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SUMMARYNeuroinflammation characterizes multiple neurologic diseases, including primary inflammatory conditions such as multiple sclerosis (MS) and classical neurodegenerative diseases. Aberrant activation of the innate immune system contributes to disease progression in these conditions, but drugs that modulate innate immunity, particularly within the central nervous system (CNS), are lacking. The CNS-pene-trant natural product bryostatin-1 (bryo-1) attenuates neuroinflammation by targeting innate myeloid cells. Supplies of natural bryo-1 are limited but a recent scalable synthesis has enabled access to it and its analogs (termed bryologs), the latter providing a path to more efficacious, better tolerated, and more accessible agents. Here, we show that multiple synthetically accessible bryologs replicate the anti-inflammatory effects of bryo-1 on innate immune cells in vitro, and a lead bryolog attenuates neuroinflammation in vivo – actions mechanistically dependent on PKC binding. Our findings identify bryologs as promising drug candidates for targeting innate immunity in neuroinflammation and create a platform for evaluation of synthetic PKC modulators in neuroinflammatory diseases such as MS.Graphical Abstract

The marine natural product bryostatin 1 has demonstrated procognitive and antidepressant effects in animals and has been entered into human clinical trials for treating Alzheimer's disease (AD). The ability of bryostatin 1 to enhance learning and memory has largely been attributed to its effects on the structure and function of hippocampal neurons. However, relatively little is known about how bryostatin 1 influences the morphology of cortical neurons, key cells that also support learning and memory processes and are negatively impacted in AD. Here, we use a combination of carefully designed chemical probes and pharmacological inhibitors to establish that bryostatin 1 increases cortical synaptogenesis while decreasing dendritic spine density in a protein kinase C (PKC)-dependent manner. The effects of bryostatin 1 on cortical neurons are distinct from those induced by neural plasticity-promoting psychoplastogens such as ketamine. Compounds capable of increasing synaptic density with concomitant loss of immature dendritic spines may represent a unique pharmacological strategy for enhancing memory by improving signal-to-noise ratio in the central nervous system.

Bryostatin 1 is a marine natural product under investigation for HIV/AIDS eradication, the treatment of neurological disorders, and enhanced CAR T/NK cell immunotherapy. Despite its promising activity, bryostatin 1 is neither evolved nor optimized for the treatment of human disease. Here we report the design, synthesis, and biological evaluation of several close-in analogs of bryostatin 1. Using a function-oriented synthesis approach, we synthesize a series of bryostatin analogs designed to maintain affinity for bryostatin’s target protein kinase C (PKC) while enabling exploration of their divergent biological functions. Our late-stage diversification strategy provides efficient access to a library of bryostatin analogs, which per our design retain affinity for PKC but exhibit variable PKC translocation kinetics. We further demonstrate that select analogs potently increase cell surface expression of CD22, a promising CAR T cell target for the treatment of leukemias, highlighting the clinical potential of bryostatin analogs for enhancing targeted immunotherapies., Bryostatin 1 is a unique therapeutic lead, however its scarce natural sources have hampered its use in treatment of human disease. Here, the authors use a scalable synthesis of bryostatin 1 to make close-in analogs which potently induce increased cell surface expression holding potential for immunotherapy.

The ability of HIV to establish a long-lived latent infection within resting CD4+ T cells leads to persistence and episodic resupply of the virus in patients treated with antiretroviral therapy (ART), thereby preventing eradication of the disease. Protein kinase C (PKC) modulators such as bryostatin 1 can activate these latently infected cells, potentially leading to their elimination by virus-mediated cytopathic effects, the host’s immune response and/or therapeutic strategies targeting cells actively expressing virus. While research in this area has focused heavily on naturally-occurring PKC modulators, their study has been hampered by their limited and variable availability, and equally significantly by sub-optimal activity and in vivo tolerability. Here we show that a designed, synthetically-accessible analog of bryostatin 1 is better-tolerated in vivo when compared with the naturally-occurring product and potently induces HIV expression from latency in humanized BLT mice, a proven and important model for studying HIV persistence and pathogenesis in vivo. Importantly, this induction of virus expression causes some of the newly HIV-expressing cells to die. Thus, designed, synthetically-accessible, tunable, and efficacious bryostatin analogs can mediate both a “kick” and “kill” response in latently-infected cells and exhibit improved tolerability, therefore showing unique promise as clinical adjuvants for HIV eradication., Author summary HIV can persist for many years in a latent (non-expressing) state in individuals treated with antiretroviral therapy, and these latently-infected cells represent a major barrier to curing HIV infection. One potential approach to eliminating the reservoir cells is to induce them to express viral proteins while maintaining antiretroviral therapy, allowing these cells to be killed by the virus or the immune response. However, this approach has been hampered by a lack of compounds that can safely and effectively reverse HIV from latency in a living organism. Here we show that a designed, synthetic protein kinase C modulating compound is better-tolerated than the naturally-occurring product (bryostatin 1) in mice and potently induces HIV expression from latency in a mouse model containing a human immune system. Importantly, this induction of virus expression causes some of the newly HIV-expressing cells to die. Hence, this compound shows unique promise as a component of the so-called “kick and kill” approach for HIV eradication.