Nanoparticles Hitchhike on Monocytes for Glioblastoma Treatment after Low-Dose Radiotherapy.

Glioblastomas (GBMs) are aggressive primary brain tumors with fatal outcome. Traditional chemo-radiotherapy has poor therapeutic effect and significant side effects, due to the drug and radiotherapy (RT) resistance, natural blood-brain barrier, and high-dose RT damage. Even more, tumor-associated monocytes (macrophages and microglia, TAMs) constitute up to 30%-50% of the GBM cellular content, and the tumor microenvironment (TME) in GBM is extremely immunosuppressive. Here, we synthesized nanoparticles (D@MLL) that hitchhike on circulating monocytes to target intracranial GBMs with the assistance of low-dose RT. The chemical construction of D@MLL was DOX·HCl loaded MMP-2 peptide-liposome, which could target monocytes by the surface modified lipoteichoic acid. First, low-dose RT at the tumor site increases monocyte chemotaxis and induces M1 type polarization of TAMs. Subsequently, the intravenous injected D@MLL targets circulating monocytes and hitchhikes with them to the central site of the GBM area. DOX·HCl was then released by the MMP-2 response, inducing immunogenic cell death, releasing calreticulin and high-mobility group box 1. This further contributed to TAMs M1-type polarization, dendritic cell maturation, and T cell activation. This study demonstrates the therapeutic advantages of D@MLL delivered by endogenous monocytes to GBM sites after low-dose RT, and it provides a high-precision treatment for GBMs.