Preclinical efficacy of the anti-hepatocyte growth factor antibody ficlatuzumab in a mouse brain orthotopic glioma model evaluated by bioluminescence, PET, and MRI

Abstract

Purpose: Ficlatuzumab is a novel therapeutic agent targeting the hepatocyte growth factor (HGF)/c-MET pathway. We summarize extensive preclinical work using this agent in a mouse brain orthotopic model of glioblastoma.

Experimental design: Sequential experiments were done using eight- to nine-week-old nude mice injected with 3 × 10(5) U87 MG (glioblastoma) cells into the brain. Evaluation of ficlatuzumab dose response for this brain tumor model and comparison of its response to ficlatuzumab and to temozolamide were conducted first. Subsequently, various small-animal imaging modalities, including bioluminescence imaging (BLI), positron emission tomography (PET), and MRI, were used with a U87 MG-Luc 2 stable cell line, with and without the use of ficlatuzumab, to evaluate the ability to noninvasively assess tumor growth and response to therapy. ANOVA was conducted to evaluate for significant differences in the response.

Results: There was a survival benefit with ficlatuzumab alone or in combination with temozolamide. BLI was more sensitive than PET in detecting tumor cells. Fluoro-D-thymidine (FLT) PET provided a better signal-to-background ratio than 2[(18)F]fluoro-2-deoxy-d-glucose (FDG) PET. In addition, both BLI and FLT PET showed significant changes over time in the control group as well as with response to therapy. MRI does not disclose any time-dependent change. Also, the MRI results showed a temporal delay in comparison to the BLI and FLT PET findings, showing similar results one drug cycle later.

Conclusions: Targeting the HGF/c-MET pathway with the novel agent ficlatuzumab appears promising for the treatment of glioblastoma. Various clinically applicable imaging modalities including FLT, PET, and MRI provide reliable ways of assessing tumor growth and response to therapy. Given the clinical applicability of these findings, future studies on patients with glioblastoma may be appropriate.

Figure 1

Whole-body BLI and small-animal PET images of the head [coronal (i); sagittal (ii)] showing tumor (white arrows) visibility at 4 weeks post-tumor cell implantation. Both mice shown have similar luminescence of 4 × 10⁷ p/s/cm²/sr. The FLT signal is greater than that of brain background, whereas the FDG signal is not.

Figure 2

Representative imaging of BLI (A), FLT PET (B), and MRI (C). For each group of images, the same mouse is shown from each of the 3 groups: control, low-dose, and high-dose (x-axis). Also for each group of images, each animal is shown at baseline, post-drug 1, post-drug 2, and post-drug 3 (y-axis).

Figure 3

A–C, (top row, left to right) Control animal 1, H&E 400× (A) with 3 mitotic figures (white arrowheads) in a single HPF; Ki-67 400× (B) labeling approximately 80% of tumor cell nuclei; caspase 400× (C) labeling a subset of tumor cell nuclei. D–F, (second row, left to right) low-dose animal 3, H&E 400× (D) with one mitotic figure (white arrowhead) in a single HPF; Ki-67 400× (E) labeling approximately 50% of tumor cell nuclei; caspase 400× (F) labels rare tumor cell nuclei. G–I, (third row, left to right) high-dose animal 2, H&E 400× (G) with one mitotic figure (black arrowhead) in a single HPF; Ki-67 400× (H) labeling approximately 20% of tumor cell nuclei; caspase 400× (I) labeling a subset of tumor cell nuclei.

Figure 4

A, change in tumor bioluminescence signal (a), mean FLT PET signal (b), maximum FLT PET signal (c), and volume (d) (mean ± SD) over the course of the experiment in the control, low-dose, and high-dose groups. The values and error bars represent the mean and SD, respectively. Results shown are normalized to their respective baseline value. The P values shown are the results of the ANOVA for each group. For those groups with significant differences, the significantly different pairs are indicated. B, change in mean PET signal (mean ± SD) over the course of the experiment in the control, low-dose, and high-dose groups. Results shown are normalized to the baseline value. The P values shown are the results of the ANOVA for each group. For those groups with significant differences, the significantly different pairs are highlighted. C, change in maximum PET signal (mean ± SD) over the course of the experiment in the control, low-dose, and high-dose groups. Results shown are normalized to the baseline value. The P values shown are the results of the ANOVA for each group. For those groups with significant differences, the significantly different pairs are highlighted. D, change in tumor volumes as measured by MRI over the course of the experiment in the control, low-dose, and high-dose groups. The P values shown are the results of the ANOVA for each group. For those groups with significant differences, the significantly different pairs are highlighted.