Somatostatin receptor-targeted anti-cancer therapy

Somatostatin receptors (SSTRs), especially SSTR subtype 2, are found expressed at relatively higher levels in many tumor cells and in tumoral blood vessels relative to normal tissues. This creates an opportunity for developing various cytotoxic SST conjugates that selectively target SSTR2-specific sites. Accordingly, some potent chemotherapeutic agents such as camptothecin (CPT), methotrexate (MTX), paclitaxel (PTX) and doxorubicin (DOX) have been coupled to SSTR2-preferential somatostatin (SST) analogs. These new cytotoxic SST conjugates display significant SSTR-selective anti-tumor abilities in many different types of tumors. For instance, the CPT-SST conjugate JF-10-81, in which CPT is coupled to the N-terminus of a SSTR2-specific SST analog (JF-07-69), had wide ranging anti-tumor and anti-angiogenic ability. This conjugate also showed an ability to overcome multi-drug resistance (MDR) in SSTR-over-expressing and CPT-insensitive human pancreatic carcinoid BON cells. Notably, another DOX-SST conjugate, AN-238, made by coupling pyrrolino-DOX to the SST analog RC-121, displayed indirect anti-tumor activity against SSTR-negative, non-small cell lung cancer H-157 tumor growth by directly targeting SSTR-positive tumoral vessels of host mice. These cytotoxic SST conjugates should deliver chemotherapeutic agents to receptor-specific sites, enhance anti-tumor efficacy, reduce toxic side effects to normal tissues, and to some extent, overcome MDR. These and other peptide conjugates may possibly represent a newer generation of receptor-targeted cancer therapeutics. This review discusses the progress with reference to SST-based and SSTR-selective cytotoxic cancer therapy.     

Paclitaxel poliglumex (XYOTAX; CT-2103): an intracellularly targeted taxane

Paclitaxel poliglumex (CT-2103; XYOTAX) is an innovative macromolecular taxane designed to increase the therapeutic index of paclitaxel. This large macromolecule conjugate of paclitaxel and poly-L-glutamic acid accumulates in tumor tissues by taking advantage of the enhanced permeability of tumor vasculature and lack of lymphatic drainage. Paclitaxel poliglumex prolongs exposure to active drug and minimizes systemic exposure. Preclinical studies in animal tumor models demonstrate enhanced safety and efficacy relative to paclitaxel when administered as a single agent or in conjunction with radiation. Clinical pilot studies with paclitaxel poliglumex showed improved outcomes compared to standard taxanes and allowed a more convenient administration schedule. Human pharmacokinetic data are consistent with prolonged tumor exposure to active drug and a limited systemic exposure. Based on these results, three ongoing randomized phase III trials were initiated to test the efficacy of paclitaxel poliglumex in patients with advanced non-small cell lung carcinoma.     

紫杉醇对肺癌细胞株A549 Wnt/β-catenin信号通路相关基因和蛋白表达的影响

目的：探讨紫杉醇对肺癌细胞株A549 Wnt/β-连环素（β-catenin）信号通路相关基因和蛋白表达的影响。方法：免疫组化法检测1nmol·L-1紫杉醇组和对照组A549细胞中β-catenin蛋白的表达,逆转录聚合酶链式反应检测0.1、1、10nmol·L-1紫杉醇组和对照组A549细胞中dkk-3（抑癌基因）、c-myc（原癌基因）mRNA表达,干预时间均为48h。结果：与对照组比较,1nmol·L-1紫杉醇组β-catenin蛋白表达明显降低,0.1、1、10nmol·L-1紫杉醇组c-mycmRNA表达明显降低,而dkk-3mRNA表达明显增加（P均〈0.05）,且基因表达呈浓度依赖性。结论：紫杉醇能通过下调A549细胞内β-catenin蛋白表达,诱导dkk-3mRNA表达,从而阻断Wnt信号转导通路,减少c-myc表达。     

Antitumour activity of ANG1005, a conjugate between paclitaxel and the new brain delivery vector Angiopep-2

Background and purpose:Paclitaxel is highly efficacious in the treatment of breast, head and neck, non-small cell lung cancers and ovarian carcinoma. For malignant gliomas, paclitaxel is prevented from reaching its target by the presence of the efflux pump P-glycoprotein (P-gp) at the blood-brain barrier. We investigated the utilization of a new drug delivery system to increase brain delivery of paclitaxel.Experimental approach:Paclitaxel molecules were conjugated to a brain peptide vector, Angiopep-2, to provide a paclitaxel-Angiopep-2 conjugate named ANG1005. We determined the brain uptake capacity, intracellular effects and antitumour properties of ANG1005 in vitro against human tumour cell lines and in vivo in human xenografts. We then determined ANG1005 activity on brain tumours with intracerebral human tumour models in nude mice.Key results:We show by in situ brain perfusion that ANG1005 enters the brain to a greater extent than paclitaxel and bypasses the P-gp. ANG1005 has an antineoplastic potency similar to that of paclitaxel against human cancer cell lines. We also demonstrate that ANG1005 caused a more potent inhibition of human tumour xenografts than paclitaxel. Finally, ANG1005 administration led to a significant increase in the survival of mice with intracerebral implantation of U87 MG glioblastoma cells or NCI-H460 lung carcinoma cells.Conclusions and implications:These results demonstrate the antitumour potential of a new drug, ANG1005, and establish that conjugation of anticancer agents with the Angiopep-2 peptide vector could increase their efficacy in the treatment of brain cancer.British Journal of Pharmacology (2008) 155, 185-197; doi:10.1038/bjp.2008.260; published online 23 June 2008.     

Role of somatostatin analogs in the clinical management of non-neuroendocrine solid tumors

The somatostatin analogs octreotide, lanreotide and RC-160 (vapreotide) are known to have direct and indirect antitumor effects. Direct effects include the arrest of tumor growth and stimulation of apoptosis, resulting in tumor shrinkage. Indirect antiproliferative effects may occur through antiangiogenesis, immunomodulatory effects and the suppression of tumor-stimulating growth factors. With a safety profile of somatostatin analogs established over 20 years of clinical use in the treatment of neuroendocrine tumors, somatostatin analogs are attractive therapeutic options for patients with non-neuroendocrine tumors. In early clinical trials of somatostatin analogs, however, some cancer patients responded well, while others showed a lack of benefit. This variability in clinical response may reflect the selective binding affinities of octreotide, lanreotide and RC-160, which bind with high affinity to just two of the five different somatostatin receptor subtypes. Treatment response may therefore depend on the specific receptor subtype(s) present in the tumor, the relative proportion of receptor(s) expressed on the tumor cell surface and the absolute quantity of each receptor subtype. Greater understanding of the role of somatostatin receptors, their binding affinities and modes of action has led to increased research into the use of somatostatin analogs, particularly octreotide, in cancer treatment as monotherapies, in combination with hormonal treatments and cytotoxic therapies, and in both adjuvant and neoadjuvant settings. A review of the literature suggests that the antitumor potential of somatostatin analogs should be investigated further and additional studies might determine how these analogs can best be used to improve the treatment of patients with non-neuroendocrine tumors.     

Investigation of cancer cell lines for peptide receptor-targeted drug development

Many tumors highly express specific populations of G-protein-coupled receptors (GPCRs) that could be utilized for receptor-targeted therapy. We confirmed significant quantities of mRNAs specific for certain somatostatin (SST), vasoactive intestinal peptide (VIP), and bombesin (BN) receptors in various commercially available tumor cell lines. Very few of the tumor cell lines examined displayed the high receptor-binding affinity despite exhibiting the expression of appropriate mRNAs and proteins of the cognate receptors. However, binding assays establish that some tumor cell lines, such as pancreatic cancer CFPAC-1, prostate cancer DU-145, and pancreatic carcinoid BON, demonstrate high BN receptor binding. BON cells also demonstrate high somatostatin receptor (SSTR) affinity binding. We also found that tumor cell lines, such as BON and host cells expressing SST receptor subtypes 1 or 2 (CHO-R1 or CHO-R2), underwent a decrease in cell surface receptor density in multiple passages. BON and CHO-R2 cells also rapidly internalize a significant proportion of cell surface ligand–receptor complexes. The tumor cells CFPAC-1, DU-145, and BON with high receptor binding could be useful for peptide drug studies. BON cells were further applied to test SST/BN analogs and cytotoxic conjugates. Furthermore, the in vivo antitumor assay showed that the cytotoxic conjugate CPT-SST targeting all SSTR subtypes displayed a potent tumor-suppressive ability to BON tumors expressing multiple SSTR subtypes.     

G2/M blockade by paclitaxel induces caveolin-1 expression in A549 lung cancer cells: caveolin-1 as a marker of cytotoxicity

Caveolins are highly expressed in terminally differentiated cells, but this expression is down-regulated in various cancer cell lines. Exposure to low doses of paclitaxel (taxol) is sufficient to up-regulate caveolin-1, suggesting that a mild cytotoxic stress induces a response implying caveolin and caveolae. Here we show that this up-regulation is sustained even after the cessation of paclitaxel treatment. After exposure to a cytostatic dose of paclitaxel (50 nM), A549 lung cancer cells are blocked in the G2/M cell cycle phase. After removal of paclitaxel, cell death occurs, accompanied with an increase in caveolin expression, suggesting an effect of caveolin in this process. Three days post-paclitaxel treatment, surviving A549 cells were passaged and only a half of them adhered to the culture dish. Adhering cells (still mainly in the G2/M cell cycle phase) were still unable to grow and progressively entered in an apoptotic state. This study suggests that effects of a low dose of paclitaxel were still present even 1 week after drug removal and that caveolin-1 is a good marker of cytotoxicity.     

Therapy of experimental hepatic cancers with cytotoxic peptide analogs targeted to receptors for luteinizing hormone-releasing hormone, somatostatin or bombesin

As there is no effective systemic therapy for advanced hepatocellular carcinoma (HCC), we investigated the presence of receptors for somatostatin, bombesin and luteinizing hormone-releasing hormone (LHRH) in SK-Hep-1 human hepatic carcinoma and the effects of cytotoxic analogs of somatostatin (AN-238), bombesin (AN-215) and LHRH (AN-207) on the growth of this tumor. Nude mice bearing SK-Hep-1 HCCs were treated with AN-238, AN-215, AN-207 and their combination, or cytotoxic radical 2-pyrrolinodoxorubicin (AN-201). Tumor growth reduction was determined and cell proliferation characteristics and apoptosis were studied by histologic analysis. The expression of receptors for somatostatin, bombesin and LHRH was investigated by radioreceptor assays and immunohistochemistry. High-affinity binding sites for somatostatin, bombesin and LHRH were detected in SK-Hep-1 cancers. All three cytotoxic peptide analogs inhibited growth of SK-Hep-1 tumors and decreased the cell proliferation rate. Combination therapy with two or three cytotoxic analogs resulted in the strongest tumor inhibition. Receptors for somatostatin, bombesin and LHRH are expressed in SK-Hep-1 human HCC. Cytotoxic peptide analogs targeted to these receptors inhibit growth of this tumor. Targeting to multiple receptors enhances the efficacy of therapy. The results of our study encourage additional experimental investigations to permit the introduction of these cytotoxic analogs into clinical trials.     

Mixed micelles of PEG(2000)-DSPE and vitamin-E TPGS for concurrent delivery of paclitaxel and parthenolide: enhanced chemosenstization and antitumor efficacy against non-small cell lung cancer (NSCLC) cell lines

Concurrent combination of chemotherapeutic drugs is a promising alternative to single-agent therapies in cancer. In the present study, paclitaxel and parthenolide were loaded into mixed micelles and tested against taxol sensitive (A549) and resistant (A549-T24) NSCLC cell lines. Combination chemotherapy was further evaluated by isobologram analyses and combination index calculations. Drugs were loaded into micelles by the film casting method using PEG(2000)-DSPE and vitamin E-TPGS. Micelle characterization studies included the determination of particle size, encapsulation efficiency, in vitro release kinetics, as well as 1H NMR analysis. The in vitro release of both drugs was slower from the mixed micelles, which maintained an encapsulation efficiency >95% and chemical stability over a storage period of 45 days. The IC50 of paclitaxel and parthenolide determined by MTT assay were 108.6nM and 21μM, respectively, while the combination had an IC50 of 64.15nM in A549 cells. In the taxol resistant cell lines, the IC50 values of paclitaxel and parthenolide were 233nM and 32μM, respectively, while the combination had an IC(50) of 128nM. The efficacy of paclitaxel and parthenolide against both cell lines significantly increased when the drugs were coencapsulted in mixed micelles. Mixed micelles caused 79% cell death, which was significantly higher than the 46% cell death caused by the drugs in solution against taxol sensitive cell lines. In taxol resistant cell lines, the cell death caused by mixed micelles was 70% as compared to 45% cell death caused by un-encapsulated drugs. Co-encapsulation of parthenolide with paclitaxel in mixed micelles increased the anticancer activity of paclitaxel against resistant and sensitive lung cancer cell lines.     

Paclitaxel delivery using carrier made from curcumin derivative: Synergism between carrier and the loaded drug for effective cancer treatment

To fully make use of the synergism between paclitaxel and curcumin (CUR) in cancer treatment, carrier made from CUR derivative was synthesized and used to deliver paclitaxel into cancer cells. The methoxylpolyethylene oxide‐linked palmitate‐modified curcumin (mPEO–CUR–PA) was synthesized and the obtained amphiphilic mPEO–CUR–PA molecules were allowed to self‐assemble into microspheres. In vitro release of free CUR from mPEO–CUR–PA in the presence of lipase was proofed and the ability of cells to endocytose mPEO–CUR–PA microspheres was verified. Cytotoxic activity of the mPEO–CUR–PA microspheres toward cancer cell lines (S102 and A549) was evaluated and compared with that of the unmodified CUR. Paclitaxel was then loaded into the microspheres and the paclitaxel‐loaded mPEO–CUR–PA microspheres showed up to fivefold to 44‐fold increased in vitro cytotoxicity (in terms of % cell mortality) in susceptible (HCC‐S102 and A549) and paclitaxel‐resistant (A549RT‐eto) cancer cells, respectively, compared with that of free paclitaxel.     

Targeting cytotoxic conjugates of somatostatin, luteinizing hormone-releasing hormone and bombesin to cancers expressing their receptors: a "smarter" chemotherapy

Chemotherapy is one of the main modalities in the therapy of cancer. However, an improvement in the efficacy and a reduction in the toxicity of chemotherapeutic agents remains a great challenge to oncologists. A specific delivery of cytotoxic drugs to cancerous cells may help improving both aspects. Peptide hormones, for which receptors have been found in various human cancers, can serve as carriers for a local delivery of cytotoxic agents or radiopharmaceuticals to the tumors, as demonstrated by the successful clinical use of radiolabeled somatostatin analog Octreoscan for the detection and treatment of some somatostatin receptor-positive tumors. Thus, in recent years we developed a series of cytotoxic peptide hormone conjugates based on derivatives of hypothalamic hormones such as somatostatin and luteinizing hormone-releasing hormone (LHRH), and the brain-gut hormone bombesin. To create targeted conjugates with high cytotoxic activity, a derivative of doxorubicin (DOX), 2-pyrrolino-DOX (AN-201), which is 500-1, 000 times more active than its parent compound, was developed. This agent was coupled to somatostatin octapeptide RC-121 to form cytotoxic conjugate AN-238, and to [D-Lys6]LHRH carrier to produce analog AN-207. Cytotoxic bombesin hybrid AN-215 also contains AN-201. DOX was likewise linked to [D-Lys6]LHRH to form AN-152. A comprehensive testing of these cytotoxic conjugates in experimental models of various human and rodent cancers led to their selection as candidates for clinical trials.     

Effect of Particle Size of Nanospheres and Microspheres on the Cellular-Association and Cytotoxicity of Paclitaxel in 4T1 Cells

Purpose. To compare the effect of size of delivery systems on the cell-association and in vitro cytotoxicity of paclitaxel.Methods. Four sizes of PLGA-paclitaxel particles were prepared to study the effect of particle size on the cell-association of paclitaxel in 4T1 monolayer in the presence, and absence, of BCRP inhibitor, endocytic inhibitor, and P-glycoprotein (P-gp) inhibitor. Paclitaxel cell-association studies were repeated in Caco-2, Cor-L23/R, and bovine brain microvessel endothelial cells (BBMECs), as well as the association of etoposide in 4T1 cells. Cytotoxicity of paclitaxel to 4T1 cells delivered in nanospheres was compared to microspheres.Results. The concentration of paclitaxel and etoposide associated with 4T1 cells was 4.8 and 29 times greater, respectively, as the size increased from 310 to 2077 nm. Paclitaxel association consistently increased in Caco-2 and Cor-L23/R as the size of the delivery system increased. The endocytic inhibitor, 2-deoxyglucose, significantly decreased the cellular paclitaxel association when delivered by nanospheres but not microspheres. Consistent with the cell-association results, paclitaxel was thrice more cytotoxic to 4T1 cells when delivered in microspheres.Conclusions. Cell-association of paclitaxel increased in 4T1, Caco-2, and Cor-L23/R as particle size increased. Paclitaxel delivered from 1-m microspheres was thrice more cytotoxic to 4T1 cells compared to the drug delivered from nanospheres or solution.     

长效生长抑素类似物治疗消化系统肿瘤新进展

生长抑素(somatostatin,SS)广泛存在于人体各种正常组织,具有抑制性生理功能,共有5种SS受体亚型,肿瘤组织亦表达不同的SS受体.SS类似物在治疗胃肠和胰腺内分泌肿瘤中起重要作用,近年来很多研究表明SS类似物对治疗非内分泌性、实体性肿瘤可能同样有效.长效生长抑素类似物如长效奥曲肽(octreotide)和兰瑞肽(lanreotide)两种剂型,能与SS受体亚型-2(SSR2)、受体亚型-5(SSR-5)结合,维持长期稳定的血浆药物浓度,产生持久的抑制多种激素分泌作用.现就近年来长效生长抑素类似物治疗消化系统肿瘤新进展做一综述.     

Somatostatin sst2 receptor-mediated inhibition of parietal cell function in rat isolated gastric mucosa.

1. The aim of this study was to determine the location and functional characteristics of the somatostatin (SRIF) receptor type(s) which mediate inhibition of acid secretion in rat isolated gastric mucosa. 2. Gastrin (1 nM-1 microM), dimaprit (10 microM-300 microM) and isobutyl methylxanthine (IBMX, 1 microM-100 microM) all caused concentration-dependent increases in acid output. Responses to gastrin were almost completely inhibited by ranitidine (10 microM) at a concentration which abolished the secretory response to dimaprit. In contrast, responses to IBMX were not changed by ranitidine suggesting that IBMX acts directly on the parietal cell and not indirectly by releasing histamine from enterochromaffin-like (ECL) cells. 3. SRIF-14 (1 nM-1 microM) had no effect on basal acid output, but inhibited acid output produced by gastrin, dimaprit and IBMX in a concentration-dependent manner with respective EC50 values of 46, 54 and 167 nM. The peptidase inhibitors, amastatin (10 microM) and phosphoramidon (1 microM), had no effect on SRIF-induced inhibition of dimaprit stimulated gastric acid secretion. 4. The inhibitory effect of a range of SRIF analogues on gastrin-, dimaprit- and IBMX-induced acid secretion was also studied. Irrespective of the secretagogue used to increase acid output, the rank order of potencies was similar (BIM-23027 = seglitide = octreotide > SRIF-14 = SRIF-28 > L-362,855). The linear peptide BIM-23056 was devoid of agonist or antagonist activity in concentrations up to 1 microM. 5. The sst2 receptor selective peptides, BIM-23027, seglitide and octreotide were the most potent inhibitors of gastrin-, dimaprit- and IBMX-induced acid secretion suggesting that SRIF receptors resembling the recombinant sst2 receptors are involved. Furthermore, since dimaprit and IBMX stimulate gastric acid secretion independently of histamine release, sst2 receptor-mediated inhibition must occur at the level of the parietal cell itself.     

紫杉醇类前药的研究进展

紫杉醇(paclitaxel)及其半合成类似物多西紫杉醇(docetaxel) 是迄今为止发现的最为有效的抗癌药物之一,然而该类药物对正常组织、系统具有严重的毒性,而且水溶性较低以及对多药耐药 (MDR) 细胞几乎无活性等,使其临床应用受到限制。近年来,在提高紫杉醇类前药生物利用度和靶向性以及解决紫杉醇对于多药耐药肿瘤细胞无效等方面的研究和开发取得了很大进展。该文对近十几年来紫杉醇类前药的研究进展进行综述。 关键词：紫杉醇;前药;轭合物;水溶性;靶向性 中图分类号:     

Paclitaxel conjugation with the analog of the gonadotropin-releasing hormone as a targeting moiety

A new targeted conjugates in which paclitaxel was used as a cytostatic compound and an analog of the gonadotropin-releasing hormone (GnRH) as a targeting moiety were synthesized. The molecule of the peptide hormone GnRH was modified to allow its connection to paclitaxel via spacer. The conjugates were prepared as prodrugs using 2'-hydroxyl group of paclitaxel. 4-Maleimidobutyric acid and chloroacetic acid served as spacers. The structures of the prepared derivatives were analysed by NMR and HR-MS. The conjugates MP264 and MP265 were chosen and their antiproliferative effect was tested in the breast cancer cell line MCF-7 using the MTT test of cell viability and neutral red uptake test. In MCF-7 cells, conjugate MP265 showed higher antiproliferative effect than paclitaxel alone. Receptor saturation tests showed that the unconjugated peptide analog of GnRH decreased efficacy of conjugate MP265 in concentration- and time-dependent manner. In conclusion, the paclitaxel conjugate with the analog of GnRH exhibited targeted antiproliferative effect for which its further testing will be implemented.     

Novel peptide conjugates for tumor-specific chemotherapy

One of the major problems in cancer chemotherapy are the severe side effects that limit the dose of the anticancer drugs because of their unselectivity for tumor versus normal cells. In the present work, we show that coupling of anthracyclines to peptides is a promising approach to obtain selectivity. The peptide-drug conjugate was designed to bind to specific receptors expressed on the tumor cells with subsequent internalization of the ligand-receptor complex. Neuropeptide Y (NPY), a 36-amino acid peptide of the pancreatic polypeptide family, was chosen as model peptide because NPY receptors are overexpressed in a number of neuroblastoma tumors and the thereof derived cell lines. Daunorubicin and doxorubicin, two widely used antineoplastic agents in tumor therapy, were covalently linked to NPY via two spacers that differ in stability: an acid-sensitive hydrazone bond at the 13-keto position of daunorubicin and a stable amide bond at the 3'-amino position of daunorubicin and doxorubicin. Receptor binding of these three conjugates ([C(15)]-NPY-Dauno-HYD, [C(15)]-NPY-Dauno-MBS, and [C(15)]-NPY-Doxo-MBS) was determined at the human neuroblastoma cell line SK-N-MC, which selectively expresses the NPY Y(1) receptor subtype, and cytotoxic activity was evaluated using a XTT-based colorimetric cellular cytotoxicity assay. The different conjugates were able to bind to the receptor with affinities ranging from 25 to 51 nM, but only the compound containing the acid-sensitive bond ([C(15)]-NPY-Dauno-HYD) showed cytotoxic activity comparable to the free daunorubicin. This cytotoxicity is Y(1) receptor-mediated as shown in blocking studies with BIBP 3226, because tumor cells that do not express NPY receptors were sensitive to free daunorubicin, but not to the peptide-drug conjugate. The intracellular distribution was investigated by confocal laser scanning microscopy. We found evidence that the active conjugate [C(15)]-NPY-Dauno-HYD releases daunorubicin, which is localized close to the nucleus, whereas the inactive conjugate [C(15)]-NPY-Dauno-MBS is distributed distantly from the nucleus and does not seem to release the drug within the cell.     

罗非昔布联合奥曲肽增强对胰腺癌生长的抑制作用

目的　探讨高选择性环氧合酶 2抑制剂———罗非昔布联合奥曲肽能否协同增强对人胰腺癌生长的抑制。方法　采用3 H 胸腺嘧啶核苷参入法了解这两种药物单独或联合应用对人胰腺癌细胞株BXPC 3DNA合成的影响 ,根据中效原理判断联合用药是否产生协同效应。观察这两种药物单用或联合应用对裸鼠人胰腺癌移植瘤生长的影响。结果　罗非昔布显著抑制胰腺癌细胞3 H 胸腺嘧啶核苷参入 ,药物浓度与3 H 胸腺嘧啶核苷参入值呈负相关 ,r=- 0 990 ,P <0 0 1。罗非昔布联合奥曲肽在多数效应范围内的合用指数小于 1,有协同作用。与对照组比较 ,罗非昔布或奥曲肽均能抑制裸鼠胰腺癌移植瘤的生长 ,但联合用药的抑瘤率(97 4 % )明显高于单用奥曲肽 (5 7 0 % )或罗非昔布(87 7% ) ,P <0 0 1。结论　罗非昔布联合奥曲肽可协同增强对人胰腺癌的生长抑制     

Somatostatin-induced control of cytosolic free calcium in pituitary tumour cells

1. In rat pituitary tumour cells (GC cells), spontaneous oscillations of the intracellular concentration of Ca2+ ([Ca2+]i) induce growth hormone (GH) secretion that is inhibited by octreotide, a somatostatin (SRIF) agonist which binds to SRIF subtype (sst) receptor 2. The effects of its functional activation on the control of [Ca2+]i were investigated using fluorimetric measurements of [Ca2+]i. 2. SRIF decreases the basal [Ca2+]i and the [Ca2+]i rise in response to forskolin (FSK) through the inhibition of L-type voltage-dependent Ca2+ channels. 3. Pretreatment with octreotide or with L-Tyr8++ Cyanamid 154806, a sst2 receptor antagonist, abolishes the SRIF-induced inhibition of [Ca2+]i. Octreotide is known to operate through agonist-induced desensitization, while the antagonist operates through receptor blockade. 4. sst1 and sst2 receptor-immunoreactivities (-IRs) are localized to cell membranes. sst2, but not sst1 receptor-IR, internalizes after cell exposure to octreotide. 5. SRIF-induced inhibition of basal [Ca2+]i or FSK-induced Ca2+ entry is blocked by pertussis toxin (PTX). 6. FSK-induced cyclic AMP accumulation is only partially decreased by SRIF or octreotide, indicating that sst2 receptors are coupled to intracellular pathways other than adenylyl cyclase (AC) inhibition. 7. In the presence of H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA), SRIF-induced inhibition of basal [Ca2+]i is still present, although reduced in amplitude. 8. SRIF inhibits [Ca2+]i by activating sst2 receptors. Inhibition of AC activity is only partly responsible for this effect, and other transduction pathways may be involved.     

Synthesis, physico-chemical and biological characterization of a paclitaxel macromolecular prodrug.

Paclitaxel was attached to poly(hydroxyethylaspartamide) via a succinic spacer arm by a two-step protocol: (1) synthesis of 2'-O-succinyl-paclitaxel; (2) synthesis of PHEA-2'-O-succinyl-paclitaxel. The 2'-O-succinyl-paclitaxel derivative and the macromolecular conjugate were characterized by UV, IR, NMR and mass spectrometry analysis. The reaction yields were over 95% and the purity of products over 98%. Paclitaxel release and degradation from 2'-O-succinyl-paclitaxel occurred at a faster rate at pH 5.5 than 7.4. After 30 h of incubation at pH 5.5 and 7.4 the released free paclitaxel was about 40 and 20%, respectively. In plasma both drug release and degradation were found to occur at a higher rate than in buffer at pH 7.4 suggesting that an enzymatic mechanism could be involved. The paclitaxel release and degradation from PHEA-2'-O-succinyl-paclitaxel were negligible at pH 5.5 and 7.4 and very slow in plasma. Investigation carried out using murine myeloid cell line showed that the polymeric prodrug maintains partial pharmacological activity of paclitaxel. The DL50 of the conjugate (over 40 ng/ml) as compared to free paclitaxel (about 1 ng/ml) was correlated to the slow drug release. Finally a pharmacokinetic study carried out by intravenous inoculation of the macromolecular prodrug to mice demonstrated that the polymer conjugation modify dramatically the in vivo fate of the drug. The conjugate disappeared from the bloodstream much more quickly as compared to both free drug and naked polymer. Massive accumulation of bioconjugate in the liver (80% of the dose) was found to persist throughout 1 week.