Imaging Oncogene Expression

Abstract

In 2003, approximately 39,800 women in the US will die from breast cancer. Mammography and physical examination miss up to 40% of early breast cancers. Moreover, if an abnormality is found, an invasive diagnostic procedure must still be performed to determine if the breast contains atypia or cancer, even though approximately 85% of abnormalities are benign. Scintigraphic imaging of gene expression in vivo by noninvasive means could direct physicians to appropriate targets for intervention at the onset of disease and thereby significantly impact patient management. Until now, no method has been available to image specific overexpressed oncogene mRNAs in vivo by scintigraphic imaging. We hypothesize that gamma-emitting Tc-99m-PNA-peptides can be taken up by human ER+ and ER- breast cancer xenografts, hybridize to complementary mRNA targets in those cells, and concentrate sufficiently in tumor tissue to allow noninvasive imaging of oncogene overexpression. To prepare the probes, peptide analogs of insulin-like growth factor 1 (IGF1) were extended from a solid support by Fmoc coupling. Peptide nucleic acid (PNA) dodecamers antisense to CCND1 and MYC mRNAs were then extended from the N-terminus of IGF1, followed by a chelator peptide, using Fmoc coupling for all residues. The cysteine thiols were cyclized on the solid support, either before or after PNA extension. This simplified synthetic approach allows preparation of a variety of multipeptide disulfide-bridged PNA chimeras. A chelating peptide-PNA chimera antisense to MYC mRNA was then labeled efficiently with Tc-99m, yielding a single product. Tissue distribution studies of antisense and mismatch chimeras at 4 h and 24 h after administration displayed modest accumulation in the liver and kidneys, with appreciable levels in tumors. This result enables testing of Tc-99m-peptide-PNA probes to image gene expression in tumors.

Noninvasive Imaging of Human Telomerase Reverse Transcriptase (hTERT) Messenger RNA with 99mTc-Radiolabeled Antisense Probes in Malignant Tumors

“…Pioneering work in this field was reported by Dewanjee MK et al in 1994, who used a 15-mer phosphorothioate antisense oligodeoxyribonucleotide labeled with 111 In to image constitutive c-myc gene expression in a murine mammary carcinoma model (17). Up to now, ASONs targeting c-MYC, P-glycoprotein (Pgp), CCND1, mdr1, bcl-2, k-ras, unr, IgV H FR1 mRNA, and so forth have been chosen to be labeled with radionuclides such as 99m Tc, 111 In, 68 Ga, 64 Cu, 131 I and so forth (18)(19)(20)(21)(22)(23)(24)(25)(26), whose results all facilitate the development of antisense imaging. Despite an extensive literature search, we failed to find any research publication describing in vivo imaging of hTERT expression by antisense technology.…”

Preparation, 99mTc-labeling and biodistribution studies of a PNA oligomer containing a new ligand derivative of 2,2′-dipicolylamine

“…In such constructs, the role of the PNA is to direct the bioconjugate to a specific mRNA -a unique or a uniquely over-expressed mRNA in a diseased cell -while the function of the radioactive probe is to allow imaging to possibly provide information on cellular gene expression pattern and detect molecular changes at relatively early stages [13,42]. Hence, a number of in vivo biodistribution/hybridization studies of radiolabeled PNAs were undertaken [14,[17][18][19][20]22,[24][25][26][27][28][29][30][31][32][33]36,39,41,[43][44][45][46]. The majority of these reports involved the use of 99m Tc, probably due its ideal nuclear properties and the convenient availability from a commercial generator [47][48][49][50].…”

Detection ofin situmammary cancer in a transgenic mouse model:in vitroandin vivoMRI studies demonstrate histopathologic correlation

“…If mice are to be used as successful models of human cancer biology, then imaging methods that detect in situ tumors are required to accurately assess preventive, diagnostic and therapeutic interventions. To date, however, there have been no reports of in vivo imaging of in situ or even nonpalpable invasive mammary gland cancers in mice (Abbey et al 2004, Artemov et al 2003, Bremer et al 2005, Galie et al 2004, Geninatti Crich et al 2006, Hsueh et al 2006, Jenkins et al 2005, Robinson et al 2003, Rodrigues et al 2004, 2006, Seemann et al 2006, Tian et al 2003). In fact, most imaging studies of mouse mammary cancer have focused on large tumors that are extremely advanced.…”