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Glioblastoma is incurable and in urgent need of improved therapeutics1. Here we identify a small compound, gliocidin, that kills glioblastoma cells while sparing non-tumour replicative cells. Gliocidin activity targets a de novo purine synthesis vulnerability in glioblastoma through indirect inhibition of inosine monophosphate dehydrogenase 2 (IMPDH2). IMPDH2 blockade reduces intracellular guanine nucleotide levels, causing nucleotide imbalance, replication stress and tumour cell death2. Gliocidin is a prodrug that is anabolized into its tumoricidal metabolite, gliocidin–adenine dinucleotide (GAD), by the enzyme nicotinamide nucleotide adenylyltransferase 1 (NMNAT1) of the NAD+salvage pathway. The cryo-electron microscopy structure of GAD together with IMPDH2 demonstrates its entry, deformation and blockade of the NAD+pocket3. In vivo, gliocidin penetrates the blood–brain barrier and extends the survival of mice with orthotopic glioblastoma. The DNA alkylating agent temozolomide induces Nmnat1expression, causing synergistic tumour cell killing and additional survival benefit in orthotopic patient-derived xenograft models. This study brings gliocidin to light as a prodrug with the potential to improve the survival of patients with glioblastoma.

Cancer-specific inhibitors that reflect the unique metabolic needs of cancer cells are rare. Here we describe Gboxin, a small molecule that specifically inhibits the growth of primary mouse and human glioblastoma cells but not that of mouse embryonic fibroblasts or neonatal astrocytes. Gboxin rapidly and irreversibly compromises oxygen consumption in glioblastoma cells. Gboxin relies on its positive charge to associate with mitochondrial oxidative phosphorylation complexes in a manner that is dependent on the proton gradient of the inner mitochondrial membrane, and it inhibits the activity of F0F1ATP synthase. Gboxin-resistant cells require a functional mitochondrial permeability transition pore that regulates pH and thus impedes the accumulation of Gboxin in the mitochondrial matrix. Administration of a metabolically stable Gboxin analogue inhibits glioblastoma allografts and patient-derived xenografts. Gboxin toxicity extends to established human cancer cell lines of diverse organ origin, and shows that the increased proton gradient and pH in cancer cell mitochondria is a mode of action that can be targeted in the development of antitumour reagents.

KASH (Klarsicht, Anc-1, Syne-1 homology) domain-containing proteins anchor the nucleus to the actin cytoskeleton or to microtubules. KASH proteins thus play pivotal roles in a variety of developmental processes where nuclear positioning is critical. Two KASH proteins have been identified in Drosophila: Muscle-specific protein-300 (Msp-300) and Klarsicht (Klar). Msp-300 anchors nuclei to actin, and has been reported to be essential for positioning of nurse cell nuclei during oogenesis, and thus production of mature ooctyes. Klar is required for positioning of photoreceptor and cone cell nuclei in the developing eye, which is critical for proper eye morphology. Here, we asked whether KASH domain-containing forms of Msp-300 are required for nuclear positioning in the eye, and we found that they are not. Moreover, in the course of this work, we discovered that contrary to previous reports, KASH domain-containing forms of Msp-300 are not required for viability, nor for oogenesis. However, we did find that Msp-300 has a function in egg laying, normally redundant with a function of Klar.

KASH (Klarsicht/ Anc-1/ Syne homology) domain proteins are cytoskeleton-associated proteins localized uniquely to the outer nuclear membrane. Klarsicht is a KASH protein required for nuclear migration in differentiating cells of the Drosophila eye. The C-terminal KASH domain of Klarsicht resides in the perinuclear space, and the cytoplasmic moiety connects to the microtubule organizing center. In C. elegans and vertebrate cells, SUN (Sad1/ UNC-84) domain proteins reside in the inner nuclear membrane and tether KASH proteins to the outer nuclear membrane. Is there a Drosophila SUN protein that performs a similar function, and if so, is it like Klarsicht, obviously essential for nuclear positioning only in the eye? Here, we identify Drosophila Klaroid, a SUN protein that tethers Klarsicht. klaroid loss-of-function mutants are indistinguishable phenotypically from klarsicht mutants. Remarkably, neither gene is essential for Drosophila viability or fertility, and even in klaroid klarsicht double mutants, the only obvious external morphological defect is rough eyes. In addition, we find that klaroid and klarsicht are required for nuclear migration in differentiating neurons and in non-neural cells. Finally, while perinuclear Klaroid is ubiquitous in the eye, Klarsicht expression is limited to differentiating cells and may be part of the trigger for apical nuclear migration.

NF1-associated malignant peripheral nerve sheath tumors (MPNSTs) are the major cause of mortality in neurofibromatosis. MPNSTs arise from benign peripheral nerve plexiform neurofibromas that originate in the embryonic neural crest cell lineage. Using reporter transgenes that label early neural crest lineage cells in multiple NF1 MPNST mouse models, we discover and characterize a rare MPNST cell population with stem-cell-like properties, including quiescence, that is essential for tumor initiation and relapse. Following isolation of these cells, we derive a cancer-stem-cell-specific gene expression signature that includes consensus embryonic neural crest genes and identify Nestin as a marker for the MPNST cell of origin. Combined targeting of cancer stem cells along with antimitotic chemotherapy yields effective tumor inhibition and prolongs survival. Enrichment of the cancer stem cell signature in cognate human tumors supports the generality and relevance of cancer stem cells to MPNST therapy development.