The application and mechanism of PD pathway blockade for cancer therapy

Application of molecular imaging in immune checkpoints therapy: From response assessment to prognosis prediction

Recently, immune checkpoint therapy (ICT) represented by programmed cell death1 (PD-1) and its major ligands, programmed death ligand 1 (PD-L1), has achieved significant success. Detection of PD-L1 by immunohistochemistry (IHC) is a classic method to guide the treatment of ICT patients. However, PD-L1 expression in the tumor microenvironment is highly complex. Thus, PD-L1 IHC is inadequate to fully understand the relevance of PD-L1 levels in the whole body and their dynamics to improve therapeutic outcomes. Intriguingly, numerous studies have revealed that molecular imaging technologies could potentially meet this need. Therefore, the purpose of this narrative review is to summarize the preclinical and clinical application of ICT guided by molecular imaging technology, and to explore the future opportunities and practical difficulties of these innovations.

Arsenic sulfide reverses cisplatin resistance in non-small cell lung cancer in vitro and in vivo through targeting PD-L1

BACKGROUND

Recent studies have found that programmed death ligand 1 (PD-L1) might be involved in chemotherapy resistance in non-small cell lung cancer (NSCLC). Arsenic sulfide (As₄ S₄ ) has been recognized to have antitumor activities and enhance the cytotoxic effect of chemotherapy drugs. In this study, we aimed to verify the relationship between PD-L1 and cisplatin (DDP) resistance and identify whether As₄ S₄ could reverse DDP resistance through targeting PD-L1 in NSCLC.

METHODS

The effect of As₄ S₄ and DDP on cell proliferation and apoptosis was investigated in NSCLC cell lines. The expression of p53 and PD-L1 proteins was measured by western blotting analysis. The levels of miR-34a-5p, miR-34a-3p and PD-L1 in cells were measured by real-time qPCR analysis. Mouse xenograft models were established by inoculation with A549/DDP (DDP-resistant) cells.

RESULTS

Depletion of PD-L1 inhibited DDP resistance in A549/DDP and H1299/DDP cells. As₄ S₄ was capable of sensitizing A549/DDP cells to DDP by enhancing apoptosis. As₄ S₄ upregulated p53 expression and downregulated PD-L1 expression in A549/DDP cells. As₄ S₄ increased miR-34a-5p level in A549/DDP cells. Inhibition of p53 by PFT-α partially restored the levels of PD-L1 and miR-34a-5p. Pretreatment with PFT-α suppressed the apoptosis rate induced by cotreatment of As₄ S₄ and DDP in A549/DDP cells. Cotreatment of DDP and As₄ S₄ notably reduced the tumor size when compared with DDP treatment alone in vivo.

CONCLUSIONS

Upregulation of PD-L1 was correlated with DDP resistance in NSCLC cells. Mechanistic analyses indicated that As₄ S₄ might sensitize NSCLC cells to DDP through targeting p53/miR-34a-5p/PD-L1 axis.

Immuno-PET imaging of 68Ga-labeled nanobody Nb109 for dynamic monitoring the PD-L1 expression in cancers

The checkpoint blockade immunotherapy has become a potent treatment strategy for cancers, and programmed death ligand-1 (PD-L1) is a prominent checkpoint ligand that is highly expressed in some cancers. The identification of immune checkpoint marker PD-L1 is critical for improving the success of immunotherapy. Accordingly, the binding specificity and dynamic monitoring property of a non-blocking nanobody tracer ⁶⁸Ga-NOTA-Nb109 to PD-L1 were assessed in this study. The endogenous expression level of PD-L1 in several cancer cells was measured by flow cytometry, Western blot, and cellular uptake assay. Sensitivity and specificity of ⁶⁸Ga-NOTA-Nb109 in monitoring the expression of PD-L1 in vivo were evaluated by PET imaging of different tumor-bearing models (U87, high PD-L1 expression; HCT 116, medium PD-L1 expression; and NCI-H1299, low PD-L1 expression). In vivo PET imaging results agreed well with those detected in vitro. In addition, PET imaging of PD-L1 expression in U87 and NCI-H1299 xenografts using ¹⁸F-FDG was also performed for comparison. The maximum tumor-to-muscle uptake ratio of ⁶⁸Ga-NOTA-Nb109 was more than twofold that of ¹⁸F-FDG in U87 xenograft. The change of PD-L1 expression in NCI-H1299 cells and xenografts induced by cisplatin (CDDP) was sensitively monitored by ⁶⁸Ga-NOTA-Nb109. This study demonstrated the feasibility of tracer ⁶⁸Ga-NOTA-Nb109 for specifically targeting endogenous PD-L1 and dynamic monitoring the change of PD-L1 expression, and could guide the immunotherapy and immunochemotherapy for refractory cancers.

Small-molecule PD-L1 inhibitor BMS1166 abrogates the function of PD-L1 by blocking its ER export

Therapeutic monoclonal antibodies against the PD-L1/PD-1 (programmed death ligand-1/programmed cell death protein-1) axis have achieved great successes in cancer treatments, but the development of small-molecule immunomodulators of the pathway has lagged far behind. We established a cellular coculture assay with two stable transfectant cell lines, a PD-L1-expressing tumor cell line PC9/PD-L1 and a PD-1-expressing T cell line Jurkat/PD-1. Western blotting analyses were used to monitor the PD-L1/PD-1 interaction and signaling. We analyzed PD-L1 glycosylation by lectin binding assay and glycosidase digestion, and examined subcellular localization of PD-L1 by immunocytochemical staining. Luciferase assay and real-time PCR were used to evaluate T cell activation in the coculture experiments. We found that coculturing of the PC9/PD-L1 cells with the Jurkat/PD-1 cells induced a lysosomal degradation of PD-1. A small-molecule PD-L1 inhibitor BMS1166 developed by Bristol-Myers Squibb inhibited the coculture-induced PD-1 degradation through a unique mechanism. BMS1166 specifically affected PD-L1 glycosylation and prevented transporting of the under-glycosylated form of PD-L1 from endoplasmic reticulum (ER) to Golgi, leading to accumulation of PD-L1 in ER. In doing so, BMS1166 blocked PD-L1/PD-1 signaling. Coculturing PD-L1-expressing cells with PD-1-expressing cells induced degradation of PD-1, which could be used as a readout to identify inhibitors of PD-L1/PD-1 signaling. The small-molecule PD-L1 inhibitor BMS1166 abolished the glycosylation and maturation of PD-L1 by blocking its exporting from ER to Golgi. Our study discovered a new strategy to identify inhibitors of the PD-L1/PD-1 signaling pathway and to develop new drugs for the treatment of cancer.

Construction of Anti-hPD-L1 HCAb Nb6 and in Situ 124I Labeling for Noninvasive Detection of PD-L1 Expression in Human Bone Sarcoma

Immunotherapy is considered the fourth major treatment mode for cancer following surgery, chemotherapy, and radiotherapy. In recent years, tumor immunotherapy has achieved breakthrough progress; therefore, it is important to screen patients to identify those who will respond to tumor immunotherapy. Here, we report the construction of a novel heavy chain-only antibody (HCAb) and its corresponding ¹²⁴I-labeled probe. Using phage display technology, we generated a novel anti-hPD-L1-specific HCAb named Nb6 (selected from 95 monoclones) with high affinity for hPD-L1. The positron-emitting ¹²⁴I-labeled hPD-L1-targeted HCAb probe was prepared for further evaluation, and nonradioactive natural iodine (^natI)-labeled anti-hPD-L1 Nb6 was synthesized as a reference compound. ¹²⁵I-anti-hPD-L1 Nb6 uptake in OS-732 cells in vitro can be blocked by the precursor. The binding affinity of ¹²⁵I-anti-hPD-L1 Nb6 to OS-732 cell lines was 2.19 nM. For in vivo studies, an osteosarcoma OS-732 tumor-bearing mouse model was successfully constructed. Polymerase chain reaction (PCR) and Western blot analyses were performed to confirm the presence of the hPD-L1 gene and antigen in the tumor tissue of the OS-732 mouse model. Biodistribution showed that uptake of ¹²⁴I-anti-hPD-L1 Nb6 probes at 24 h was 4.43 ± 0.33% ID/g in OS-732 tumor tissues. Tumor lesions can be clearly delineated on micro-PET (positron emission tomography)/CT (computed tomography) imaging 24 h after injection of ¹²⁴I-anti-hPD-L1 Nb6, while the blocking group shows substantially decreased uptake on imaging. Pathological staining validated hPD-L1 expression on the surface of the tumor cell membrane; thus, ¹²⁴I-anti-hPD-L1 Nb6 can be used for in vivo noninvasive PET imaging. When administered in tandem, Nb6 and ¹²⁴I-anti-hPD-L1 Nb6 may provide a novel strategy to clinically screen patients for hPD-L1 to identify those who would benefit from immunotherapy of malignant tumors such as osteosarcoma.

Novel Small Molecule Inhibitors of Programmed Cell Death (PD)-1, and its Ligand, PD-L1 in Cancer Immunotherapy: A Review Update of Patent Literature

Background:

In the last few decades, cancer immunotherapy has been extensively researched, and novel checkpoint signaling mechanisms involving Programmed Death (PD)-1 and PDLigand 1 (PD-L1) receptors have been targeted. The PD-1/PD-L1 binding and interaction play a critical role in the development of malignancies.

Objective:

The present review focuses on recent patents on the pharmacological and biological cancerregulating properties of PD-1/PD-L1 inhibitors involved in immunotherapeutic cancer drug development.

Methods:

Thorough patent literature search published during the last seven years, including the World Intellectual Property Organization (WIPO®), United States Patent Trademark Office (USPTO®), Espacenet®, and Google Patents, to identify PD-1/PD-L1-targeting small molecule immunomodulators.

Results:

Several small molecule PD-1/PD-L1 inhibitors were patented for regulation of tumor progression by academic and industry-associated investigators. Most of the claimed patents have been validated and confined to in vitro and in vivo mouse models limiting their entry into clinical settings. Majority of the patents are claimed by the researchers at Aurigene Ltd. (India) on novel peptidomimetic compounds. It is worth to be noted that macrocyclic compounds such as the peptides QP20, HD20, WQ20, SQ20, and CQ-22 from Bristol-Myers Squibb (BMS) Company, biaryl, and heterocyclic derivatives including 1,3-dihydroxy-phenyl compounds were efficient in regulating the PD-1/PD-L1 protein-protein binding and interaction compared to those of the approved monoclonal antibodies.

Conclusion:

PD-1/PD-L1 inhibitors show significant anti-cancer responses as stand-alone agents and in combination with other cancer therapies. More efficient experimental studies and clinical trials are necessary to evaluate the host-tumor cells’ interactions. Understanding the cancer microenvironment, and identifying specific biomarkers and X-ray crystalline structures of PD-1/PD-L1 complexes, including molecular and genomic signature studies are essential to determine the feasibility of PD-1/PD-L1 inhibitors for development into drug-like cancer immunotherapeutics.

Indoleamine-2,3-dioxygenase 1/cyclooxygenase 2 expression prediction for adverse prognosis in colorectal cancer

AIM

To evaluate indoleamine-2,3-dioxygenase 1/cyclooxygenase 2 (IDO1/COX2) expression as an independent prognostic biomarker for colorectal cancer (CRC) patients.

METHODS

We retrospectively studied the medical records of 95 patients who received surgical resection from August 2008 to January 2010. All patients were randomly assigned to adjuvant treatment with or without celecoxib groups after surgery. We performed standard immunohistochemistry to assess the expression levels of IDO1/COX2 and evaluated the correlation of IDO1/COX2 with clinicopathological factors and overall survival (OS) outcomes.

RESULTS

The expression of nuclear IDO1 was significantly correlated with body mass index (P < 0.001), and IDO1 expression displayed no association with sex, age, tumor differentiation, T stage, N stage, carcinoembryonic antigen, cancer antigen 19-9, CD3+ and CD8+ tumor infiltrating lymphocytes, and COX2. In univariate analysis, we found that nuclear IDO1 (P = 0.039), nuclear/cytoplasmic IDO1 [hazard ratio (HR) = 2.044, 95% confidence interval (CI): 0.871-4.798, P = 0.039], nuclear IDO1/COX2 (HR = 3.048, 95%CI: 0.868-10.7, P = 0.0049) and cytoplasmic IDO1/COX2 (HR = 2.109, 95%CI: 0.976-4.558, P = 0.022) all yielded significantly poor OS outcomes. Nuclear IDO1 (P = 0.041), nuclear/cytoplasmic IDO1 (HR = 3.023, 95%CI: 0.585-15.61, P = 0.041) and cytoplasmic IDO1/COX2 (HR = 2.740, 95%CI: 0.764-9.831, P = 0.038) have significantly poor OS outcomes for the CRC celecoxib subgroup. In our multivariate Cox model, high coexpression of cytoplasmic IDO1/COX2 was found to be an independent predictor of poor outcome in CRC (HR = 2.218, 95%CI: 1.011-4.48, P = 0.047) and celecoxib subgroup patients (HR = 3.210, 95%CI: 1.074-9.590, P = 0.037).

CONCLUSION

Our results showed that cytoplasmic IDO1/COX2 coexpression could be used as an independent poor predictor for OS in CRC.

Programmed death ligand 1 expression and tumor infiltrating lymphocytes in neurofibromatosis type 1 and 2 associated tumors

Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1) or its ligand (PD-L1) have been shown to be effective in treating patients with a variety of cancers. Biomarker studies have found positive associations between clinical response rates and PD-L1 expression on tumor cells, as well as the presence of tumor infiltrating lymphocytes (TILs). It is currently unknown whether tumors associated with neurofibromatosis types 1 and 2 (NF1 and NF2) express PD-L1. We performed immunohistochemistry for PD-L1 (clones SP142 and E1L3N), CD3, CD20, CD8, and CD68 in NF1-related tumors (ten dermal and six plexiform neurofibromas) and NF2-related tumors (ten meningiomas and ten schwannomas) using archival formalin-fixed paraffin-embedded tissues. Expression of PD-L1 was considered positive in cases with > 5% membranous staining of tumor cells, in accordance with previously published biomarker studies. PD-L1 expression in tumor cells (using the SP142 and E1L3N clones, respectively) was assessed as positive in plexiform neurofibromas (6/6 and 5/6) dermal neurofibromas (8/10 and 6/10), schwannomas (7/10 and 10/10), and meningiomas (4/10 and 2/10). Sparse to moderate presence of CD68, CD3, or CD8 positive TILs was found in 36 (100%) of tumor specimens. Our findings indicate that adaptive resistance to cell-mediated immunity may play a major role in the tumor immune microenvironment of NF1 and NF2-associated tumors. Expression of PD-L1 on tumor cells and the presence of TILs suggest that these tumors might be responsive to immunotherapy with immune checkpoint inhibitors, which should be explored in clinical trials for NF patients.