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- Title
<sup>123</sup>I-labeled HIV-1 tat peptide radioimmunoconjugates are imported into the nucleus of human breast cancer cells and functionally interact in vitro and in vivo with the cyclin-dependent kinase inhibitor, p21<sup>WAF-1/Cip-1</sup>.
- Authors
Meiduo Hu; Chen, Paul; Wang, Judy; Scollard, Deborah A.; Vallis, Katherine A.; Reilly, Raymond M.
- Abstract
To evaluate the internalization and nuclear translocation of 123I-tat-peptide radioimmunoconjugates in MDA-MB-468 breast cancer cells and their ability to interact with the cyclin-dependent kinase inhibitor, p21WAF-1/Cip-1. Peptides [GRKKRRQRRRPPQGYGC] harboring the nuclear-localizing sequence from HIV tat domain were conjugated to anti-p21WAF-1/Cip-1 antibodies. Immunoreactivity was assessed by Western blot using lysate from MDA-MB-468 cells exposed to EGF to induce p21WAF-1/Cip-1. Internalization and nuclear translocation were measured. The ability of tat-anti-p21WAF-1/Cip-1 to block G1-S phase arrest in MDA-MB-468 cells caused by EGF-induced p21WAF-1/Cip-1 was evaluated. Tumor and normal tissue uptake were determined at 48 h p.i. in athymic mice implanted s.c. with MDA-MB-468 xenografts injected intratumorally with EGF. There was 13.4±0.2% of radioactivity internalized by MDA-MB-468 cells incubated with 123I-tat-anti-p21WAF-1/Cip-1 and 34.6±3.1% imported into the nucleus. Tat-anti-p21WAF-1/Cip-1(8 μ M) decreased the proportion of EGF-treated cells in G1 phase from 81.9±0.7% to 46.1±0.7% ( p<0.001), almost restoring the G1 phase fraction to that of unexposed cells (25.8±0.2%). Non-specific tat-mouse IgG did not block EGF-induced G1-S phase arrest. Tumor uptake of radioactivity was higher in mice injected with EGF to induce p21WAF-1/Cip-1 than in mice not receiving EGF (3.1±0.4% versus 1.8±0.2% ID/g; p=0.04). Western blot analysis of tumors revealed a threefold increase in the p21WAF-1/Cip-1/β-actin ratio. We conclude that intracellular and nuclear epitopes in cancer cells can be functionally targeted with tat-radioimmunoconjugates to exploit many more epitopes for imaging and radiotherapeutic applications than have previously been accessible.
- Subjects
BREAST cancer; PROTEIN kinases; TUMORS; WESTERN immunoblotting; NUDE mouse; CELLULAR pathology; CANCER cells
- Publication
European Journal of Nuclear Medicine & Molecular Imaging, 2007, Vol 34, Issue 3, p368
- ISSN
1619-7070
- Publication type
Article
- DOI
10.1007/s00259-006-0189-0