MYCN amplification is a key molecular hallmark of high-risk neuroblastoma. Previously considered an "undruggable" target, MYCN transcription can be disrupted by inhibiting the bromodomain and the extraterminal (BET) domain family of proteins that regulates MYCN transcription epigenetically. JQ1 is a potent, small-molecule BET inhibitor that induces cell-cycle arrest and initiates apoptosis in neuroblastoma. Here, we sought to validate the antitumorigenic effects of JQ1 in neuroblastoma and to evaluate whether blocking N-myc expression with JQ1 promotes neural differentiation. We determined the effects in vitro of JQ1 treatment on human neuroblastoma cell growth in both monolayer and sphere-forming conditions. Subcutaneous neuroblastoma xenografts were used for an in vivo study. Western blotting and immunohistochemistry were performed to evaluate the effects on neural differentiation and stem cell markers. JQ1 treatment blocked neuroblastoma cell growth in both monolayer and sphere-forming conditions; JQ1 also attenuated the growth of neuroblastoma xenograft in athymic nude mice. Neurofilament expression was enhanced with JQ1 treatment, indicating that JQ1 induces neuronal differentiation. Sphere forming conditions resulted in increased expression of multiple stem cell markers; these effects were reversed with JQ1 treatment. BET inhibition attenuates progression and promotes neural differentiation of neuroblastoma in vitro and in vivo in mice, providing insight into potential clinical applications of BET inhibitors in the treatment of patients with neuroblastoma.

Neuroblastoma (NBL) cells highly express disialoganglioside GD2, which is restricted and weakly expressed in selected healthy cells, making it a desirable target of immunotherapy. Over the past two decades, application of dinutuximab, an anti-GD2 monoclonal antibody (mAb), has been one of the few new therapies to substantially improve outcomes to current levels. Given the persistent challenge of relapse and therapeutic resistance, there is an urgent need for new effective and tolerable treatment options for high-risk NBL. Recent breakthroughs in immune checkpoint inhibitor (ICI) therapeutics have not translated into high-risk NBL, like many other major pediatric solid tumors. Given the suppressed tumor microenvironment (TME), single ICIs like anti-CTLA4 and anti-PD1 have not demonstrated significant antitumor response rates. Meanwhile, emerging studies are reporting novel advancements in GD2-based therapies, targeted therapies, nanomedicines, and other immunotherapies such as adoptive transfer of natural killer (NK) cells and chimeric antigen receptors (CARs), and these hold interesting promise for the future of high-risk NBL patient care. Herein, we summarize the current state of the art in NBL therapeutic options and highlight the unique challenges posed by NBL that have limited the successful adoption of immune-modifying therapies. Through this review, we aim to direct the field’s attention to opportunities that may benefit from a combination immunotherapy strategy.

Surgery or radiation therapy is nearly universally applied for pediatric solid tumors. In many cases, in diverse tumor types, distant metastatic disease is present and evades surgery or radiation. The systemic host response to these local control modalities may lead to a suppression of antitumor immunity, with potential negative impact on the clinical outcomes for patients in this scenario. Emerging evidence suggests that the perioperative immune responses to surgery or radiation can be modulated therapeutically to preserve anti-tumor immunity, with the added benefit of preventing these local control approaches from serving as pro-tumorigenic stimuli. To realize the potential benefit of therapeutic modulation of the systemic response to surgery or radiation on distant disease that evades these modalities, a detailed knowledge of the tumor-specific immunology as well as the immune responses to surgery and radiation is imperative. In this Review we highlight the current understanding of the tumor immune microenvironment for the most common peripheral pediatric solid tumors, the immune responses to surgery and radiation, and current evidence that supports the potential use of immune activating agents in the perioperative window. Finally, we define existing knowledge gaps that limit the current translational potential of modulating perioperative immunity to achieve effective anti-tumor outcomes.