生物谷报道：大多数的癌细胞由于凋亡机制不健全，所以导致恶性生长或者产生对抗肿瘤药物的抗性。由于蛋白间的互相作用在对细胞凋亡过程中起了决定性的调控作用，因此，利用具有生物活性的多肽来模拟蛋白互作，从而调控凋亡途径杀灭癌细胞的治疗策略，看起来是极具吸引力的。
然而，天然的多肽往往有生物利用率低、细胞膜穿透性弱和代谢稳定性差等局限，因此，一门新的学科应运而生——peptidomimetics，是指利用人工合成的物质模拟天然多肽的结构，或者利用构象性模板（conformational template）诱导相邻的多肽序列形成特异的结构。人工合成的或者改造过的多肽，力图保留天然的多肽的生物活性但克服其缺陷，以达到治疗所需要的要求。
在最新一期的《Science》（3 Sep, 2004）上，美国的两个研究组分别从细胞凋亡的固有途径和外来途径入手，利用这个peptidomimetics的策略启动细胞凋亡来治疗癌症。
生物谷专家认为：在线粒体介导的凋亡途径（也就是固有途径）中，Bcl-2家族的各种蛋白起到了重要的调控作用。而这些蛋白都共有的结构域是BH3(BCL-2 homology 3) ，正是通过这个共同结构域，促进凋亡和抑制的蛋白互相作用，控制线粒体膜的整合性，一旦促进凋亡的蛋白形成优势，导致线粒体透性增加，释放细胞色素C等因子，启动整个细胞的凋亡。研究者合成改造后的BH3多肽"stabilized alpha-helix of BCL-2 domains" (SAHBs)，SAHBs能够杀灭血癌细胞，并能阻止移植的血癌细胞在小鼠体能的生长。
另一篇文章，tumor necrosis factor (TNF ) 和 TNF-related apoptosis-inducing ligand (TRAIL)，能够利用凋亡的外来途径活化caspases，最终杀灭癌细胞，但是细胞中存在的inhibitor-of-apoptosis protein （IAP）却抑制caspase的活性，不过，各种IAPs又可以被Smac所抑制。因此，研究者通过研究Smac和IAPs的结合部位的结构特性，合成了Smac的模拟物，并证明这种合成物能够和TNF 或TRAIL共同作用，杀灭癌细胞。
这两篇文章，分别出自细胞凋亡的大牛Korsmeyer和王晓东（都是和其他的实验室合作），而且，所用的方法，Korsmeyer还是偏向于动物模型和而王晓东则采用擅长的生化方法。不管怎样，二者都给出了peptidomimetics这个概念令人兴奋的证据。
相关图片如下：
Fig. 1. C2-symmetric compound 3 is a potent Smac mimetic in vitro. (A) Chemical structures of the small molecules described in this study. (B) Fluorescence polarization assay for the interaction of Smac and mimetics with the Bir3 domain of human XIAP. A synthetic Smac peptide [AVPIAQKSEK (12)] was C-terminally labeled with Alexafluor488 (Molecular Probes), and its complex with recombinant XIAP Bir3 (residues 241 to 356) was used to evaluate competitive Bir3 domain binding by synthetic small molecules (14). (C) Polyacrylamide gel electrophoresis under nondenaturing conditions and Coomassie Blue staining were used to evaluate the binding of 3 to recombinant full-length human XIAP. XIAP (5 µM) and Smac (8 µM) were incubated for 30 min at 37°C with or without prior treatment with varying amounts of 3. Asterisks indicate that compound alone (40 µM) was present along with XIAP in lanes 3, 10, and 12. (D) Time course comparison of caspase 3 activation by recombinant Smac and small molecule mimetics. HeLa S100 was activated with 1 mM dATP. Either Smac (100 nM) or a small molecule (100 nM) was then added. The onset of caspase 3 activity was monitored as a fluorogenic substrate (Ac-DEVD-AMC, CalBiochem) was cleaved in situ (rfu, relative fluorescence units). (E) Bar graph representation of the same experiment performed in (D) except with varying concentrations of Smac and compound 3. (F) Smac and compound 3 compete with glutathione S-transferase (GST)–tagged human XIAP for active caspase 9 binding. Procaspase 9 (0.9 µM) was activated with 20 nM Apaf-1, 100 nM cytochrome C, and 1 mM dATP and then incubated with recombinant GST-XIAP for 3 hours at 30°C either in the absence (lane 2) or presence (lane 3) of Smac (1 µM), compound 3 (1 µM, lane 4), or compound 4 (1 µM, lane 5). Western blots for active caspase 9 that subsequently associates with added glutathione-coated beads are shown.
Fig. 2. Compound 3 and TRAIL act synergistically to induce apoptosis in cell culture. (A) Human glioblastoma (T98G) cells were cultured in Dulbecco's minimum essential medium (DMEM) containing fetal calf serum (10%) and treated with TRAIL (50 ng/mL) alone or compound (100 nM) alone for 15 and 19 hours, respectively. When used together, the small molecule was added 4 hours before TRAIL (total incubation time, 19 hours). Cell death (% of total population) was quantified by trypan blue staining. Values represent the average of three independent experiments (error bars indicate 1 standard derivation). (B) Activation of caspase 8 and caspase 3 by 3 in combination with TRAIL. T98G cells were treated with TRAIL (50 ng/ml) alone or 3 (100 nM) alone (for 8 and 12 hours, respectively) or were treated first with various concentrations of 3 for 4 hours and then with TRAIL for 8 hours. Cell extracts were prepared and subjected to Western blot analysis with the use of antibodies specific for caspase 8 and proteolyzed PARP. Asterisk indicates cross-reactive band. (C) Affinity purification of IAP proteins using a biotinylated form of compound 3 (fig. S2). Biotinylated 3 was immobilized onto streptavidin-conjugated beads and incubated with T98G cell extracts. The recovered beads were boiled, and released proteins were resolved by gel electrophoresis. The gel was probed with antibodies to XIAP, cIAP1 and cIAP2: Lane 1, precipitation using a negative control compound. Lane 2, precipitation using biotinylated 3. Lane 3, same as lane 2, except the cell extract was treated first with 3 (5 µM) for 4 hours.
Fig. 3. Compound 3 and TNF act synergistically to induce apoptosis in cell culture. (A) HeLa cells were cultured in DMEM containing fetal calf serum (10%) and treated with TNF (10 ng/mL) alone or compound (100 nM) alone for 15 and 19 hours, respectively. When used together, the small molecule was added 4 hours before TNF (total incubation time, 19 hours). Cell death (% of total population) was quantified by trypan blue staining. Values represent the average of three independent experiments (error bars, 1 standard derivation). (B) Hela cells were treated with TNF (10 ng/ml) alone, cycloheximide (CHX, 10 µM) alone, or a combination of TNF and CHX for 15 hours. (C) (Top) Time course of caspase 8 and caspase 3 activation in Hela cells treated with TNF and/or 3. Hela cells were treated with TNF (10 ng/ml) alone, 3 (100 nM) alone, or treated with 3 for 4 hours and then with TNF. Cell extracts were made at indicated times and subjected to Western blot analysis with antibodies to caspase 8 or proteolyzed PARP. (Bottom) Time course of caspase 3 activation in Hela cells treated with TNF, CHX, or both.
Fig. 4. Enhanced helicity, protease resistance, and serum stability of hydrocarbon-stapled BID BH3 compounds. (A and B) ,-disubstituted nonnatural amino acids containing olefinic side chains of varying length were synthesized as previously reported (16, 31, 32). Nonnatural amino acid substitutions were made to flank three (substitution positions i and i+4) or six (i and i+7) amino acids within the BID BH3 peptide, so that reactive olefinic residues would reside on the same face of the helix. (C) Circular dichroism was used to measure the percentages of SAHB maintained in helical configuration when dissolved in aqueous potassium phosphate solution (pH7) (supporting online material). (D) Fluoresceinated SAHBA and BID BH3 peptide were incubated at 37°C in mouse serum or injected intravenously (10 mg/kg) into NOD SCID mice. Serum concentrations of SAHBA and BID BH3 peptide were measured at the indicated time points with a fluorescence-based high-performance liquid chromatography detection assay. Both assays demonstrated enhanced serum stability of SAHBA.
Fig. 5. SAHBA targets the binding pocket of BCL-XL, displays enhanced BCL-2 binding affinity, and specifically activates cytochrome c release from mitochondria in vitro. (A) HSQC experiments show similar spectral changes in 15N-BCL-XL upon binding SAHBA or BID BH3 peptide. (B) Kd's for binding of individual peptides to glutathione S-transferase–BCL-2 were determined by fluorescence polarization. (C) Mouse liver mitochondria (wild-type or Bak–/–, 0.5 mg/ml) were incubated for 40 min with 25 to 200 nM concentrations of BID BH3 peptide, SAHBA, or SAHBA(GE), and cytochrome c was measured in the supernatant and sedimented mitochondria by an enzyme-linked immunosorbent assay.
Fig. 6. SAHBA penetrates Jurkat leukemia cells by fluid-phase endocytosis and localizes to the mitochondrial membrane. Jurkat leukemia cells were incubated with FITC-labeled peptides for 4 hours at 37°C, followed by FACS analysis (A). FITC-SAHBA uptake occurred in a time-dependent manner at 37°C (B), but no FITC-SAHBA labeling was evident by 4 hours, when the experiment was performed at 4°C (C). Live confocal images demonstrated a colocalization of FITC-SAHBA with 4.4-kD dextran-labeled endosomes (D) but not transferrin-labeled endosomes (E) at 4 hours. A mitochondrial colocalization was evident by 24 hours, as demonstrated by the merged images of FITC-SAHBA and MitoTracker in live cells (F) and those of FITC-SAHBA and Tom20 (a mitochondrial outer-membrane marker) in fixed cells (G). Arrows highlight sites of colocalization corresponding to the surface of mitochondria cut in cross section (G).
Fig. 7. SAHBA triggers apoptosis in Jurkat cells and inhibits a panel of human leukemia cells. FACS analysis of annexin V–treated cells was used to monitor apoptosis of Jurkat cells treated with 0.5 to 5 µM concentrations of BID BH3 peptide, SAHBA, or SAHBA(GE) for 20 hours (A). Jurkat, REH, MV4;11, SEMK2, and RS4;11 leukemia cells were treated with serial dilutions of SAHBA (B), BID BH3 peptide (C), or SAHBA(GE) (D), and MTT assays were performed at 48 hours to measure viability.
Fig. 8. SAHBA suppresses growth of human leukemia cells in vivo, prolonging the survival of leukemic mice. (A) Leukemic SCID beige mice [with a day-1 natural logarithm (ln) bioluminescence range of 14.4 to 15.9] were treated with intravenous injections of 10 mg/kg SAHBA or vehicle (5% DMSO in D5W) daily for 7 days and were monitored for survival; leukemia burden was quantified by total body luminescence (photons/s/mouse) on days 1, 3, and 5. The disease course from days 3 to 5 differed between SAHBA-treated animals and controls (P = 0.016, Fisher's exact test [box in (A)], as illustrated by representative Xenogen images of bioluminescent leukemic mice (B); red signal represents the highest level of leukemia on the colorimetric scale. (C) Median survival was prolonged in SAHBA-treated animals as compared to controls (P = 0.004, log rank test). (D) To compare SAHBA with SAHBA(GE), leukemic mice (with a day 1 ln bioluminescence range of 17.1 to 17.9) were treated daily with SAHB (10 mg/kg) or vehicle, and animals were imaged on days 1 and 3 to measure total body luminescence.
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