Development and challenges in the discovery of 5-HT1A and 5-HT7 receptor ligands.

Serotonin (5-hydroxytryptamine) is a small molecule that acts both in the central and peripheral nervous system as a neurotransmitter and a hormone, respectively. Serotonin is synthesized via a multi-stage pathway beginning with l-tryptophan, which is converted by an enzyme called tryptophan hydroxylase into L-5-Hydroxytryptophan. It is well-known for its significance in the control of mood, anxiety, depression, and insomnia as well as in normal human functions such as sleep, sexual activity, and appetite. Thus, for medical chemists and pharmaceutical firms, serotonin is one of the most desirable targets. Among the seven different classes of serotonin receptors, the 5-HT1A was one of the first discovered serotonin receptors, and the 5-HT7 was the last addition to the serotonin receptor family. Both the classes were thoroughly examined. 5-HT1A neurotransmission-related dysfunctions are linked to many psychological conditions such as anxiety, depression, and movement disorders. 5-HT7 is a member of the cell surface receptor GPCR superfamily and is regulated by the serotonin neurotransmitter. It has been the focus of intensive research efforts since its discovery, which was prompted by its presence in functionally important regions of the brain. The thalamus and hypothalamus have the highest 5-HT7 receptor densities. They are also found in the hippocampus and cortex at higher densities. Thermoregulation, circadian rhythm, learning and memory, and sleep are all associated with the 5-HT7 receptor. It is also suspected that this receptor may be involved in the control of mood, indicating that it may be a beneficial target for depression treatment. Several differently structured molecules such as aminotetralins, ergolines, arylpiperazines, indolylalkylamines, aporphines, and aryloxyalkyl-amines are known to bind to 5-HT1A and 5-HT7 receptor sites. In brain serotonin receptors 5-HT1A and 5-HT7 are strongly co-expressed in regions involved in depression. However, their functional interaction has not been identified. An overview of the 5-HT1A and 5-HT7 receptor ligands belonging to different chemical groups is mentioned in this review.

Modified benzoxazolone (ABO-AA) based single photon emission computed tomography (SPECT) probes for 18 kDa translocator protein.

Acetamidobenzoxazolone (ABO) has been modified to ABO-AA, 2-(2-(5-bromo/chloro benzoxazolone)acetamide)-3-(1H-indol-3-yl)propionate to improve pharmacokinetics and lipophilicity (log p = 2.04). The final compound was synthesized in better yield and in fewer steps than previously reported MBIP-Br (70% vs. 62%). Computational docking confirmed binding of MBIP-Cl with translocator protein (TSPO) as well as with mutant TSPO (-8.99 for PDB: 4RYQ and -9.30 for PDB: 4UC1, respectively). Ex-vivo biodistribution and scintigraphy showed that 99m Tc-MBIP-Cl is better than 99m Tc-MBIP-Br in terms of uptake in TSPO-rich organs and release kinetics 0-120 min postinjection. At 15 min, uptake was 2.75-fold (12.91%ID/g vs. 4.69%ID/g) in lung and seven-fold (5.16%ID/g vs. 0.72%ID/g) in heart for 99m Tc-MBIP-Cl compared to that of 99m Tc-MBIP-Br which gives warrant to utilize this single photon emission computed tomography agent in higher animals.

Development and Gamma Scintigraphy Study of Trigonella foenum-graecum (Fenugreek) Polysaccharide-Based Colon Tablet.

The major concern with the use of some synthetic excipients is their safety towards biological tissues, hence influencing the reliability of products. With the aim to minimize dependency on highly toxic synthetic excipients, the present study was designed to deliver metronidazole (MNZ) into the colonic region for localized treatment of amoebiasis using natural polysaccharide-based drug delivery. Compression-coated tablets were prepared using water extractable natural polysaccharide from Trigonella foenum-graecum (FG). Physical properties of the tablets were evaluated and dissolution study was performed at pH 1.2, 6.8, and 7.4 with rat cecal material. Results indicate that all batches demonstrated pH-dependent drug release and prevented release into the stomach, allowing traces into the intestine and highest availability into the colon. A significant correlation (r2 = 0.975) was found between the coating levels of extracted polysaccharide and lag time release of drug. Gamma scintigraphy images of in vivo study conducted on human volunteers showed a small intestinal transit time, i.e., 3-5 (4.2 ± 0.4) h and confirmed that the tablets reached the colon within 6-8 h. The present study revealed that the FG polysaccharide-based double compression tablets may be promising colon-specific drug carriers with reduced toxic effects of commonly used synthetic excipients.

Nanoparticles toxicity: an overview of its mechanism and plausible mitigation strategies.

Over the last decade, nanoparticles have found great interest among scientists and researchers working in various fields within the realm of biomedicine including drug delivery, gene delivery, diagnostics, targeted therapy and biomarker mapping. While their physical and chemical properties are impressive, there is growing concern about the toxicological potential of nanoparticles and possible adverse health effects as enhanced exposure of biological systems to nanoparticles may result in toxic effects leading to serious contraindications. Toxicity associated with nanoparticles (nanotoxicity) may include the undesired response of several physiological mechanisms including the distressing of cells by external and internal interaction with nanoparticles. However, comprehensive knowledge of nanotoxicity mechanisms and mitigation strategies may be useful to overcome the hazardous situation while treating diseases with therapeutic nanoparticles. With the same objectives, this review discusses various mechanisms of nanotoxicity and provides an overview of the current state of knowledge on the impact of nanotoxicity on biological control systems and organs including liver, brain, kidneys and lungs. An attempt also been made to present various approaches of scientific research and strategies that could be useful to overcome the effect of nanotoxicity during the development of nanoparticle-based systems including coating, doping, grafting, ligation and addition of antioxidants.

Protective Effect of Organ Preservation Fluid Supplemented With Nicorandil and Rutin Trihydrate: A Comparative Study in a Rat Model of Renal Ischemia.

OBJECTIVES: The objective of organ preservation is sustained viability of detached/removed/isolated organs and subsequent successful posttransplant outcomes. Nicorandil (an ATP-sensitive potassium channel opener) is an efficacious agent to preserve lungs and heart. Rutin trihydrate (an antioxidant) inhibits free radical-mediated cytotoxicity and lipid peroxidation. We aimed to evaluate the efficacy of nicorandil and rutin trihydrate to enhance kidney preservation. MATERIALS AND METHODS: We prepared 2 versions of organ preservation fluid, supplemented with either nicorandil or rutin trihydrate, and used 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays to evaluate the efficacy of these solutions in vitro (HEK293 human embryonic kidney cells), according to various cellular parameters such as ATP levels, reactive oxygen species, and cell viability. We also investigated the in vivo preservation efficacy in a rat model of renal ischemia and evaluated the immunohistological expression of apoptotic markers (caspase 3) in preserved rat kidney. RESULTS: We observed significant improvement of intracellular ATP levels (32 999 ± 1454 pmol/cell, n = 3; P < .05) in cells preserved in the nicorandil- supplemented solution compared with Custodiol solution (23 216 ± 1315 pmol/cell). Reactive oxygen species declined 1.25-fold (P < .05) in the presence of rutin trihydrate. Cell viability assays revealed a 4.8-fold increase in viability of renal cells preserved in the solutions supplemented with nicorandil or rutin trihydrate after 24-hour incubation compared with controls. In vivo, there were significant effects on serum creatinine (0.5480 ± 0.052, 0.956 ± 0.043 mg/dL) and blood urea nitrogen (85.36 ± 4.64, 92.85 ± 3.15 mg/dL) with the nicorandil and rutin trihydrate solutions, respectively. We observed suppressed expression of the apoptotic marker caspase 3 in groups treated with the 2 supplemented preservation fluids. CONCLUSIONS: Our results showed that solutions of organ preservation fluid supplemented with either nicorandil or rutin trihydrate can ameliorate cellular problems/dysfunction and facilitate sustained impro - vement of tissue survival and subsequent organ viability.

Breast intraductal nanoformulations for treating ductal carcinoma in situ II: Dose de-escalation using a slow releasing/slow bioconverting prodrug strategy.

Ductal carcinoma in situ (DCIS) represents approximately 20-25% of newly diagnosed breast cancers. DCIS is treated by surgery and possibly radiotherapy. Chemotherapy is only used as adjuvant or neoadjuvant therapy but not as primary therapy. The present study investigated the intraductal administration of Ciclopirox (CPX) formulated in nanosuspensions (NSs) or nanoparticles (NPs) to treat DCIS locally in a Fischer 344 rat model orthotopically implanted with 13762 Mat B III cells. Slow converting esterase responsive CPX prodrugs (CPDs) were successfully synthesized at high purity (> 95%) by directly acetylating the hydroxyl group or by appending a self-immolative linker between CPX and a phenolic ester. Direct esterification CPDs were not sufficiently stable so self-immolative CPDs were formulated in NSs and NPs. Prodrug release was evaluated from poly(lactic-co-glycolic acid) NPs, and CPD4 demonstrated the slowest release rate with the rank order of CPD2 (R = methyl) > CPD3 (R = t-butyl) > CPD4 (R = phenyl). Intraductally administered CPX NS, CPD4 NS, and an innovative mixture of CDP4 NS and NPs (at 1 mg CPX equivalent/duct) demonstrated significant (p < 0.05) in vivo anti-tumor efficacy compared with immediate release (IR) CPX NS and non-treated controls. CPX mammary persistence at 6 h and 48 h after CPD4 NS or NP administration was also greater than after the immediate release CPX NS. A strong correlation between CPX mammary persistence and efficacy is demonstrated. In conclusion, nanoformulations utilizing a slow releasing/slow bioconverting CPX prodrug delivery strategy resulted in significant dose de-escalation (~ five fold) while maintaining anti-tumor efficacy.

Breast intraductal nanoformulations for treating ductal carcinoma in situ I: Exploring metal-ion complexation to slow ciclopirox release, enhance mammary persistence and efficacy.

INTRODUCTION: Ductal Carcinoma In Situ (DCIS) represents a significant fraction (~20-25%) of all newly diagnosed breast cancer cases and, if left untreated, a significant fraction of patients will progress to invasive disease. Surgery is the only treatment option. Ciclopirox (CPX), an FDA-approved antifungal drug, has exhibited promising antitumor activity by down-regulating the expression of vital antiapoptotic cellular proteins and inhibiting the genetic expression of several oncogenic pathways. In this study, the feasibility of using nanoscale delivery systems to control release and prolong mammary tissue persistence of a lipophilic metal complex of CPX and Zinc (CPXZn) after intraductal administration was investigated. METHODS: CPX and CPX-Zn nanosuspensions (NSs) were prepared using an evaporative nanoprecipitation-ultra-sonication method. Flash nanoprecipitation was used to prepare PLGA nanoparticles (NPs) loaded with CPXZn. Our established orthotopic DCIS rat model was used to evaluate efficacy. Briefly, two days after 13762 Mat B III cell intraductal inoculation, rats were divided into treatment groups and a single intraductal injection of CPX NS, CPX-Zn NS or CPX-Zn NPs was administered. In the first study arm, the efficacy of CPX NS (1, 3, 5 mg/duct) was evaluated. In the second arm, the in vivo efficacy of CPX NS, CPX-Zn NS and CPX-Zn loaded NPs was evaluated and compared at equivalent CPX doses. The mammary persistence of CPX from CPX NS, CPX-Zn NS, and CPX-Zn PLGA NPs was also assessed. RESULTS: CPX-Zn complex was successfully synthesized and characterized by several spectral analyses. CPX release was slowed from the CPX-Zn NS and further slowed by incorporating CPX-Zn into PLGA NPs as compared to the CPX NS with release half times following the order: CPX NS < CPX-Zn NS << CPX-Zn NP. Intraductal CPX NS administration was dose and time dependent in suppressing tumor initiation suggesting prolonged mammary exposure may improve efficacy. In the second arm, mammary tissue persistence of CPX followed the rank order CPX NS < CPX-Zn NS << CPX-Zn NP at 6 h and 48 h post-administration. Prolonged mammary CPX exposure was highly correlated to improved efficacy. Prolonged CPX tissue persistence, attributed to slower release from the zinc complex and the PLGA NPs, resulted in a 5-fold dose reduction compared to the CPX NS. CONCLUSIONS: The current results demonstrate that slowing drug release in the mammary duct after intraductal administration overcomes the rapid ductal clearance of CPX, prolongs mammary tissue persistence, improves efficacy against DCIS lesions in vivo, and requires 5-fold less CPX to achieve equivalent efficacy. The studies also provide a strategic path forward for developing a locally administered drug delivery system for treating DCIS, for which no primary chemotherapy option is available.

Block Copolymer Based Nanoparticles for Theranostic Intervention of Cervical Cancer: Synthesis, Pharmacokinetics, and in Vitro/in Vivo Evaluation in HeLa Xenograft Models.

Polymer-based nanoparticles have proven to be viable carriers of therapeutic agents. In this study, we have developed nanoparticles (NPs) from polypeptide-polyethylene glycol based triblock and diblock copolymers. The synthesized block copolymers poly(ethylene glycol)-b-poly(glutamic acid)-b-poly(ethylene glycol) (GEG) and poly(ethylene glycol)-b-poly(glutamic acid) (EG) conjugated with folic acid for targeting specificity (EGFA) have been used to encapsulate methotrexate (MTX) to form M-GEG and M-EGFA NPs aimed at passive and active targeting of cervical carcinoma. In-vitro SRB cytotoxicity and hemolysis assays revealed that these NPs were cytocompatible to healthy human cells and hemocompatible to human RBCs. Cellular uptake by FACS demonstrated their prompt internalization by human cervical carcinoma (HeLa) cells and points toward an apoptotic mechanism of cell kill as confirmed by AO/EB staining as well as histological analysis of explanted HeLa tumors. Pharmacokinetics and biodistribution studies were performed in New Zealand albino rabbits and HeLa xenografted Athymic mice models, respectively, by radiolabeling these NPs with 99mTc. Passive tumor accumulation and active targeting of MTX-loaded polymeric nanoparticles to folate expressing cells were confirmed by intravenous administration of these 99mTc-labeled M-GEG and M-EGFA NPs in HeLa tumor bearing nude mice and clearly visualized by whole-body gamma-SPECT images of these mice. Survival studies of these xenografted mice established the antiproliferative effect of these MTX-loaded NPs while corroborating the targeting effect of folic acid. These studies proved that the M-GEG NPs and M-EGFA NPs could be effective alternatives to conventional chemotherapy along with simultaneous diagnostic abilities and thus potentially viable theranostic options for human cervical carcinoma.

Amphiphilic PEO-b-PBLG diblock and PBLG-b-PEO-b-PBLG triblock copolymer based nanoparticles: doxorubicin loading and in vitro evaluation.

Huisgen's 1,3-dipolar cycloaddition ("Click Chemestry") has been used to prepare amphiphilic PEO-b-PBLG diblock and PBLG-b-PEO-b-PBLG triblock copolymers as potential carriers of anticancer drugs. Spherical and flower shaped micelles (D ≈ 100 nm) were obtained from diblock and triblock copolymers respectively. DOX was effectively encapsulated up to 18 wt.% and 50-60% of it was steadily released from the micelles over a period of 7 d. Flow cytometry and fluorescence microscopy confirmed the effective intracellular uptake as well as the sustained release of DOX from micelles. These results suggest that the diblock as well as triblock copolymers are promising carriers for intra-cellular drug delivery.

Design, synthesis, and antimycobacterial property of PEG-bis(INH) conjugates.

Poly(ethylene glycol) derivatives of isoniazid with varying molecular weight of poly(ethylene glycol) were designed as antimycobacterial agents. Poly(ethylene glycol)-diacrylate of three different molecular weights (MW 258, 575, and 700) was conjugated with isoniazid by the Michael addition approach. The poly(ethylene glycol)-bis(isoniazid) conjugates thus obtained were completely characterized by FT-IR, (1)H and (13)C NMR, and ESI-MS spectroscopic techniques. Comparative MTT assay of the poly(ethylene glycol)-bis(isoniazid) conjugates showed much lower cytotoxicity than the neat isoniazid. MIC studies on Mycobaterium tuberculosis H37Rv showed potential antimycobacterial activity than the free isoniazid on a molar basis. The poly(ethylene glycol)-bis(isoniazid) conjugates were successfully radiolabeled with 99m-Technetium with more than 97% efficiency and stability to assess their in vivo fate. The (99m)Tc labeled poly(ethylene glycol)-bis(isoniazid) conjugates showed higher blood retention time in New Zealand rabbits which increased with increasing molecular weight of poly(ethylene glycol). Biodistribution studies in infection-induced murine models (BALB/c mice) showed significant retention of these conjugates at the site of infection for 72 h. The results of this study illustrate the potential utility of the PEGylated isoniazid conjugates as long circulating carriers for improved antitubercular drug therapy.

Kinetics of formation for lanthanide (III) complexes of DTPA-(Me-Trp)2 used as imaging agent.

Diethlenetriamine-N,N,N'N''N''-pentaacetic acid (DTPA)-bis (amide) analogs have been synthesized and evaluated as a potential biomedical imaging agents. Imaging and biodistribution studies were performed in mice that showed a significant accumulation of DTPA analogs in brain. The stability and protonation constants of the complexes formed between the ligand [DTPA-(Me-Trp)(2)] and Gd(3+), Eu(3+), and Cu(2+) have been determined by pH potentiometry (Gd(3+), Eu(3+)) and spectrophotometry (Cu(2+)) at 25 °C and at constant ionic strength maintained by 0.10 M KCl. The kinetic inertness of Gd [DTPA-(Me-Trp)(2)] was characterized by the rates of exchange reactions with Zn(2+) and Eu(3+). In the Eu(3+) exchange, a second-order [H(+)] dependence was found for the pseudo-first-order rate constant [k(0) = (4.5 ± 1.2) × 10(-6)/s; k(1) = 0.58 ± 0.1 /M/s, k(2) = (6.6 ± 0.2) × 10(4) /M(2)/s, k(3) = (4.8 ± 0.8) × 10(-4) /M/s]. In the Eu(3+) exchange, at pH <5.0, the rate decreases with increasing concentration of the exchanging ion. At physiological pH, the kinetic inertness of [DTPA-(Me-Trp)(2)] is more inert than GdDTPA(2-), the most commonly used MRI contrast agent (t(1/2) = 127 h). High kinetic stability is an important requirement for the Gd complexes used as contrast enhancement agents in magnetic resonance imaging.

Polyethylene-glycolylated isoniazid conjugate for reduced toxicity and sustained release.

BACKGROUND: The antitubercular drug, isoniazid (INH), has been conjugated with a bifunctional polyethylene glycol derivative (MW 575) with the objective of designing a novel drug-delivery system that has reduced toxicity compared with the neat drug, without compromising its biological activity. The polyethylene glycol-bis(INH) conjugate was synthesized in high yield and was completely characterized by infrared, NMR and mass spectroscopies. RESULTS: This conjugate was labeled with a 99mTc radionuclide with less than 95% labeling efficiency. MTT assay revealed lower cytotoxicity of the conjugate compared with INH. Blood kinetics in rabbits and biodistribution in mice compared the blood retention of the drug and its polymer conjugate and their uptake in various organs, respectively. Biodistribution and gamma-scintigraphy in infection-induced animal models showed significantly high accumulation of the polymer-drug conjugate at the site of infection and retention for a long duration. CONCLUSION: This conjugate could prove to be a good lead molecule for infection diagnosis and therapy.

Comparative evaluation of glutamate-sensitive radiopharmaceuticals: Technetium-99m-glutamic acid and technetium-99m-diethylenetriaminepentaacetic acid-bis(glutamate) conjugate for tumor imaging.

Single-photon emission computed tomography has become a significant imaging modality with huge potential to visualize and provide information of anatomic dysfunctions that are predictive of future diseases. This imaging tool is complimented by radiopharmaceuticals/radiosubstrates that help in imaging specific physiological aspects of the human body. The present study was undertaken to explore the utility of technetium-99m (99(m)Tc)-labeled glutamate conjugates for tumor scintigraphy. As part of our efforts to further utilize the application of chelating agents, glutamic acid was conjugated with a multidentate ligand, diethylenetriaminepentaacetic acid (DTPA). The DTPA-glutamate conjugate [DTPA-bis(Glu)] was well characterized by IR, NMR, and mass spectroscopy. The biological activity of glutamic acid was compared with its DTPA conjugate by radiocomplexation with 99(m)Tc (labeling efficiency ≥98%). In vivo studies of both the radiolabeled complexes 99(m)Tc-Glu and 99(m)Tc-DTPA-bis(Glu) were then carried out, followed by gamma scintigraphy in New Zealand albino rabbits. Improved serum stability of 99(m)Tc-labeled DTPA conjugate indicated that 99(m)Tc remained bound to the conjugate up to 24 hours. Blood clearance showed a relatively slow washout of the DTPA conjugate when compared with the labeled glutamate. Biodistribution characteristics of the conjugate in Balb/c mice revealed that DTPA conjugation of glutamic acid favors less accumulation in the liver and bone and rapid renal clearance. Tumor scintigraphy in mice showed increasing tumor accumulation, stable up to 4 hours. These preliminary studies show that 99(m)Tc-DTPA-bis(Glu) can be a useful radiopharmaceutical for diagnostic applications in single-photon emission computed tomography imaging.

Design, synthesis, and fluorescence lifetime study of benzothiazole derivatives for imaging of amyloids.

The imaging of the distribution of ß-amyloid plaques in the brain is becoming an important diagnostic modality in Alzheimer's disease. The present study reports the synthesis of novel benzothiazole derivatives. The final products were characterized by spectral techniques such as FTIR, (1)H NMR, and electrospray ionization-mass spectrometry. The structure-activity relationship of these benzothiazole derivatives is also reported. The K(i) values of these derivatives were evaluated by competitive binding assay studies. The analogs were labeled with (99m)Tc for the potential diagnostic imaging of Alzheimer's disease using stannous chloride as a reducing agent. The radiochemical stability was found to be ≥ 90% for both the compounds and they were stable for 10-12 hours in human serum. Biodistribution studies of the (99m)Tc complex in normal mice were performed after intravenous injection through the tail vein. The data showed high initial brain uptakes at 2 minutes (2.2% ± 0.1% ID/g), and brain activities washed out to 0.3% ± 0.02% ID/g at 6 hours. In conclusion, benzothiazole derivatives showed excellent binding affinities for ß-amyloid aggregates and high initial brain uptakes in normal mice.