Title : Nanomaterial-mediated systemically administered m-RNA-based gene therapy directed exclusively to cancer, present successes and future prospects
Abstract:
The presentation focuses on systemically administered targeted gene therapy using mRNA instead of DNA; why the former is superior for this purpose will be discussed. Lipid nanoparticles (LNPs) and, more recently, extracellular vesicles (EVs, aka exosomes) have proven effective vectors. An example of LNP-mediated directed mRNA delivery is that of Cas9 gene for editing of PTEN by the CRISPR/Cas system. Also, an mRNA-LNP drug, NTLA-2001, is in clinical trial for treating transthyretin amyloidosis. EVs are nature’s own antigen delivery system, posing minimal immunogenicity/toxicity risk and their surface integrins confer intrinsic tissue tropism. They have been engineered to display targeting moieties, which are fused to EV anchor domains. Emphasis here will be on the lactadherin C1-C2 anchor domain (which binds to the EV surface) and itsfusion to a high affinity anti-HER2 scFv, resulting in HER2 receptor targeting EVs. These were loaded with mRNA that encodes the enzyme HChrR6, which can activate several prodrugs, including CNOB and CB1954 (tretazicar). (The loaded and targeted EVs are called ‘EXODEPTs’.) Systemic delivery of EXODEPTs along with either CNOB or tretazicar resulted in the killing of HER2+ breast cancer xenografts in mice without any off-target effects, indicating gene delivery exclusively to the cancer. Attaining specific tumor targeting and loading of the EVs with the HChrR6 mRNA were greatly facilitated by the fact that the activated drug of CNOB, MCHB, is highly fluorescent and can be visualized non-invasively in living mice. Tretazicar (whose activation could also be visualized vicariously by MCHB) was effective at its safe dose; the EVs needed to be delivered only twice; and there were no side effects. Thus, the results augment clinical transfer potential of this regimen. Examples of EV targeting using other anchor proteins, e.g., Lamp2b and CD47, will also be briefly discussed. As the EV anchor domains can be fused to other targeting moieties, the approach is generic for specific gene delivery also in other diseases.
