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Central nervous system (CNS) cancers are responsible for high rates of morbidity and mortality worldwide. Malignant CNS tumors such as adult Glioblastoma (GBM) and pediatric embryonal CNS tumors such as medulloblastoma (MED) and atypical teratoid rhabdoid tumors (ATRT) present relevant therapeutic challenges due to the lack of response to classic treatment regimens with radio and chemotherapy. Recent findings on the Zika virus’ (ZIKV) ability to infect and kill CNS neoplastic cells draw attention to the virus’ oncolytic potential. Studies demonstrating the safety of using ZIKV for treating malignant CNS tumors, enabling the translation of this approach to clinical trials, are scarce in the literature. Here we developed a co-culture model of mature human cerebral organoids assembled with GBM, MED or ATRT tumor cells and used these assembloids to test ZIKV oncolytic effect, replication potential and preferential targeting between normal and cancer cells. Our hybrid co-culture models allowed the tracking of tumor cell growth and invasion in cerebral organoids. ZIKV replication and ensuing accumulation in the culture medium was higher in organoids co-cultured with tumor cells than in isolated control organoids without tumor cells. ZIKV infection led to a significant reduction in tumor cell proportion in organoids with GBM and MED cells, but not with ATRT. Tumoroids (3D cultures of tumor cells alone) were efficiently infected by ZIKV. Interestingly, ZIKV rapidly replicated in GBM, MED, and ATRT tumoroids reaching significantly higher viral RNA accumulation levels than co-cultures. Moreover, ZIKV infection reduced viable cells number in MED and ATRT tumoroids but not in GBM tumoroids. Altogether, our findings indicate that ZIKV has greater replication rates in aggressive CNS tumor cells than in normal human cells comprising cerebral organoids. However, such higher ZIKV replication in tumor cells does not necessarily parallels oncolytic effects, suggesting cellular intrinsic and extrinsic factors mediating tumor cell death by ZIKV.

High-grade pediatric Central Nervous System (CNS) tumors are frequent, highly aggressive, and the most common cause of cancer-associated death in children. Due to their unique features, such as heterogeneous tumor molecular characteristics, distinct microenvironment, challenging anatomical localization and the presence of the blood brain barrier, brain tumors are especially difficult to treat and often present a poor response to standard therapies (surgery, radio and chemotherapy). Because of that, there is a need for investigating more effective therapeutic approaches and, within this context, Oncolytic Viruses (OVs) have emerged as a promising new class of immunotherapeutic agents. These viruses have a natural or artificial tropism for cancer cells and their central mechanism of action is the direct oncolytic effect followed by activation of the immune response. As a consequence, the OV therapy can be safer than traditional approaches, and its use may help overcome some pediatric CNS tumor treatment challenges. In this review, we initially examine the potential therapeutic advantages that are intrinsically related to OVs infection mechanism. Then, we address the surpassing resistance mechanisms of available treatments for pediatric brain tumors and present some challenges to be taken into consideration in clinical application. We next provide an overview of preclinical studies focusing on the mechanisms of infection and also in vitro and in vivo findings of emergent and underexplored OVs, namely Zika virus, Measles virus, Reovirus, Poliovirus, Seneca Valley virus, Vaccinia virus, Myxoma virus and Parvovirus. Finally, we summarize the latest clinical trials using these underexplored OVs against pediatric solid tumors.