Although the efficacy of polyamine restriction is not as apparent in humans as in animals [47, 48], inhibition of polyamine synthesis by DFMO successfully suppressed the progression of neoplastic disease [49–52]. However, a major factor

that directly influences the prognosis of patients with malignant disease is the capability of cancer cells to invade surrounding tissues and organs and evade immune cell defenses to metastasize to distant organs. In animal experiments, inhibition of polyamine synthesis by DFMO and/or MGBG not only reduced tumor growth but also decreased BKM120 datasheet the amount of metastasis, resulting in prolonged survival of tumor bearing animals [43, 44, 46, 53–55]. Therefore, the effect of polyamines on the metastatic potential of cancer cells, the host’s

anti-tumor immunity, LEE011 and the corresponding mechanisms involved should be taken into consideration. 5. Mechanism of metastasis and involvement of polyamines (Figure 2) There are several steps that occur during metastasis: separation of cancer cells from the tumor cluster (5-a); transmigration of cells from the original cluster to the circulation (5-b); and rooting and colonization in new organs and tissues (5-c) [56, 57]. In addition, metastasis is completed only when cancer cells can successfully escape from the anti-tumor immune function of the host during this process (5-d). In this section, the mechanism of cancer metastasis and the involvement of polyamines are discussed. Glutamate dehydrogenase 5-a. Separation of cancer cells from the tumor cluster, and the role of polyamines Cancer metastasis begins when cancer cells separate from the tumor cluster. This separation is initiated by decreased cell adhesion, which is normally

maintained by the presence of Akt inhibitor adhesion molecules involved in intercellular binding and binding between cells and the extracellular matrix. Hypoxia, a common condition in cancer tissues, exerts a strong pressure on cells to separate from the tumor cluster and migrate into circulation [58, 59]. Despite their de novo angiogenesis, solid tumors have scattered regions where oxygen delivery is compromised due to diffusion limitations, structural abnormalities of tumor microvessels, and disturbed microcirculation [60]. The cellular response to hypoxia involves the stabilization and resultant increase in levels of hypoxia inducible factor-1 (HIF-1), a transcription factor that enhances gene expression to promote angiogenesis, anaerobic metabolism, cell survival, and invasion [61]. Among these, suppression of adhesion molecules induced by hypoxia-induced HIF-1 stabilization is a strong selective pressure that enhances outgrowth of cells with high-grade malignancy. CD44 and E-cadherin are adhesion molecules whose expression decreases in response to hypoxia [62, 63]. In cells exposed to chronic hypoxia, polyamine synthesis is decreased, while the ability to take up polyamines from the surroundings is increased [64, 65].