ation of caspase 9 (Fig. 5A). In light of mitochondrial damage, it is usually associated with the generation of reactive oxygen species (ROS) which could contribute to cell death (52), the effects of MCL in the expression levels of ROS and antioxidants (e.g., reduced Indole-3-carbinol glutathione) warrants further studies. On the basis of the knowledge that MCL could induce the damage of mitochondria and cell-cycle transition, and the activation of caspase cascades, Bcl-2 family proteins play multiple regulatory functions in signal transduction involved in these activities (7, 27).
We further investigated changes in protein levels of some Bcl-2 family members in MCL-treated NPC cells. There are 3 types of Bcl-2 family members: multidomain Clofarabine antiapoptotic proteins (Bcl-2, BclxL, Mcl-1L, and Bfl-1/A1), multidomain proapoptotic proteins (Bax, Bok/Mtd, Bcl-XS, and Bak), and BH3-only proapoptotic proteins (Bad, Bid, BimEL, Bmf, Mcl-1S, PUMA, and NOXA; ref. 27). Three representative members from each subfamily were included in this study, including Bcl-2, Bak, and Bid. Bcl2 phosphorylation has been shown to inhibit cell-cycle progression by delaying the G1–S transition (27, 53). Furthermore, the proapoptotic proteins Bak and Bid can inhibit cell-cycle progression, inhibit cell survival, and increase apoptosis (7, 27, 39).
Strikingly, MCL had no significant effects on the production of these proteins. Huand colleagues (7) studied the apoptotic activity of ApoG2 toward NPC cells (including CNE-1 and CNE-2) and observed that ApoG2 totally blocked the functions of Bcl-2 family Salinomycin Procoxacin proteins without affecting their expression levels. Whether the same phenomenon is true of MCL remains to be investigated. Consistent with the significant apoptosis-inducing activity in vitro, administration of MCL at a physiologically safe dose resulted in a pronounced reduction in the growth of CNE-2 xenograft tumor in nude mice. Daily intraperitoneal injection of 1.0 mg MCL/kg body weight (1.0 mg/kg/d) abated both tumor volume and weight in mice by induction of tumor cell apoptosis . The dose used had no toxicity on mice in the control group. This finding is reminiscent of other reports (11, 13). The LD50 of MCL is 3.16 mg/1 kg body weight in Swiss mice (13).
Two RIP proteins from BG exhibit profound apoptosis-inducing activity in premalignant order Troxerutin and malignant prostate cancer cells in vitro and in vivo. The dose used for the in vivo assay in male mice was intraperitoneal 0.5 mg/kg body weight, twice a week . Although some proteins manifest significant antitumor activities both in vitro and in vivo (11, 42, 54), and some are under phase III clinical trial (such as a ribonuclease Onconase cytopathology from Rana pipiens ref. 55), there are still some bottlenecks with regard to the development of protein therapeutics in humans. For example, proteins would be digested after oral intake and whether the fragments produced still remain biologically active needs investigation. A gratifying report is that MAP30, a 30-kDa RIP from BG, could yield, after digestion, biologically active fragments, which retained full activities against tumor cells . Furthermore, we would like to consider other routes of drug administration, such as intravenous injection and direct injection, into the tumor.