A new marker for imaging cancer cells

An international team of scientists, attended by scientists from the POLATOM Radioisotope Center of the National Centre for Nuclear Research in Świerk, proposed the use of a new chemical compound for imaging prostate and breast cancer.[99mTc] Tc-DB15 consists of the diagnostic radioactive isomer * Tc-99m ** technetium, bound to an antagonist (or receptor blocking substance) of the Gastrin-Releasing Peptide Receptor (GRPR) found in certain types of cancer cells.

The use of the compound[99mTc] Tc-DB15 allows the detection of neoplasms thanks to the use of Tc-99m, which emits photons with energies in the gamma range during decay. These photons are then recorded in a SPECT (Single Photon Emission Computed Tomography) tomograph. This device, similar to PET (Positron Emission Tomography), observes the photons from the decay of Tc-99m, and after developing a special algorithm, generates a three-dimensional image of the patient with clearly visible sites of photon emission from the decay of the radioisotope. Technet-99m, attached to the receptor antagonist, accumulates in cells with increased GRPR density, i. e. in cancer cells. As a result, it makes it possible to locate and determine the activity of neoplastic cells. Cell receptor antagonists, used in diagnostics, can also potentially be used in theranostics, i. e. therapy combined with diagnostics, using ionizing radiation to kill cancer cells.

Initial in vitro studies of the new marker on breast and prostate cancer cells showed that the cancer cells accumulate the marker well. Further in vivo studies were performed in mice implanted with GRPR-positive prostate and breast cancer cells. It has been shown that after administration, the preparation concentrates quickly in neoplastic cells. After the safety of the study drug was confirmed, two female patients suffering from breast cancer whose cells had GRPR receptors were subjected to this method of imaging. The research was carried out on the basis of a research protocol approved by the Bioethics Committee of the Medical University of Karol Marcinkowski in Poznań. The patients gave their informed consent to participate in the research.

„Modern medicine uses very similar strategies to the one proposed by us, such as the treatment of breast tumors with HER2 receptors. „– explains professor Renata Mikołajczak, co-author of the research – „The new procedure, based on the use of antagonistic compounds for GRPR receptors, would be another personalized method in the treatment of a specific type of cancer cells, and increasing the number of techniques allows for precise and effective treatment of various types of cancer. „

* An isomer of a given element is an element with the same mass and atomic number, i. e. having the same number of protons and neutrons in the nucleus, where at least one of the nucleons is at a higher energy level. Isomers are metastable, which means they have a limited lifetime and decay by emitting photons. The tracer used in this study is the technetium isomer, Tc-99m. The half-life of this isomer is 6 hours. This means that after 6 hours 50% of the elements have decayed, after another 6 hours half of what was left, i. e. a further 25% of the original amount. After 24 hours, more than 90% of the atoms of this element decay. This feature, and the emission of a gamma photon with an energy of 140 keV, make Tc-99m the most widely used diagnostic marker in nuclear medicine.

** Tc-99m is mainly obtained from the decomposition of Molybdenum Mo-99 in the so-called radionuclide generators, produced, among others, by POLATOM, enabling the acquisition of Tc-99m from Mo-99 decay. Molybdenum-99 is in turn obtained from the decay of Uranium U-235. This method of production is used in the MARIA reactor of the National Center for Nuclear Research in Świerk. Mo-99 has a half-life of 66 hours, thus the generators can be easily delivered to the radiopharmaceutical application site (e. g., hospital).

Source / Graphics: https://www.mdpi.com/2072-6694/13/20/5093