CRISPRa induced expression of native MRI reporter proteins

摘要：CRISPR-Cas等基因组编辑技术为治疗和治疗疾病提供了新的治疗工具

Abstract: Genome editing technologies such as CRISPR-Cas encompass new therapeutic tools for treating and curing a broad set of diseases ranging from cancer to genetic abnormalities to metabolic diseases, even stretching as far as combating aging and regenerating tissue. Extending beyond permanent genome modification, the expanding ensemble of CRISPR technologies based on engineered Cas proteins now possess capabilities for programmable epigenetic regulation, transcriptional control of native genes, and RNA editing; moreover, these systems can be combined for orthogonal control of gene expression. These technologies open up unlimited therapeutic applications but the critical requirement that the targeted or transplanted cells be monitored and tracked in vivo for verifying both intended and unintended consequences, is unmet. Here we propose a new paradigm in imaging reporters based on CRISPR-Cas, well suited for in vivo imaging of cell and gene therapies. Rather than introduce exogenous imaging reporter genes into the genome or cell, we hypothesize that cell and gene therapies can be imaged in vivo by using CRISPR-mediated transcriptional activation (CRISPRa) technology to induce expression of native proteins that function as imaging reporters. We call this paradigm CRISPRa-MRI. The benefits of CRISPRa-MRI are that these proteins would be inherently human, would only be transiently expressed without disrupting the genome and would enable multiplexing either with other reporter proteins or CRISPR therapeutics, simultaneously. As a proof- of-concept, we will focus on the hepatic organic anion transporting polypeptides (OATPs) mouse OATP1A1 (mOATP1A1) and human OATP1B3 (hOATP1B3), recognizing that many other transporters, metal binding proteins and cell surface receptors are also viable endogenous reporter candidates. mOATP1A1 and hOATP1B3 both specifically transport the FDA-approved MRI contrast agent Gd-EOB-DTPA into cells, the accumulation of which results in robust bright MRI signal. Normally, expression of these transporters is limited to the liver, but by using CRISPRa these silent imaging reporter genes can be ‘turned on’ and used to image any cell type or lineage. CRISPRa-MRI can co-opt the technology used for CRISPR editing or therapeutics in the engineered cells or gene therapy, avoiding the potential for insertional mutagenesis or chronic expression of an exogenous gene which may lead to immunogenicity or toxicity, while at the same time eliminating the additional challenge of delivery and expression of conventional reporter genes. Here we propose to develop a CRISPRa strategy for activating endogenous mOATP1A1 and hOATP1B3 in vitro (Specific Aim 1) and then test its performance for in vivo imaging of directly targeted tissues or CRISPRa induction in cells post-transplantation (Specific Aim 2). The promise of imaging reporter genes for cell and gene-based therapies in humans is, as yet, largely unfulfilled. CRISPRa-MRI is a completely novel strategy that can help achieve the potential of imaging reporter genes in humans, especially for monitoring therapies based on CRISPR gene editing or epigenetic modulation.