In many cancers, high proliferation rates correlate with elevation of rRNA and tRNA levels, and nucleolar hypertrophy. However, the underlying mechanisms linking increased nucleolar transcription and tumorigenesis are only minimally understood. Here we show that IMP dehydrogenase-2 (IMPDH2), the rate-limiting enzyme for de novo guanine nucleotide biosynthesis, is overexpressed in the highly lethal brain cancer, glioblastoma (GBM). This leads to increased rRNA and tRNA synthesis, stabilization of the nucleolar GTP-binding protein, Nucleostemin, and enlarged, malformed nucleoli. Pharmacological or genetic inactivation of IMPDH2 in GBM reverses these effects and inhibits cell proliferation, whereas untransformed glia cells are unaffected by similar IMPDH2 perturbations. Impairment of IMPDH2 activity triggers nucleolar stress and growth arrest of GBM cells even in the absence of functional p53. Our results reveal that upregulation of IMPDH2 is a prerequisite for aberrant nucleolar function and increased anabolic processes in GBM, which constitutes a primary event in gliomagenesis.

Replication conditional oncolytic human adenovirus has long been considered a promising biological therapeutic to target high-grade gliomas (HGG), a group of essentially lethal primary brain cancer. The last decade has witnessed initiation and some completion of a number of Phase I and II clinical investigations of oncolytic adenovirus for HGG in the US and Europe. Results of these trials in patients are pivotal for not only federal approval but also filling an existing knowledge gap that primarily derives from the stark differences in permissivity to human adenovirus between humans and preclinical mouse models. DNX-2401 (Delta-24-RGD), the current mainstream oncolytic adenovirus with modifications in E1A and the fiber, has been shown to induce impressive objective response and long-term survival (>3 years) in a fraction of patients with recurrent HGG. Responders exhibited initial enlargement of the treated lesions for a few months post treatment, followed by shrinkage and near complete resolution. In accord with preclinical research, post-treatment specimens revealed virus-mediated alteration of the immune tumor microenvironment as evidenced by infiltration of CD8+ T cells and M1-polarized macrophages. These findings are encouraging and together with further information from ongoing studies have a potential to make oncolytic adenovirus a viable option for clinical management of HGG. This review deals with this timely topic; we will describe both preclinical and clinical development of oncolytic adenovirus therapy for HGG, summarize updated knowledge on clinical trials and discuss challenges that the field currently faces.

◥Purpose: Extracellular matrix (ECM) component hyaluronan (HA) facilitates malignant phenotypes of glioblastoma (GBM), however, whether HA impacts response to GBM immunotherapies is not known. Herein, we investigated whether degradation of HA enhances oncolytic virus immunotherapy for GBM.Experimental Design: Presence of HA was examined in patient and murine GBM. Hyaluronidase-expressing oncolytic adenovirus, ICOVIR17, and its parental virus, ICOVIR15, without transgene, were tested to determine if they increased animal survival and modulated the immune tumor microenvironment (TME) in orthotopic GBM. HA regulation of NF-kB signaling was examined in virus-infected murine macrophages. We combined ICOVIR17 with PD-1 checkpoint blockade and assessed efficacy and determined mechanistic contributions of tumorinfiltrating myeloid and T cells.Results: Treatment of murine orthotopic GBM with ICOVIR17 increased tumor-infiltrating CD8 þ T cells and macrophages, and upregulated PD-L1 on GBM cells and macrophages, leading to prolonged animal survival, compared with control virus ICOVIR15. High molecular weight HA inhibits adenovirus-induced NF-kB signaling in macrophages in vitro, linking HA degradation to macrophage activation. Combining ICOVIR17 with anti-PD-1 antibody further extended the survival of GBM-bearing mice, achieving long-term remission in some animals. Mechanistically, CD4 þ T cells, CD8 þ T cells, and macrophages all contributed to the combination therapy that induced tumor-associated proinflammatory macrophages and tumor-specific T-cell cytotoxicity locally and systemically.Conclusions: Our studies are the first to show that immune modulatory ICOVIR17 has a dual role of mediating degradation of HA within GBM ECM and subsequently modifying the immune landscape of the TME, and offers a mechanistic combination immunotherapy with PD-L1/PD-1 blockade that remodels innate and adaptive immune cells.

Despite the current standard of multimodal management, glioblastoma (GBM) inevitably recurs and effective therapy is not available for recurrent disease. A subset of tumor cells with stem-like properties, termed GBM stem-like cells (GSCs), are considered to play a role in tumor relapse. Although oncolytic herpes simplex virus (oHSV) is a promising therapeutic for GBM, its efficacy against recurrent GBM is incompletely characterized. Transforming growth factor beta (TGF-β) plays vital roles in maintaining GSC stemness and GBM pathogenesis. We hypothesized that oHSV and TGF-β inhibitors would synergistically exert anti-tumor effects for recurrent GBM. Here we established a panel of patient-derived recurrent tumor models from GBMs that relapsed after post-surgical radiation and chemotherapy, based on GSC-enriched tumor sphere cultures. These GSCs are resistant to the standard-of-care temozolomide but susceptible to oHSVs G47Δ and MG18L. Inhibition of TGF-β receptor kinase with selective targeted small molecules reduced clonogenic sphere formation in all tested recurrent GSCs. The combination of oHSV and TGF-βR inhibitor was synergistic in killing recurrent GSCs through, in part, an inhibitor-induced JNK-MAPK blockade and increase in oHSV replication. In vivo, systemic treatment with TGF-βR inhibitor greatly enhanced the anti-tumor effects of single intratumoral oHSV injections, resulting in cures in 60% of mice bearing orthotopic recurrent GBM. These results reveal a novel synergistic interaction of oHSV therapy and TGF-β signaling blockade, and warrant further investigations aimed at clinical translation of this combination strategy for GBM patients.