Plasmid DNA-induced cytokines together with cyclophosphamide decrease size and number of melanoma lung metastases

The aim of this study was to investigate whether the local induction of pro-inflammatory cytokines in mouse lungs would increase the therapeutic effect of cyclophosphamide (CTX) used to treat experimental B16(F10) melanoma lung metastases. CTX shows antiangiogenic properties and inhibits the growth of metastases, albeit without numerical reduction. To destroy small metastases remaining after CTX treatment, pro-inflammatory cytokines were induced by systemically administering plasmid DNA-PEl polyplexes. The CpG sequences present in plasmid DNA are immunostimulatory, i.e. they induce pro-inflammatory cytokines, such as IL-12, TNF-alpha, IFN-gamma and IFN-alpha. The latter has great therapeutic potential as it activates NK cells directly involved in eliminating metastatic foci. Our data indicated, for the first time, that combining cyclophosphamide delivery and local induction of pro-inflammatory cytokines in the lungs with plasmid DNA resulted in reduction in the size of malignant melanoma metastases and their number in mouse lungs. Both effects appeared to contribute to a significant extension of survival.