PO-418 Targeting heat shock protein 70 (HSP70) in melanoma with functionalized theranostic superparamagnetic iron oxide nanoparticles

Introduction Nanotechnologies based on superparamagnetic iron oxide nanoparticles (SPIONs) have emerged as a promising tool for the theranostics of advanced and metastatic melanoma. Decoration of the nanoparticle surface with specific moieties that have specific anti-tumour immunotherapeutic activity could provide a theranostic potential for the nanocomplexes. Targeting Hsp70 that is presented on the cell membrane of tumour cells but on corresponding normal cells could provide the specificity of melanoma treatment. Combination of functionalized particles with blocking of immune checkpoint inhibitors could further enhance the therapeutic benefit. Material and methods Developed nanoparticles conjugated with granzyme B (GrB-SPIONs) were in vitro assessed (employing confocal and electron microscopies, flow cytometry) for specific targeting of the membrane-bound Hsp70 in B16 melanoma cells. Intratumoral administration of GrB-SPIONs as a monotherapy or in combination with anti-CTLA-4 monoclonal antibodies and adoptive T-cell transfer was performed in the orthotopic model of B16 melanoma in C57/Bl6 mice. IHC sections were performed to assess the intratumoral distribution of nanoparticles as well as the caspase-3 expression in the melanoma following the treatment. Results and discussions Internalised GrB-SPIONs in Hsp70-positive B16 melanoma cells induced apoptotic death in dose- and time-dependent manner (as shown by flow cytometry). Monotherapy with intratumorally injected GrB-SPIONs in B16 animal model resulted in delayed tumour progression (MRI volumometry). Biodistribution analysis employing highly sensitive magnetic resonanse imaging (7T) confirmed the retention of particles in the tumour (that was further proved by histological studies). Subsequent therapy with anti-CTLA-4 antibodies and adoptive T-cell transfer synergistically improved the efficacy of GrB-SPIONs nanocomplexes. Inhibitory immune checkpoint blockade significantly enhanced the apoptosis in tumour cells as was demonstrated by the caspase-3 IHC analysis. Conclusion These findings reveal that GrB-SPIONs can specifically target Hsp70-positive melanoma cells. Combinatorial regimen of targeted nanocomplexes and immune checkpoint inhibitors has a high therapeutic potency that could be translated into clinial trials.