Abstract 3510: SOT201 is a novel targeted IL-15Rbg agonist to alleviate PD-1-mediated immune cell suppression and potentiate anti-tumor efficacy

SOT201 is a novel immunocytokine consisting of a monoclonal humanized, Fc silenced antibody against PD-1 fused to a covalent RLI-15 complex of a human IL-15 mutein linked to the high-affinity binding site of the IL-15Rα, the sushi+ domain. SOT201 is developed for immunotherapeutic treatment of various types of cancers. The activity of SOT201 is based on spatiotemporal reinvigorating of anti-tumor immune responses by disrupting co-inhibitory T-cell signaling by blocking PD-1 and synergistically activating adaptive as well as innate immunity by IL-15-mediated signaling via the IL-2/IL-15βγ receptor on T cells, NK, NKT, and γδ T cells. SOT201 showed a superior potentiation of T cell stimulation over pembrolizumab in mixed lymphocyte reaction in vitro. Studies in cynomolgus monkeys showed that decreased affinity of IL-15 mutein in SOT201 for its IL-15Rβγ is well optimized to ensure favorable pharmacokinetic properties while inducing strong CD8+ T cell and NK cell activation and expansion. Synergistic action on CD8+ T cell activation of both anti-PD-1 and RLI-15 moieties was confirmed using mouse surrogate SOT201 molecules in vivo. Strong anti-tumor efficacy after SOT201 treatment was achieved in a human PD-1 transgenic mouse model implanted with the MC38-hPD-L1 cell line. These data represent a promising therapeutic candidate molecule leveraging the synergistic concerted action of anti-PD-1 blockage and simultaneous immune cell activation directed preferentially to the high PD-1+ T cell tumor environment. The therapeutic potential of SOT201 is currently being prepared for evaluation in a Phase I clinical study in metastatic advanced cancer patients as well as for PD-1 resistant/refractory patients as our clinical stage IL-2/IL-15Rβγ agonist SOT101 already showed a clinical benefit in these patients in its ongoing Phase I study.

Citation Format: Irena Adkins, Zuzana Antosova, Klara Danova, Kamila Hladikova, Katerina Augustynkova, Katerina Sajnerova, Nada Podzimkova, Pavel Marasek, Guy de Martynoff, David Bechard, Ulrich Moebius, Radek Spisek. SOT201 is a novel targeted IL-15Rbg agonist to alleviate PD-1-mediated immune cell suppression and potentiate anti-tumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3510.

Vimentin Phosphorylation Is Required for Normal Cell Division of Immature Astrocytes

Vimentin (VIM) is an intermediate filament (nanofilament) protein expressed in multiple cell types, including astrocytes. Mice with VIM mutations of serine sites phosphorylated during mitosis (VIM^SA/SA) show cytokinetic failure in fibroblasts and lens epithelial cells, chromosomal instability, facilitated cell senescence, and increased neuronal differentiation of neural progenitor cells. Here we report that in vitro immature VIM^SA/SA astrocytes exhibit cytokinetic failure and contain vimentin accumulations that co-localize with mitochondria. This phenotype is transient and disappears with VIM^SA/SA astrocyte maturation and expression of glial fibrillary acidic protein (GFAP); it is also alleviated by the inhibition of cell proliferation. To test the hypothesis that GFAP compensates for the effect of VIM^SA/SA in astrocytes, we crossed the VIM^SA/SA and GFAP^−/− mice. Surprisingly, the fraction of VIM^SA/SA immature astrocytes with abundant vimentin accumulations was reduced when on GFAP^−/− background. This indicates that the disappearance of vimentin accumulations and cytokinetic failure in mature astrocyte cultures are independent of GFAP expression. Both VIM^SA/SA and VIM^SA/SAGFAP^−/− astrocytes showed normal mitochondrial membrane potential and vulnerability to H₂O₂, oxygen/glucose deprivation, and chemical ischemia. Thus, mutation of mitotic phosphorylation sites in vimentin triggers formation of vimentin accumulations and cytokinetic failure in immature astrocytes without altering their vulnerability to oxidative stress.

Nestin Regulates Neurogenesis in Mice Through Notch Signaling From Astrocytes to Neural Stem Cells

The intermediate filament (nanofilament) protein nestin is a marker of neural stem cells, but its role in neurogenesis, including adult neurogenesis, remains unclear. Here, we investigated the role of nestin in neurogenesis in adult nestin-deficient (Nes–/–) mice. We found that the proliferation of Nes–/– neural stem cells was not altered, but neurogenesis in the hippocampal dentate gyrus of Nes–/– mice was increased. Surprisingly, the proneurogenic effect of nestin deficiency was mediated by its function in the astrocyte niche. Through its role in Notch signaling from astrocytes to neural stem cells, nestin negatively regulates neuronal differentiation and survival; however, its expression in neural stem cells is not required for normal neurogenesis. In behavioral studies, nestin deficiency in mice did not affect associative learning but was associated with impaired long-term memory.

Increased Neuronal Differentiation of Neural Progenitor Cells Derived from Phosphovimentin-Deficient Mice

Vimentin is an intermediate filament (also known as nanofilament) protein expressed in several cell types of the central nervous system, including astrocytes and neural stem/progenitor cells. Mutation of the vimentin serine sites that are phosphorylated during mitosis (VIM^SA/SA) leads to cytokinetic failures in fibroblasts and lens epithelial cells, resulting in chromosomal instability and increased expression of cell senescence markers. In this study, we investigated morphology, proliferative capacity, and motility of VIM^SA/SA astrocytes, and their effect on the differentiation of neural stem/progenitor cells. VIM^SA/SA astrocytes expressed less vimentin and more GFAP but showed a well-developed intermediate filament network, exhibited normal cell morphology, proliferation, and motility in an in vitro wound closing assay. Interestingly, we found a two- to fourfold increased neuronal differentiation of VIM^SA/SA neurosphere cells, both in a standard 2D and in Bioactive3D cell culture systems, and determined that this effect was neurosphere cell autonomous and not dependent on cocultured astrocytes. Using BrdU in vivo labeling to assess neural stem/progenitor cell proliferation and differentiation in the hippocampus of adult mice, one of the two major adult neurogenic regions, we found a modest increase (by 8%) in the fraction of newly born and surviving neurons. Thus, mutation of the serine sites phosphorylated in vimentin during mitosis alters intermediate filament protein expression but has no effect on astrocyte morphology or proliferation, and leads to increased neuronal differentiation of neural progenitor cells.