PO-411 Combinatorial therapy with immune checkpoint blockade and theranostic tumor-targeted nanoparticles in eradication of tumours

IntroductionTargeted superparamagnetic iron oxide nanoparticles (SPIONs) have emerged as a promising detection tool for the molecular magnetic resonance imaging (MRI). Decoration of the surface with specific moieties that have anti-tumour immunotherapeutic activity could provide a theranostic potential for the nanocomplexes. Combination of functionalized particles with blocking of immune checkpoint inhibitors could further enhance the therapeutic benefit.Material and methodsSynthesised 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 cancer cells. Application of GrB-SPIONs as a monotherapy or in combination with single dose (10Gy) radiotherapy (SARRP, X-strahl) was performed in the orthotopic models of human U87 glioblastoma in NMRI nu/nu mice, GL261 glioma in C57/Bl6 mice, C6 glioma in rats. Combinatorial therapy of anti-CTLA-4 and anti-PD-1 anitbodies with GrB-SPIONs and radiotherapy was performed.Results and discussionsInternalised GrB-SPIONs in Hsp70-positive tumour cells induced apoptotic death in dose- and time-dependent manner (as shown by flow cytometry). Monotherapy with GrB-SPIONs in animal models resulted in delayed tumour progression (MRI volumometry) and increased survival. Biodistribution analysis employing highly sensitive non-linear magnetic response measurements (NLR-M2 ) confirmed the retention of particles in the tumour (that was further proved by histological studies). Addition of radiotherapy further promoted therapeutic benefit of systemically administered nanoparticles. Subsequent therapy with anti-CTLA-4 and anti-PD-1 antibodies synergistically improved the efficacy of GrB-SPIONs nanocomplexes with radiotherapy. Inhibitory immune checkpoint blockade significantly enhanced inflitration of tumour tissue with activated CD8 +and natural killer (NK1.1) cells and decreased suppressive PD-1 +cells.ConclusionThese findings reveal that GrB-SPIONs can specifically target Hsp70-positive cancer cells that could be used simultaneously for nonivasive MRI diagnosis of tumours and therapy. Combinatorial regimen of targeted nanocomplexes and immune checkpoint inhibitors has a high theraputic potency that could be translated into clinial trials.