Fernandes, R. | Search bioRxiv

bioRxiv2021

Anti-GD2 antibody disrupts GD2:Siglec-7 interactions and synergizes with CD47 blockade to mediate tumor eradication

The disialoganglioside GD2 is consistently overexpressed in neuroblastoma and osteosarcoma, and is variably expressed in other sarcomas, gliomas, neuroendocrine tumors, and epithelial cancers. Anti-GD2 antibodies have improved the survival rates of patients with neuroblastoma only when administered as part of intense chemotherapy-based cytotoxic regimens, which are associated with debilitating late effects including hearing loss, growth retardation, and secondary leukemias. Despite broad expression of GD2 on osteosarcoma, anti-GD2 antibody has not mediated significant antitumor activity in that disease or any other GD2+ cancers. CD47 is a checkpoint molecule overexpressed on tumor cells that inhibits macrophage activity, and CD47 blockade has demonstrated promising clinical activity in early human trials. We investigated whether anti-CD47 antibody could enhance the efficacy of anti-GD2 antibody in neuroblastoma and other GD2+ malignancies. We demonstrate substantial synergy of these two agents, resulting in the recruitment of tumor associated macrophages (TAMs) to mediate robust and durable anti-tumor responses. The responses are driven by GD2-specific factors that reorient the balance of macrophage activity towards phagocytosis of tumor cells, including disruption of a newly described GD2:Siglec-7 axis. These results demonstrate the unique synergy of combining anti-GD2 with anti-CD47, which has the potential to significantly enhance outcomes for children with neuroblastoma and osteosarcoma and will soon be investigated in a first-in-human clinical trial.

immunology↗

bioRxiv2020

A Crystallographic Snapshot of SARS-CoV-2 Main Protease Maturation Process

SARS-CoV-2 is the causative agent of COVID-19. The dimeric form of the viral main protease is responsible for the cleavage of the viral polyprotein in 11 sites, including its own N and C-terminus. Although several mechanisms of self-cleavage had been proposed for SARS-CoV, the lack of structural information for each step is a setback to the understanding of this process. Herein, we used X-ray crystallography to characterize an immature form of the main protease, which revealed major conformational changes in the positioning of domain-three over the active site, hampering the dimerization and diminishing its activity. We propose that this form preludes the cis-cleavage of N-terminal residues within the dimer, leading to the mature active site. Using fragment screening, we probe new cavities in this form which can be used to guide therapeutic development. Furthermore, we characterized a serine site-directed mutant of the main protease bound to its endogenous N and C-terminal residues during the formation of the tetramer. This quaternary form is also present in solution, suggesting a transitional state during the C-terminal trans-cleavage. This data sheds light in the structural modifications of the SARS-CoV-2 main protease during maturation, which can guide the development of new inhibitors targeting its intermediary states.

biochemistry↗