A novel liposomal formulation of flavopiridol

Evaluation of the antifungal properties of nanoliposomes containing rhinacanthin-C isolated from the leaves of Rhinacanthus nasutus

Fungal infections represent a challenging threat to the human health. Microsporum gypseum and Trichophyton rubrum are pathogenic fungi causing various topical mycoses in humans. The globally emerging issue of resistance to fungi demands the development of novel therapeutic strategies. In this context, the application of nanoliposomes as vehicles for carrying active therapeutic agents can be a suitable alternative. In this study, rhinacanthin-C was isolated from Rhinacanthus naustus and encapsulated in nano-liposomal formulations, which were prepared by the modified ethanol injection method. The two best formulations composed of soybean phosphatidylcholine (SPC), cholesterol (CHL), and tween 80 (T80) in a molar ratio of 1:1:0 (F1) and 1:1:0.5 (F2) were proceeded for experimentation. The physical characteristics and antifungal activities were performed and compared with solutions of rhinacanthin-C. The rhinacanthin-C encapsulating efficiencies in F1 and F2 were 94.69 ± 1.20% and 84.94 ± 1.32%, respectively. The particle sizes were found to be about 221.4 ± 13.76 nm (F1) and 115.8 ± 23.33 nm (F2), and zeta potential values of -38.16 mV (F1) and -40.98 mV (F2). Similarly, the stability studies of rhinacanthin-C in liposomes demonstrated that rhinacanthin-C in both formulations was more stable in mediums with pH of 4.0 and 6.6 than pure rhinacanthin-C when stored at the same conditions. Rhinacanthin-C in F1 was slightly more stable than F2 when stored in mediums with a pH of 10.0 after three months of storage. However, rhinacanthin-C in both formulations was less stable than pure rhinacanthin-C in a basic medium of pH 10.0. The antifungal potential was evaluated against M. gypsum and T. rubrum. The findings revealed a comparatively higher zone of inhibition for F1. In the MIC study, SPC: CHL: T80 showed higher inhibition against M. gypseum and a slightly higher inhibition against T. rubrum compared to free rhinacanthin-C solution. Moreover, rhinacanthin-C showed significant interaction against 14α-demethylase in in silico study. Overall, this study demonstrates that nanoliposomes containing rhinacanthin-C can improve the stability and antifungal potential of rhinacanthin-C with sustained and prolonged duration of action and could be a promising vehicle for delivery of active ingredients for targeting various fungal infections.

From co-delivery to synergistic anti-inflammatory effect: Studies on chitosan-stabilized Janus emulsions having chloroquine phosphate and flavopiridol in Complete Freund's Adjuvant induced arthritis rat model

For the first time, the co-delivery of chloroquine phosphate and flavopiridol by intra-articular route was achieved to provide local joint targeting in Complete Freund's Adjuvant-induced arthritis rat model. The presence of paired-bean structure onto the dispersed oil droplets of o/w nanosized emulsions allows efficient entrapment of two drugs (85.86-96.22 %). The dual drug-loaded emulsions displayed a differential in vitro drug release behavior, near normal cell viability in MTT assay, better cell uptake (internalization) and better reducing effect of mean immunofluorescence intensity of inflammatory proteins such as NF-κB and iNOS at in vitro RAW264.7 macrophage cell line. The radiographical study, ELISA test, RT-PCR study and H & E staining also indicated a reduction in joint tissue swelling, IL-6 and TNF-α levels diminution, fold change diminution in the mRNA expressions for NF-κB, IL-1β, IL-6 and PGE2 and maintenance of near normal histology at bone cartilage interface respectively. The results of metabolomic pathway analysis performed by LC-MS/MS method using the rat blood (plasma) collected from disease control and dual drug-loaded emulsions treatment groups revealed a new follow-up study to understand not only the disease progression but also the formulation therapeutic efficacy assessment.

The Pharmacological Implications of Flavopiridol: An Updated Overview

Flavopiridol is a flavone synthesized from the natural product rohitukine, which is derived from an Indian medicinal plant, namely Dysoxylum binectariferum Hiern. A deeper understanding of the biological mechanisms by which such molecules act may allow scientists to develop effective therapeutic strategies against a variety of life-threatening diseases, such as cancer, viruses, fungal infections, parasites, and neurodegenerative diseases. Mechanistic insight of flavopiridol reveals its potential for kinase inhibitory activity of CDKs (cyclin-dependent kinases) and other kinases, leading to the inhibition of various processes, including cell cycle progression, apoptosis, tumor proliferation, angiogenesis, tumor metastasis, and the inflammation process. The synthetic derivatives of flavopiridol have overcome a few demerits of its parent compound. Moreover, these derivatives have much improved CDK-inhibitory activity and therapeutic abilities for treating severe human diseases. It appears that flavopiridol has potential as a candidate for the formulation of an integrated strategy to combat and alleviate human diseases. This review article aims to unravel the potential therapeutic effectiveness of flavopiridol and its possible mechanism of action.

Multifunctional targetable liposomal drug delivery system in the management of leukemia: Potential, opportunities, and emerging strategies

The concern impeding the success of chemotherapy in leukemia treatment is descending efficacy of drugs because of multiple drug resistance (MDR). The previous failure of traditional treatment methods is primarily responsible for the present era of innovative agents to treat leukemia effectively. The treatment option is a chemotherapeutic agent in most available treatment strategies, which unfortunately leads to high unavoidable toxicities. As a result of the recent surge in marketed products, theranostic nanoparticles, i.e., multifunctional targetable liposomes (MFTL), have been approved for improved and more successful leukemia treatment that blends therapeutic and diagnostic characteristics. Since they broadly offer the required characteristics to get past the traditional/previous limitations, such as the absence of site-specific anti-cancer therapeutic delivery and ongoing real-time surveillance of the leukemia target sites while administering therapeutic activities. To prepare MFTL, suitable targeting ligands or tumor-specific antibodies are required to attach to the surface of the liposomes. This review exhaustively covered and summarized the liposomal-based formulation in leukemia treatment, emphasizing leukemia types; regulatory considerations, patents, and clinical portfolios to overcome clinical translation hurdles have all been explored.

Antineoplastic activity of biogenic silver and gold nanoparticles to combat leukemia: Beginning a new era in cancer theragnostic

The American Cancer Society estimated around 61,090 new cases of leukemia were diagnosed, and around 23,660 people died from this disease in the United States alone in 2021. Due to its burden on society, there is an unmet need to explore innovative approaches to overcome leukemia. Among different strategies that have been explored, nanotechnology appears to be a promising and effective approach for therapeutics. Specifically, biogenic silver and gold nanoparticles (NPs) have attracted significant attention for their antineoplastic activity toward leukemia cancer cells due to their unique physicochemical properties. Indeed, these nanostructures have emerged as useful approaches in anti-leukemic applications, either as carriers to enhance drug bioavailability and its targeted delivery to a specific organ or as a novel therapeutic agent. This review explores recent advances in green synthesized nanomaterials and their potential use against leukemia, especially focusing on silver (Ag) and gold (Au) nanostructures. In detail, we have reviewed various eco-friendly methods of bio-synthesized NPs, their analytical properties, and toxicity effects against leukemic models. This overview confirms the satisfactory potency of biogenic NPs toward leukemic cells and desirable safety profiles against human native cells, which opens a promising door toward commercializing these types of nontherapeutic agents if challenges involve clinical validations, reproducibility, and scalability could be resolved.

Development and characterization of a novel flavopiridol formulation for treatment of acute myeloid leukemia

For more than 30 years, treatment of acute myeloid leukemia (AML) has remained largely unchanged and reliant on chemotherapeutic drug combinations, specifically cytarabine and daunorubicin (the 7 + 3 regimen). One broad spectrum drug, flavopiridol (also known as Alvocidib) has shown significant activity against AML through the inhibition of cyclin-dependent kinases. Flavopiridol is a semisynthetic flavonoid and our research team recently described methods to formulate another flavonoid, quercetin, through the ability of flavonoids to bind divalent metals. This method relies on use of copper-containing liposomes to enhance the apparent solubility of flavopiridol and to create formulations suitable for intravenous (i.v.) use. Similar to quercetin, flavopiridol is defined as an aqueous-insoluble compound (< 1 mg/mL in water) and this research sought to evaluate whether the copper-binding capabilities of flavopiridol could be used to prepare an injectable formulation that would exhibit enhanced exposure and improved efficacy. Flavopiridol powder was added directly to preformed copper-containing liposomes (DSPC:Chol or DSPC:DSPE-PEG2000) and the resulting formulations were characterized. Pharmacokinetic and efficacy studies were then conducted. The liposomal flavopiridol formulations were well-tolerated in mice following i.v. administration at a dose of 5 mg/kg with no apparent acute or chronic toxicities. In vivo pharmacokinetics of the optimized DSPC/DSPE-PEG2000 liposomal flavopiridol formulation demonstrated a 30-fold increase in AUC (0.804 μg-hr/mL versus 26.92 μg-hr/mL) compared to the free flavopiridol formulation. The resultant liposomal formulation also demonstrated significant therapeutic activity in MV4-11 and MOLM-13 subcutaneous AML models. Additional studies will be required to define whether formulation changes can be made to enhance flavopiridol retention in the selected composition. The results suggest that further increases in flavopiridol retention will result in improved therapeutic activity.

Cell cycle inhibitors for the treatment of acute myeloid leukemia: a review of phase 2 & 3 clinical trials

Introduction: Acute myeloid leukemia (AML) is a clinically heterogeneous hematologic malignancy with poor long term outcomes. Cytotoxic chemotherapy remains the backbone of therapy especially among younger patients; however the effective incorporation of targeted therapies continues to be an area of active research in an effort to improve response durations and survival. Cell cycle inhibitors (CCI) are a novel class of agents which may be of particular interest for development in patients with AML. Areas covered: We will review the concept of CCIs along with available pre-clinical and clinical data in the treatment of AML both in North America and abroad. Specific drug targets reviewed include cyclin D kinase, Aurora kinase, CHK1, and WEE1. Expert opinion: Utilization of CCIs in patients with AML is an emerging approach that has shown promise in pre-clinical models. It has been challenging to translate this concept into clinical success thus far, due to marginal single-agent activity and significant toxicity profiles, however clinical evaluation is ongoing. Addition of these agents to cytotoxic chemotherapy and other targeted therapies provides a potential combinatorial path forward for this novel class of therapies. Developing optimal combinations while balancing toxicity are among the top clinical challenges that must be overcome before we can anticipate adoption of these agents into the armamentarium of AML therapy.

Research advances in nanomedicine, immunotherapy, and combination therapy for leukemia

In the past decade, clinical and laboratory studies have led to important new insights into the biology of leukemia and its treatment. This review describes the progress of leukemia research in the United States in recent years. Whereas the traditional method of treatment is chemotherapy, it is nonselective and could induce systemic toxicities. Thus, in parallel with research on new chemotherapies, great emphasis has been placed on developing immunotherapies. Here, we will review the current immunotherapies available in research and development that overcome current challenges, specifically looking in the field of chimeric antigen receptor T-cell (CAR-T) therapies, checkpoint inhibitors, and antibody-drug conjugates. With about 100 clinical trials for CAR-T therapies and 30 in checkpoint inhibitors for leukemia treatment, scientists are trying to make these technologies cheaper, faster, and more feasible. Further describing the delivery of these therapeutics, we look at the current progress, clinical, and preclinical status of nano-based medicines such as liposomes, polymeric micelles, and metal nanoparticles. Taking advantage of their physicochemical and biologic properties, nanoparticles have been shown to increase the efficacy of commonly administered chemotherapies with reduced adverse effects.

Photoactive Liposomal Formulation of PVP-Conjugated Chlorin e6 for Photodynamic Reduction of Atherosclerotic Plaque

Background: Liposomes serve as delivery systems for biologically active compounds. Existing technologies inefficiently encapsulate large hydrophilic macromolecules, such as PVP-conjugated chlorin e6 (Photolon). This photoactive drug has been widely tested for therapeutic applications, including photodynamic reduction of atherosclerotic plaque. Methods: A novel formulation of Photolon was produced using “gel hydration technology”. Its pharmacokinetics was tested in Sus scrofa f. domestica. Its cellular uptake, cytotoxicity, and ability to induce a phototoxic reaction were demonstrated in J774A.1, RAW264.7 macrophages, and vascular smooth muscle (T/G HA-VSMC) as well as in vascular endothelial (HUVEC) cells. Results: Developed liposomes had an average diameter of 124.7 ± 0.6 nm (polydispersity index (PDI) = 0.055) and contained >80% of Photolon). The half-life of formulation in S. scrofa was 20 min with area under the curve (AUC) equal to 14.7. The formulation was noncytotoxic in vitro and was rapidly (10 min) and efficiently accumulated by macrophages, but not T/G HA-VSMC or HUVEC. The accumulated quantity of photosensitizer was sufficient for induction of phototoxicity in J774A.1, but not in T/G HA-VSMC. Conclusions: Due to the excellent physical and pharmacokinetic properties and selectivity for macrophages, the novel liposomal formulation of Photolon is a promising therapeutic candidate for use in arteriosclerosis treatment when targeting macrophages but not accompanying vascular tissue is critical for effective and safe therapy.

Recent Treatment Advances and the Role of Nanotechnology, Combination Products, and Immunotherapy in Changing the Therapeutic Landscape of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia that is becoming more prevalent particularly in the older (65 years of age or older) population. For decades, "7 + 3" remission induction therapy with cytarabine and an anthracycline, followed by consolidation therapy, has been the standard of care treatment for AML. This stagnancy in AML treatment has resulted in less than ideal treatment outcomes for AML patients, especially for elderly patients and those with unfavourable profiles. Over the past two years, six new therapeutic agents have received regulatory approval, suggesting that a number of obstacles to treating AML have been addressed and the treatment landscape for AML is finally changing. This review outlines the challenges and obstacles in treating AML and highlights the advances in AML treatment made in recent years, including Vyxeos®, midostaurin, gemtuzumab ozogamicin, and venetoclax, with particular emphasis on combination treatment strategies. We also discuss the potential utility of new combination products such as one that we call "EnFlaM", which comprises an encapsulated nanoformulation of flavopiridol and mitoxantrone. Finally, we provide a review on the immunotherapeutic landscape of AML, discussing yet another angle through which novel treatments can be designed to further improve treatment outcomes for AML patients.

Novel SN38 derivative-based liposome as anticancer prodrug: an in vitro and in vivo study

Background

Many novel drug delivery systems have been extensively studied to exploit the full therapeutic potential of SN38, which is one of the most potent antitumor analogs of camptothecins (CPTs), whose clinical application is seriously hindered by poor water solubility, low plasmatic stability, and severe toxicity, but results are always unsatisfactory.

Methods

In this study, combining the advantages of prodrug and nanotechnology, a lipophilic prodrug of SN38, SN38-PA, was developed by conjugating palmitic acid to SN38 via ester bond at C₁₀ position, and then the lipophilic prodrug was encapsulated into a long-circulating liposomal carrier by film dispersion method.

Results

The SN38-PA liposomes were characterized as follows: an average particle size of 80.13 nm, an average zeta potential of -33.53 mv, and the entrapment efficiency of 99%. Compared with CPT-11, SN38-PA liposome was more stable in close lactone form, more efficient in conversion rate to SN38, and more potent in cytotoxicity against tumor cells. Pharmacokinetic study showed that SN38-PA liposome had significantly enhanced plasma half-life (t_1/2) value of SN38 and increased area under the curve (AUC) of SN38, which was 7.5-fold higher than that of CPT-11. Biodistribution study showed that SN38-PA liposome had more active metabolite SN38 in each tissue. Finally, the pharmacodynamic study showed that SN38-PA liposome had higher antitumor effect with the antitumor inhibition rate of 1.61 times than that of CPT-11.

Conclusion

These encouraging data merit further investigation on this novel SN38-PA liposome.

A novel nanoproliposomes of lercanidipine: Development, in vitro and preclinical studies to support its effectiveness in hypertension therapy

AIM

The aim of the present study was to develop nanoproliposomes of lercanidipine, in order to overcome its poor biopharmaceutical properties and to improve its therapeutic efficacy in treating hypertension.

MAIN METHODS

The nanoproliposomes were prepared using a modified thin-film hydration method, and the formula was optimized by varying the ratio of lipids and the types of cryoprotectants. This optimized formulation was characterized in terms of its particle size, solid-state, drug release, in-situ absorption, in-vivo pharmacokinetics, and in-vivo anti-hypertensive activity in DOCA-salt induced hypertensive rats. Finally, a PK-PD correlation was established in order to understand the clinical implications of the developed novel nanoproliposomes.

KEY FINDINGS

The nanoproliposomes showed a particle size of 174.7nm and an entrapment efficiency of 85.4%. The in-vitro release displayed initial rapid release (19.33%) followed by a sustained release profile, releasing 88.37% of the encapsulated drug. The in-situ studies showed a significant increase in absorption rate across the rat intestinal membrane. The pharmacokinetics of this novel form indicated a 2.75-fold increase in the absolute bioavailability as compared to pure lercanidipine. In addition, the nanoproliposomes were found to be efficient in treating hypertension in DOCA-salt induced hypertensive rats. The PK-PD correlation demonstrated no time lag between effect and exposure, indicating that a direct PK-PD relationship can be expected in the clinic.

SIGNIFICANCE

These findings suggest that nanoproliposomes are promising carriers in improving the oral bioavailability and bioactivity of lercanidipine, and can be an effective therapy in the management of hypertension.

Alvocidib (flavopiridol) for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Alvocidib, which has orphan drug designation in chronic lymphocytic leukemia (CLL) from the FDA and the EMA, is a plant-derived semisynthetic flavone that acts as a cyclin-dependent kinase inhibitor. It induces apoptosis in CLL cells in vitro and was introduced into clinical trials in CLL as an intravenous infusion in 1997, which proved disappointing. Since the drug avidly binds to plasma proteins, higher serum concentrations were required for clinical antileukemia activity than those suggested by in vitro studies. Subsequent studies utilizing bolus plus infusional doses revealed significant activity against CLL, even in patients with unfavorable characteristics. However, significant toxicity including high rates of major tumor lysis syndrome, cytokine release syndrome and secretory diarrhea were also observed.

AREAS COVERED

The chemistry, pharmacodynamics, pharmacokinetics and metabolism of alvocidib are briefly discussed and phase I-II studies in CLL are discussed in detail. To date, no phase III studies in CLL have been reported.

EXPERT OPINION

A number of much less toxic drugs with similar efficacy against CLL both with and without unfavorable cytogenetics have come to market. Furthermore, enthusiasm for the development of alvocidib as a single agent for the treatment of CLL has waned, primarily due to its toxicity.

PEGylated liposomes of anastrozole for long-term treatment of breast cancer: in vitro and in vivo evaluation

The aim of present study was to develop conventional and PEGylated (long circulating), liposomes containing anastrozole (ANS) for effective treatment of breast cancer. ANS is a third-generation non-steroidal aromatase inhibitor of the triazole class used for the treatment of advanced and late-stage breast cancer in post-menopausal women. Under such disease conditions the median duration of therapy should be prolonged until tumor regression ends (>31 months). Liposomes were prepared by the thin film hydration method by using ANS and various lipids such as soyaphosphatidyl choline, cholesterol and methoxy polyethylene glycol distearoyl ethanolamine in different concentration ratios and evaluated for physical characteristics, in vitro drug release and stability. Optimized formulations of liposome were studied for in vitro cytotoxic activity against the BT-549 and MCF-7 cell lines and in vivo behavior in Wistar rats. Preformulation studies, both Fourier transform infrared study and differential scanning calorimetry analysis showed no interaction between the drug and the excipients used in the formulations. The optimized formulations AL-07 and AL-09 liposomes showed encapsulation efficiencies in the range 65.12 ± 1.05% to 69.85 ± 3.2% with desired mean particle size distribution of 101.1 ± 5.9 and 120.2 ± 2.8 nm and zeta potentials of -43.7 ± 4.7 and -62.9 ± 3.5 mV. All the optimized formulations followed Higuchi-matrix release kinetics and when plotted in accordance with the Korsemeyer-Peppas method, the n-value 0.5 < n < 1.0 suggests an anomalous (non-Fickian) transport. Likewise, the PEGylated liposomes showed greater tumor growth inhibition on BT-549 and MCF-7 cell lines from in vitro cytotoxicity studies (p < 0.05). Pharmacokinetic study of conventional and PEGylated liposomes in Wistar rats demonstrated a 3.33- and 20.28-fold increase in AUC(0-∞) values when compared to pure drug (p < 0.001). Among the formulations, PEGylated liposomes showed encouraging results by way of their long circulation and sustained delivery properties for effective treatment of breast cancer.

Effects of triglycerides on the hydrophobic drug loading capacity of saturated phosphatidylcholine-based liposomes

A high drug-loading capacity is a critical factor for the clinical development of liposomal formulations. The accommodation of hydrophobic drugs within the liposomal membrane is often limited in saturated phosphatidylcholine (PC)-based liposomes owing to the rigidity of the lipid acyl chain. In the current study, we explored the possibility of improving the hydrophobic drug loading capacity of liposomes by incorporating triglyceride into liposomal membranes. Incorporation of Captex 300, a medium chain triglyceride, into liposomes composed of dimyristoylphosphatidylcholine and cholesterol greatly increased the fluidity and lamellarity of the resultant liposomes. Liposomal incorporation of medium or long chain, but not short chain, triglycerides greatly enhanced the concentration of loaded paclitaxel (PTX) in saturated PC-based liposomes. The enhancing effect of triglyceride saturated at a triglyceride content corresponding to the amount required to fluidize the liposome structure. In addition, the enhancing effect was not observed in unsaturated PC-based liposomes and was not associated with the solubility of PTX in each triglyceride. Triglycerides also enhanced the loading of docetaxel, another hydrophobic drug. Taken together, our results suggest that triglyceride incorporation in saturated PC-based liposomes provide an improved dosage form that enables increased hydrophobic drug loading by altering the fluidity and structure of liposomal membranes.

A novel liposomal formulation of FTY720 (fingolimod) for promising enhanced targeted delivery

We describe here the development and characterization of the physicochemical and pharmacokinetic properties of a novel liposomal formulation for FTY720 delivery, LP-FTY720. The mean diameter of LP-FTY720 was ~157 nm, and the FTY720 entrapment efficiency was ~85%. The liposomal formulation protected FTY720 from degradation in aqueous buffer and showed toxicity in CLL patient B cells comparable to that of free FTY720. Following intravenous injection in ICR mice, LP-FTY720 had an increased elimination phase half-life (~28 vs. ~19 hr) and decreased clearance (235 vs. 778 mL/h/kg) compared to the free drug. Antibodies against CD19, CD20 and CD37 were incorporated into LP-FTY720, which provided targeted delivery to CLL patient B cells and thus achieved higher killing efficacy. The novel liposomal carrier of FTY720 demonstrated improved pharmacokinetic properties, comparable activity, and a potential platform for targeted delivery to CLL by overcoming the limited application of free FTY720 to B malignancy treatment.

FROM THE CLINICAL EDITOR

This team reports on a novel liposomal formulation for FTY720 delivery, demonstrating improved pharmacokinetic properties, comparable activity, and a potential platform for targeted delivery to CLL using antibodies incorporated in the liposomes. The method expected to overcome the limited application of free FTY720 to B malignancy treatment.

Emerging drug profile: cyclin-dependent kinase inhibitors

Abstract As the rational application of targeted therapies in cancer supplants traditional cytotoxic chemotherapy, there is an ever-greater need for a thorough understanding of the complex machinery of the cell and an application of this knowledge to the development of novel therapeutics and combinations of agents. Here, we review the current state of knowledge of the class of targeted agents known as cyclin-dependent kinase (CDK) inhibitors, with a focus on chronic lymphocytic leukemia (CLL). Flavopiridol (alvocidib) is the best studied of the CDK inhibitors, producing a dramatic cytotoxic effect in vitro and in vivo, with the principal limiting factor of acute tumor lysis. Unfortunately, flavopiridol has a narrow therapeutic window and is relatively non-selective with several off-target (i.e. non-CDK) effects, which prompted development of the second-generation CDK inhibitor dinaciclib. Dinaciclib appears to be both more potent and selective than flavopiridol, with at least an order of magnitude greater therapeutic index, and is currently in phase III clinical trials. In additional to flavopiridol and dinaciclib, we also review the current status of other members of this class, and provide commentary as to the future direction of combination therapy including CDK inhibitors.

Improved pharmacokinetics and reduced toxicity of brucine after encapsulation into stealth liposomes: role of phosphatidylcholine

OBJECTIVE

Brucine was encapsulated into stealth liposomes using the ammonium sulfate gradient method to improve therapeutic index.

MATERIALS AND METHODS

Four brucine stealth liposomal formulations were prepared, which were made from different phosphatidylcholines (PCs) with different phase transition temperatures (T(m)). The PCs used were soy phosphatidylcholine (SPC), dipalmitoyl phosphatidylcholine (DPPC), hydrogenated soy phosphatidylcholine (HSPC), and distearoyl phosphatidylcholine (DSPC). The stabilities, pharmacokinetics, and toxicities of these liposomal formulations were evaluated and compared.

RESULTS

Size, zeta potential, and entrapment efficiency of brucine-loaded stealth liposomes (BSL) were not influenced by PC composition. In vitro release studies revealed that drug release rate increased with decreased T(m) of PCs, especially with the presence of rat plasma. After intravenous administration, the area under the curve (AUC) values of BSL-SPC, BSL-DPPC, BSL-HSPC, and BSL-DSPC in plasma were 7.71, 9.24, 53.83, and 56.83-fold as large as that of free brucine, respectively. The LD(50) values of brucine solution, BSL-SPC, BSL-DPPC, BSL-HSPC, and BSL-DSPC following intravenous injection were 13.17, 37.30, 37.69, 51.18, and 52.86 mg/kg, respectively. It was found in calcein retention experiments that the order of calcein retention in rat plasma was SPC < DPPC << HSPC < DSPC stealth liposomes.

CONCLUSION

PC composition could exert significant influence on the stabilities, pharmacokinetics, and toxicities of brucine-loaded stealth liposomes. DSPC or HSPC with T(m) above 50°C should be used to prepare the stealth liposomal formulation for the intravenous delivery of brucine. However, it was found in the present paper that the pharmacokinetics and toxicity of BSL were not influenced by the PC composition when the T(m) of the PC was in the range of -20°C to 41°C.

Improvement of drug safety by the use of lipid-based nanocarriers

Drug toxicity is an important factor that contributes significantly to adverse drug events in current healthcare practice. Application of lipid-based nanocarriers in drug formulation is one approach to improve drug safety. Lipid-based delivery systems include micelles, liposomes, solid lipid nanoparticles, nanoemulsions and nanosuspensions. These carriers are generally composed of physiological lipids well tolerated by human body. Delivery of water-insoluble drugs in these formulations increases their solubility and stability in aqueous media and eliminates the need for toxic co-solvents or pH adjustment to solubilize hydrophobic drugs. Association or encapsulation of peptides/proteins within lipid-based carriers protects the labile biologics against enzymatic degradation, hence reducing the therapeutic dose required and risk of dose-dependent toxicity. Most importantly, lipid-based nanocarriers alter the pharmacokinetics and biodistribution of drugs through passive and active targeting, leading to increased drug accumulation at target sites while significantly decreasing non-specific distribution to other tissues. Furthermore, surface modification of these nanocarriers reduces immunogenicity of drug-carrier complexes, imparts stealth by preventing opsonization and removal by phagocytes and minimizes interaction with circulating blood components. In view of heightening attention on drug safety in patient treatment, lipid-based nanocarrier is therefore an important and promising option for formulation of pharmaceutical products to improve treatment safety and efficacy.

The impact of multi-targeted cyclin-dependent kinase inhibition in breast cancer cells: clinical implications

INTRODUCTION

The progression of the mammalian cell cycle is driven by the transient activation of complexes consisting of cyclins and cyclin-dependent kinases (CDKs). Loss of control over the cell cycle results in accelerated cell division and malignant transformation and can be caused by the upregulation of cyclins, the aberrant activation of CDKs or the inactivation of cellular CDK inhibitors. For these reasons, cell cycle regulators are regarded as very promising therapeutic targets for the treatment of human malignancies.

AREAS COVERED

This review covers the structures and anti-breast cancer activity of selected pharmacological pan-specific CDK inhibitors. Multi-targeted CDK inhibitors affect CDKs involved in the regulation of both cell cycle progression and transcriptional control. The inhibition of CDK7/CDK9 has a serious impact on the activity of RNA polymerase II; when its carboxy-terminal domain is unphosphorylated, it is unable to recruit the cofactors required for transcriptional elongation, resulting in a global transcriptional block. Multi-targeted inhibition of CDKs represses anti-apoptotic proteins and thus promotes the induction of apoptosis. Moreover, the inhibition of CDK7 in estrogen receptor (ER)-positive breast cancer cells prevents activating phosphorylation of ER-α.

EXPERT OPINION

These diverse modes of action make multi-targeted CDK inhibitors promising drugs for the treatment of breast cancers.

Effect of liposomal celecoxib on proliferation of colon cancer cell and inhibition of DMBA-induced tumor in rat model

Celecoxib, a selective cyclooxygenase-2 inhibitor, has shown potential anticancerous activity against majority of solid tumors especially on patients with colon cancer. However, associations of serious side effects limit the usage of celecoxib in colon cancer treatment. To address this issue and provide an alternative strategy to increase the efficacy of celecoxib, liposomal formulation of celecoxib was prepared and characterized. Anticancer activity of liposomal celecoxib on colon cancer cell HCT 15 was evaluated in vitro. Furthermore, tumor inhibition efficiency by liposomal celecoxib was studied on 7,12-dimethyl benz(a)anthracene (DMBA)-induced tumor in rat model. In order to elucidate the antioxidant activity of celecoxib-loaded liposomes, antioxidant superoxide dismutase (SOD) generation and lipid peroxide (LPx) formation in both liver and kidney tissues were examined. Characterization of the formed unilamellar liposomes revealed the formation of homogeneous suspension of neutral (empty) or anionic (celecoxib-loaded) liposomes with a well-defined spherical shape which have a mean size of 103.5 nm (empty liposome) and 169 nm (liposomal celecoxib). High-performance liquid chromatography (HPLC) analysis and hemolytic assay demonstrated 46% of celecoxib entrapment efficiency and significantly low hemolysis, respectively. Liposomal celecoxib exhibited dose-dependent cytotoxicity and apoptotic activity against HCT 15 cells which are comparable to free celecoxib. In vivo study demonstrated inhibition of tumor growth. Biochemical analysis of the liposomal celecoxib-treated group significantly inhibited the LPx formation (oxygen-free radicals) and increased the activity of SOD. Our results present the potential of inhibiting colon cancer in vitro and DMBA-induced tumor in rat model in vivo by liposomal celecoxib.

Ethanol injection method for hydrophilic and lipophilic drug-loaded liposome preparation

In this article, a hydrophobic (beclomethasone dipropionate; BDP) and a hydrophilic (cytarabine; Ara-C) drugs have been encapsulated in liposomes in order to be administered via the pulmonary route. For this aim, a liposome preparation method, which is easy to scale up, the ethanol injection method, has been selected. The effects of critical process and formulation parameters have been investigated. The drug-loaded liposomes were prepared and characterized in terms of size, zeta potential, encapsulation efficiency, release study, cell uptake, and aerodynamic behavior. Small multilamellar vesicles, with sizes ranging from about 80 to 170 nm, were successfully obtained. Results indicated a significant influence of phospholipid and cholesterol amounts on liposome size and encapsulation efficiency. The higher encapsulation efficiencies were about 100% for the hydrophobic drug (BDP) and about 16% for the hydrophilic one (Ara-C). The in vitro release study showed a prolonged release profile for BDP, in contrast with Ara-C, which was released more rapidly. The cell-uptake test revealed that fluorescent liposomes have been well internalized into the cytoplasm of SW-1573 human lung carcinoma cells, confirming the possibility to use liposomes for lung cell targeting. Nebulized Ara-C and BDP liposomes presented aerodynamic diameters compatible with deep lung deposition. In conclusion, the elaborated liposomes seem to be promising carriers for both Ara-C and BDP pulmonary delivery.

Flavopiridol in chronic lymphocytic leukemia: a concise review

Patients with chronic lymphocytic leukemia (CLL) with high-risk cytogenetic features such as del(17p13) have limited treatment options and decreased overall survival. Dysfunction of p53 leads to resistance to fludarabine-based therapies. Cyclin-dependent kinase inhibitors (CDKi) are a novel class of agents that induce apoptosis in CLL cells independent of p53 mutational status. The synthetic flavone flavopiridol demonstrated promising in vitro activity in CLL. In initial phase I studies using a continuous infusion dosing schedule in a variety of malignancies, no clinical activity was observed. Detailed pharmacokinetic modeling led to the development of a novel dosing schedule designed to achieve target drug concentrations in vivo. In phase I testing, this dosing schedule resulted in acute tumor lysis syndrome (TLS) as the dose-limiting toxicity. With the implementation of a standardized protocol to prevent severe TLS, flavopiridol was administered safely, and responses were observed in heavily pretreated, fludarabine-refractory patients, cytogenetically high-risk patients, and patients with bulky lymphadenopathy. In a pharmacokinetic analysis, flavopiridol area under the plasma concentration-time curve (AUC) correlated with clinical response and cytokine release syndrome. Phase II studies are under way with encouraging preliminary results. Flavopiridol is currently under active investigation in combination with other agents and as a means to eradicate minimal residual disease in patients following cytoreductive chemotherapy. Several other investigational CDKi in preclinical and early clinical development are briefly discussed in this review.

Novel potent pharmacological cyclin-dependent kinase inhibitors

Progression of the cell cycle is controlled by various activating and inhibiting cellular factors. The subtle balance between these counteracting regulators in normal cells ensures proper cell cycle progression and facilitates cellular responses to a variety of stress stimuli. Key activators include cyclin-dependent kinases (CDKs) and, consequently, loss or inactivation of CDK inhibitors contributes to the escape of cancer cells from cell cycle control and hyperactivation of CDKs occurs in various neurodegenerative disorders. However, these adverse effects may be compensated by pharmacological counterparts. Inhibitors of CDKs representing various classes of compounds with diverse CDK inhibitory patterns have been developed, but inhibitors that have high selectivity and offer highly targeted activity against both cell cycle and transcriptional CDKs are of particular interest. This review focuses on pharmacological CDK inhibitors that have entered clinical trials and some compounds that have been evaluated preclinically. Recent discoveries in cell cycle regulation have provided rationales for clinical applications of CDK inhibitors in both monotherapeutic and combined therapeutic regimens.

Development of cell-cycle inhibitors for cancer therapy

The cell cycle governs the transition from quiescence through cell growth to proliferation. The key parts of the cell cycle machinery are the cyclin-dependent kinases (CDKS) and the regulatory proteins called cyclins. The CDKS are rational targets for cancer therapy because their expression in cancer cells is often aberrant and their inhibition can induce cell death. Inhibitors of CDKS can also block transcription.Several drugs targeting the cell cycle have entered clinical trials. These agents include flavopiridol, indisulam, AZD5438, SNS-032, bryostatin-1, seliciclib, PD 0332991, and SCH 727965. Phase i studies have demonstrated that these drugs can generally be administered safely. Phase ii studies have shown little single-agent activity in solid tumors, but combination studies with cytotoxic chemotherapy have been more promising. In hematologic malignancies, reports have shown encouraging single-agent and combination activity. Pharmacodynamic studies show that the dose and schedule of these drugs are crucial to permit maximum therapeutic effect.