Mesothelin-Targeted Thorium-227 Conjugate (MSLN-TTC): Preclinical Evaluation of a New Targeted Alpha Therapy for Mesothelin-Positive Cancers

Chimeric antigen receptor-immune cells against solid tumors: Structures, mechanisms, recent advances, and future developments

ABSTRACT

The advent of chimeric antigen receptor (CAR)-T cell immunotherapies has led to breakthroughs in the treatment of hematological malignancies. However, their success in treating solid tumors has been limited. CAR-natural killer (NK) cells have several advantages over CAR-T cells because NK cells can be made from pre-existing cell lines or allogeneic NK cells with a mismatched major histocompatibility complex (MHC), which means they are more likely to become an "off-the-shelf" product. Moreover, they can kill cancer cells via CAR-dependent/independent pathways and have limited toxicity. Macrophages are the most malleable immune cells in the body. These cells can efficiently infiltrate into tumors and are present in large numbers in tumor microenvironments (TMEs). Importantly, CAR-macrophages (CAR-Ms) have recently yielded exciting preclinical results in several solid tumors. Nevertheless, CAR-T, CAR-NK, and CAR-M all have their own advantages and limitations. In this review, we systematically discuss the current status, progress, and the major hurdles of CAR-T cells, CAR-NK cells, and CAR-M as they relate to five aspects: CAR structure, therapeutic mechanisms, the latest research progress, current challenges and solutions, and comparison according to the existing research in order to provide a reasonable option for treating solid tumors in the future.

Preclinical Efficacy of a PSMA-Targeted Actinium-225 Conjugate (225Ac-Macropa-Pelgifatamab): A Targeted Alpha Therapy for Prostate Cancer

PURPOSE

Initially, prostate cancer responds to hormone therapy, but eventually resistance develops. Beta emitter-based prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs.

EXPERIMENTAL DESIGN

The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide.

RESULTS

Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi; all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models.

CONCLUSIONS

These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase I study has been initiated (NCT06052306).

Targeted Therapy in Mesotheliomas: Uphill All the Way

Mesothelioma (MM) is an aggressive and lethal disease with few therapeutic opportunities. Platinum-pemetrexed chemotherapy is the backbone of first-line treatment for MM. The introduction of immunotherapy (IO) has been the only novelty of the last decades, allowing an increase in survival compared to standard chemotherapy (CT). However, IO is not approved for epithelioid histology in many countries. Therefore, therapy for relapsed MM remains an unmet clinical need, and the prognosis of MM remains poor, with an average survival of only 18 months. Increasing evidence reveals MM complexity and heterogeneity, of which histological classification fails to explain. Thus, scientific focus on possibly new molecular markers or cellular targets is increasing, together with the search for target therapies directed towards them. The molecular landscape of MM is characterized by inactivating tumor suppressor alterations, the most common of which is found in CDKN2A, BAP1, MTAP, and NF2. In addition, cellular targets such as mesothelin or metabolic enzymes such as ASS1 could be potentially amenable to specific therapies. This review examines the major targets and relative attempts of therapeutic approaches to provide an overview of the potential prospects for treating this rare neoplasm.

Adoptive cell therapy for solid tumors beyond CAR-T: Current challenges and emerging therapeutic advances

Adoptive cellular immunotherapy using immune cells expressing chimeric antigen receptors (CARs) is a highly specific anti-tumor immunotherapy that has shown promise in the treatment of hematological malignancies. However, there has been a slow progress toward the treatment of solid tumors owing to the complex tumor microenvironment that affects the localization and killing ability of the CAR cells. Solid tumors with a strong immunosuppressive microenvironment and complex vascular system are unaffected by CAR cell infiltration and attack. To improve their efficacy toward solid tumors, CAR cells have been modified and upgraded by "decorating" and "pruning". This review focuses on the structure and function of CARs, the immune cells that can be engineered by CARs and the transformation strategies to overcome solid tumors, with a view to broadening ideas for the better application of CAR cell therapy for the treatment of solid tumors.

Nano-radiopharmaceuticals as therapeutic agents

In recent years, there has been an increased interest in exploring the potential synergy between nanotechnology and nuclear medicine. The application of radioactive isotopes, commonly referred to as radiopharmaceuticals, is recognized in nuclear medicine for diagnosing and treating various diseases. Unlike conventional pharmaceutical agents, radiopharmaceuticals are designed to work without any pharmacological impact on the body. Nevertheless, the radiation dosage employed in radiopharmaceuticals is often sufficiently high to elicit adverse effects associated with radiation exposure. Exploiting their capacity for selective accumulation on specific organ targets, radiopharmaceuticals have utility in treating diverse disorders. The incorporation of nanosystems may additionally augment the targeting capability of radiopharmaceuticals, leveraging their distinct pharmacokinetic characteristics. Conversely, radionuclides could be used in research to assess nanosystems pharmacologically. However, more investigation is needed to verify the safety and effectiveness of radiopharmaceutical applications mediated by nanosystems. The use of nano-radiopharmaceuticals as therapeutic agents to treat various illnesses and disorders is majorly covered in this review. The targeted approach to cancer therapy and various types of nanotools for nano-radiopharmaceutical delivery, is also covered in this article.

Novel HER-2 Targeted Therapies in Breast Cancer

Human epidermal growth factor 2 (HER-2)-positive breast cancer represents 15-20% of all breast cancer subtypes and has an aggressive biological behavior with worse prognosis. The development of HER-2-targeted therapies has changed the disease's course, having a direct impact on survival rates and quality of life. Drug development of HER-2-targeting therapies is a prolific field, with numerous new therapeutic strategies showing survival benefits and gaining regulatory approval in recent years. Furthermore, the acknowledgement of the survival impact of HER-2-directed therapies on HER-2-low breast cancer has contributed even more to advances in the field. The present review aims to summarize the newly approved therapeutic strategies for HER-2-positive breast cancer and review the new and exploratory HER-2-targeted therapies currently under development.

Macrocyclic 1,2-Hydroxypyridinone-Based Chelators as Potential Ligands for Thorium-227 and Zirconium-89 Radiopharmaceuticals

Thorium-227 (227Th) is an α-emitting radionuclide that has shown preclinical and clinical promise for use in targeted α-therapy (TAT), a type of molecular radiopharmaceutical treatment that harnesses high energy α particles to eradicate cancerous lesions. Despite these initial successes, there still exists a need for bifunctional chelators that can stably bind thorium in vivo. Toward this goal, we have prepared two macrocyclic chelators bearing 1,2-hydroxypyridinone groups. Both chelators can be synthesized in less than six steps from readily available starting materials, which is an advantage over currently available platforms. The complex formation constants (log βmlh) of these ligands with Zr4+ and Th4+, measured by spectrophotometric titrations, are greater than 34 for both chelators, indicating the formation of exceedingly stable complexes. Radiolabeling studies were performed to show that these ligands can bind [227Th]Th4+ at concentrations as low as 10-6 M, and serum stability experiments demonstrate the high kinetic stability of the formed complexes under biological conditions. Identical experiments with zirconium-89 (89Zr), a positron-emitting radioisotope used for positron emission tomography (PET) imaging, demonstrate that these chelators can also effectively bind Zr4+ with high thermodynamic and kinetic stability. Collectively, the data reported herein highlight the suitability of these ligands for use in 89Zr/227Th paired radioimmunotheranostics.

Comparative Study of a Decadentate Acyclic Chelate, HOPO-O10, and Its Octadentate Analogue, HOPO-O8, for Radiopharmaceutical Applications

Radiolanthanides and actinides are aptly suited for the diagnosis and treatment of cancer via nuclear medicine because they possess unique chemical and physical properties (e.g., radioactive decay emissions). These rare radiometals have recently shown the potential to selectively deliver a radiation payload to cancer cells. However, their clinical success is highly dependent on finding a suitable ligand for stable chelation and conjugation to a disease-targeting vector. Currently, the commercially available chelates exploited in the radiopharmaceutical design do not fulfill all of the requirements for nuclear medicine applications, and there is a need to further explore their chemistry to rationally design highly specific chelates. Herein, we describe the rational design and chemical development of a novel decadentate acyclic chelate containing five 1,2-hydroxypyridinones, 3,4,3,3-(LI-1,2-HOPO), referred to herein as HOPO-O10, based on the well-known octadentate ligand 3,4,3-(LI-1,2-HOPO), referred to herein as HOPO-O8, a highly efficient chelator for 89Zr[Zr4+]. Analysis by 1H NMR spectroscopy and mass spectrometry of the La3+ and Tb3+ complexes revealed that HOPO-O10 forms bimetallic complexes compared to HOPO-O8, which only forms monometallic species. The radiolabeling properties of both chelates were screened with [135La]La3+, [155/161Tb]Tb3+, [225Ac]Ac3+ and, [227Th]Th4+. Comparable high specific activity was observed for the [155/161Tb]Tb3+ complexes, outperforming the gold-standard 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, yet HOPO-O10 surpassed HOPO-O8 with higher [227Th]Th4+ affinity and improved complex stability in a human serum challenge assay. A comprehensive analysis of the decadentate and octadentate chelates was performed with density functional theory for the La3+, Ac3+, Eu3+, Tb3+, Lu3+, and Th4+ complexes. The computational simulations demonstrated the enhanced stability of Th4+-HOPO-O10 over Th4+-HOPO-O8. This investigation reveals the potential of HOPO-O10 for the stable chelation of large tetravalent radioactinides for nuclear medicine applications and provides insight for further chelate development.

Recent Pre-Clinical Advancements in Nuclear Medicine: Pioneering the Path to a Limitless Future

The theranostic approach in oncology holds significant importance in personalized medicine and stands as an exciting field of molecular medicine. Significant achievements have been made in this field in recent decades, particularly in treating neuroendocrine tumors using 177-Lu-radiolabeled somatostatin analogs and, more recently, in addressing prostate cancer through prostate-specific-membrane-antigen targeted radionuclide therapy. The promising clinical results obtained in these indications paved the way for the further development of this approach. With the continuous discovery of new molecular players in tumorigenesis, the development of novel radiopharmaceuticals, and the potential combination of theranostics agents with immunotherapy, nuclear medicine is poised for significant advancements. The strategy of theranostics in oncology can be categorized into (1) repurposing nuclear medicine agents for other indications, (2) improving existing radiopharmaceuticals, and (3) developing new theranostics agents for tumor-specific antigens. In this review, we provide an overview of theranostic development and shed light on its potential integration into combined treatment strategies.

A Targeted Thorium-227 Conjugate Demonstrates Efficacy in Preclinical Models of Acquired Drug Resistance and Combination Potential with Chemotherapeutics and Antiangiogenic Therapies

Targeted alpha therapies (TAT) are an innovative class of therapies for cancer treatment. The unique mode-of-action of TATs is the induction of deleterious DNA double-strand breaks. Difficult-to-treat cancers, such as gynecologic cancers upregulating the chemoresistance P-glycoprotein (p-gp) and overexpressing the membrane protein mesothelin (MSLN), are promising targets for TATs. Here, based on the previous encouraging findings with monotherapy, we investigated the efficacy of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) both as monotherapy and in combination with chemotherapies and antiangiogenic compounds in ovarian and cervical cancer models expressing p-gp. MSLN-TTC monotherapy showed equal cytotoxicity in vitro in p-gp-positive and -negative cancer cells, while chemotherapeutics dramatically lost activity on p-gp-positive cancer cells. In vivo, MSLN-TTC exhibited dose-dependent tumor growth inhibition with treatment/control ratios of 0.03-0.44 in various xenograft models irrespective of p-gp expression status. Furthermore, MSLN-TTC was more efficacious in p-gp-expressing tumors than chemotherapeutics. In the MSLN-expressing ST206B ovarian cancer patient-derived xenograft model, MSLN-TTC accumulated specifically in the tumor, which combined with pegylated liposomal doxorubicin (Doxil), docetaxel, bevacizumab, or regorafenib treatment induced additive-to-synergistic antitumor efficacy and substantially increased response rates compared with respective monotherapies. The combination treatments were well tolerated and only transient decreases in white and red blood cells were observed. In summary, we demonstrate that MSLN-TTC treatment shows efficacy in p-gp-expressing models of chemoresistance and has combination potential with chemo- and antiangiogenic therapies.

Updated Clinical Perspectives and Challenges of Chimeric Antigen Receptor-T Cell Therapy in Colorectal Cancer and Invasive Breast Cancer

In recent years, the incidence of colorectal cancer (CRC) and breast cancer (BC) has increased worldwide and caused a higher mortality rate due to the lack of selective anti-tumor therapies. Current chemotherapies and surgical interventions are significantly preferred modalities to treat CRC or BC in advanced stages but the prognosis for patients with advanced CRC and BC remains dismal. The immunotherapy technique of chimeric antigen receptor (CAR)-T cells has resulted in significant clinical outcomes when treating hematologic malignancies. The novel CAR-T therapy target antigens include GUCY2C, CLEC14A, CD26, TEM8/ANTXR1, PDPN, PTK7, PODXL, CD44, CD19, CD20, CD22, BCMA, GD2, Mesothelin, TAG-72, CEA, EGFR, B7H3, HER2, IL13Ra2, MUC1, EpCAM, PSMA, PSCA, NKG2D. The significant aim of this review is to explore the recently updated information pertinent to several novel targets of CAR-T for CRC, and BC. We vividly described the challenges of CAR-T therapies when treating CRC or BC. The immunosuppressive microenvironment of solid tumors, the shortage of tumor-specific antigens, and post-treatment side effects are the major hindrances to promoting the development of CAR-T cells. Several clinical trials related to CAR-T immunotherapy against CRC or BC have already been in progress. This review benefits academicians, clinicians, and clinical oncologists to explore more about the novel CAR-T targets and overcome the challenges during this therapy.

Radionuclide-based theranostics - a promising strategy for lung cancer

PURPOSE

This review aims to provide a comprehensive overview of the latest literature on personalized lung cancer management using different ligands and radionuclide-based tumor-targeting agents.

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths worldwide. Due to the heterogeneity of lung cancer, advances in precision medicine may enhance the disease management landscape. More recently, theranostics using the same molecule labeled with two different radionuclides for imaging and treatment has emerged as a promising strategy for systemic cancer management. In radionuclide-based theranostics, the target, ligand, and radionuclide should all be carefully considered to achieve an accurate diagnosis and optimal therapeutic effects for lung cancer.

METHODS

We summarize the latest radiotracers and radioligand therapeutic agents used in diagnosing and treating lung cancer. In addition, we discuss the potential clinical applications and limitations associated with target-dependent radiotracers as well as therapeutic radionuclides. Finally, we provide our views on the perspectives for future development in this field.

CONCLUSIONS

Radionuclide-based theranostics show great potential in tailored medical care. We expect that this review can provide an understanding of the latest advances in radionuclide therapy for lung cancer and promote the application of radioligand theranostics in personalized medicine.

Efficacy of a HER2-Targeted Thorium-227 Conjugate in a HER2-Positive Breast Cancer Bone Metastasis Model

Human epidermal growth factor receptor 2 (HER2) is overexpressed in 15-30% of breast cancers but has low expression in normal tissue, making it attractive for targeted alpha therapy (TAT). HER2-positive breast cancer typically metastasizes to bone, resulting in incurable disease and significant morbidity and mortality. Therefore, new strategies for HER2-targeting therapy are needed. Here, we present the preclinical in vitro and in vivo characterization of the HER2-targeted thorium-227 conjugate (HER2-TTC) TAT in various HER2-positive cancer models. In vitro, HER2-TTC showed potent cytotoxicity in various HER2-expressing cancer cell lines and increased DNA double strand break formation and the induction of cell cycle arrest in BT-474 cells. In vivo, HER2-TTC demonstrated dose-dependent antitumor efficacy in subcutaneous xenograft models. Notably, HER2-TTC also inhibited intratibial tumor growth and tumor-induced abnormal bone formation in an intratibial BT-474 mouse model that mimics breast cancer metastasized to bone. Furthermore, a match in HER2 expression levels between primary breast tumor and matched bone metastases samples from breast cancer patients was observed. These results demonstrate proof-of-concept for TAT in the treatment of patients with HER2-positive breast cancer, including cases where the tumor has metastasized to bone.

DTPA(DOTA)-Nimotuzumab Radiolabeling with Generator-produced Thorium for Radioimmunotherapy of EGFR-overexpressing Carcinomas

INTRODUCTION

The feasibility of preparing the "in-house" generators and the Th- DTPA(DOTA)-Nimotuzumab radioimmunoconjugate was evaluated. 226Th is perspective for TAT, however, due to short half-life it is preferable to apply this radionuclide for readily available epithelial malignancies. Nimotuzumab being specific for EGFR expressing cells as a targeting moiety is considered to be suitable for thorium delivery.

METHODS

TEVA extraction chromatographic resin and anion exchange resin AG 1x8 were used as sorbents for 226Th generator. In order to determine features of labeling by Th4+ we applied 234Th as a longer-lived analog of short-lived 226Th and the immunoconjugates DTPA(DOTA)-Nimotuzumab were used for radiolabeling.

RESULTS

The generator on the base of TEVA resin has shown higher volume activity of the product compared to the AG 1x8. The 226Th volume concentration was up to 80%/mL. The radiolabeling of BFCA by thorium radioisotopes reached 95% at the MR(Th:p-SCN-Bn-DTPA) = 1:100 and 86% for MR(Th:p-SCN-Bn-DOTA) = 1:5000 at 90°C. The procedure of Nimotuzumab labeling with Th4+ for radiotherapy of EGFR-overexpressing carcinomas was established. The overall labeling yield in both radioimmunoconjugates - DTPA and DOTA functionalized - was in the range of 45-50%. The immunoconjugate Nimotuzumab-p-SCN-Bn-DTPA was obtained with a molar ratio 1:25 (Nimotuzumab: BFCA), within 1 hour of conjugation at 25°C and labelled via postconjugation approach. Whereas Nimotuzumab-p-SCN-Bn-DOTA was obtained at the same conditions, but radiolabeled by the method of pre-conjugation.

CONCLUSION

Thorium-234 incorporation into both radioimmunoconjugates reached 45-50%. It has been shown that Th-DTPA-Nimotuzumab radioimmunoconjugate specifically bound with EGFR overexpressing epidermoid carcinoma A431 cells.

The role of rare earth elements and dietary intake in tongue cancer: a mediation analysis in southeast China

Objective

The current research aimed to examine how dietary intake and rare earth elements may affect the development of tongue cancer.

Methods

The serum levels of 10 rare earth elements (REEs) in 171 cases and 171 healthy matched controls were measured by inductively coupled plasma mass spectrometry (ICP-MS). The conditional logistic regression was used to examine the relationship between dietary intake, serum levels of 10 REEs, and tongue cancer. Mediation effect and multiplicative interaction analysis were then performed to estimate the potential contribution of REEs in dietary intake associated with tongue cancer.

Results

Compared with the control group, patients with tongue cancer consumed significantly less fish, seafood, fruit, green leafy vegetables, and non-green leafy vegetables, with higher serum praseodymium (Pr), dysprosium (Dy), and lanthanum (La) levels, and lower serum cerium (Ce) and scandium (Sc) levels. The interaction effect was observed between some REEs and food categories. Green vegetables' impact on the risk of tongue cancer is partially attributed to the La and Thorium (Th) elements (P < 0.05, the mediated proportion were 14.933% and 25.280%, respectively). The effect of non-green leafy vegetables for tongue cancer mediated via Pr, Dy, and Th (P < 0.05, the mediated proportion were 0.408%, 12.010%, and 8.969%, respectively), and the Sc components in seafood (P < 0.05, the mediated proportion was 26.120%) is partly responsible for their influence on the risk of tongue cancer.

Conclusion

The correlation between REEs and dietary intakes for tongue cancer is compact but intricate. Some REEs interact with food intake to influence tongue cancer, while others act as a mediator.

Emerging Targeted Therapies for HER2-Positive Breast Cancer

Breast cancer is the most common cancer in women and the leading cause of death. HER2 overexpression is found in approximately 20% of breast cancers and is associated with a poor prognosis and a shorter overall survival. Tratuzumab, a monoclonal antibody directed against the HER2 receptor, is the standard of care treatment. However, a third of the patients do not respond to therapy. Given the high rate of resistance, other HER2-targeted strategies have been developed, including monoclonal antibodies such as pertuzumab and margetuximab, trastuzumab-based antibody drug conjugates such as trastuzumab-emtansine (T-DM1) and trastuzumab-deruxtecan (T-DXd), and tyrosine kinase inhibitors like lapatinib and tucatinib, among others. Moreover, T-DXd has proven to be of use in the HER2-low subtype, which suggests that other HER2-targeted therapies could be successful in this recently defined new breast cancer subclassification. When patients progress to multiple strategies, there are several HER2-targeted therapies available; however, treatment options are limited, and the potential combination with other drugs, immune checkpoint inhibitors, CAR-T cells, CAR-NK, CAR-M, and vaccines is an interesting and appealing field that is still in development. In this review, we will discuss the highlights and pitfalls of the different HER2-targeted therapies and potential combinations to overcome metastatic disease and resistance to therapy.

Tackling Issues Observed during the Development of a Liquid Chromatography Method for Small Molecule Quantification in Antibody-Chelator Conjugate

In the context of targeted radionuclide therapy, antibody-chelator conjugates (ACCs) are an evolving class of antibody-related drugs with promising applications as tumor-targeted pharmaceuticals. Generally, a typical ACC consists of a recombinant monoclonal antibody (mAb) coupled to radionuclide via a chelating agent. Characterizing the ACC structure represents an analytical challenge since various impurities must be constantly monitored in the presence of formulation components during the quality control (QC) process. In this contribution, a reliable method devoted to the monitoring of an ACC sample, and its small molecule-related synthesis impurities, has been developed via liquid chromatography (LC). A problem-solving approach of common analytical issues was used to highlight some major issues encountered during method development. This included separation of poorly retained impurities (issue #1); interferences from the formulation components (issue #2); analysis of impurities in presence of ACC at high concentration (issue #3); and recovery of impurities during the whole analytical procedure (issue #4). To the best of our knowledge, this is the first time that a chromatographic method for the analysis of ACC synthesis impurities is presented. In addition, the developed approach has the potential to be more widely applied to the characterization of similar ACCs and other antibody-related drugs.

Targeting HER2-positive breast cancer: advances and future directions

The long-sought discovery of HER2 as an actionable and highly sensitive therapeutic target was a major breakthrough for the treatment of highly aggressive HER2-positive breast cancer, leading to approval of the first HER2-targeted drug - the monoclonal antibody trastuzumab - almost 25 years ago. Since then, progress has been swift and the impressive clinical activity across multiple trials with monoclonal antibodies, tyrosine kinase inhibitors and antibody-drug conjugates that target HER2 has spawned extensive efforts to develop newer platforms and more targeted therapies. This Review discusses the current standards of care for HER2-positive breast cancer, mechanisms of resistance to HER2-targeted therapy and new therapeutic approaches and agents, including strategies to harness the immune system.

Medical application of the monoclonal antibody SKM9-2 against sialylated HEG1, a new precision marker for malignant mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive tumor of the pleural cavity. Pathologically distinguishing MPM from other pleural lesions is often difficult. We searched for marker antigens to facilitate the pathological diagnosis of MPM and found useful markers for the pathological detection of malignant mesothelioma. Among them, the anti-mesothelioma monoclonal antibody SKM9-2, which was isolated as a clone binding to specimens of MPM (but not to specimens of lung adenocarcinoma) by immunohistochemical screening, showed higher specificity and sensitivity than traditional mesothelioma markers. SKM9-2 recognizes both sialylated O-glycans and peptide sequences in HEG1, and its glycan modifications are specific to mesothelioma. New effective treatments for MPM are needed because the prognosis of patients with MPM is usually poor. SKM9-2 can be used as a seed for next-generation antibody drugs with strong cytotoxic activities. In this review, we have summarized our research on antibody development for MPM diagnosis and treatment.

Development of radiopharmaceuticals for targeted alpha therapy: Where do we stand?

Targeted alpha therapy is an oncological treatment, where cytotoxic doses of alpha radiation are locally delivered to tumor cells, while the surrounding healthy tissue is minimally affected. This therapeutic strategy relies on radiopharmaceuticals made of medically relevant radionuclides chelated by ligands, and conjugated to targeting vectors, which promote the drug accumulation in tumor sites. This review discusses the state-of-the-art in the development of radiopharmaceuticals for targeted alpha therapy, breaking down their key structural components, such as radioisotope, targeting vector, and delivery formulation, and analyzing their pros and cons. Moreover, we discuss current drawbacks that are holding back targeted alpha therapy in the clinic, and identify ongoing strategies in field to overcome those issues, including radioisotope encapsulation in nanoformulations to prevent the release of the daughters. Lastly, we critically discuss potential opportunities the field holds, which may contribute to targeted alpha therapy becoming a gold standard treatment in oncology in the future.

Tumor growth inhibition and immune system activation following treatment with thorium-227 conjugates and PD-1 check-point inhibition in the MC-38 murine model

Targeted thorium-227 conjugates comprise the combination of a monoclonal antibody with specificity for a tumor cell antigen and a 3,2-HOPO chelator enabling complexation of thorium-227 (Th-227). The radiolabeled conjugate functions as an effective delivery system of alpha-particle radiation to the surface of the tumor cell inducing difficult to repair complex DNA damage and cell death. In addition, the mechanism of action of targeted alpha therapy (TAT) appears to involve a significant component linked to stimulation of the immune system. We report herein evidence of immune activation and long-lasting immune protection of a TAT in a syngeneic model using the MC-38 murine cell line. Firstly, MC-38 cells were irradiated ex vivo with the thorium labeled antibody before subcutaneous implantation into mice. These mice were then rechallenged with MC-38 cells contra-laterally. In the group receiving irradiated cells, 9 out of 10 animals had no measurable tumor growth compared to aggressive tumor growth in the control group. Secondly, in an efficacy study, 500 kBq/kg of thorium labeled antibody alone or in combination with PD-1 checkpoint inhibitor gave statistically significant tumor growth inhibition compared to vehicle control. Animals with no measurable tumors were once again rechallenged contra-laterally with MC-38 cells. The re-growth of tumors was significantly delayed (approx. 60 days) in the treatment group compared to age-matched controls (approx. 30 days) in the monotherapy group. Interestingly, in the TAT/ PD-1 combination group no re-growth was observed demonstrating the potential of combining a TAT with checkpoint inhibition therapy. Finally, tumors were excised from treated mice and analyzed by flow cytometry and immunohistochemistry (IHC). Analysis revealed significant infiltration of CD8+ T-cells and mature dendritic cells compared to vehicle controls. Together these results indicated that an ongoing immune response from treatment with alpha radiation could be enhanced by check-point inhibition.

Efficient Production of the PET Radionuclide 133La for Theranostic Purposes in Targeted Alpha Therapy Using the 134Ba(p,2n)133La Reaction

Targeted Alpha Therapy is a research field of highest interest in specialized radionuclide therapy. Over the last decades, several alpha-emitting radionuclides have entered and left research topics towards their clinical translation. Especially, 225Ac provides all necessary physical and chemical properties for a successful clinical application, which has already been shown by [225Ac]Ac-PSMA-617. While PSMA-617 carries the DOTA moiety as the complexing agent, the chelator macropa as a macrocyclic alternative provides even more beneficial properties regarding labeling and complex stability in vivo. Lanthanum-133 is an excellent positron-emitting diagnostic lanthanide to radiolabel macropa-functionalized therapeutics since 133La forms a perfectly matched theranostic pair of radionuclides with the therapeutic radionuclide 225Ac, which itself can optimally be complexed by macropa as well. 133La was thus produced by cyclotron-based proton irradiation of an enriched 134Ba target. The target (30 mg of [134Ba]BaCO3) was irradiated for 60 min at 22 MeV and 10−15 µA beam current. Irradiation side products in the raw target solution were identified and quantified: 135La (0.4%), 135mBa (0.03%), 133mBa (0.01%), and 133Ba (0.0004%). The subsequent workup and anion-exchange-based product purification process took approx. 30 min and led to a total amount of (1.2−1.8) GBq (decay-corrected to end of bombardment) of 133La, formulated as [133La]LaCl3. After the complete decay of 133La, a remainder of ca. 4 kBq of long-lived 133Ba per 100 MBq of 133La was detected and rated as uncritical regarding personal dose and waste management. Subsequent radiolabeling was successfully performed with previously published macropa-derived PSMA inhibitors at a micromolar range (quantitative labeling at 1 µM) and evaluated by radio-TLC and radio-HPLC analyses. The scale-up to radioactivity amounts that are needed for clinical application purposes would be easy to achieve by increasing target mass, beam current, and irradiation time to produce 133La of high radionuclide purity (>99.5%) regarding labeling properties and side products.

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.

Glypican-3-Targeted 227Th -Therapy Reduces Tumor Burden in an Orthotopic Xenograft Murine Model of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a significant cause of morbidity and mortality worldwide, with limited therapeutic options for advanced disease. Targeted α-therapy is an emerging class of targeted cancer therapy in which α-particle-emitting radionuclides, such as ²²⁷Th, are delivered specifically to cancer tissue. Glypican-3 (GPC3) is a cell surface glycoprotein highly expressed on HCC. In this study, we describe the development and in vivo efficacy of a ²²⁷Th-labeled GPC3-targeting antibody conjugate (²²⁷Th-octapa-αGPC3) for treatment of HCC in an orthotopic murine model. Methods: The chelator p-SCN-Bn-H₄octapa-NCS (octapa) was conjugated to a GPC3-targeting antibody (αGPC3) for subsequent ²²⁷Th radiolabeling (octapa-αGPC3). Conditions were varied to optimize radiolabeling of ²²⁷Th. In vitro stability was evaluated by measuring the percentage of protein-bound ²²⁷Th by γ-ray spectroscopy. An orthotopic athymic Nu/J murine model using HepG2-Red-FLuc cells was developed. Biodistribution and blood clearance of ²²⁷Th-octapa-αGPC3 were evaluated in tumor-bearing mice. The efficacy of ²²⁷Th-octapa-αGPC3 was assessed in tumor-bearing animals with serial measurement of serum α-fetoprotein at 23 d after injection. Results: Octapa-conjugated αGPC3 provided up to 70% ²²⁷Th labeling yield in 2 h at room temperature. In the presence of ascorbate, at least 97.8% of ²²⁷Th was bound to αGPC3-octapa after 14 d in phosphate-buffered saline. In HepG2-Red-FLuc tumor-bearing mice, highly specific GPC3 targeting was observed, with significant ²²⁷Th-octapa-αGPC3 accumulation in the tumor over time and minimal accumulation in normal tissue. Twenty-three days after treatment, a significant reduction in tumor burden was observed in mice receiving a 500 kBq/kg dose of ²²⁷Th-octapa-αGPC3 by tail-vein injection. No acute off-target toxicity was observed, and no animals died before termination of the study. Conclusion:²²⁷Th-octapa-αGPC3 was observed to be stable in vitro; maintain high specificity for GPC3, with favorable biodistribution in vivo; and result in significant antitumor activity without significant acute off-target toxicity in an orthotopic murine model of HCC.

Radiopharmaceutical Quality Control Considerations for Accelerator-Produced Actinium Therapies

Background: Alpha-particle-emitting radiotherapies are of great interest for the treatment of disseminated cancer. Actinium-225 (²²⁵Ac) produces four α-particles through its decay and is among the most attractive radionuclides for use in targeted radiotherapy applications. However, supply issues for this isotope have limited availability and increased cost for research and translation. Efforts have focused on accelerator-based methods that produce ²²⁵Ac in addition to long-lived ²²⁷Ac. Objective: The authors investigated the impact of ²²⁵Ac/²²⁷Ac material in the radiolabeling and radiopharmaceutical quality control evaluation of a DOTA chelate-conjugated peptide under good manufacturing practices. The authors use an automated module under identical conditions with either generator or accelerator-produced actinium radiolabeling. Methods: The authors have performed characterization of the radiolabeled products, including thin-layer chromatography, high-pressure liquid chromatography, gamma counting, and high-energy resolution gamma spectroscopy. Results: Peptide was radiolabeled and assessed at >95% radiochemical purity with high yields for generator produced ²²⁵Ac. The radiolabeling results produced material with subtle but detectable differences when using ²²⁵Ac/²²⁷Ac. Gamma spectroscopy was able to identify peptide initially labeled with ²²⁷Th, and at 100 d for quantification of ²²⁵Ac-bearing peptide. Conclusion: Peptides produced using ²²⁵Ac/²²⁷Ac material may be suitable for translation, but raise new issues that include processing times, logistics, and contaminant detection.

Mesothelin: An Immunotherapeutic Target beyond Solid Tumors

Simple Summary

This review summarizes the current knowledge on mesothelin’s function, its role in cancer, and opportunities for immunotherapeutic targeting of mesothelin. Immunotherapies including monoclonal antibodies, antibody–drug conjugates, chimeric antigen receptor T and NK-cells, targeted alpha therapies, and bispecific T cell engaging molecules are reviewed. We show future directions for mesothelin targeting in hematological malignancies, including acute myeloid leukemia.

Abstract

Modern targeted cancer therapies rely on the overexpression of tumor associated antigens with very little to no expression in normal cell types. Mesothelin is a glycosylphosphatidylinositol-anchored cell surface protein that has been identified in many different tumor types, including lung adenocarcinomas, ovarian carcinomas, and most recently in hematological malignancies, including acute myeloid leukemia (AML). Although the function of mesothelin is widely unknown, interactions with MUC16/CA125 indicate that mesothelin plays a role in the regulation of proliferation, growth, and adhesion signaling. Most research on mesothelin currently focuses on utilizing mesothelin to design targeted cancer therapies such as monoclonal antibodies, antibody–drug conjugates, chimeric antigen receptor T and NK cells, bispecific T cell engaging molecules, and targeted alpha therapies, amongst others. Both in vitro and in vivo studies using different immunotherapeutic modalities in mesothelin-positive AML models highlight the potential impact of this approach as a unique opportunity to treat hard-to-cure AML.

Harnessing -Emitting Radionuclides for Therapy: Radiolabeling Method Review

Targeted α-therapy (TAT) is an emerging powerful tool treating late-stage cancers for which therapeutic options are limited. At the core of TAT are targeted radiopharmaceuticals, where isotopes are paired with targeting vectors to enable tissue- or cell-specific delivery of α-emitters. DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and DTPA (diethylenetriamine pentaacetic acid) are commonly used to chelate metallic radionuclides but have limitations. Significant efforts are underway to develop effective stable chelators for α-emitters and are at various stages of development and community adoption. Isotopes such as 149Tb, 212/213Bi, 212Pb (for 212Bi), 225Ac, and 226/227Th have found suitable chelators, although further studies, especially in vivo studies, are required. For others, including 223Ra, 230U, and, arguably 211At, the ideal chemistry remains elusive. This review summarizes the methods reported to date for the incorporation of 149Tb, 211At, 212/213Bi, 212Pb (for 212Bi), 223Ra, 225Ac, 226/227Th, and 230U into radiopharmaceuticals, with a focus on new discoveries and remaining challenges.

Targeted α-therapy in non-prostate malignancies

Progress in unraveling the complex biology of cancer, novel developments in radiochemistry, and availability of relevant α-emitters for targeted therapy have provided innovative approaches to precision cancer management. The approval of 223Ra dichloride for treatment of men with osseous metastatic castrate-resistant prostate cancer unleashed targeted α-therapy as a safe and effective cancer management strategy. While there is currently active research on new α-therapy regimens for prostate cancer based on the prostate-specific membrane antigen, there is emerging development of radiopharmaceutical therapy with a range of biological targets and α-emitting radioisotopes for malignancies other than the prostate cancer. This article provides a brief review of preclinical and first-in-human studies of targeted α-therapy in the cancers of brain, breast, lung, gastrointestinal, pancreas, ovary, and the urinary bladder. The data on leukemia, melanoma, myeloma, and neuroendocrine tumors will also be presented. It is anticipated that with further research the emerging role of targeted α-therapy in cancer management will be defined and validated.

Imaging and dosimetry for alpha-particle emitter radiopharmaceutical therapy: improving radiopharmaceutical therapy by looking into the black box

Radiopharmaceutical therapy using α-particle emitting radionuclides (αRPT) is a novel treatment modality that delivers highly potent alpha-particles to cancer cells or their environment. We review the advantages and challenges of imaging and dosimetry in implementing αRPT for cancer patients.

Why bother with alpha particles?

The approval of 223RaCl2 for cancer therapy in 2013 has heralded a resurgence of interest in the development of α-particle emitting radiopharmaceuticals. In the last decade, over a dozen α-emitting radiopharmaceuticals have entered clinical trials, spawned by strong preclinical studies. In this article, we explore the potential role of α-particle therapy in cancer treatment. We begin by providing a background for the basic principles of therapy with α-emitters, and we explore recent breakthroughs in therapy with α-emitting radionuclides, including conjugates with small molecules and antibodies. Finally, we discuss some outstanding challenges to the clinical adoption of α-therapies and potential strategies to address them.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Simple Summary

Immunotherapy development in pediatric AML has been slow due to the paucity of validated AML-specific targets. We recently identified mesothelin (MSLN) as a therapeutic target in pediatric AML. Mice receiving T cell engaging bispecific antibodies (BsAbs) targeting MSLN and CD3 achieved complete remission and durable responses in two MSLN-positive patient-derived xenograft (PDX) models. This is a first report showing MSLN-targeting BsAbs are a viable immunotherapy for MSLN-positive pediatric AML.

Abstract

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLN^AMA-CD3^L2K and MSLN^AMA-CD3^AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLN^AMA-CD3^AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Chimeric Antigen Receptor T-Cell Therapy in Lung Cancer: Potential and Challenges

Chimeric antigen receptor T (CAR-T) cell therapy has exhibited a substantial clinical response in hematological malignancies, including B-cell leukemia, lymphoma, and multiple myeloma. Therefore, the feasibility of using CAR-T cells to treat solid tumors is actively evaluated. Currently, multiple basic research projects and clinical trials are being conducted to treat lung cancer with CAR-T cell therapy. Although numerous advances in CAR-T cell therapy have been made in hematological tumors, the technology still entails considerable challenges in treating lung cancer, such as on−target, of−tumor toxicity, paucity of tumor-specific antigen targets, T cell exhaustion in the tumor microenvironment, and low infiltration level of immune cells into solid tumor niches, which are even more complicated than their application in hematological tumors. Thus, progress in the scientific understanding of tumor immunology and improvements in the manufacture of cell products are advancing the clinical translation of these important cellular immunotherapies. This review focused on the latest research progress of CAR-T cell therapy in lung cancer treatment and for the first time, demonstrated the underlying challenges and future engineering strategies for the clinical application of CAR-T cell therapy against lung cancer.

Immunostimulatory effects of targeted thorium-227 conjugates as single agent and in combination with anti-PD-L1 therapy

Background

Targeted thorium-227 conjugates (TTCs) are an emerging class of targeted alpha therapies (TATs). Their unique mode of action (MoA) is the induction of difficult-to-repair clustered DNA double-strand breaks. However, thus far, their effects on the immune system are largely unknown. Here, we investigated the immunostimulatory effects of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) in vitro and in vivo in monotherapy and in combination with an inhibitor of the immune checkpoint programmed death receptor ligand 1 (PD-L1) in immunocompetent mice.

Methods

The murine cell line MC38 was transfected with the human gene encoding for MSLN (hMSLN) to enable binding of the non-cross-reactive MSLN-TTC. The immunostimulatory effects of MSLN-TTC were studied in vitro on human cancer cell lines and MC38-hMSLN cells. The efficacy and MoA of MSLN-TTC were studied in vivo as monotherapy or in combination with anti-PD-L1 in MC38-hMSLN tumor-bearing immunocompetent C57BL/6 mice. Experiments were supported by RNA sequencing, flow cytometry, immunohistochemistry, mesoscale, and TaqMan PCR analyses to study the underlying immunostimulatory effects. In vivo depletion of CD8+ T cells and studies with Rag2/Il2Rg double knockout C57BL/6 mice were conducted to investigate the importance of immune cells to the efficacy of MSLN-TTC.

Results

MSLN-TTC treatment induced upregulation of DNA sensing pathway transcripts (IL-6, CCL20, CXCL10, and stimulator of interferon genes (STING)-related genes) in vitro as determined by RNASeq analysis. The results, including phospho-STING activation, were confirmed on the protein level. Danger-associated molecular pattern molecules were upregulated in parallel, leading to dendritic cell (DC) activation in vitro. MSLN-TTC showed strong antitumor activity (T:C 0.38, p<0.05) as a single agent in human MSLN-expressing MC38 tumor-bearing immunocompetent mice. Combining MSLN-TTC with anti-PD-L1 further enhanced the efficacy (T:C 0.08, p<0.001) as evidenced by the increased number of tumor-free surviving animals. MSLN-TTC monotherapy caused migration of CD103+ cDC1 DCs and infiltration of CD8+ T cells into tumors, which was enhanced on combination with anti-PD-L1. Intriguingly, CD8+ T-cell depletion decreased antitumor efficacy.

Conclusions

These in vitro and in vivo data on MSLN-TTC demonstrate that the MoA of TTCs involves activation of the immune system. The findings are of relevance for other targeted radiotherapies and may guide clinical combination strategies.

Hitting the Bull's-Eye: Mesothelin's Role as a Biomarker and Therapeutic Target for Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited treatment options and poor prognosis. MPM originates from the mesothelial lining of the pleura. Mesothelin (MSLN) is a glycoprotein expressed at low levels in normal tissues and at high levels in MPM. Many other solid cancers overexpress MSLN, and this is associated with worse survival rates. However, this association has not been found in MPM, and the exact biological role of MSLN in MPM requires further exploration. Here, we discuss the current research on the diagnostic and prognostic value of MSLN in MPM patients. Furthermore, MSLN has become an attractive immunotherapy target in MPM, where better treatment strategies are urgently needed. Several MSLN-targeted monoclonal antibodies, antibody-drug conjugates, immunotoxins, cancer vaccines, and cellular therapies have been tested in the clinical setting. The biological rationale underpinning MSLN-targeted immunotherapies and their potential to improve MPM patient outcomes are reviewed.

Darolutamide Potentiates the Antitumor Efficacy of a PSMA-targeted Thorium-227 Conjugate by a Dual Mode of Action in Prostate Cancer Models

PURPOSE

Androgen receptor (AR) inhibitors are well established in the treatment of castration-resistant prostate cancer and have recently shown efficacy also in castration-sensitive prostate cancer. Although most patients respond well to initial therapy, resistance eventually develops, and thus, more effective therapeutic approaches are needed. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and presents an attractive target for radionuclide therapy. Here, we evaluated the efficacy and explored the mode of action of the PSMA-targeted thorium-227 conjugate (PSMA-TTC) BAY 2315497, an antibody-based targeted alpha-therapy, in combination with the AR inhibitor darolutamide.

EXPERIMENTAL DESIGN

The in vitro and in vivo antitumor efficacy and mode of action of the combination treatment were investigated in preclinical cell line-derived and patient-derived prostate cancer xenograft models with different levels of PSMA expression.

RESULTS

Darolutamide induced the expression of PSMA in androgen-sensitive VCaP and LNCaP cells in vitro, and the efficacy of darolutamide in combination with PSMA-TTC was synergistic in these cells. In vivo, the combination treatment showed synergistic antitumor efficacy in the low PSMA-expressing VCaP and in the high PSMA-expressing ST1273 prostate cancer models, and enhanced efficacy in the enzalutamide-resistant KUCaP-1 model. The treatments were well tolerated. Mode-of-action studies revealed that darolutamide induced PSMA expression, resulting in higher tumor uptake of PSMA-TTC, and consequently, higher antitumor efficacy, and impaired PSMA-TTC-mediated induction of DNA damage repair genes, potentially contributing to increased DNA damage.

CONCLUSIONS

These results provide a strong rationale to investigate PSMA-TTC in combination with AR inhibitors in patients with prostate cancer.

Treatment with Radiopharmaceuticals and Radionuclides in Breast Cancer: Current Options

Radiopharmaceutical therapy (RPT) is an effective and safe treatment for many types of cancer. RPT acts by binding radioactive atoms to tumor-associated antigens, monoclonal antibodies, nanoparticles, peptides, and small molecules. These treatments ensure that a concentrated dose is delivered to the targeted tumor tissue while preserving the normal tissues surrounding the tumor. Given these features, RPT is superior to traditional methods. This review article aimed to performa comprehensive review and evaluation of the potential of radionuclides and radiopharmaceuticals used in breast cancer treatment in preclinical studies conducted in the last five years.

Overview of the Most Promising Radionuclides for Targeted Alpha Therapy: The "Hopeful Eight"

Among all existing radionuclides, only a few are of interest for therapeutic applications and more specifically for targeted alpha therapy (TAT). From this selection, actinium-225, astatine-211, bismuth-212, bismuth-213, lead-212, radium-223, terbium-149 and thorium-227 are considered as the most suitable. Despite common general features, they all have their own physical characteristics that make them singular and so promising for TAT. These radionuclides were largely studied over the last two decades, leading to a better knowledge of their production process and chemical behavior, allowing for an increasing number of biological evaluations. The aim of this review is to summarize the main properties of these eight chosen radionuclides. An overview from their availability to the resulting clinical studies, by way of chemical design and preclinical studies is discussed.

Theoretical Study of Actinide(III)-DOTA Complexes

1,4,7,10-Tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) is a prominent chelating ligand used in imaging contrast agents and radiopharmaceuticals. The present study explores the stabilities, structures, and bonding properties of its complexes with trivalent actinides (Ac, U, Np, Pu, Am, Cm, Cf) using density functional theory and relativistic multireference calculations. For reference purposes, the La- and Lu-DOTA complexes are also included. Similar to La3+, the large An3+ ions prefer the TSAP conformer of the ligand. The An-ligand bonding is mainly electrostatic, with minor charge transfer contributions to the An 6d orbitals. For the assessment of the thermodynamic stabilities in aqueous solution, PCM radii to use in conjunction with the SMD solvation model were developed. Basically, the thermodynamic stability of the DOTA complexes increases along the An row but with notable counteracting of spin-orbit coupling.

In Vitro and In Vivo Comparison of 3,2-HOPO Versus Deferoxamine-Based Chelation of Zirconium-89 to the Antimesothelin Antibody Anetumab

Introduction: [²²⁷Th]Th-3,2-HOPO-MSLN-mAb, a mesothelin (MSLN)-targeted thorium-227 therapeutic conjugate, is currently in phase I clinical trial; however, direct PET imaging using this conjugate is technically challenging. Thus, using the same MSLN antibody, we synthesized 3,2-HOPO and deferoxamine (DFO)-based zirconium-89 antibody conjugates, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb, respectively, and compared them in vitro and in vivo.

Methods: [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb were evaluated in vitro to determine binding affinity and immunoreactivity in HT29-MSLN and PDX (NCI-Meso16, NCI-Meso21) cells. For both the zirconium-89 conjugates, in vivo studies (biodistribution/imaging) were performed at days 1, 3, and 6, from which tissue uptake was determined.

Results: Both the conjugates demonstrated a low nanomolar binding affinity for MSLN and >95% immunoreactivity. In all the three tumor types, biodistribution of [⁸⁹Zr]Zr-DFO-MSLN-mAb resulted in higher tumor uptake(15.88-28-33%ID/g) at all time points compared with [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb(7–13.07%ID/g). [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb femur uptake was always higher than [⁸⁹Zr]Zr-DFO-MSLN-mAb, and imaging results concurred with the biodistribution studies.

Conclusions: Even though the conjugates exhibited a high binding affinity for MSLN, [⁸⁹Zr]Zr-DFO-MSLN-mAb showed a higher tumor and lower femur uptake than [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb. Nevertheless, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb could be used to study organ distribution and lesion uptake with the caveat of detecting MSLN-positive bone lesions. Clinical trial (NCT03507452).

Towards Targeted Alpha Therapy with Actinium-225: Chelators for Mild Condition Radiolabeling and Targeting PSMA-A Proof of Concept Study

Currently, targeted alpha therapy is one of the most investigated topics in radiopharmaceutical cancer management. Especially, the alpha emitter 225Ac has excellent nuclear properties and is gaining increasing popularity for the treatment of various tumor entities. We herein report on the synthesis of two universal 225Ac-chelators for mild condition radiolabeling and binding to conjugate molecules of pharmacological interest via the copper-mediated click chemistry. A convenient radiolabeling procedure was investigated as well as the complex stability proved for both chelators and two PSMA (prostate-specific membrane antigen)-targeting model radioconjugates. Studies regarding affinity and cell survival were performed on LNCaP cells followed by biodistribution studies, which were performed using LNCaP tumor-bearing mice. High efficiency radiolabeling for all conjugates was demonstrated. Cell binding studies revealed a fourfold lower cell affinity for the PSMA radioconjugate with one targeting motif compared to the radioconjugate owing two targeting motifs. Additionally, these differences were verified by in vitro cell survival evaluation and biodistribution studies, both showing a higher cell killing efficiency for the same dose, a higher tumor uptake (15%ID/g) and a rapid whole body clearance after 24 h. The synthesized chelators will overcome obstacles of lacking stability and worse labeling needs regarding 225Ac complexation using the DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid) chelator. Moreover, the universal functionalization expands the coverage of these chelators in combination with any sensitive bio(macro)molecule, thus improving treatment of any addressable tumor target.

Malignant mesothelioma: Advances in immune checkpoint inhibitor and mesothelin-targeted therapies

Malignant mesothelioma is an aggressive cancer with a poor prognosis and limited treatment options. For many years, the only US Food and Drug Administration-approved first-line treatment for unresectable mesothelioma was pemetrexed plus cisplatin. However, the recent approval of nivolumab plus ipilimumab as frontline treatment for patients with pleural mesothelioma marks a significant milestone for the treatment of this disease. In this review, the authors describe recent advances in therapeutic strategies for the treatment of patients with advanced, unresectable mesothelioma, highlighting the emerging use of immunotherapy and mesothelin-targeted therapies for the management of malignant mesothelioma.

Recent Advances in Radiometals for Combined Imaging and Therapy in Cancer

Nuclear medicine is defined as the use of radionuclides for diagnostic and therapeutic applications. The imaging modalities positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are based on γ-emissions of specific energies. The therapeutic technologies are based on β^- -particle-, α-particle-, and Auger electron emitters. In oncology, PET and SPECT are used to detect cancer lesions, to determine dosimetry, and to monitor therapy effectiveness. In contrast, radiotherapy is designed to irreparably damage tumor cells in order to eradicate or control the disease's progression. Radiometals are being explored for the development of diagnostic and therapeutic radiopharmaceuticals. Strategies that combine both modalities (diagnostic and therapeutic), referred to as theranostics, are promising candidates for clinical applications. This review provides an overview of the basic concepts behind therapeutic and diagnostic radiopharmaceuticals and their significance in contemporary oncology. Select radiometals that significantly impact current and upcoming cancer treatment strategies are grouped as clinically suitable theranostics pairs. The most important physical and chemical properties are discussed. Standard production methods and current radionuclide availability are provided to indicate whether a cost-efficient use in a clinical routine is feasible. Recent preclinical and clinical developments and outline perspectives for the radiometals are highlighted in each section.

Novel mesothelin antibody-drug conjugates: current evidence and future role in the treatment of ovarian cancer

Introduction: Ovarian cancer is the deadliest gynecologic malignancy in the United States, and effective therapies for recurrent, advanced, and progressive disease are limited. Mesothelin is known to be expressed in ovarian cancers, and antibody-drug conjugates targeting mesothelin are a promising novel therapeutic agent.Areas Covered: This article reviews the currently available literature of anti-mesothelin antibody-drug conjugates as a novel treatment for ovarian cancer. Preclinical in vitro and in vivo data as well as clinical results are reviewed for each available agent. Additionally, adverse effects are covered.Expert Opinion: Anti-mesothelin antibody-drug conjugates and their combination with chemotherapeutic agents have undergone phase II trials with encouraging results and demonstrated favorable adverse effect profiles. Phase III data will be necessary to establish its role in ovarian cancer, particularly in recurrent, advanced, or progressive disease.

Alpha emitting nuclides for targeted therapy

Targeted alpha therapy (TAT) is an area of research with rapidly increasing importance as the emitted alpha particle has a significant effect on inducing cytotoxic effects on tumor cells while mitigating dose to normal tissues. Two significant isotopes of interest within the area of TAT are thorium-227 and actinium-225 due to their nuclear characteristics. Both isotopes have physical half-lives suitable for coordination with larger biomolecules, and additionally actinium-225 has potential to serve as an in vivo generator. In this review, the authors will discuss the production, purification, labeling reactions, and biological studies of actinium-225 and thorium-227 complexes and clinical studies.

Radiopharmaceutical Chemistry and Drug Development-What's Changed?

Radiation oncologists and nuclear medicine physicians have seen a resurgence in the clinical use of radiopharmaceuticals for the curative or palliative treatment of cancer. To enable the discovery and the development of new targeted radiopharmaceutical treatments, the United States National Cancer Institute has adapted its clinical trial enterprise to accommodate the requirements of a development program with investigational agents that have a radioactive isotope as part of the studied drug product. One change in perspective has been the consideration of investigational radiopharmaceuticals as drugs, with maximum tolerable doses determined by normal organ toxicity frequency like in drug clinical trials. Other changes include new clinical trial enterprise elements for biospecimen handling, adverse event reporting, regulatory conduct, writing services, drug master files, and reporting of patient outcomes. Arising from this enterprise, the study and clinical use of alpha-particle and beta-particle emitters have emerged as an important approach to cancer treatment. Resources allocated to this enterprise have brought forward biomarkers of molecular pathophysiology now used to select treatment or to evaluate clinical performance of radiopharmaceuticals. The clinical use of diagnostic and therapeutic radionuclide pairs is anticipated to accelerate radiopharmaceutical clinical development.

Prognosis of patients with malignant mesothelioma by expression of programmed cell death 1 ligand 1 and mesothelin in a contemporary cohort in Finland

OBJECTIVES

We aimed to describe mesothelin (MSLN) and programmed cell death 1 ligand 1 (PD-L1) tumour overexpression amongst patients with malignant mesothelioma (MM), and their associations with survival, amongst a cohort of patients with MM in Finland.

METHODS

Between 2004 and 2017, 91 adults with histologically confirmed MM were identified from the Auria Biobank in Finland and followed-up using linked data from electronic health records and national statistics. Biomarker content in tumour cell membranes was determined using automated Immunohistochemistry on histological sections. Stained tumour sections were scored for MSLN and PD-L1 intensity. Adjusted associations between MSLN/PD-L1 co-expression and mortality were evaluated by estimating hazard ratios (HRs) with 95% confidence intervals (CIs) using Cox regression.

RESULTS

Biomarker overexpression occurred in 52 patients for MSLN and 34 patients for PD-L1 and was associated with tumour histology and certain comorbidities. Fifteen per cent of patients had a tumour that overexpressed both biomarkers; r =-0.244, p-value: 0.02. Compared with MSLN+/PD-L1+ patients, HRs (95% CIs) for death were 4.18 (1.71-10.23) for MSLN-/PD-L1+ patients, 3.03 (1.35-6.77) for MSLN-/PD-L1- patients, and 2.13 (0.97-4.67) for MSLN+/PD-L1- patients.

CONCLUSIONS

Both MSLN and PD-L1 markers were independent prognostic indicators in patients with MM. Overexpression of MSLN was associated with longer survival; yet their combined expression gave a better indication of survival. The risk of death was four times higher amongst MSLN-/PD-L1+ patients than in MSLN+/PD-L1+ patients.

Further Understanding of High-Grade Serous Ovarian Carcinogenesis: Potential Therapeutic Targets

High-grade serous ovarian carcinoma (HGSOC) is the most common type of ovarian cancer and the most lethal gynecologic malignancy due to advanced stage at presentation. Recent years have witnessed progress in the therapy of HGSOC with the introduction of PARP (poly-adenosine diphosphate ribose polymerase) inhibitors and the anti-angiogenic monoclonal antibody bevacizumab to the backbone of chemotherapy or as maintenance therapy after chemotherapy. The improved molecular understanding of ovarian cancer pathogenesis, which has brought these therapies into the clinic, aspires to extend the boundaries of therapies through elucidation of other molecular aspects of ovarian carcinogenesis. This accumulating knowledge has started to be translated to additional targeted therapies that are in various stages of development. These include inhibitors of the function of other proteins involved in homologous recombination deficiency (HRD), such as WEE1 kinase, ATM/ATR kinases and CDK12 inhibitors. Despite disappointing results with immune checkpoint inhibitors monotherapy, harnessing the immune system in HGSOC with combination therapies that promote antigen production and immune cell activation is an avenue being explored. This paper examines arising HGSOC therapies based on molecular understanding of pathogenesis.