Step forward with Bi-213: Cyclen-based phosphonates show improved radiolabeling and stability

Bi-213 is an attractive alpha-emitter for targeted radiotherapy of cancer. It is commonly introduced into small peptides via a DOTA complex, and into antibodies via CHX-A-DTPA. We investigated Bi-213-labeling efficiency, kinetics and stability of phosphonic and phosphinic acid analogs of DOTA.JRC.E.5-Nuclear chemistr

Efficient formation of inert Bi-213 chelates by tetraphosphorus acid analogues of DOTA: Towards improved alpha-therapeutics

Background: The recently growing interest in targeted alpha-therapy (TAT) calls for improvement of the labelling chemistry of the corresponding radionuclides. 213BiIII is a short-lived alpha emitter which emits only one alpha particle in its decay chain. Hence, it might be safer in application than other respective nuclides, such as 223Ra or 225Ac, because no alpha-emitting daughters are released upon recoil. We investigated cyclen derivatives with phosphorus-containing pendant arms regarding their suitability for 213Bi labelling. Results: The concentration dependency of 213Bi labelling at 25 °C and 95 °C was determined for DOTP, DOTPH, DOTPEt, and DOTPI, as well as for DOTA and CHX-A"-DTPA for comparison. The labelling efficiency of the phosphorus-containing ligands was at least comparable to CHX-A"-DTPA and exceeded that of DOTA. DOTP was most efficient, requiring chelator concentrations for labelling which were approx. two orders of magnitude lower than those required for CHX-A"-DTPA, both at 25 °C and 95 °C. The 213Bi complexes of phosphorus ligands furthermore showed a higher stability against demetallation (> 96% of intact complex after 120-min incubation in plasma were found for DOTP, DOTPH, and DOTPEt, compared to 85% for DOTA and 76% for CHX-A"-DTPA). Conclusion: Cyclen derivatives bearing four N-methylenephosphonic or -phosphinic acid substituents, e.g., DOTP, are capable of complexing the alpha-emitting radionuclide 213BiIII with higher efficiency and in-vitro stability than the current gold standards DOTA and CHX-A"-DTPA.JRC.G.I.5-Advanced Nuclear Knowledg

Interallelic and Intergenic Incompatibilities of the <em>Prdm9</em> (<em>Hst1</em>) Gene in Mouse Hybrid Sterility

<div><p>The Dobzhansky-Muller model of incompatibilities explains reproductive isolation between species by incorrect epistatic interactions. Although the mechanisms of speciation are of great interest, no incompatibility has been characterized at the gene level in mammals. The <em>Hybrid sterility 1</em> gene (<em>Hst1</em>) participates in the arrest of meiosis in F₁ males of certain strains from two <em>Mus musculus</em> subspecies, e.g., PWD from <em>M. m. musculus</em> and C57BL/6J (henceforth B6) from <em>M. m. domesticus</em>. <em>Hst1</em> has been identified as a meiotic PR-domain gene (<em>Prdm9</em>) encoding histone 3 methyltransferase in the male offspring of PWD females and B6 males, (PWD×B6)F₁. To characterize the incompatibilities underlying hybrid sterility, we phenotyped reproductive and meiotic markers in males with altered copy numbers of <em>Prdm9</em>. A partial rescue of fertility was observed upon removal of the B6 allele of <em>Prdm9</em> from the azoospermic (PWD×B6)F₁ hybrids, whereas removing one of the two <em>Prdm9</em> copies in PWD or B6 background had no effect on male reproduction. Incompatibility(ies) not involving <em>Prdm9^B6</em> also acts in the (PWD×B6)F₁ hybrids, since the correction of hybrid sterility by <em>Prdm9^B6</em> deletion was not complete. Additions and subtractions of <em>Prdm9</em> copies, as well as allelic replacements, improved meiotic progression and fecundity also in the progeny-producing reciprocal (B6×PWD)F₁ males. Moreover, an increased dosage of <em>Prdm9</em> and reciprocal cross enhanced fertility of other sperm-carrying male hybrids, (PWD×B6-C3H.<em>Prdm9</em>)F₁, harboring another <em>Prdm9</em> allele of <em>M. m. domesticus</em> origin. The levels of <em>Prdm9</em> mRNA isoforms were similar in the prepubertal testes of all types of F₁ hybrids of PWD with B6 and B6-C3H.<em>Prdm9</em> despite their different prospective fertility, but decreased to 53% after removal of <em>Prdm9^B6</em>. Therefore, the <em>Prdm9^B6</em> allele probably takes part in posttranscriptional dominant-negative hybrid interaction(s) absent in the parental strains.</p> </div

Sex body formation in the <i>Prdm9^PWD/−</i> F₁ hybrid male.

<p>Surface-spread nuclei of adult testicular cells treated with a hypotonic solution were indirectly labeled using antibodies marking the synaptonemal complex (anti-SYCP1 and anti-SYCP3) to discern the stage of primary spermatocytes and the phosphorylated form of the histone variant H2AX (anti-γH2AX) to visualize the sex body and then observed under a fluorescent microscope. Left, pachytene carrying a sex body (67 cases found per total of 100 nuclei from four biological replicates); right, pachytene without a sex body (33/100 nuclei).</p