Combination immunotherapy of PEG-modified preladenant thermosensitive liposomes and PD-1 inhibitor effectively enhances the anti-tumor immune response and therapeutic effects

Immunotherapy is a promising cancer treatment strategy. In contrast, programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors are associated with low response rates and are only useful in a small group of cancer patients. A combination of treatments may be effective for overcoming this clinical issue. Preladenant is an adenosine (ADO) receptor inhibitor that can block the ADO pathway and improve the tumor microenvironment (TME), thereby enhancing the immunotherapeutic effect of PD-1 inhibitors. However, its poor water solubility and low targeting limit its clinical applications. We designed a PEG-modified thermosensitive-liposome (pTSL) loaded with ADO small molecule inhibitor preladenant (P-pTSL) to overcome these problems and enhance the effect of PD-1 inhibitor on breast cancer immunotherapy. The prepared P-pTSL was round and uniformly distributed with a particle size of (138.9 ± 1.22) nm, PDI: 0.134 ± 0.031, and zeta potential (-10.1 ± 1.63) mV; preladenant was released slowly at 37 °C but released fast at 42 °C from P-pTSL, which was 76.52 ± 0.44%. P-pTSL has good long-term and serum stability and excellent tumor-targeting ability in mice. Moreover, the combination with PD-1 inhibitor significantly enhanced the anti-tumor effect, and the improvement of related factors in serum and lymph was more obvious under the condition of 42 °C thermotherapy in vitro.