Molecular Imaging of bcl-2 Expression in Small Lymphocytic Lymphoma Using 111In-Labeled PNA–Peptide Conjugates
Fang Jia 1,
Said Daibes Figueroa 2,
Fabio Gallazzi 3,
Baghavathy S. Balaji 1,
Mark Hannink 4,
Susan Z. Lever 5,
Timothy J. Hoffman 6,
and
Michael R. Lewis 7*
1 Department of Veterinary Medicine and Surgery, University of Missouri-Columbia, Columbia, Missouri
2 Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri
3 Molecular Biology Program, University of Missouri-Columbia, Columbia, Missouri
4 Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri
5 Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri
6 Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri; Department of Internal Medicine, University of Missouri-Columbia, Columbia, Missouri
7 Department of Veterinary Medicine and Surgery, University of Missouri-Columbia, Columbia, Missouri; Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri; Department of Radiology, University of Missouri-Columbia, Columbia, Missouri; Nuclear Science and Engineering Institute, University of Missouri-Columbia, Columbia, Missouri
* To whom correspondence should be addressed. E-mail: LewisMic{at}missouri.edu.
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Abstract |
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The bcl-2 gene is overexpressed in non-Hodgkin's lymphoma (NHL), such as small lymphocytic lymphoma (SLL), and many other cancers. Noninvasive imaging of bcl-2 expression has the potential to identify patients at risk for relapse or treatment failure. The purpose of this study was to synthesize and evaluate radiolabeled peptide nucleic acid (PNA)-peptide conjugates targeting bcl-2 gene expression. An 111In-labeled PNA complementary to the translational start site of bcl-2 messenger RNA was attached to Tyr3-octreotate for somatostatin receptor-mediated intracellular delivery. Methods: DOTA-anti-bcl-2-PNA-Tyr3-octreotate (1) and 3 control conjugates (DOTA-nonsense-PNA-Tyr3-octreotate (2), DOTA-anti-bcl-2-PNA-Ala[3,4,5,6]-substituted congener (3), and DOTA-Tyr3-octreotate (4) [DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid]) were synthesized by standard solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. In vitro studies were performed in Mec-1 SLL cells, which express both bcl-2 messenger RNA and somatostatin receptors. Biodistributions and microSPECT/CT studies were performed in Mec-1–bearing SCID (severe combined immunodeficiency) mice, a new animal model of human SLL. Results: 111In-Labeled conjugate 1 was taken up by Mec-1 cells through a somatostatin receptor-mediated mechanism. Biodistribution studies showed specific tumor uptake of conjugate 1, the somatostatin analog 4, and the PNA nonsense conjugate 2, but not of the mutant peptide conjugate 3. Mec-1 tumors could be detected by microSPECT/CT using 111In-labeled DOTA-Tyr3-octreotate (4) and the targeted anti-bcl-2 conjugate (1), but not using the 2 negative control conjugates 2 and 3. Conclusion: A new 111In-labeled antisense PNA–peptide conjugate demonstrated proof of principle for molecular imaging of bcl-2 expression in a new mouse model of human SLL. This imaging agent may be useful for identifying NHL patients at risk for relapse and conventional treatment failure.
Key Words:
bcl-2, peptide nucleic acid, somatostatin receptor, microSPECT/CT, non-Hodgkin's lymphoma
