mTOR is activated in epilepsy, but the mechanisms of mTOR activation in post-traumatic epileptogenesis are unknown. It is also not clear whether mTOR inhibition has an antiepileptogenic, or merely anti-convulsive effect. The rat hippocampal organotypic culture model of post-traumatic epilepsy was used to study the effects of long term (four weeks) inhibition of signaling pathways that interact with mTOR. Ictal activity was quantified by measurement of lactate production and electrical recordings, and cell death was quantified with LDH release measurements and Nissl-stained neuron counts. Lactate and LDH measurements were well-correlated with electrographic activity and neuron counts, respectively. Inhibition of PI3K and Akt prevented activation of mTOR, and was as effective as inhibition of mTOR in reducing ictal activity and cell death. A dual inhibitor of PI3K and mTOR, NVP-BEZ235, was also effective. Inhibition of mTOR with rapamycin reduced axon sprouting. Late start of rapamycin treatment was effective in reducing epileptic activity and cell death, while early termination of rapamycin treatment did not result in increased epileptic activity or cell death. The conclusions of the study are: (1), the organotypic hippocampal culture model of posttraumatic epilepsy comprises a rapid assay of antiepileptogenic and neuroprotective activities and, in this model (2), mTOR activation depends on PI3K-Akt signaling, and (3) transient inhibition of mTOR has sustained effects on epilepsy.

Exogenous Insulin-Like Growth Factor-1 (IGF-1) is neuroprotective in animal models of brain injury, and has been considered as a potential therapeutic. Akt-mTOR and MAPK are downstream targets of IGF-1 signaling that are activated after brain injury. However, both brain injury and mTOR are linked to epilepsy, raising the possibility that IGF-1 may be epileptogenic. Here, we considered the role of IGF-1 in development of epilepsy after brain injury, using the organotypic hippocampal culture model of post-traumatic epileptogenesis. We found that IGF-1 was neuroprotective within a few days of injury but that long-term IGF-1 treatment was pro-epileptic. Pro-epileptic effects of IGF-1 were mediated by Akt-mTOR signaling. We also found that IGF-1 – mediated increase in epileptic activity led to neurotoxicity. The dualistic nature of effects of IGF-1 treatment demonstrates that anabolic enhancement through IGF-1 activation of mTOR cascade can be beneficial or harmful depending on the stage of the disease. Our findings suggest that epilepsy risk may need to be considered in the design of neuroprotective treatments for brain injury.

Over 600,000 Americans and 8 million worldwide die of cancer each year. The success of immune checkpoint blockade with anti-PD-1 therapy has been a remarkable clinical advance. However, most patients do not respond to anti-PD-1 monotherapy and the majority of those who initially do respond eventually succumb to the disease. There is currently an unmet need to identify therapeutic strategies to overcome resistance and further enhance the efficacy of anti-PD-1 therapy. Tim-4 is a phosphatidylserine (PS) receptor that has been reported to be expressed on myeloid cells. Prior work has demonstrated that Tim-4 deficiency or blockade in mice is associated with features of autoimmunity and enhanced anti-tumor immunity. Using flow cytometry, immunohistochemistry, and in vivo biodistribution, we determined that Tim-4 is expressed predominantly on tissue-resident macrophages, such as Kupffer cells, peritoneal macrophages, pleural macrophages, and lymph node macrophages, but not tumor-associated macrophages, in mice and humans. We provide evidence that Tim-4+ macrophages produce high levels of the cytokines TNF-α and TGF-β, which have been linked to T cell dysfunction, and also the TGF-β activating integrin αv (CD51). Antibody blockade of Tim-4 enhances the anti-tumor activity of anti-PD-1 therapy after subcutaneous tumor inoculation of B16 melanoma, CT26 colon carcinoma, and MC38 colon carcinoma. Finally, combined blockade of Tim-4 and PD-1 resulted in substantially more curative responses in a MC38 model of peritoneal carcinomatosis, compared to anti-PD-1 monotherapy. This was associated with enhanced CD8+ T cell infiltration into the peritoneal cavity, increased CD8+ T cell/Foxp3+ regulatory T cell ratio, and reduced expression of the exhaustion marker PD-1. Thus, we show that Tim-4+ tissue-resident macrophages impair anti-tumor T cell immunity and antibody blockade of Tim-4 is a strategy that should be considered for clinical studies in cancers resistant to anti-PD-1 monotherapy. Citation Format: Andrew Chow, Sara Schad, Sai K. Sharma, Sadna Budhu, Aditi Gupta, Corrin Pimentel, Hong Zhong, Jason S. Lewis, John T. Poirier, Jedd D. Wolchok, Charles M. Rudin, Taha Merghoub. Tim-4+ tissue-resident macrophages impair antitumor T-cell immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 978.

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