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99mTc-peptide-peptide nucleic acid probes for imaging oncogene mRNAs in tumours
1Departments of Radiology, Thomas Jefferson University, Philadelphia 19107, USA.
Abstract:
Imaging oncogene mRNA in tumours would provide a powerful tool for the early detection of occult malignant lesions. The goal was to prepare a chimera consisting of a dodecamer antisense peptide nucleic acid (PNA) specific for c-MYC oncogene overexpressed in human breast cancer cells and a chelating moiety that facilitates quantitative radiolabelling with 99mTc and evaluate it for hybridization and tissue distribution in laboratory animals. The pentapeptide chelator-PNA dodecamer specific for c-MYC mRNA was extended from a solid support by 9-fluorenylmethyloxycarbonyl (Fmoc) coupling. Similarly, a chelator-PNA chimera with four central mismatches was also prepared which served as a control. The chimeras were purified, characterized and evaluated for hybridization to c-MYC mRNA by fluorescent, real-time polymerase chain reaction (RT-PCR). The chimeras were labelled with 99mTc and their tissue distribution was examined in athymic nude mice bearing experimental human breast tumours. 99mTc radiolabelling was quantitative and presented a single peak in reversed phase liquid chromatography. Fluorescent real-time polymerase chain reactions using primer and fluorescent probe sets previously calculated for c-MYC mRNA demonstrated inhibition of reverse transcription by the c-MYC specific chimera as compared to that of the control. Tissue distribution studies of antisense and mismatch chimeras at 4 h and 24 h after administration displayed modest accumulation in the liver, and appreciable levels in tumours. These observations suggest that 99mTc-peptide-PNA probes might be useful for imaging gene expression in tumours, and the approach is worthy of further investigation.
Insights
Researchers developed a novel 99mTc-labeled peptide-PNA chimera to image c-MYC oncogene mRNA in breast tumors. This tool shows potential for early detection of occult malignant lesions by visualizing gene expression.
Area of Science:
- Biomedical Imaging
- Molecular Oncology
- Nucleic Acid Chemistry
Background:
- Imaging oncogene mRNA in tumors is crucial for early detection of occult malignant lesions.
- c-MYC oncogene overexpression is implicated in human breast cancer.
Purpose of the Study:
- To prepare and evaluate a chimera of an antisense peptide nucleic acid (PNA) specific for c-MYC mRNA and a chelating moiety for quantitative radiolabeling with 99mTc.
- To assess the hybridization and tissue distribution of the 99mTc-labeled chimera in laboratory animals for potential tumor imaging.
Main Methods:
- Synthesis of a dodecamer antisense PNA specific for c-MYC mRNA conjugated to a pentapeptide chelator.
- Preparation of a control chimera with four central mismatches.
- Evaluation of hybridization using fluorescent real-time polymerase chain reaction (RT-PCR).
- Radiolabeling with 99mTc and subsequent tissue distribution studies in athymic nude mice bearing human breast tumors.
Main Results:
- Quantitative 99mTc radiolabeling of the chimera was achieved.
- The c-MYC specific chimera demonstrated inhibition of reverse transcription in RT-PCR, confirming hybridization to c-MYC mRNA.
- Tissue distribution studies showed modest liver accumulation and appreciable levels in tumors at 4 and 24 hours post-administration.
Conclusions:
- The developed 99mTc-peptide-PNA probes show promise for imaging gene expression in tumors.
- This approach warrants further investigation for the early detection of occult malignant lesions.