Biol. Pharm. Bull. 29(4) 670—674 (2006)

logical changes including cell shrinkage, membrane bleebing, nuclear breakdown, and DNA fragmentation, and is essential for the maintenance of tissue homeostasis and the elimination of harmful cells. An apoptotic death stimulus activates caspases, the major executioners of this process, either directly or via the activation of the mitochondrial death program. The mitochondria-mediated pathway involves an increase of mitochondrial permeability and the release of cytochrome c into the cytosol. Cytochrome c promotes the activation of caspase-3 in the cytosol, resulting in the cleavage of an inactive 32 kDa precursor into a 17 kDa and an 11 kDa subunit, which dimerize to form an active enzyme. During the progression of apoptosis, caspase-3 is one of the strongest candidates for the cleavage of 116 kDa native poly (ADP-ribose) polymerase (PARP) into an 86 kDa and a 36 kDa fragment. The cleavage of this PARP protein ultimately results in cellular, morphological, and biochemical alterations of apoptosis. Dong-Chong-Xia-Cao in Chinese, which translates as “winter worm and summer grass,” is an entomogenous fungus that colonizes the larvae or pupae of insects. It includes many different genera, such as Cordyceps, Paecilomyces, Torrubiella, and Podonectria. The entomopathogenic mycelia naturally grow in the intestine of pupa or larva in the autumn, and fruiting bodies of the fungus protrude from the body in the following summer. The fungal fruiting body and the caterpillar host are chemically similar, have similar pharmacological properties, and are traditionally dried and consumed together. Cordyceps sinensis and Cordyceps militaris are representative insect-born fungi of the genus Cordyceps used for medicinal purposes in eastern Asian countries. The known bioactive compounds of these Cordyceps species include cordycepin, ophicordin, a polysaccharide, galactomannan, and L-tryptophan. The recent scientific evaluation of Cordyceps sinensis has confirmed the efficacy of this extract in the treatment of cardiovascular and endocrine disorders, in immune enhancement, in hepatic protection, in the inhibition of tumor growth, and in relieving fatigue and stress. Cordyceps militaris, together with Paecilomyces japonica, another entomopathogenic fungi, has been listed as a food additive in Korea since 2000, and is often used in different types of tonic drinks sold in Korea due to its folkloric activities, which have not been verified scientifically. Although some recent studies have reported its effectiveness in inhibiting angiogenesis, cancer cell growth, and inflammation, scientific evidences of the biological activities of Cordyceps militaris are still very limited compared to other frequently used insect-born fungi of the Cordyceps species, such as Cordyceps sinensis. It was previously reported by these authors that the hot water extracts of Cordyceps militaris of silkworm pupa (CMP) or silkworm larva (CML) exhibited an anti-proliferation effect on tumor cells as well as a life prolongation effect in mice bearing ascitic tumors. Moreover, both CMP and CML showed tumor growth inhibitory and immunomodulatory activities in ICR mice bearing sarcoma-180 solid tumors. Despite the fact that there are ample evidences of its antitumor activities in vitro and in vivo, the working mechanism of Cordyceps militaris remains unclear. Therefore, the purpose of this study was to investigate whether the hot water extract of Cordyceps militaris affects the apoptosis of human leukemia cells (HL-60) through the activation of caspase-3, which might explain one of its action mechanisms underlying the growth inhibition of cancer cells.