Immunomodulation of Intracranial Melanoma in Response to Blood-Tumor Barrier Opening with Focused Ultrasound - Bulk RNA seq

Activating microbubbles (MBs) with focused ultrasound (FUS) for blood-brain (BBB) and blood-tumor barrier (BTB) opening permits targeted therapeutic delivery. While the effects of FUS-mediated BBB opening have been investigated for normal brain tissue, no such studies exist for intracranial tumors. As this technology advances into clinical immunotherapy trials, it will be crucial to understand how FUS modulates the tumor immune microenvironment. Here, bulk RNA sequencing revealed that FUS BTB/BBB opening (1 MHz, 0.5 MPa peak-negative pressure) of intracranial B16F1cOVA tumors increases the expression of genes related to proinflammatory cytokine and chemokine signaling, pattern recognition receptor signaling, and antigen processing and presentation. Flow cytometry revealed increased maturation (i.e. CD86) of dendritic cells (DCs) in the meninges and altered antigen loading of DCs in both the tumor and meninges. For DCs in tumor draining lymph nodes, FUS had no effect on maturation and elicited only a trend towards increased presentation of tumor-derived peptide by MHC. Neither tumor endothelial cell adhesion molecule expression nor homing of activated T cells was affected by FUS. In conclusion, FUS-mediated BTB/BBB opening elicits signatures of inflammation; however, the response is mild, transient, and unlikely to elicit a systemic response independent of administration of immune adjuvants. Groups of 3-4 tumor bearing mice were treated with sham or FUS-mediated BBB disruption for harvest at both 6 h and 24 h post treatment, for a total of 4 groups. At either 6 or 24 hours following FUS activation of MB, B16F1cOVA brain tumors harvested and processed for bulk mRNA sequencing followed by bioinformatics analyses.