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

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.