Timing Is Critical for an Effective Anti-Metastatic Immunotherapy: The Decisive Role of IFNγ/STAT1-Mediated Activation of Autophagy

Abstract

BackgroundImmunotherapy is often recommended as an adjuvant treatment to reduce the chance of cancer recurrence or metastasis. Interestingly, timing is very important for a successful immunotherapy against metastasis, although the precise mechanism is still unknown.Methods and FindingsUsing a mouse model of melanoma metastasis induced by intravenous injection of B16-F10 cells, we investigated the mechanism responsible for the diverse efficacy of the prophylactic or therapeutic TLR4 and TLR9 agonist complex against metastasis. We found that the activation of TLR4 and TLR9 prevented, but did not reverse, metastasis because the potency of this combination was neither sufficient to overcome the tumor cell-educated immune tolerance nor to induce efficacious autophagy in tumor cells. The prophylactic application of the complex promoted antimetastatic immunity, leading to the autophagy-associated death of melanoma cells via IFNγ/STAT1 activation and attenuated tumor metastasis. IFNγ neutralization reversed the prophylactic benefit induced by the complex by suppressing STAT1 activation and attenuating autophagy in mice. However, the therapeutic application of the complex did not suppress metastasis because the complex could not reverse tumor cell-induced STAT3 activation and neither activate IFNγ/STAT1 signaling and autophagy. Suppressing STAT3 activation with the JAK/STAT antagonist AG490 restored the antimetastatic effect of the TLR4/9 agonist complex. Activation of autophagy after tumor inoculation by using rapamycin, with or without the TLR4/9 agonist complex, could suppress metastasis.Conclusion and SignificanceOur studies suggest that activation of IFNγ/STAT1 signaling and induction of autophagy are critical for an efficacious anti-metastatic immunotherapy and that autophagy activators may overcome the timing barrier for immunotherapy against metastasis.

Oncostatin M Modulates the Mesenchymal–Epithelial Transition of Lung Adenocarcinoma Cells by a Mesenchymal Stem Cell-Mediated Paracrine Effect

“…The numbers of metastatic nodules in the lung was counted (top right), and the tumor volume in lung was calculated from the histographs using the formula (length  width 2 )/2 (bottom right). (43). We showed that knockdown of STAT1, but not STAT3 ( Supplementary Fig.…”

“…STAT1 is an important downstream target of OSM-dependent pathways. Activation of STAT1 has been reported to be critical for the efficacy of anti-metastatic immunotherapies (43). The anticancer effect of OSM against chondrosarcoma is thought to work through the JAK3/STAT1 pathway (27).…”

Simultaneous TLR2 inhibition and TLR9 activation synergistically suppress tumor metastasis in mice

“…Treatment with TLR2-neutralizing antibody plus CpG ODN enhances the antitumor immunity and reduces immune suppression in the tumor microenvironment To find whether the differential immune responses induced by A number of studies indicate that IFN-γ can induce antitumor activity through STAT1 activation and autophagy induction [14,18,19] . By contrast, TGF-β1, IDO and COX2 are immunosuppressive factors that can promote tumor progression through the activation of Treg cells and suppression of T cell proliferation and responses [20] .…”

“…However, the combination regimen does not suppress tumor growth. This result may be due to the following: 1) the importance of TLR2 and TLR9 on host immune cells and tumor cells for positively modulating metastatic behavior compared to their minimal influence on primary subcutaneously implanted tumor growth [12,13,21,22] ; 2) the failure of the combination regimen to promote sufficient immune cell infiltration into the primary tumor to produce a potent cytotoxic suppression of tumor growth due to the anatomical site of administration [23] ; 3) the inability of the therapeutic administration of the combination regimen to overcome the immunosuppressive barrier after the suitable microenvironment for tumor growth has been established [14] . The TLR9 agonist CpG ODN is a promising anti-cancer immunotherapy based on its ability to safely stimulate Th1-dominant innate and adaptive immunity in humans [7] .…”

“…The TLR2-neutralizing (200 µg/kg), anti-IgG antibody (200 µg/kg), CpG (0.5 mg/kg) and CpG control (0.5 mg/kg) were injected on day 3. The treatment with CpG or CpG control was repeated every three days and the treatment with TLR2-neutralizing or anti-IgG antibody was repeated every seven days [12,14] . The sham and control mice received a PBS vehicle treatment alone.…”