Recent progress in the development of molecular cancer therapeutics has revealed new types of antitumor drugs, such as Herceptin, Gleevec, and Iressa, as potent therapeutics for specific tumors. Our work has focused on molecular cancer therapeutics, mainly in the areas of drug resistance, apoptosis and apoptosis resistance, and survival-signaling, which is related to drug resistance. In this review, we describe our research on molecular cancer therapeutics, including molecular mechanisms and therapeutic approaches. Resistance to chemotherapeutic drugs is a principal problem in the treatment of cancer. P-Glycoprotein (P-gp), encoded by the MDR1 gene, is a multidrug transporter and has a major role in multidrug resistance (MDR). Targeting

Induction of selective degradation of target proteins by small molecules (protein knockdown) would be useful for biological research and treatment of various diseases. To achieve protein knockdown, we utilized the ubiquitin ligase activity of cellular inhibitor of apoptosis protein 1 (cIAP1), which is activated by methyl bestatin (MeBS, 2). We speculated that formation of an artificial (nonphysiological) complex of cIAP1 and a target protein would be induced by a hybrid molecule consisting of MeBS (2) linked to a ligand of the target protein, and this would lead to cIAP1-mediated ubiquitination and subsequent proteasomal degradation of the target protein. To verify this hypothesis, we focused on cellular retinoic acid-binding proteins (CRABP-I and -II) and designed hybrid molecules (compounds 4) consisting of MeBS (2) coupled via spacers of various lengths to all-trans retinoic acid (ATRA, 3), a ligand of CRABPs. Compounds 4 induced selective loss of CRABP-I and -II proteins in cells. We confirmed that 4b induced formation of a complex of cIAP1 and CRABP-II in vitro and induced proteasomal degradation of CRABP-II in cells. When neuroblastoma IMR-32 cells were treated with 4b, the level of CRABP-II was reduced and cell migration was inhibited, suggesting potential value of CRABP-II-targeting therapy for controlling tumor metastasis. Our results indicate that 4b possesses sufficient activity, permeability, and stability in cells to be employed in cellular assays. Hybrid molecules such as 4 should be useful not only as chemical tools for studying the biological/physiological functions of CRABPs but also as candidate therapeutic agents targeting CRABPs.

Apollon (also known as BRUCE or BIRC6) is a large protein containing baculoviral-IAP-repeat (BIR) and ubiquitin-conjugating enzyme (UBC) domains at the amino- and carboxy termini, respectively. Apollon inhibits apoptosis, but its molecular and physiological function remains unclear. Here we report that Apollon binds to, ubiquitinates and facilitates proteasomal degradation of SMAC and caspase-9, which both contain IAP-binding motifs. Targeted disruption of Apollon in mice caused embryonic and neonatal lethality. Notably, SMAC induced apoptosis in Apollon-deficient cells, but not in Apollon-expressing cells. Furthermore, the IAP-binding motif of SMAC was required to induce apoptosis in Apollon-deficient cells. These results suggest that Apollon has an essential function in preventing SMAC-induced apoptosis.

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Many diseases, especially cancers, result from aberrant or overexpression of pathogenic proteins. Specific inhibitors against these proteins have shown remarkable therapeutic effects, but these are limited mainly to enzymes. An alternative approach that may have utility in drug development relies on selective degradation of pathogenic proteins via small chimeric molecules linking an E3 ubiquitin ligase to the targeted protein for proteasomal degradation. To this end, we recently developed a protein knockdown system based on hybrid small molecule SNIPERs (pecific and ongeneticAP-dependent roteinasers) that recruit inhibitor of the apoptosis protein (IAP) ubiquitin ligases to specifically degrade targeted proteins. Here, we extend our previous study to show a proof of concept of the SNIPER technology By incorporating a high affinity IAP ligand, we developed a novel SNIPER against estrogen receptor α (ERα), SNIPER(ER)-87, that has a potent protein knockdown activity. The SNIPER(ER) reduced ERα levels in tumor xenografts and suppressed the growth of ERα-positive breast tumors in mice. Mechanistically, it preferentially recruits X-linked IAP (XIAP) rather than cellular IAP1, to degrade ERα via the ubiquitin-proteasome pathway. With this IAP ligand, potent SNIPERs against other pathogenic proteins, BCR-ABL, bromodomain-containing protein 4 (BRD4), and phosphodiesterase-4 (PDE4) could also be developed. These results indicate that forced ubiquitylation by SNIPERs is a useful method to achieve efficient protein knockdown with potential therapeutic activities and could also be applied to study the role of ubiquitylation in many cellular processes.

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To study the existence of the erythropoietin receptor (Epo-R) mRNA in brain capillary endothelial cells, the reverse transcription (RT) PCR was performed using total RNAs from rat brain capillary endothelial cells (RBECs) and MBEC4, which is one of the established mouse brain capillary endothelial cell lines. Southern analysis of the RT-PCR products indicated that both RBECs and MBEC4 expressed an authentic form of Epo-R mRNA as a minor form and an intron-5-inserted form of Epo-R mRNA, thus a soluble form of Epo-R mRNA, as a major form. Furthermore, the effect of recombinant human erythropoietin (rHuEpo) on the DNA synthesis in RBECs was analyzed. rHuEpo showed a dose-dependent mitogenic action on RBECs as a competence factor. Radioiodinated rHuEpo was bound specifically to RBECs with time, cell number and dose dependencies. Binding studies with "'I-rHuEpo showed that RBECs had a single class of receptors with low-affinity (K,, = 860 pM) and that the number of siteskell (10300) was abundant. These results suggest that brain capillary endothelial cells express not only an authentic form of Epo-R but also a soluble form of Epo-R and that erythropoietin acts directly on brain capillary endotheha1 cells as a competence factor.Keywords: erythropoietin ; recombinant human erythropoietin ; erythropoietin receptor; brain capillary endothelial cells.Hypoxemia resulting from lung and heart diseases, anemia and high-altitude residence induces a series of modifications in the mammals. As an adaptation mechanism to hypoxia, mammals increase the number of the capillaries/tissue mass [I] and the erythrocytes in the blood (21 to maintain an adequate 0, delivery.Erythropoietin (Epo) is a serum glycoprotein hormone required for survival, proliferation, and differentiation of committed erythroid progenitor cells and its production is accelerated in the kidney by hypoxia [3-51. Recently, i t has been reported that Epo may act on such non-erythroid cells as endothelial cells [6-91, smooth Chemistry, Osaka Prefecture University, Sakai, Osaka, Japan 593 [9]. Although these results suggest that Epo may function as an angiogenic factor for adapting to hypoxia, after embryogenesis, angiogenesis proceeds by the growth of new capillary vessels from an established microvasculature following stimulation by various physiological or pathological processes [18, 191. Furthermore, the mean microvessel density increases in brain [20] and no new capillaries develop in muscle [21] under hypoxic conditions such as exposure to high altitudes, implying that capillary endothelial cells from various tissues each has specific characteristics.HUVECs express Epo-R mRNA [7]. In the present study, we use rat brain capillary endothelial cells (RBECs) and MBEC4, which is one of the established mouse brain capillary endothelial cell lines [22], to analyze the existence of Epo-R mRNA in brain capillary endothelial cells, which have been thought to be associated with angiogenesis under hypoxic conditions, and provide evidence that both RBECs and MBEC4 express ...