Design, synthesis and characterization of 2D PEG/Cu-BDC nanocatalysts

There are two most important procedures within the synthesis of PEG/Cu-BDC, with the colour change from clear to yellow in step one owing to the technology of Cu₂O and yellow to blue within the conversion means of Cu⁺ to Cu²⁺ [41]. The morphology, composition, construction, and porosity of the as-obtained Cu-BDC nanosheets have been confirmed by various characterization methods. As noticed by transmission electron microscopy (TEM), Cu₂O confirmed cubic morphology with a imply dimension of 60 nm, whereas PEG/Cu-BDC nanosheets have been sq. with a diameter of roughly 90 nm (Fig. 2a, b). As for X-ray diffraction (XRD) patterns, the disappearing of Cu₂O peaks and rising of the principle (2 0 − 1) crystallographic planes in Fig. 2c illustrated the entire conversion of Cu₂O to Cu-BDC nanosheets. As well as, the X-ray photoelectron spectroscopy (XPS) evaluation affirmed that the Cu-BDC nanosheets have been composed of Cu, C, and O components (Fig. 2d). The Cu 2p core peak of Cu-BDC nanosheets revealed two most important parts at 954.4 eV and 934.4 eV, with a satellite tv for pc peak positioned at 962.6 eV and 943.7 eV, respectively, validating the presence of Cu²⁺ within the construction of Cu-BDC nanosheets (Fig. 2e) [42, 43]. Furthermore, Fourier-transform infrared spectroscopy (FTIR) spectrum of Cu-BDC nanosheets was proven in Fig. 2f. The attribute peaks at 1578, 1501, 1156, and 1017 cm⁻¹ belonging to the benzene rings of the ligands have been noticed. The attribute bands at 1624 and 1439 cm⁻¹ have been listed to the symmetric and antisymmetric stretching vibrations of –COOH group. Moreover, thermogravimetric evaluation (TGA) was carried out to analyze the thermal stability of Cu-BDC nanosheets. As depicted in Fig. 2g, the obtained TGA profile of Cu-BDC nanosheets below air (or N₂) environment illustrated that the construction of Cu-BDC remained steady as much as 300 °C. The load loss was decided to be 16 wt% by heating to 300 °C, which was attributed to the liberation of the coordinated N, N-dimethylformamide (DMF) molecule. The incidence of weight reduction was noticed starting from 300 to 330 °C, owing to the decomposition of the BDC ligand of Cu-BDC nanosheets. Moreover, the Brunauer–Emmett–Teller (BET) floor areas have been decided to be 53.2, 254.7, and 307.6 m² g⁻¹ for the Cu-BDC nanosheets pretreated at 120, 200, and 250 °C for 12 h earlier than examination, respectively, indicating the porosity evolution after warmth remedies by eliminating the visitor DMF molecules.

Construction, morphology, and composition characterization of PEG/Cu-BDC. a TEM photographs of Cu₂O. b TEM photographs of PEG/Cu-BDC. c XRD patterns of Cu₂O and PEG/Cu-BDC. d XPS spectrum of the PEG/Cu-BDC. e XPS spectrum of Cu 2p in PEG/Cu-BDC. f FTIR spectrum of PEG/Cu-BDC. g TGA curves of PEG/Cu-BDC in air and N₂. h N₂ absorption–desorption isotherms of PEG/Cu-BDC activated at 120, 200, and 250 ℃ for 12 h previous to the assessments, respectively

In vitro Fenton-like response enabled by 2D PEG/Cu-BDC nanocatalysts

There have been two crucial procedures within the Fenton-like response mediated by PEG/Cu-BDC, GSH consumption and ·OH technology. The GSH depletion was confirmed with the help of an indicator, DTNB [5,5′-dithio-bis-2-(nitrobenzoic acid)], which generates yellow compound (5-thio-2-nitrobenzoic acid) displaying a particular peak at 405 nm after response with GSH. As displayed in Fig. 3a, the GSH stage saved declining with the elevating focus of PEG/Cu-BDC. As well as, the GSH depletion was evidently accelerated after incubation of PEG/Cu-BDC at pH 6.5 below the identical situation (Fig. 3b–d). The outcomes illustrated that the obtained PEG/Cu-BDC considerably consumed GSH in acidic TME. Moreover, the ·OH technology property of PEG/Cu-BDC at totally different pHs was additionally assessed utilizing a ·OH indicator, 3,3′,5,5′-tetramethylbenzidine (TMB), which reveals the attribute peak at 652 nm after oxidation by ·OH. As depicted in Fig. 3e, negligible absorbance change at 652 nm will be detected after incubation of TMB with H₂O₂. In distinction, PEG/Cu-BDC accelerated the ·OH technology within the presence of GSH and H₂O₂ by measuring the absorbance of TMB at 652 nm, whereas a slight increment within the absorbance at 652 nm will be noticed after incubation of TMB with PEG/Cu-BDC within the presence of GSH. As well as, the ·OH technology enhanced with the extension of response durations in addition to the rising proportion of H₂O₂ (Fig. 3f–h). Moreover, the electron spin resonance (ESR) spectroscopy was additionally recorded to verify the ·OH manufacturing utilizing a ·OH seize agent, 5, 5-dimethyl-1-pyrroline-Noxide (DMPO). The presence of the attribute indicators within the ESR spectra validated the excessive functionality of PEG/Cu-BDC in producing ·OH (Fig. 3i). All these outcomes confirmed that GSH and H₂O₂ can function an “AND” logic gate to activate the Cu⁺-catalyzed Fenton-like reactions for environment friendly ·OH technology within the presence of PEG/Cu-BDC nanocatalysts.

In vitro GSH depletion and ·OH technology enabled by PEG/Cu-BDC. a UV–Vis absorption spectra of DTNB resolution containing totally different proportions of GSH and PEG/Cu-BDC. b, c UV–Vis absorption spectra of DTNB resolution containing GSH and PEG/Cu-BDC at (b) pH 6.5 and (c) pH 7.4. d The comparability of GSH consumption fee below pH 6.5 and seven.4, respectively. e UV–Vis absorption spectra of oxidized TMB resolution after varied remedies. f, g UV–Vis absorption spectra of oxidized TMB resolution containing the proportions of PEG/Cu-BDC to H₂O₂ of (f) 1: 1 and (g) 1:2. h The ·OH technology fee in several proportions of PEG/Cu-BDC to H₂O₂. i EPR spectra of DMPO containing totally different proportions of PEG/Cu-BDC to H₂O₂

In vitro tumor cell-killing exercise of 2D PEG/Cu-BDC nanocatalysts

The intracellular uptake of 2D PEG/Cu-BDC nanocatalysts was assessed utilizing confocal laser scanning microscopy (CLSM) statement after incubation of 4T1 and MDA-MB-231 breast tumor cells with fluorescein isothiocyanate (FITC)-labeled PEG/Cu-BDC for various durations. On the premise of the obtained CLSM photographs, the inexperienced fluorescence of FITC-labeled PEG/Cu-BDC enhanced with the extension of the incubation length, which demonstrated that PEG/Cu-BDC may very well be effectively endocytosed by 4T1 and MDA-MB-231 breast tumor cells (Figs. 4a, 5a). After affirmation of the environment friendly internalization of PEG/Cu-BDC, the ROS technology in 4T1 and MDA-MB-231 breast tumor cells was evaluated after incubation with varied concentrations of PEG/Cu-BDC utilizing 2, 7-dichlorodihydrofluorescein diacetate (DCFH-DA) as an indicator. The inexperienced fluorescence sign brightened with the rising focus of PEG/Cu-BDC, and the sign reached the utmost at an incubation focus of 100 μg mL⁻¹, demonstrating the environment friendly ROS technology enabled by PEG/Cu-BDC nanocatalysts (Figs. 4b, 5b).

Mobile uptake and therapeutic efficacy of PEG/Cu-BDC towards 4T1 breast tumor cells. a CLSM photographs of 4T1 breast tumor cells after incubated with FITC-labeled PEG/Cu-BDC for varied durations (1, 2, 4, and 6 h). Scale bars: 30 μm. b Intracellular ROS technology in 4T1 breast tumor cells after cultured with varied concentrations of PEG/Cu-BDC (0, 20, 50, and 100 μg mL⁻¹). Scale bars: 50 μm. c Mobile viability of the 4T1 breast tumor cells after incubated with PEG/Cu-BDC for twenty-four and 48 h, respectively (n = 5 biologically impartial samples). d Stay/lifeless staining of 4T1 breast tumor cells with calcein AM and PI, respectively. Scale bars: 100 μm. e Move cytometry evaluation displaying apoptosis of 4T1 breast tumor cells after incubation with totally different concentrations (0, 20, 50, and 100 μg mL⁻¹) of PEG/Cu-BDC for twenty-four h

Mobile uptake and therapeutic efficacy of PEG/Cu-BDC towards MDA-MB-231 breast tumor cells. a CLSM photographs of MDA-MB-231 breast tumor cells after incubated with FITC-labeled PEG/Cu-BDC for varied durations (1, 2, 3, and 4 h). Scale bars: 30 μm. b Intracellular ROS technology in MDA-MB-231 breast tumor cells after cultured with varied concentrations of PEG/Cu-BDC (0, 10, 20, 50, and 100 μg mL⁻¹). Scale bars: 50 μm. c Mobile viability of MDA-MB-231 breast tumor cells after incubated with PEG/Cu-BDC for twenty-four and 48 h, respectively (n = 5 biologically impartial samples). d Stay/lifeless staining of MDA-MB-231 breast tumor cells with calcein AM and PI, respectively. Scale bars: 100 μm

The tumoricidal exercise of PEG/Cu-BDC nanocatalysts towards 4T1 and MDA-MB-231 breast tumor cells was then assessed by the usual counting kit-8 (CCK-8) assay, CLSM statement, and move cytometry (FCM) evaluation. To additional quantitively examine the anti-tumor effectivity, 4T1 and MDA-MB-231 breast tumor cells have been cultured with totally different concentrations of PEG/Cu-BDC for twenty-four and 48 h. As depicted in Figs. 4c and 5c, the cell viabilities of 4T1 breast tumor cells have been 38.6% and 29.86%, respectively, akin to 44.23% and 33.07% for MDA-MB-231 breast tumor cells after therapy with 100 μg mL⁻¹ of PEG/Cu-BDC for twenty-four and 48 h. To substantiate the excessive biocompatibility of PEG/Cu-BDC nanocatalyst in direction of regular cells, the cell viability of PEG/Cu-BDC nanocatalyst towards regular endothelial cells was additionally evaluated. As proven in Extra file 1: Fig. S1, the cell viability was decided to be 90.3% after therapy with 100 μg mL⁻¹ for regular endothelial cells, which was considerably increased than that of 38.6% for 4T1 cells. Moreover, a calcein acetoxymethyl ester (calcein-AM) and propidium iodide (PI) assay was additional utilized to tell apart the reside and lifeless cells via shade instantly. As offered in Figs. 4d and 5d, the pink PI fluorescence sign enhanced with the elevating focus of PEG/Cu-BDC. Moreover, the move cytometry evaluation was carried out for instance that the therapeutic effectivity enhanced with the elevated focus, which was in accordance with the CLSM statement outcomes (Fig. 4e).

RNA sequencing was additional performed to analyze the antitumor mechanism of PEG/Cu-BDC by analyzing the mRNA profiling in 4T1 cells after incubation with saline and PEG/Cu-BDC nanosheets, respectively. As proven in Fig. 6a, the field plots in relation with 6 totally different teams (3 teams for management and three teams for PEG/Cu-BDC) have been on the similar stage, which revealed the homogeneity of cell samples, laying basis for the next mechanism investigation. There have been 5041 differentially expressed genes in each saline and PEG/Cu-BDC handled teams, together with 2608 up-regulated and 2433 down-regulated ones, respectively (Fig. 6b, c). On the premise of the differentially expressed genes, a number of key genes which can be related to cell apoptosis and proliferation have been listed within the warmth map after therapy with PEG/Cu-BDC incubation. Amongst these differentially expressed genes related to ferroptosis [44] and Hedgehog signaling pathway [45], 9 and 12 genes have been up-regulated and down-regulated, respectively (Fig. 6d). Moreover, gene ontology (GO) (Extra file 1: Figs. S2, S3) and Kyoto Encyclopedia of Genes and Genomes (KEGG) (Fig. 6e, f) pathway enrichment evaluation have been carried out to know how Cu-BDC nanosheets acted on tumor cells by GSH “AND” H₂O₂-activated CDT. Within the midst of those KEGG pathways, ferroptosis is the principle trigger in inducing cell dying of PEG/Cu-BDC, through which the genetic expression within the glutathione metabolism pathway was up-regulated, thus resulting in GSH depletion and ROS elevation in 4T1 cells (Extra file 1: Fig. S4).

Mechanistic examine of 2D PEG/Cu-BDC nanocatalysts in inducing augmented CDT impact. a The field plot of those 6 samples, through which all samples have been nearly on the similar stage, indicating the standard homogenization of the cell samples. b The chart displaying the differentially expressed genes in saline- and PEG/Cu-BDC-treated teams (n = 3 biologically impartial samples). c The gene expression heat-map of 4T1 cells in saline- and PEG/Cu-BDC-treated teams (n = 3 biologically impartial samples). d The gene expression heat-map of the associated genes within the ferroptosis and Hedgehog signaling pathways. e, f The highest 20 (e) up-regulated, and (f) down-regulated KEGG pathways after therapy with saline and PEG/Cu-BDC nanosheets (P-value < 0.05)

In vivo therapeutic efficacy of 2D PEG/Cu-BDC nanocatalysts

Organic behaviors comprehending blood half-life, biodistribution, and biocompatibility have been the preconditions of drug motion for in vivo utility. As depicted in Fig. 7a, the blood half-life of 2D PEG/Cu-BDC nanocatalysts was decided to be 1.16 h after intravenous injection, which revealed the fascinating pharmacokinetic efficiency of PEG/Cu-BDC. As well as, the biodistribution investigation was additionally carried out to disclose the buildup of PEG/Cu-BDC in tumor tissues and main organs at 4, 8, and 24 h after intravenous administration. As proven in Fig. 7b, PEG/Cu-BDC nanosheets primarily collected within the liver tissues, and their accumulation in tumor tissues was decided to be 3.98% at 24 h post-injection.

In vivo organic behaviors and therapeutic efficacy of 2D PEG/Cu-BDC nanocatalysts on 4T1 tumor-bearing mice. a In vivo pharmacokinetic profile of PEG/Cu-BDC (n = 3 biologically impartial samples). b The biodistribution of PEG/Cu-BDC in tumor tissues and main organs (coronary heart, liver, lung, spleen, and kidney) at totally different durations post-injection (4, 8, and 24 h) (n = 3 biologically impartial samples). c Physique weight variations, d relative tumor volumes, e tumor progress charges, and f tumor inhibition charges of the mice in several therapy teams (P values: *P < 0.05, **P < 0.01, and ***P < 0.001). g H&E, TUNEL, and Ki-67 staining of tumor sections (Scale bar: 100 μm), and h H&E staining of the foremost organs in several therapy teams (Scale bar: 100 μm)

The systemic toxicity of 2D PEG/Cu-BDC nanocatalysts in vivo was assessed by blood evaluation and hematoxylin–eosin (H&E) staining of the foremost visceral organs of the wholesome feminine Kunming mice. As proven in Extra file 1: Fig. S5, the routine blood parameters and serum biochemical indexes exhibited no vital distinction in all therapy teams. As well as, the principle organs in each management and PEG/Cu-BDC-treated teams have been collected for H&E staining. Negligible irritation lesions and harm indicators have been noticed for the principle organs in all therapy teams, indicating excessive biocompatibility and biosafety of the engineered PEG/Cu-BDC nanocatalysts for potential therapeutic use (Extra file 1: Figs. S6, S7).

The antineoplastic exercise of the engineered 2D PEG/Cu-BDC nanocatalysts was assessed on feminine nude mice embedding with 4T1 and MDA-MB-231 breast tumor cells subcutaneously. The mice in three teams have been injected with saline, doxorubicin (10 mg kg⁻¹), and PEG/Cu-BDC (10 mg kg⁻¹), respectively. The physique weights and tumor sizes of the mice have been recorded. Through the therapeutic processes, whether or not within the 4T1 or MDA-MB-231 breast tumor-bearing mice, the quantitative values and the variation tendency of the physique weights in all teams have been nearly an identical, indicating that negligible toxicity in vivo was attributable to PEG/Cu-BDC administration (Figs. 7c, 8a). In 4T1 breast tumor-bearing mice, after 14-day therapy, the relative tumor quantity (V/V₀) within the management and doxorubicin-treated teams reached 25.2 and 10.43 with the tumor progress fee of 100% and 41.37%, respectively, whereas the worth of V/V₀ within the PEG/Cu-BDC-treated group was merely 5.59 with the expansion fee of twenty-two.17% (Fig. 7d). By way of MDA-MB-231 breast tumor-bearing mice, the worth of V/V₀ and tumor progress fee within the PEG/Cu-BDC therapy group approached half of that within the saline-treated group (Fig. 8b, c). Moreover, the common tumor weights, tumor sizes or progress inhibition charges in all therapy teams intuitively validated that extreme harm towards tumor tissues was attributable to PEG/Cu-BDC administration (Figs. 7e, f, 8d–f).

The therapeutic efficacy of 2D PEG/Cu-BDC nanocatalysts on MDA-MB-231 tumor-bearing mice. a Physique weight variations, b relative tumor volumes, c tumor progress charges, d tumor inhibition charges, and f tumor weights of the tumor-bearing mice in several therapy teams (P values: *P < 0.05, **P < 0.01, and ***P < 0.001). e Pictures of the tumors dissected from the tumor-bearing mice after varied remedies. g H&E, TUNEL, and Ki-67 staining of the tumor sections in several therapy teams (Scale bars: 50 μm). h H&E staining of the foremost organs after totally different remedies (Scale bars: 50 μm)

Moreover, the histological analysis of consultant tumor tissues of the mice in all therapy teams was performed to analyze the therapeutic mechanism of PEG/Cu-BDC by H&E and terminal deoxynucleotidyl transferase uridine triphosphate nick finish labeling (TUNEL) staining. Compared with doxorubicin-treated group, extra distinguished histological harm sign was noticed within the PEG/Cu-BDC-treated group from H&E and TUNEL staining photographs (Figs. 7g, 8g). Moreover, Ki-67 antibody staining assay was carried out to evaluate the tumor-cell proliferative property of the mice in varied therapy teams. By evaluating the Ki-67 staining photographs in different therapy teams, PEG/Cu-BDC offered conspicuous suppressive impact on the proliferative exercise of tumor tissues. To higher validate the therapeutic efficacy of PEG/Cu-BDC nanocatalyst, the quantitative evaluation of Ki-67 and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining was carried out. Compared with the management group, the odds of Ki-67 optimistic tumor cells have been distinctly decreased to 23.3% and 12.5% for PEG/Cu-BDC nanocatalyst-treated 4T1 and MDA-MB-231 tumor-bearing mice, respectively, whereas the numbers of apoptotic cells have been apparently elevated (80.7% and 66.7% for 4T1 and MDA-MB-231 tumor-bearing mice, respectively) after therapy with PEG/Cu-BDC nanocatalyst (Extra file 1: Figs. S8, S9). Furthermore, no apparent harm sign of the principle organs was detected from H&E staining photographs in several therapy teams, demonstrating that PEG/Cu-BDC options negligible hostile impact on the well being of the mice (Figs. 7h, 8h).