New genes useful in suicide gene therapy are those encoding toxins such as plant
ribosome-inactivating proteins (RIPs), which can irreversibly block
protein synthesis, triggering apoptotic cell death. Plasmids expressing a cytosolic
saporin (SAP) gene from common soapwort (Saponaria officinalis) are generated by placing the region encoding the mature plant toxin under the control of strong viral promoters and may be placed under
tumor-specific promoters. The ability of the resulting constructs to inhibit
protein synthesis is tested in cultured tumor cells co-transfected with a
luciferase reporter gene. SAP expression driven by the cytomegalovirus (CMV) promoter (pCI-SAP) demonstrates that only 10 ng ofplasmid
DNA per 1.6 x 10(4)
B16 melanoma cells drastically reduces
luciferase reporter activity to 18% of that in control cells (1). Direct intratumoral
injections are performed in an aggressive
melanoma model.
B16 melanoma-bearing mice injected with pCI-SAP complexed with
lipofectamine or N-(2,3-dioleoyloxy-1-propyl) trimethylammonium
methyl sulfate (
DOTAP) show a noteworthy attenuation in
tumor growth, and this effect is significantly augmented by repeated administrations of the
DNA complexes. Here, we describe in detail this cost-effective and safe suicide gene approach.