RADIOLABELED ANTISENSE PROBES - DIAGNOSIS AND THERAPY

The antisense radiopharmaceuticals labeled with I-125, In-111, Tc-99m and Sm-153 radionuclides were developed and tested for stability, permeability in cultured transformed cells and cellular elements of blood. The specific and abundant mRNAs for amplified oncogenes in cancer cells will be specific intracellular receptors for these tracers. Most of the studies were carried out with the In-111 labeled probes. The pharmacokinetics of several In-111 labeled deoxynucleotides (oxo and thio derivatives, sense and antisense) of different nucleotide lengths and sequences, specific for binding mRNAs of beta-actin, histone4 c-myc, c-myb and c-erbB2 were studied in Balb/c and nude mice, Beagle dogs and Yorkshire pigs. The paradigm of maximal probe uptake was tested in mammary-tumor-bearing Balb/c and human tumor xenograft (MCF-7) in nude mice. For neutrophil labeling, we have targeted the histone4 mRNA in the neutrophils for direct labeling in whole blood. Using the P388 cell line (murine monocytic leukemia) and neutrophils from canine, porcine and human blood as model cells, we had screened several labeled deoxyoligo-nucleotides for optimum nucleotide length (15, 20, 25 mer) and sequence (transcription initiation site, coding and cap region), prepared several In-111 labeled aminohexyl polyaminopolycarboxylate conjugated deoxyoligonucleotides (AHON) and evaluated their potential for optimal uptake in c-myc- and c-erbB2-rich MCF-7 and P388 cells. The pharmacokinetics of antisense probes was further evaluated in Balb/c (mouse mammary tumor) and nude mice (human breast tumor xenograft). The (99)mTc labeled DTPA-phosphorothioate derivatives were labeled by ligand-exchange with Tc-99m glucoheptonate and conditions of radiolabeling with Tc-99m AHON were optimized. Sm-153 radionuclide was chelated with DTPA-conjugated phosphodiester and phosphorothioate. The phosphorothioate derivative is more susceptible to radiolysis from beta-rays than phosphodiester. Similar higher radiolysis was also observed with I-125 and I-131 labeled oligonucleotide derivatives. Further evaluation of In-111, Tc-99m and Sm-153 labeled oncogene probes in cell cultures and animal models will result in future clinical evaluations for diagnosis and therapy in cancer patients.