David Gallo

Carbon Monoxide Expedites Metabolic Exhaustion to Inhibit Tumor Growth

One classical feature of cancer cells is their metabolic acquisition of a highly glycolytic phenotype. Carbon monoxide (CO), one of the products of the cytoprotective molecule heme oxygenase-1 (HO-1) in cancer cells, has been implicated in carcinogenesis and therapeutic resistance. However, the functional contributions of CO and HO-1 to these processes are poorly defined. In human prostate cancers, we found that HO-1 was nuclear localized in malignant cells, with low enzymatic activity in moderately differentiated tumors correlating with relatively worse clinical outcomes. Exposure to CO sensitized prostate cancer cells but not normal cells to chemotherapy, with growth arrest and apoptosis induced in vivo in part through mitotic catastrophe. CO targeted mitochondria activity in cancer cells as evidenced by higher oxygen consumption, free radical generation, and mitochondrial collapse. Collectively, our findings indicated that CO transiently induces an anti-Warburg effect by rapidly fueling cancer cell bioenergetics, ultimately resulting in metabolic exhaustion.

Nitric Oxide–Dependent Bone Marrow Progenitor Mobilization by Carbon Monoxide Enhances Endothelial Repair After Vascular Injury

Background— Carbon monoxide (CO) has emerged as a vascular homeostatic molecule that prevents balloon angioplasty–induced stenosis via antiproliferative effects on vascular smooth muscle cells. The effects of CO on reendothelialization have not been evaluated. Methods and Results— Exposure to CO has diametrically opposite effects on endothelial cell (EC) and vascular smooth muscle cell proliferation in rodent models of carotid injury. In contrast to its effect of blocking vascular smooth muscle cell growth, CO administered as a gas or as a CO-releasing molecule enhances proliferation and motility of ECs in vitro by >50% versus air controls, and in vivo, it accelerates reendothelialization of the denuded artery by day 4 after injury versus day 6 in air-treated animals. CO enhanced EC proliferation via rapid activation of RhoA (Ras homolog gene family, member A), followed by downstream phosphorylation of Akt, endothelial nitric oxide (NO) synthase phosphorylation, and a 60% increase in NO generation by ECs. CO drives cell cycle progression through phosphorylation of retinoblastoma, which is dependent in part on endothelial NO synthase–generated NO. Similarly, endothelial repair in vivo requires NO-dependent mobilization of bone marrow–derived EC progenitors, and CO yielded a 4-fold increase in the number of mobilized green fluorescent protein–Tie2–positive endothelial progenitor cells versus controls, with a corresponding accelerated deposition of differentiated green fluorescent protein–Tie2–positive ECs at the site of injury. CO was ineffective in augmenting EC repair and the ensuing development of intimal hyperplasia in eNOS−/− mice. Conclusions— Collectively, the present data demonstrate that CO accelerates EC proliferation and vessel repair in a manner dependent on NO generation and enhanced recruitment of bone marrow–derived endothelial progenitor cells.

Cross-Regulation of Carbon Monoxide and the Adenosine A2a Receptor in Macrophages

Adenosine and heme oxygenase-1 (HO-1) exert a wide range of anti-inflammatory and immunomodulatory actions, making them crucial regulatory molecules. Despite the diversity in their modes of action, the similarity of biological effects of adenosine and HO-1 led us to hypothesize a possible interrelationship between them. We assessed a potential role for HO-1 in the ability of adenosine or 5′-N-ethylcarboxamidoadenosine (NECA), a stable adenosine analog, to modify the response of LPS-stimulated macrophages. Adenosine and NECA markedly induced HO-1 and blocked LPS-induced TNF-α production via adenosine A2aR-mediated signaling; blocking of HO-1 by RNA interference abrogated the effects of adenosine and NECA on TNF-α. HO-1 overexpression or exposure to carbon monoxide (CO), a product of HO-1 enzymatic activity, resulted in augmented A2aR mRNA and protein levels in RAW264.7 cells and primary macrophages. The induction of A2aR expression by HO-1 or CO resulted in an increase in the sensitivity to the anti-inflammatory effects of adenosine and NECA, which was lost in macrophages isolated from A2aR-deficient mice. Moreover, a decrease in cAMP levels upon NECA stimulation of naive macrophages was counterbalanced by CO exposure to up-regulate A2aR levels. This implies adenosine receptor isoform switch as a selective modification in macrophage phenotype. Taken together, these data suggest the existence of a positive feedback loop among adenosine, HO-1, CO, and the A2aR in the chronological resolution of the inflammatory response.

Carbon monoxide enhances early liver regeneration in mice after hepatectomy.

Hepatocyte proliferation early after liver resection is critical in restoring liver mass and preserving function as the liver regenerates. Carbon monoxide (CO) generated by heme oxygenase‐1 (HO‐1) strongly influences cellular proliferation and both HO‐1 and CO are accepted hepatoprotective molecules. Mice lacking functional HO‐1 were unable to mount an appropriate regenerative response following partial hepatectomy (PHTx) compared to wildtype controls. We therefore hypothesized that exogenous administration of CO at low, nontoxic concentrations would modulate hepatocyte (HC) proliferation and liver regeneration. Animals treated with a low concentration of CO 1 hour prior to 70% hepatectomy demonstrated enhanced expression of hepatocyte growth factor (HGF) in the liver compared to controls that correlated with a more rapid onset of HC proliferation as measured by phospho‐histone3 staining, increased expression of cyclins D1 and E, phosphorylated retinoblastoma, and decreased expression of the mitotic inhibitor p21. PHTx also increased activation of the HGF receptor c‐Met, which was detected more then 9 hours earlier in the livers of CO‐treated mice. Blockade of c‐Met resulted in abrogation of the CO effects on HC proliferation. Corresponding with increased HC proliferation, treatment with CO maintained liver function with normal prothrombin times versus a 2‐fold prolongation in controls. In a lethal 85% PHTx, CO‐treated mice showed a greater survival rate compared to controls. In vitro, CO increased HGF expression in hepatic stellate cells, but not HC, and when cocultured together led to increased HC proliferation. In summary, we demonstrate that administration of exogenous CO enhances rapid and early HC proliferation and, importantly, preserves function following PHTx. Taken together, CO may offer a viable therapeutic option to facilitate rapid recovery following PHTx. (HEPATOLOGY 2011;)

Abstract LB-358: Heme oxygenase-1 and carbon monoxide arrest tumor growth via modulation of cellular respiration

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Heme oxygenase-1 (HO-1) and carbon monoxide (CO) are endogenous cytoprotective molecules yet their role in tumor growth, metastasis, cell death and DNA damage has not been elucidated. HO-1 expression was assessed in prostate cancer biopsies from 482 patients and strong nuclear staining, indicative of loss of enzymatic activity was observed in moderately differentiated tumors. Employing prostate cancer (PCa) as our model we treated PCa cells with the chemotherapeutics camptothecin or doxorubicin and observed an increase in cytosolic HO-1 activity that correlated with increased cell death. Overexpression of HO-1 or exogenous pretreatment with CO increased tumor cell sensitivity to chemotherapeutics one thousand fold. In contrast, CO blocked chemotherapeutic-induced cell death of normal prostate epithelial cells. In vivo, CO exposure of mice with established PC3 xenografts resulted in complete growth arrest and sensitization of tumors to doxorubicin with mitotic blockade and enhanced apoptosis of the tumor cells. Exposure to CO showed similar effects in a model of PC3 orthotopic tumors with significant inhibition in markers of invasion. Further, CO blocked development of PIN and prostate tumors in the model of TRAMP mice with concomitant targeting of mitochondria. Further, CO inhibited growth of lung adenocarcinoma in the inducible KRas model of carcinogenesis. Collectively, our data demonstrate the importance of cellular localization of HO-1 in human PCa progression and importantly that CO in part, regulates cellular sensitivity to DNA damaging agents and offers a novel therapeutic adjuvant for the treatment of cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-358. doi:1538-7445.AM2012-LB-358