Immunophenotyping Reveals Longitudinal Changes in Circulating Immune Cells During Radium-223 Therapy in Patients With Metastatic Castration-Resistant Prostate Cancer

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.

Association between the Immunophenotype of Peripheral Blood from mCRPC Patients and the Outcomes of Radium-223 Treatment

(1) Background: Prostate cancer is the second most common cancer in men, with androgen suppression as the standard treatment. Despite initially responding to castration, most metastatic prostate cancer patients eventually experience progression. In these cases, Radium-223 is the chosen treatment. We hypothesized that the immunophenotype of circulating leukocytes conditions the response to Radium-223 treatment. (2) Material and Methods: In this prospective study, we collected peripheral blood from twelve mCRPC patients and nine healthy donors before (baseline) and during treatment with Radium-223. Immunophenotyping and the percentages of leukocyte-platelet complexes were determined by flow cytometry. The increments or decrements of leukocyte subsets between the baseline and the second Radium-223 injection were also calculated. (3) Results: At baseline, the mCRPC patients had a lower percentages of CD4⁺ T cells and B cells and higher percentages of NK and neutrophils than the HDs. In addition, they had more OX40⁺ CD4⁺ T cells, PD-L1⁺ CD8^low cells, PD-L1⁺ B cells, PD-L1⁺ NK cells, and monocyte-platelet complexes than the HDs. Moreover, patients with slow and fast progression had different percentages of PD-L1⁺ CD8⁺ T cells. In particular, slow progression patients underwent an increment of PD-L1⁺ CD8⁺ T cells after two cycles of Radium-223. (4) Conclusions: The characterization of circulating immune cells before initiating Radium-223 treatment could become a non-invasive indicator of the response.

Immunomodulatory effects of targeted radionuclide therapy

It is now clear that conventional radiation therapy can reinstate cell death immunogenicity. Recent preclinical data indicate that targeted radionuclide therapy that irradiate tumors at continuous low dose rate also can elicit immunostimulatory effects and represents a promising strategy to circumvent immune checkpoint inhibitor resistance. In this perspective, we discuss the accumulating preclinical and clinical data suggesting that activation of the immune system through the cGAS-STING axis and the release of extracellular vesicles by irradiated cells, participate to this antitumor immunity. This should need to be considered for adapting clinical practices to state of the art of the radiobiology and to increase targeted radionuclide therapy effectiveness.

Radiopharmaceuticals heat anti-tumor immunity

Radiopharmaceutical therapy (RPT) has proven to be an effective cancer treatment with minimal toxicity. With several RPT agents approved by FDA, the remarkable potential of this therapy is now being recognized, and the anti-tumor immunity induced by RPT is beginning to be noticed. This review evaluates the potential of RPT for immune activation, including promoting the release of danger associated-molecular pattern molecules that recruit inflammatory cells into the tumor microenvironment, and activating antigen-presenting cells and cytotoxic T cells. We also discuss the progress of combining RPT with immunotherapy to increase efficacy.

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.

Combining Targeted Radionuclide Therapy and Immune Checkpoint Inhibition for Cancer Treatment

The development of immunotherapy, in particular immune checkpoint inhibitors (ICI), has revolutionized cancer treatment in the past decades. However, its efficacy is still limited to subgroups of patients with cancer. Therefore, effective treatment combination strategies are needed. Here, radiotherapy is highly promising, as it can induce immunogenic cell death, triggering the release of pro-inflammatory cytokines, thereby creating an immunogenic phenotype and sensitizing tumors to ICI. Recently, targeted radionuclide therapy (TRT) has attained significant interest for cancer treatment. In this approach, a tumor-targeting radiopharmaceutical is used to specifically deliver a therapeutic radiation dose to all tumor cells, including distant metastatic lesions, while limiting radiation exposure to healthy tissue. However, fundamental differences between TRT and conventional radiotherapy make it impossible to directly extrapolate the biological effects from conventional radiotherapy to TRT. In this review, we present a comprehensive overview of studies investigating the immunomodulatory effects of TRT and the efficacy of combined TRT-ICI treatment. Preclinical studies have evaluated a variety of murine cancer models in which α- or β-emitting radionuclides were directed to a diverse set of targets. In addition, clinical trials are ongoing to assess safety and efficacy of combined TRT-ICI in patients with cancer. Taken together, research indicates that combining TRT and ICI might improve therapeutic response in patients with cancer. Future research has to disclose what the optimal conditions are in terms of dose and treatment schedule to maximize the efficacy of this combined approach.