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Key Points Fluorescence imaging can transform the way surgeries are performed, through the intraoperative identification of vital structures, lymph nodes and cancer in real time Near-infrared (NIR) fluorescence is particularly advantageous for use in clinical settings owing to improved depth penetration and low autofluorescence in the NIR wavelength range compared with shorter wavelengths Many targeted NIR fluorophores are currently in preclinical development; however, no cancer-targeted NIR fluorophores or devices for intraoperative NIR fluorescence detection of cancer have received commercial approval for human use Multiple early phase clinical trials are underway to evaluate targeted fluorophores for real-time, intraoperative cancer detection in humans The use of targeted fluorophores for the intraoperative detection of cancer might improve survival rates and functional outcomes in patients with cancer Currently, substantial regulatory challenges and clinical trial considerations constitute barriers for the adoption of fluorescence-guided surgery in clinical settings Intraoperative fluorescence enables highly specific real-time detection of tumours at the time of surgery. In particular, near-infrared (NIR) fluorescence is a promising tool currently being tested in clinical settings. Zhang et al . discuss the latest developments in NIR fluorophores, cancer-targeting strategies, and detection instrumentation for intraoperative cancer detection, as well as the challenges associated with their effective application in clinical settings. Over the past two decades, synergistic innovations in imaging technology have resulted in a revolution in which a range of biomedical applications are now benefiting from fluorescence imaging. Specifically, advances in fluorophore chemistry and imaging hardware, and the identification of targetable biomarkers have now positioned intraoperative fluorescence as a highly specific real-time detection modality for surgeons in oncology. In particular, the deeper tissue penetration and limited autofluorescence of near-infrared (NIR) fluorescence imaging improves the translational potential of this modality over visible-light fluorescence imaging. Rapid developments in fluorophores with improved characteristics, detection instrumentation, and targeting strategies led to the clinical testing in the early 2010s of the first targeted NIR fluorophores for intraoperative cancer detection. The foundations for the advances that underline this technology continue to be nurtured by the multidisciplinary collaboration of chemists, biologists, engineers, and clinicians. In this Review, we highlight the latest developments in NIR fluorophores, cancer-targeting strategies, and detection instrumentation for intraoperative cancer detection, and consider the unique challenges associated with their effective application in clinical settings.

Murine syngeneic tumor models have revealed efficacious systemic antitumor responses following primary tumor in situ vaccination combined with targeted radionuclide therapy to secondary or metastatic tumors. Here we present studies on the safety and feasibility of this approach in a relevant translational companion dog model (n = 17 dogs) with advanced cancer. The three component of the combination immuno-radiotherapy approach were employed either separately or in combination in companion dogs with advanced stage cancer. In situ vaccination was achieved through the administration of hypofractionated external beam radiotherapy and intratumoral hu14.18-IL2 fusion immunocytokine injections to the index tumor. In situ vaccination was subsequently combined with targeted radionuclide therapy using a theranostic pairing of IV 86Y-NM600 (for PET imaging and subject-specific dosimetry) and IV 90Y-NM600 (therapeutic radionuclide) prescribed to deliver an immunomodulatory 2 Gy dose to all metastatic sites in companion dogs with metastatic melanoma or osteosarcoma. In a subset of dogs, immunologic parameters preliminarily assessed. The components of the immuno-radiotherapy combination were well tolerated either alone or in combination, resulting in only transient low grade (1 or 2) adverse events with no dose-limiting events observed. In subject-specific dosimetry analyses, we observed 86Y-NM600 tumor:bone marrow absorbed-dose differential uptakes ≥2 in 4 of 5 dogs receiving the combination, which allowed subsequent safe delivery of at least 2 Gy 90Y-NM600 TRT to tumors. NanoString gene expression profiling and immunohistochemistry from pre- and post-treatment biopsy specimens provide evidence of tumor microenvironment immunomodulation by 90Y-NM600 TRT. The combination of external beam radiotherapy, intratumoral immunocytokine, and targeted radionuclide immuno-radiotherapy known to have activity against syngeneic melanoma in murine models is feasible and well tolerated in companion dogs with advanced stage, spontaneously arising melanoma or osteosarcoma and has immunomodulatory potential. Further studies evaluating the dose-dependent immunomodulatory effects of this immuno-radiotherapy combination are currently ongoing.

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.

Radiopharmaceutical therapy (RPT) synergises with immune checkpoint inhibitors (ICI), but comparison of immunomodulation by different radioisotopes is lacking. Here, we evaluate mechanisms of response and timing of ICI administration relative to α- ( 225 Ac) and β-emitting ( 90 Y, 177 Lu) radioisotope therapy, coupled with alkylphosphocholine NM600, when combined with dual (anti-PD-L1 and anti-CTLA4) ICI, using syngeneic poorly immunogenic (B78 and Myc-CaP) and immunogenic (MC38) murine models. Regardless of the isotope, RPT delivering 2 Gy mean tumor dose promotes tumor regression and improves survival in B78 or MC38 tumor-bearing mice when combined with early ICI administration. Greatest anti-tumor responses are seen in MC38 to 90 Y-NM600 + ICI and in B78 and Myc-CaP to 225 Ac-NM600 + ICI. Flow cytometry and single-cell RNA and T cell receptor sequencing reveal that, combined with ICI, β-emitting radioisotopes expand existing adaptive immunity, whereas α-emitting radiopharmaceuticals initiate immune priming. Thus, appropriate application of α- or β-emitting RPT in combination with ICI achieves distinct antitumor immune responses. Preclinical studies indicate a synergistic effect of radiotherapy treatment (RT) and Immune checkpoint inhibitors (ICI) on tumor growth and metastasis. However, little is known about the immunomodulatory performance of different radioisotopes on the tumor microenvironment. Here, the authors employ alpha- versus beta-particle emitting radiopharmaceuticals in combination with dual ICI therapy and dissect mechanisms of in vivo immunomodulation and timing of ICI administration relative to RT, by comparing responses in immunogenic and non-immunogenic preclinical mouse models.

Clinical interest in combining targeted radionuclide therapies (TRT) with immunotherapies is growing. External beam radiation therapy (EBRT) activates a type 1 interferon (IFN1) response mediated via stimulator of interferon genes (STING), and this is critical to its therapeutic interaction with immune checkpoint blockade. However, little is known about the time course of IFN1 activation after EBRT or whether this may be induced by decay of a TRT source. We examined the IFN1 response and expression of immune susceptibility markers in B78 and B16 melanomas and MOC2 head and neck cancer murine models using qPCR and western blot. For TRT, we used Y chelated to NM600, an alkylphosphocholine analog that exhibits selective uptake and retention in tumor cells including B78 and MOC2. We observed significant IFN1 activation in all cell lines, with peak activation in B78, B16, and MOC2 cell lines occurring 7, 7, and 1 days, respectively, following RT for all doses. This effect was STING-dependent. Select IFN response genes remained upregulated at 14 days following RT. IFN1 activation following STING agonist treatment was identical to RT suggesting time course differences between cell lines were mediated by STING pathway kinetics and not DNA damage susceptibility. delivery of EBRT and TRT to B78 and MOC2 tumors resulted in a comparable time course and magnitude of IFN1 activation. In the MOC2 model, the combination of Y-NM600 and dual checkpoint blockade therapy reduced tumor growth and prolonged survival compared to single agent therapy and cumulative dose equivalent combination EBRT and dual checkpoint blockade therapy. We report the time course of the STING-dependent IFN1 response following radiation in multiple murine tumor models. We show the potential of TRT to stimulate IFN1 activation that is comparable to that observed with EBRT and this may be critical to the therapeutic integration of TRT with immunotherapies.

Radiation therapy can modulate the tumor microenvironment (TME), influencing antitumor immune responses. This study compared the immunomodulatory effects of alpha-emitting ( Ac) and beta-emitting ( Lu) radiopharmaceutical therapies (RPT) using NM600 in murine prostate cancer models. We assessed immunological changes in TRAMP-C1 and Myc-CaP tumor models treated with Ac-NM600 or Lu-NM600. Flow cytometry was used to profile immune cell populations, activation markers, and checkpoint molecules, while multiplex assays analyzed cytokine and chemokine expression. In general, Ac-NM600 elicited stronger immunomodulatory effects than Lu-NM600, including cell line dependent increased CD8/Treg ratios, activation of effector and memory T cells, and depletion of suppressive Tregs and MDSCs. The treatment elevated Th1 cytokines, pro-inflammatory chemokines, and checkpoint molecules like PD-1 on CD8+ T cells and PD-L1 on MDSCs, creating a more \"hot\" TME. Alpha-emitting Ac-NM600 demonstrated superior ability to enhance antitumor immunity compared to beta-emitting Lu-NM600. These findings support the use of Ac-NM600 in combination with immunotherapies for advanced prostate cancer treatment.

RationaleAndrogen deprivation therapy (ADT) is pivotal in treating recurrent prostate cancer and is often combined with external beam radiation therapy (EBRT) for localized disease. However, for metastatic castration-resistant prostate cancer, EBRT is typically only used in the palliative setting, because of the inability to radiate all sites of disease. Systemic radiation treatments that preferentially irradiate cancer cells, known as radiopharmaceutical therapy or targeted radionuclide therapy (TRT), have demonstrable benefits for treating metastatic prostate cancer. Here, we explored the use of a novel TRT, 90Y-NM600, specifically in combination with ADT, in murine prostate tumor models.Methods6-week-old male FVB mice were implanted subcutaneously with Myc-CaP tumor cells and given a single intravenous injection of 90Y-NM600, in combination with ADT (degarelix). The combination and sequence of administration were evaluated for effect on tumor growth and infiltrating immune populations were analyzed by flow cytometry. Sera were assessed to determine treatment effects on cytokine profiles.ResultsADT delivered prior to TRT (ADT→TRT) resulted in significantly greater antitumor response and overall survival than if delivered after TRT (TRT→ADT). Studies conducted in immunodeficient NRG mice failed to show a difference in treatment sequence, suggesting an immunological mechanism. Myeloid-derived suppressor cells (MDSCs) significantly accumulated in tumors following TRT→ADT treatment and retained immune suppressive function. However, CD4+ and CD8+ T cells with an activated and memory phenotype were more prevalent in the ADT→TRT group. Depletion of Gr1+MDSCs led to greater antitumor response following either treatment sequence. Chemotaxis assays suggested that tumor cells secreted chemokines that recruited MDSCs, notably CXCL1 and CXCL2. The use of a selective CXCR2 antagonist, reparixin, further improved antitumor responses and overall survival when used in tumor-bearing mice treated with TRT→ADT.ConclusionThe combination of ADT and TRT improved antitumor responses in murine models of prostate cancer, however, this was dependent on the order of administration. This was found to be associated with one treatment sequence leading to an increase in infiltrating MDSCs. Combining treatment with a CXCR2 antagonist improved the antitumor effect of this combination, suggesting a possible approach for treating advanced human prostate cancer.

BackgroundSystemic radiation treatments that preferentially irradiate cancer cells over normal tissue, known as targeted radionuclide therapy (TRT), have shown significant potential for treating metastatic prostate cancer. Preclinical studies have demonstrated the ability of external beam radiation therapy (EBRT) to sensitize tumors to T cell checkpoint blockade. Combining TRT approaches with immunotherapy may be more feasible than combining with EBRT to treat widely metastatic disease, however the effects of TRT on the prostate tumor microenvironment alone and in combinfation with checkpoint blockade have not yet been studied.MethodsC57BL/6 mice-bearing TRAMP-C1 tumors and FVB/NJ mice-bearing Myc-CaP tumors were treated with a single intravenous administration of either low-dose or high-dose 90Y-NM600 TRT, and with or without anti-PD-1 therapy. Groups of mice were followed for tumor growth while others were used for tissue collection and immunophenotyping of the tumors via flow cytometry.Results90Y-NM600 TRT was safe at doses that elicited a moderate antitumor response. TRT had multiple effects on the tumor microenvironment including increasing CD8 +T cell infiltration, increasing checkpoint molecule expression on CD8 +T cells, and increasing PD-L1 expression on myeloid cells. However, PD-1 blockade with TRT treatment did not improve antitumor efficacy. Tregs remained functional up to 1 week following TRT, but CD8 +T cells were not, and the suppressive function of Tregs increased when anti-PD-1 was present in in vitro studies. The combination of anti-PD-1 and TRT was only effective in vivo when Tregs were depleted.ConclusionsOur data suggest that the combination of 90Y-NM600 TRT and PD-1 blockade therapy is ineffective in these prostate cancer models due to the activating effect of anti-PD-1 on Tregs. This finding underscores the importance of thorough understanding of the effects of TRT and immunotherapy combinations on the tumor immune microenvironment prior to clinical investigation.

We have previously described the remarkable capacity of radioiodinated alkyl phospholipids to be sequestered and retained by a variety of tumors in vivo. We have already established the influence of certain structural parameters of iodinated alkyl phospholipids on tumor avidity, such as stereochemistry at the sn-2 carbon of alkylglycerol phosphocholines, meta-or para-position of iodine in the aromatic ring of phenylalkyl phosphocholines, and the length of the alkyl chain in alkyl phospholipids. In order to determine the additional structural requirements for tumor uptake and retention, three new radioiodinated alkylphospholipid analogs, 2–4, were synthesized as potential tumor imaging agents. Polar head groups were modified to determine structure-tumor avidity relationships. The trimethylammonio group in 1 was substituted with a hydrogen atom in 2, an ammonio group in 3 and a tertiary butyl group in 4. All analogs were separately labeled with iodine-125 or iodine-124 and administered to Walker 256 tumor-bearing rats or human PC-3 tumor-bearing SCID mice, respectively. Tumor uptake was assessed by gamma-camera scintigraphy (for [I-125]-labeled compounds) and high-resolution micro-PET scanning (for [I-124]-labeled compounds). It was found that structural modifications in the polar head group of alkyl phospholipids strongly influenced the tumor uptake and tissue distribution of these compounds in tumor-bearing animals. Phosphoethanolamine analog 3 (NM401) displayed a very slight accumulation in tumor as compared with phosphocholine analog 1 (NM346). Analogs 2 (NM400) and 4 (NM402) lacking the positively charged nitrogen atom failed to display any tumor uptake and localized primarily in the liver. This study provided important insights regarding structural requirements for tumor uptake and retention. Replacement of the quaternary nitrogen in the alkyl phospholipid head group with non-polar substituents resulted in loss of tumor avidity.

BackgroundThe antitumor effects of external beam radiation therapy (EBRT) are mediated, in part, by an immune response. We have reported that a single fraction of 12 Gy EBRT combined with intratumoral anti-GD2 hu14.18-IL2 immunocytokine (IC) generates an effective in situ vaccine (ISV) against GD2-positive murine tumors. This ISV is effective in eradicating single tumors with sustained immune memory; however, it does not generate an adequate abscopal response against macroscopic distant tumors. Given the immune-stimulatory capacity of radiation therapy (RT), we hypothesized that delivering RT to all sites of disease would augment systemic antitumor responses to ISV.MethodsWe used a syngeneic B78 murine melanoma model consisting of a ‘primary’ flank tumor and a contralateral smaller ‘secondary’ flank tumor, treated with 12 Gy EBRT and intratumoral IC immunotherapy to the primary and additional EBRT to the secondary tumor. As a means of delivering RT to all sites of disease, both known and occult, we also used a novel alkylphosphocholine analog, NM600, conjugated to 90Y as a targeted radionuclide therapy (TRT). Tumor growth, overall survival, and cause of death were measured. Flow cytometry was used to evaluate immune population changes in both tumors.ResultsAbscopal effects of local ISV were amplified by delivering as little as 2–6 Gy of EBRT to the secondary tumor. When the primary tumor ISV regimen was delivered in mice receiving 12 Gy EBRT to the secondary tumor, we observed improved overall survival and more disease-free mice with immune memory compared with either ISV or 12 Gy EBRT alone. Similarly, TRT combined with ISV resulted in improved overall survival and a trend towards reduced tumor growth rates when compared with either treatment alone. Using flow cytometry, we identified an influx of CD8+ T cells with a less exhausted phenotype in both the ISV-targeted primary and the distant secondary tumor following the combination of secondary tumor EBRT or TRT with primary tumor ISV.ConclusionsWe report a novel use for low-dose RT, not as a direct antitumor modality but as an immunomodulator capable of driving and expanding antitumor immunity against metastatic tumor sites following ISV.