Along with vaccines and checkpoint blockade, immune adjuvants may have an important role in tumor immunotherapy. Oligodeoxynucleotides containing unmethylated cytidyl guanosyl dinucleotide motifs (CpG ODN) are TLR9 ligands with attractive immunostimulatory properties, but intratumoral administration has been required to induce an effective anti-tumor immune response. Following on recent studies with radiation-targeted delivery of nanoparticles, we examined enhanced tumor-specific delivery of amphiphile-CpG, an albumin-binding analog of CpG ODN, following systemic administration 3 days after tumor irradiation. The combination of radiation and CpG displayed superior tumor control over either treatment alone. Intravital imaging of fluorescently labeled amphiphilic-CpG revealed increased accumulation in irradiated tumors along with decreased off-target accumulation in visceral organs. Within 48 hrs after amphiphile-CpG administration, immune activation could be detected by increased Granzyme B and Interferon gamma activity in the tumor as well as in circulating monocytes and activated CD8+ T cells. Using radiotherapy to enhance the targeting of CpG to tumors may help advance this once promising therapy to clinical relevance.

The excitement surrounding the potential of gene therapy has been tempered due to the challenges that have thus far limited its successful implementation in the clinic such as issues regarding stability, transfection efficiency, and toxicity. In this study, low molecular weight linear polyethyleneimine (2.5 kDa) was modified by conjugation to a lipid, lithocholic acid, and complexed with a natural polysaccharide, dermatan sulfate (DS), to mask extra cationic charges of the modified polymer. In vitro examination revealed that these modifications improved complex stability with plasmid DNA (pDNA) and transfection efficiency. This novel ternary polyplex (pDNA/3E/DS) was used to investigate if tumor-targeted radiotherapy led to enhanced accumulation and retention of gene therapy vectors in vivo in tumor-bearing mice. Imaging of biodistribution revealed that tumor irradiation led to increased accumulation and retention as well as decreased off-target tissue buildup of pDNA in not only pDNA/3E/DS, but also in associated PEI-based polyplexes and commercial DNA delivery vehicles. The DS-containing complexes developed in this study displayed the greatest increase in tumor-specific pDNA delivery. These findings demonstrate a step forward in nucleic acid vehicle design as well as a promising approach to overall cancer gene therapy through utilization of radiotherapy as a tool for enhanced delivery.