Bacterial cupredoxin azurin as an inducer of apoptosis and regression in human breast cancer

Abstract

Azurin, a copper-containing redox protein released by the pathogenic bacterium Pseudomonas aeruginosa, is highly cytotoxic to the human breast cancer cell line MCF-7, but is less cytotoxic toward p53-negative (MDA-MB-157) or nonfunctional p53 cell lines like MDD2 and MDA-MB-231. The purpose of this study was to investigate the underlying mechanism of the action of bacterial cupredoxin azurin in the regression of breast cancer and its potential chemotherapeutic efficacy. Azurin enters into the cytosol of MCF-7 cells and travels to the nucleus, enhancing the intracellular levels of p53 and Bax, thereby triggering the release of mitochondrial cytochrome c into the cytosol. This process activates the caspase cascade (including caspase-9 and caspase-7), thereby initiating the apoptotic process. Our results indicate that azurininduced cell death stimuli are amplified in the presence of p53. In vivo injection of azurin in immunodeficient mice harboring xenografted human breast cancer cells in the mammary fat pad leads to statistically significant regression (85%, P ¼ 0.0179, Kruskal-Wallis Test) of the tumor. In conclusion, azurin blocks breast cancer cell proliferation and induces apoptosis through the mitochondrial pathway both in vitro and in vivo, thereby suggesting a potential chemotherapeutic application of this bacterial cupredoxin for the treatment of breast cancer.

Microbial based therapy of cancer: A new twist to an age old practice

“…58 MCF-7 cells containing wild type p53 were highly susceptible to azurin treatment compared to the p53 null cell lines. The intracellular p53 level increased after azurin treatment in MCF 7 cells; however a fraction of p53 as well as a small amount of azurin was also translocated to the mitochondria.…”

“…57 It preferentially binds to the N-terminal and middle region of the p53 but only weakly to the C-terminal. 58 To the best of our knowledge azurin is the first bacterial protein reported to be interacting with p53, and hence it has the potential of being used in p53-based anti-cancer therapies. It modulates p53 activity and induces the apoptotic cell death (Fig.…”

“…Current studies are directed at analyzing the relative importance of transcriptional and nontranscriptional p53-dependent cell death in response to azurin treatment. A clinically important finding of Punj et al 58 was that azurin allowed significant regression of breast cancer in vivo in athymic mice injected with 1 mg of azurin daily as compared to untreated mice. A mean tumor volume of 15% was observed 29 days after the start of the experiment in treated mice as compared to controls, demonstrating 85% regression of tumor growth.…”

“…In view of this, we tested if azurin can induce an immune response in C57BL/6 mice treated with 1 mg/ml of azurin, intra-peritoneally daily for 28 days, as reported in previous studies. 46,58 The mice were monitored for 40 days, bled every 10 days, and tested for azurin specific antibody response. After 40 days, mice treated with azurin demonstrated a very low level of azurinspecific antibody (titer of 1:800), predominantly of the IgG class, which is insignificant considering that these mice had received repeated injections of azurin.…”

Structural studies on Laz, a promiscuous anticancer Neisserial protein

“…3 Azurin exhibits significant cytotoxicity against cancer cells, while little cytotoxicity is observed against normal cells. 4 The protein can preferentially enter cancer cells and bind to the tumor suppressor protein p53. 5 The complex formed by azurin and p53 as well as its electron transfer partner cytochrome c induces apoptosis in cancer cells through cell cycle arrest at the G1 phase or caspase-mediated mitochondrial cytochrome c release.…”