MSOR4 Presentation Time: 5:15 PM

Abstract

Purpose

Diffusing alpha-emitters radiation therapy (DaRT) is a unique treatment modality for solid tumors capitalizing on Radium-224-loaded (Alpha DaRT) sources designed to disperse alpha-emitting atoms into the tumor tissue. These diffused radioactive atoms create a destructive 'kill-zone' millimeters away from the source, without harming adjacent tissue. This treatment was reported to effectively inhibit tumor growth in various human and murine cancers in pre-clinical testing. Here, the effect of Alpha DaRT was investigated in-vitro and in-vivo using subcutaneous (s.c.) Glioblastoma Multiforme (GBM) tumors in combination with GBM ‘standard of care’ treatments (Temozolomide, TMZ or Bevacizumab, BEV). We also studied the effect of the Alpha DaRT monotherapy in orthotopic GBM tumors.

Methods and Materials

The effect of alpha radiation with TMZ was evaluated in human U87 cells by cytotoxicity and colony formation assays. VEGF secretion was assessed using ELISA assay. U87 s.c. tumor-bearing mice were treated with Alpha DaRT or inert (non-radioactive) sources in combination with TMZ or BEV, and monitored for efficacy. To assess tumor vasculature, we performed immunohistochemical staining of the vascular marker CD31. Alpha DaRT effective diameter receiving high dose (>10 Gy) was determined by autoradiography. The clearance of radioactive atoms from the tumor was determined by radioactivity measurements of the tumor and source 4 days post implantation compared with the initial activity. Murine GL-261 GBM cells were used for the inoculation of orthotopic GBM, and their growth was monitored using MRI before they were treated with Alpha DaRT or Inert sources.

Results

The combined treatment of alpha radiation and TMZ doubled the cytotoxic effect compared to the monotherapies. U87 cells treated with the combined treatment showed lower survival fraction than the monotherapies or than x-ray combined with TMZ treatment. U87 s.c. tumor bearing mice treated with Alpha DaRT and TMZ showed increased delay in tumor growth compared to the monotherapies. Unlike other radiation types, alpha radiation did not increase VEGF secretion by U87 cells. As expected, BEV administration decreased CD31 staining and when combined with Alpha DaRT, the effective diameter was increased and the clearance of the radioactivity was reduced. In-vivo studies showed that administration of BEV a few days after Alpha DaRT insertion improved tumor control - in comparison to Alpha DaRT or BEV alone. Improved results were obtained in larger tumors when the BEV protocol was initiated before the Alpha DaRT insertion. We were able to establish an orthotopic model of GBM and fabricate a designated Alpha DaRT applicator and source suitable for mice brains. We successfully monitored tumor growth and Alpha DaRT insertion using MRI as well as in-vivo real-time imager.

Conclusions

Our results demonstrated the feasibility of Alpha DaRT therapy in the mouse brain and suggest that Alpha DaRT in combination with 'standard of care' therapies constitutes a promising approach for the treatment of GBM.