HCN Channel Activity Balances Quiescence and Proliferation in Neural Stem Cells and Is a Selective Target for Neuroprotection During Cancer Treatment

Children suffering from neurologic cancers undergoing chemotherapy and radiotherapy are at high risk of reduced neurocognitive abilities likely via damage to proliferating neural stem cells (NSC). Therefore, strategies to protect NSCs are needed. We argue that induced cell-cycle arrest/quiescence in NSCs during cancer treatment can represent such a strategy. Here, we show that hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels are dynamically expressed over the cell cycle in NSCs, depolarize the membrane potential, underlie spontaneous calcium oscillations and are required to maintain NSCs in the actively proliferating pool. Hyperpolarizing pharmacologic inhibition of HCN channels during exposure to ionizing radiation protects NSCs cells in neurogenic brain regions of young mice. In contrast, brain tumor-initiating cells, which also express HCN channels, remain proliferative during HCN inhibition. IMPLICATIONS: Our finding that NSCs can be selectively rescued while cancer cells remain sensitive to the treatment, provide a foundation for reduction of cognitive impairment in children with neurologic cancers.

The chromatin-remodeling factor CHD4 is required for maintenance of childhood acute myeloid leukemia

Epigenetic alterations contribute to leukemogenesis in childhood acute myeloid leukemia and therefore are of interest for potential therapeutic strategies. Herein, we performed large-scale ribonucleic acid interference screens using small hairpin ribonucleic acids in acute myeloid leukemia cells and non-transformed bone marrow cells to identify leukemia-specific dependencies. One of the target genes displaying the strongest effects on acute myeloid leukemia cell growth and less pronounced effects on nontransformed bone marrow cells, was the chromatin remodeling factor CHD4 Using ribonucleic acid interference and CRISPR-Cas9 approaches, we showed that CHD4 was essential for cell growth of leukemic cells in vitro and in vivo Loss of function of CHD4 in acute myeloid leukemia cells caused an arrest in the G0 phase of the cell cycle as well as downregulation of MYC and its target genes involved in cell cycle progression. Importantly, we found that inhibition of CHD4 conferred anti-leukemic effects on primary childhood acute myeloid leukemia cells and prevented disease progression in a patient-derived xenograft model. Conversely, CHD4 was not required for growth of normal hematopoietic cells. Taken together, our results identified CHD4 as a potential therapeutic target in childhood acute myeloid leukemia.

Understanding cytoskeleton regulators in glioblastoma multiforme for therapy design

The cellular cytoskeleton forms the primary basis through which a cell governs the changes in size, shape, migration, proliferation, and forms the primary means through which the cells respond to their environment. Indeed, cell and tissue morphologies are used routinely not only to grade tumors but also in various high-content screening methods with an aim to identify new small molecules with therapeutic potential. This study examines the expression of various cytoskeleton regulators in glioblastoma multiforme (GBM). GBM is a very aggressive disease with a low life expectancy even after chemo- and radiotherapy. Cancer cells of GBM are notorious for their invasiveness, ability to develop resistance to chemo- and radiotherapy, and to form secondary site tumors. This study aims to gain insight into cytoskeleton regulators in GBM cells and to understand the effect of various oncology drugs, including temozolomide, on cytoskeleton regulators. We compare the expression of various cytoskeleton regulators in GBM-derived tumor and normal tissue, CD133-postive and -negative cells from GBM and neural cells, and GBM stem-like and differentiated cells. In addition, the correlation between the expression of cytoskeleton regulators with the clinical outcome was examined to identify genes associated with longer patient survival. This was followed by a small molecule screening with US Food and Drug Administration (FDA)-approved oncology drugs, and its effect on cellular cytoskeleton was compared to treatment with temozolomide. This study identifies various groups of cytoskeletal regulators that have an important effect on patient survival and tumor development. Importantly, this work highlights the advantage of using cytoskeleton regulators as biomarkers for assessing prognosis and treatment design for GBM.

RETRACTED: Vulnerability of glioblastoma cells to catastrophic vacuolization and death induced by a small molecule

Glioblastoma multiforme (GBM) is the most aggressive form of brain cancer with marginal life expectancy. Based on the assumption that GBM cells gain functions not necessarily involved in the cancerous process, patient-derived glioblastoma cells (GCs) were screened to identify cellular processes amenable for development of targeted treatments. The quinine-derivative NSC13316 reliably and selectively compromised viability. Synthetic chemical expansion reveals delicate structure-activity relationship and analogs with increased potency, termed Vacquinols. Vacquinols stimulate death by membrane ruffling, cell rounding, massive macropinocytic vacuole accumulation, ATP depletion, and cytoplasmic membrane rupture of GCs. The MAP kinase MKK4, identified by a shRNA screen, represents a critical signaling node. Vacquinol-1 displays excellent in vivo pharmacokinetics and brain exposure, attenuates disease progression, and prolongs survival in a GBM animal model. These results identify a vulnerability to massive vacuolization that can be targeted by small molecules and point to the possible exploitation of this process in the design of anticancer therapies.