A new chemically modified chimeric TNT-3 monoclonal antibody directed against DNA for the radioimmunotherapy of solid tumors.

In the last several years, our laboratory has developed a new approach to the radioimmunotherapy of solid tumors, designated Tumor Necrosis Treatment (TNT), that exploits the presence of degenerating and necrotic cells within tumors by utilizing MAbs directed against universal, intracellular antigens. The first TNT MAb developed by our laboratory, designated TNT-1, was directed against nucleosomal determinants consisting of histone H1 and DNA. Since absolute tumor accretion of MAb is a critical determinant of antitumor efficacy in radioimmunotherapy, we sought to identify new antinuclear antibodies that displayed high tumor localization properties. In the present study, we describe a murine antinuclear antibody, TNT-3, which demonstrates 3-fold higher tumor uptake than TNT-1. Because of this characteristic, a chimeric derivative designated chTNT-3 was developed and evaluated for antigen binding and tumor targeting. ELISA studies using a series of nuclear antigens confirmed that TNT-3 is directed against single-stranded DNA and does not cross react with TNT-1. Immunohistology reveals predominantly nuclear staining reactivity in human tissues and tumors. Since it was shown by our laboratory that charge modification can significantly improve the pharmacokinetic performance of monoclonal antibodies, chTNT-3 was chemically modified with biotin to generate an improved therapeutic reagent designated chTNT-3/B. Comparative studies with unmodified MAb demonstrated that biotinylation significantly shortened its clearance time in mice and produced lower normal tissue levels, while maintaining an equal amount of uptake in tumor xenografts for up to 10 days. These in vivo characteristics suggest that chTNT-3/B is an improved TNT reagent for the radioimmunotherapy of solid tumors.

Potential role of the inactivated X chromosome in ovarian epithelial tumor development.

BACKGROUND: Ovarian epithelial tumors can be divided into subcategories often regarded as different stages of neoplastic transformation. Cystadenomas belong to the least aggressive subgroup and are noninvasive and nonmetastatic. Ovarian tumors of low malignant potential (LMP) are intermediate between cystadenomas and carcinomas and show markedly reduced invasive and metastatic abilities. Invasion and metastasis are the hallmarks of carcinomas, which constitute the most aggressive subgroup and can be further subdivided into different grades. PURPOSE: We performed comparative allelotype analyses of ovarian cystadenomas, LMP tumors, and carcinomas, reasoning that such analyses could provide clues about the molecular determinants of their phenotypic differences. Because we realized that allelic losses involving the X chromosome might be associated with LMP tumor development, we determined whether such losses were interstitial and whether they involved the active or the inactive X chromosome. METHODS: Frequencies of loss of heterozygosity (LOH) at specific loci in every chromosomal arm were determined in 16 ovarian cystadenomas, 23 ovarian LMP tumors, 15 low-grade ovarian carcinomas, and 35 high-grade ovarian carcinomas by use of either the polymerase chain reaction (PCR) or Southern blot analyses. We took advantage of the fact that DNA methylation is an important mechanism of X-chromosome inactivation to determine whether losses involving the X chromosome were in the active or the inactive copy. We analyzed the methylation status of retained alleles on the X chromosome by determining whether they could be amplified by PCR after digestion with the methylation-sensitive restriction endonuclease Hpa II. RESULTS: High-grade carcinomas contained frequent(>50%) LOH in four autosomal chromosome arms, i.e., 6q, 13q, 17p, and 17q. Except for 13q, these same chromosomal arms showed frequent LOH in low-grade carcinomas. LOH in autosomal chromosomes was comparatively rare in LMP tumors and was absent in cystadenomas. In contrast, half (eight of 16) of LMP tumors informative for a locus in the proximal portion of chromosome Xq showed LOH at that locus. These losses were the result of interstitial deletions in six of the eight cases and involved the inactive copy of the X chromosome exclusively. Similar losses in the X chromosome were not seen in either cystadenomas or low-grade carcinomas. CONCLUSIONS AND IMPLICATIONS: LOH at multiple loci is associated with the development of ovarian carcinomas but not with the development of cystadenomas and LMP tumors. However, the integrity of a locus in chromosome Xq that possibly escapes X-chromosome inactivation is important for the control of LMP tumor development. The fact that this locus does not appear to be involved in the genesis of low-grade carcinomas suggests that LMP tumors are not precursors of such carcinomas.