PD-L1-Targeted Radionuclide Therapy Combined with αPD-L1 Antibody Immunotherapy Synergistically Improves the Antitumor Effect

Recent advances in nanotechnology for programmed death ligand 1-targeted cancer theranostics

Programmed cell death ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1) checkpoint inhibitor-based immunotherapy has provided a unique and potent weapon against cancer in clinical practice. The likelihood of achieving beneficial effects from PD-L1/PD-1 immune checkpoint blockade (ICB) therapy is clinically assessed by detecting PD-L1 expression through invasive tissue biopsies. However, PD-L1 expression is susceptible to tumor heterogeneity and dynamic response to ICB therapy. Moreover, currently, anti-PD-L1 immunotherapy still faces challenges of the low targeting efficiency of antibody drugs and the risk of immune-associated adverse events. To overcome these issues, advanced nanotechnology has been developed for the purpose of quantitative, non-invasive, and dynamic analyses of PD-L1, and to enhance the efficiency of ICB therapy. In this review, we first introduce the nanoprobe-assisted in vitro/in vivo modalities for the selective and sensitive analysis of PD-L1 during the diagnostic and therapeutic process. On the other hand, the feasibility of fabricating diverse functional nanocarriers as smart delivery systems for precisely targeted delivery of PD-L1 immune checkpoint inhibitors and combined therapies is highlighted. Finally, the current challenges are discussed and future perspectives for PD-L1-targeted cancer theranostics in preclinical research and clinical settings are proposed.

Development of novel peptide-based radiotracers for detecting PD-L1 expression and guiding cancer immunotherapy

PURPOSE

Due to tumor heterogeneity, immunohistochemistry (IHC) showed poor accuracy in detecting the expression of programmed cell death ligand-1 (PD-L1) in patients. Positron emission tomography (PET) imaging is considered as a non-invasive technique to detect PD-L1 expression at the molecular level visually, real-timely and quantitatively. This study aimed to develop novel peptide-based radiotracers [68Ga]/[18F]AlF-NOTA-IMB for accurately detecting the PD-L1 expression and guiding the cancer immunotherapy.

METHODS

NOTA-IMB was prepared by connecting 2,2'-(7-(2-((2,5-dioxopyrrolidin-1-yl)oxy)- 2-oxoethyl)-1,4,7-triazonane-1,4-diyl) diacetic acid (NOTA-NHS) with PD-L1-targeted peptide IMB, and further radiolabeled with 68Ga or 18F-AlF. In vitro binding assay was conducted to confirm the ability of [68Ga]/[18F]AlF-NOTA-IMB to detect the expression of PD-L1. In vivo PET imaging of [68Ga]NOTA-IMB and [18F]AlF-NOTA-IMB in different tumor-bearing mice was performed, and dynamic changes of PD-L1 expression level induced by immunotherapy were monitored. Radioautography, western blotting, immunofluorescence staining and biodistribution analysis were carried out to further evaluate the specificity of radiotracers and efficacy of PD-L1 antibody immunotherapy.

RESULTS

[68Ga]NOTA-IMB and [18F]AlF-NOTA-IMB were both successfully prepared with high radiochemical yield (> 95% and > 60%, n = 5) and radiochemical purity (> 95% and > 98%, n = 5). Both tracers showed high affinity to human and murine PD-L1 with the dissociation constant (Kd) of 1.00 ± 0.16/1.09 ± 0.21 nM (A375-hPD-L1, n = 3) and 1.56 ± 0.58/1.21 ± 0.39 nM (MC38, n = 3), respectively. In vitro cell uptake assay revealed that both tracers can specifically bind to PD-L1 positive cancer cells A375-hPD-L1 and MC38 (5.45 ± 0.33/3.65 ± 0.15%AD and 5.87 ± 0.27/2.78 ± 0.08%AD at 120 min, n = 3). In vivo PET imaging and biodistribution analysis showed that the tracer [68Ga]NOTA-IMB and [18F]AlF-NOTA-IMB had high accumulation in A375-hPD-L1 and MC38 tumors, but low uptake in A375 tumor. Treatment of Atezolizumab induced dynamic changes of PD-L1 expression in MC38 tumor-bearing mice, and the tumor uptake of [68Ga]NOTA-IMB decreased from 3.30 ± 0.29%ID/mL to 1.58 ± 0.29%ID/mL (n = 3, P = 0.026) after five treatments. Similarly, the tumor uptake of [18F]AlF-NOTA-IMB decreased from 3.27 ± 0.63%ID/mL to 0.89 ± 0.18%ID/mL (n = 3, P = 0.0004) after five treatments. However, no significant difference was observed in the tumor uptake before and after PBS treatment. Biodistribution, radioautography, western blotting and immunofluorescence staining analysis further demonstrated that the expression level of PD-L1 in tumor-bearing mice treated with Atezolizumab significantly reduced about 3 times and correlated well with the PET imaging results.

CONCLUSION

[68Ga]NOTA-IMB and [18F]AlF-NOTA-IMB were successfully prepared for PET imaging the PD-L1 expression noninvasively and quantitatively. Dynamic changes of PD-L1 expression caused by immunotherapy can be sensitively detected by both tracers. Hence, the peptide-based radiotracers [68Ga]NOTA-IMB and [18F]AlF-NOTA-IMB can be applied for accurately detecting the PD-L1 expression in different tumors and monitoring the efficacy of immunotherapy.

Radiopharmaceuticals as combinatorial partners for immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of multiple cancer types. However, only a fraction of patients with cancer responds to ICIs employed as stand-alone therapeutics, calling for the development of safe and effective combinatorial regimens to extend the benefits of ICIs to a larger patient population. In addition to exhibiting a good safety and efficacy profile, targeted radionuclide therapy (TRT) with radiopharmaceuticals that specifically accumulate in the tumor microenvironment has been associated with promising immunostimulatory effects that (at least in preclinical cancer models) provide a robust platform for the development of TRT/ICI combinations. We discuss preclinical and clinical findings suggesting that TRT stands out as a promising partner for the development of safe and efficient combinatorial regimens involving ICIs.

Eucommia lignans alleviate the progression of diabetic nephropathy through mediating the AR/Nrf2/HO-1/AMPK axis in vivo and in vitro

Lignans derived from Eucommia ulmoides Oliver (Eucommia lignans) inhibit the progression of inflammatory diseases, while their effect on the progression of diabetic nephropathy (DN) remained unclear. This work was designed to assess the function of Eucommia lignans in DN. The major constituents of Eucommia lignans were analyzed by UPLC-Q-TOF-MS/MS. The binding between Eucommia lignans and aldose reductase (AR) was predicted by molecular docking. Eucommia lignans (200, 100, and 50 mg·kg^-1) were used in model animals to evaluate their renal function changes. Rat glomerular mesangial cells (HBZY-1) were transfected with sh-AR, sh-AMPK, and oe-AR in the presence of high glucose (HG) or HG combined with Eucommia lignans to evaluate whether Eucommia lignans affected HG-induced cell injury and mitochondrial dysfunction through the AR/Nrf2/HO-1/AMPK axis. Eucommia lignans significantly attenuated the progression of DN in vivo. Eucommia lignans notably reversed HG-induced upregulation of inflammatory cytokines and mitochondrial injury, while downregulating the levels of Cyto c, caspase 9, AR, and NOX4 in HBZY-1 cells. In contrast, HG-induced downregulation of Nrf2, HO-1 and p-AMPKα levels were abolished by Eucommia lignans. Meanwhile, knockdown of AR exerted similar therapeutic effect of Eucommia lignans on DN progression, and AR overexpression reversed the effect of Eucommia lignans. Eucommia lignans alleviated renal injury through the AR/Nrf2/HO-1/AMPK axis. Thus, these findings might provide evidence for the use of Eucommia lignans in treating DN.

Aptamer-Based Immunotheranostic Strategies

The escape from immune surveillance is a hallmark of cancer progression. The classic immune checkpoint molecules PD-1, PD-L1, CTLA-4, LAG-3, TIM-3 novel ones are part of a sophisticated system of up- and downmodulation of the immune system, which is unregulated in cancer. In recent years, there have been remarkable advances in the development of targeting strategies, focused principally on immunotherapies aiming at blocking those molecules involved in the evasion of the immune system. However, there are still challenges to predicting their efficacy due to the wide heterogeneity of clinical responses. Thus, there is a need to develop new strategies, and theranostics has much to contribute in this field. Besides that, aptamers have emerged as promising molecules with the potential to generate a huge impact in the immunotheranostic field. They are single-stranded oligonucleotides with a unique self-folding tridimensional structure, with high affinity and specificity for the target. In particular, their small size and physicochemical characteristics make them a versatile tool for designing theranostic strategies. Here, we review the progress in theranostic strategies based on aptamers against immune checkpoints, and highlight the potential of those approaches.

Nanomedicine embraces cancer radio-immunotherapy: mechanism, design, recent advances, and clinical translation

Cancer radio-immunotherapy, integrating external/internal radiation therapy with immuno-oncology treatments, emerges in the current management of cancer. A growing number of pre-clinical studies and clinical trials have recently validated the synergistic antitumor effect of radio-immunotherapy, far beyond the "abscopal effect", but it suffers from a low response rate and toxicity issues. To this end, nanomedicines with an optimized design have been introduced to improve cancer radio-immunotherapy. Specifically, these nanomedicines are elegantly prepared by incorporating tumor antigens, immuno- or radio-regulators, or biomarker-specific imaging agents into the corresponding optimized nanoformulations. Moreover, they contribute to inducing various biological effects, such as generating in situ vaccination, promoting immunogenic cell death, overcoming radiation resistance, reversing immunosuppression, as well as pre-stratifying patients and assessing therapeutic response or therapy-induced toxicity. Overall, this review aims to provide a comprehensive landscape of nanomedicine-assisted radio-immunotherapy. The underlying working principles and the corresponding design strategies for these nanomedicines are elaborated by following the concept of "from bench to clinic". Their state-of-the-art applications, concerns over their clinical translation, along with perspectives are covered.

Developments in Combining Targeted Radionuclide Therapies and Immunotherapies for Cancer Treatment

Targeted radionuclide therapy (TRT) and immunotherapy are rapidly growing classes of cancer treatments. Basic, translational, and clinical research are now investigating therapeutic combinations of these agents. In comparison to external beam radiation therapy (EBRT), TRT has the unique advantage of treating all disease sites following intravenous injection and selective tumor uptake and retention-a particularly beneficial property in metastatic disease settings. The therapeutic value of combining radiation therapy with immune checkpoint blockade to treat metastases has been demonstrated in preclinical studies, whereas results of clinical studies have been mixed. Several clinical trials combining TRT and immune checkpoint blockade have been initiated based on preclinical studies combining these with EBRT and/or TRT. Despite the interest in translation of TRT and immunotherapy combinations, many questions remain surrounding the mechanisms of interaction and the optimal approach to clinical implementation of these combinations. This review highlights the mechanisms of interaction between anti-tumor immunity and radiation therapy and the status of basic and translational research and clinical trials investigating combinations of TRT and immunotherapies.

Radioimmunotherapy study of 131I-labeled Atezolizumab in preclinical models of colorectal cancer

Background

Programmed cell death 1 ligand 1(PD-L1) is overexpressed in many tumors. The radionuclide-labeled anti-PD-L1 monoclonal antibody can be used for imaging and therapy of PD-L1 overexpressing cancer. Here, we described 131I-labeled Atezolizumab (131I-Atezolizumab, targeting PD-L1) as a therapeutic agent for colorectal cancer with PD-L1 overexpression.

Methods

131I-Atezolizumab was prepared by the Iodogen method. The expression levels of PD-L1 in different human colorectal cells were determined by flow cytometry, western blot and cell binding assay. The immunoreactivity of 131I-Atezolizumab to PD-L1 high-expressing cells was determined by immunoreactive fraction. The killing abilities of different concentrations of 131I-Atezolizumab on cells with high and low expression of PD-L1 were detected by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Cerenkov luminescence imaging (CLI) and radioimmunotherapy (RIT) of 131I-Atezolizumab were performed on two human colorectal cancer models. The distribution and tumor targeting of 131I-Atezolizumab were evaluated by imaging. Tumor volume and survival time were used as indicators to evaluate the anti-tumor effect of 131I-Atezolizumab.

Results

The expression level of PD-L1 in vitro determined by the cell binding assay was related to the data of flow cytometry and western blot. 131I-Atezolizumab can specifically bind to PD-L1 high-expressing cells in vitro to reflect the expression level of PD-L1. Immunoreactive fraction of PD-L1 high-expressing RKO cells with 131I-Atezolizumab was 52.2%. The killing ability of 131I-Atezolizumab on PD-L1 high-expressing cells was higher than that of low-expressing cells. CLI proved that the specific uptake level of tumors depends on the expression level of PD-L1. Effect of 131I-Atezolizumab RIT showed an activity-dependent tumor suppressor effect on RKO tumor-bearing mice with high PD-L1 expression. 131I-Atezolizumab (37 MBq) can improve the median survival time of mice (34 days), compared to untreated mice (27 days) (P = 0.027). Although a single activity(37 MBq) of 131I-Atezolizumab also inhibited the tumors of HCT8 tumor-bearing mice with low PD-L1 expression (P < 0.05), it could not prolong the survival of mice(P = 0.29).

Conclusion

131I-Atezolizumab can be used as a CLI agent for screening PD-L1 expression levels. It may be used as a radioimmunotherapy drug target for PD- L1 overexpressing tumors.

SPLUNC1 regulates LPS-induced progression of nasopharyngeal carcinoma and proliferation of myeloid-derived suppressor cells

Nasopharyngeal carcinoma (NPC) is one of the aggressive malignant tumors with high mortality, and the proliferation of myeloid-derived suppressor cells (MDSCs) could promote the metastasis of NPC through inhibiting the function of T cells. Meanwhile, SPLUNC1 was known to inhibit the malignant behavior of NPC cells, while the detailed function of SPLUNC1 in LPS-modified immune microenvironment of NPC remains unclear. To assess the impact of SPLUNC1 in immune microenvironment during the progression of NPC, NPC cells were exposed to LPS and then co-cultured with MDSCs for 48 h. RT-qPCR and western blot were performed to evaluate the mRNA and protein level of SPLUNC1, CXCL-2 and CXCR-2, respectively. The level of IL-1β, IL-6, TNF-α, PD-L1, Arg-1 and iNOS were tested by ELISA. Meanwhile, the expression of CD33⁺ was tested by flow cytometry. The expression of CXCL-2 and CXCR-2 in NPC cells was higher, compared to that in NP69 cells. In contrast, SPLUNC1 level in NPC cells was much lower than that in NP69 cells. SPLUNC1 level was negatively correlated with CXCL-2 and CXCR-2. Overexpression of SPLUNC1 reversed LPS-induced inflammatory responses and proliferation in NPC cells. In addition, SPLUNC1 upregulation could reverse LPS-induced proliferation of MDSCs in tumor microenvironment. Meanwhile, SPLUNC1 overexpression could regulate CXCL-2/CXCR-2 axis through decreasing CXCL-2 and CXCR-2 protein and mRNA expression. SPLUNC1 regulates LPS-induced progression of nasopharyngeal carcinoma and proliferation of MDSCs. Thus, our study might provide a theoretical basis for discovering new strategies against NPC.

Evaluating the Combined Anticancer Response of Checkpoint Inhibitor Immunotherapy and FAP-Targeted Molecular Radiotherapy in Murine Models of Melanoma and Lung Cancer

Simple Summary

Although newer cancer medicines that help the immune system recognize and attack cancer cells have improved responses to therapy, most patients ultimately have cancer recurrence. Additional therapies and therapy combinations are needed so that responses can last longer or indefinitely. Molecular targeted radiotherapy is another kind of therapy that targets radioactive particles directly to cancer in the hopes of killing cancer cells to stop tumor growth with limited side effects. Prior studies have shown that targeted radiotherapies activate the immune system and can work together with immunotherapy to improve response. Here, we tested a promising new therapy targeting fibroblast activation protein (FAP) with a therapeutic radionuclide ¹⁷⁷Lu alone and with immunotherapy in mouse models of melanoma and lung cancer. The FAP-targeted radiotherapy reduced tumor growth in both models and melanoma, resulting in tumor regression. We saw increased tumor cell death in dual-treated tumors. We also found that myeloid cells were affected by the combined therapy to a greater degree than the additive effect of either therapy. These results demonstrate that this is a promising new therapy regimen and requires further preclinical and clinical study to better understand the molecular mechanisms underpinning response.

Abstract

Immunotherapy has dramatically improved outcomes for some cancer patients; however, novel treatments are needed for more patients to achieve a long-lasting response. FAP-targeted molecular radiotherapy has shown efficacy in both preclinical and clinical models and has immunomodulatory effects. Here, we studied if combined immunotherapy and radiotherapy could increase antitumor efficacy in murine models of lung cancer and melanoma and interrogated the mechanisms by which these treatments attenuate tumor growth. Using LLC1 and B16F10 murine models of lung cancer and melanoma, respectively, we tested the efficacy of ¹⁷⁷Lu-FAPI-04 alone and in combination with immunotherapy. Alone, ¹⁷⁷Lu-FAPI-04 significantly reduced tumor growth in both models. In animals with melanoma, combined therapy resulted in tumor regression while lung tumor growth was attenuated, but tumors did not regress. Combined therapy significantly increased caspase-3 and decreased Ki67 compared with immunotherapy alone. Flow cytometry demonstrated that tumor-associated macrophages responded in a tumor-dependent manner which was distinct in animals treated with both therapies compared with either therapy alone. These data demonstrate that ¹⁷⁷Lu-FAPI-04 is an effective anticancer therapy for melanoma and lung cancer which mediates effects at least partially through induction of apoptosis and modulation of the immune response. Translational studies with immunotherapy and ¹⁷⁷Lu-FAPI-04 are needed to demonstrate the clinical efficacy of this combined regimen.