Intratumoral injection of schwannoma with attenuated Salmonella typhimurium induces antitumor immunity and controls tumor growth.

Schwannomas are slow-growing benign neoplasms that develop throughout the body causing pain, sensory/motor dysfunction, and death. Because bacterial immunotherapy has been used in the treatment of some malignant neoplasms, we evaluated attenuated Salmonella typhimurium strains as immunotherapies for benign murine schwannomas. Several bacterial strains were tested, including VNP20009, a highly attenuated strain that was previously shown to be safe in human subjects with advanced malignant neoplasms, and a VNP20009 mutant that was altered in motility and other properties that included adherence and invasion of cultured mammalian cells. VNP20009 controlled tumor growth in two murine schwannoma models and induced changes in cytokine and immune effector cell profiles that were consistent with induction of enhanced innate and adaptive host immune responses compared with controls. Intratumoral (i.t.) injection of S. typhimurium led to tumor cell apoptosis, decreased tumor angiogenesis, and lower growth of the injected schwannoma tumors. Invasive VNP20009 was significantly more efficacious than was a noninvasive derivative in controlling the growth of injected tumors. Bacterial treatment apparently induced systemic antitumor immunity in that the growth of rechallenge schwannomas implanted following primary bacterial treatment was also reduced. Checkpoint programmed death-1 (PD-1) blockade induced by systemic administration of anti-PD-1 antibodies controlled tumor growth to the same degree as i.t. injection of S. typhimurium, and together, these two therapies had an additive effect on suppressing schwannoma growth. These experiments represent validation of a bacterial therapy for a benign neoplasm and support development of S. typhimurium VNP20009, potentially in combination with PD-1 inhibition, as a schwannoma immunotherapy.

Inhibition of Neuron-Restrictive Silencing Factor (REST/NRSF) Chromatin Binding Attenuates Epileptogenesis.

The mechanisms by which brain insults lead to subsequent epilepsy remain unclear. Insults including trauma, stroke, infections, and long seizures (status epilepticus, SE) increase the nuclear expression and chromatin binding of the neuron-restrictive silencing factor/RE-1 silencing transcription factor (NRSF/REST). REST/NRSF orchestrates major disruption of the expression of key neuronal genes, including ion channels and neurotransmitter receptors, potentially contributing to epileptogenesis. Accordingly, transient interference with REST/NRSF chromatin binding after an epilepsy-provoking SE suppressed spontaneous seizures for the 12 d duration of a prior study. However, whether the onset of epileptogenesis was suppressed or only delayed has remained unresolved. The current experiments determined if transient interference with REST/NRSF chromatin binding prevented epileptogenesis enduringly or, alternatively, slowed epilepsy onset. Epileptogenesis was elicited in adult male rats via systemic kainic acid-induced SE (KA-SE). We then determined if decoy, NRSF-binding-motif oligodeoxynucleotides (NRSE-ODNs), given twice following KA-SE (1) prevented REST/NRSF binding to chromatin, using chromatin immunoprecipitation, or (2) prevented the onset of spontaneous seizures, measured with chronic digital video-electroencephalogram. Blocking NRSF function transiently after KA-SE significantly lengthened the latent period to a first spontaneous seizure. Whereas this intervention did not influence the duration and severity of spontaneous seizures, total seizure number and seizure burden were lower in the NRSE-ODN compared with scrambled-ODN cohorts. Transient interference with REST/NRSF function after KA-SE delays and moderately attenuates insult-related hippocampal epilepsy, but does not abolish it. Thus, the anticonvulsant and antiepileptogenic actions of NRSF are but one of the multifactorial mechanisms generating epilepsy in the adult brain.

Culture of attenuated Salmonella Typhimurium VNP20009 in animal-product-free media does not alter schwannoma growth control.

Schwannomas are slow-growing benign peripheral nerve sheath tumors derived from Schwann-lineage cells that develop in association with NF2-related schwannomatosis (NF2) and schwannomatosis (NF3), as well as spontaneously. Individuals affected with NF2 and NF3 have multiple schwannomas with tumors arising throughout life. Surgical resection, the standard management, is limited in scope and efficacy and is itself associated with significant morbidity. We have previously shown that direct intratumoral injection of attenuated Salmonella Typhimurium (S. Typhimurium), strain VNP20009, showed a potent anti-tumor effect in preclinical NF-2 schwannoma models. The United States Federal Drug Administration (FDA) requires that bacterial products utilized in clinical trials be produced without exposure to animal-derived-products. In this context, we developed, characterized, and tested the antitumor efficacy of an attenuated S. Typhimurium serially passaged in animal-product-free media, naming it VNP20009-AF for "VNP20009-animal-product-free." Our in vitro data did not indicate any significant changes in the viability, motility, or morphology of VNP20009-AF, compared to its parental strain. In vivo efficacy data demonstrated that VNP20009-AF and VNP20009 controlled tumor growth to the same degree in both human NF2-schwannoma xenograft and murine-NF2 schwannoma allograft models. Together, these data support the use of VNP20009-AF for the translation of bacterial schwannoma therapy into clinical trials.

Early stress-induced impaired microglial pruning of excitatory synapses on immature CRH-expressing neurons provokes aberrant adult stress responses.

Several mental illnesses, characterized by aberrant stress reactivity, often arise after early-life adversity (ELA). However, it is unclear how ELA affects stress-related brain circuit maturation, provoking these enduring vulnerabilities. We find that ELA increases functional excitatory synapses onto stress-sensitive hypothalamic corticotropin-releasing hormone (CRH)-expressing neurons, resulting from disrupted developmental synapse pruning by adjacent microglia. Microglial process dynamics and synaptic element engulfment were attenuated in ELA mice, associated with deficient signaling of the microglial phagocytic receptor MerTK. Accordingly, selective chronic chemogenetic activation of ELA microglia increased microglial process dynamics and reduced excitatory synapse density to control levels. Notably, selective early-life activation of ELA microglia normalized adult acute and chronic stress responses, including stress-induced hormone secretion and behavioral threat responses, as well as chronic adrenal hypertrophy of ELA mice. Thus, microglial actions during development are powerful contributors to mechanisms by which ELA sculpts the connectivity of stress-regulating neurons, promoting vulnerability to stress and stress-related mental illnesses.

Unexpected Transcriptional Programs Contribute to Hippocampal Memory Deficits and Neuronal Stunting after Early-Life Adversity.

Early-life adversity (ELA) is associated with lifelong memory deficits, yet the responsible mechanisms remain unclear. We impose ELA by rearing rat pups in simulated poverty, assess hippocampal memory, and probe changes in gene expression, their transcriptional regulation, and the consequent changes in hippocampal neuronal structure. ELA rats have poor hippocampal memory and stunted hippocampal pyramidal neurons associated with ~140 differentially expressed genes. Upstream regulators of the altered genes include glucocorticoid receptor and, unexpectedly, the transcription factor neuron-restrictive silencer factor (NRSF/REST). NRSF contributes critically to the memory deficits because blocking its function transiently following ELA rescues spatial memory and restores the dendritic arborization of hippocampal pyramidal neurons in ELA rats. Blocking NRSF function in vitro augments dendritic complexity of developing hippocampal neurons, suggesting that NRSF represses genes involved in neuronal maturation. These findings establish important, surprising contributions of NRSF to ELA-induced transcriptional programming that disrupts hippocampal maturation and memory function.

Dexamethasone Attenuates Hyperexcitability Provoked by Experimental Febrile Status Epilepticus.

The role of neuroinflammation in the mechanisms of epilepsy development is important because inflammatory mediators provide tractable targets for intervention. Inflammation is intrinsically involved in the generation of childhood febrile seizures (FSs), and prolonged FS [febrile status epilepticus (FSE)] precedes a large proportion of adult cases of temporal lobe epilepsy (TLE). As TLE is often refractory to therapy and is associated with serious cognitive and emotional problems, we investigated whether its development can be prevented using anti-inflammatory strategies. Using an immature rat model of FSE [experimental FSE (eFSE)], we administered dexamethasone (DEX), a broad anti-inflammatory agent, over 3 d following eFSE. We assessed eFSE-provoked hippocampal network hyperexcitability by quantifying the presence, frequency, and duration of hippocampal spike series, as these precede and herald the development of TLE-like epilepsy. We tested whether eFSE provoked hippocampal microgliosis, astrocytosis, and proinflammatory cytokine production in male and female rats and investigated blood-brain barrier (BBB) breaches as a potential contributor. We then evaluated whether DEX attenuated these eFSE sequelae. Spike series were not observed in control rats given vehicle or DEX, but occurred in 41.6% of eFSE-vehicle rats, associated with BBB leakage and elevated hippocampal cytokines. eFSE did not induce astrocytosis or microgliosis but provoked BBB disruption in 60% of animals. DEX significantly reduced spike series prevalence (to 7.6%) and frequency, and abrogated eFSE-induced cytokine production and BBB leakage (to 20%). These findings suggest that a short, postinsult intervention with a clinically available anti-inflammatory agent potently attenuates epilepsy-predicting hippocampal hyperexcitability, potentially by minimizing BBB disruption and related neuroinflammation.