Detection, Characterization, and Inhibition of FGFR-TACC Fusions in IDH Wild-type Glioma

Abstract

Purpose: Oncogenic fusions consisting of fibroblast growth factor receptor (FGFR) and TACC are present in a subgroup of glioblastoma (GBM) and other human cancers and have been proposed as new therapeutic targets. We analyzed frequency and molecular features of FGFR-TACC fusions and explored the therapeutic efficacy of inhibiting FGFR kinase in GBM and grade II and III glioma.

Experimental design: Overall, 795 gliomas (584 GBM, 85 grades II and III with wild-type and 126 with IDH1/2 mutation) were screened for FGFR-TACC breakpoints and associated molecular profile. We also analyzed expression of the FGFR3 and TACC3 components of the fusions. The effects of the specific FGFR inhibitor JNJ-42756493 for FGFR3-TACC3-positive glioma were determined in preclinical experiments. Two patients with advanced FGFR3-TACC3-positive GBM received JNJ-42756493 and were assessed for therapeutic response.

Results: Three of 85 IDH1/2 wild-type (3.5%) but none of 126 IDH1/2-mutant grade II and III gliomas harbored FGFR3-TACC3 fusions. FGFR-TACC rearrangements were present in 17 of 584 GBM (2.9%). FGFR3-TACC3 fusions were associated with strong and homogeneous FGFR3 immunostaining. They are mutually exclusive with IDH1/2 mutations and EGFR amplification, whereas they co-occur with CDK4 amplification. JNJ-42756493 inhibited growth of glioma cells harboring FGFR3-TACC3 in vitro and in vivo. The two patients with FGFR3-TACC3 rearrangements who received JNJ-42756493 manifested clinical improvement with stable disease and minor response, respectively.

Conclusions: RT-PCR sequencing is a sensitive and specific method to identify FGFR-TACC-positive patients. FGFR3-TACC3 fusions are associated with uniform intratumor expression of the fusion protein. The clinical response observed in the FGFR3-TACC3-positive patients treated with an FGFR inhibitor supports clinical studies of FGFR inhibition in FGFR-TACC-positive patients.

Figure 1. Structure of FGFR-TACC gene fusions identified by RT-PCR-Sanger sequencing

Predicted FGFR-TACC fusion proteins encoded by the transcripts identified by RT-PCR. Regions corresponding to FGFR3 or TACC3 are shown in red or blue, respectively. FGFR1 and TACC1 corresponding regions are shown in yellow and green. On the left are indicated the FGFR and TACC exons joined in the fused mRNA; the presence of TACC3 introns is also reported when they are spliced in the fusion cDNA. On the right, the number of patients harboring the corresponding fusion variant is indicated. The novel transcripts discovered in this study are highlighted in red. Black arrows indicate the position of the primers used for the FGFR-TACC fusions screening.

Figure 2. Identification and immunostaining of FGFR3-TACC3-positive tumors

Results from RT-PCR screening in representative samples from the Pitié-Salpêtrière Hospital (A, C) and the Besta (B, D) datasets. M, DNA ladder. Schematic representation of the FGFR3-TACC3 fusion transcripts identified in samples GBM-4620 (C) and GBM-021 (D). The junction sequences on the mRNA and the reading frame at the breakpoint are reported. Representative microphotographs of H&E and FGFR3 immunostaining in the FGFR3-TACC3 positive samples GBM-4620 (E) and GBM-021 (F) and two FGFR3-TACC3 negative samples (panels G and H); a, H&E, 10X magnification; b, H&E, 40X magnification; c, FGFR3, 10X magnification; d, FGFR3, 40X magnification.

Figure 3. Pre-clinical evaluation of FGFR3-TACC3 inhibition by JNJ-42756493

(A) Mouse astrocytes expressing FGFR3-TACC3 (F3T3), FGFR3-TACC3-KD (F3T3-KD) or the empty vector (Vector) were treated with the indicated concentration of JNJ-42756493. Cell viability was determined by the MTT assay. Error bars show mean±SEM (n=6). (B) Survival analysis of GIC-1123 treated with JNJ-42756493. (C) The FGFR-TK inhibitor JNJ-42756493 suppresses tumor growth of subcutaneous tumors generated by GIC-1123. After tumor establishment (arrow) mice were treated with vehicle or JNJ-42756493 (12 mg/kg) for 14 days. Values are mean tumor volumes±SD, (n=9 mice per group). P-value of the slope calculated from the treatment starting point (arrow) is 0.04. (D) Photograph showing the tumors dissected from vehicle or JNJ-42756493 treated mice after two weeks of treatment.

Figure 4. Baseline and post-treatment Magnetic Resonance Imaging (MRI) of patients treated with JNJ-42756493

Patient 1 (Panels A–D). (A) Post-gadolinium T1 weighted images show the target lesion on the right parietal lobe. The interval (days) from the beginning of follow-up is indicated above each MRI. (B) Analysis of sum of product diameters (SPD) before and during the anti-FGFR treatment (RANO criteria). (C) Analysis of tumor volume (cm³) before and during the anti-FGFR treatment. During anti-FGFR treatment a stabilization of the tumor was observed according to RANO criteria and volumetry. (D) Perfusion images at baseline and after 20 days of anti-FGFR treatment. rCBV (relative cerebral blood volume). Post-gadolinium T1 weighted images with color overlay of rCBV are shown. Patient 2 (Panels E–G). (E) Two different MRI slice levels of superior and middle part of the lesion are presented. (F) Analysis of sum of product diameters (SPD) before and during the anti-FGFR treatment. During the anti-FGFR treatment a reduction of 22% of tumor size was observed. (G) Volumetric evaluation showed a 28% tumor reduction. Vertical red arrow indicates the start of anti-FGFR treatment (baseline).