(803) LRP1-Targeted Polymeric Nanoconjugates for BBB Penetration and Time-Specific Delivery of PD-L1–Blocking Peptides in Melanoma Brain Metastases

Introduction/Rationale: MBM show CNS tropism and limited benefit from ICB. While AXL inhibitors can improve responses, toxicity remains a concern. The TiME features few effector T cells, abundant TAMs, and glial PD-L1, promoting immune evasion. BBB-penetrant strategies with Immuno-Nano-Conjugates (INCs) are under development; intrathecal delivery has not improved survival. LRP-1–mediated INCs delivery may enable BBB transport and TiME reprogramming. Here we report a targeted nanoplatform to cross the BBB and deliver PD-L1–blocking peptides to the TiME.

Methods: INCs were constructed by attaching a malic acid–based polymer to (i) P-12, a PD-L1–blocking peptide, and (ii) Angiopep-2 (AP2), enabling LRP-1–mediated transcytosis. We evaluated efficacy, safety, toxicity, and biodistribution in a BBB-on-a-chip brain tumor model and in vivo in murine MBM and subcutaneous melanoma models. To translate findings, we analyzed metastatic melanoma transcriptomics (TCGA-SKCM, n=471) and generated Kaplan–Meier survival curves.

Results: INCs crossed the BBB and penetrated the BBB-on-a-chip tumor model. Delivery produced selective uptake by activated TiME and promoted immune activation. In vivo, INCs achieved higher brain accumulation than ICB agents and demonstrated meaningful efficacy with favorable safety. High AXL expression correlated with poor ICB response and immunosuppressive myeloid signatures, linking to reduced survival. In subcutaneous melanoma, combining P-12–based peptides with Bemcentinib yielded greater tumor reduction than anti-PD-1 alone, suggesting circumvention of ICB resistance. These findings support a path toward safe clinical translation.

Conclusion: LRP-1–mediated INC delivery enhances PD-L1 blockade exposure in MBM TiME, supporting a strategy to treat resistant MBM. AXL is a key target for rational combination with nanoplatforms. Further validation in MBM models is planned, and ongoing preclinical testing.