Studies have demonstrated the paradoxical role

Studies have demonstrated the paradoxical role of HO-1 in tumorigenesis. At initial stages of carcinogenesis, it protects DNA by lowering the ROS-mediated mutational rate, but later, HO-1 promotes cancer cell survival and proliferation. One PDAC therapeutic strategy is to increase ROS production and disrupt the antioxidant capacity of targeted cancer cells. Gemcitabine and other chemotherapeutic drugs induce ROS production in PDAC cells,, which leads to increased expression of antioxidant-encoding genes, such as GSH and HO-1, through the activation of antioxidant-responsive genes, including Nrf2. In PDAC, increased expression of Nrf2 plays a significant role in reducing intracellular ROS levels and may contribute to PDAC progression. Higher nuclear expression of Nrf2 has been associated with poor survival of PDAC patients. HO-1 is among the various genes regulated by Nrf2. HO-1 expression is involved in tumor resistance to chemotherapeutic agents, such as cisplatin and gemcitabine., In conclusion, gemcitabine induced oxidative stress in PDAC cells, which led to the increases in the antioxidants including HO-1. This in turn, provides a neutralized environment required for PDAC cell proliferation. Therefore, manipulating ROS levels by modulating the antioxidant enzyme HO-1 could be a successful strategy for targeting cancer survivin (baculoviral IAP repeat-containing protein 5) (21-28) without causing significant damage to normal cells. Many of the HO-1 effects have been attributed HO-1 degradation products, such as CO, Fe, and biliverdin. In tumor cells, CO has been shown to induce angiogenesis, increase growth factors synthesis, modulate metabolism, and promote tumor growth. Others, however, have reported that CO had an antiproliferative effect and inhibited microvascular density of tumors in vivo. Further studies are needed to establish the effects of CO on PDAC tumor growth. Other HO-1 degradation products biliverdin and bilirubin were both shown to impose antitumor effects in some tumors, including colon cancer and PDAC. In colon cancer cells, bilirubin and biliverdin showed an antiapoptotic effect. Finally, our studies explored the effect of HO-1 inhibition on CSC marker expression in PDAC cells. Although present only in a small fraction, CSCs in PDAC were shown to play an important role in tumor growth, progression, and resistance to gemcitabine therapy. In addition, detection of CSC markers has been associated with worse clinical outcomes in patients with PDAC. CD133, CD44, and other cell surface markers were used to identify pancreatic CSC. Our results show that HO-1 inhibition in combination with gemcitabine were able to reduce the expression of CD44 and CD133 in Capan-1 and CD18/HPAF cell lines. To our knowledge, this is the first study to describe the effect of HO-1 inhibition on PDAC CSCs populations. As explained earlier, HO-1 is one of the stress-associated enzymes whose expression is stimulated by hypoxia.,53, 54, 55 The hypoxia-induced transcriptional activation of HO-1 was shown to be by a HIF-1-mediated mechanism. The role of hypoxia and HIFs in regulating CSC genes has been demonstrated. The expression of the transmembrane glycoprotein prominin-1 (CD133) has been shown to be increased in hypoxia-treated cancer cells and promote the expansion of the CD133+ tumor cell population. Both, HIF-1α and HIF-2α were involved in the hypoxia-dependent induction of CD133. Therefore our plan was to test whether induction of CD133 and other stemness markers is mediated by HO-1 induction. Our results showed that inhibiting HO-1 resulted in reduced stemness markers, indicating that induction of stemness markers under hypoxia could be mediated by HO-1. The antiapoptotic role of HO-1 overexpression is by upregulating p21, that confers cells resistance to apoptosis., Other signaling molecules were also reported for HO-1 pathway of apoptosis resistance. Activating AKT signaling pathway and inhibiting JNK/c-Jun/caspase-3 signalling pathway were suggested as a mechanism of myocardiac cells protection by HO-1 in hypoxia/reoxygenation injury.