Targeted endoradiotherapy using nucleotides

Neural Stem Cells as Carriers of Nucleoside-Conjugated Nanogels: A New Approach toward Cell-Mediated Delivery

Neural stem cells (NSCs) present attractive natural drug delivery systems (DDSs). Their migratory potential enables crossing of the blood-brain barrier and efficient and selective accumulation near malignant cells. Here, we present the potential of NSCs as DDSs for nucleoside analogue-conjugated nanogels (NGs). Two different approaches were investigated: the intracellular loading and extracellular cell surface decoration with NGs. For both designs, the tumor-specific migratory potentials of NSCs remained unchanged; however, the intracellular loading showed a shorter NG retention. The cell surface decoration protocol yielded a high loading capacity of 100% after 1 h and a prolonged drug retention. A redox-sensitive linker between NGs and the nucleoside analogue 5-ethynyl-2'-deoxycytidine (EdC) allowed a tumor environment-specific drug release and its efficient and preferential incorporation into the DNA of the tumor cells. Interestingly, the tumor-trafficking potentials of NSCs were significantly potentiated by irradiation of tumor cells. In conclusion, this study indicates the potentials of cell surface-decorated NSCs as DDSs for tumor-specific release, cellular uptake, and incorporation of EdC into DNA.

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

Auger electron therapy of glioblastoma using [125I]5-iodo-2'-deoxyuridine and concomitant chemotherapy - Evaluation of a potential treatment strategy

INTRODUCTION

Treatment of glioblastomas (GBM) using the Auger electron emitting compound [125I]5-Iodo-2'-deoxyuridine ([125I]I-UdR), combined with the thymidylate synthase inhibitor methotrexate (MTX) and concomitant chemotherapy with temozolomide (TMZ) has recently shown very promising therapeutic effects in vitro and in vivo in animals. The aim of the current study was to investigate if the therapeutic effects of this multimodal treatment strategy could be further increased by the thymidylate synthase inhibitor, 5-fluoro-2'-deoxyuridine (F-UdR), in comparison to MTX, and if the co-treatment should be given in a neoadjuvant or adjuvant setting.

METHODS

A patient-derived GBM cancer stem cell (CSC)-enriched cell line, grown as neurospheres, was employed to evaluate DNA-incorporation of [125I]I-UdR, determined by a DNA precipitation assay, using either pre-treatment or co-treatment with MTX or F-UdR. The therapeutic effects in the CSC-enriched cell line after exposure to various combinations of MTX, F-UdR, TMZ and [125I]I-UdR were also investigated by a CellTiter-Blue assay.

RESULTS

The highest general increase in [125I]I-UdR incorporation was observed with F-UdR co-treatment, which resulted in approx. 2.5-fold increase in the DNA-associated activity. Also the cell viability was significantly decreased when F-UdR was combined with [125I]I-UdR compared to [125I]I-UdR alone at all activity concentrations tested. MTX was redundant when combined with 400 and 500 Bq/ml [125I]I-UdR. TMZ was effective in combination with either [125I]I-UdR alone or with both thymidylate synthase inhibitors combined with 50-100 Bq/ml [125I]I-UdR.

CONCLUSIONS

Overall, our study revealed a higher incorporation and therapeutic effect of [125I]I-UdR when GBM cells were co-treated with F-UdR compared to MTX. The therapeutic effects were further increased when TMZ was combined with [125I]I-UdR in combination with the thymidylate synthase inhibitors.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Auger electron therapy in combination with thymidylate synthase inhibition and concomitant chemotherapy has the potential to become a future therapeutic treatment option for patients with glioblastoma.

Nuclear Medicine in Times of COVID-19: How Radiopharmaceuticals Could Help to Fight the Current and Future Pandemics

The emergence and global spread of COVID-19, an infectious disease caused by the novel coronavirus SARS-CoV-2, has resulted in a continuing pandemic threat to global health. Nuclear medicine techniques can be used for functional imaging of (patho)physiological processes at the cellular or molecular level and for treatment approaches based on targeted delivery of therapeutic radionuclides. Ongoing development of radiolabeling methods has significantly improved the accessibility of radiopharmaceuticals for in vivo molecular imaging or targeted radionuclide therapy, but their use for biosafety threats such as SARS-CoV-2 is restricted by the contagious nature of these agents. Here, we highlight several potential uses of nuclear medicine in the context of SARS-CoV-2 and COVID-19, many of which could also be performed in laboratories without dedicated containment measures. In addition, we provide a broad overview of experimental or repurposed SARS-CoV-2-targeting drugs and describe how radiolabeled analogs of these compounds could facilitate antiviral drug development and translation to the clinic, reduce the incidence of late-stage failures and possibly provide the basis for radionuclide-based treatment strategies. Based on the continuing threat by emerging coronaviruses and other pathogens, it is anticipated that these applications of nuclear medicine will become a more important part of future antiviral drug development and treatment.

Targeting of prostate-specific membrane antigen for radio-ligand therapy of triple-negative breast cancer

Background

Triple-negative breast cancer has extremely high risk of relapse due to the lack of targeted therapies, intra- and inter-tumoral heterogeneity, and the inherent and acquired resistance to therapies. In this study, we evaluate the potential of prostate-specific membrane antigen (PSMA) as target for radio-ligand therapy (RLT).

Methods

Tube formation was investigated after incubation of endothelial HUVEC cells in tumor-conditioned media and monitored after staining using microscopy. A binding study with ⁶⁸Ga-labeled PSMA-addressing ligand was used to indicate targeting potential of PSMA on tumor-conditioned HUVEC cells. For mimicking of the therapeutic application, tube formation potential and vitality of tumor-conditioned HUVEC cells were assessed following an incubation with radiolabeled PSMA-addressing ligand [¹⁷⁷Lu]-PSMA-617. For in vivo experiments, NUDE mice were xenografted with triple-negative breast cancer cells MDA-MB231 or estrogen receptor expressing breast cancer cells MCF-7. Biodistribution and binding behavior of [⁶⁸Ga]-PSMA-11 was investigated in both tumor models at 30 min post injection using μPET. PSMA- and CD31-specific staining was conducted to visualize PSMA expression and neovascularization in tumor tissue ex vivo.

Results

The triple-negative breast cancer cells MDA-MB231 showed a high pro-angiogenetic potential on tube formation of endothelial HUVEC cells. The induced endothelial expression of PSMA was efficiently addressed by radiolabeled PSMA-specific ligands. ¹⁷⁷Lu-labeled PSMA-617 strongly impaired the vitality and angiogenic potential of HUVEC cells. In vivo, as visualized by μPET, radiolabeled PSMA-ligand accumulated specifically in the triple-negative breast cancer xenograft MDA-MB231 (T/B ratio of 43.3 ± 0.9), while no [⁶⁸Ga]-PSMA-11 was detected in the estrogen-sensitive MCF-7 xenograft (T/B ratio of 1.1 ± 0.1). An ex vivo immunofluorescence analysis confirmed the localization of PSMA on MDA-MB231 xenograft-associated endothelial cells and also on TNBC cells.

Conclusions

Here we demonstrate PSMA as promising target for two-compartment endogenous radio-ligand therapy of triple-negative breast cancer.

Modulation of glutathione promotes apoptosis in triple-negative breast cancer cells

Triple-negative breast cancer has an extremely high rate of relapse. This is particularly due to the existence and survival of cancer stem cells (CSCs) characterized by increased amounts of glutathione (GSH). In this study, we evaluated the potential of pharmacological GSH depletion to sensitize CSCs to ionizing radiotherapy with an I-125-labeled nucleoside analog, 5-iodo-4'-thio-2'-deoxyuridine (ITdU). CSCs were isolated using CD24^-- and CD44⁺-specific microbeads. GSH and reactive oxygen species (ROS) were evaluated by fluorescence-activated cell sorting. GSH synthesis was inhibited with buthionine sulfoximine (BSO). Apoptotic cells were identified with propidium iodide and double-strand DNA breaks were detected by γ-H2AX staining. For therapy study, BSO treated and untreated mice xenografted with breast CSCs received weekly I-125-ITdU. Therapy efficiency was monitored by fluorodeoxyglucose-18-µ-positron emission tomography. We showed that GSH modulation sensitizes CD24^- and CD44⁺ breast cancer cells to endogenous nanoradiotherapy. BSO synergistically affects ROS generation induced by I-125-ITdU. In an in vivo study, we demonstrated a complete tumor regression as a consequence of preconditioning with a GSH-synthesis inhibitor prior to treatment with I-125-ITdU. GSH modulation in combination with an oxidative stress-generating treatment such as endogenous radiotherapy using an Auger emitter offers an extraordinary opportunity for selective and efficient eradication of drug-resistant CSCs.-Miran, T., Vogg, A. T. J., Drude, N., Mottaghy, F. M., Morgenroth, A. Modulation of glutathione promotes apoptosis in triple-negative breast cancer cells.

Dual addressing of thymidine synthesis pathways for effective targeting of proliferating melanoma

Here, we examined the potential of blocking the thymidine de novo synthesis pathways for sensitizing melanoma cells to the nucleoside salvage pathway targeting endogenous DNA irradiation. Expression of key nucleotide synthesis and proliferation enzymes thymidylate synthase (TS) and thymidine kinase 1 (TK1) was evaluated in differentiated (MITF^high [microphthalmia‐associated transcription factor] IGR1) and invasive (MITF^mediumIGR37) melanoma cells. For inhibition of de novo pathways cells were incubated either with an irreversible TS inhibitor 5‐fluoro‐2′‐deoxyuridine (FdUrd) or with a competitive dihydrofolate‐reductase (DHFR) inhibitor methotrexate (MTX). Salvage pathway was addressed by irradiation‐emitting thymidine analog [^123/125I]‐5‐iodo‐4′‐thio‐2′‐deoxyuridine (^123/125I‐ITdU). The in vivo targeting efficiency was visualized by single‐photon emission computed tomography. Pretreatment with FdUrd strongly increased the cellular uptake and the DNA incorporation of ¹²⁵I‐ITdU into the mitotically active IGR37 cells. This effect was less pronounced in the differentiated IGR1 cells. In vivo, inhibition of TS led to a high and preferential accumulation of ¹²³I‐ITdU in tumor tissue. This preclinical study presents profound rationale for development of therapeutic approach by highly efficient and selective radioactive targeting one of the crucial salvage pathways in melanomas.

Hedgehog signaling sensitizes glioma stem cells to endogenous nano-irradiation

The existence of therapy resistant glioma stem cells is responsible for the high recurrence rate and incurability of glioblastomas. The Hedgehog pathway activity plays an essential role for self-renewal capacity and survival of glioma stem cells. We examined the potential of the Sonic hedgehog ligand for sensitizing of glioma stem cells to endogenous nano-irradiation. We demonstrate that the Sonic hedgehog ligand preferentially and efficiently activats glioma stem cells to enter the radiation sensitive G2/M phase. Concomitant inhibition of de novo thymidine synthesis with fluorodeoxyuridine and treatment with the Auger electron emitting thymidine analogue 5-[I-125]-Iodo-4′-thio-2′-deoxyuridine ([I-125]ITdU) leads to a fatal nano-irradiation in sensitized glioma stem cells. Targeting of proliferating glioma stem cells with DNA-incorporated [I-125]ITdU efficiently invokes the intrinsic apoptotic pathway despite active DNA repair mechanisms. Further, [I-125]ITdU completely inhibits survival of glioma stem cells in vitro. Analysis of non-stem glioblastoma cells and normal human astrocytes reveals that glioma stem cells differentially respond to Sonic hedgehog ligand. These data demonstrate a highly efficient and controllable single-cell kill therapeutic model for targeting glioma stem cells.

Breaking the invulnerability of cancer stem cells: two-step strategy to kill the stem-like cell subpopulation of multiple myeloma

In multiple myeloma, the presence of highly resistant cancer stem cells (CSC) that are responsible for tumor metastasis and relapse has been proven. Evidently, for achieving complete response, new therapeutic paradigms that effectively eradicate both, CSCs and bulk cancer populations, need to be developed. For achieving that goal, an innovative two-step treatment combining targeting of thymidine de novo synthesis pathway and a nanoirradiation by the Auger electron emitting thymidine analogue (123/125)I-5-iodo-4'-thio-2'-deoxyuridine ((123/125)I-ITdU) could be a promising approach. The pretreatment with thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FdUrd, 1 μmol/L for 1 hour) efficiently induced proliferation and terminal differentiation of isolated myeloma stem-like cells. Moreover, FdUrd stimulation led to a decreased activity of a functional CSC marker, aldehyde dehydrogenase (ALDH). The metabolic conditioning by FdUrd emerged to be essential for enhanced incorporation of (125)I-ITdU (incubation with 50 kBq/2 × 10(4) cells for 4 days) and, consequently, for the induction of irreparable DNA damage. (125)I-ITdU showed a pronounced antimyeloma effect on isolated tumor stem-like cells. More than 85% of the treated cells were apoptotic, despite activation of DNA repair mechanisms. Most important, exposure of metabolically conditioned cells to (125)I-ITdU resulted in a complete inhibition of clonogenic recovery. This is the first report showing that pretreatment with FdUrd sensitizes the stem-like cell compartment in multiple myeloma to apoptosis induced by (125)I-ITdU-mediated nanoirradiation of DNA.

Synthesis of peptide radiopharmaceuticals for the therapy and diagnosis of tumor diseases

Despite the advances in molecular biology and biochemistry, the prognosis of patients suffering from tumor diseases remains poor. The limited therapeutic success can be explained by the insufficient performance of the common chemotherapeutic drugs that lack the ability to specifically target tumor tissues. Recently peptide radiopharmaceuticals have been developed that enable the concurrent imaging and therapy of tumors expressing a specific target. Here, with a special emphasis on the synthesis of the building blocks required for the complexation of metallic radioisotopes, the requirements to the design and synthesis of radiolabeled peptides for clinical applications are described.

Cancer therapy and vaccination

Cancer remains one of the leading causes of death worldwide, both in developed and in developing nations. It may affect people at all ages, even fetuses, but the risk for most varieties increases with age. Current therapeutic approaches which include surgery, chemotherapy and radiotherapy are associated with adverse side effects arising from lack of specificity for tumors. The goal of any therapeutic strategy is to impact on the target tumor cells with limited detrimental effect to normal cell function. Immunotherapy is cancer specific and can target the disease with minimal impact on normal tissues. Cancer vaccines are capable of generating an active tumor-specific immune response and serve as an ideal treatment due to their specificity for tumor cells and long lasting immunological memory that may safeguard against recurrences. Cancer vaccines are designed to either prevent (prophylactic) or treat established cancer (therapeutic). Identification of tumor-associated antigens (TAAs) and tumor-specific antigens (TSAs) has led to increased efforts to develop vaccination strategies. Vaccines may be composed of whole cells or cell extracts, genetically modified tumor cells to express costimulatory molecules, dendritic cells (DCs) loaded with TAAs, immunization with soluble proteins or synthetic peptides, recombinant viruses or bacteria encoding tumor-associated antigens, and plasmid DNA encoding TSAs or TAAs in conjunction with appropriate immunomodulators. All of these antitumor vaccination approaches aim to induce specific immunological responses and localized to TAAs, destroying tumor cells alone and leaving the vast majority of other healthy cells of the body untouched.