Neomorphic DNA-binding enables tumor-specific therapeutic gene expression in fusion-addicted childhood sarcoma.

Chimeric fusion transcription factors are oncogenic hallmarks of several devastating cancer entities including pediatric sarcomas, such as Ewing sarcoma (EwS) and alveolar rhabdomyosarcoma (ARMS). Despite their exquisite specificity, these driver oncogenes have been considered largely undruggable due to their lack of enzymatic activity.Here, we show in the EwS model that - capitalizing on neomorphic DNA-binding preferences - the addiction to the respective fusion transcription factor EWSR1-FLI1 can be leveraged to express therapeutic genes.We genetically engineered a de novo enhancer-based, synthetic and highly potent expression cassette that can elicit EWSR1-FLI1-dependent expression of a therapeutic payload as evidenced by episomal and CRISPR-edited genomic reporter assays. Combining in silico screens and immunohistochemistry, we identified GPR64 as a highly specific cell surface antigen for targeted transduction strategies in EwS. Functional experiments demonstrated that anti-GPR64-pseudotyped lentivirus harboring our expression cassette can specifically transduce EwS cells to promote the expression of viral thymidine kinase sensitizing EwS for treatment to otherwise relatively non-toxic (Val)ganciclovir and leading to strong anti-tumorigenic, but no adverse effects in vivo. Further, we prove that similar vector designs can be applied in PAX3-FOXO1-driven ARMS, and to express immunomodulatory cytokines, such as IL-15 and XCL1, in tumor entities typically considered to be immunologically 'cold'.Collectively, these results generated in pediatric sarcomas indicate that exploiting, rather than suppressing, the neomorphic functions of chimeric transcription factors may open inroads to innovative and personalized therapies, and that our highly versatile approach may be translatable to other cancers addicted to oncogenic transcription factors with unique DNA-binding properties.

High-affinity CD16-polymorphism and Fc-engineered antibodies enable activity of CD16-chimeric antigen receptor-modified T cells for cancer therapy.

BACKGROUND: CD16-chimeric antigen receptors (CAR) T cells recognise the Fc-portion of therapeutic antibodies, which can enable the selective targeting of different antigens. Limited evidence exists as to which CD16-CAR design and antibody partner might be most effective. We have hypothesised that the use of high-affinity CD16 variants, with increased Fc-terminus antibody affinity, combined with Fc-engineered antibodies, would provide superior CD16-CAR T cell efficacy. METHODS: CD16-CAR T (wild-type or variants) cells were co-cultured with Panc-1 pancreatic cancer, Raji lymphoma or A375 melanoma cells in the presence or absence of anti-CD20, anti-MCSP, wild-type or the glycoengineered antibody variants. The endpoints were proliferation, activation, and cytotoxicity in vitro. RESULTS: The CD16 158 V variant of CD16-CAR T cells showed increased cytotoxic activity against all the tested cancer cells in the presence of the wild-type antibody directed against MCSP or CD20. Glycoengineered antibodies enhanced CD16-CAR T cell activity irrespective of CD16 polymorphisms as compared with the wild-type antibody. The combination of the glycoengineered antibodies with the CD16-CAR 158 V variant synergised as seen by the increase in all endpoints. CONCLUSION: These results indicate that CD16-CAR with the high-affinity CD16 variant 158 V, combined with Fc-engineered antibodies, have high anti-tumour efficacy.