The effect of the histological properties of tumors on transfection efficiency of electrically assisted gene delivery to solid tumors in mice

Abstract

Uniform DNA distribution in tumors is a prerequisite step for high transfection efficiency in solid tumors. To improve the transfection efficiency of electrically assisted gene delivery to solid tumors in vivo, we explored how tumor histological properties affected transfection efficiency. In four different tumor types (B16F1, EAT, SA-1 and LPB), proteoglycan and collagen content was morphometrically analyzed, and cell size and cell density were determined in paraffin-embedded tumor sections under a transmission microscope. To demonstrate the influence of the histological properties of solid tumors on electrically assisted gene delivery, the correlation between histological properties and transfection efficiency with regard to the time interval between DNA injection and electroporation was determined. Our data demonstrate that soft tumors with larger spherical cells, low proteoglycan and collagen content, and low cell density are more effectively transfected (B16F1 and EAT) than rigid tumors with high proteoglycan and collagen content, small spindle-shaped cells and high cell density (LPB and SA-1). Furthermore, an optimal time interval for increased transfection exists only in soft tumors, this being in the range of 5-15 min. Therefore, knowledge about the histology of tumors is important in planning electrogene therapy with respect to the time interval between DNA injection and electroporation.

Control by pulse parameters of DNA electrotransfer into solid tumors in mice

“…This appears to be due to their histological properties. 26 Luciferase activity in tumors as a function of LV pulse amplitude, number and duration…”

“…This high field is lower than that used for skin (200 V cm À1 ), but much higher than that used in the combination protocol for muscle (80-100 V cm À1 ). 18 The differences in transfection efficiency between different tissues, as well as different tumor histological types, can be explained by the unique characteristics of each tissue, 5,26 namely, the delivery and distribution of macromolecules, including plasmid DNA, is affected by the amount of DNases, necrosis and macrophage infiltration as well as increased interstitial fluid pressure and the amount of extracellular matrix components, such as collagen and hyaluronan. In addition, in vitro and in vivo studies have elucidated the effect of the shape, size and orientation of cells in tissue and cell density on electric field distribution, which are all crucial factors for effective electrotransfection.…”

“…In addition, in vitro and in vivo studies have elucidated the effect of the shape, size and orientation of cells in tissue and cell density on electric field distribution, which are all crucial factors for effective electrotransfection. 24,26,30 We pointed out in a recent study 26 that the histological properties of tumors are responsible for different transfection efficiencies obtained and this may also be true for the different transfection efficiencies obtained in different tissues using the same electric pulse parameters.…”

“…Field effects are dependent on cell shape and size, the orientation of the cells versus the field orientation and the composition of the tissue. [24][25][26] Nevertheless, it has been suggested that the function of 'HV' and 'LV' pulses is the same for both tissues, the 'HV' pulse permeabilizes target cells and the 'LV' pulse electrophoretically transports the DNA to the cells.…”

Cancer Electrogene Therapy with Interleukin-12

“…On the other hand, Lucas et al used electric pulses that mainly produce electropermeabilization [40,69]. In the case of B16 melanoma that have a soft consistency with large cells and minimal content of the extracellular matrix [73], high voltage electric pulses of microsecond duration resulted in better transfection efficiency compared to electrophoretic electric pulses, therefore leading to better antitumor effectiveness. Furthermore, Lucas et al demonstrated that intratumoral IL-12 electrogene therapy leads to high local IL-12 and IFN-levels, tumor infiltration of lymphocytes and a reduced number of vessels in the tumors.…”