A PSMA scan is a nuclear medicine imaging technique used in the diagnosis and staging of prostate cancer. It is carried out by injection of a radiopharmaceutical with a positron or gamma emitting radionuclide and a prostate-specific membrane antigen (PSMA) targeting ligand. After injection, imaging of positron emitters such as gallium-68 (68Ga), copper-64 (64Cu), and fluorine-18 (18F) is carried out with a positron emission tomography (PET) scanner. For gamma emitters such as technetium-99m (99mTc) and indium-111 (111In) single-photon emission computed tomography (SPECT) imaging is performed with a gamma camera.
As well as the diagnosis and staging of prostate cancer, PSMA imaging can also be used to assess suitability for and plan treatment with external beam radiotherapy and PSMA-targeted radionuclide therapy. [1] [2]
Attempts have been made to target the overexpression of PSMA in prostate cancer cells for several decades, although PSMA is also found in other tissue. PSMA targeting molecules have included antibodies, aptamers, peptides, and small-molecule inhibitors. [3] [4] Initially, development focussed on the antibody capromab. Later research has focussed on small molecule ligands that bind to the extracellular active centre of PSMA, such as PSMA-11. [5] These ligands for PSMA-scanning target the large extracellular region of the PSMA glycoprotein. [6]
PSMA however is also over-expressed in non prostate cancer cells, including kidney, salivary gland, lacrimal gland and duodenal mucosa, where physiological uptake may be seen on imaging. [7]
European Association of Urology (EAU) guidelines recognise that PSMA can provide accurate staging, however there is a lack of outcome data to inform further management. [8] The American Society of Clinical Oncology (ASCO) guidelines for imaging of advanced prostate cancer also recommend PSMA imaging (among other PET radiopharmaceuticals), while acknowledging that these are not FDA approved and therefore limited to a clinical trial or other controlled research setting. [9]
Radionuclide | Name | INN | Brand name(s) | FDA approval | EMA approval | References |
---|---|---|---|---|---|---|
18F | DCFPyL | PIFLUFOLASTAT F-18 |
| Yes | Yes | [10] [11] |
18F | PSMA-1007 | |||||
18F | rhPSMA-7.3 | Posluma | Yes | |||
68Ga | PSMA-11 | Gallium (68Ga) gozetotide |
| Yes | Yes | [3] |
68Ga | THP-PSMA | Gallium (68Ga) gozetotide | GalliProst | [12] | ||
99mTc | PSMA-11 | |||||
99mTc | iPSMA | TLX599-CDx | [13] | |||
111In | capromab pendetide | Prostascint | Yes | [14] | ||
111In | PSMA-I&T | [3] | ||||
In part thanks to the wide range of similar PSMA radiopharmaceuticals, [4] [15] approval by regulatory authorities is at varying stages. Even so, use has been widespread in some areas, particularly as part of clinical trials. For example, European Association of Urology (EAU) guidelines have included recommendations to perform PSMA PET scans in certain circumstances since 2018, and there has been widespread agreement of the utility of PSMA scanning for several years. [16] [17] [18] [19]
A kit for manufacture of a 68Ga-PSMA-11 product, branded Illucix, was approved by Australia's Therapeutic Goods Administration (TGA) in 2021. [20]
A marketing authorisation application for 68Ga-PSMA-11 (INN Gallium (68Ga) gozetotide), under the brand name Illucix, was made to the Danish Medicines Agency, on behalf of several EU countries and the UK. Approval is expected in 2022. [21] [22]
In 2022 a marketing authorisation application was made by the manufacturer of 18F-DCFPyL (branded Pylclari) to the European Medicines Agency. [11]
Polish manufacturer and distributor of radiopharmaceutical procuts, Polatom, has been granted a US patent for a 99mTc-PSMA-T4 kit. [23] [24] In the UK, Tc-99m labelled PSMA has product authorisation but lacks funding. [25]
A new drug submission was made to Canada's regulator in 2021, for 68Ga-PSMA-11. [26]
The first approved PSMA imaging agent was indium-111 (111In) capromab pendetide (branded Prostascint). It received Food and Drug Administration (FDA) approval in 1996. [14] However, the agent had poor sensitivity and saw little widespread use. [18]
The first PET PSMA imaging agent, 68Ga-PSMA-11, was approved by the FDA in 2020. [27] Listed indications include suspected metastasis prior to initial treatment, and recurrence of prostate cancer (based on elevated serum prostate-specific antigen (PSA) level). [28] This was followed by two further 68Ga-PSMA-11 agents in 2021 and 2022 (branded Illucix and Locametz). [29] [30] Listed indications for Lucametz additionally includes selection of patients prior to 177Lu-PSMA radionuclide therapy. [31]
An 18F-PSMA agent (18F-DCFPyL) (branded Pylarify) was approved by the FDA in 2021. [32] Indications are as for 68Ga-PSMA-11. [33] [34]
Another 18F-PSMA agent (18F-rhPSMA-7.3) (branded Posluma) was approved by the FDA in 2023. [35]
68Ga-PSMA-11 (Illucixwas) was granted initial authorisation in 2021, with full approval expected in 2022. [36] [37]
Nuclear medicine, or nucleology, is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging is, in a sense, radiology done inside out, because it records radiation emitted from within the body rather than radiation that is transmitted through the body from external sources like X-ray generators. In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.
A radioligand is a microscopic particle which consists of a therapeutic radioactive isotope and the cell-targeting compound - the ligand. The ligand is the target binding site, it may be on the surface of the targeted cancer cell for therapeutic purposes. Radioisotopes can occur naturally or be synthesized and produced in a cyclotron/nuclear reactor. The different types of radioisotopes include Y-90, H-3, C-11, Lu-177, Ac-225, Ra-223, In-111, I-131, I-125, etc. Thus, radioligands must be produced in special nuclear reactors for the radioisotope to remain stable. Radioligands can be used to analyze/characterize receptors, to perform binding assays, to help in diagnostic imaging, and to provide targeted cancer therapy. Radiation is a novel method of treating cancer and is effective in short distances along with being unique/personalizable and causing minimal harm to normal surrounding cells. Furthermore, radioligand binding can provide information about receptor-ligand interactions in vitro and in vivo. Choosing the right radioligand for the desired application is important. The radioligand must be radiochemically pure, stable, and demonstrate a high degree of selectivity, and high affinity for their target.
A bone scan or bone scintigraphy is a nuclear medicine imaging technique used to help diagnose and assess different bone diseases. These include cancer of the bone or metastasis, location of bone inflammation and fractures, and bone infection (osteomyelitis).
Prostate cancer screening is the screening process used to detect undiagnosed prostate cancer in men without signs or symptoms. When abnormal prostate tissue or cancer is found early, it may be easier to treat and cure, but it is unclear if early detection reduces mortality rates.
Fluorine-18 is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96.7% of the time and electron capture 3.3% of the time. Both modes of decay yield stable oxygen-18.
A gallium scan is a type of nuclear medicine test that uses either a gallium-67 (67Ga) or gallium-68 (68Ga) radiopharmaceutical to obtain images of a specific type of tissue, or disease state of tissue. Gallium salts like gallium citrate and gallium nitrate may be used. The form of salt is not important, since it is the freely dissolved gallium ion Ga3+ which is active. Both 67Ga and 68Ga salts have similar uptake mechanisms. Gallium can also be used in other forms, for example 68Ga-PSMA is used for cancer imaging. The gamma emission of gallium-67 is imaged by a gamma camera, while the positron emission of gallium-68 is imaged by positron emission tomography (PET).
TAH molecule, also known as N-acetyl-L-aspartyl-L-glutamate peptidase I, NAAG peptidase, or prostate-specific membrane antigen (PSMA) is an enzyme that in humans is encoded by the FOLH1 gene. Human GCPII contains 750 amino acids and weighs approximately 84 kDa.
Copper-64 (64Cu) is a positron and beta emitting isotope of copper, with applications for molecular radiotherapy and positron emission tomography. Its unusually long half-life (12.7-hours) for a positron-emitting isotope makes it increasingly useful when attached to various ligands, for PET and PET-CT scanning.
Iobenguane, or MIBG, is an aralkylguanidine analog of the adrenergic neurotransmitter norepinephrine (noradrenaline), typically used as a radiopharmaceutical. It acts as a blocking agent for adrenergic neurons. When radiolabeled, it can be used in nuclear medicinal diagnostic and therapy techniques as well as in neuroendocrine chemotherapy treatments.
Cabazitaxel, sold under the brand name Jevtana, is a semi-synthetic derivative of a natural taxoid. It is a microtubule inhibitor, and the fourth taxane to be approved as a cancer therapy.
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Advanced Accelerator Applications is a France-based pharmaceutical group, specialized in the field of nuclear medicine. The group operates in all three segments of nuclear medicine to diagnose and treat serious conditions in the fields of oncology, neurology, cardiology, infectious and inflammatory diseases.
Fluciclovine (18F), also known as anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid, and sold under the brand name Axumin, is a diagnostic agent used for positron emission tomography (PET) imaging in men with suspected prostate cancer recurrence based on elevated prostate specific antigen (PSA) levels.
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Gallium (68Ga) gozetotide or Gallium (68Ga) PSMA-11 sold under the brand name Illuccix among others, is a radiopharmaceutical made of 68Ga conjugated to prostate-specific membrane antigen (PSMA) targeting ligand, Glu-Urea-Lys(Ahx)-HBED-CC, used for imaging prostate cancer by positron emission tomography (PET). The PSMA targeting ligand specifically directs the radiolabeled imaging agent towards the prostate cancerous lesions in men.
Lutetium (177Lu) vipivotide tetraxetan, sold under the brand name Pluvicto, is a radiopharmaceutical medication used for the treatment of prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer (mCRPC). Lutetium (177Lu) vipivotide tetraxetan is a targeted radioligand therapy.
Flotufolastat F-18, sold under the brand name Posluma, is a radioactive diagnostic agent for use with positron emission tomography (PET) imaging for prostate cancer. The active ingredient is flotufolastat F-18 gallium.