Improving the delivery and efficacy of molecular medicine via extracellular matrix modulation : insights from intravital microscopy

Abstract

The extracellular matrix of tumors is a major barrier to the delivery of molecular medicine. We used fluorescence recovery after photobleaching combined with intravital microscopy to quantitate the transport properties of the tumor interstitium. We found that the presence of fibrillar collagen correlated with hindered diffusion in vivo, and also in vitro, in collagen gels prepared to mimic tumor extracellular matrix. Modification of the tumor collagen matrix directly with purified bacterial collagenase, or indirectly with relaxin treatment, resulted in increased diffusion coefficients of macromolecules within tumors in vivo. In order to quantitate the changes in collagen content and structure induced by relaxin treatment, we adapted and further developed the imaging technique of intravital second harmonic generation microscopy. Using second harmonic generation imaging in combination with a fluorescently labeled gene therapeutic vector, we demonstrated that the spread of these viral vectors within tumors is limited by the fibrillar collagen in the extracellular matrix. Matrix modification via the introduction of bacterial collagenase along with the initial virus injection resulted in a significant improvement in the range of viral distribution within the tumor.

(cont.) This resulted in an extended range of infection of cells within the tumor, and improved virus propagation, ultimately leading to enhanced therapeutic outcome. Thus, we show that fibrillar collagen is an important barrier to the distribution of molecular medicine within tumors, and that matrix modifying treatments can significantly enhance both vector distribution, as well as ultimately therapeutic response.