Tissue-specific promoters for cancer gene therapy

Adenoviral cancer gene therapy approaches have resulted in promising recent results. Following only a decade of intense development, some of the crucial obstacles are now being overcome. Insufficient transduction has been the main limitation of earlier approaches. A new approach for increasing transduction of tumour cells is utilisation of replication-competent oncolytic agents, such as conditionally replicating adenoviruses (CRADs). The anti-tumour effect is caused by replication of the virus per se and, thus, replication must be restricted to tumour cells to protect normal tissues from damage. Tissue-specific promoters (TSPs) represent a powerful tool for decreasing the toxicity of cancer gene therapy to normal tissues and have previously been utilised for specific mutation compensation or delivery of prodrug-converting enzymes. However, TSPs can also be used for controlling crucial viral replication regulators and consequent restriction of replication to tumour cells. Initial clinical trials have demonstrated the safety and suggested efficacy for TSP-controlled CRADs as a novel approach for cancer gene therapy.     

Bone marrow-targeted liposomal carriers

Introduction: Bone marrow-targeted drug delivery systems appear to offer a promising strategy for advancing diagnostic, protective and/or therapeutic medicine for the hematopoietic system. Liposome technology can provide a drug delivery system with high bone marrow targeting that is mediated by specific phagocytosis in bone marrow.

Area covered: This review focuses on a bone marrow-specific liposome formulation labeled with technetium-99 m. Interspecies differences in bone marrow distribution of the bone marrow-targeted formulation are emphasized. This review provides a liposome technology to target bone marrow. In addition, the selection of proper species for the investigation of bone marrow targeting is suggested.

Expert opinion: It can be speculated that the bone marrow macrophages have a role in the delivery of lipids to the bone marrow as a source of energy and for membrane biosynthesis or in the delivery of fat-soluble vitamins for hematopoiesis. This homeostatic system offers a potent pathway to deliver drugs selectively into bone marrow tissues from blood. High selectivity of the present bone marrow-targeted liposome formulation for bone marrow suggests the presence of an active and specific mechanism, but specific factors affecting the uptake of the bone marrow mononuclear phagocyte system are still unknown. Further investigation of this mechanism will increase our understanding of factors required for effective transport of agents to the bone marrow, and may provide an efficient system for bone marrow delivery for therapeutic purposes.     

Chloroplast overexpression of rice caffeic acid O‐methyltransferase increases melatonin production in chloroplasts via the 5‐methoxytryptamine pathway in transgenic rice plants

Recent analyses of the enzymatic features of various melatonin biosynthetic genes from bacteria, animals, and plants have led to the hypothesis that melatonin could be synthesized via the 5‐methoxytryptamine (5‐MT) pathway. 5‐MT is known to be synthesized in vitro from serotonin by the enzymatic action of O‐methyltransferases, including N‐acetylserotonin methyltransferase (ASMT) and caffeic acid O‐methyltransferase (COMT), leading to melatonin synthesis by the subsequent enzymatic reaction with serotonin N‐acetyltransferase (SNAT). Here, we show that 5‐MT was produced and served as a precursor for melatonin synthesis in plants. When rice seedlings were challenged with senescence treatment, 5‐MT levels and melatonin production were increased in transgenic rice seedlings overexpressing the rice COMT in chloroplasts, while no such increases were observed in wild‐type or transgenic seedlings overexpressing the rice COMT in the cytosol, suggesting a 5‐MT transport limitation from the cytosol to chloroplasts. In contrast, cadmium treatment led to results different from those in senescence. The enhanced melatonin production was not observed in the chloroplast COMT lines relative over the cytosol COMT lines although 5‐MT levels were equally induced in all genotypes upon cadmium treatment. The transgenic seedlings with enhanced melatonin in their chloroplasts exhibited improved seedling growth vs the wild type under continuous light conditions. This is the first report describing enhanced melatonin production in chloroplasts via the 5‐MT pathway with the ectopic overexpression of COMT in chloroplasts in plants.     

An ultra-high-affinity small organic ligand of fibroblast activation protein for tumor-targeting applications

We describe the development of OncoFAP, an ultra-high-affinity ligand of fibroblast activation protein (FAP) for targeting applications with pan-tumoral potential. OncoFAP binds to human FAP with affinity in the subnanomolar concentration range and cross-reacts with the murine isoform of the protein. We generated various fluorescent and radiolabeled derivatives of OncoFAP in order to study biodistribution properties and tumor-targeting performance in preclinical models. Fluorescent derivatives selectively localized in FAP-positive tumors implanted in nude mice with a rapid and homogeneous penetration within the neoplastic tissue. Quantitative in vivo biodistribution studies with a lutetium-177–labeled derivative of OncoFAP revealed a preferential localization in tumors at doses of up to 1,000 nmol/kg. More than 30% of the injected dose had already accumulated in 1 g of tumor 10 min after intravenous injection and persisted for at least 3 h with excellent tumor-to-organ ratios. OncoFAP also served as a modular component for the generation of nonradioactive therapeutic products. A fluorescein conjugate mediated a potent and FAP-dependent tumor cell killing activity in combination with chimeric antigen receptor (CAR) T cells specific to fluorescein. Similarly, a conjugate of OncoFAP with the monomethyl auristatin E-based Vedotin payload was well tolerated and cured tumor-bearing mice in combination with a clinical-stage antibody-interleukin-2 fusion. Collectively, these data support the development of OncoFAP-based products for tumor-targeting applications in patients with cancer.

Small organic ligands which selectively bind with high affinity to tumor-associated antigens are increasingly applied as targeting delivery vehicles of small payloads such as radionuclides (1, 2), drugs (3–5), and fluorophores (6, 7) to tumor sites. In principle, the use of small ligands for targeting applications offers several advantages compared to intact immunoglobulins, including superior penetration of solid neoplastic lesions (8), lower immunogenicity (9), and a reduced cost of goods (10). Low molecular weight compounds may reach their target in vivo in a matter of seconds, thanks to rapid extravasation after intravenous administration (8). A strikingly selective accumulation of small ligands in neoplastic masses has been demonstrated for a small number of targets including somatostatin receptor type 2 (SSTR-2) (11), prostate-specific membrane antigen (PSMA) (12), and carbonic anhydrase IX (CAIX) (13), for which high-affinity small organic ligands are available. Those ligands are typically specific for defined tumor entities, such as neuroendocrine tumors (11), prostate cancer (3), and clear cell renal cell carcinoma (2).¹⁷⁷Lu-DOTATATE (Lutathera), a small-molecule product targeting SSTR-2, has been approved based on phase III data in which a clinically meaningful 82% reduction in the risk of disease progression or death was demonstrated in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs) (14). Similar data are expected from the currently ongoing phase III VISION trial for ¹⁷⁷Lu-PSMA-617 (clinical trial no. {"type":"clinical-trial","attrs":{"text":"NCT03511664","term_id":"NCT03511664"}}NCT03511664), a radiolabeled small molecule that binds with high affinity to PSMA and that enables targeted beta particle therapy in metastatic castration-resistant prostate cancer patients (15). PHC-102, a ^99mTc-labeled small-molecule derivative targeting CAIX, exhibited favorable uptake in primary and metastatic lesions in patients with renal cell carcinoma (RCC) (2). In light of the promising performance of small organic ligands, it would be desirable to discover and develop small molecules with a broader tumor-targeting potential, therefore covering multiple cancer types.Fibroblast activation protein (FAP) is a type II integral membrane serine protease which is abundantly expressed in the stroma of more than 90% of the epithelial cancers, including malignant breast, colorectal, skin, prostate, and pancreatic cancers (16, 17), while exhibiting a restricted expression in normal adult tissues (18, 19). Haberkorn and coworkers (1, 20, 21) have recently described a series of FAP ligands capable of selective accumulation in FAP-positive tumors in mice and in patients. One of these products (named FAPI-04) showed impressive tumor to background ratios at early time points (i.e., few hours after administration) in a broad range of different cancer types in patients. More than 28 tumor types including breast, lung, pancreatic, head and neck, esophagus, and colorectal cancer presented a remarkably high uptake of a FAP-targeted small molecule labeled with gallium-68 (1, 20, 21). For this reason, FAP has recently been dubbed as “the next billion-dollar target for theranostic products” (22).Here, we describe how the chemical modification of a quinoline moiety in position 8 led to the discovery of OncoFAP, a small organic FAP ligand with a dissociation constant in the subnanomolar concentration range. OncoFAP exhibited a strikingly selective and efficient tumor-targeting performance when equipped with various types of payloads, including radionuclides, fluorophores, and cytotoxic drugs. The targeting delivery of radionuclides to solid tumors is rapidly gaining in popularity, as it may open theranostic opportunities, associated with the use of gallium-68 for positron emission tomography (PET) imaging and of lutetium-177 for therapeutic applications (23). The delivery of fluorescein to tumors enables the conditional activation of chimeric antigen receptor (CAR) T cells, which display a potent biocidal activity only in the presence of fluorescein-labeled adaptor molecules specific to a tumor antigen (24, 25). Finally, small-molecule–drug conjugates (SMDCs) promise to represent a valid alternative to antibody–drug conjugates for cancer therapy, with better tumor penetration and a lower cost of goods (8, 26, 27).     

3-取代吲哚-2-酮类化合物的设计、合成及抗肿瘤活性研究

目的设计合成对微管蛋白和血管内皮细胞生长因子受体2(VEGFR-2)激酶具有双重抑制作用的3-取代吲哚-2-酮类化合物,考察其体外抑瘤活性。方法以取代的苯胺为起始原料,经缩合、环合、还原、取代等反应制得系列目标化合物,并考察该系列化合物对微管蛋白和肿瘤细胞的抑制活性。结果共合成了11个新的目标化合物。实验结果显示,化合物j9对微管蛋白和VEGFR-2激酶具有双重抑制活性。所有目标化合物对3种肿瘤细胞株均有中等强度的抑制活性。结论该类化合物是一类具有多靶点作用的抗肿瘤化合物。     

双配体修饰聚合物泡囊的制备及细胞摄取

目的构建一种主动靶向的新型纳米药物载体——聚合物泡囊(polymer vesicles,PVs),并考察其细胞摄取。方法以马来酰亚胺-聚乙二醇-聚乳酸-羟基乙酸共聚物(MAL-PEG-PLGA)为载体材料,通过自组装制备PVs,用转铁蛋白(Tf)与Tet-1对PVs进行修饰,构建纳米药物载体(Tf/Tet-1-PVs)。以香豆素-6作为荧光探针包载于药物载体,考察脑微血管内皮细胞(BCEC)及神经细胞(Neuro-2a)对载体系统的摄取。结果 PVs粒径约80nm,形态圆整,电镜观察具有明显膜层结构。BCEC细胞和Neuro-2a细胞对Tf/Tet-1-PVs的摄取均显著优于空白对照组和单配体修饰对照组。结论 PVs经双配体Tf及Tet-1修饰后可促进脑微血管内皮细胞和神经细胞的摄取。     

Role of polymer–drug conjugates in organ-specific delivery systems

Polymers have been utilized to deliver the drug to targeted site in controlled manner, achieving the high-therapeutic efficacy. Polymeric drug conjugates having variable ligands as attachments have been proved to be biodegradable, stimuli sensitive and targeted systems. Numerous polymeric drug conjugates having linkers degraded by acidity or intracellular enzymes or sensitive to over expressed groups of diseased organ/tissue have been synthesized during last decade to develop targeted delivery systems. Most of these organs have number of receptors attached with different cells such as Kupffer cells of liver have mannose-binding receptors while hepatocytes have asialoglycoprotein receptors on their surface which mainly bind with the galactose derivatives. Such ligands can be used for achieving high targeting and intracellular delivery of the drug. This review presents detailed aspects of receptors found in different cells of specific organ and ligands with binding efficiency to these specific receptors. This review highlights the need of further studies on organ-specific polymer–drug conjugates by providing detailed account of polymeric conjugates synthesized till date having organ-specific targeting.     

Preliminary evaluation of [18F]AlF-NOTA-MAL-Cys39-exendin-4 in insulinoma with PET

Background: High expression of glucagon-like peptide-1 receptor (GLP-1R) in insulinoma supplies a potential drug target for tumor imaging. Exendin-4 can specifically bind to GLP-1R as an agonist and its analogs are extensively used in receptor imaging studies.

Purpose: A new GLP-1R imaging agent, [¹⁸F]AlF-NOTA-MAL-Cys³⁹-exendin-4, was designed and prepared for insulinoma imaging.

Methods: Cys³⁹-exendin-4 was conjugated with NOTA-MAL, then the compound was radiolabeled with [¹⁸F]AlF complex to obtained [¹⁸F]AlF-NOTA-MAL-Cys³⁹-exendin-4. The tumor-targeting characters of the tracer were evaluated in INS-1 cells and BALB/c nude mice models.

Results: [¹⁸F]AlF-NOTA-MAL-Cys³⁹-exendin-4 can be efficiently produced with a yield of 17.5?±?3.2% (non-decay corrected) and radiochemical purity of >95%. The IC₅₀ value of displacement [¹⁸F]AlF-NOTA-MAL-Cys³⁹-exendin-4 with Cys³⁹-exendin-4 was 13.52?±?1.36?nM. PET images showed excellent tumor visualization with high uptake (9.15?±?1.6%ID/g at 30?min and 7.74?±?0.87%ID/g at 60?min). The tumor to muscle, pancreas and liver ratios were 63.25, 3.85 and 7.29 at 60?min after injection. GLP-1R binding specificity was demonstrated by co-injection with an excess of unlabeled Cys³⁹-exendin-4 and the tumor uptake was found to be reduced significantly.

Conclusion: [¹⁸F]AlF-NOTA-MAL-Cys³⁹-exendin-4 shows favorable characteristics for insulinoma imaging and may be translated to clinical studies.     

Elastin-like polypeptides and their applications in anticancer drug delivery systems: a review

Abstract

Elastin-like polypeptides (ELPs) are large molecular weight biopolymers. They have been widely studied as macromolecular carriers for targeted delivery of drugs. The aim of the present article is to review the available information on ELPs (including our recent investigations), their properties, drug delivery applications to tumor sites and future perspectives. This review also provides information on the use of short synthetic ELPs for making ELP-drug conjugates, for targeted delivery of anticancer drugs. In the present review we also focus on the point that short ELPs can also be used for targeting anticancer drugs to tumor sites as they behave similar to long ELPs regarding their capacity to undergo inverse temperature transition (ITT) behavior.