Discovery and development of DNA-PKcs PROTACs to reduce organ transplant rejection
Summary
DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a therapeutic target for the treatment of cancer due to its role in double-stranded DNA damage repair. Recent studies have demonstrated its significant function in the immune system, which broadens the therapeutic potential of DNA-PKcs to include treatment of immune-related disorders. Published data from the Burdine laboratory indicates that DNA-PKcs is required for immune mechanisms that induce rejection of transplanted allogeneic grafts. In this study, loss of DNA-PKcs activity decreased cytotoxic T cell activation and significantly extended graft survival highlighting the potential clinical use of DNA-PKcs inhibitors for transplant rejection therapy.
DNA-PKcs has two functioning domains, a kinase domain and a N-terminal DNA-binding domain. While the two domains often function in concert to augment DNA-PKcs activity they also have independent functions. For instance, through its DNA-binding domain, DNA-PKcs binds to promoters of active genes and acts as a scaffolding protein for formation of the transcriptional complex. This is particularly important during an immune response where DNA-PKcs drives expression of genes that promote lymphocyte activation. Current DNA-PKcs inhibitors are designed to block catalytic activity of the kinase domain but, despite inhibition, DNA-PKcs still retains DNA-binding ability and scaffolding functionality. Therefore, the goal of this proposal is to design a novel drug molecule that can simultaneously impair kinase function as well as DNA-binding ability and scaffolding properties of DNA-PKcs to more effectively suppress immune function. We hypothesize that this approach will significantly reduce organ rejection in transplant patients.
Aim 1: Generate and determine biological effects of small molecule PROTACs that degrade DNA-PKcs. We will generate PROTAC (proteolysis targeting chimera) degraders that induce selective intracellular proteolysis of DNA-PKcs to eliminate both catalytic activity and DNA-binding functionality. DNA-PKcs PROTACs will be characterized in vitro including effects on known downstream targets, T cell activation, and DNA-binding ability. The PROTAC with greatest ability to modulate in vitro immune biology will be progressed to Aim 2.
Aim 2: Complete a preclinical pharmacokinetic study and evaluate effects of a DNA-PKcs PROTAC on organ rejection in a pig kidney transplant model. In preparation for preclinical studies, a preliminary pharmacokinetic study will be performed to help guide appropriate dose and dose-frequency of the PROTAC. Following an IACUC-approved protocol, we will perform pig kidney transplant studies to determine if DNA-PKcs PROTACs prevent organ rejection. Serum samples and kidney biopsies will be obtained for proteomic analysis to identify mechanisms by which DNA-PKcs PROTACs modify the immune system in vivo.
This proposal outlines the discovery and development of novel DNA-PKcs PROTACs that have the potential to greatly impact the transplant community. PROTACs will be designed to maximize potential for a strong intellectual property (IP) position, which will improve chances for commercialization. Dr. Frett has previously translated three academic projects into three separate SBIR/STTR grants, and the current project is an excellent candidate for similar development. Further, given the interest in DNA-PKcs for cancer therapy, a DNA-PKcs PROTAC has the potential for commercialization within the cancer community.
Keywords:
- DNA-PKcs
- PROTAC
- Transplant rejection