Patients afflicted with the triple-negative subtype of breast cancer (TNBC) have a higher risk of recurrence and progression relative to other subtypes. The recurrent disease has usually acquired resistance to standard therapies and these patients face a poor prognosis. This clinical trajectory suggests that therapies that can prevent the formation of distant metastases or kill established lesions in secondary organs should improve survival.
We have developed and characterized, both functionally and molecularly, four isogenic MDA-MB-231 TNBC xenograft lines, designated 231_ATCC, 231_LNA, 231_LM2 and 231_HM (highly-metastatic). Together these lines comprise a novel model system for study of the factors driving breast cancer progression and metastasis in vivo. Isolated primary tumour cells were profiled using PAT-Seq (Poly-A Tail)-Seq, a RNA-based ‘next-generation’ digital sequencing protocol developed in our laboratory (1), which generates precise data on alternative mRNA polyadenylation and poly-A tail length in addition to transcript abundance. Candidate metastasis promoting genes are functionally assessed by stable silencing in breast cancer cell lines and then execution of a suite of in vitro and in vivo assays.
Interrogation of PAT-Seq expression data revealed upregulated expression of FGF-13 (FHF-2), a non-canonical member of the FGF family with a unique cytoplasmic localization, in aggressively metastatic MDA-MB-231HM tumours. Silencing of FGF-13 expression did not substantially affect breast cancer cell proliferation in vitro or in vivo, although colony forming ability in 2D was dramatically reduced. FGF-13 also mediated resistance to killing with platinum-based chemotherapeutic agents in vitro. Unexpectedly, reduction of FGF-13 levels increased both migration and basement membrane invasion of MDA-MB-231HM cells in vitro. Despite the observed FGF-13 mediated inhibition of cell motility, loss of FGF-13 dramatically reduced spontaneous metastasis of MDA-MB-231HM xenografts from the inguinal mammary gland to lung and liver in immuno-compromised mice in vivo.
The results demonstrate that FGF-13 may be a novel driver of metastasis as well as cisplatin resistance in human breast cancer and suggest that development of molecular strategies to inhibit the relevant cellular function(s) of FGF-13 in breast cancer cells should be considered.