Relapsed/refractory T cell acute lymphoblastic leukemia (T-ALL) is difficult to salvage especially in heavily pretreated patients, thus novel targeted agents are sorely needed. Hyperactivated JAK/STAT and BCL2 overexpression promote increased T-ALL proliferation and survival, and targeting these pathways with ruxolitinib and venetoclax may provide an alternative approach to achieve clinical remissions. Ruxolitinib and venetoclax show a dosedependent effect individually, but combination treatment synergistically reduces survival and proliferation of Jurkat and Loucy cells in vitro. Using a xenograft CXCR4+ Jurkat model, the combination treatment fails to improve survival, with death from hind limb paralysis. Despite ontarget inhibition by the drugs, histopathology demonstrates increased leukemic infiltration into the central nervous system (CNS), which expresses CXCL12, as compared to liver or bone marrow. Liquid chromatography-tandem mass spectroscopy shows that neither ruxolitinib nor venetoclax can effectively cross the blood-brain barrier, limiting efficacy against CNS T-ALL. Deletion of CXCR4 on Jurkat cells by CRISPR/Cas9 results in prolonged survival and a reduction in overall and neurologic clinical scores. While combination therapy with ruxolitinib and venetoclax shows promise for treating T-ALL, additional inhibition of the CXCR4-CXCL12 axis will be needed to eliminate both systemic and CNS T-ALL burden and maximize the possibility of complete remission.

Treatment of metastatic pediatric solid tumors remain a significant challenge, particularly in relapsed and refractory settings. Standard treatment has included surgical resection, radiation, chemotherapy, and, in the case of neuroblastoma, immunotherapy. Despite such intensive therapy, cancer recurrence is common, and most tumors become refractory to prior therapy, leaving patients with few conventional treatment options. Natural killer (NK) cells are non-major histocompatibility complex (MHC)-restricted lymphocytes that boast several complex killing mechanisms but at an added advantage of not causing graft-versus-host disease, making use of allogeneic NK cells a potential therapeutic option. On top of their killing capacity, NK cells also produce several cytokines and growth factors that act as key regulators of the adaptive immune system, positioning themselves as ideal effector cells for stimulating heavily pretreated immune systems. Despite this promise, clinical efficacy of adoptive NK cell therapy to date has been inconsistent, prompting a detailed understanding of the biological pathways within NK cells that can be leveraged to develop “next generation” NK cell therapies. Here, we review advances in current approaches to optimizing the NK cell antitumor response including combination with other immunotherapies, cytokines, checkpoint inhibition, and engineering NK cells with chimeric antigen receptors (CARs) for the treatment of pediatric solid tumors.

Understanding the role of immune checkpoints has undeniably changed the landscape of cancer immunotherapy. Programmed cell death protein 1 (PD-1) is induced after T cells are activated and serves as a marker of activation that provides inhibitory signals to T cells after engagement of its ligand, programmed death ligand 1 (PD-L1). PD-1 is also a marker of chronic antigen stimulation, since checkpoint blockade with monoclonal antibodies against PD-1 abrogates T cell exhaustion, generating robust antitumor responses (1, 2). Cancers that have been clinically approved for PD-1 inhibition include melanoma, renal cell carcinoma, metastatic non-small cell lung cancer, urothelial carcinoma, classical Hodgkin lymphoma, and others (3, 4). Interestingly PD-1 blockade can induce responses in various cancers with low expression of major histocompatibility complex class I (MHCI), necessary for cytotoxic CD8 + T cell recognition, suggesting enhanced cytolytic activity by CD4 + T cells or effector cells capable of cytotoxicity independently of MHC.NK cells are cytotoxic lymphocytes that can eliminate virally infected cells and tumors using cytotoxicity mechanisms similar to CD8 + T cells, but that do not require recognition of MHC (5). Using deductive reasoning from the "missing self " hypothesis, blocking PD-1 on NK cells may augment antitumor effects for tumors that are refractory to T cell treatments due to low MHC expression (6). The fundamental basis behind applying checkpoint blockade against PD-1 on NK cells must, of course, assume that NK cells express PD-1.

Copalic acid, one of the diterpenoid acids in copaiba oil, inhibited the chaperone function of α-crystallin and heat shock protein 27kD (HSP27). It also showed potent activity in decreasing an HSP27 client protein, androgen receptor (AR), which makes it useful in prostate cancer treatment or prevention. To develop potent drug candidates to decrease the AR level in prostate cancer cells, more copalic acid analogs were synthesized. Using the level of AR as the readout, 15 of the copalic acid analogs were screened and two compounds were much more potent than copalic acid. The compounds also dose-dependently inhibited AR positive prostate cancer cell growth. Furthermore, they inhibited the chaperone activity of α-crystallin as well.

Relapsed/refractory T cell acute lymphoblastic leukemia (T-ALL) is difficult to salvage especially in heavily pretreated patients, thus novel targeted agents are sorely needed.Hyperactivated JAK/STAT and BCL2 overexpression promote increased T-ALL proliferation and survival, and targeting these pathways with ruxolitinib and venetoclax may provide an alternative approach to achieve clinical remissions. Ruxolitinib and venetoclax show a dosedependent effect individually, but combination treatment synergistically reduces survival and proliferation of Jurkat and Loucy cells in vitro. Using a xenograft CXCR4+ Jurkat model, the combination treatment fails to improve survival, with death from hind limb paralysis. Despite ontarget inhibition by the drugs, histopathology demonstrates increased leukemic infiltration into the central nervous system (CNS), which expresses CXCL12, as compared to liver or bone marrow. Liquid chromatography-tandem mass spectroscopy shows that neither ruxolitinib nor venetoclax can effectively cross the blood-brain barrier, limiting efficacy against CNS T-ALL.Deletion of CXCR4 on Jurkat cells by CRISPR/Cas9 results in prolonged survival and a reduction in overall and neurologic clinical scores. While combination therapy with ruxolitinib and venetoclax shows promise for treating T-ALL, additional inhibition of the CXCR4-CXCL12 axis will be needed to eliminate both systemic and CNS T-ALL burden and maximize the possibility of complete remission.