VEGFR2-Targeted Transfection of Melanoma Tumors via Ultrasound Mediated Destruction of Plasmid-Bearing Microbubbles

Survival rates for late stage melanoma can be as low as 7% and despite improvements in cancer therapy, surgery remains the primary treatment for melanoma. In this study we examined microbubble-mediated gene delivery to B16-F1 mouse melanoma tumors as an alternative therapeutic strategy. To determine an appropriate target for tumor-specific gene delivery, targeted-microbubble imaging was used to compare the expression patterns of the angiogenesis marker VEGFR2 and the inflammation marker VCAM-1 in B16 melanomas since angiogenesis and inflammation are both associated with tumor progression. Results showed that bubbles targeted to VEGFR2 bound specifically to the tumor endothelium and not to non-tumor tissue endothelium. However, VCAM-1-targeted bubble binding was elevated in both tumor and non-tumor tissue. Since VCAM-1 is not constitutively expressed on endothelial cells, this suggests systemic inflammation in tumor-bearing mice. This will be explored in future work since systemic inflammation can have negative implications for tumor immunotherapies.

Next, VEGFR2-targeted microbubbles were used to deliver RFP reporter plasmid as a proof of concept for gene delivery to melanoma tumors. Plasmids were attached to cationic bubbles via charge coupling. Sonoporation was induced via a 1 MHz transducer set at 0.37 W/cm2 in intensity and 100% duty cycle. Immunohistochemical staining of RFP expression in tumor and muscle tissue showed tumor specific transfection. Transfection mostly occurred near blood vessels, demonstrating that microbubble-mediated delivery of therapeutic genes would be most useful for highly perfused tumors. Future work would include increasing the DNA payload and bubble transfection efficiency using the cationic polymer PEI to possibly transfect cells further away from the vessel wall.