selective targeting of the cells that are driving long-term growth (ie, the CSCs) and that treatment failure is often the result of CSCs escaping traditional therapies. The CSC hypothesis has gained a great deal of attention because of the identification of a new target that may be responsible for poor outcomes of many aggressive cancers, including malignant glioma. As attractive as this hypothesis sounds, especially when applied to tumors that respond poorly to current treatments, we will argue in this article that the proposal of a stemlike cell that initiates and drives solid tissue cancer growth and is responsible for therapeutic failure is far from proven. We will present the point of view that for most advanced solid tissue cancers such as glioblastoma multiforme, targeting a putative rare CSC population will have little effect on patient outcomes. This review will cover problems with the CSC hypothesis, including applicability of the hierarchical model, inconsistencies with xenotransplantation data, and nonspecificity of CSC markers.

Deep brain stimulation and the role of astrocytes

Deep brain stimulation (DBS) has emerged as a powerful surgical therapy for the management of treatment-resistant movement disorders, epilepsy and neuropsychiatric disorders. Although DBS may be clinically effective in many cases, its mode of action is still elusive. It is unclear which neural cell types are involved in the mechanism of DBS, and how high-frequency stimulation of these cells may lead to alleviation of the clinical symptoms. Neurons have commonly been a main focus in the many theories explaining the working mechanism of DBS. Recent data, however, demonstrates that astrocytes may be active players in the DBS mechanism of action. In this review article, we will discuss the potential role of reactive and neurogenic astrocytes (neural progenitors) in DBS.

Differential Connexin Function Enhances Self-Renewal in Glioblastoma

SUMMARY The coordination of complex tumor processes requires cells to rapidly modify their phenotype and is achieved by direct cell-cell communication through gap junction channels composed of connexins. Previous reports have suggested that gap junctions are tumor suppressive based on connexin43 (Cx43), but this does not take into account differences in connexin-mediated ion selectivity and intercellular communication rate that drive gap junction diversity. We find that glioblastoma cancer stem cells (CSCs) possess functional gap junctions that can be targeted using clinically relevant compounds to reduce self-renewal and tumor growth. Our analysis reveals that CSCs express Cx46, while Cx43 is predominantly expressed in non-CSCs. During differentiation, Cx46 is reduced, while Cx43 is increased, and targeting Cx46 compromises CSC maintenance. The difference between Cx46 and Cx43 is reflected in elevated cell-cell communication and reduced resting membrane potential in CSCs. Our data demonstrate a pro-tumorigenic role for gap junctions that is dependent on connexin expression.

Increased precursor cell proliferation after deep brain stimulation for Parkinson's disease: a human study.

Objective Deep brain stimulation (DBS) has been used for more than a decade to treat Parkinsons disease (PD); however, its mechanism of action remains unknown. Given the close proximity of the electrode trajectory to areas of the brain known as the “germinal niches,” we sought to explore the possibility that DBS influences neural stem cell proliferation locally, as well as more distantly. Methods We studied the brains of a total of 12 idiopathic Parkinsons disease patients that were treated with DBS (the electrode placement occurred 0.5–6 years before death), and who subsequently died of unrelated illnesses. These were compared to the brains of 10 control individuals without CNS disease, and those of 5 PD patients with no DBS. Results Immunohistochemical analyses of the subventricular zone (SVZ) of the lateral ventricles, the third ventricle lining, and the tissue surrounding the DBS lead revealed significantly greater numbers of proliferating cells expressing markers of the cell cycle, plasticity, and neural precursor cells in PD-DBS tissue compared with both normal brain tissue and tissue from PD patients not treated with DBS. The level of cell proliferation in the SVZ in PD-DBS brains was 2–6 fold greater than that in normal and untreated PD brains. Conclusions Our data suggest that DBS is capable of increasing cellular plasticity in the brain, and we hypothesize that it may have more widespread effects beyond the electrode location. It is unclear whether these effects of DBS have any symptomatic or other beneficial influences on PD.

Neural-Colony Forming Cell Assay: An Assay To Discriminate Bona Fide Neural Stem Cells from Neural Progenitor Cells

The neurosphere assay (NSA) is one of the most frequently used methods to isolate, expand and also calculate the frequency of neural stem cells (NSCs). Furthermore, this serum-free culture system has also been employed to expand stem cells and determine their frequency from a variety of tumors and normal tissues. It has been shown recently that a one-to-one relationship does not exist between neurosphere formation and NSCs. This suggests that the NSA as currently applied, overestimates the frequency of NSCs in a mixed population of neural precursor cells isolated from both the embryonic and adult mammalian brain. This video practically demonstrates a novel collagen based semi- solid assay, the neural-colony forming cell assay (N-CFCA), which has the ability to discriminate stem from progenitor cells based on their long-term proliferative potential, and thus provides a method to enumerate NSC frequency. In the N-CFCA, colonies ≥2 mm in diameter are derived from cells that meet all the functional criteria of a NSC, while colonies < 2mm are derived from progenitors. The N-CFCA procedure can be used for cells prepared from different sources including primary and cultured adult or embryonic mouse CNS cells. Here we use cells prepared from passage one neurospheres generated from embryonic day 14 mice brain to perform N-CFCA. The cultures are replenished with proliferation medium every seven days for three weeks to allow the plated cells to exhibit their full proliferative potential and then the frequency of neural progenitor and bona fide neural stem cells is calculated respectively by counting the number of colonies that are < 2mm and the ones that are ≥2mm in reference to the number of cells that were initially plated.

Disrupting abnormal electrical activity with deep brain stimulation: is epilepsy the next frontier?

Given the tremendous success of deep brain stimulation (DBS) for the treatment of movement and neuropsychiatric disorders, clinicians have begun to open up to the possible use of electrical stimulation for the treatment of patients with uncontrolled seizures. This process has resulted in the discovery of a wide array of DBS targets, including the cerebellum, hypothalamus, hippocampus, basal ganglia, and various thalamic nuclei. Despite the ambiguity of the mechanism of action and the unknowns surrounding potentially ideal stimulation settings, several recent trials have empirically demonstrated reasonable efficacy in selected cases of medication-refractory seizures. These exciting results have fueled a number of studies aimed at firmly establishing DBS as an effective treatment for selected cases of intractable epilepsy, and many companies are aiming at Food and Drug Administration approval. We endeavor to review the studies in the context of the various DBS targets and their relevant circuitry for epilepsy. Based on the unfolding research, DBS has the potential to play an important role in treating refractory epilepsy. The challenge, as in movement disorders, is to assemble interdisciplinary teams to screen, implant, and follow patients, and to clarify patient selection. The future will undoubtedly be filled with optimization of targets and stimulation parameters and the development of best practices. With tailored therapeutic approaches, epilepsy patients have the potential to improve with DBS.

Transplantation of Defined Populations of Differentiated Human Neural Stem Cell Progeny

Many neurological injuries are likely too extensive for the limited repair capacity of endogenous neural stem cells (NSCs). An alternative is to isolate NSCs from a donor, and expand them in vitro as transplantation material. Numerous groups have already transplanted neural stem and precursor cells. A caveat to this approach is the undefined phenotypic distribution of the donor cells, which has three principle drawbacks: (1) Stem-like cells retain the capacity to proliferate in vivo. (2) There is little control over the cells’ terminal differentiation, e.g., a graft intended to replace neurons might choose a predominantly glial fate. (3) There is limited ability of researchers to alter the combination of cell types in pursuit of a precise treatment. We demonstrate a procedure for differentiating human neural precursor cells (hNPCs) in vitro, followed by isolation of the neuronal progeny. We transplanted undifferentiated hNPCs or a defined concentration of hNPC-derived neurons into mice, then compared these two groups with regard to their survival, proliferation and phenotypic fate. We present evidence suggesting that in vitro-differentiated-and-purified neurons survive as well in vivo as their undifferentiated progenitors, and undergo less proliferation and less astrocytic differentiation. We also describe techniques for optimizing low-temperature cell preservation and portability.

A pilot study of human brain tissue post-magnetic resonance imaging: Information from the National Deep Brain Stimulation Brain Tissue Network (DBS-BTN)

INTRODUCTION The safety of magnetic resonance imaging (MRI) for deep brain stimulation (DBS) patients is of great importance to both movement disorders clinicians and to radiologists. The present study utilized the Deep Brain Stimulation Brain Tissue Networks (DBS-BTNs) clinical and neuropathological database to search for evidence of adverse effects of MRI performed on implanted DBS patients. HYPOTHESIS Performing a 1.5 T MRI with a head receive coil on patients with implanted DBS devices should not result in evidence of adverse clinical or pathological effects in the DBS-BTN cohort. Further, exposing post-mortem DBS-BTN brains with DBS leads to extended 3T MRI imaging should not result in pathological adverse effects. METHODS An electronic literature search was performed to establish clinical and neuropathological criteria for evidence of MRI-related adverse reactions in DBS patients. A retrospective chart review of the DBS-BTN patients was then performed to uncover potential adverse events resulting from MRI scanning. DBS patient characteristics and MRI parameters were recorded for each patient. In addition, 3T MRI scans were performed on 4 post-mortem brains with DBS leads but without batteries attached. Detailed neuropathological studies were undertaken to search for evidence of MRI-induced adverse tissue changes. RESULTS No clinical signs or symptoms or MRI-induced adverse effects were discovered in the DBS-BTN database, and on detailed review of neuroimaging studies. Neuropathological examination did not reveal changes consistent with MRI-induced heating damage. The novel study of four brains with prolonged 3T post-mortem magnetic field exposure (DBS leads left in place) also did not reveal pathological changes consistent with heat related damage. DISCUSSION The current study adds important information to the data on the safety of MRI in DBS patients. Novel post-mortem MRI studies provide additional information regarding the safety of 3T MRI in DBS patients, and could justify additional studies especially post-mortem scans with battery sources in place. CONCLUSION The lack of pathological findings in the DBS-BTN database and the lack of tissue related changes following prolonged exposure to 3T MRI in the post-mortem brains suggest that MRI scanning in DBS patients may be relatively safe, especially under current guidelines requiring a head receive coil. Subsequent studies exploring the safety of 1.5 T versus 3T MRI in DBS patients should utilize more in depth post-mortem imaging to better simulate the human condition.

Deep brain stimulation response in pathologically confirmed cases of multiple system atrophy.

Deep brain stimulation is a treatment for select cases of medication refractory movement disorders including Parkinsons disease. Deep brain stimulation has not been recommended for treatment in multiple system atrophy patients. However, the paucity of literature documenting the effects of deep brain stimulation in multiple system atrophy patients and the revelation of a levodopa responsive subtype of multiple system atrophy suggests further investigation is necessary. This study summarizes the positive and negative effects of deep brain stimulation treatment in two pathologically confirmed multiple system atrophy patients from the University of Florida Deep Brain Stimulation-Brain Tissue Network. Clinical diagnosis for the two patient cases did not match the neuropathological diagnosis. We noted that in both pathologically confirmed multiple system atrophy patients, death occurred as a result of myocardial infarction. Importantly, there was reported transient benefit in levodopa responsive features that indicate deep brain stimulation may be an option for select multiple system atrophy patients.

The "brittle response" to Parkinson's disease medications: characterization and response to deep brain stimulation.

Objective Formulate a definition and describe the clinical characteristics of PD patients with a “brittle response” (BR) to medications versus a “non-brittle response” (NBR), and characterize the use of DBS for this population. Methods An UF IRB approved protocol used a retrospective chart review of 400 consecutive PD patients presenting to the UF Center for Movement Disorders and Neurorestoration. Patient records were anonymized and de-identified prior to analysis. SPSS statistics were used to analyze data. Results Of 345 included patients, 19 (5.5%) met criteria for BR PD. The BR group was comprised of 58% females, compared to 29% in the NBR group (P = .008). The former had a mean age of 63.4 compared to 68.1 in the latter. BR patients had lower mean weight (63.5 vs. 79.6, P = <.001), longer mean disease duration (12.6 vs. 8.9 years, P = .003), and had been on LD for more years compared to NBR patients (9.8 vs. 5.9, P = .001). UPDRS motor scores were higher (40.4 vs. 30.0, P = .001) in BR patients. No differences were observed regarding the Schwab and England scale, PDQ-39, and BDI-II. Sixty-three percent of the BR group had undergone DBS surgery compared to 18% (P = .001). Dyskinesias were more common, severe, and more often painful (P = <.001) in the BR group. There was an overall positive benefit from DBS. Conclusion BR PD occurred more commonly in female patients with a low body weight. Patients with longer disease duration and longer duration of LD therapy were also at risk. The BR group responded well to DBS.