Treatment of Recurrent Glioblastoma by Chronic Convection-Enhanced Delivery of Topotecan

ABSTRACTGlioblastoma, the most common primary brain malignancy, is invariably fatal. Systemic chemotherapy is ineffective mostly because of drug delivery limitations. To overcome this, we devised an internalized pump-catheter system for direct chronic convection-enhanced delivery (CED) into peritumoral brain tissue. Topotecan (TPT) by chronic CED in 5 patients with refractory glioblastoma selectively eliminated tumor cells without toxicity to normal brain. Large, stable drug distribution volumes were non-invasively monitored with MRI of co-infused gadolinium. Analysis of multiple radiographically localized biopsies taken before and after treatment showed a decreased proliferative tumor signature resulting in a shift to a slow-cycling mesenchymal/astrocytic-like population. Tumor microenvironment analysis showed an inflammatory response and preservation of neurons. This novel drug delivery strategy and innovative clinical trial paradigm overcomes current limitations in delivery and treatment response assessment as shown here for glioblastoma and is potentially applicable for other anti-glioma agents as well as other CNS diseases.

Differential Responses of Neural Retina Progenitor Populations to Chronic Hyperglycemia

Diabetic retinopathy is a frequent complication of longstanding diabetes, which comprises a complex interplay of microvascular abnormalities and neurodegeneration. Zebrafish harboring a homozygous mutation in the pancreatic transcription factor pdx1 display a diabetic phenotype with survival into adulthood, and are therefore uniquely suitable among zebrafish models for studying pathologies associated with persistent diabetic conditions. We have previously shown that, starting at three months of age, pdx1 mutants exhibit not only vascular but also neuro-retinal pathologies manifesting as photoreceptor dysfunction and loss, similar to human diabetic retinopathy. Here, we further characterize injury and regenerative responses and examine the effects on progenitor cell populations. Consistent with a negative impact of hyperglycemia on neurogenesis, stem cells of the ciliary marginal zone show an exacerbation of aging-related proliferative decline. In contrast to the robust Müller glial cell proliferation seen following acute retinal injury, the pdx1 mutant shows replenishment of both rod and cone photoreceptors from slow-cycling, neurod-expressing progenitors which first accumulate in the inner nuclear layer. Overall, we demonstrate a diabetic retinopathy model which shows pathological features of the human disease evolving alongside an ongoing restorative process that replaces lost photoreceptors, at the same time suggesting an unappreciated phenotypic continuum between multipotent and photoreceptor-committed progenitors.

BRAF-Inhibitor-Induced Metabolic Alterations in A375 Melanoma Cells

Acquired drug tolerance has been a major challenge in cancer therapy. Recent evidence has revealed the existence of slow-cycling persister cells that survive drug treatments and give rise to multi-drug-tolerant mutants in cancer. Cells in this dynamic persister state can escape drug treatment by undergoing various epigenetic changes, which may result in a transient metabolic rewiring. In this study, with the use of untargeted metabolomics and phenotype microarrays, we characterize the metabolic profiles of melanoma persister cells mediated by treatment with vemurafenib, a BRAF inhibitor. Our findings demonstrate that metabolites associated with phospholipid synthesis, pyrimidine, and one-carbon metabolism and branched-chain amino acid metabolism are significantly altered in vemurafenib persister cells when compared to the bulk cancer population. Our data also show that vemurafenib persisters have higher lactic acid consumption rates than control cells, further validating the existence of a unique metabolic reprogramming in these drug-tolerant cells. Determining the metabolic mechanisms underlying persister cell survival and maintenance will facilitate the development of novel treatment strategies that target persisters and enhance cancer therapy.

Book review: C. Popan (2019). Bicycle Utopias Imagining Fast and Slow Cycling Futures. Routledge.

Cosmin’s book ‘Bicycle Utopias:Imagining Fast and Slow Cycling Futures’ invites us to imagine a different world wherepredominantly bikes are used (at least) for short-distance travel within citiesand claims that the domination of cars is unsustainable and certainly notinevitable.  It also discusses the meritsof slow cycling and warns that the needs for speed and eternal economic growth arenot sustainable. He uses utopia as one of the methods to examine our commonlyheld beliefs and practices, along with auto-ethnography and other methods. Thisbook will certainly make the reader think, question their practices andpriorities, realize that today’s actions can shape the future, and that acar-centric world is not sustainable. A city dominated by slow cycling couldencourage the development of the local economy and small coops for cyclerepairs, deliveries, and generally helps create a virtuous cycle ofsustainable, sociable and healthy living.  

Fine-tuned repression of Drp1 driven mitochondrial fission primes a 'stem/progenitor-like state' to support neoplastic transformation

Gene knockout of the master regulator of mitochondrial fission, Drp1, prevents neoplastic transformation. Also, mitochondrial fission and its opposing process of mitochondrial fusion are emerging as crucial regulators of stemness. Intriguingly, stem/progenitor cells maintaining repressed mitochondrial fission are primed for self-renewal and proliferation. Using our newly derived carcinogen transformed human cell model we demonstrate that fine-tuned Drp1 repression primes a slow cycling 'stem/progenitor-like state', which is characterized by small networks of fused mitochondria and a gene-expression profile with elevated functional stem/progenitor markers (Krt15, Sox2 etc) and their regulators (Cyclin E). Fine tuning Drp1 protein by reducing its activating phosphorylation sustains the neoplastic stem cell markers. Whereas, fine-tuned reduction of Drp1 protein maintains the characteristic mitochondrial shape and gene-expression of the primed 'stem/progenitor-like state' to accelerate neoplastic transformation, and more complete reduction of Drp1 protein prevents it. Therefore, our data highlights a 'goldilocks'; level of Drp1 repression supporting stem/progenitor state dependent neoplastic transformation.

OS13.3.A Establishment of a novel system to specifically trace and ablate quiescent/slow cycling cells in high-grade glioma

BACKGROUND High-grade gliomas are the most common malignant brain tumors, with poor prognosis due to recurrence and tumor infiltration after surgical removal and chemotherapy. Quiescent/slow cycling stem cells have been proposed to be one of the main players of tumor relapse but their involvement in in the infiltration remain unclear. Despite they have been described in mouse models or after transcriptional profiling of human tumor samples, their direct visualization, targeting and ablation remains a challenge. MATERIAL AND METHODS Tumors were induced over-expressing oncogenic forms of MET and p53 in the subventricular zone (SVZ) of P2 mouse brain as well as human forebrain organoids. The co-expression with specific cell cycle sensors as well as lineage specific CreERT2 under control of stem cells promoters allowed to visualize and target glioma stem cells. RESULTS Here, we used a fluorescent cell cycle sensor to visualize quiescent tumor cells in mouse brain cancer and human cancer organoids. In particular, we characterized them within the tumor revealing the invasiveness capacity of slow cycling tumor cells. Furthermore, we generated a new system to specifically trace and ablate such cells. Indeed, lineage tracing experiments allowed to trace quiescent Prom1 progeny in the tumors after temozolomide treatment. In addition, the selective ablation of qProm1 in mouse brain cancer reduced tumor infiltration. Finally, time-lapse experiments showed that slow cycling cells are also able to infiltrate co-cultured human brain cancer organoids. CONCLUSION Overall, our data show that quiescent/slow cycling cells are key driver of tumor invasiveness, the major malignant feature of high-grade brain cancer.

Modulating cell differentiation in cancer models

Cancer has been traditionally viewed as a disease characterised by excessive and uncontrolled proliferation, leading to the development of cytotoxic therapies against highly proliferating malignant cells. However, tumours frequently relapse due to the presence of slow-cycling cancer stem cells eluding chemo and radiotherapy. Since these malignant stem cells are largely undifferentiated, inducing their lineage commitment has been proposed as a potential intervention strategy to deplete tumours from their most resistant components. Pro-differentiation approaches have thus far yielded clinical success in the reversion of acute promyelocytic leukaemia (APL), and new developments are fast widening their therapeutic applicability to solid carcinomas. Recent advances in cancer differentiation discussed here highlight the potential and outstanding challenges of differentiation-based approaches.

Chondrocytes in the resting zone of the growth plate are maintained in a Wnt-inhibitory environment

Chondrocytes in the resting zone of the postnatal growth plate are characterized by slow cell cycle progression, and encompass a population of parathyroid hormone-related protein (PTHrP)-expressing skeletal stem cells that contribute to the formation of columnar chondrocytes. However, how these chondrocytes are maintained in the resting zone remains undefined. We undertook a genetic pulse-chase approach to isolate slow cycling, label-retaining chondrocytes (LRCs) using a chondrocyte-specific doxycycline-controllable Tet-Off system regulating expression of histone 2B-linked GFP. Comparative RNA-seq analysis identified significant enrichment of inhibitors and activators for Wnt signaling in LRCs and non-LRCs, respectively. Activation of Wnt/β-catenin signaling in PTHrP+ resting chondrocytes using Pthlh-creER and Apc-floxed allele impaired their ability to form columnar chondrocytes. Therefore, slow-cycling chondrocytes are maintained in a Wnt-inhibitory environment within the resting zone, unraveling a novel mechanism regulating maintenance and differentiation of PTHrP+ skeletal stem cells of the postnatal growth plate.

Emerging Insights into Targeted Therapy-Tolerant Persister Cells in Cancer

Drug resistance is perhaps the greatest challenge in improving outcomes for cancer patients undergoing treatment with targeted therapies. It is becoming clear that “persisters,” a subpopulation of drug-tolerant cells found in cancer populations, play a critical role in the development of drug resistance. Persisters are able to maintain viability under therapy but are typically slow cycling or dormant. These cells do not harbor classic drug resistance driver alterations, and their partial resistance phenotype is transient and reversible upon removal of the drug. In the clinic, the persister state most closely corresponds to minimal residual disease from which relapse can occur if treatment is discontinued or if acquired drug resistance develops in response to continuous therapy. Thus, eliminating persister cells will be crucial to improve outcomes for cancer patients. Using lung cancer targeted therapies as a primary paradigm, this review will give an overview of the characteristics of drug-tolerant persister cells, mechanisms associated with drug tolerance, and potential therapeutic opportunities to target this persister cell population in tumors.