Apoptin enhances the oncolytic properties of vaccinia virus and modifies mechanisms of tumor regression

Abstract

A recombinant vaccinia virus VVdGF-ApoS24/2 expressing apoptin selectively kills human cancer cells in vitro [Kochneva et al., 2013]. We compared the oncolytic activity of this recombinant with that of the parental strain L-IVP using a model of human A431 carcinoma xenografts in nude mice. Single intratumoral injections (2×107 PFU/mouse) of the viruses produced a dramatic decrease in tumor volumes, which was higher after injection of apoptin-producing virus. The tumor dried out after the injection of recombinant while injection of L-IVP strain resulted in formation of cavities filled with cell debris and liquid. Both viruses rapidly spread in xenografts and replicate exclusively in tumor cells causing their destruction within 8 days. Both viruses induced insignificant level of apoptosis in tumors. Unlike the previously described nuclear localization of apoptin in cancer cells the apoptin produced by recombinant virus was localized to the cytoplasm. The apoptin did not induce a typical apoptosis, but it rather influenced pathway of cell death and thereby caused tumor shrinkage. The replacement of destroyed cells by filamentous material is the main feature of tumor regression caused by the VVdGF-ApoS24/2 virus. The study points the presence of complicated mechanisms of apoptin effects at the background of vaccinia virus replication.

Features of the Antitumor Effect of Vaccinia Virus Lister Strain

“…Our previous study [ 20 ] revealed high titers of the L-IVP strain in carcinoma A431 xenografts on days 2 and 4 after virus injection: 2.3 × 10 8 PFU/mL and 1.2 × 10 9 PFU/mL. The maximum viral concentration in the tumor was reached on day 8 post injection (2.6 × 10 9 PFU/mL).…”

“…Indeed, on day 55 the tumor volume in virus and saline injected mice differed by more than 6 times. These results led to the conclusion that active replication of the virus provides rapid destruction of the A431 carcinoma [ 20 ]. The Ehrlich solid carcinoma tumors injected with the L-IVP strain also decreased in size in comparison with saline-injected control mice ( Figure 4 ).…”

“…Tumors were generated in 8–10 week old Nu/Nu mice (20–26 g) by subcutaneous injections of 5 × 10 6 A431 cells (in 100 mL PBS) in the left hind region. Tumors were measured in two dimensions using a digital caliper, and their volume was calculated by the following formula: [length × width 2 × 0.5] [ 20 ]. When tumors reached 200–250 mm 3 in volume (10 days after tumor cells injection), the mice received a single injection of the LIVP strain (1 × 10 7 PFU/mouse in 100 mL of saline) into tumor.…”

“…After transfer to other laboratories, this strain was also known as Liverpool, Merieux 37 and Nigeria. The Lister strain also was transferred to the Institute for Viral Preparations (Moscow, USSR) and used under the acronym L-IVP for vaccination against smallpox and for scientific research [ 17 , 20 , 21 ]. Many studies have shown the advantages of genetically modified Lister strain as an oncolytic agent in comparison with other VACV strains and other viruses [ 22 ].…”

“…Our study of apoptin-producing recombinant obtained using L-IVP strain in comparison with the parental strain revealed rapid destruction of human carcinoma A431 xenografts in nude mice after intratumoral injection of both viruses [ 20 ]. The L-IVP strain clearly demonstrated oncolytic effects via direct destruction of tumor cells (signs of inflammatory reactions and leukocyte accumulation in tumor tissue, and viral destruction of blood vessels were not observed).…”