Fibulin-4 expressed in metastatic breast cancer is a target of peptide-based imaging probes and experimental therapeutics.

There is a lack of approaches to detect and kill metastatic cells. As an agent for metastasis targeting, a cyclic peptide BLMP6 has been previously characterized. As a step toward translation, we designed AZDye555-labeled BLMP6 and demonstrated its homing to metastases of human MDA-MB-231 cells in mice. We show that 68Ga-radiolabeled BLMP6 can be used for the detection of MDA-MB-231 metastases. We designed a peptide-drug conjugate consisting of monomethyl auristatin E (MMAE) and BLMP6. We show that MMAE-BLMP6 kills MDA-MB-231 cells in cell culture and in vivo. In mouse models of lung metastases, treatment with MMAE-BLMP6 suppressed metastasis growth and improved survival. Based on BLMP6 similarity to latent transforming growth factor β binding protein 4 (LTBP4), we identified fibulin-4 as a BLMP6 target. We show that BLMP6 mimics the LTBP4 domain binding to fibulin-4 and selectively binds to fibulin-4 in vitro. Fibulin-4 knockout in cancer cells abrogated BLMP6 homing to lung metastases in mice. Fibulin-4 expression was found to be increased in invasive and metastatic human breast cancer and correlated with the binding of AZDye555-BLMP6 in human tissue sections. Our results suggest that fibulin-4 and BLMP6 may be further developed for the detection and targeting of metastatic human cancers.