intracellular delivery of biological drugs such as peptides and nucleic acids
proximity-activated targeting of drugs to sites of inflammation and matrix remodeling
long-term, “on-demand” drug release from localized depots
These delivery systems are designed to improve the therapeutic index of existing drugs and/or to serve as enabling technologies for manipulation of intracellular targets currently considered to be “undruggable”. To achieve optimal, finely-tuned properties for these varied biomedical applications, polymers are utilized that respond to one or more environmental stimuli including pH, matrix metalloproteinases, reactive oxygen species, and temperature. Below, a sampling of topics currently under investigation in the ATL are highlighted.
Several projects in the ATL are aimed at development of novel applications using the RAFT (reversible addition fragmentation chain transfer) polymerization technique. These projects leverage the exquisite synthetic control afforded by RAFT to create pharmaceutical grade polymer-based therapeutics with well-defined molecular weight, architecture, and chemo-selective bioconjugation sites. Current RAFT-based projects include development of multi-functional, tumor-targeted drugs for breast cancer therapy and new technologies that can achieve environmentally-dependent and/or “cell-demanded” drug release in response to reactive oxygen species and/or enzyme activity. We are also developing multi-block and functionalized polymer structures optimized to supra-assemble into macroscale structures such as hydrogels.
Researchers in the ATL have developed novel, biodegradable materials that are broken down by cell-generated reactive oxygen species (ROS). This method of material degradation matches the rate of new tissue in-growth in vivo, optimizing tissue repair/regeneration. These materials include injectable poly(thioketal-urethane) (PTK-UR) scaffolds that form porous constructs after delivery to a wound site, and thermally-responsive PPS-based hydrogels that are liquids at room temperature but form stable gels at body temperature. These tissue regenerative materials can be used in many applications, including wound healing, sustained local drug delivery, and therapeutic cell delivery.
Development of nanomedicines is a significant focus in the ATL, and this work is broad-reaching in terms of types of materials employed, classes of drugs delivered, and pathological applications pursued. We develop nanomedicines with two goals in mind: (1) to improve the safety and efficacy of existing drugs and (2) to enable modulation of undruggable targets. To improve the safety and efficacy of existing drugs, we explore nano-formulation approaches that alter drug pharmacokinetics and increase biodistribution to desired target tissues. This is achieved through approaches that optimize nanocarrier physical and chemical properties (size, shape, and charge) and through targeting mechanisms (environmental targeting of cues such as enzymes and ROS that are upregulated at pathological sites and more conventional receptor-ligand targeting to promote preferential internalization by specific cell types). To modulate targets and pathways that are “undruggable” by conventional small molecule drugs, we are developing intracellular acting biologic drugs such as peptide inhibitors, short interfering RNA (siRNA) gene inhibitors, and peptide nucleic acid / locked nucleic acid micro-RNA inhibitors. These various classes of biologics can enable selective and more robust modulation of protein-protein interactions and certain kinases and enzymes that cannot be robustly and selectively modulated with small molecule approaches. We utilize polymer based and porous silicon nanocarriers predominantly and pursue applications for systemic delivery nanomedicines including cancer, osteoarthritis, and cardiovascular disease.
The Duvall Lab also develops and applies microparticles intended for long-term retention and controlled-release of drug cargo at a local injection site. A recent microparticle system integrates mechanisms for “on demand” drug release modulated by the “need” in the local environment rather than simply prolonging the release, which is enabled by simple hydrolytically-degradable polyester-based constructs. Specifically, this delivery approach enabled “on demand” release of an antioxidant controlled by the level of reactive oxygen species (ROS) in the local environment. A recent proof-of-concept application for this microparticle system focused on the delivery of the antioxidant and anti-inflammatory molecule curcumin to promote recovery from ischemic injury in the context of diabetes. We are pursuing additional applications of this microparticle system in inflammation-associated diseases. A related research focus (highlighted in a separate section below) is on scaffold-based controlled release of RNAi nanomedicines for sustained, local gene silencing for tissue regenerative applications.
We recently started a new research thrust focused on optimizing albumin “piggybacking” as an elegantly simple natural carrier approach for improving pharmacokinetics of siRNA. RNA molecules have very short circulation time and poor tumor bioavailability due to rapid renal clearance. Designing modified RNAs that dock onto albumin (a long-lasting and highly abundant blood serum protein that is a natural fatty acid carrier) can significantly extend RNA circulation time, tumor accumulation, and homogeneity of tumor penetration. This is a promising strategy for high penetrance delivery of RNAs targeting currently undruggable tumor drivers.
One of the major barriers for use of intracellular-acting biologic drugs is the inefficiency of escape from the endo-lysosomal vesicles after cellular entry via endocytosis pathways. There are a lack of quantitative and easily to implement, objective methods for rapidly assessing escape from the endosomal pathway. We are developing tools for both high throughput and in vivo screening of endosomal escape and intracellular bioavailability. In recent work, we validated high throughput methods for in vitro screening for endosome escape based on intracellular redistribution of Galectin 8, a component of the innate immune system, which concentrates onto disrupted endosomes. We are also implementing and developing split GPF and other related technologies for screening delivery formulations ability to disrupt specific endosomal compartments and achieve intracellular bioavailability.
Another research thrust in the ATL utilizes a pH-responsive, endosomolytic RAFT polymer for intracellular delivery of therapeutic peptides. Current work in this area targets mitogen activated protein kinase (MAPK) signaling pathways that prevent vascular smooth muscle cells (VSMCs) from transitioning to a pathological phenotype. In this application, we seek to inhibit SMC proliferation after vascular graft transplantation, preventing intimal hyperplasia (IH) and ultimately improving long-term graft patency in peripheral and cardiac vascular bypass procedures.
The Duvall Lab also develops polymer-based, controlled delivery systems to efficiently knockdown gene targets to promote tissue formation and repair within nonhealing diabetic skin wounds. We are interested in local modulation of vascularization and also local reprogramming of macrophages to modulate the wound microenvironment to make it more conducive to tissue repair. Our specific focus to this point has been on silencing of PHD2 (prolyl hydroxylase domain 2), which is a negative regulator of the transcription factor HIF1 Silencing PHD2 promotes the expression of numerous pro-angiogenic and pro-healing genes. Other potential applications for this platform technology include repair of bone or critically-sized defects in other tissues.
We are currently exploring new breast cancer targets that have not been successfully drugged by small molecule inhibitors, including selective modulation of the different arms of the mTOR signaling pathway using RNA interference. We are also developing and applying targeted nanomedicines that reduce bone destruction as a result of cancer metastasis to bone by drugging key transcription factors.
Current treatment of osteoarthritis revolves around pain management, and there are not any clinically approved disease modifying osteoarthritis drugs (DMOADs) that actually inhibit or delay this progressive, degenerative, and debilitating disease. We are developing long-lasting microparticle technologies with inherent antioxidant effect and for sustained drug delivery capabilities. We also are having great success in forthcoming work using matrix targeted nanoparticles for sustained retention and selective silencing of OA-driving genes.