Radiopharmaceutical Drugs
Radiopharmaceutical therapy (RPT), also known as radioligand therapy (RLT), is emerging as a novel and promising approach to combat cancer. This innovative therapeutic method harnesses the potency of radioactive substances, termed radioligands, to precisely target and eliminate cancer cells while preserving healthy tissue. Through the targeted binding of radioligands to receptors or proteins on cancer cells, this precise treatment modality delivers localized radiation, effectively eradicating malignant cells.
Mechanism of Action
Radiopharmaceutical therapy functions by coupling a radioactive isotope to a targeting molecule, or ligand, that attaches to specific markers on cancer cells. The ligand guides the radioisotope to the cancer cells, where the emitted radiation disrupts the cells’ DNA, ultimately inducing cell demise. This precise methodology facilitates the direct delivery of radiation to the tumor site, while safeguarding neighboring healthy tissue.
Therapeutic radioiostopes produce high but localized levels of radioactivity, most commonly alpha particles that directly damage the DNA of cancer cells, preventing them from dividing and growing. Alpha particles do not travel far and can be stopped by an inch of air, a single sheet of paper and cannot penetrate the skin. If it is adjacent to a tissue/cell it will penetrate the tissue/cell, thus targeted binding to cancer cells. This type of radiation is used for prostate cancer.
Types of Radiopharmaceuticals or Radioligands
Peptide Receptor Radionuclide Therapy (PRRT): PRRT utilizes peptides that bind to receptors overexpressed on cancer cells. Examples are somatostatin analogs for neuroendocrine tumors and prostate-specific membrane antigen (PSMA) for prostate cancer.
Monoclonal Antibody Therapy: Monoclonal antibodies are engineered to target specific antigens on cancer cells. Examples include Zevalin (ibritumomab tiuxetan) for non-Hodgkin lymphoma and Bexxar (tositumomab) for certain types of leukemia.
Small Molecule Radiopharmaceuticals: These are small molecules that can penetrate tissues efficiently and bind to specific targets. Examples include Lutathera (lutetium Lu 177) for neuroendocrine tumors and Xofigo (radium-223) for metastatic castration-resistant prostate cancer.
Radioembolization: Radioembolization, also known as selective internal radiation therapy (SIRT), uses tiny glass or resin beads, known as microspheres, to deliver radiation directly to tumors through the bloodstream. These beads are introduced into blood vessels, from where they navigate to the tumor and dispense a concentrated dose of radiation. An example of radioembolization utilized at Johns Hopkins is TheraSphere (Y90 microspheres), employed in treating liver tumors. (https://www.hopkinsmedicine.org/radiation-oncology/treatments/radiopharma).
FDA-Approved Radiopharmaceuticals:
Several radioligands have received FDA approval for the treatment of various cancers, including:
- Lutathera (lutetium-177) for gastroenteropancreatic neuroendocrine tumors.
- Xofigo (radium-223) for symptomatic bone metastases from prostate cancer.
- Zevalin (ibritumomab tiuxetan) and Bexxar (tositumomab) for non-Hodgkin lymphoma.
- Pluvicto (Lu-PSMA-617) for castrate resistant metastatic prostate cancer.
Promising Radiopharmaceuticals in Development
In addition to FDA-approved options, ongoing research is exploring new radioligands and treatment approaches. Some promising candidates include:
- PSMA-Targeted Radioligands: Novel PSMA-targeted radioligands, such as Actinium-225-PSMA-617, are being evaluated in clinical trials for the treatment of advanced prostate cancer.
- Alpha-Emitting Radionuclides: Alpha-emitting radionuclides, like actinium-225 and thorium-227, offer the potential for enhanced tumor killing due to their high linear energy transfer. These are being investigated in various cancer types, including prostate cancer and leukemia.
- Combination Therapies: Researchers are exploring combination therapies involving radioligand therapy with other treatment modalities, such as chemotherapy, immunotherapy, and targeted therapy, to enhance efficacy and overcome resistance mechanisms.
Marin Biological Laboratories Offers Services for Radiopharmaceutical Drug Discovery & Development
Cell-based assays are integral to the development and evaluation of radiopharmaceuticals, providing valuable insights into their mechanisms and potential therapeutic applications. These assays encompass a range of techniques, including binding assays, internalization assays, and cytotoxicity assays.
Cell Viability Assays: These assays measure the viability and proliferation of cells exposed to radiopharmaceuticals.
Receptor Binding Assays: Radiopharmaceuticals often target specific receptors on cells. Receptor binding assays determine the affinity and specificity of radiopharmaceuticals for their target receptors using radioligand binding techniques.
Internalization Studies: Internalization studies assess the ability of radiopharmaceuticals to enter target cells after binding to cell surface receptors. Techniques such as flow cytometry or fluorescence microscopy can be used to visualize and quantify internalization.
DNA Damage Assays: DNA damage assays determine the effects of radiopharmaceuticals in inducing DNA damage in target cells.
Apoptosis/Necrosis Assays: These assays designed to quantify the induction of apoptosis or necrosis in target cells by radiopharmaceuticals.
In Vitro Radiopharmaceutical Uptake Studies: These studies assess the uptake of radiopharmaceuticals by target cells over time.
Functional Assays: Functional assays assess the biological activity of radiopharmaceuticals by measuring their effects on cellular functions or signaling pathways.
Reporter Gene Assays: Reporter gene assays utilize cells engineered to express a reporter gene in response to activation of a specific signaling pathway or cellular process.
Radioimmunoassay (RIA) in Studying Pharmacokinetics (PK) of Radiopharmaceuticals
Radioimmunoassay (RIA) is a highly sensitive in vitro technique for measuring concentrations of substances, such as antigens or hormone levels in the blood, using antibodies. In the context of radiopharmaceuticals, RIA can be applied to measure the concentrations of specific antigens, such as hormone levels, that are relevant to the pharmacokinetic behavior of radiopharmaceuticals. Therefore, RIA can be a valuable tool for studying the pharmacokinetics of radiopharmaceuticals, particularly in measuring the concentrations of relevant antigens in biological samples with high sensitivity and specificity.
Marin Biological Laboratories Offers Addition Services
- Cell-based potency assays
- Lot release assays
- Radioimmunoassays (RIA)
MarinBio has a license for seven radioisotopes.
