Use of knottin as a PSMA-tropic peptide carrier

Prostate cancer is the most common type of cancer in males. Approximately 1.3 million cases of prostate cancer and over 400,000 deaths from the disease are diagnosed annually. The number of deaths is expected to double by 2040. Common methods of prostate cancer treatment have many disadvantages; one of them is the relapse risk. The shortcomings of traditional therapy have led to peptide-receptor radionuclide therapy. The aim of the study is to examine binding efficiency of Lu177 labeled knottins containing PSMA-tropic peptide in different domains in vitro and their biodistribution in vivo. Materials and Methods. We used prostate cancer cell (LNCaP, PC3) and ovarian fibroblast cell (CHO-K1) cultures. The peptides were synthesized using a peptide synthesizer (ResPepSL, Intavis). We studied peptide stability, their toxicity, binding to cell cultures, and biodistribution on the example of breast adenocarcinoma-bearing BALB/c mice. Chromatographic methods and radiometric techniques were used. Results. The synthesized peptides with GTIQPYPFSWGY sequence inserted into U5-cytotoxin-Sth1a node are more stable in blood plasma and saline than 177Lu-PSMA-617a, but have a similar degree of binding. Biodistribution studies in BALB/c mice show a higher binding index of the synthesized peptide if compared to 177Lu-PSMA-617. Conclusion. Modified peptides with a PSMA-tropic peptide inserted into the structure of U5-Sth1a toxin demonstrate high stability both in saline and in blood plasma, as well as good binding to cell cultures and tumors.