PET Imaging of CCND1 mRNA in Human MCF7 Estrogen Receptor–Positive Breast Cancer Xenografts with Oncogene-Specific [64Cu]Chelator-Peptide Nucleic Acid-IGF1 Analog Radiohybridization Probes

Treatment of breast cancer is hampered by a large unmet need for rapid, sensitive, specific staging and stratification of palpable and nonpalpable abnormalities. Mammography and physical examination miss many early breast cancers, yet detect many benign lesions. Cyclin D1, encoded by CCND1 messenger RNA (mRNA), and insulin-like growth factor 1 receptor (IGFIR) are key regulators of cell proliferation that are overexpressed in most breast cancers. Therefore, we hypothesized that malignant breast masses could be imaged and quantitated externally by PET with a dual-specificity probe that targets both CCND1 mRNA and IGF1R. Methods: We designed a CCND1-specific peptide nucleic acid (PNA) hybridization sequence (CTGGT-GTTCCAT), separated by a C-terminal spacer to a cyclized IGF1 peptide analog (D-Cys-Ser-Lys-Cys), for IGF1 R-mediated endocytosis. On the N-terminus we attached a chelator (1,4,7-tris(carboxymethylaza)cyclododecane-10-azaacetyl [D03A]) for the positron-emitting nuclide 64 Cu. We administered the [ 64 Cu]CCNDI-IGF1 analog radiohybridization probes, as well as sequence controls, by tail vein to immunocompromised female NCr mice bearing human MCF7 estrogen-dependent, receptor-positive xenografts. We imaged the mice by PET and CT 4 and 24 h later, and measured tissue distribution of the radiohybridization probes. Results: We observed 8 ± 2-fold higher PET intensity in the center of the breast cancer xenografts than in the contralateral tissues at 24 h after injection of the [ 64 Cu]CCNDI-IGF1 analog radiohybridization probe. IGF1 blocking yielded significantly weaker images (P < 0.05) relative to the tumor-free side at 24 h after injection, as did a PNA mismatch probe, a peptide mismatch probe, and free 64 CuCl 2 . Conclusion: These results are consistent with our hypothesis for radiohybridization PET of overexpressed CCND1 mRNA, dependent on IGF1 R-mediated endocytosis, in suspect masses. Early noninvasive detection of initial cancerous transformation, as well as invasive or recurrent breast cancer, with dual-specificity radiohybridization probes, might enable molecularly targeted staging, stratification, and choice of therapy.