We reported recently that a three-component nanoparticle, consisting of a targeting antibody, a transfecting peptide and an 111In-antiRIalpha MORF antisense oligomer, provided Auger electron-mediated, antisense-mediated, cytotoxicity of cells in culture. We have now measured the cytotoxicity of the nanoparticle in culture with the 111In replaced by 125I, another attractive Auger electron emitter. The nanoparticle consisted of streptavidin linking the 125I labeled antiRIalpha mRNA antisense MORF oligomer, the tat transfecting peptide and the anti-Her2 Trastuzumab antibody. Cytotoxicity was evaluated by a clonogenic survival assay in BT-474 (Her2+) human breast cancer cells. In a dose escalation study, as measured by the surviving fraction, the cytotoxicity of tumor cells to the 125I-labeled antisense nanoparticle was significantly higher than that for the identical sense control. When compared with our previous study with 111In as label, a similar level of cytotoxicity was achieved but the observed minimal therapeutic dose for the 125I-labeled nanoparticle in BT-474 cells was lower than that for 111In-labeled nanoparticle in SK-BR-3 cells. Thus, a radiolabeled antisense MORF oligomer delivered into cells by a three-component nanoparticle is an effective vehicle for Auger radiotherapy when radiolabeled with 111In or 125I.

Stem cell factor (SCF) is known to act synergistically with other hematopoietic factors in increasing the colony formation of hematopoietic progenitor cells. We have shown that interleukin-3 (IL-3)-dependent proliferation of NFS-60 cells is associated with the induction of a specific calmodulin-binding protein of about 68 kD (CaM-BP68). To evaluate the relationship between proliferative stimulation and the induction of CaM-BP68 by cytokines, we examined whether the increased proliferative potential of NFS-60 cells in response to SCF is reflected in an increased induction of the CaM-BP68. We observed that SCF alone has a limited effect on proliferative stimulation and on the induction of CaM-BP68 in factor-deprived NFS-60 cells. However, when combined with IL-3, granulocyte colony-stimulating factor (G-CSF), or IL-6, it caused a significant increase in cytokine-dependent proliferative stimulation, as well as in the induction of CaM-BP68. Furthermore, an increase in IL-3-dependent induction of CaM-BP68 in the presence of SCF coincided with a corresponding increase in thymidine kinase activity, whose expression is linked to G1/S transition of the cells. At low concentrations SCF caused a synergistic increase in IL-3-dependent induction of both CaM-BP68 and thymidine kinase activity. In contrast to the changes in CaM-BP68 and thymidine kinase activity, no significant changes in DNA polymerase alpha were observed in factor-deprived NFS-60 cells in response to IL-3 and/or SCF. These observations suggest an increased expression of CaM-BP68 and thymidine kinase are associated with the synergistic effect of SCF on factor-dependent proliferation of hematopoietic progenitor cells.