Isofraxidin enhances hyperthermia­induced apoptosis via redox modification in acute monocytic leukemia U937 cells.

The cell­killing potential of most chemotherapeutic agents is enhanced by a temperature elevation. Isofraxidin (IF) is a coumarin compound widely found in plants, such as the Umbelliferae or Chloranthaceae families. IF induces anticancer effects in lung and colorectal cancer. To the best of our knowledge, the combined effects of hyperthermia (HT) and IF on heat­induced apoptosis have not been reported. Acute monocytic leukemia U937 cells were exposed to HT with or without IF pre­treatment. Apoptosis was measured by Annexin V­FITC/PI double staining assay using flow cytometry and cell viability was observed by cell counting kit assay, DNA fragmentation. The mechanism involved in the combination was explored by measuring changes in the mitochondrial membrane potential, (MMP), intracellular ROS generation, expression of apoptosis related protein, and intracellular calcium ion level. It was demonstrated that IF enhanced HT­induced apoptosis in U937 cells. The results demonstrated that combined treatment enhanced mitochondrial membrane potential loss and transient superoxide generation increased protein expression levels of caspase­3, caspase­8 and phosphorylated­JNK and intracellular calcium levels. Moreover, the role of caspases and JNK was confirmed using a pan caspase inhibitor (zVAD­FMK) and JNK inhibitor (SP600125) in U937 cells. Collectively, the data demonstrated that IF enhanced HT­induced apoptosis via a reactive oxygen species mediated mitochondria/caspase­dependent pathway in U937 cells.

Hyperthermia and radiation reduce the toxic side-effects of bufadienolides for cancer therapy.

Bufadienolides are constituents of the traditional Chinese medicine Chan Su and are found in toad venom. Cardiovascular side-effects are one of the limiting factors towards developing bufadienolides as chemotherapeutic agents. Thus, in the present study, low doses of bufalin and cinobufotalin, prominent members of the bufadienolides, were investigated for their cytotoxic activity in combination with hyperthermia (HT) or radiation (Rad) therapy. In addition, the underlying mechanism involved was investigated. A DNA fragmentation assay, viability assay and microscopic observation were primarily used to assess the effect of low doses of the two drugs in human lymphoma U937 cells. Furthermore, the effects of these drugs on the mitochondrial membrane potential (MMP) and apoptotic-associated protein activation were investigated. HT/bufadienolide- and RT/bufadienolide-treated samples significantly increased the DNA fragmentation percentile and decreased the MMP, as well as increasing the apoptotic features observed microscopically within a relatively short time (6 h) after treatment. The two combinations affected the expression of important apoptotic markers, including caspase-3 and BH3 interacting domain death agonist. The findings of the current study confirm the additive effect of HT with this group of drugs, directing a novel therapeutic avenue for the clinical use of bufadienolides at lower doses with more restrained cardio toxic side-effects.

Enhancement of hyperthermia-induced apoptosis by 5Z-7-oxozeaenol, a TAK1 inhibitor, in A549 cells.

KRAS mutant lung cancers have long been considered as untreatable with drugs. Transforming growth factor-ß-activated kinase 1 (TAK1) appears to play an anti-apoptotic role in response to multiple stresses and has been reported to be a responsive kinase that regulates cell survival in KRAS-dependent cells. In this study, in order to find a useful approach to treat KRAS mutant lung cancer, we focused on the combined effects of 5Z-7-oxozeaenol, a TAK1 inhibitor, with hyperthermia (HT) in KRAS mutant lung cancer cell line A549. Annexin V-FITC/PI assay, cell cycle analysis, and colony formation assay revealed a significant enhancement in apoptosis induced by HT treatment, when the cells were pre-incubated with 5Z-7-oxozeaenol in a dose-dependent manner. The enhanced apoptosis by 5Z-7-oxozeaenol was accompanied by a significant increase in reactive oxygen species (ROS) generation and loss of mitochondrial membrane potential (MMP). In addition, western blot showed that 5Z-7-oxozeaenol enhanced HT-induced expressions of cleaved caspase-3, cleaved caspase-8, and HSP70 and decreased HT-induced expressions of Bcl-2, p-p38, p-JNK, and LC3. Moreover, 5Z-7-oxozeaenol pre-treatment resulted in a marked elevation of intracellular calcium level which might be associated with endoplasmic reticulum (ER) stress-related pathway. Taken together, our data provides further insights of the mechanism of action of 5Z-7-oxozeaenol and HT treatment, and their potential application as a novel approache to treat patients with KRAS mutant lung cancer.

Isofraxidin, a potent reactive oxygen species (ROS) scavenger, protects human leukemia cells from radiation-induced apoptosis via ROS/mitochondria pathway in p53-independent manner.

Ionizing radiation (IR) leads to oxidizing events such as excessive reactive oxygen species (ROS) in the exposed cells, resulting in further oxidative damage to lipids, proteins and DNA. To screen the potential radio-protective drug, the intracellular ROS was measured in irradiated U937 cells pretreated with 80 candidate traditional herbal medicine, respectively. Isofraxidin (IF) was one possible radio-protector in these 80 drugs. This study investigated the radio-protective role of IF, a Coumarin compound, in human leukemia cell lines, for the first time. Results indicate that IF protects against IR-induced apoptosis in U937 cells in the time- and concentration- dependent manner. IF decreases IR-induced intracellular ROS generation, especially hydroxyl radicals formation, inhibits IR-induced mitochondrial membrane potential loss and reduces IR-induced high intracellular Ca(2+) levels regardless of ER stress. IF down-regulates the expression of caspase-3, phospho-JNK, phospho-p38 and activates Bax in mitochondria. IF inhibits cytochrome c release from mitochondria to cytosol. IF also moderates IR-induced Fas externalization and caspase-8 activation. IF also exhibits significant protection against IR-induced cell death in other leukemia cell lines such as Molt-4 cells and HL60 cells regardless of p53. Taken together, the data demonstrate that IF protects leukemia cells from radiation-induced apoptosis via ROS/mitochondria pathway in a p53-independent manner.