Therapeutic Synergism of Gemcitabine and CpG-Oligodeoxynucleotides in an Orthotopic Human Pancreatic Carcinoma Xenograft

Abstract

CpG-oligodeoxynucleotides (CpG-ODN) exhibit potent immunostimulatory activity by binding with Toll-like receptor 9 (TLR9). Based on the finding that TLR9 is highly expressed and functional in pancreatic tissue, we evaluated the antitumor effects of chemotherapy combined with CpG-ODNs in the orthotopic mouse model of a human pancreatic tumor xenograft. Chemotherapy consisted of the maximum tolerated dose of gemcitabine (i.v., 100 mg/kg, q3dx4). CpG-ODNs were delivered (i.p., 20 Mg/mouse), weekly, after the end of chemotherapy. CpG-ODNs alone had little effect on tumor growth, whereas gemcitabine alone significantly delayed the median time of disease onset (palpable i.p. tumor) and of bulky disease development (extensive peritoneal tumor burden), but did not enhance survival time. When the gemcitabine regimen was followed by administration of the immunostimulator, development of bulky disease was delayed, survival time was significantly improved (median survival time, 106 days; P < 0.02 versus gemcitabine-treated mice). Autoptic examination showed that tumor spread in the peritoneal cavity was reduced to a greater extent than with gemcitabine alone. All treatment regimens were well-tolerated. The use of nude mice excluded a T cell-mediated immune response, whereas the high pancreatic expression of TLR9 might have contributed to the tumor response. The clear improvement of survival observed in an orthotopic murine model of human pancreatic cancer by the combined use of CpG-ODNs with chemotherapy suggests the promise of this therapeutic regimen in the clinical setting. (Cancer Res 2005; 65(14): 6388-93)

Development of TLR9 agonists for cancer therapy

“…To induce rejection of larger or poorly immunogenic tumors, the CpG ODN generally needs to be combined with either a tumor vaccine (reviewed in ref. 71) or with other effective antitumor strategies, such as monoclonal antibody therapy (72)(73)(74)(75)(76)(77)(78), other immune therapies (including in combination with ligands for TLR3 or TLR5) (79)(80)(81)(82)(83)(84), angiogenesis inhibitors (85), radiation therapy (86), surgery (87,88), cryotherapy (89), and chemotherapy (87,(90)(91)(92)(93)(94)(95) (Table 4). In humans also, monotherapy with the TLR9 agonist CPG 7909 (now called PF-3512676 when used in oncology without a vaccine) or another B-class CpG ODN, 1018 ISS, activates NK cells and induces a Th1 cytokine response in humans with B cell lymphomas (37,96).…”

TLR9 Agonists Oppositely Modulate DNA Repair Genes in Tumor versus Immune Cells and Enhance Chemotherapy Effects

“…These receptors are considered sensors for microbial infections or other danger signals and, together with other molecular sensors, serve as a first line of defense, inducing soluble and cellular mediators of innate immunity and initiating key steps of the adaptive immune response (3). Particular clinical interest now revolves around TLR9, which is expressed not only on cells of the immune system but also on endothelial cells, fibroblasts, and epithelial cells (3)(4)(5)(6) and which recognizes bacterial and viral DNA with unmethylated CpG motifs. Synthetic oligodeoxynucleotides (ODN) expressing CpG motifs mimic the immunostimulatory activity of bacterial DNA and are commonly used to activate TLR9 for therapeutic applications (3).…”

“…In immunocompromised athymic mice, the mechanisms underlying the improved antitumor effect when CpG-ODN was combined with gimatecan (17), gemcitabine (6), or topotecan (18,19) have to be different from those in immunocompetent mice and remain unclear. It is noteworthy that, although these 3 chemotherapeutic agents differ in mechanisms of action, their cytotoxic activity is generally the consequence of DNA damage.…”

Innate Immunity-Based Immunotherapy of Cancer

“…In animal experiments, significant anti-tumor effects of TLR9 agonists have been demonstrated in a variety of settings; not only in monotherapy (Lonsdorf et al, 2003;Baines & Celis, 2003), but also in combination therapy with monoclonal antibody therapy (Buhtoiarov et al, 2006;Daftarian et al, 2004;Davila et al, 2003;Dercamp et al, 2005;Guiducci et al, 2005;Vicari et al, 2002;Wooldridge et al, 1997), cytokines, chemokines and related factors (Chaudhry et al, 2006;Ishii et al, 2003;Merad et al, 2002;Okano et al, 2005), TLR3 and TLR5 ligands (Sfondrini et al, 2006;Whitmore et al, 2004), EGFR-related signaling and angiogenesis inhibition (Damiano et al, 2006), radiotherapy (Mason et al, 2005), surgery (Ohashi et al, 2006;Weigel et al, 2003), cryotherapy (den Brok et al, 2006), and chemotherapy (Balsari et al, 2004;Pratesi et al, 2005;Taieb et al, 2006;van der Most et al, 2006;H. Wang et al 2006; X.S.…”