Tumor cell growth, even in advanced stages of
ovarian cancer, is nearly always restricted to the peritoneal cavity; therefore, repeated
intraperitoneal injections of
oligodeoxynucleotides containing dinucleotides with unmethylated CpG motifs (
CpG-ODN) recruiting and activating innate effector cells throughout the abdominal cavity to the
tumor site might control
tumor cell growth and
ascites formation. After a single
CpG-ODN treatment, in IGROV-1 ovarian
tumor ascites-bearing athymic mice, the number of
tumor cells declined rapidly and markedly, and
ascites volumes declined shortly
after treatment (5 h), increasing thereafter at a slower rate than in controls. When administered every 7 days for 4 weeks,
CpG-ODN had only a marginal effect on survival time, whereas administration 5 days/wk for 3 or 4 weeks led to a significantly increased survival time as compared with controls (P<0.005) and completely controlled
ascites growth without apparent toxicity, although a disorganization of lymphoid organs was observed. Bio-plex assay of
cytokine levels in peritoneal fluid of
ascites-bearing mice after
CpG-ODN treatment revealed an increase in
interleukin (IL)-6,
IL-10,
IL-12, and
interferon-gamma at 24 hours, which returned to control mice levels at 48 to 96 hours, whereas the high levels of angiogenic factors remained unchanged. Depletion of natural killer or monocytes/macrophages only slightly influenced the
CpG-ODN-induced reduction of
ascites tumor cells, indicating that the antitumor activity might not be related to a specific cell/
cytokine but rather to the repertoire of cells and
cytokines accumulated in the peritoneal cavity. Thus, our data suggest a relevant role for repeated activation of cells and
cytokines of innate immunity in the
therapy of
ovarian cancer patients with malignant
ascites.