https://orcid.org/0000-0001-5988-9244
PolymiRize: addressing a clinical gap
Cardiovascular disease (CVD) remains the leading cause of death in Europe, with over 6 million diagnoses annually, placing a significant socio-economic burden on healthcare systems.1 Cardiovascular diseases are complex and typically involve a range of biological processes and mechanisms that contribute to disease progression. Targeting only one process or pathway may not fully address the underlying causes, leaving other mechanisms unchecked. Therefore, addressing multiple pathways simultaneously could, in theory, provide a more comprehensive approach to slowing or halting disease progression, potentially leading to better clinical outcomes compared with single-target treatments. In the small molecule therapy field, multidrug strategies (such as polypills) are receiving attention to both improve compliance and outcomes. Currently, these formulations primarily address late-stage disease and have limited targeting of the underlying cellular and molecular mechanisms that drive disease progression.2 To address this gap, we propose the development of ‘molecular polypills’ capable of tackling the multifactorial, molecular disruptions central to many CVDs. This concept forms the foundation of the recently funded project PolymiRize (a European Research Council-Advanced Grant; supported by the UK European guarantee).
Several complex disease aetiologies could benefit from multiplexed interventions. While combining therapies as separate entities is possible, a single intervention with an integrated multiplexing strategy is the goal of PolymiRize. One of our focuses is on the acute injury in vascular graft implantation. Vein graft disease post-coronary or peripheral bypass grafting with autologous saphenous vein involves diverse cell populations and distinct molecular pathways that are believed to be individually causal.3 The acute injury to the vein during surgery and graft implantation placing the vein under higher blood pressure initiates endothelial and smooth muscle cell (SMC) damage leading to intimal hyperplasia that ultimately drives graft failure through accelerated atherosclerosis. Without further intervention, ∼30–50% of vein grafts fail within 10 years, often resulting in myocardial infarction or heart failure.3 Current therapies such as statins and antiplatelet agents address late-stage events,4 but early disease-causing mechanisms remain to be targeted. Therapeutically, systemically delivered small-molecule treatments are sub-optimal for vein graft disease, but localized, in-theatre gene delivery provides a promising alternative for early intervention and can be applied precisely at the time of grafting.
MicroRNAs: a versatile solution to multiplex
The PolymiRize project, therefore, seeks to address the multifaceted mechanisms underlying vein graft disease in a single gene therapy vector approach. How to achieve this? MicroRNAs (miRNAs), recently recognized with the Nobel Prize in Medicine and Physiology, are particularly well-suited for this approach. Their small size (∼20 nucleotides in their mature form) and ability to regulate multiple targets within the same pathways by silencing or degrading mRNA sequences5 make them ideal for addressing the multifactorial nature of the disease. Furthermore, their often-natural genetic organization as ‘miRNA clusters’ in the genome allows coordinated multiplexing of therapeutic miRNAs in a single transcript.6 MicroRNAs have, of course, emerged as crucial regulators in cardiovascular physiology, especially in controlling SMC phenotypes, and are increasingly recognized as promising therapeutic targets for CVD.7 For instance, miR-132 antagonism is currently undergoing Phase II clinical trials for heart failure.8 PolymiRize will select therapeutic miRNAs based on specific therapeutic effects elicited by the miRNA. For vein graft disease, we will prioritize miRNAs that modulate SMC pathological functions, including proliferation, migration, and de-differentiation, and identify the most efficient miRNA that beneficially modulates each phenotype separately. The pathways will be individually targeted as they are driven by distinct mechanisms. Next, for miRNAs that block each phenotype, an innovative pipeline will rank the most effective miRNAs. The top-ranking miRNA for each will then be integrated into a single miRNA cluster in order to multiplex the miRNAs in a single piece of genetic material. The clustering takes advantage of the natural phenomenon of miRNA clusters and simply replaces the native miRNA hairpins of the miR-17-92 cluster with the therapeutic miRNA hairpins that we have identified. This modular structure allows easy interchangeability, enabling the modified transgene to utilize the cell's miRNA processing machinery to express the desired miRNA multiplex.9 Upon gene therapy vector assembly, recombinant adenovirus vector will be made and delivered to SMC in the vein graft ex vivo, prior to graft implantation. Upon gene transfer to the vein, the therapeutic miRNAs will be simultaneously expressed in the vein graft. The approach is outlined in Figure 1.
The PolymiRize concept. On the left, key pathophysiological events during the progress of vein graft failure are illustrated. During injury, vascular smooth muscle cells lose their contractile, quiescent state and have increased proliferation and stimulated migration, ultimately contributing to vascular occlusion and late failure. On the right, PolymiRize’s key outputs: The process begins with agnostic identification of microRNAs through high-throughput screening, relevant to cell-specific phenotypes to be targeted. The most effective combinations of these microRNAs will be selected and vector configurations created by using microRNA clusters, where the endogenous microRNAs are removed and the therapeutic microRNAs then engineered. The final phase involves gene therapy vector preparation and evaluating therapeutic effects in ex vivo and in vivo models, ultimately advancing towards clinical application (created with BioRender.com)
Towards a molecular polypill for cardiovascular disease
Through proof-of-concept in vitro and preclinical in vivo studies, the ultimate aim is to create molecular polypills for a range of cardiovascular diseases with multifaceted pathogenesis. Vein grafting is just on exemplar where we aim to achieve proof of concept. A second approach is remodelling post-myocardial infarction. The objective therein would be multiplexed miRNAs that simultaneously target phenotypes such as muscle proliferation, vascular regeneration, and mitigation of myocardial fibrosis. The approach will offer a versatile and powerful tool for tackling the multifactorial nature of CVD and essential proof of concept is sought in PolymiRize.
PolymiRize stands as a large-scale initiative in miRNA multiplexing, testing new concepts in CVD. Despite its potential, miRNA multiplexing faces significant challenges, such as ensuring short- and long-term safety, minimizing off-target effects, avoiding immune responses, and achieving precise, cell-specific targeting. The complexity of the cardiovascular system adds another layer of difficulty to effective gene delivery. Extensive preclinical testing, particularly in rodents and then large animal models, will be necessary to confirm its safety and efficacy before clinical application. As vector and delivery technologies advance, the ability to target specific cells more accurately will improve both safety and effectiveness. This approach, while focused on miRNAs, could also be expanded to include the modulation of protein-coding or other non-coding RNA genes, broadening its therapeutic potential. Simultaneously, it will provide deeper insights into CVD mechanisms. The scalability of the multiplexing approach paves the way for the development of what might appear to be complex treatments but are relatively simple as a single product that would be delivered to the patient. With encouraging preclinical data awaiting the grant enactment, the next phase is translating these innovations into clinical practice, making multiplexed miRNA therapies a futuristic yet realistic modality for future CVD treatments.
Acknowledgements
We would like to acknowledge Professor David Newby and Dr Julie Rodor for their expert review of our text and many other members of the Baker lab for input into the PolymiRize concept.
Declarations
Disclosure of Interest
All authors declare no disclosure of interest for this contribution.
Funding
The authors would like to thank the European Research Council for selecting PolymiRize for funding and the United Kingdom Research and Innovation for funding it through the Horizon Europe UK Guarantee Mechanism 2023. Our laboratory is also supported by the British Heart Foundation Chair of Translational Cardiovascular Sciences to A.H.B. (CH/11/2/28733).
