A Drosophila Model To Identify Polyamine−Drug Conjugates That Target the Polyamine Transporter in an Intact Epithelium

Elucidating the Role of Chmp1 Overexpression in the Transport of Polyamines in Drosophila melanogaster

Polyamines are small organic cations that are essential for many biological processes such as cell proliferation and cell cycle progression. While the metabolism of polyamines has been well studied, the mechanisms by which polyamines are transported into and out of cells are poorly understood. Here, we describe a novel role of Chmp1, a vesicular trafficking protein, in the transport of polyamines using a well-defined leg imaginal disc assay in Drosophila melanogaster larvae. We show that Chmp1 overexpression had no effect on leg development in Drosophila, but does attenuate the negative impact on leg development of Ant44, a cytotoxic drug known to enter cells through the polyamine transport system (PTS), suggesting that the overexpression of Chmp1 downregulated the PTS. Moreover, we showed that the addition of spermine did not rescue the leg development in Chmp1-overexpressing leg discs treated with difluoromethylornithine (DFMO), an inhibitor of polyamine metabolism, while putrescine and spermidine did, suggesting that there may be unique mechanisms of import for individual polyamines. Thus, our data provide novel insight into the underlying mechanisms that are involved in polyamine transport and highlight the utility of the Drosophila imaginal disc assay as a fast and easy way to study potential players involved in the PTS.

Towards the Development of Frustrated Lewis Pair (FLP) Catalyzed Hydrogenations of Tertiary and Secondary Carboxylic Amides

The development of the frustrated Lewis pair catalyzed hydrogenation of tertiary and secondary amides is reviewed. Detailed insight into our strategies in order to overcome challenges during the reaction development process is provided. Furthermore, the developed chemistry is extended to the hydrogenation of polyamides and of trifluoroacetamides for the convenient introduction of trifluoroethyl groups into organic molecules.

Study on the interaction of polyamine transport (PAT) and 4-Chloro-naphthalimide-homospermidine conjugate (4-ClNAHSPD) by molecular docking and dynamics

Polyamine transporter (PAT) is a protein that can deliver "drug-polyamine" conjugates to tumor cells. 4-Chloro-naphthalimide- homospermidine (4-ClNAHSPD) displayed good antitumor activity and excellent cell selectivity via PAT pathway. In this paper, 4-ClNAHSPD and spermidine (SPD) were docked against PAT. The results showed that 4-ClNAHSPD could bind to PAT through hydrogen bond, Van der Waals, salt bridge or attractive charge and hydrophobic interaction. The interaction of SPD and PAT, however, was hydrogen bond and Van der Waals interaction. Moreover, their binding sites were also different. The primary binding sites of 4-ClNAHSPD with PAT are the residues of VAL59, HIS222, ASP61, ASP179 and GLU64, while SPD interacts with PAT in the sites of ASP37, ASP244, APS275 and SER36. The docked ligand-protein complexes were simulated for 5000ps. In simulations, various binding sites further resulted in the diverse root-mean-square deviation (RMSD) and root-mean-square deviation fluctuation (RMSF) values. The RMSD and RMSF values of 4-ClNAHSPD-PAT indicated that 4-ClNAHSPD caused a weak conformational change of PAT in a different style from SPD. More importantly, the interaction force numbers of 4-ClNAHSPD-PAT were also changed after the simulation. These results supported that 4-ClNAHSPD harnesses PAT pathway for cellular entrance.Communicated by Ramaswamy H. Sarma.

Evaluation of Polyamine Transport Inhibitors in a Drosophila Epithelial Model Suggests the Existence of Multiple Transport Systems

Increased polyamine biosynthesis activity and an active polyamine transport system are characteristics of many cancer cell lines and polyamine depletion has been shown to be a viable anticancer strategy. Polyamine levels can be depleted by difluoromethylornithine (DFMO), an inhibitor of the key polyamine biosynthesis enzyme ornithine decarboxylase (ODC). However, malignant cells frequently circumvent DFMO therapy by up-regulating polyamine import. Therefore, there is a need to develop compounds that inhibit polyamine transport. Collectively, DFMO and a polyamine transport inhibitor (PTI) provide the basis for a combination therapy leading to effective intracellular polyamine depletion. We have previously shown that the pattern of uptake of a series of polyamine analogues in a Drosophila model epithelium shares many characteristics with mammalian cells, indicating a high degree of similarity between the mammalian and Drosophila polyamine transport systems. In this report, we focused on the utility of the Drosophila epithelial model to identify and characterize polyamine transport inhibitors. We show that a previously identified inhibitor of transport in mammalian cells has a similar activity profile in Drosophila. The Drosophila model was also used to evaluate two additional transport inhibitors. We further demonstrate that a cocktail of polyamine transport inhibitors is more effective than individual inhibitors, suggesting the existence of multiple transport systems in Drosophila. Our findings reinforce the similarity between the Drosophila and mammalian transport systems and the value of the Drosophila model to provide inexpensive early screening of molecules targeting the transport system.

Cancer Drug Development Using Drosophila as an in vivo Tool: From Bedside to Bench and Back

The fruit fly Drosophila melanogaster has been used for modeling cancer and as an in vivo tool for the validation and/or development of cancer therapeutics. The impetus for the use of Drosophila in cancer research stems from the high conservation of its signaling pathways, lower genetic redundancy, short life cycle, genetic amenability, and ease of maintenance. Several cell signaling pathways in Drosophila have been used for cancer drug development. The efficacy of combination therapy and uptake/bioavailability of drugs have also been studied. Drosophila has been validated using several FDA-approved drugs, suggesting a potential application of this model in drug repurposing. The model is emerging as a powerful tool for high-throughput screening and should significantly reduce the cost and time associated with drug development. In this review we discuss the applications of Drosophila in cancer drug development. The advantages and limitations of the model are discussed.

Spatiotemporal patterning of polyamines in Drosophila development

While several studies have implicated polyamines (PAs) in development, little research has been done in genetically tractable model systems like Drosophila. Here, we integrate transcriptional and metabolic data across Drosophila development, and are the first to show temporal, stage-specific regulation of PA accumulation in embryonic trachea and eye discs using immunohistochemistry. Understanding the regulation driving this accumulation can provide insight into PA metabolism and transport. Our findings suggest that Drosophila has great potential for investigating PAs in developmental biology.

Chemical genetics and drug screening in Drosophila cancer models

Drug candidates often fail in preclinical and clinical testing because of reasons of efficacy and/or safety. It would be time- and cost-efficient to have screening models that reduce the rate of such false positive candidates that appear promising at first but fail later. In this regard, it would be particularly useful to have a rapid and inexpensive whole animal model that can pre-select hits from high-throughput screens but before testing in costly rodent assays. Drosophila melanogaster has emerged as a potential whole animal model for drug screening. Of particular interest have been drugs that must act in the context of multi-cellularity such as those for neurological disorders and cancer. A recent review provides a comprehensive summary of drug screening in Drosophila, but with an emphasis on neurodegenerative disorders. Here, we review Drosophila screens in the literature aimed at cancer therapeutics.

An integrated Drosophila model system reveals unique properties for F14512, a novel polyamine-containing anticancer drug that targets topoisomerase II

F14512 is a novel anti-tumor molecule based on an epipodophyllotoxin core coupled to a cancer-cell vectoring spermine moiety. This polyamine linkage is assumed to ensure the preferential uptake of F14512 by cancer cells, strong interaction with DNA and potent inhibition of topoisomerase II (Topo II). The antitumor activity of F14512 in human tumor models is significantly higher than that of other epipodophyllotoxins in spite of a lower induction of DNA breakage. Hence, the demonstrated superiority of F14512 over other Topo II poisons might not result solely from its preferential uptake by cancer cells, but could also be due to unique effects on Topo II interactions with DNA. To further dissect the mechanism of action of F14512, we used Drosophila melanogaster mutants whose genetic background leads to an easily scored phenotype that is sensitive to changes in Topo II activity and/or localization. F14512 has antiproliferative properties in Drosophila cells and stabilizes ternary Topo II/DNA cleavable complexes at unique sites located in moderately repeated sequences, suggesting that the drug specifically targets a select and limited subset of genomic sequences. Feeding F14512 to developing mutant Drosophila larvae led to the recovery of flies expressing a striking phenotype, "Eye wide shut," where one eye is replaced by a first thoracic segment. Other recovered F14512-induced gain- and loss-of-function phenotypes similarly correspond to precise genetic dysfunctions. These complex in vivo results obtained in a whole developing organism can be reconciled with known genetic anomalies and constitute a remarkable instance of specific alterations of gene expression by ingestion of a drug. "Drosophila-based anticancer pharmacology" hence reveals unique properties for F14512, demonstrating the usefulness of an assay system that provides a low-cost, rapid and effective complement to mammalian models and permits the elucidation of fundamental mechanisms of action of candidate drugs of therapeutic interest in humans.

Image enhancement for tracking the translucent larvae of Drosophila melanogaster

Drosophila melanogaster larvae are model systems for studies of development, synaptic transmission, sensory physiology, locomotion, drug discovery, and learning and memory. A detailed behavioral understanding of larvae can advance all these fields of neuroscience. Automated tracking can expand fine-grained behavioral analysis, yet its full potential remains to be implemented for the larvae. All published methods are unable to track the larvae near high contrast objects, including the petri-dish edges encountered in many behavioral paradigms. To alleviate these issues, we enhanced the larval contrast to obtain complete tracks. Our method employed a dual approach of optical-contrast boosting and post-hoc image processing for contrast enhancement. We reared larvae on black food media to enhance their optical contrast through darkening of their digestive tracts. For image processing we performed Frame Averaging followed by Subtraction then Thresholding (FAST). This algorithm can remove all static objects from the movie, including petri-dish edges prior to processing by the image-tracking module. This dual approach for contrast enhancement also succeeded in overcoming fluctuations in illumination caused by the alternating current power source. Our tracking method yields complete tracks, including at the edges of the behavioral arena and is computationally fast, hence suitable for high-throughput fine-grained behavioral measurements.

Conjugation of substituted naphthalimides to polyamines as cytotoxic agents targeting the Akt/mTOR signal pathway

Though several naphthalimide derivatives have exhibited antitumor activity in clinical trials, some issues such as toxicity prompted further structural modifications on the naphthalimide backbone. A series of naphthalimides conjugated with polyamines were synthesized to harness the polyamine transporter (PAT) for drug delivery, which was beneficial for the tumor cell selectivity. Bioevaluation in human hepatoma HepG2 cells treated with alpha-difluoromethylornithine (DFMO) or spermidine (Spd), human hepatoma Bel-7402 and normal QSG-7701 hepatocyte confirmed the PAT recognition and cell selectivity. In addition, the novel naphthalimide polyamine conjugate kills cells via apoptosis, and the Akt/mTOR signal pathway was first identified as the upstream cellular target through the apoptotic mechanism research. The presence of DFMO or Spd only either elevated or attenuated the cell apoptosis, but did not change the signal pathway. Collectively, the proper polyamine recognition element (i.e., homospermidine) mediated effective drug delivery via the PAT, and helped the proper cytotoxic goods (i.e., diverse naphthalimides) exert antitumor properties.

Caenorhabditis elegans P5B-type ATPase CATP-5 operates in polyamine transport and is crucial for norspermidine-mediated suppression of RNA interference

Physiological polyamines are required in various biological processes. In the current study, we used norspermidine, a structural analog of the natural polyamine spermidine, to investigate polyamine uptake in the model organism Caenorhabditis elegans. Norspermidine was found to have two remarkable effects: it is toxic for the nematode, without affecting its food, Escherichia coli; and it hampers RNA interference. By characterizing a norspermidine-resistant C. elegans mutant strain that has been isolated in a genetic screen, we demonstrate that both effects, as well as the uptake of a fluorescent polyamine-conjugate, depend on the transporter protein CATP-5, a novel P(5B)-type ATPase. To our knowledge, CATP-5 represents the first P(5)-type ATPase that is associated with the plasma membrane, being expressed in the apical membrane of intestinal cells and the excretory cell. Moreover, genetic interaction studies using C. elegans polyamine synthesis mutants indicate that CATP-5 has a function redundant to polyamine synthesis and link reduced polyamine levels to retarded postembryonic development, reduced brood size, shortened life span, and small body size. We suggest that CATP-5 represents a crucial component of the pharmacologically important polyamine transport system, the molecular nature of which has not been identified so far in metazoa.

2,2',4,4',6,6'-Hexamethyl-N-(3-phthalimidoprop-yl)-N,N'-(propane-1,3-di-yl)dibenzene-sulfonamide

In the title compound, C₃₂H₃₈N₃O₆S₂, an inter­mediate in the synthesis of polyamine drugs, the dihedral angle between the phenyl rings of the two 2,4,6-trimethyl­benzene­sulfonyl groups is 27.1 (3)°. In the crystal structure, mol­ecules are linked by inter­molecular N—H⋯O hydrogen bonds, thereby forming an infinite one-dimensional chain propagating along [010].