- 06 Apr, 2021
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sciences and nursing
Prostate-specific membrane (PSMA) is popularly used with regard to prostate cancer. It has long been considered as a sure target for molecular imaging and therapy. Prostate cancer is leading because of death among the male in the entire world. Effective management of this menace calls for early diagnosis together with an accurate staging of the PCa. Failure to diagnose cancer early enough result to a fast spreading of cancer beyond the prostate to unmanageable stages hence leading to death. Currently, there is no specific universal imagine that has been approved for the detection of early stages of prostate cancer. Prostate-specific membrane antigen (PSMA) has hence been the most preferred because it is overexpressed in almost 90-100% of the local PCa lesions. It is also evidenced in the cancerous lymph nodes and bone metastases. In addition, PSMA can be found other tissues such as normal prostate epithelium, renal tubular, small intestines and salivary glands.
Nanobodies are the smallest antibody-based fragments that have the required molecular imaging characteristics. Some of the properties include high target specificity and fast background clearance. The study targeted at developing a novel anti- PSMA Nanobody (JVZ-007). The novel was meant to be in the case of target imaging and treatment of prostate cancer. The authors hence described the process involved in the development of Nanobody targeting PSMA, showing good tumor targeting and fast blood clearance. This was expected to result in impressive tumor-to background rations in a few hours after injection.
Method
The authors first developed a nanobody library by immunization of Allam together with human PCa cell lines. The nanobodies were taken by biopanning on the PSMA. Evaluation of the imaging probe was done by the use of JVZ-007 had a c-myc-hexahistidine tag in order to allow purification and detection. Site-specific conjugation chelates that were used for radiolabeling was achieved by changing the c to -myc-hexahistidine a single cysteine at the C terminus. Lysine was used for the conjugation of JVZ-007- myc-hexahistidine to 2-diethylenetriaminepentaacetic acid. However, C-terminal cysteine was used for the conjugation of JVZ-007-cys to maleimide-DTPA. Cell binding experiments by the use of flow cytometer and autoradiography was used for the analysis of PSMA targeting. In addition, internalization assays that gas different PCa cell lines and xenografts (PDXs) obtained from the patient was also used. The evaluation of the targeting characteristics of the radiolabeled nanobodies was in the lab by both SPECT/CT imaging experiments and biodistribution. Mice with PSMA-positive PC-310 and PSMA-negative PC-3 tumors were also used in the analysis.
Results
Chatalic, et al., (2015) managed to conjugate JVZ-007 to DTPA that later radiolabeled with 111In at room temperature. 111In-JVZ007-c-myc-his and 111In-JVZ007-cys internalized in LNCaP cells and attached to PSMA-expressing PDXs. The attached was not done in the case of PSMA-negative PDXs and human kidneys. Both 111InJVZ-007-c-myc-his and 111In-JVZ-007-cys recorded good tumor targeting together with fast blood clearance. Injection of gelofusine and lysine reduced the renal uptake of 111In JVZ-007-c-myc-his. Finally, the PC-310 tumors were well visualized by SPECT/CT when using both tracers.
Isoflurane/O2 anesthesia was used to scan mice at 3 and 4 hours injection on small-animal nano-SPECT (Mediso) with a heated bed. Supplemental data was used to describe scanning, reconstruction and counting parameters. The Animal Experiments Committee under the Dutch Experiment on animals Act first approved all the animals used in the study. The study also adhered to the European Convention for the protection of vertebrates Animals.
Discussion
The use of PSMA small molecules inhibitors is more advantageous because it easily localizes to tumor lesions, soft tissue, and bone metastases. It also shows high uptake in the kidneys and salivary. The reduction in the renal uptake was attributed to the co-administration of gelofusine and lysine. The initial high renal uptake, on the other hand, was due to reabsorption in the renal proximal tubule. The His-tag increased the retention rate of the radiolabeled nanobodies in the Kidneys. The reduced renal retention increased