Neuroretinal hypoxic signaling in a new preclinical murine model for proliferative diabetic retinopathy

Clinical Pathological Features and Current Animal Models of Type 3 Macular Neovascularization

Type 3 macular neovascularization (MNV3), or retinal angiomatous proliferation (RAP), is a distinct type of neovascular age-related macular degeneration (AMD), which is a leading cause of vision loss in older persons. During the past decade, systematic investigation into the clinical, multimodal imaging, and histopathological features and therapeutic outcomes has provided important new insight into this disease. These studies favor the retinal origin of MNV3 and suggest the involvement of retinal hypoxia, inflammation, von Hippel–Lindau (VHL)–hypoxia-inducible factor (HIF)–vascular endothelial growth factor (VEGF) pathway, and multiple cell types in the development and progression of MNV3. Several mouse models, including the recently built Rb/p107/Vhl triple knockout mouse model by our group, have induced many of the histological features of MNV3 and provided much insight into the underlying pathological mechanisms. These models have revealed the roles of retinal hypoxia, inflammation, lipid metabolism, VHL/HIF pathway, and retinoblastoma tumor suppressor (Rb)–E2F cell cycle pathway in the development of MNV3. This article will summarize the clinical, multimodal imaging, and pathological features of MNV3 and the diversity of animal models that exist for MNV3, as well as their strengths and limitations.

The Role of HIF1α-PFKFB3 Pathway in Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness for adults in developed countries. Both microvasculopathy and neurodegeneration are implicated in mechanisms of DR development, with neuronal impairment preceding microvascular abnormalities, which is often underappreciated in the clinic. Most current therapeutic strategies, including anti-vascular endothelial growth factor (anti-VEGF)-antibodies, aim at treating the advanced stages (diabetic macular edema and proliferative diabetic retinopathy) and fail to target the neuronal deterioration. Hence, new therapeutic approach(es) intended to address both vascular and neuronal impairment are urgently needed. The hypoxia-inducible factor 1α (HIF1α)-6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) pathway is critically implicated in the islet pathology of diabetes. Recent evidence highlighted the pathway relevance for pathologic angiogenesis and neurodegeneration, two key aspects in DR. PFKFB3 is key to the sprouting angiogenesis, along with VEGF, by determining the endothelial tip-cell competition. Also, PFKFB3-driven glycolysis compromises the antioxidative capacity of neurons leading to neuronal loss and reactive gliosis. Therefore, the HIF1α-PFKFB3 signaling pathway is unique as being a pervasive pathological component across multiple cell types in the retina in the early as well as late stages of DR. A metabolic point-of-intervention based on HIF1α-PFKFB3 targeting thus deserves further consideration in DR.

Protective effects of piperine on the retina of mice with streptozotocin-induced diabetes by suppressing HIF-1/VEGFA pathway and promoting PEDF expression

AIM

To evaluate the protective mechanisms of piperine in the retina of mice with streptozotocin-induced diabetes.

METHODS

In experiments in vitro, stimulation by chemical hypoxia was established in ARPE-19 cells. Then, the expression of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor A (VEGFA), and pigment epithelium-derived factor (PEDF) was assessed at the mRNA and protein levels. In experiments in vivo, diabetes mellitus was established by intraperitoneally injecting 150 mg/kg streptozotocin once. After 3wk of the onset of diabetes, 15 mg/kg piperine was intraperitoneally injected once daily for 1 or 3wk. Then, the retinal morphology and mRNA and protein expression were assessed.

RESULTS

In hypoxia, 1-100 µmol/L piperine significantly decreased the expression of VEGFA mRNA and increased the expression of PEDF mRNA without affecting HIF-1α mRNA. Meanwhile, 100 µmol/L piperine substantially decreased the protein level of VEGFA and increased the protein level of PEDF. The HIF-1α protein level was also hampered by piperine. In the diabetic retina of mice, the morphological damage was alleviated by piperine. Likewise, the retinal vascular leakage was substantially decreased by piperine. Further, the protein levels of HIF-1α and VEGFA were significantly reduced by piperine. Moreover, the level of the antiangiogenic factor of PEDF dramatically increased by piperine.

CONCLUSION

Piperine may exert protective effects on the retina of mice with diabetes via regulating the pro-antiangiogenic homeostasis composed of HIF-1/VEGFA and PEDF.

miR-142-5p regulates the progression of diabetic retinopathy by targeting IGF1

As one of leading causes of blindness, diabetic retinopathy (DR) is a progressive microvascular complication of diabetes mellitus (DM). Despite significant efforts have been devoted to investigate DR over the years, the molecular mechanisms still remained unclear. Emerging evidences demonstrated that microRNAs (miRNAs) were tightly associated with pathophysiological development of DR. Hence, this study was aimed to illustrate the role and molecular mechanisms of miR-412-5p in progression of DR. Streptozotocin (STZ) treatment in rats and human retinal endothelial cell (HREC) models were used to simulate DR conditions in vivo and in vitro. Hematoxylin-eosin (HE) staining was used to demonstrate the morphology of retinal tissues of rats. Qualitative real-time polymerase chain reaction (qRT-PCR) detected miR-142-5p and vascular endothelial growth factor (VEGF) expression levels. Cell counting kit-8 (CCK8) assay and immunofluorescence (IF) measured the cell proliferation rates. Western blot tested the expression status of IGF1/IGF1R-mediated signaling pathway. Dual-luciferase reporter assays demonstrated the molecular mechanism of miR-142-5p. miR-142-5p level was down-regulated in retinal tissues of DR rats and high glucose (HG)-treated HRECs. Insulin-like growth factor 1 (IGF1) was identified as a direct target of miR-142-5p. The reduced miR-142-5p level enhanced HRECs proliferation via activating IGF/IGF1R-mediated signaling pathway including p-PI3K, p-ERK, p-AKT, and VEGF activation, ultimately giving rise to cell proliferation. Either miR-142-5p overexpression or IGF1 knockdown alleviated the pathological effects on retinal tissues in DR rats. Collectively, miR-142-5p participated in DR development by targeting IGF1/p-IGF1R signaling pathway and VEGF generation. This miR-142-5p/IGF1/VEGF axis provided a novel therapeutic target for DR clinical treatment.

Uncovering the protective mechanism of Taohong Siwu decoction against diabetic retinopathy via HIF-1 signaling pathway based on network analysis and experimental validation

Background

Diabetic retinopathy (DR) is a common and serious microvascular complication of diabetes. Taohong Siwu decoction (THSWD), a famous traditional Chinese medicine (TCM) prescription, has been proved to have a good clinical effect on DR, whereas its molecular mechanism remains unclear. Our study aimed to uncover the core targets and signaling pathways of THSWD against DR.

Methods

First, the active ingredients of THSWD were searched from Traditional Chinese Medicine Systems Pharmacology (TCMSP) Database. Second, the targets of active ingredients were identified from ChemMapper and PharmMapper databases. Third, DR associated targets were searched from DisGeNET, DrugBank and Therapeutic Target Database (TTD). Subsequently, the common targets of active ingredients and DR were found and analyzed in STRING database. DAVID database and ClueGo plug-in software were used to carry out the gene ontology (GO) and KEGG enrichment analysis. The core signaling pathway network of “herb-ingredient-target” was constructed by the Cytoscape software. Finally, the key genes of THSWD against DR were validated by quantitative real-time PCR (qRT-PCR).

Results

A total of 2340 targets of 61 active ingredients in THSWD were obtained. Simultaneously, a total of 263 DR-associated targets were also obtained. Then, 67 common targets were found by overlapping them, and 23 core targets were identified from protein-protein interaction (PPI) network. Response to hypoxia was found as the top GO term of biological process, and HIF-1 signaling pathway was found as the top KEGG pathway. Among the key genes in HIF-1 pathway, the mRNA expression levels of VEGFA, SERPINE1 and NOS2 were significantly down-regulated by THSWD (P < 0.05), and NOS3 and HMOX1 were significantly up-regulated (P < 0.05).

Conclusion

THSWD had a protective effect on DR via regulating HIF-1 signaling pathway and other important pathways. This study might provide a theoretical basis for the application of THSWD and the development of new drugs for the treatment of DR.

Hypoxic drive caused type 3 neovascularization in a preclinical model of exudative age-related macular degeneration

Hypoxia associated with the high metabolic demand of rods has been implicated in the pathology of age-related macular degeneration (AMD), the most common cause of adult blindness in the developed world. The majority of AMD-associated severe vision loss cases are due to exudative AMD, characterized by neovascularization. To further investigate the causes and histopathology of exudative AMD, we conditionally induced hypoxia in a novel preclinical AMD model (Pde6gcreERT2/+;Vhl-/-) by targeting Vhl and used multimodal imaging and immunohistochemistry to track the development of hypoxia-induced neovascularization. In addition to developing a preclinical model that phenocopies exudative AMD, our studies revealed that the photoreceptor hypoxic response initiates and drives type 3 neovascularization, mainly in the outer retina. Activation of the VHL-HIF1a-VEGF-EPO pathway in the adult retina led to long-term neovascularization, retinal hemorrhages and compromised retinal layers. Our novel preclinical model would accelerate the testing of therapies that use metabolomic approaches to ameliorate AMD.

hsa_circ_0041795 contributes to human retinal pigment epithelial cells (ARPE 19) injury induced by high glucose via sponging miR-646 and activating VEGFC

Diabetic retinopathy (DR)is a common diabetes complication, resulting in the loss of vision. circRNAshave been reported to serve as ceRNA via targeting corresponding miRNAs and modulating mRNA expression in various diseases. Recently, increasing reports has indicated circRNAs can exert a significant role inDR progression. However, the expression and mechanism of hsa_circ_0041795 in human retinal pigment epithelial cells ARPE-19 treated by high glucose remains poorly known. Hence, we aimed to work figure out the effect of hsa_circ_0041795 in high glucose (HG)-induced ARPE-19 cell damage and study its molecular mechanisms. In our current research, we found that hsa_circ_0041795 was obviously up-regulated in HG-treated ARPE-19 cells. High dose of glucose greatly depressed ARPE-19 cell survival and contributed to cell apoptosis. In addition, we observed that loss of hsa_circ_0041795 enhanced cell proliferation and inhibit ARPE-19 cell apoptosis, after HG incubation. Furthermore, data of ELISA indicated that hsa_circ_0041795 siRNA significantly restrained inflammatory factors expression, such as TNF-α, IL-1β and IL-6 in ARPE-19 cells treated with HG. miR-646 has been recognized in multiple diseases and currently, we predicted that miR-646 acted as a target of hsa_circ_0041795. Moreover, we found that miR-646 inhibitors dramatically reversed the effect of hsa_circ_0041795 siRNA on ARPE-19 cells. Additionally, a dual-luciferase reporter assay proved that VEGFC was a direct target of miR-646. Our results demonstrated that hsa_circ_0041795 might exhibit a novel therapeutic potential in the treatment of DR.

CAPN5 genetic inactivation phenotype supports therapeutic inhibition trials

Small molecule pharmacological inhibition of dominant human genetic disease is a feasible treatment that does not rely on the development of individual, patient-specific gene therapy vectors. However, the consequences of protein inhibition as a clinical therapeutic are not well-studied. In advance of human therapeutic trials for CAPN5 vitreoretinopathy, genetic inactivation can be used to infer the effect of protein inhibition in vivo. We created a photoreceptor-specific knockout (KO) mouse for Capn5 and compared the retinal phenotype to both wild-type and an existing Capn5 KO mouse model. In humans, CAPN5 loss-of-function (LOF) gene variants were ascertained in large exome databases from 60,706 unrelated subjects without severe disease phenotypes. Ocular examination of the retina of Capn5 KO mice by histology and electroretinography showed no significant abnormalities. In humans, there were 22 LOF CAPN5 variants located throughout the gene and in all major protein domains. Structural modeling of coding variants showed these LOF variants were nearby known disease-causing variants within the proteolytic core and in regions of high homology between human CAPN5 and 150 homologs, yet the LOF of CAPN5 was tolerated as opposed to gain-of-function disease-causing variants. These results indicate that localized inhibition of CAPN5 is a viable strategy for hyperactivating disease alleles.

Extracellular superoxide dismutase (SOD3) regulates oxidative stress at the vitreoretinal interface

Oxidative stress is a pathogenic feature in vitreoretinal disease. However, the ability of the inner retina to manage metabolic waste and oxidative stress is unknown. Proteomic analysis of antioxidants in the human vitreous, the extracellular matrix opposing the inner retina, identified superoxide dismutase-3 (SOD3) that localized to a unique matrix structure in the vitreous base and cortex. To determine the role of SOD3, Sod3^-/- mice underwent histological and clinical phenotyping. Although the eyes were structurally normal, at the vitreoretinal interface Sod3^-/- mice demonstrated higher levels of 3-nitrotyrosine, a key marker of oxidative stress. Pattern electroretinography also showed physiological signaling abnormalities within the inner retina. Vitreous biopsies and epiretinal membranes collected from patients with diabetic vitreoretinopathy (DVR) and a mouse model of DVR showed significantly higher levels of nitrates and/or 3-nitrotyrosine oxidative stress biomarkers suggestive of SOD3 dysfunction. This study analyzes the molecular pathways that regulate oxidative stress in human vitreous substructures. The absence or dysregulation of the SOD3 antioxidant at the vitreous base and cortex results in increased oxidative stress and tissue damage to the inner retina, which may underlie DVR pathogenesis and other vitreoretinal diseases.

Attenuation of Retinal Vascular Development in Neonatal Mice Subjected to Hypoxic-Ischemic Encephalopathy

A significant proportion of children that survive hypoxic-ischemic encephalopathy (HIE) develop visual impairment. These visual deficits are generally attributed to injuries that occur in the primary visual cortex and other visual processing systems. Recent studies suggested that neuronal damage might also occur in the retina. An important structure affecting the viability of retinal neurons is the vasculature. However, the effects of HIE on the retinal neurovasculature have not been systemically evaluated. Here we investigated whether exposure of postnatal day 9 (P9) neonatal mice to HIE is sufficient to induce neurovascular damage in the retina. We demonstrate that the blood vessels on the surface of the retina, from mice subjected to HIE, were abnormally enlarged with signs of degeneration. The intermediate and deep vascular layers in these retinas failed to form normally, particularly in the periphery. All the vascular damages observed here were irreversible in nature up to 100 days post HIE. We also observed loss of retinal neurons, together with changes in both astrocytes and Müller cells mainly in the inner retina at the periphery. Collectively, our findings suggest that HIE results in profound alterations in the retinal vasculature, indicating the importance of developing therapeutic strategies to protect neurovascular dysfunction not only in the brain but also in the retina for infants exposed to HIE.

Downregulation of MicroRNA 29a/b exacerbated diabetic retinopathy by impairing the function of Müller cells via Forkhead box protein O4

BACKGROUND

Diabetic retinopathy is a neurological disease, which can lead to blindness in severe cases. The pathogenesis underlying diabetic retinopathy is unclear. The aim of this study was to explore the role of dysregulated microRNA 29a/b in the onset and progression of diabetic retinopathy.

METHODS

Diabetes mellitus was induced in rats using 60 mg/kg of streptozotocin. Glucose (5.5 and 25 mM) was used to stimulate rat retinal Müller cells. Real-time polymerase chain reaction and Western blot analyses were used to determine gene expression. A luciferase reporter assay was conducted to validate the relationship of microRNA 29a/b with glioma-associated oncogene homolog 1 and Forkhead box protein O4.

RESULTS

The expression of microRNA 29a/b and glutamine synthetase decreased in both diabetes mellitus rats and rat retinal Müller cells stimulated with high glucose, whereas the expression of sonic hedgehog, glioma-associated oncogene homolog 1, glial fibrillary acidic protein, and vascular endothelial growth factor, as well as the content of glutamate, increased. Dysregulated microRNA 29a/b was directly regulated by the sonic hedgehog-glioma-associated oncogene homolog 1 signalling pathway, and microRNA 29a and microRNA 29b targeted Forkhead box protein O4 and regulated its expression.

CONCLUSION

Downregulation of microRNA 29a/b, mediated by the sonic hedgehog-glioma-associated oncogene homolog 1 signalling pathway, exacerbated diabetic retinopathy by upregulating Forkhead box protein O4.

p53 Plays a Key Role in the Apoptosis of Human Ovarian Cancer Cells Induced by Adenovirus-Mediated CRM197

Cross-reacting material 197 (CRM197) is a mutant form of the diphtheria toxin. Recent studies have found that CRM197 exerts an experimental antitumor effect on several types of tumors. This study applied a novel treatment of adenovirus-mediated CRM197 (AdCRM197) to human ovarian cancer cells. Interestingly, it was found that A2780 cells were sensitive to AdCRM197, but SKOV3 cells were resistant to it. Since SKOV3 cells are p53 deletion cells, while A2780 cells are p53 wild-type cells, it was postulated that p53 might play a key role in AdCRM197-induced apoptosis. This presumption was demonstrated by means of knockdown of p53 of the A2780 cells through lentivirus-mediated RNA interference. This knockdown resulted in the A2780 cells becoming resistant to AdCRM197. To verify this presumption further, the wild-type p53 gene in the SKOV3 cells was replaced with adenovirus-mediated p53 (Adp53). As expected, AdCRM197 plus Adp53 resulted in apoptosis of the SKOV3 cells. The combined treatment of AdCRM197 plus Adp53 also showed a good antitumor effect in the in vivo experiment on nude mice with xenograft tumors. Taking these results together, it is concluded that AdCRM197 induces apoptosis of human ovarian cancer cells via the p53 pathway. Moreover, it was found that Adp53 can reverse the resistance of p53-deletion human ovarian cancer cells to AdCRM197. The combination of AdCRM197 and Adp53 may be a potentially effective method for overcoming the resistance of p53-deficient human ovarian cancer to AdCRM197.

Effective improvement of the neuroprotective activity after spinal cord injury by synergistic effect of glucocorticoid with biodegradable amphipathic nanomicelles

Dexamethasone acetate (DA) produces neuroprotective effects by inhibiting lipid peroxidation and inflammation by reducing cytokine release and expression. However, its clinical application is limited by its hydrophobicity, low biocompatibility and numerous side effects when using large dosage. Therefore, improving DA's water solubility, biocompatibility and reducing its side effects are important goals that will improve its clinical utility. The objective of this study is to use a biodegradable polymer as the delivery vehicle for DA to achieve the synergism between inhibiting lipid peroxidation and inflammation effects of the hydrophobic-loaded drugs and the amphipathic delivery vehicle. We successfully prepared DA-loaded polymeric micelles (DA/MPEG-PCL micelles) with monodispersed and approximately 25 nm in diameter, and released DA over an extended period in vitro. Additionally, in the hemisection spinal cord injury (SCI) model, DA micelles were more effective in promoting hindlimb functional recover, reducing glial scar and cyst formation in injured site, decreasing neuron lose and promoting axon regeneration. Therefore, our data suggest that DA/MPEG-PCL micelles have the potential to be applied clinically in SCI therapy.

Retinal and choroidal angiogenesis: a review of new targets

Retinal and choroidal neovascularization are a major cause of significant visual impairment, worldwide. Understanding the various factors involved in the accompanying physiopathology is vital for development of novel treatments, and most important, for preserving patient vision. The intraocular use of anti-vascular endothelial growth factor therapeutics has improved management of the retinal and choroidal neovascularization but some patients do not respond, suggesting other vascular mediators may also contribute to ocular angiogenesis. Several recent studies examined possible new targets for future anti-angiogenic therapies. Potential targets of retinal and choroidal neovascularization therapy include members of the platelet-derived growth factor family, vascular endothelial growth factor sub-family, epidermal growth factor family, fibroblast growth factor family, transforming growth factor-β superfamily (TGF-β1, activins, follistatin and bone morphogenetic proteins), angiopoietin-like family, galectins family, integrin superfamily, as well as pigment epithelium derived factor, hepatocyte growth factor, angiopoietins, endothelins, hypoxia-inducible factors, insulin-like growth factors, cytokines, matrix metalloproteinases and their inhibitors and glycosylation proteins. This review highlights current antiangiogenic therapies under development, and discusses future retinal and choroidal pro- and anti-angiogenic targets as wells as the importance of developing of new drugs.

Zonisamide-loaded triblock copolymer nanomicelles as a novel drug delivery system for the treatment of acute spinal cord injury

Spinal cord injury (SCI) commonly leads to lifelong disability due to the limited regenerative capacity of the adult central nervous system. Nanomicelles can be used as therapeutic systems to provide effective treatments for SCI. In this study, a novel triblock monomethyl poly(ethylene glycol)-poly(l-lactide)-poly(trimethylene carbonate) copolymer was successfully synthesized. Next, polymeric nanomicelles loaded with zonisamide (ZNS), a Food and Drug Administration-approved antiepileptic drug, were prepared and characterized. The ZNS-loaded micelles (ZNS-M) were further utilized for the treatment of SCI in vitro and in vivo. The obtained ZNS-M were ~50 nm in diameter with good solubility and dispersibility. Additionally, these controlled-release micelles showed significant antioxidative and neuron-protective effects in vitro. Finally, our results indicated that ZNS-M treatment could promote motor function recovery and could increase neuron and axon density in a hemisection SCI model. In summary, these results may provide an experimental basis for the use of ZNS-M as a clinically applicable therapeutic drug for the treatment of SCI in the future.

The Promotion of Erythropoiesis via the Regulation of Reactive Oxygen Species by Lactic Acid

The simultaneous increases in blood lactic acid and erythrocytes after intense exercise could suggest a link between lactate and the erythropoiesis. However, the effects of lactic acid on erythropoiesis remain to be elucidated. Here, we utilized a mouse model to determine the role of lactic acid in this process in parallel with studies using leukaemic K562 cells. Treatment of K562 cells in vitro with lactic acid increased the mRNA and protein expression of haemoglobin genes and the frequency of GPA⁺ cells. Also, increases in haematocrit and CD71⁻/Ter119⁺ erythroid cells were observed in lactic acid-treated mice, which showed a physiological increase in blood lactate. Mouse bone marrow CD34⁺/CD117⁻ cells showed an increase in erythroid burst-forming units after stimulation with lactic acid in vitro. Furthermore, lactic acid increased the intracellular reactive oxygen species (ROS) content in bone marrow and in K562 cells. Erythroid differentiation induced in Haematopoietic Stem Cells (HSCs) and K562 cells by lactic acid was abolished by reducing ROS levels with SOD or 2-mercaptoethanol, which suggests that ROS is a critical regulator of this process. These findings provide a better understanding of the role of lactic acid in cellular metabolism and physiological functions.

From Lead to Drug Candidate: Optimization of 3-(Phenylethynyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine Derivatives as Agents for the Treatment of Triple Negative Breast Cancer

Herein we report the sophisticated process of structural optimization toward a previously disclosed Src inhibitor, compound 1, which showed high potency in the treatment of triple negative breast cancer (TNBC) both in vitro and in vivo but had considerable toxicity. A series of 3-(phenylethynyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine derivatives were synthesized. In vitro cell-based phenotypic screening together with in vivo assays and structure-activity relationship (SAR) studies finally led to the discovery of N-(3-((4-amino-1-(trans-4-hydroxycyclohexyl)-1H-pyrazolo[3,4-d]pyrimidin-3-yl)ethynyl)-4-methylphenyl)-4-methyl-3-(trifluoromethyl)benzamide (13an). 13an is a multikinase inhibitor, which potently inhibited Src (IC₅₀ = 0.003 μM), KDR (IC₅₀ = 0.032 μM), and several kinases involved in the MAPK signal transduction. This compound showed potent anti-TNBC activities both in vitro and in vivo, and good pharmacokinetic properties and low toxicity. Mechanisms of action of anti-TNBC were also investigated. Collectively, the data obtained in this study indicate that 13an could be a promising drug candidate for the treatment of TNBC and hence merits further studies.

Efficient intravesical therapy of bladder cancer with cationic doxorubicin nanoassemblies

Nanoparticles have promising applications in drug delivery for cancer therapy. Herein, we prepared cationic 1,2-dioleoyl-3-trimethylammonium propane/methoxypoly (ethyleneglycol) (DPP) nanoparticles to deliver doxorubicin (Dox) for intravesical therapy of bladder cancer. The DPP micelles have a mean dynamic diameter of 18.65 nm and a mean zeta potential of +19.6 mV. The DPP micelles could prolong the residence of Dox in the bladder, enhance the penetration of Dox into the bladder wall, and improve cellular uptake of Dox. The encapsulation by DPP micelles significantly improved the anticancer effect of Dox against orthotopic bladder cancer in vivo. This work described a Dox-loaded DPP nanoparticle with potential applications in intravesical therapy of bladder cancer.