Gamma knife surgery as monotherapy with clinically relevant doses prolongs survival in a human GBM xenograft model

Abstract

Object: Gamma knife surgery (GKS) may be used for recurring glioblastomas (GBMs). However, patients have then usually undergone multimodal treatment, which makes it difficult to specifically validate GKS independent of established treatments. Thus, we developed an experimental brain tumor model to assess the efficacy and radiotoxicity associated with GKS.

Methods: GBM xenografts were implanted intracerebrally in nude rats, and engraftment was confirmed with MRI. The rats were allocated to GKS, with margin doses of 12 Gy or 18 Gy, or to no treatment. Survival time was recorded, tumor sections were examined, and radiotoxicity was evaluated in a behavioral open field test.

Results: In the first series, survival from the time of implantation was 96 days in treated rats and 72 days in controls (P < 0.001). In a second experiment, survival was 72 days in the treatment group versus 54 days in controls (P < 0.006). Polynuclear macrophages and fibrosis was seen in groups subjected to GKS. Untreated rats with GBM xenografts displayed less mobility than GKS-treated animals in the open field test 4 weeks after treatment (P = 0.04).

Conclusion: GKS administered with clinically relevant doses prolongs survival in rats harboring GBM xenografts, and the associated toxicity is mild.

Figures

Figure 1

GKS of nude rats harboring GBM xenografts. The rats are fixed in a stereotactic frame (a) attached to a transparent hood prior CT scanning (b). These scans are merged with MRI images (c). Shown is a dose administered with a 4 mm collimator (red) and the accompanying 80% isodose curve (yellow).

Figure 2

GKS prolongs survival in nude rats harboring GBM xenografts. Shown are the treatment groups as indicated for the experiment using pA (a–d) and pB (e) and (f) GBM xenografts. Treated rats (both 12 and 18 Gy collectively) versus controls from the time of implantation, (a) and from the time of treatment (b). Comparison of the individual treatment groups from the time of implantation (c) and from the time of treatment (d). Survival from the time of tumor (pB) implantation (e) and from the time of treatment (f).

Figure 3

MRI imaging demonstrates reduced tumor growth following GKS treatment. Shown are T2-sequences, with tumor lesion presenting as a high signal intensity area, compared to the surrounding brain. Untreated rat brain tumor (left) and tumor receiving 12 Gy margin dose (right) at the day of treatment (a). Untreated rat brain tumor (left) and GKS treated tumors (right) one week after treatment (b). The yellow line indicates the location of the 12 Gy dose at the time of treatment.

Figure 4

H/E and IHC staining of GBM xenografts. H/E staining of the tumors (a) which appear hypercellular, but with more prominent angiogenesis and necrosis in the pB GBM xenografts (lower panels). Granulomatous cerebral angiitis with polynuclear macrophages in the perivascular space can be seen in the pA GBM xenograft treated with 18 Gy (Upper right panel). Scale bars: 50 μm. IHC and TUNEL staining (brown) show robust expression of Nestin, Vimentin, and Ki-67 and TUNEL positive cells. Panels at low magnification show Nestin positive cells in the pA xenograft migrating along the Corpus Callosum (b). Scale bars pA: Nestin 250 μm, Vimentin: 100 μm, Ki-67 from pA ctrl: 100 μm, all other panels: 25 μm. Scale bars pB: Nestin and Vimentin: 100 μm, all other panels: 50 μm.

Figure 5

Behavioral open field study comparing rats harboring GBM xenografts with and without GKS treatment, as well as controls. Graphic presentation of latencies to enter the periphery for nude rats, 2 days and 4 weeks after treatment. Three animals were tested from each group as indicated.