叶酸受体介导的抗肿瘤药物研究进展

   叶酸受体在大多数人体肿瘤细胞表面过度表达,而在正常细胞中的存在很少,甚至检测不到,这就使叶酸受体介导的抗肿瘤药物可以靶向性地作用于叶酸受体呈阳性的肿瘤细胞,减少传统抗癌药物对正常细胞的毒副作用,提高药物的选择性。本文对叶酸受体介导的抗肿瘤药物的作用机制进行综述,介绍近几年研究者设计并合成的叶酸-药物缀合物及其活性测试的结果。     

叶酸受体介导的靶向给药系统研究进展

叶酸受体在多种肿瘤细胞表面过度表达,能与特异性的配体结合并将药物靶向运输到特定的肿瘤细胞。本文介绍了叶酸受体介导的靶向给药系统的作用机制和几种常见的药物载体系统。     

叶酸受体介导的靶向纳米给药系统研究进展

叶酸受体在许多恶性肿瘤细胞表面过度表达,而在正常细胞中则几乎不表达或只有少量表达。利用叶酸受体表达的特性,通过将叶酸修饰于药物载体表面,可使药物靶向输送至叶酸受体过度表达的肿瘤细胞中,从而避免对正常细胞产生毒性,提高药物疗效;而纳米给药系统因粒径较小等原因可使药物在肿瘤部位浓集。本文对近年来叶酸受体介导的靶向纳米给药系统进行了综述。     

叶酸受体介导的靶向给药研究进展

叶酸受体可以与叶酸及其类似物特异性结合,通过介导细胞内化将其摄入细胞胞浆。利用叶酸受体在肿瘤和关节炎细胞的过度表达,使药物与叶酸结合,以叶酸受体为作用靶点,即可将药物主动靶向肿瘤和关节炎细胞,从而提高药物在肿瘤、关节炎的组织分布,达到靶向诊断、治疗的目的。本文就叶酸受体及其组织分布,叶酸受体介导的内吞作用,叶酸受体介导的肿瘤和关节炎的靶向诊断、治疗的研究进展进行了综述。     

叶酸受体介导的靶向给药研究进展

目的：介绍叶酸受体介导的靶向给药研究进展。方法：根据近年来的文献资料，对叶酸受体介导的靶向给药研究进行综述。结果：叶酸受体可以与叶酸及其类似物特异性结合，从而提高药物在肿瘤、关节炎的组织分布，达到靶向诊断、治疗的目的。结论：叶酸受体介导的靶向给药是一种很有前景的给药方式。     

叶酸纳米给药系统抗肿瘤作用研究进展

叶酸受体(folate receptor,FR)在多种肿瘤细胞表面高度表达,而在正常细胞表面不表达或低表达,能与特定的叶酸(folic acid,FA)高度特性结合,是肿瘤特异性药物递送的有效靶点。本文对叶酸受体、叶酸及其配体、叶酸纳米制剂内吞作用机制及叶酸纳米制剂抗肿瘤作用进行了综述。     

叶酸受体介导的肿瘤靶向治疗研究进展

叶酸是一种小分子量的维生素，其受体是一种糖蛋白，在肿瘤细胞膜表面高度表达；而在绝大多数正常组织中，几乎不表达。利用叶酸对叶酸受体的高度亲和性，可用于将药物与叶酸偶联，将药物靶向至肿瘤。对此，本文进行了综述。     

叶酸受体介导的肿瘤靶向纳米递药系统

叶酸受体在上皮源性的恶性肿瘤细胞膜表面高度表达。叶酸靶向纳米递药系统具有叶酸-叶酸受体主动靶向和纳米递药系统被动靶向的双重优势,可实现化疗药物对肿瘤组织的靶向递送,有效提高药物疗效,减少毒副作用。本文就近年来研究较多的叶酸-脂质体、叶酸-树枝状聚合物、叶酸-聚合物胶束、叶酸-纳米球等叶酸受体介导的肿瘤靶向递药系统进行综述。     

叶酸介导的纳米给药系统抗肿瘤作用研究进展

恶性肿瘤的发病率呈逐年上升的趋势,其严重危害人类的健康.目前,临床上应用的传统抗肿瘤药物存在靶向性差,细胞毒性强,患者不易耐受的缺点.因此,提高抗肿瘤药物的靶向性、减轻药物的不良反应已成为抗肿瘤药物新型给药系统研究的热点方向.随着肿瘤分子水平研究的不断深入,发现某些受体在肿瘤细胞的表面过度表达,这种肿瘤特异性受体为治疗提供了新的靶点[1～3].本文就叶酸受体的组织分布和其分子生物学特性,纳米材料作为药物载体的优越性,以及叶酸修饰的纳米材料作为抗肿瘤药物载体的研究等方面进行深入探讨.     

叶酸受体介导的小分子抗肿瘤药物研究进展

靶向肿瘤细胞的药物研发近年来受到了极大的关注,除了阻断细胞信号通路的蛋白激酶抑制剂外,叶酸受体介导的药物释放也引起了研究者的广泛注意。叶酸受体在大多数人体肿瘤细胞中高度表达,而在正常细胞中很少表达或不表达。叶酸可以通过叶酸受体介导的内吞作用进入细胞,这为药物选择性释放提供了很好的途径。本文对近些年来基于叶酸受体介导的药物作用机制、设计策略,以及研发的叶酸-抗肿瘤药物缀合物进行综述,并介绍了该领域临床研究取得的最新进展。     

Folate receptor-targeted immunotherapy of cancer: mechanism and therapeutic potential

The vitamin, folic acid, has become a useful ligand for targeted cancer therapies because it binds to a tumor-associated antigen known as the folate receptor (FR). By linking folic acid to therapeutic agents, folate-targeted cancer therapies can deliver therapeutic drugs specifically to FR-positive tumor cells. This chapter provides a summary of a specific application of folate-targeted therapies whereby folic acid is exploited to carry an attached hapten (a highly antigenic molecule) to the surfaces of tumor cells for the purpose of rendering the tumors more immunogenic. The basic strategy is to (i) saturate (label) the surface of FR-positive tumor cells with a folate-hapten conjugate against which the cancer-bearing host already has a pre-existing or induced immunity, (ii) allow the surface bound haptens to attract anti-hapten antibodies to the tumor cell surface, and (iii) stimulate Fc receptor-bearing immune cells to mount an antitumor response against the anti-hapten antibody opsonized tumor cells. In immune competent murine tumor models, hapten-marked cancer cells have been shown to be quickly recognized by antibodies and the associated Fc receptor-expressing immune cells dedicated to eliminating antibody-coated target cells. Given the need for cancer cells to escape immune surveillance in order to proliferate and survive in vivo, folate-targeted immunotherapies that mark an otherwise immunologically "invisible" cancer cell as distinctively "non-self" may provide a key strategy for combating malignant disease.     

Folate receptor-targeted mixed polysialic acid micelles for combating rheumatoid arthritis: in vitro and in vivo evaluation

Objective: Rheumatoid arthritis (RA) is associated with chronic inflammation. The suppression of inflammation is key to the treatment of RA. Glucocorticoids (GCs) are classical anti-inflammatory drugs with several disadvantages such as poor water solubility and low specificity in the body. These disadvantages are the reasons for the quick elimination and side effects of GCs in vivo. Micelles are ideal carriers for GCs delivery to inflamed synovium. We set out to improve the targeting and pharmacokinetic profiles of GCs by preparing a targeting micelle system.

Methods: In this study, natural chlosterol (CC) and folic acid (FA) were used to fabricate polysialic acid (PSA) micelles for the targeted delivery of Dexamethasone (Dex). The biodistribution and therapeutic efficacy of the resulting micelles were evaluated in vitro and in vivo.

Results: PSA-CC and FA-PSA-CC micelles showed a size below 100?nm and a moderate negative charge. PSA-CC and FA-PSA-CC micelles could also enhance the intracellular uptake of Dex and the suppression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in vitro and in vivo. Arthritis mice showed reduced paw thickness and clinical arthritis index using PSA-CC and FA-PSA-CC micelle treatment. Micellized Dex demonstrated a 4?～?5 fold longer elimination half-life and a 2?～?3 folds higher bioavailability than commercial Dex injection. FA modification significantly improved the anti-inflammatory efficacy of PSA-CC micelles.

Conclusion: FA-PSA-CC micelles demonstrated significant advantages in terms of the suppression of inflammation and the treatment of inflammatory arthritis. These reliable and stable micelles possess a high potential to be transferred for clinical use.     

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.     

Folate analogues. 34. Synthesis and antitumor activity of non-polyglutamylatable inhibitors of dihydrofolate reductase

Five analogues of methotrextate (MTX), 10-deazaaminopterin (10-DAM), and 10-ethyl-10-deazaaminopterin (10-EDAM) in which the glutamate moiety was replaced by either a gamma-methyleneglutamate or beta-hydroxyglutamate were synthesized and evaluated for their antifolate activity. These analogous are 4-amino-4-deoxy-N10-methylpteroyl-beta-hydroxyglutamic acid (1), 4-amino-4-deoxy-10-deazapteroyl-beta-hydroxyglutamic acid (2), 4-amino-4-deoxy-N10-methylpteroyl-gamma-methyleneglutamic acid (3, MMTX), 4-amino-4-deoxy-10-deazapteroyl-gamma-methyleneglutamic acid (4, MDAM), and 4-amino-4-deoxy-10-ethyl-10-deazapteroyl-gamma-methyleneglutamic acid (5, MEDAM). None of these compounds were metabolized to the respective polyglutamate derivative as judged by their inability to serve as substrates for CCRF-CEM human leukemia cell folylpolyglutamate synthetase (FPGS) in vitro. All compounds inhibited recombinant human-dihydrofolate reductase (DHFR) at nearly equivalent magnitude as MTX. Growth-inhibition studies with H35 hepatoma, Manca human lymphoma, and CCRF-CEM human leukemia cells established greater cytotoxic effects with compounds 3-5 than with compounds 1 and 2. gamma-Methyleneglutamate derivatives 3-5 were transported to H35 hepatoma cells better than MTX or beta-hydroxyglutamate derivatives 1 and 2. Compound 3 was 2.5 times better than MTX in competing with folinic acid transport in H35 hepatoma cells. Compound 1 did not have a significant inhibitory effect on folinic acid transport even at 50 microM under identical conditions. The IC50 for compound 1 against H35-hepatoma cell growth was 8.5-fold higher than MTX. Compounds with the gamma-methyleneglutamate moiety (3-5) exhibited almost equal or lower IC50 values than MTX against the growth of CCRF-CEM human leukemia cells. These studies show that on continuous exposure, the non-polyglutamylatable inhibitors DHFR (3-5) can exhibit superior antifolate activity compared to the polyglutamylatable methotrexate, presumably due to their enhanced transport to these cell lines. Compounds 3-5 appear to be excellent models to study the role of polyglutamylation of antifolates in antitumor activity and host toxicity.     

Asialoglycoprotein receptor-targeted superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide (SPIO) nanoparticles are primarily used as contrast agents in magnetic resonance imaging. SPIO have also been derivatized to add targeting and drug-carrier functionality as drug delivery devices. The preparation and characterization of amino-functionalized SPIO (ASPIO) and lactose-derivatized galactose-terminal-ASPIO are now reported. The target for galactose-terminal-ASPIO is the cell-surface asialoglycoprotein receptor (ASGPR) expressed by hepatocytes. Two batches of ASPIO with average particle sizes of 61 [42]nm and 127 [125]nm [full-width half maximum; FWHM] were prepared. The small ASPIO increased from 61 nm to 278 [309]nm upon lactosylation (Gal-ASPIO-278) and to 302 [280] by N-acetylation (NAcASPIO-302); the larger ASPIO afforded galactosyl-terminal ASPIO of 337 [372]nm and N-acetylated ASPIO of 326 [308]nm. The LD50 of Gal-ASPIO-278 was 1500 microg/mL to HepG2 cells; Gal-ASPIO-278 associated with HepG2 cells in vitro, whereas NAcSPIO-302, prepared from the same ASPIO batch, did not. Gal-ASPIO-278 and NAcASPIO-302 were not bound by ASPGR non-expressing 143B cells. The association of Gal-ASPIO-278 to HepG2 cells was reduced by free galactose, supporting the model of ASGPR-mediated binding. These data underline the potential application of Gal-ASPIO as a targeted ligand for ASPGR-expressing cells in vivo.     

Clinical translation of folate receptor-targeted therapeutics

INTRODUCTION: Folate receptor-α (FR-α) has been established as a membrane marker for ovarian cancer. In addition, it is frequently overexpressed in other major types of epithelial tumors. FR-α-based tumor-targeted therapy and drug carriers have been an active area of laboratory research for more than 20 years. Recently, there has been a great increase in the effort to finally translate this promising technology into the clinic and bring FR-targeted therapeutics into the market. AREAS COVERED: Two FR-targeted therapeutic agents have moved into Phase III clinical trials, the monoclonal antibody farletuzumab and the low molecular weight vintafolide, combined with etarfolatide as a companion imaging agent, representing two alternative strategies for targeting the FR. EXPERT OPINION: Each of the two strategies has advantages and disadvantages. Identification of the best target patient population is likely critical to the ultimate success of FR-targeted agents in the clinic. A successful clinical strategy may require the integration between FR expression analysis and an optimal combination of FR-targeted therapy and standard chemotherapy. Advancement into Phase III trials and the ongoing clinical development of several additional folate conjugates are likely to usher in a new era of clinical translation and validation of FR-targeted imaging and therapeutic agents.     

Clinical translation of folate receptor-targeted therapeutics

Introduction: Folate receptor?α (FR?α) has been established as a membrane marker for ovarian cancer. In addition, it is frequently overexpressed in other major types of epithelial tumors. FR?α-based tumor-targeted therapy and drug carriers have been an active area of laboratory research for more than 20 years. Recently, there has been a great increase in the effort to finally translate this promising technology into the clinic and bring FR-targeted therapeutics into the market.

Areas covered: Two FR-targeted therapeutic agents have moved into Phase III clinical trials, the monoclonal antibody farletuzumab and the low molecular weight vintafolide, combined with etarfolatide as a companion imaging agent, representing two alternative strategies for targeting the FR.

Expert opinion: Each of the two strategies has advantages and disadvantages. Identification of the best target patient population is likely critical to the ultimate success of FR-targeted agents in the clinic. A successful clinical strategy may require the integration between FR expression analysis and an optimal combination of FR-targeted therapy and standard chemotherapy. Advancement into Phase III trials and the ongoing clinical development of several additional folate conjugates are likely to usher in a new era of clinical translation and validation of FR-targeted imaging and therapeutic agents.