The role of natural killer cells in combinatorial anti-cancer therapy using Sindbis viral vectors and irinotecan

Abstract

Oncolytic viruses (OVs) have shown great anti-cancer potential in animal models, but only modest success in early clinical trials. A better understanding of the mechanisms underlining OV efficacy is needed to resolve this discrepancy. In the clinic, OV therapy will likely be combined with traditional chemotherapy, underscoring the need to also evaluate the interactions between these therapeutic modalities. Here we show that combining Sindbis viral vector therapy with the topoisomerase inhibitor irinotecan (CPT-11) results in the long-term survival of about 35% of SCID mice bearing aggressively growing ES2 human ovarian cancer. Single-agent treatments did not result in long-term survival. Flow cytometry analysis, bioluminescent imaging and survival experiments revealed that Sindbis and CPT-11 utilize non-overlapping natural killer (NK)-cell-dependent and -independent anti-cancer mechanisms, respectively. Notably, the combinatorial therapy was only effective in the presence of NK cells. These results highlight the hidden role of immune cell activation in combinatorial cancer therapy involving OVs and provide a potential method for tackling tumor cell resistance to cancer therapy while limiting treatment-related side effects.Cancer Gene Therapy (2012) 19, 588--591; doi:10.1038/cgt.2012.33; published online 8 June 2012Keywords: irinotecan; NK cells; ovarian cancer; Sindbis MATERIALS AND METHODS MiceAll animal experiments were performed in accordance with NIH and institutional guidelines. In this study, we used 6--12-week-old female 'ES1/ SCID' mice from our own colony, which were generated by breeding C.B-17-SCID mice with Ces1c Foxn1/J mice (The Jackson Laboratory, Bar Harbor, ME), and were selected for the absence of T and B cells and for a deficiency in plasma esterase activity. CPT-11 can be cleaved into the more potent topoisomerase inhibitor SN-38 by mouse plasma esterase, of which there is no human homolog. Therefore, plasma esterase-deficient mice (ES1/SCID mice) more closely resemble the human condition for experiments utilizing CPT-11. 1 Cell linesBaby hamster kidney and human ovarian carcinoma (ES2) cells were obtained from the American Type Culture Collection. Baby hamster kidney cells were maintained in minimum essential a-modified media (aMEM, Mediatech) with 10% fetal calf serum. ES2 cells were cultured in McCoy's 5A medium (Mediatech, Herndon, VA, USA) supplemented with 10% fetal calf serum. All basal media were supplemented with 100 mg ml À1 of penicillin--streptomycin (Mediatech) and 0.5 mg ml À1 of amphotericin B (Mediatech). ES2/Fluc cells were derived from the ES2 cell line by stable transfection of a plasmid, pIRES2-Fluc/EGFP, as previously described. 2 Sindbis vector production Sindbis vectors (Sin/LacZ and Sin/IL-12) were produced as previously described. 2 CPT-11 formulationIrinotecan hydrochloride injection (CPT-11) was obtained from Teva Parenteral Medicines (Irvine, CA) and was diluted in phosphate-buffered saline (PBS) for mouse injections.

Cancer immunotherapy via combining oncolytic virotherapy with chemotherapy: recent advances

“…Irinotecan has been shown to inhibit HSV-1 viral replication and lytic oncolysis in colon cancer cell lines 164. In contrast, other groups show synergy with OVs/irinotecan, including HSV-1 encoding CYP2B1,127 reovirus,128 and Sindbis virus 126. However, only the study on Sindbis virus looked at immune components in irinotecan synergy, concluding that natural killer cells are essential for the process 126…”

High efficiency of alphaviral gene transfer in combination with 5-fluorouracil in a mouse mammary tumor model

“…One study showed that application of a Sindbis vector with oncolytic properties in combination with the topoisomerase inhibitor irinotecan in SCID mice bearing human ovarian cancer resulted in prolonged animal survival [33]. The authors highlight the role of natural killer cells in the induction of the anti-cancer effect by the combined treatment.…”

Tissue-Specific Attenuation of Oncolytic Sindbis Virus Without Compromised Genetic Stability

“…SV has shown promise as an anticancer agent in several preclinical models (Tseng et al, 2004;Zhang et al, 2004;Saito et al, 2009;Huang et al, 2011;Granot and Meruelo, 2012); however, translation of these findings to use in the clinic could be hindered by its pathology, which manifests as Pogosta disease in humans.…”

“…In addition to these properties, SV replicates extremely rapidly, with daughter virions beginning to bud from infected cells within 4 hr of infection . Bearing these properties in mind, we find it unsurprising that SV has shown promise as anticancer agent in several animal models (Tseng et al, 2004;Zhang et al, 2004;Saito et al, 2009;Huang et al, 2011;Granot and Meruelo, 2012) and is being targeted for clinical translation.…”