Heiko Wurdak

Intravenous delivery of oncolytic reovirus to brain tumor patients immunologically primes for subsequent checkpoint blockade

Intravenous infusion of oncolytic reovirus in patients leads to infection of brain tumors, infiltration by cytotoxic T cells, and up-regulation of PD-L1. Viruses team up with cancer immunotherapy Immune checkpoint inhibitors have shown great promise for cancer therapy, but they do not treat all cancers, and neither breast nor brain tumors are usually treatable with these drugs. However, Bourgeois-Daigneault et al. discovered a way to address this for breast cancer, and Samson et al. discovered a way to address this for brain tumors. In both cases, the authors found that oncolytic virus treatment given early, before surgical resection, alters the antitumor immune response and potentiates the effects of subsequent treatment with immune checkpoint inhibitors. Although these studies differ in the details of their methods and the immune effects induced by the oncolytic viruses, they indicate the potential of such viruses for enhancing the potential of checkpoint therapy and expanding it to new types of cancer. Immune checkpoint inhibitors, including those targeting programmed cell death protein 1 (PD-1), are reshaping cancer therapeutic strategies. Evidence suggests, however, that tumor response and patient survival are determined by tumor programmed death ligand 1 (PD-L1) expression. We hypothesized that preconditioning of the tumor immune microenvironment using targeted, virus-mediated interferon (IFN) stimulation would up-regulate tumor PD-L1 protein expression and increase cytotoxic T cell infiltration, improving the efficacy of subsequent checkpoint blockade. Oncolytic viruses (OVs) represent a promising form of cancer immunotherapy. For brain tumors, almost all studies to date have used direct intralesional injection of OV, because of the largely untested belief that intravenous administration will not deliver virus to this site. We show, in a window-of-opportunity clinical study, that intravenous infusion of oncolytic human Orthoreovirus (referred to herein as reovirus) leads to infection of tumor cells subsequently resected as part of standard clinical care, both in high-grade glioma and in brain metastases, and increases cytotoxic T cell tumor infiltration relative to patients not treated with virus. We further show that reovirus up-regulates IFN-regulated gene expression, as well as the PD-1/PD-L1 axis in tumors, via an IFN-mediated mechanism. Finally, we show that addition of PD-1 blockade to reovirus enhances systemic therapy in a preclinical glioma model. These results support the development of combined systemic immunovirotherapy strategies for the treatment of both primary and secondary tumors in the brain.

Regulating the ARNT/TACC3 axis: Multiple approaches to manipulating protein/protein interactions with small molecules

For several well-documented reasons, it has been challenging to develop artificial small molecule inhibitors of protein/protein complexes. Such reagents are of particular interest for transcription factor complexes given links between their misregulation and disease. Here we report parallel approaches to identify regulators of a hypoxia signaling transcription factor complex, involving the ARNT subunit of the HIF (Hypoxia Inducible Factor) activator and the TACC3 (Transforming Acidic Coiled Coil Containing Protein 3) coactivator. In one route, we used in vitro NMR and biochemical screening to identify small molecules that selectively bind within the ARNT PAS (Per-ARNT-Sim) domain that recruits TACC3, identifying KG-548 as an ARNT/TACC3 disruptor. A parallel, cell-based screening approach previously implicated the small molecule KHS101 as an inhibitor of TACC3 signaling. Here, we show that KHS101 works indirectly on HIF complex formation by destabilizing both TACC3 and the HIF component HIF-1α. Overall, our data identify small molecule regulators for this important complex and highlight the utility of pursuing parallel strategies to develop protein/protein inhibitors.

RAD51 Is a Selective DNA Repair Target to Radiosensitize Glioma Stem Cells

Summary Patients with glioblastoma die from local relapse despite surgery and high-dose radiotherapy. Resistance to radiotherapy is thought to be due to efficient DNA double-strand break (DSB) repair in stem-like cells able to survive DNA damage and repopulate the tumor. We used clinical samples and patient-derived glioblastoma stem cells (GSCs) to confirm that the DSB repair protein RAD51 is highly expressed in GSCs, which are reliant on RAD51-dependent DSB repair after radiation. RAD51 expression and RAD51 foci numbers fall when these cells move toward astrocytic differentiation. In GSCs, the small-molecule RAD51 inhibitors RI-1 and B02 prevent RAD51 focus formation, reduce DNA DSB repair, and cause significant radiosensitization. We further demonstrate that treatment with these agents combined with radiation promotes loss of stem cells defined by SOX2 expression. This indicates that RAD51-dependent repair represents an effective and specific target in GSCs.

KHS101 disrupts energy metabolism in human glioblastoma cells and reduces tumor growth in mice

Modulation of energy metabolism with the small-molecule KHS101 promoted tumor-selective death of human glioblastoma cells and reduced tumor growth in mice. A serendipitous metabolic target for glioblastoma Glioblastoma (GBM), one of the most aggressive brain cancers, is associated with poor prognosis and low survival rate. GBM stem cells contribute to aggressive GBM growth. Polson et al. hypothesized that promoting neural differentiation could have therapeutic effects. While testing the therapeutic properties of the small-molecule KHS101, previously shown to promote neural differentiation, the authors made the serendipitous discovery that KHS101 exerted cytotoxic activity in multiple patient-derived GBM cell lines by disrupting cell metabolism and promoting autophagy. In vivo administration of KHS101 reduced tumor growth and prolonged survival in patient-derived xenograft mouse models of GBM. The authors suggest that targeting cell metabolism using small molecules might be effective for treating GBM. Pharmacological inhibition of uncontrolled cell growth with small-molecule inhibitors is a potential strategy for treating glioblastoma multiforme (GBM), the most malignant primary brain cancer. We showed that the synthetic small-molecule KHS101 promoted tumor cell death in diverse GBM cell models, independent of their tumor subtype, and without affecting the viability of noncancerous brain cell lines. KHS101 exerted cytotoxic effects by disrupting the mitochondrial chaperone heat shock protein family D member 1 (HSPD1). In GBM cells, KHS101 promoted aggregation of proteins regulating mitochondrial integrity and energy metabolism. Mitochondrial bioenergetic capacity and glycolytic activity were selectively impaired in KHS101-treated GBM cells. In two intracranial patient-derived xenograft tumor models in mice, systemic administration of KHS101 reduced tumor growth and increased survival without discernible side effects. These findings suggest that targeting of HSPD1-dependent metabolic pathways might be an effective strategy for treating GBM.

Spontaneous Glioblastoma Spheroid Infiltration of Early-Stage Cerebral Organoids Models Brain Tumor Invasion:

Organoid methodology provides a platform for the ex vivo investigation of the cellular and molecular mechanisms underlying brain development and disease. The high-grade brain tumor glioblastoma multiforme (GBM) is considered a cancer of unmet clinical need, in part due to GBM cell infiltration into healthy brain parenchyma, making complete surgical resection improbable. Modeling the process of GBM invasion in real time is challenging as it requires both tumor and neural tissue compartments. Here, we demonstrate that human GBM spheroids possess the ability to spontaneously infiltrate early-stage cerebral organoids (eCOs). The resulting formation of hybrid organoids demonstrated an invasive tumor phenotype that was distinct from noncancerous adult neural progenitor (NP) spheroid incorporation into eCOs. These findings provide a basis for the modeling and quantification of the GBM infiltration process using a stem-cell-based organoid approach, and may be used for the identification of anti-GBM invasion strategies.

Abstract 3303: Radioresistance in glioma stem cells driven by Rad51 dependent homologous recombination repair

A cell population with stem cell like characteristics is thought to underlie treatment resistance and local recurrence in glioma. In this work we investigate the role of the DNA repair protein RAD51 in these cells and the impact of inhibiting homologous recombination repair on radiation resistance in vitro and in vivo. We used a model of inducible differentiation of patient derived glioma cells to investigate repair protein levels, repair foci formation and kinetics in clonogenic, stem-like populations and their differentiated counterparts. We examined co-expression of stem cell markers with RAD51 protein at whole population level using western blotting, immunocytochemistry and RT-PCR in cultured cells and immunohistochemistry in tumor material. Single cell expression was analysed using the Fluidigm C1 platform. We examined the effect of two specific inhibitors of RAD51 (B02, RI-1) on the same cell pairs in vitro and used the γH2AX assay to assess differences in repair kinetics. We used subcutaneous models of glioma to evaluate the effect of one of these agents (RI-1) on tumour growth delay with and without fractionated radiation doses in vivo. Primary glioma stem cells expressed high levels of RAD51 protein and exhibited high numbers of foci per nucleus following radiation exposure. Levels of both protein and repair foci fell after cells were transferred to differentiating conditions (serum+BMP4), as did expression of stem cell markers (NESTIN, SOX2). Single cell analysis showed a highly significant association between SOX2 and RAD51 expression (P These data suggest that RAD51 dependent DNA repair by homologous recombination represents a specific target in the stem-like fraction of glioblastoma and inhibiting this pathway is a promising approach to radiosensitisation. Citation Format: Henry King, Helen Payne, Tim Brend, Anjana Patel, Alex Wright, Teklu Englu, Lucy Stead, Heiko Wurdak, Susan C. Short. Radioresistance in glioma stem cells driven by Rad51 dependent homologous recombination repair. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3303. doi:10.1158/1538-7445.AM2015-3303

The small molecule KHS101 induces bioenergetic dysfunction in glioblastoma cells through inhibition of mitochondrial HSPD1

Pharmacological inhibition of uncontrolled cell growth with small molecule inhibitors is a potential strategy against glioblastoma multiforme (GBM), the most malignant primary brain cancer. Phenotypic profiling of the neurogenic small molecule KHS101 revealed the chemical induction of lethal cellular degradation in molecularly-diverse GBM cells, independent of their tumor subtype, whereas non-cancerous brain cells remained viable. Mechanism-of-action (MOA) studies showed that KHS101 specifically bound and inhibited the mitochondrial chaperone HSPD1. In GBM but not non-cancerous brain cells, KHS101 elicited the aggregation of an enzymatic network that regulates energy metabolism. Compromised glycolysis and oxidative phosphorylation (OXPHOS) resulted in the metabolic energy depletion in KHS101-treated GBM cells. Consistently, KHS101 induced key mitochondrial unfolded protein response factor DDIT3 in vitro and in vivo, and significantly reduced intracranial GBM xenograft tumor growth upon systemic administration, without discernible side effects. These findings suggest targeting of HSPD1-dependent oncometabolic pathways as an anti-GBM therapy.

Induced Differentiation of Brain Tumour Stem Cells

Glioblastoma multiforme (GBM) is considered the most common and deadliest form of tumour arising in the human central nervous system. GBMs are inherently resistant to therapy and complete surgical resection is rarely achieved, and consequently, patient prognosis is poor. The discovery of stem-like cells in GBM channelled research towards the analysis of this ‘brain tumour stem cell’ (BTSC) population. Altered growth factor signalling combined with genetic, epigenetic and microRNA (miRNA) networks act to maintain the BTSC phenotype and aggressive nature of GBM tumours. Differentiation therapy presents as an intriguing option to specifically target BTSCs through ‘forced’ differentiation towards neuronal and glial lineages, thus eliminating BTSCs and sensitising the remaining tumour mass to current therapeutic strategies. Here we review current research and opinions surrounding this relatively recent concept in brain cancer biology that may prove to be a tool to treat high-grade brain tumours and improve patient survival.