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Investigating the EPR effect of nanomedicines in human renal tumors via ex vivo perfusion strategy
Graphical abstract
The EPR effect of 41 renal tumors collected from clinical patients were analyzed via perfusion strategy, correlating the EPR effect in human tumors with that in animal models and confirming that more than 87 % of the examined renal tumors possess the considerable EPR effect, which yet showed significant diversity and heterogeneity in different patients.
Introduction
The enhanced permeability and retention (EPR) effect of solid tumors, caused by the pathologically leaky vasculature and poor lymphatic drainage of the tumor tissues [[1], [2], [3]], has been regarded as the mainstay of modern anticancer nanomedicines [[4], [5], [6]]. After systemic administration, nanomedicines are expected to accumulate preferably at tumor tissues, accordingly enhancing the pharmaceutical properties, improving the therapeutic index, and reducing the adverse effects of conventional chemodrugs [[7], [8], [9], [10], [11]]. Several nanomedicines, such as liposome-, albumin-, and polymeric-micelle-based drug delivery systems, have been approved for anticancer therapy and numerous nanotechnology-based therapeutics are in the pre-clinical or clinical research [7,[12], [13], [14]]. Although the number of publications referring to the EPR effect has grown exponentially, the flourish of creativity has largely failed to translate into improved clinical outcomes [[15], [16], [17]]. Recent clinical outcomes of nanomedicines have indicated that the EPR effect in human tumors was not as reliable as previously thought [[18], [19], [20]]. Therefore, the development of modern nanomedicines is in a dire need of solid evidence of the EPR effect in human solid tumors [21].
In general, most of the tested nanomedicines only reduce side effects but cannot provide superior efficacy when employed in clinical practice [10,22]. Although the EPR effect has been well-studied in small animal models with xenografted human tumors, its relevancy to human solid tumors remains controversial [5,[23], [24], [25], [26]]. Indeed, xenograft tumors are significantly different from actual human cancers in many factors, including their developmental rates, the size relative to host, metabolic rates, and host lifespan [6,22]. Moreover, sufficient evidence has suggested that human solid tumors exhibited significant complexity and heterogeneity due to genetic diversity [5,7,27,28]. Thus, in the era of “personalized medicine” and “precision medicine” [[29], [30], [31], [32]], whether the EPR effect in humans can be reliably predicted from animal models still need to be reconsidered. Also, mainly limited by ethical reasons for conducting experiments on patients, the feasible strategies for investigating the EPR effect in human tumors have not yet been fully developed. Several pioneering reports employing the radially labeled liposomes and polymer-drug nanoparticles have been used to assess the tumor accumulation of nanomedicines in human tumors and demonstrated their successful localization in tumors [19,21,33,34]. However, these methods usually require exerting experiments on patients, which may cause ethical problems and lag in detection. Thus, there remains a need for a rapid and efficient method to detect the EPR effect in human tumors [21].
Herein, we report the use of X-ray computed tomography (CT) to real-time investigate the EPR effect in human renal tumors via ex vivo perfusion models and to study the correlation between the EPR effect in human solid tumors and that in rabbit xenografted tumors (Fig. 1). CT has been regarded as one of the most commonly used imaging modalities in cancer diagnosis, due to its non-invasiveness, convenience, and veracity [[35], [36], [37]]. Previously, we have reported the facile and scalable synthesis of the iohexol nanoparticles (INPs) via polymerization-induced self-assembly (PISA) for efficient CT imaging of tumors in a rabbit model [38]. The cross-linked iohexol cores are favourable for the CT imaging capacity and stability of INPs [39]. Therefore, we speculate these INPs hold the potential for investigating the EPR effect in human solid tumors and correlating the EPR effect in animal tumor models with human solid tumors (Fig. 1a). Herein, we first studied the accumulation and retention of the single-shell INPs (SS-INPs) in both in vivo and ex vivo rabbit renal tumor models, aiming for revealing the connection between in vivo and ex vivo rabbit models (Q1 in Fig. 1a). the EPR effect in human renal tumors via the ex vivo perfusion model was then studied (Fig. 1b) and correlated with that in the rabbits (Q2 in Fig. 1a). Subsequently, the heterogeneities and complexities in human renal tumors were summarized to reveal the factors that may affect the EPR effect in human tumors (Q3 in Fig. 1a). Taken together, these size-controllable, biocompatible and scalable INPs, together with the ex vivo perfusion models, could provide a feasible strategy to investigate the EPR effect of human solid tumors instead of conducting experiments on patients, establishing a foundation for the design and development of antitumor nanomedicines in the future.
Section snippets
Preparation and characterizations of the iohexol nanoparticles
Typically, the single-shell iohexol nanoparticles (SS-INPs) were prepared via PISA using a PEGylated macroinitiator (PEG-TTC), iohexol-derived acrylates, and hydroxypropyl methacrylates (HPMAs) at the predetermined feed ratios (Supplementary Fig. S1) [38]. Polymerization-induced self-assembly (PISA) enables the one-pot, size-controllable synthesis of nanoparticles (NPs) with ultra-high NP concentrations (up to 30 wt%) [[40], [41], [42]]. Hydrodynamic diameters and surface charge of the INPs
Conclusion
In summary, we have developed a unique strategy for the real-time investigation of the EPR effect in human solid tumors using the ex vivo perfusion model. We confirmed that the similarity of the INP accumulation in ex vivo perfusion and in vivo rabbit models, enabling the likelihood of using ex vivo perfusion models to reflect the actual situation in the body. Also, we found the EPR effect in both human renal tumors is well correlated with that in rabbit xenografted tumors. Notably, we
Author contributions
Y.D carried out the experimental work, the parameter estimations and planned as well as performed the mass transfer experiments, and wrote the manuscript. L.S and Y.L designed the project and participated in the review of manuscript. Y.X and W.S collected and analyzed the experimental data about CT signals. W.Y provided the ex vivo human kidney model. P.N developed the animal models, and took part in the animal experimental work. X.L and Y.C participated in the synthesis and characterization of
Declaration of Competing Interest
The authors declare that they have no competing interests.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (Nos. 21620102005, 51933006, 51603231, 51773099 and 51473044), National Key Research and Development Programs of China (2018YFA0209700), and the State Key Laboratory of Medicinal Chemical Biology (Grant No. 2019016), Nankai University.
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These authors contributed equally.