Patient selection using novel RNA-based approaches: Early experience from a phase I study with the pan-FGFR inhibitor BAY 1163877 in patients with urothelial bladder cancer.

Abstract

386 Background: FGFRs play a role in a variety of malignancies, including urothelial bladder cancer (UBC). Whereas genetic alterations of FGFRs in UBC are known, non-genetic and epigenetic activation of FGFR gene expression have also been described. BAY 1163877 is an oral inhibitor of FGFRs 1-3 with antitumor activity in FGFR mRNA overexpressing xenograft models not limited to DNA alterations. We report the results from a phase I expansion cohort in UBC patients pre-screened for treatment with BAY 1163877 based on FGFR1-3 mRNA overexpression and/or activating mutations in the FGFR3 gene. Methods: FGFR mRNA levels were assessed in paraffin-embedded archival or fresh biopsy specimens by RNAscope and NanoString technology and activating mutations by RT-PCR-based mutation assay. Tumor response to treatment was assessed by RECIST, v1.1. Adverse events were assessed using CTCAE v4.03 criteria. Results: A total of 80 patients from multiple indications were enrolled in the phase I study; 800 mg BID was established as the recommended phase 2 dose. Sixty seven UBC patients were screened, with 31 tumor biopsies (46%) determined to overexpress FGFR mRNA: 2 patients each with FGFR1 and FGFR2, and 27 patients with FGFR3. Of the 27 patients with FGFR3 mRNA overexpression, 5 had in parallel an activating mutation in FGFR3 gene. Eight UBC patients met eligibility criteria and entered treatment; all had elevated FGFR3 mRNA expression and 4 had alterations in FGFR3 DNA (3 mutations and 1 translocation). Seven patients (87.5%) had tumor shrinkage in target lesions as best response, with 3/8 partial responses (PR; 37.5%). One patient with a PR presented with elevated FGFR3 mRNA without evidence of aberrant DNA. BAY 1163877 was generally well tolerated and AEs manageable with dose modification. The most common AEs in the overall population were increased phosphorus (66% all grade, 1 grade-3 event) and diarrhea (33% all grade, 2 grade-3 events). Conclusions: Selection of patients for treatment with BAY 1163877 based on FGFR mRNA expression levels in archival tissue was feasible. BAY 1163877 had a favorable safety profile and promising anti-tumor activity in UBC patients. Clinical trial information: NCT01976741.