Utilizing and experimental and computational approach to ligand design for chelating oxorhenium(V) and oxotechnetium(V)

Abstract

Drugs that contain radioactive atoms for either imaging or therapy are considered radiopharmaceuticals. Targeted radiotherapy, delivering the radiopharmaceutical via intra venous injection to localize in a specific (cancerous) tissue, provides the ability to treat unknown or inaccessible tumors. One way to target tumor cells with radiotherapy, the bifunctional chelate approach, requires the use of a biological targeting vector (peptide, antibody, or antibody fragment) that attaches to a specific binding site on tumor cell surfaces. The biological targeting vector is conjugated to a chelator that complexes the radiometal. Previous work with rhenium and technetium has shown that many chelators show kinetic inertness with technetium, but lose rhenium in vivo. This work aims to identify a bifunctional chelate(s) that will 1) complex [superscript 186/188]Re[superscript V] in the chelator, 2) deliver the therapeutic radionuclide to tumor tissue, and 3) prevent the loss of the metal in vivo. A computational screening of several chelators and synthesis of two of those chelators has been accomplished in this work. Benchmark computations identified appropriate computational methods to provide accurate energetic trends and structural data for monooxorhenium(V) complexes. Next, computations were used to examine a group of monoamine-monoamide dithiol (MAMA) and bisaminodithiol (BAT) ligands with respect to a previously synthesized 222MAMA ligand. 222MAMA and 323MAMA chelators were synthesized to determine the optimal chelator for the oxorhenium(V) and oxotechnetium(V) cores for use in a bifunctional chelator. Metal complexes (with [superscript nat]Re, [superscript 186]Re, and [superscript 99m]Tc) were prepared with precursors and the entire 222MAMA-6-Ahx-BBN(7-14)NH2 bifunctional chelator. Additionally, in vitro cell binding assays with PC-3 tumor cells utilizing ReO-222MAMA-6-Ahx-BBN(7-14)NH2 and in vivo biodistributions with CF-1 (normal) mice utilizing [superscript 99m]TcO-222MAMA-6-Ahx-BBN(7-14)NH2 will be discussed.