CpG-coated prussian blue nanoparticles-based photothermal therapy combined with anti-CTLA-4 immune checkpoint blockade triggers a robust abscopal effect against neuroblastoma

Abstract

High-risk neuroblastoma, which is associated with regional and systemic metastasis, is a leading cause of cancer-related mortality in children. Responding to this need for novel therapies for high-risk patients, we have developed a “nanoimmunotherapy,” which combines photothermal therapy (PTT) using CpG oligodeoxynucleotide-coated Prussian blue nanoparticles (CpG-PBNPs) combined with anti-CTLA-4 (aCTLA-4) immunotherapy. Our in vitro studies demonstrate that in addition to causing ablative tumor cell death, our nanoimmunotherapy alters the surface levels of co-stimulatory, antigen-presenting, and co-inhibitory molecules on neuroblastoma tumor cells. When administered in a syngeneic, murine model of neuroblastoma bearing synchronous Neuro2a tumors, the CpG-PBNP-PTT plus aCTLA-4 nanoimmunotherapy elicits complete tumor regression in both primary (CpG-PBNP-PTT-treated) and secondary tumors, and long-term survival in a significantly higher proportion (55.5%) of treated-mice compared with the controls. Furthermore, the surviving, nanoimmunotherapy-treated animals reject Neuro2a rechallenge, suggesting that the therapy generates immunological memory. Additionally, the depletion of CD4 + , CD8 + , and NK + populations abrogate the observed therapeutic responses of the nanoimmunotherapy. These findings demonstrate the importance of concurrent PTT-based cytotoxicity and the antitumor immune effects of PTT, CpG, and aCTLA-4 in generating a robust abscopal effect against neuroblastoma.

An Engineered Prussian Blue Nanoparticles‐Based Nanoimmunotherapy Elicits Robust and Persistent Immunological Memory in a TH‐MYCN Neuroblastoma Model

“…Here, we expand upon our previous work using Prussian blue nanoparticles (PBNPs) as agents of photothermal therapy (PTT; PBNP‐PTT) [ 10–16 ] by investigating the efficacy of PTT using PBNPs coated with unmethylated cytosine‐phosphate‐guanine oligodeoxynucleotides (CpG) in a syngeneic, murine model of NB. [ 17,18 ] PBNPs are ideal candidates for use as PTT agents, as they are biodegradable with limited toxicity, [ 13–15 ] and are FDA approved.…”

“…[ 17,18 ] PBNPs are ideal candidates for use as PTT agents, as they are biodegradable with limited toxicity, [ 13–15 ] and are FDA approved. [ 19 ] We have previously reported that PBNP‐PTT elicits efficient conversion of near‐infrared (NIR) wavelength light into heat by biocompatible PBNPs causing local heating of the tumor and stimulating immunogenic cell death (ICD), [ 10,13–16 ] a favorable cell death phenotype that engages an antitumor immune response. [ 20,21 ] This triggers release of tumor‐associated antigens as well as damage‐related molecular patterns from the dying tumor cells which then stimulates the activation of immune cells to target nearby unirradiated residual cancer cells in a system known as the “abscopal effect.” [ 22–25 ] We and others have previously reported that using PTT in combination with immunotherapy further improves the antitumor response of PTT compared with either therapy administered alone, by boosting immunity of the treated subjects and extending long‐term durable protection against cancer recurrence.…”

“…[ 20,21 ] This triggers release of tumor‐associated antigens as well as damage‐related molecular patterns from the dying tumor cells which then stimulates the activation of immune cells to target nearby unirradiated residual cancer cells in a system known as the “abscopal effect.” [ 22–25 ] We and others have previously reported that using PTT in combination with immunotherapy further improves the antitumor response of PTT compared with either therapy administered alone, by boosting immunity of the treated subjects and extending long‐term durable protection against cancer recurrence. [ 13,15,16 ]…”

“…[ 28 ] CpG has been previously studied in the context of NB. [ 13,15,16,29,30 ] Also, Molenkamp et al demonstrated that intratumoral injection of CpG alone or in combination with radiotherapy increases T cell immune response in cancer patients. [ 31 ] However, CpG injected directly into a tumor is rapidly eliminated, thus restricting its immunostimulatory benefits.…”

Combining Photothermal‐Photodynamic Therapy Mediated by Nanomaterials with Immune Checkpoint Blockade for Metastatic Cancer Treatment and Creation of Immune Memory

“…[33,40,73] In this case, the ablative effects on the primary tumor are mainly catalyzed by the nanomaterials' PTT/PDT, while strong abscopal effects on the secondary tumor/metastases mediated by the CD8 + T cells are often abrogated by CTLA-4, IDO1, and PD-1/PD-L1 immunosuppressive actions. [29,30,70,72,74,75] In order to revert this immunosuppressive environment, ICIs have been combined with nanomaterials' mediated PTT/PDT (Table 2).…”