Tumor-Microenvironment-Responsive Nanomedicine for Enhanced Cancer Immunotherapy

Abstract

The past decades have witnessed great progress in cancer immunotherapy, which has profoundly revolutionized oncology, whereas low patient response rates and potential immune-related adverse events remain major clinical challenges. With the advantages of controlled delivery and modular flexibility, cancer nanomedicine has offered opportunities to strengthen antitumor immune responses and to sensitize tumor to immunotherapy. Furthermore, tumor-microenvironment (TME)-responsive nanomedicine has been demonstrated to achieve specific and localized amplification of the immune response in tumor tissue in a safe and effective manner, increasing patient response rates to immunotherapy and reducing the immune-related side effects simultaneously. Here, the recent progress of TME-responsive nanomedicine for cancer immunotherapy is summarized, which responds to the signals in the TME, such as weak acidity, reductive environment, high-level reactive oxygen species, hypoxia, overexpressed enzymes, and high-level adenosine triphosphate. Moreover, the potential to combine nanomedicine-based therapy and immunotherapeutic strategies to overcome each step of the cancer-immunity cycle and to enhance antitumor effects is discussed. Finally, existing challenges and further perspectives in this rising field with the hope for improved development of clinical applications are discussed.

Keywords: drug delivery; immunotherapy; nanomedicine; stimulus-responsive; tumor microenvironment.

Scheme 1

Schematic diagram of TME‐responsive nanomedicine for cancer immunotherapy.

Scheme 2

Illustration of specific biosignals in the TME, including low pH, redox, overexpressed enzymes, hypoxia, and overexpressed ATP.

Figure 1

a) Scheme of GDR and GDR/OVA nanovaccine. b) The expression of i) CD83 and ii) CD86 on bonemarrow‐derived dendritic cells (BMDCs) were measured using flow cytometry. The productions of iii) IL‐12 and iv) TNF‐α in culture supernatants were measured using enzyme linked immunosorbent assay (ELISA). Reproduced with permission.^{[ 23 ]} Copyright 2016, Elsevier Ltd. c) The proposed mechanism of enhance PDT and antitumor immune responses induced by DEX–HAase adjuvant and PD‐L1 checkpoint blockade. d) The size change curve of DEX–HAase nanoparticle in pH 6.0 and 7.4 PBS solution. e) CTL infiltration in tumors. CD3⁺CD8⁺ cells were defined as CTLs. f) The ratio of CD8⁺ T cells to regulatory T cells of mice post various treatments. g) The production of TNF‐α in serum of mice determined on the ninth day post various treatments. Reproduced with permission.^{[ 24 ]} Copyright 2019, Wiley‐VCH. h) Schematic illustrations for preparation of RPTDH/R848 nanoparticles. i,j) CD3⁺ (i) and CD8⁺ (j) T cell infiltration in tumor. Reproduced with permission.^{[ 27 ]} Copyright 2019, Elsevier Ltd. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 2

a) Chemical structure of the acid‐activatable POP micelleplexes coloaded with PPa and siRNA. (b) Photographs and H&E staining of the metastatic foci of the B16‐F10 tumors (scale bar 100 µm, n = 6). Reproduced with permission.^{[ 28 ]} Copyright 2016, American Chemical Society. c) Illustration of pH‐response dissociable micelleplex‐mediated photodynamic tumor immunotherapy in vivo. d) TEM images of PCPP@MTPP@siPD‐L1 micelleplexes after various treatments with pH 7.4, pH 6.8, and pH 5.0 for 4 h. MTPP: (5‐(3‐Hydroxy‐p‐(4‐trimethylammonium) butoxyphenyl)‐10, 15, 20 triphenylporphyrin chlorine. e) Zeta potentials variation of PCPP@MTPP@siPD‐L1 micelleplexes under various pH value conditions. Reproduced with permission.^{[ 29 ]} Copyright 2018, Wiley‐VCH. f) Preparation of NR_P+I and schematic illustration of chemo‐immunotherapy. g) TEM images of NG_P+I in pH 7.4, NG_P+I in pH 6.5, NR_P+I in pH 7.4, and NR_P+I in pH 6.5. The scale bar is 1 µm. h) pH‐dependent particle sizes of NG_P+I and NR_P+I. i) In vitro stability of NG_P+I and NR_P+I in saline at 37 °C for 1 week. Reproduced with permission.^{[ 30 ]} Copyright 2017, American Chemical Society. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 3

a) A scheme indicating the step‐by‐step synthesis of H‐MnO₂–PEG nanoparticles and the subsequent dual‐drug loading. b) TEM images of H‐MnO₂–PEG after incubation in buffers with different pHs (7.4 and 5.5) for various periods of time. Reproduced with permission.^{[ 32 ]} Copyright 2017, Springer Nature. c) Schematic illustration of pH‐responsive STING‐NVs that efficiently load CDG at physiological pH, stabilized CDG, delivered CDG to immune cells, conditionally released CDG in the acidic endosome, and facilitated endosome escape of CDG for cancer immunotherapy. d) pH‐responsive cumulative CDG release from STING‐NVs. e) The signal ratio of FluoCDG outside/inside (O/I) endolysosome. Reproduced with permission.^{[ 33 ]} Copyright 2020, Wiley‐VCH. f) The design of pH low insertion peptide (pHLIP)‐modified Fc molecules or antibodies and the proposed immunotherapeutic mechanism. g) Quantification of the increase in NK cell activation (CRTAM‐positive) CRTAM: class‐I restricted T cell‐associated molecule. h) the percentage of proliferating cell nuclear antigen (PCNA)‐positive cells in metastasis tumors treated by various formulations. Reproduced with permission.^{[ 34 ]} Copyright 2018, Wiley‐VCH. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 4

a) Schematic illustration of the HCJSP prodrug nanoparticle prepared via the host–guest interaction between HA–CD and AD‐SS–JQ1 and AD‐SS–PPa. AD‐SS: disulfide bond modified adamantane. b) Schematic illustration of mechanism of combination immunotherapy. c,d) Representative western blot and semiquantitative analysis of the expression of c‐Myc (d), human kidney‐2 (HK‐2), and lactate dehydrogenase A (LDHA) after treated with 0.5, 1.0, or 2.0 µm of JQ1 for 24 h. e) Flow cytometric examination of PD‐L1 expression in Panc02 cells treated with Interferon γ (IFN‐γ)/JQ1 alone or combination for 24 h. f) Quantitative analysis of the lung metastatic nodules of in the Pano02 tumor‐bearing mice at the end of the antitumor study. Reproduced under the terms of the CC‐BY license.^{[ 49 ]} Copyright 2021, Published by Wiley‐VCH. g) FM@VP nanoparticle cluster assembling scheme. h, i) Box plots of tumor volumes in primary (h) and distant tumors (i) on day 29. Reproduced with permission.^{[ 51 ]} Copyright 2020, Elsevier Ltd. j) Schematic illustration of ER‐targeting PS TCPP‐T^ER specifically accumulates in the ER and produces ROS in situ upon laser irradiation to induce ER stress and amplifies ICD. TCPP‐T^ER: 4,4′,4″,4′″‐(porphyrin‐5,10,15,20‐tetrayl)tetrakis(N‐(2‐((4‐methylphenyl)sulfonamido)‐ethyl)benzamide. k) Reduction‐responsive release of TCPP‐T^ER from Ds‐sP/TCPP‐T^ER at pH 7.4 with or without 10 × 10⁻³ m GSH. l) Western blot assay of HMGB1 and calreticulin (CRT) expression levels in 4T1 cells treated with Ds‐sP/TCPP or Ds‐sP/TCPP‐T^ER with or without 670 nm laser irradiation. Reproduced with permission.^{[ 52 ]} Copyright 2020, American Chemical Society. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 5

a) Schematic illustration showing the synergistic immunotherapy using the ROS‐sensitive complexes for controlled sequential release of aCD47 and aPD1 in the TME. b–e) Flow cytometry analyzed the percentage of CD45⁺ cells (b), M2‐like macrophages (CD206^hiF4/80⁺CD11b⁺) (c), CD4⁺Foxp3⁺ T cells (d), and CD8⁺ T cells (e) in B16‐F10 tumors. Reproduced with permission.^{[ 65 ]} Copyright 2019, American Chemical Society. f) Schematic illustration the mechanism of P3C‐Asp in combination with aPD‐1 in cancer immunotherapy. g)The proposed release mechanism of P3C‐Asp in the presence of H₂O₂. h) In vitro aspirin release profiles of P3C‐Asp in phosphate buffer with Tween 80 (0.2%, w/v) at four conditions: pH 7.4, pH 6.8 with 100 × 10⁻⁶ m H₂O₂, and pH 6.8 with 10 × 10⁻³ m H₂O₂, n = 3. Reproduced with permission.^{[ 68 ]} Copyright 2019, Chinese Chemical Society. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 6

a) A schematic illustration of the preparation and application of the CAGE complex. b) Hypoxia‐responsive CpG ODN release from CAGE. CpG ODN was labeled with fluorescein isothiocyanate (FITC), and the amount of released CpG ODN was investigated by measuring fluorescence intensity of FITC‐labeled CpG in supernatant. c) CpG/glycol chitosan (GC) complex in the supernatant observed by TEM. d) Quantitative assay of CpG ODN accumulated in tumor‐draining lymph nodes (TDLN) after intravenous (i.v.) injection of CAGE/CpG complex. e–g) The corresponding quantification of recruited (e), mature (f), and OVA‐presenting DC population (g). Reproduced with permission.^{[ 70 ]} Copyright 2018, American Chemical Society. h) Fabrication of DOX–MVs via cooperative assembly of BCP‐grafted MFNs. MVs: manganese ferrite vesicles; MFNs: manganese ferrite nanoparticles. i) Schematic illustration of the mechanism of DOX–MV‐based chemo‐immunotherapy to achieve systemic immune responses. j,k) In vitro cytotoxicity of MVs, DOX, and DOX–MVs against 4T1 cells incubated under normoxic and hypoxic conditions, respectively. l,m) Cytokine levels in the sera from mice isolated 7 days after mice were rechallenged with secondary tumors (on day 47). Reproduced with permission.^{[ 72 ]} Copyright 2021, Wiley‐VCH. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 7

a) Schematic illustration of the TME‐responsive prodrug nanoplatform with deep tumor penetration for efficient synergistic cancer immunotherapy. b) TEM images of mPEG–Pep–IDOi/ICG NPs and mPEG–Pep–IDOi/ICG NPs treated with MMP‐2. mPEG: polyethylene glycol monomethyl ether. c) Expression of the costimulatory molecules CD86 and CD80 on BMDCs induced by different formulations with/without NIR‐laser‐irradiation‐pretreated B16‐F10 cells. NIR: near infrared. Reproduced with permission.^{[ 74 ]} Copyright 2020, Elsevier Ltd. d) Assembly strategy for aPD‐L1@HC/PM NPs and illustration of the step‐by‐step detached release behavior of aPD‐L1, Ce6, and 1‐mt and the immunotherapy capability via the cascade‐amplifying cancer‐immunity cycle. HC/PM is a mixture of hyaluronic acid (HC) and dextro‐1‐methyl tryptophan (1‐mt)‐conjugated polylysine (PM). e,f) CD3⁺CD4⁺ T cells (e) and CD3⁺CD8⁺ T cells (f) in distant tumors after different treatment. g) Photographs and H&E staining of lung metastatic nodules of the B16‐F10 tumors. Reproduced with permission.^{[ 77 ]} Copyright 2019, American Chemical Society. h) Schematic diagram of dual‐drug chemo‐ and immune‐combinational therapy mechanism. i) Confocal laser scanning microscope (CLSM) images of DLTPT and HAase+DLTPT incubated with 4T1 multicellular tumor spheroids for 6 h. j) CD4⁺ T cells, CD8⁺ T cells, the ratio of (CD8⁺ T and CD4⁺ T cells) and Treg and CD3⁺CD4⁺ Foxp3 (Treg) in tumor. Reproduced with permission.^{[ 78 ]} Copyright 2021, American Association for the Advancement of Science. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 8

a) Schematic on the preparation process of PNB–IR780/siP and illustration of the pH/ATP cascade‐responsive nanocourier targeting tumor delivery and mediated photothermal tumor immunotherapy in vivo. b) ATP‐triggered uploading of siP from different micelles for 10 min. c) PD‐L1 mRNA expression on 4T1 cells treated with various preparations (n = 3, mean ± SD). a: PBS, b: PB–IR780/siP at pH 7.4, c: PB–IR780/siP at pH 6.8, d: PNE–IR780/siP at pH 7.4, e: PNE–IR780/siP at pH 6.8, f: PNB–IR780/siP at pH 7.4, g: PNB–IR780/siP at pH 6.8, h: Lipo–siP at pH 7.4, i: Lipo–siP at pH 6.8. d) Quantitative presentation of PD‐L1 protein. e) Representative bioluminescence images and H&E assays of lungs. f) The frequency of tumor‐infiltrating CD4⁺ T cells, CD8⁺ T cells, and Tregs in mice with various treatments (n = 3, mean ± SD). g) CD8⁺ T cells: Treg ratios and CD4⁺ T cells: Treg ratios in the distal tumors (n = 3, mean ± SD). SD: standard deviation. Reproduced with permission.^{[ 82 ]} Copyright 2021, Elsevier Ltd. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.005.

Figure 9

a) Schematic illustration of the BCPN for improved immunotherapy by cooperatively modulating the immune tumor microenvironment. b) Representative CLSM images of fluorescence distribution in 4T1 multicellular spheroid (MCSs) after 12 h incubation with acid‐sensitive binary cooperative prodrug nanoparticle (^ASPN@NR) pretreated in acid buffers. c) The tumor growth curves in 4T1‐tumor‐bearing mice following the indicated treatments. d) The number of lung metastatic nodules of mice bearing 4T1 tumors at the end of the antitumor study. Reproduced with permission.^{[ 83 ]} Copyright 2018, Wiley‐VCH. e) The proposed antitumor mechanism of the NLG919@DEAP‐DPPA‐1 nanoparticle. f,g) The percentages of CD8⁺ T cells (f) and IFN‐γ‐producing cytotoxic T cells (g) in tumors from various treatment groups (n = 3) were analyzed using flow cytometry on day 12 after the commencement of treatment. h,i) The expression of IFN‐γ (h) and IL‐2 (i) in tumors from various treatment groups (n = 3). Reproduced with permission.^{[ 85 ]} Copyright 2018, American Chemical Society. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.005.

Figure 10

a) The schematic illustration of the construction, drug delivery, and tumor response of SL@BRNPs, and the combinational therapy. b–d) The statistical results of the corresponding immune cells include CD8⁺ T cells (b), Tregs (c), and the ratios of CD8⁺ T cells/Tregs (d). The groups 1, 2, 3, respectively, correspond to group SL@BRNPs/iRGD + anti‐PD‐L1, SL@BRNPs/iRGD, and PBS. iRGD: tumor penetrating peptide (cRGDKGPDC). e) The growth of metastasis semiquantified by bioluminescence intensity. Reproduced with permission.^{[ 87 ]} Copyright 2019, Wiley‐VCH. f) Schematic illustration of synergistic immunotherapy mechanisms of transformable NPs. g) The TEM images of 2‐NPs incubated in pH 7.4 PBS and in pH 6.8 PBS containing 100 ng mL⁻¹ MMP‐2 for 0, 1, 2, 4, and 8 h, and of 2‐NFs (originated from 2‐NPs treated with MMP‐2 for 8 h) in pH 6.8 PBS containing 10 × 10⁻³ m GSH for 12 h as well as in pH 5.5 PBS for 24 h. h) The experimental groups and the meaning of labels. i) The number of nodules on the surface of lungs excised from 4T1‐tumor‐bearing mice at day 26 (n = 8). j) CD8⁺/Tregs ratio in tumor tissues (n = 8). k) The images and H&E staining of lungs. Mice were treated with saline, PEG–Wpeptide (i.v.), Wpeptide (intratumoral, i.T.), blank NFs (i.v.), 2‐NPs (i.v.), 2‐NPs + PEG–Wpeptide (i.v.), and 3‐NPs (i.v.), respectively (the blue scale bar is 2.5 mm and the black scale bar is 500 µm). Reproduced with permission.^{[ 146 ]} Copyright 2019, Wiley‐VCH. p‐Values: *p < 0.05; **p < 0.01; ***p < 0.005.