Purpose: Cancer Immunotherapy represents an important alternative to current standard treatment methods for inoperable cancers such as late-stage melanoma. A primary goal of cancer immunotherapy is to break immune tolerance in the immunosuppressive tumor microenvironment and mount an efficient immune effector response against tumor cells. One method of achieving this is to stimulate the immune system against tumor-associated antigens (TAA) expressed by cancer cells through viral vaccines such as the adenovirus or co-delivering TAA with adjuvants such as CpG oligonucleotides (ODNs). Viral therapies such as an adenovirus have been shown to elicit a cytotoxic T cell (CTL) responses in murine melanoma models and combining this with intratumoral administration of soluble CpG ODN may further enhance this effect as was demonstrated in a thymoma mouse model. Despite the promising progress achieved with combinational immunotherapies, there is still room for improvement. One possibility is to vary the type of CpG ODNs used from the predominantly used CpG B to CpG A (G10) which has been shown to elicit a greater CTL response but is far less stable than CpG B due to its phosphodiester backbone being susceptible to enzymatic degradation. Encapsulating G10 into nanoparticles (NP) such as virus-like-particles (VLP) will protect it from premature degradation. The Qβ bacteriophage VLP has been shown to spontaneously form around CpG ODNs forming a high loading CpG NP (0.25 mg/mg of protein), which is much higher than polymeric NP particles encapsulating CpG (approximately 5 µg CpG/mg particles).
The goal of this project is to demonstrate that combining recombinant adenovirus type 5 vectors encoding TRP-2 (Ad5-TRP2) with intratumoral administration of CpG loaded Qβ –VLP (CMP-001) offers robust anti-tumor activity in a murine melanoma model greater than either treatment alone.
Methods: 6-8 week old C57bl/6j mice were anesthetized and injected subcutaneously with 3 × 105 B16.F10 cells (passage number 18) in 100 µl phosphate buffered saline on the right hand side rear dorsal area. One day later, mice were given 108 PFU/mL of Ad5-TRP2 contralaterally. When tumors grew to a palpable size (approximately 5-8 mm in any direction), mice were given 100 µg of G10 either soluble (sG10), or encapsulated in virus like particles (CMP-001) every 3 days for 3 administrations.
Results: DLS measurements revealed the size of CMP-001 to be 35 nm with a polydispersity index (PDI) of 0.06 (figure 1). The administration of CMP-001 along with Ad5-TRP2 slowed the tumor growth as shown in figure 2 A. These results were supported by the survival data which demostrated a significant increase in the median survival (10 days) of mice who were treated with Ad5 TRP2 + CMP-001 vs AD5 TRP 2 alone (figure 2B).
Conclusion: The data shows that combining Ad-TRP-2 with intratumoral administration of the CMP-001 offers robust anti-tumor activity in the B16.F10 murine melanoma model.