# LT1-3, a Slit2-Derived Peptide, Exhibits Anti-Tumor Activity and Improves Cisplatin Therapy

## TL;DR

LT1-3, a peptide from Slit2, inhibits lung cancer cell growth and improves cisplatin therapy without harming normal cells.

## Contribution

LT1-3 is a novel Slit2-derived peptide that synergizes with cisplatin and is non-toxic to normal cells.

## Key findings

- LT1-3 inhibits lung cancer cell proliferation and invasion without toxicity to normal cells.
- Combining LT1-3 with cisplatin synergistically improves survival in tumor-bearing mice.
- LT1-3's effects are influenced by TP53 and regulated by JNK1 and PKA pathways.

## Abstract

The LT1-3 peptide inhibits proliferation and invasion of lung cancer cells while being non-toxic to normal cells.

LT1-3 enhances the efficacy of cisplatin and appears to reduce its side effects.

LT1-3 is suitable for combination with cisplatin as a first-line treatment for lung cancer and can be added to immunotherapy and platinum doublet therapy.

LT1-3 can be continued as maintenance therapy, offering a promising new approach to improve treatment outcomes and patient quality of life.

The Slit2/Robo signaling pathway acts as a tumor suppressor in various cancers. This study identified an 8-amino acid peptide, LT1-3, derived from the Slit2 LamG domain, and demonstrated its ability to inhibit lung cancer cell proliferation and invasion independently of Robo receptors. Notably, LT1-3 was non-toxic to normal cells (Beas-2B, MRC5, and HUVECs). Combination treatment of LT1-3 and cisplatin synergistically inhibited the proliferation of lung cancer cells (CL1-5, A549, H1355, H460, H23, H661), but had no inhibitory effect on H1299 and H1975. Furthermore, combination therapy prolonged the median survival of tumor-bearing immunodeficient nude mice from 27.5 days (control) to 37.5 days (LT1-3 or cisplatin) and further to 47.5 days (LT1-3/cisplatin combination). The tumor suppressor TP53 positively influences LT1-3-mediated proliferation inhibition, while MAPK8 (JNK1) and PRKACA (PKA) have been identified as negative regulators. With the exception of the p53R273 variants, most TP53 mutants retained their function in this context. The p53 reactivator APR-246 restores sensitivity of p53R273H-expressing cells to LT1-3. JNK inhibition sensitizes p53-deficient or p53R273H-expressing cells to LT1-3-mediated proliferation inhibition. LT1-3, alone or in combination with a JNK inhibitor, enhances cisplatin efficacy, even in the presence of p53 mutations. Therefore, LT1-3 possesses multifunctional antitumor properties, directly inhibiting tumor cells and enhancing the efficacy of cisplatin, without causing toxicity to normal cells. Combining LT1-3 with cisplatin holds promise as a first-line therapy for lung cancer, while LT1-3 alone may be suitable for maintenance therapy.