Targeted therapeutics in inflammatory atherosclerosis
Atherosclerosis, a chronic inflammatory vascular disease, which has been recently identified in 5000-year mummies, remains undefeated. It is the most common underlying cause of deadly cardiovascular diseases (CVD), including heart attacks, strokes, and peripheral vascular diseases. Collectively, CVD is the number one killer among the non-communicable diseases globally (17.7 million people annually), far more deadly than cancer (8.8 million). This tremendous socioeconomic burden calls for further investigation and investment to develop effective, innovative, and clinically viable interventions for the treatment of atherosclerosis. One important initiative in this direction is NanoAthero, a European Consortium that funded the research work presented in this thesis. This program aims to demonstrate the preliminary clinical feasibility of the use of nanosystems for targeted imaging and treatment of advanced atherosclerosis. The enthusiasm generated for the use of nanocarrier drug delivery systems in atherosclerosis is mainly driven by the significant progress made in the field of oncological nanomedicine. Capitalizing on the achievements in the nanomedicine field, the main aim of this thesis is to contribute to the development and use of targeted nanomedicines in atherosclerosis. To this end, we adopted a ‘disease first’ approach to develop efficient targeted nanomedicines, in which particular attention is paid to the underlying pathophysiological processes in atherosclerosis. Macrophages are key players in these processes that affect atherosclerotic plaque inflammation and vulnerability to rupture. Moreover, their phagocytic capacity makes macrophages ideal targets for nanomedicine-based approaches. Understanding the role of plaque-associated macrophages and their interactions with the different nanocarriers is crucial for the successful development of efficacious, clinically relevant nanotherapeutics for atherosclerotic cardiovascular diseases.
Chapter 1 presents a general introduction to the subject and an outline of this thesis. Chapter 2 provides an overview of the interplay between the advances in nanomedicine and our understanding of chronic inflammatory disorders, including atherosclerosis. Although atherosclerosis and other chronic inflammatory diseases may represent different phenotypical outcomes, they possess a common denominator, inflammation, and share interactive pathophysiological features in which monocyte recruitment, macrophage polarization, and enhanced vascular permeability play critical roles. Understanding and exploiting the commonalities in monocyte/macrophage dynamics and functions in chronic inflammatory diseases can facilitate efficient nanomedicine development for such diseases. Chapter 3 gives a first example of such a nanomedicine. Liposomes, the best-known example of a nanomedicine, are loaded with docosahexaenoic acid (DHA), a natural polyunsaturated fatty acid, an omega-3 polyunsaturated fatty acid (PUFA, also known as the health promoting ingredient of fish oil) are usually only taken orally by patients with cardiovascular disease and cancer. In liposomes, the omega-3 fatty acid showed strong antioxidant and anti-inflammatory effects in vitro, and also resulted in a potent inhibition of tumor cell growth. This 'nanonutraceutical' represents a rational, new approach for targeting relatively safe so-called nutraceutical components in chronic inflammatory diseases (including atherosclerosis) and cancer. Chapter 4 describes multiple pathway screening assays to select small molecule drug candidate(s) as potential drug cargos for targeted delivery in atherosclerosis. We evaluated the effects of these compounds on the primary pathways that involve macrophages in atherosclerosis, including lipid metabolism, endoplasmic reticulum (ER) stress, macrophage cell proliferation, the release of proinflammatory cytokines, and unbalanced oxidative stress. Among the different small molecule drugs, liver X receptor (LXR) agonists (lipid efflux stimulators), and statins (HMG-CoA reductase inhibitors) were identified to have an overall superior anti-atherogenic effect, attributed to their beneficial impact on the multiple pathways. Subsequently, examples from these classes of drug are loaded into nanomedicines, leading to the high-density protein (HDL) nanoformulation described in Chapter 5 with the LXR agonist GW3965, which failed in clinical trials due to liver toxicity, and those in Chapter 6 described simvastatin nanoformulations in polymeric micelles, liposomes, and HDL. In vitro and in vivo results demonstrate that targeting of these anti-inflammatory drugs to macrophages can yield therapeutic benefits. In the last research chapter (Chapter 7) nanoparticles made from the biologically active polymer hyaluronan are examined for anti-inflammatory effects. This latter approach is particularly interesting because the results show that drug incorporation is not necessary to obtain anti-atherosclerotic activity in vivo. Chapter 8 summarizes the results of the thesis and provides perspectives for the future application of nanomedicines to treat atherosclerosis.
