Genetic Code Expansion for Site-Specific Labeling of Antibodies with Radioisotopes

Evolution of Pyrrolysyl-tRNA Synthetase: From Methanogenesis to Genetic Code Expansion

Over 20 years ago, the pyrrolysine encoding translation system was discovered in specific archaea. Our Review provides an overview of how the once obscure pyrrolysyl-tRNA synthetase (PylRS) tRNA pair, originally responsible for accurately translating enzymes crucial in methanogenic metabolic pathways, laid the foundation for the burgeoning field of genetic code expansion. Our primary focus is the discussion of how to successfully engineer the PylRS to recognize new substrates and exhibit higher in vivo activity. We have compiled a comprehensive list of ncAAs incorporable with the PylRS system. Additionally, we also summarize recent successful applications of the PylRS system in creating innovative therapeutic solutions, such as new antibody-drug conjugates, advancements in vaccine modalities, and the potential production of new antimicrobials.

Tuning the Functionality of Designer Translating Organelles with Orthogonal tRNA Synthetase/tRNA Pairs

Site-specific incorporation of noncanonical amino acids (ncAAs) can be realized by genetic code expansion (GCE) technology. Different orthogonal tRNA synthetase/tRNA (RS/tRNA) pairs have been developed to introduce a ncAA at the desired site, delivering a wide variety of functionalities that can be installed into selected proteins. Cytoplasmic expression of RS/tRNA pairs can cause a problem with background ncAA incorporation into host proteins. The application of orthogonally translating organelles (OTOs), inspired by the concept of phase separation, provides a solution for this issue in mammalian cells, allowing site-specific and protein-selective ncAA incorporation. So far, only Methanosarcina mazei (Mm) pyrrolysyl-tRNA synthetase (PylRS) has been used within OTOs, limiting the method's potential. Here, we explored the implementation of four other widely used orthogonal RS/tRNA pairs with OTOs, which, to our surprise, were unsuccessful in generating mRNA-selective GCE. Next, we tested several experimental solutions and developed a new chimeric phenylalanyl-RS/tRNA pair that enables ncAA incorporation in OTOs in a site-specific and protein-selective manner. Our work reveals unaccounted design constraints in the spatial engineering of enzyme functions using designer organelles and presents a strategy to overcome those in vivo. We then discuss current limitations and future directions of in-cell engineering in general and protein engineering using GCE specifically.

Recent Technological and Intellectual Property Trends in Antibody-Drug Conjugate Research

Antibody-drug conjugate (ADC) therapy, an advanced therapeutic technology comprising antibodies, chemical linkers, and cytotoxic payloads, addresses the limitations of traditional chemotherapy. This study explores key elements of ADC therapy, focusing on antibody development, linker design, and cytotoxic payload delivery. The global rise in cancer incidence has driven increased investment in anticancer agents, resulting in significant growth in the ADC therapy market. Over the past two decades, notable progress has been made, with approvals for 14 ADC treatments targeting various cancers by 2022. Diverse ADC therapies for hematologic malignancies and solid tumors have emerged, with numerous candidates currently undergoing clinical trials. Recent years have seen a noteworthy increase in ADC therapy clinical trials, marked by the initiation of numerous new therapies in 2022. Research and development, coupled with patent applications, have intensified, notably from major companies like Pfizer Inc. (New York, NY, USA), AbbVie Pharmaceuticals Inc. (USA), Regeneron Pharmaceuticals Inc. (Tarrytown, NY, USA), and Seagen Inc. (Bothell, WA, USA). While ADC therapy holds great promise in anticancer treatment, challenges persist, including premature payload release and immune-related side effects. Ongoing research and innovation are crucial for advancing ADC therapy. Future developments may include novel conjugation methods, stable linker designs, efficient payload delivery technologies, and integration with nanotechnology, driving the evolution of ADC therapy in anticancer treatment.

Alpha-Emitting Radionuclides: Current Status and Future Perspectives

The use of radionuclides for targeted endoradiotherapy is a rapidly growing field in oncology. In particular, the focus on the biological effects of different radiation qualities is an important factor in understanding and implementing new therapies. Together with the combined approach of imaging and therapy, therapeutic nuclear medicine has recently made great progress. A particular area of research is the use of alpha-emitting radionuclides, which have unique physical properties associated with outstanding advantages, e.g., for single tumor cell targeting. Here, recent results and open questions regarding the production of alpha-emitting isotopes as well as their chemical combination with carrier molecules and clinical experience from compassionate use reports and clinical trials are discussed.

Remodeling the cellular stress response for enhanced genetic code expansion in mammalian cells

Genetic code expansion (GCE) reprograms the translational machinery to site-specifically incorporate noncanonical amino acids (ncAAs) into a selected protein. The efficiency of GCE in mammalian cells might be compromised by cellular stress responses, among which, the protein kinase R(PKR)-dependent eIF2α phosphorylation pathway can reduce translation rates. Here we test several strategies to engineer the eIF2α pathway and boost the rate of translation and show that such interventions increase GCE efficiency in mammalian cells. In particular, addition of the N-terminal PKR fragment (1-174) provides a substantial enhancement in cytoplasmic GCE and also in GCE realized by OTOs (orthogonally translating designer organelles), which built on the principle of 2D phase separation to enable mRNA-selective ncAA incorporation. Our study demonstrates an approach for improving the efficiency of GCE and provides a means by which the power of designer organelles can be further optimized to tune protein translation.

Progress on Phage Display Technology: Tailoring Antibodies for Cancer Immunotherapy

The search for innovative anti-cancer drugs remains a challenge. Over the past three decades, antibodies have emerged as an essential asset in successful cancer therapy. The major obstacle in developing anti-cancer antibodies is the need for non-immunogenic antibodies against human antigens. This unique requirement highlights a disadvantage to using traditional hybridoma technology and thus demands alternative approaches, such as humanizing murine monoclonal antibodies. To overcome these hurdles, human monoclonal antibodies can be obtained directly from Phage Display libraries, a groundbreaking tool for antibody selection. These libraries consist of genetically engineered viruses, or phages, which can exhibit antibody fragments, such as scFv or Fab on their capsid. This innovation allows the in vitro selection of novel molecules directed towards cancer antigens. As foreseen when Phage Display was first described, nowadays, several Phage Display-derived antibodies have entered clinical settings or are undergoing clinical evaluation. This comprehensive review unveils the remarkable progress in this field and the possibilities of using clever strategies for phage selection and tailoring the refinement of antibodies aimed at increasingly specific targets. Moreover, the use of selected antibodies in cutting-edge formats is discussed, such as CAR (chimeric antigen receptor) in CAR T-cell therapy or ADC (antibody drug conjugate), amplifying the spectrum of potential therapeutic avenues.