Improved cell-specificity of adeno-associated viral vectors for medullary thyroid carcinoma using calcitonin gene regulatory elements.

Targeted gene therapy using recombinant adeno-associated virus (rAAV) vectors is a potential therapeutic strategy for treating cancer, and tissue-specific promoters may help with tissue targeting. Medullary thyroid carcinoma (MTC) is a disease of the calcitonin secreting thyroid C cells, and calcitonin is highly expressed in MTC tumors compared to other cells. To target MTC cells, we evaluated an rAAV serotype 2 vector (rAAV2-pM+104-GFP) containing a modified calcitonin/calcitonin gene related peptide promoter (pM+104) and a green fluorescent protein (GFP) reporter gene. In vitro transduction experiments comparing the MTC TT cell line with non-MTC cell lines demonstrated that rAAV2-pM+104-GFP infection yielded significantly (p < 0.05) higher GFP expression in TT cells than in non-MTC cell lines (HEK293 and HeLa), and significantly higher expression than in TT cells infected with the positive control rAAV2-pCBA-GFP vector. The rAAV2-pCBA-GFP control vector included a well-characterized, ubiquitously expresses control promoter, the chicken beta actin promoter with a cytomegalovirus enhancer (pCBA). In vivo experiments using a TT cell xenograft tumor mouse model showed that tumors directly injected with 2 x 1010 vg of rAAV2-pM+104-GFP vector resulted in GFP expression detected in 21.7% of cells, 48 hours after the injection. Furthermore, GFP expression was significantly higher for rAAV-pM+104-GFP treatments with a longer vector treatment duration and higher vector dose, with up to 52.6% (q < 0.05) GFP cells detected 72 hours after injecting 1x 1011 vg/tumor. These data show that we have developed an rAAV vector with improved selectivity for MTC.