UC San Diego

While cancer treatment modalities have improved in recent decades, each subsequent improvement in therapy has brought mixed results and has fallen short of achieving a lasting cure. From chemotherapy and radiotherapy to small molecule inhibitors and monoclonal antibodies to antibody-drug conjugates, each has brought a unique approach and improvement to preceding modalities. Yet, the limitations of these approaches are evident. The discovery of RNA interference (RNAi) and its potential to treat genetic diseases like cancer opened a new therapeutic avenue. Yet, for many years, RNAi faced multiple setbacks and limitations at both the biological and chemical levels. Among the challenges faced in the RNAi field are the inherently large size (>14,000 Da) and highly charged (>40 phosphates) nature of siRNA molecules, which prevents them from passively diffusing across the cell membrane the way that small molecular inhibitors do. Other obstacles include nucleases, innate immunity, and potential off-target silencing effects from siRNAs. Many of the same problems that affect siRNAs also affect antisense oligonucleotides. Delivery with an antibody would significantly improve the prospects of an oligonucleotide reaching its target. But building an antibody with a clearly defined drug-antibody ratio comes with difficulties. Other challenges include delivery and identification of suitable target receptors that are expressed in sufficiently high numbers and can rapidly internalize via endocytosis. The most limiting barrier preventing adequate delivery of siRNA is the difficulty of achieving endosomal escape, which prevents oligonucleotides from reaching the cytoplasm and nucleus of cells. Over the past decade, our laboratory has worked extensively to address these challenges. Oligonucleotide stability and protection from the immune system were achieved in large part through chemical modifications during the oligo synthesis process. Furthermore, a site-specific conjugation approach was developed to create clearly defined antibody-RNA conjugates (ARCs). Currently, a work-in-progress on the chemistry side is the development of universal endosomal escape domains (uEEDs). The work described herein encompasses the development and building of a complex ARC macromolecular therapeutic that, under the right conditions, could hold great potential for the specific knockdown of previously undruggable oncogenes, such as Kras and Myc, and other aberrant genetic targets in viral infections and chronic diseases.