Shock wave permeabilization with ribosome inactivating proteins: a new approach to tumor therapy

Extracorporeal shock waves are high-pressure pulses of microsecond duration clinically used for lithotripsy. Recently, shock waves been shown to cause a transient increase of the permeability of the cell membrane. We therefore hypothesized that shock waves might be able to transfer tumoricidal agents into tumor cells and examined this in vitro and in vivo. In vitro, the ribosome inactivating proteins gelonin and saporin were transferred into L1210, SSK2, and HeLa cells, and dose-response curves were established. The drug concentration that reduced the cell proliferation by 50% (IC50) was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and the enhancement factors from shock wave application were calculated. It was found that shock waves enhanced the action of gelonin from 900-fold in L1210 cells to 40,000-fold in HeLa cells and the action of saporin from 300-fold in L1210 cells to 15,000-fold in HeLa cells. In vivo, the effect of gelonin and saporin was assessed in a murine tumor model. SSK2 fibrosarcoma tumors locally grown in C3H mice were treated with shock waves after i.p. administration of gelonin or saporin. Shock wave application delayed the tumor growth, and long-term remissions lasting >180 days were induced in 40% of the animals. In conclusion, shock waves enhanced the action of ribosome inactivating proteins and led to complete tumor remissions. The local transfer of toxic substances by shock waves into tumors constitutes a new approach to a local tumor therapy.