Amit D. Gujar

Bioresorbable silicon electronic sensors for the brain

Many procedures in modern clinical medicine rely on the use of electronic implants in treating conditions that range from acute coronary events to traumatic injury. However, standard permanent electronic hardware acts as a nidus for infection: bacteria form biofilms along percutaneous wires, or seed haematogenously, with the potential to migrate within the body and to provoke immune-mediated pathological tissue reactions. The associated surgical retrieval procedures, meanwhile, subject patients to the distress associated with re-operation and expose them to additional complications. Here, we report materials, device architectures, integration strategies, and in vivo demonstrations in rats of implantable, multifunctional silicon sensors for the brain, for which all of the constituent materials naturally resorb via hydrolysis and/or metabolic action, eliminating the need for extraction. Continuous monitoring of intracranial pressure and temperature illustrates functionality essential to the treatment of traumatic brain injury; the measurement performance of our resorbable devices compares favourably with that of non-resorbable clinical standards. In our experiments, insulated percutaneous wires connect to an externally mounted, miniaturized wireless potentiostat for data transmission. In a separate set-up, we connect a sensor to an implanted (but only partially resorbable) data-communication system, proving the principle that there is no need for any percutaneous wiring. The devices can be adapted to sense fluid flow, motion, pH or thermal characteristics, in formats that are compatible with the body’s abdomen and extremities, as well as the deep brain, suggesting that the sensors might meet many needs in clinical medicine.

A CDC20-APC/SOX2 Signaling Axis Regulates Human Glioblastoma Stem-like Cells

Glioblastoma harbors a dynamic subpopulation of glioblastoma stem-like cells (GSCs) that can propagate tumors in vivo and is resistant to standard chemoradiation. Identification of the cell-intrinsic mechanisms governing this clinically important cell state may lead to the discovery of therapeutic strategies for this challenging malignancy. Here, we demonstrate that the mitotic E3 ubiquitin ligase CDC20-anaphase-promoting complex (CDC20-APC) drives invasiveness and self-renewal in patient tumor-derived GSCs. Moreover, CDC20 knockdown inhibited and CDC20 overexpression increased the ability of human GSCs to generate brain tumors in an orthotopic xenograft model in vivo. CDC20-APC control of GSC invasion and self-renewal operates through pluripotency-related transcription factor SOX2. Our results identify a CDC20-APC/SOX2 signaling axis that controls key biological properties of GSCs, with implications for CDC20-APC-targeted strategies in the treatment of glioblastoma.

An NAD+-dependent transcriptional program governs self-renewal and radiation resistance in glioblastoma

Significance Glioblastoma, the most common primary malignant brain tumor in adults, remains challenging despite multimodality therapy, necessitating the discovery of new therapies. Nicotinamide adenine dinucleotide (NAD+) plays a pivotal role in cancer cell metabolism, but how NAD+ impacts functional signaling events in glioblastoma is not well understood. We provide clinical evidence that high expression of NAMPT, the rate-limiting step in NAD+ biosynthesis, in glioblastoma tumors is associated with poor overall survival in patients, and demonstrate NAMPT and NAD+ are required for the maintenance of patient-derived glioblastoma stem-like cells (GSCs). Moreover, we delineate a NAD+-dependent transcriptional program that governs GSC self-renewal and dictates the radiation resistance of these cells. These findings identify potential new therapeutic avenues for the treatment of glioblastoma. Accumulating evidence suggests cancer cells exhibit a dependency on metabolic pathways regulated by nicotinamide adenine dinucleotide (NAD+). Nevertheless, how the regulation of this metabolic cofactor interfaces with signal transduction networks remains poorly understood in glioblastoma. Here, we report nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting step in NAD+ synthesis, is highly expressed in glioblastoma tumors and patient-derived glioblastoma stem-like cells (GSCs). High NAMPT expression in tumors correlates with decreased patient survival. Pharmacological and genetic inhibition of NAMPT decreased NAD+ levels and GSC self-renewal capacity, and NAMPT knockdown inhibited the in vivo tumorigenicity of GSCs. Regulatory network analysis of RNA sequencing data using GSCs treated with NAMPT inhibitor identified transcription factor E2F2 as the center of a transcriptional hub in the NAD+-dependent network. Accordingly, we demonstrate E2F2 is required for GSC self-renewal. Downstream, E2F2 drives the transcription of members of the inhibitor of differentiation (ID) helix–loop–helix gene family. Finally, we find NAMPT mediates GSC radiation resistance. The identification of a NAMPT-E2F2-ID axis establishes a link between NAD+ metabolism and a self-renewal transcriptional program in glioblastoma, with therapeutic implications for this formidable cancer.

Establishing Primary Human Glioblastoma Adherent Cultures from Operative Specimens

This chapter describes a method for isolation, maintenance, and propagation of primary glioblastoma (GBM) cells in adherent monolayer cultures from patient tumor specimens. This method enables the establishment of GBM cultures with stem or progenitor-like cell characteristics, including self-renewal capacity, differentiation along restricted neural lineages, and tumor-initiating potential when orthotopically injected into immunocompromised mice. This experimentally tractable model system is therefore suitable for a wide variety of analyses in vitro as well as in vivo. Key examples of biological analyses that can be performed using these cells are also described.

The CDC20-APC/SOX2 signaling axis: An achilles' heel for glioblastoma

ABSTRACT Glioblastoma stem-like cells (GSCs) play a critical role in glioblastoma progression and recurrence. We discuss recent results on the role of the mitotic ubiquitin ligase cell division cycle 20–anaphase-promoting complex (CDC20-APC) in the governance of cardinal GSC functions through a mechanism involving the transcription factor sex-determining region Y-box 2 (SOX2). These findings expand the non-mitotic roles of CDC20-APC with implications for stem cell biology.