# The Importance of Suppressing Pathological Periostin Splicing Variants with Exon 17 in Both Stroma and Cancer

## TL;DR

Suppressing a specific form of the POSTN protein in both cancer cells and surrounding tissue may help reduce tumor growth and spread in breast cancer.

## Contribution

The study demonstrates that targeting POSTN exon 17 in both stroma and cancer cells can inhibit tumor progression and metastasis.

## Key findings

- Suppressing stromal POSTN exon 17 in mice led to smaller tumors and fewer metastases.
- Skipping POSTN exon 17 in cancer cells significantly reduced lung metastasis.
- Targeting POSTN exon 17 may be a promising therapeutic strategy for breast cancer.

## Abstract

Background: Periostin (POSTN) is a type of matrix protein that functions by binding to other matrix proteins, cell surface receptors, or other molecules, such as cytokines and proteases. POSTN has four major splicing variants (PN1–4), which are primarily expressed in fibroblasts and cancer. We have reported that we should inhibit pathological POSTN (PN1–3), but not physiological POSTN (PN4). In particular, pathological POSTN with exon 17 is present in both stroma and cancer, but it is unclear whether the stroma or cancer pathological POSTN should be suppressed. Methods and Results: We transplanted 4T1 cells (breast cancer) secreting POSTN with exon 17 into 17KO mice lacking POSTN exon 17 to suppress stromal POSTN with exon 17. The results show that 17KO mice had smaller primary tumors and fewer metastases. Furthermore, to suppress cancer POSTN with exon 17, 4T1 cells transfected with POSTN exon 17 skipping oligo or control oligo were transplanted from the tail vein into the lungs. The results show that POSTN exon 17 skipping oligo significantly suppressed lung metastasis. Conclusions: These findings suggest that it is important to suppress POSTN exon 17 in both stroma and cancer. Antibody targeting POSTN exon 17 may be a therapeutic candidate for breast cancer.