Molecular imaging of tumor photoimmunotherapy: Evidence of photosensitized tumor necrosis and hemodynamic changes

Near Infrared Photoimmunotherapy: A Review of Recent Progress and Their Target Molecules for Cancer Therapy

Near infrared photoimmunotherapy (NIR-PIT) is a newly developed molecular targeted cancer treatment, which selectively kills cancer cells or immune-regulatory cells and induces therapeutic host immune responses by administrating a cancer targeting moiety conjugated with IRdye700. The local exposure to near-infrared (NIR) light causes a photo-induced ligand release reaction, which causes damage to the target cell, resulting in immunogenic cell death (ICD) with little or no side effect to the surrounding normal cells. Moreover, NIR-PIT can generate an immune response in distant metastases and inhibit further cancer attack by combing cancer cells targeting NIR-PIT and immune regulatory cells targeting NIR-PIT or other cancer treatment modalities. Several recent improvements in NIR-PIT have been explored such as catheter-driven NIR light delivery, real-time monitoring of cancer, and the development of new target molecule, leading to NIR-PIT being considered as a promising cancer therapy. In this review, we discuss the progress of NIR-PIT, their mechanism and design strategies for cancer treatment. Furthermore, the overall possible targeting molecules for NIR-PIT with their application for cancer treatment are briefly summarised.

Phototheranostics of Splenic Myeloid-Derived Suppressor Cells and Its Impact on Spleen Metabolism in Tumor-Bearing Mice

(1) Background: MDSCs play an active role in the immune surveillance escape of cancer cells. Because MDSCs in mice are CD11b⁺Gr1⁺, near-infrared photoimmunotherapy (NIR-PIT) using the NIR dye IR700 conjugated to an MDSC-binding antibody provides an opportunity for targeted elimination of MDSCs. (2) Methods: The efficacy of Gr1-IR700-mediated NIR-PIT was evaluated in vitro using magnetically separated CD11b⁺Gr1⁺ MDSCs from spleens of 4T1-luc tumor-bearing (TB) mice. For in vivo evaluation, spleens of Gr1-IR700-injected 4T1-luc TB mice were irradiated with NIR light, and splenocyte viability was determined using CCK-8 assays. Metabolic profiling of NIR-PIT-irradiated spleens was performed using ¹H MRS. (3) Results: Flow cytometric analysis confirmed a ten-fold increase in splenic MDSCs in 4T1-luc TB mice. Gr1-IR700-mediated NIR-PIT eliminated tumor-induced splenic MDSCs in culture. Ex vivo fluorescence imaging revealed an 8- and 9-fold increase in mean fluorescence intensity (MFI) in the spleen and lungs of Gr1-IR700-injected compared to IgG-IR700-injected TB mice. Splenocytes from Gr1-IR700-injected TB mice exposed in vivo to NIR-PIT demonstrated significantly lower viability compared to no light exposure or untreated control groups. Significant metabolic changes were observed in spleens following NIR-PIT. (4) Conclusions: Our data confirm the ability of NIR-PIT to eliminate splenic MDSCs, identifying its potential to eliminate MDSCs in tumors to reduce immune suppression. The metabolic changes observed may identify potential biomarkers of splenic MDSC depletion as well as potential metabolic targets of MDSCs.

Targeted photoimmunotherapy for cancer

Photodynamic therapy (PDT) is a clinically approved procedure that can exert a curative action against malignant cells. The treatment implies the administration of a photoactive molecular species that, upon absorption of visible or near infrared light, sensitizes the formation of reactive oxygen species. These species are cytotoxic and lead to tumor cell death, damage vasculature, and induce inflammation. Clinical investigations demonstrated that PDT is curative and does not compromise other treatment options. One of the major limitations of the original method was the low selectivity of the photoactive compounds for malignant over healthy tissues. The development of conjugates with antibodies has endowed photosensitizing molecules with targeting capability, so that the compounds are delivered with unprecedented precision to the site of action. Given their fluorescence emission capability, these supramolecular species are intrinsically theranostic agents.

Exogenous Contrast Agents in Photoacoustic Imaging: An In Vivo Review for Tumor Imaging

The field of cancer theranostics has grown rapidly in the past decade and innovative 'biosmart' theranostic materials are being synthesized and studied to combat the fast growth of cancer metastases. While current state-of-the-art oncology imaging techniques have decreased mortality rates, patients still face a diminished quality of life due to treatment. Therefore, improved diagnostics are needed to define in vivo tumor growths on a molecular level to achieve image-guided therapies and tailored dosage needs. This review summarizes in vivo studies that utilize contrast agents within the field of photoacoustic imaging-a relatively new imaging modality-for tumor detection, with a special focus on imaging and transducer parameters. This paper also details the different types of contrast agents used in this novel diagnostic field, i.e., organic-based, metal/inorganic-based, and dye-based contrast agents. We conclude this review by discussing the challenges and future direction of photoacoustic imaging.

Triggering anti-GBM immune response with EGFR-mediated photoimmunotherapy

BACKGROUND

Surgical resection followed by chemo-radiation postpones glioblastoma (GBM) progression and extends patient survival, but these tumours eventually recur. Multimodal treatment plans combining intraoperative techniques that maximise tumour excision with therapies aiming to remodel the immunologically cold GBM microenvironment could improve patients' outcomes. Herein, we report that targeted photoimmunotherapy (PIT) not only helps to define tumour location and margins but additionally promotes activation of anti-GBM T cell response.

METHODS

EGFR-specific affibody molecule (ZEGFR:03115) was conjugated to IR700. The response to ZEGFR:03115-IR700-PIT was investigated in vitro and in vivo in GBM cell lines and xenograft model. To determine the tumour-specific immune response post-PIT, a syngeneic GBM model was used.

RESULTS

In vitro findings confirmed the ability of ZEGFR:03115-IR700 to produce reactive oxygen species upon light irradiation. ZEGFR:03115-IR700-PIT promoted immunogenic cell death that triggered the release of damage-associated molecular patterns (DAMPs) (calreticulin, ATP, HSP70/90, and HMGB1) into the medium, leading to dendritic cell maturation. In vivo, therapeutic response to light-activated conjugate was observed in brain tumours as early as 1 h post-irradiation. Staining of the brain sections showed reduced cell proliferation, tumour necrosis, and microhaemorrhage within PIT-treated tumours that corroborated MRI T2*w acquisitions. Additionally, enhanced immunological response post-PIT resulted in the attraction and activation of T cells in mice bearing murine GBM brain tumours.

CONCLUSIONS

Our data underline the potential of ZEGFR:03115-IR700 to accurately visualise EGFR-positive brain tumours and to destroy tumour cells post-conjugate irradiation turning an immunosuppressive tumour environment into an immune-vulnerable one.

EGFR-Targeted Photodynamic Therapy

The epidermal growth factor receptor (EGFR) plays a pivotal role in the proliferation and metastatization of cancer cells. Aberrancies in the expression and activation of EGFR are hallmarks of many human malignancies. As such, EGFR-targeted therapies hold significant potential for the cure of cancers. In recent years, photodynamic therapy (PDT) has gained increased interest as a non-invasive cancer treatment. In PDT, a photosensitizer is excited by light to produce reactive oxygen species, resulting in local cytotoxicity. One of the critical aspects of PDT is to selectively transport enough photosensitizers to the tumors environment. Accordingly, an increasing number of strategies have been devised to foster EGFR-targeted PDT. Herein, we review the recent nanobiotechnological advancements that combine the promise of PDT with EGFR-targeted molecular cancer therapy. We recapitulate the chemistry of the sensitizers and their modes of action in PDT, and summarize the advantages and pitfalls of different targeting moieties, highlighting future perspectives for EGFR-targeted photodynamic treatment of cancer.

Hyperpolarized 13C Magnetic Resonance Imaging as a Tool for Imaging Tissue Redox State, Oxidative Stress, Inflammation, and Cellular Metabolism

Significance: Magnetic resonance imaging (MRI) with hyperpolarized (HP) ¹³C-labeled redox-sensitive metabolic tracers can provide noninvasive functional imaging biomarkers, reflecting tissue redox state, oxidative stress, and inflammation, among others. The capability to use endogenous metabolites as ¹³C-enriched imaging tracers without structural modification makes HP ¹³C MRI a promising tool to evaluate redox state in patients with various diseases. Recent Advances: Recent studies have demonstrated the feasibility of in vivo metabolic imaging of ¹³C-labeled tracers polarized by parahydrogen-induced polarization techniques, which offer a cost-effective alternative to the more widely used dissolution dynamic nuclear polarization-based hyperpolarizers. Critical Issues: Although the fluxes of many metabolic pathways reflect the change in tissue redox state, they are not functionally specific. In the present review, we summarize recent challenges in the development of specific ¹³C metabolic tracers for biomarkers of redox state, including that for detecting reactive oxygen species. Future Directions: Applications of HP ¹³C metabolic MRI to evaluate redox state have only just begun to be investigated. The possibility to gain a comprehensive understanding of the correlations between tissue redox potential and metabolism under different pathological conditions by using HP ¹³C MRI is promoting its interest in the clinical arena, along with its noninvasive biomarkers to evaluate the extent of disease and treatment response.

Application of Multiparametric Magnetic Resonance Imaging to Monitor the Early Antitumor Effect of CuS@GOD Nanoparticles in a 4 T1 Breast Cancer Xenograft Model

BACKGROUND

We have developed hybrid nanoparticles (NPs) by co-loading copper sulfide (CuS) NPs and glucose oxidase (GOD) (CuS@GOD NPs) to explore their antitumor properties.

PURPOSE

To investigate the feasibility of using multiparametric magnetic resonance imaging (MRI) including intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) and R₂ * mapping to quantitatively assess the early antitumor effect of CuS@GOD NPs.

STUDY TYPE

Prospective.

ANIMAL MODEL

The orthotopic BALB/c mice 4 T1 breast cancer model. The 4 T1 xenografts in group 1 mice received normal saline, group 2 received CuS@GOD NPs, group 3 received CuS NPs plus laser, and group 4 received CuS@GOD NPs plus laser (n = 28 for each group).

FIELD STRENGTH/SEQUENCE

A 3.0 T/IVIM-DWI MRI single-shot echo-planar imaging, R₂ * mapping spoiled gradient recalled echo (SPGR) sequence, T2-weighted images (T2WI) and T1-weighted images (T1WI) fast spin echo (FSE) sequence.

ASSESSMENT

The IVIM-DWI and R₂ * mapping were performed before and after treatment at 0 hour, 0.5 hour, 1 hour, 2 hours, 4 hours, and 24 hours in four groups and the MRI parameters were obtained. Correlation analysis between the MRI parameters and histological analyses was conducted.

STATISTICAL TESTS

One-way ANOVA, Pearson's correlation analysis, two independent samples t test, intraclass correlation coefficient. P < 0.05 was considered to be statistically significant.

RESULTS

In group 4, the tumoral D value was significantly higher than that of group 2 at 24 hours (0.541 ± 0.065 vs. 0.492 ± 0.051). The f value of group 4 was significantly lower than that of groups 1 and 2 at 2 hours (10.83 ± 2.16 vs. 14.28 ± 1.86, 16.67 ± 3.53, respectively). The R₂ * value was significantly increased at 0 hour in group 4 compared to that of groups 1 and 2 (64.552 ± 4.663 vs. 42.441 ± 1.516, 43.165 ± 1.709, respectively). D, f, and R₂ * were correlated with the histological staining results (r = 0.695-0.970).

DATA CONCLUSION

The IVIM-DWI-derived D and f and R₂ * mapping-derived R₂ * could monitor early response to CuS@GOD NPs treatment in vivo.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Virus-Like Particle-Drug Conjugates Induce Protective, Long-lasting Adaptive Antitumor Immunity in the Absence of Specifically Targeted Tumor Antigens

This study examined the ability of a papillomavirus-like particle drug conjugate, belzupacap sarotalocan (AU-011), to eradicate subcutaneous tumors after intravenous injection and to subsequently elicit long-term antitumor immunity in the TC-1 syngeneic murine tumor model. Upon in vitro activation with near-infrared light (NIR), AU-011-mediated cell killing was proimmunogenic in nature, resulting in the release of damage-associated molecular patterns such as DNA, ATP, and HMGB-1, activation of caspase-1, and surface relocalization of calreticulin and HSP70 on killed tumor cells. A single in vivo administration of AU-011 followed by NIR caused rapid cell death, leading to long-term tumor regression in ∼50% of all animals. Within hours of treatment, calreticulin surface expression, caspase-1 activation, and depletion of immunosuppressive leukocytes were observed in tumors. Combination of AU-011 with immune-checkpoint inhibitor antibodies, anti-CTLA-4 or anti-PD-1, improved therapeutic efficacy, resulting in 70% to 100% complete response rate that was durable 100 days after treatment, with 50% to 80% of those animals displaying protection from secondary tumor rechallenge. Depletion of CD4⁺ or CD8⁺ T cells, either at the time of AU-011 treatment or secondary tumor rechallenge of tumor-free mice, indicated that both cell populations are vital to AU-011's ability to eradicate primary tumors and induce long-lasting antitumor protection. Tumor-specific CD8⁺ T-cell responses could be observed in circulating peripheral blood mononuclear cells within 3 weeks of AU-011 treatment. These data, taken together, support the conclusion that AU-011 has a direct cytotoxic effect on tumor cells and induces long-term antitumor immunity, and this activity is enhanced when combined with checkpoint inhibitor antibodies.

Multimodal Molecular Imaging Detects Early Responses to Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) has become a standard therapy for several cancers, however, the response to ICB is inconsistent and a method for noninvasive assessment has not been established to date. To investigate the capability of multimodal imaging to evaluate treatment response to ICB therapy, hyperpolarized ¹³C MRI using [1-¹³C] pyruvate and [1,4-¹³C2] fumarate and dynamic contrast enhanced (DCE) MRI was evaluated to detect early changes in tumor glycolysis, necrosis, and intratumor perfusion/permeability, respectively. Mouse tumor models served as platforms for high (MC38 colon adenocarcinoma) and low (B16-F10 melanoma) sensitivity to dual ICB of PD-L1 and CTLA4. Glycolytic flux significantly decreased following treatment only in the less sensitive B16-F10 tumors. Imaging [1,4-¹³C2] fumarate conversion to [1,4-¹³C2] malate showed a significant increase in necrotic cell death following treatment in the ICB-sensitive MC38 tumors, with essentially no change in B16-F10 tumors. DCE-MRI showed significantly increased perfusion/permeability in MC38-treated tumors, whereas a similar, but statistically nonsignificant, trend was observed in B16-F10 tumors. When tumor volume was also taken into consideration, each imaging biomarker was linearly correlated with future survival in both models. These results suggest that hyperpolarized ¹³C MRI and DCE MRI may serve as useful noninvasive imaging markers to detect early response to ICB therapy. SIGNIFICANCE: Hyperpolarized ¹³C MRI and dynamic contrast enhanced MRI in murine tumor models provide useful insight into evaluating early response to immune checkpoint blockade therapy.See related commentary by Cullen and Keshari, p. 3444.

Imaging Cell Death: Focus on Early Evaluation of Tumor Response to Therapy

Cell death plays a prominent role in the treatment of cancer, because most anticancer therapies act by the induction of cell death including apoptosis, necrosis, and other pathways of cell death. Imaging cell death helps to identify treatment responders from nonresponders and thus enables patient-tailored therapy, which will increase the likelihood of treatment response and ultimately lead to improved patient survival. By taking advantage of molecular probes that specifically target the biomarkers/biochemical processes of cell death, cell death imaging can be successfully achieved. In recent years, with the increased understanding of the molecular mechanism of cell death, a variety of well-defined biomarkers/biochemical processes of cell death have been identified. By targeting these established cell death biomarkers/biochemical processes, a set of molecular imaging probes have been developed and evaluated for early monitoring treatment response in tumors. In this review, we mainly present the recent advances in identifying useful biomarkers/biochemical processes for both apoptosis and necrosis imaging and in developing molecular imaging probes targeting these biomarkers/biochemical processes, with a focus on their application in early evaluation of tumor response to therapy.

Direct and indirect assessment of cancer metabolism explored by MRI

Magnetic resonance-based approaches to obtain metabolic information on cancer have been explored for decades. Electron paramagnetic resonance (EPR) has been developed to pursue metabolic profiling and successfully used to monitor several physiologic parameters such as pO₂ , pH, and redox status. All these parameters are associated with pathophysiology of various diseases. Especially in oncology, cancer hypoxia has been intensively studied because of its relationship with metabolic alterations, acquiring treatment resistance, or a malignant phenotype. Thus, pO₂ imaging leads to an indirect metabolic assessment in this regard. Proton electron double-resonance imaging (PEDRI) is an imaging technique to visualize EPR by using the Overhauser effect. Most biological parameters assessed in EPR can be visualized using PEDRI. However, EPR and PEDRI have not been evaluated sufficiently for clinical application due to limitations such as toxicity of the probes or high specific absorption rate. Hyperpolarized (HP) ¹³ C MRI is a novel imaging technique that can directly visualize the metabolic profile. Production of metabolites of the HP ¹³ C probe delivered to target tissue are evaluated in this modality. Unlike EPR or PEDRI, which require the injection of radical probes, ¹³ C MRI requires a probe that can be physiologically metabolized and efficiently hyperpolarized. Among several methods for hyperpolarizing probes, dissolution dynamic nuclear hyperpolarization is a widely used technique for in vivo imaging. Pyruvate is the most suitable probe for HP ¹³ C MRI because it is part of the glycolytic pathway and the high efficiency of pyruvate-to-lactate conversion is a distinguishing feature of cancer. Its clinical applicability also makes it a promising metabolic imaging modality. Here, we summarize the applications of these indirect and direct MR-based metabolic assessments focusing on pO₂ and pyruvate-to-lactate conversion. The two parameters are strongly associated with each other, hence the acquired information is potentially interchangeable when evaluating treatment response to oxygen-dependent cancer therapies.

Photoimmunoconjugates: novel synthetic strategies to target and treat cancer by photodynamic therapy

Photodynamic therapy (PDT) combines a photosensitizer (PS) with the physical energy of non-ionizing light to trigger cell death pathways. PDT has potential as a therapeutic modality to be used in alternative or in combination with other conventional cancer treatment protocols (e.g. surgery, chemotherapy and radiotherapy). Still, due to the lack of specificity of the current PSs to target the tumor cells, several studies have exploited their conjugation with targeting moieties. PSs conjugated with antibodies (Abs) or their fragments, able to bind antigens overexpressed in the tumors, have demonstrated potential in PDT of tumors. This review provides an overview of the most recent advances on photoimmunoconjugates (PICs) for cancer PDT, which involve the first and second-generation PSs conjugated to Abs. This is an update of our previous review "Antibodies armed with photosensitizers: from chemical synthesis to photobiological applications", published in 2015 in Org. Biomol. Chem.

Imaging of Metastatic Cancer Cells in Sentinel Lymph Nodes using Affibody Probes and Possibility of a Theranostic Approach

The accurate detection of lymph node metastases is essential for treatment success in early-stage malignant cancer. Sentinel lymph node (SLN) biopsy is the most effective procedure for detecting small or micrometastases that are undetectable by conventional imaging modalities. To demonstrate a new approach for developing a more efficient SLN biopsy procedure, we reported a two-stage imaging method combining lymphoscintigraphy and near-infrared (NIR) fluorescence imaging to depict metastatic cancer cells in SLNs in vivo. Furthermore, the theranostic potential of the combined procedure was examined by cell culture and xenograft mouse model. Anti-HER2 and anti-epidermal growth factor receptor (EGFR) affibody probes were used for NIR fluorescence imaging. Strong NIR fluorescence signal intensity of the anti-EGFR affibody probe was observed in SAS cells (EGFR positive). Radioactivity in the SLNs was clearly observed in the in vivo studies. High anti-EGFR affibody NIR fluorescence intensity was observed in the metastatic lymph nodes in mice. The addition of the IR700-conjugated anti-EGFR affibody to the culture medium decreased the proliferation of SAS cells. Decreased proliferation was shown in Ki-67 immunohistochemistry in xenograft tumors. Our data suggest that a two-stage combined imaging method using lymphoscintigraphy and affibody probes may offer the direct visualization of metastatic lymph nodes as an easily applied technique in SLN biopsy. Although further animal studies are required to assess the effect of treating lymphatic metastasis in this approach, our study results provide a foundation for the further development of this promising imaging and treatment strategy for earlier lymph node metastasis detection and treatment.