APTSTAT3-9R-9R is a STAT3 inhibitor (Ki: 231 nmol/L). STAT3 has been reported to promote the proliferation, survival, metastasis, immune escape, as well as drug resistance of cancer cells, making it a promising target for various diseases. However, though multiple STAT3 inhibitors and its regulatory or effector pathway elements have been identified, bioactive agents are limited.

In vitro: The previous study showed that APTSTAT3-9R bound to STAT3 with high specificity and affinity. Moreover, the addition of a cell-penetrating motif to the peptide to yield APTSTAT3-9R enabled uptake by murine B16F1 melanoma cells. In addition, treatment of various types of cancer cells with APTSTAT3-9R was able to inhibit STAT3 phosphorylation and reduce expression of STAT targets, such as Bcl-xL, cyclin D1, and survivin. As a result, APTSTAT3-9R could suppress the viability and proliferation of cancer cells [1].

In vivo: In a previous animal in vivo study, a human lung carcinoma xenograft model was prepared by subcutaneous implantation of A549 cancer cells. After tumors had reached a volume of approximately 50 mm3 after two weeks, APTSTAT3-9R was intratumorally injected every other day for a total of four injections. Results showed that the tumor burden was significantly reduced in the APTSTAT3-9R–treated group when compared with that in the control group; however, there was little difference in tumor size between APTscr-9R and control groups [1].