Abstract
Background Despite recent promising progress, the prognosis of acute leukemia (AL) patients remains to be improved. New therapies are therefore still needed. Spontaneous complete remission (SCR) of leukemia caused by severe bacterial infection in clinic suggests the possibility of bacterial treatment for AL. An engineered attenuated Salmonella typhimurium VNP20009 with good tolerance and safety has been shown to be highly effective as an anti-tumor agent in many solid cancer models, but it has not been applied in leukemia. Therefore, we selected VNP20009 as a candidate for the bacterial therapy of AL in this study. Methods Murine xenograft tumor models were used to verify the growth inhibition effect of VNP20009 on AL tumors. Histopathological features of the tumor were observed by H&E staining, Ki-67 immunohistochemical staining and TUNEL immunofluorescence staining. The apoptosis proteins Bax and cleaved caspase-3 in tumors were detected by Western blotting. The ratios of apoptosis, green fluorescent protein positive (GFP + ) cells and immune cells were detected by flow cytometry. Blood cell count were counted by IDEXX automatic five-classification blood cell analyzer. Detection of cytokines and chemokines in serum was completed on a Luminex Multi-factor Detection Platform. Results VNP20009 can induce apoptosis of AL cells by up-regulating the expression levels of Bax and cleaved caspase-3 . Furthermore, VNP20009 significantly inhibited the proliferation of MLL-AF9-induced AML cells and prolonged the survival of the AML-carrying mice. VNP20009 restored the counts of white blood cell and its five subsets in PB to near-physiological values, and elevated the levels of certain cytokines, such as tumor necrosis factor-α (TNF-α), leukemia inhibitory factor (LIF), interferon-γ (IFN-γ), chemokine C-X-C motif ligand-10 (CCXC-10) and C-C motif ligand-2 (CCL-2). Moreover, the ratio of immune cells, including natural killer cells (NKs), CD4 + Th1-type cells and CD8 + IFN-γ-producing effector T cells were highly upregulated in the AML mice treated with VNP20009. Conclusions VNP20009 induces the apoptosis of AL cells and activates the immune system, leading to the development of a strong and effective anti-tumor systemic response and tumor remission in acute leukemia. Keywords: acute leukemia, attenuated Salmonella typhimurium VNP20009, immunotherapy, bacterial cancer therapy, apoptosis
Inhibition of acute leukemia with attenuated Salmonella typhimurium strain VNP20009
