Molecular therapy targeting Sonic hedgehog and hepatocyte growth factor signaling in a mouse model of medulloblastoma - PubMed (original) (raw)

Molecular therapy targeting Sonic hedgehog and hepatocyte growth factor signaling in a mouse model of medulloblastoma

Valerie Coon et al. Mol Cancer Ther. 2010 Sep.

Abstract

The use of genetically engineered mice has provided insights into the molecular pathogenesis of the pediatric brain tumor medulloblastoma and revealed promising therapeutic targets. Ectopic expression of Sonic hedgehog (Shh) in cerebellar neural progenitor cells induces medulloblastomas in mice, and coexpression of hepatocyte growth factor (HGF) enhances Shh-induced tumor formation. To determine whether Shh + HGF-driven medulloblastomas were responsive to Shh signaling blockade and whether treatment response could be enhanced by combination therapy targeting both HGF and Shh signaling pathways, we carried out a survival study in mice. We induced medulloblastomas by retrovirus-mediated expression of Shh and HGF, after which we treated the mice systemically with (a) HGF-neutralizing monoclonal antibody L2G7, (b) Shh signaling inhibitor cyclopamine, (c) Shh-neutralizing monoclonal antibody 5E1, (d) L2G7 + cyclopamine, or (e) L2G7 + 5E1. We report that monotherapy targeting either HGF signaling or Shh signaling prolonged survival and that anti-HGF therapy had a more durable response than Shh-targeted therapy. The effect of L2G7 + 5E1 combination therapy on cumulative survival was equivalent to that of L2G7 monotherapy and that of L2G7 + cyclopamine therapy was worse. The principal mechanism by which Shh- and HGF-targeted therapies inhibited tumor growth was a potent apoptotic death response in tumor cells, supplemented by a weaker suppressive effect on proliferation. Our observation that combination therapy either failed to improve or even reduced survival in mice bearing Shh + HGF-induced medulloblastomas compared with monotherapy underscores the importance of preclinical testing of molecular-targeted therapies in animal models of tumors in which the targeted pathways are known to be active.

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Figures

Figure 1

Figure 1

Histopathology of medulloblastomas induced by Shh+HGF. A–B, coronal brain sections showing tumor in the cerebellum and fourth ventricle (A) and obstructive hydrocephalus in the forebrain (B) (H&E). C, classic medulloblastoma pattern showing homogeneous sheets of undifferentiated tumor cells (H&E). D, MBEN pattern, in which round, neurocytic-appearing tumor cells are arrayed in a linear pattern (upper left and inset), adjacent to an area of disorganized cytoarchitecture characteristic of the classic pattern (right) (H&E). E, immunoperoxidase staining showing that the MBEN areas (left) show abundant immunoreactivity for neuronal differentiation marker NeuN compared with classic-appearing areas (right). F, immunoperoxidase staining showing that Ki67 staining is absent in the MBEN area (left) compared with the actively proliferating cells in the classic-appearing area (right). Scale bar, 500 μm (A–B), 25 μm (C and D inset), 50 μm (D–F).

Figure 2

Figure 2

Response to Shh- and HGF-targeted therapy in mice with medulloblastomas. Kaplan-Meier survival analysis of mice injected with RCAS-Shh and RCAS-HGF on day 0 and then treated with the indicated therapeutic agents starting on day 14 (arrow). A and B show results from two independent experiments.

Figure 3

Figure 3

Analysis of proliferation and apoptosis in Shh+HGF–induced medulloblastomas. Bar graphs and representative photomicrographs showing the percentage (mean ± SEM) of tumor cells with positive immunoreactive staining for Ki67 (proliferation index) (A) and cleaved caspase-3 (apoptotic index) (B) in Shh+HGF–induced medulloblastomas from mice treated with the indicated therapeutic agents. Scale bar, 25 μm.

Figure 4

Figure 4

Analysis of Shh and HGF signaling in response to molecular-targeted therapy. Bar graphs and representative photomicrographs showing the percentage (mean ± SEM) of tumor cells with positive immunoreactive staining for Gli2 in the nucleus (Gli2 index) (A) and phosphorylated c-Met in the cytoplasm (pc-Met index) (B) in medulloblastomas from mice treated with the indicated therapeutic agents. Phototmicrographs in (B) show pc-Met+ tumor cells (right) adjacent to cerebellar cortex (left). Scale bar, 25 μm (A) and 50 μm (B).

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