Cyclophosphamide enhances glioma virotherapy by inhibiting innate immune responses

Abstract

Clinical trials are testing oncolytic viruses (OVs) as therapies for cancer. We have shown that animals that have brain tumors and are treated with a herpes simplex virus (HSV)-derived OV live significantly longer when cyclophosphamide (CPA) is preadministered. Here, we explore the mechanisms behind this finding. In a syngeneic rat glioma model, intratumoral HSV administration is associated with rapid increase of natural killer cells, microglia͞ macrophages (CD68 ؉ and CD163 ؉ ), and IFN-␥. Pretreatment with CPA enhances HSV replication and oncolysis and reduces an HSVmediated increase in CD68 ؉ and CD163 ؉ cells and intratumoral IFN-␥. Molecular imaging shows CPA pretreatment to inhibit HSVinduced infiltration of tumor-associated phagocytic cells. Our results reveal molecular and cellular mechanisms that inhibit intratumoral spread of HSV and suggest a therapeutic path for improving the efficacy of virotherapy as a treatment for cancer.gene therapy ͉ innate immunity ͉ oncolytic virus ͉ brain tumor ͉ herpes simplex virus A dvances in virology and tumor biology have enabled development of oncolytic viruses (OVs), which replicate selectively in tumor cells (1-6). OV progeny propagate throughout tumors, lysing tumor cells but not normal cells. Phase I clinical trials have shown OV therapy to be safe (7-13) but with limited efficacy. A brisk host response to OV therapy has been seen. It includes intratumoral immune cells (7) and acute-phase reaction to intravascular virus (13). Innate immune responses may be a common side effect of OV therapy, similar to the radionecrosis of radiotherapy or myelosuppression of chemotherapy.The role of host immune responses in the efficacy or toxicity of OV therapy is poorly defined. Such responses are thought beneficial because oncolysis stimulates adaptive immunity, setting up an anticancer vaccination effect (14-16). However, initial innate responses to OVs may reduce efficient anticancer effects (17-21). For example, we have shown a herpes simplex virus (HSV)-based OV therapy to be more efficient when cyclophosphamide (CPA) is present (22-25), and this increased efficiency is credited to CPA's immunosuppressive action. However, the specific immune pathways of the observed effects have not been analyzed. ResultsPreadministering CPA Inhibits Clearance of Viral Particles and Increases HSV Replication Within Injected Tumors. We have reported that CPA allows increased replication of HSV in injected tumors by suppressing immune activity (25). To determine intratumoral persistence of HSV, we compared intratumoral viral-mediated LacZ (Fig. 1) and ICP4 (infected-cell protein 4) (Fig. 6, which is published as supporting information on the PNAS web site) gene expression in immunocompetent rats 6 and 72 h after treatment with HSV, with and without CPA pretreatment. Six hours after intratumoral HSV delivery, Ϸ50% of tumor cells showed viral-mediated gene expression, regardless of CPA ( Fig. 1 A and C). However, by 72 h, without CPA, Ͻ10% of tumor cells showed viral-mediated gene expression,...

Gene therapy progress and prospects cancer: oncolytic viruses

“…These studies demonstrated that cyclophosphamide is able to inhibit neutralizing antibody induction, macrophages, regulatory T cells (Tregs) induction and intratumoral interferon (IFN)-g production. [2][3][4][5][6][7][8] It remains to be determined, however, how much this approach will benefit cancer patients who often have already various degrees of 'pre-existing' immunosuppression due to disease and chemotherapy.…”

Adenovirus-based virotherapy enabled by cellular YB-1 expression in vitro and in vivo

“…Recent results have shown that additional treatment with low-dose cyclophosphamide, which causes among other things elimination of regulatory T cells in a corresponding mouse model is beneficial for improving the efficacy of virotherapy. [38][39][40] In summary, our study is the first to show that YB-1-dependent virotherapy in combination with chemotherapy is an attractive treatment option for pancreatic cancer. We observed high replication potency in vitro and in vivo.…”

Lentiviruses with trastuzumab bound to their envelopes can target and kill prostate cancer cells

“…It has been reported that cyclophosphamide enhances glioma virotherapy by inhibiting innate immune responses. 41,63 We observed that treatment of mice with cyclophosphamide before injection of trastuzumab-bound virus enhanced the luminescent signal in the tumors (Figure 7a.4), whereas in the absence of cyclophosphamide, luminescence was only seen in the spleen area (data not shown).…”

“…administration of lentivirus, mice bearing C4-2 tumors were treated with low doses of cyclophosphamide (80 mg kg À1 , intra-peritoneal injection), as it has been reported that cyclophosphamide enhances virotherapy by inhibiting innate immune responses. 41,42 At 24 h later, concentrated lentivirus FULW/VSV-G or FULW/SB bound to trastuzumab were injected i.v.. At 10 days after the first injection of FULW/SB with bound trastuzumab, luminescent signal on the C4-2 tumors were clearly observed although some signals from the spleen area could still be seen (Figure 7a.4). When there was no pretreatment with cyclophosphamide, luminescent signals were increased in the spleen, which is enriched in macrophages (data not shown).…”