Paclitaxel esters of malic acid as prodrugs with improved water solubility

Controllable release of self-assembled reduction-sensitive paclitaxel dimer prodrug and tetrandrine nanoparticles promotes synergistic therapy against multidrug-resistant cancer

BACKGROUND

Multidrug resistance (MDR) is the main reason for chemotherapy failure. Nanocarriers combined delivery of anti-cancer drugs and MDR inhibitors is an effective strategy to avoid MDR and improve the anti-cancer activity of drugs.

METHODS

Two paclitaxel (PTX) molecules are linked by disulfide bonds into PTX₂. Then, the PTX₂ and tetrandrine (TET) are coated together by mPEG-PLGA self-assembled NPs for combinational treatment. Microstructure, physiological stability, and cytotoxicity are characterized for the co-loaded NPs.

RESULTS

The NPs exhibit excellent suitability and blood safety for intravenous injection, specifically responsive to pH 6-7, and promptly initiate chemical degradation. Ex vivo fluorescence microscopy image studies indicate that co-loaded NPs increase drug penetration into cancer cells compared with free drugs. MTT assay demonstrates that co-loaded NPs have higher cytotoxicity against HeLa and the flow cytometric analysis shows that co-loaded NPs trigger more apoptosis than the free drugs. Reactive oxygen species (ROS) assay indicates that the drug-loaded NPs generated higher levels of ROS to accelerate apoptosis in HeLa cells.

CONCLUSIONS

TET can get desirable effects of inhibiting the MDR in advance by binding with the active site on P-gp, then the disulfide bond of PTX₂ is broken by glutathione (GSH) in cancer cells and decomposed into PTX to inhibit cancer cell proliferation.

GENERAL SIGNIFICANCE

Our studies indicate that the co-loaded NPs can potentially overcome the MDR of conventional chemotherapeutic agents.

Design, Synthesis, and Characterization of a Paclitaxel Formulation Activated by Extracellular MMP9

The concept of triggered drug release offers a possibility to overcome the toxic side effects of chemotherapeutics in cancer treatment by reducing systemic exposure to the active drug. In the present work, the concept foresees the use of the extracellular enzyme MMP9 as an enzymatic trigger for drug release in the proximity of tumor cells.

METHODS

A paclitaxel-hemisuccinate-peptide conjugate as a building block for self-assembling nanoparticles was synthesized using standard conjugation approaches. The building block was purified via preparative HPLC and analyzed by LC-MS. Nanoparticles were formed using the nanoprecipitation method and characterized. For selection of a suitable in vitro model system, common bioanalytical methods were used to determine mRNA expression, enzyme amount, and activity of MMP9.

RESULTS

The MMP9-labile prodrug was synthesized and characterized. Nanoparticles were formed out of MMP9-labile conjugate-building blocks. The nanoparticle's diameter averaged at around 120 nm and presented a spherical shape. LN-18 cells, a glioblastoma multiforme derived cell line, were chosen as an in vitro model based on findings in cancer tissue and cell line characterization. The prodrug showed cytotoxicity in LN-18 cells, which was reduced by addition of an MMP9 inhibitor.

CONCLUSION

taken together, we confirmed increased MMP9 in several cancer tissues (cervical, esophageal, lung, and brain) compared to healthy tissue and showed the effectiveness of MMP9-labile prodrug in in vitro tests.

Conjugation of Paclitaxel to Hybrid Peptide Carrier and Biological Evaluation in Jurkat and A549 Cancer Cell Lines

Paclitaxel (PTX) is one of the most potent cancer drugs; however, its low solubility and strong systemic side effects limit its clinical applications. To overcome these issues, new drug formulations and chemical modifications have been proposed. In this study, we present conjugation of PTX to hybrid collagen-cell penetrating peptide (COL-CPP) carriers. The peptide carrier is highly soluble and utilizes a unique stabilization strategy: folding into a triple helix. Here, we report the formation of PTX-COL-CPP prodrug that has similar drug potency as free PTX when tested in Jurkat (human T lymphocyte of acute T cell leukemia) cells but not in A549 (human epithelial of lung carcinoma) cells. Confocal images and flow cytometry show that this behavior originates from lower cellular uptake of COL-CPP and endosomal entrapment of the prodrug in A549, but not in Jurkat cells.

Self-assembly of glutamic acid linked paclitaxel dimers into nanoparticles for chemotherapy

In this work, a glutamic acid linked paclitaxel (PTX) dimer (Glu-PTX₂) with high PTX content of 88.9wt% was designed and synthesized. Glu-PTX₂ could self-assemble into nanoparticles (Glu-PTX₂ NPs) in aqueous solution to increase the water solubility of PTX. Glu-PTX₂ NPs were characterized by electron microscopy and dynamic light scattering, exhibiting spherical morphology and favorable structural stability in aqueous media. Glu-PTX₂ NPs could be internalized by cancer cells as revealed by confocal laser scanning microscopy and exert potent cytotoxicity. It is envisaged that Glu-PTX₂ NPs would be an alternative formulation for PTX, and such amino acid linked drug dimers could also be applied to other therapeutic agents.

Nanoprodrug of retinoic acid-modified paclitaxel

A nanoprodrug with high content (75%) and increased water solubility of paclitaxel was prepared from retinoic acid-modified paclitaxel.

Advances in oral delivery of anti-cancer prodrugs

INTRODUCTION

Most anticancer drugs have poor aqueous solubility and low permeability across the gastrointestinal tract. Furthermore, extensive efflux by P-glycoproteins (P-gp) in the small intestine also limits the efficient delivery of anticancer drugs via oral route. Area covered: This review explores the prodrug strategy for oral delivery of anticancer drugs. Different categories of oral anticancer prodrugs along with recent clinical studies have been comprehensively reviewed here. Furthermore, novel anticancer prodrugs such as polymer-prodrugs and lipid-prodrugs have been discussed in detail. Finally, various nanocarrier-based approaches employed for oral delivery of anticancer prodrugs have also been discussed. Expert opinion: Premature degradation of anticancer prodrugs in the gastrointestinal tract could lead to variable pharmacokinetics and undesired toxicity. Despite their increased aqueous solubility, the oral bioavailability of several anticancer prodrugs are limited by their poor permeability across the gastrointestinal tract. These limitations can be overcome by the use of functional excipients (polymers, lipids, amino acids/dipeptides), which are specifically absorbed via transporters and receptor-mediated endocytosis. Oral delivery of anticancer prodrugs using nanocarrier-based drug delivery system is a recent development; however it should be justified based on the comparative advantages of encapsulating prodrug in a nanocarrier versus the use of anticancer prodrug molecule itself.

Design, synthesis, and evaluation of water-soluble morpholino-decorated paclitaxel prodrugs with remarkably decreased toxicity

Novel water-soluble paclitaxel prodrugs were designed and synthesized by introducing morpholino groups through different linkers. These derivatives showed 400-20,000-times greater water solubility than paclitaxel as well as comparable activity in MCF-7 and HeLa cell lines. The prodrug PM4 was tested in the S-180 tumor mouse model, with paclitaxel as the positive control. The results showed that PM4 had comparable antitumor activity as paclitaxel, with tumor inhibition of 54% versus 56%, and remarkably decreased toxicity. The survival rate of treated mice was 8/8 in the PM4 group, compared to 3/8 in the paclitaxel group.

Prodrug Strategies for Paclitaxel

Paclitaxel is an anti-tumor agent with remarkable anti-tumor activity and wide clinical uses. However, it is also faced with various challenges especially for its poor water solubility and low selectivity for the target. To overcome these disadvantages of paclitaxel, approaches using small molecule modifications and macromolecule modifications have been developed by many research groups from all over the world. In this review, we discuss the different strategies especially prodrug strategies that are currently used to make paclitaxel more effective.

A mechanically interlocked molecular system programmed for the delivery of an anticancer drug

The development of mechanically interlocked molecular systems programmed to operate autonomously in biological environments is an emerging field of research with potential medicinal applications.

The development of mechanically interlocked molecular systems programmed to operate autonomously in biological environments is an emerging field of research with potential medicinal applications. Within this framework, functional rotaxane- and pseudorotaxane-based architectures are starting to attract interest for the delivery of anticancer drugs, with the ultimate goal to improve the efficiency of cancer chemotherapy. Here, we report an enzyme-sensitive [2]-rotaxane designed to release a potent anticancer drug within tumor cells. The molecular device includes a protective ring that prevents the premature liberation of the drug in plasma. However, once located inside cancer cells the [2]-rotaxane leads to the release of the drug through the controlled disassembly of the mechanically interlocked components, in response to a determined sequence of two distinct enzymatic activations. Furthermore, in vitro biological evaluations reveal that this biocompatible functional system exhibits a noticeable level of selectivity for cancer cells overexpressing β-galactosidase.

Well-defined diblock brush polymer–drug conjugates for sustained delivery of paclitaxel

The synthesis, characterization and property studies of paclitaxel (PTXL)-containing brush polymer–drug conjugates (BPDCs) are presented and the influence of grafting structures of BPDCs on their assembly behaviour, drug release profile and therapeutic effects is discussed in this article.

Water-soluble prodrugs of paclitaxel containing self-immolative disulfide linkers

A new series of disulfide-containing prodrugs of paclitaxel were designed, synthesized and evaluated against 6 cancer cell lines. Some of these prodrugs exhibited nearly equal or slightly better anticancer activity when compared to that of paclitaxel. These prodrugs contain water-soluble groups such as amino, carboxyl, hydroxyl, amino acids, etc., and exhibited 6-140 fold increase in aqueous solubility when compared to paclitaxel. One of these prodrugs exhibited improved water solubility, better in vitro anticancer activity and significantly superior oral bioavailability in mice when compared to those of paclitaxel. Thus, we have identified a very promising lead compound for further optimization and evaluation as a potentially bioavailable water-soluble prodrug of paclitaxel.

Poly(ethylene oxide)-block-polyphosphoester-graft-paclitaxel conjugates with acid-labile linkages as a pH-sensitive and functional nanoscopic platform for paclitaxel delivery

There has been an increasing interest to develop new types of stimuli-responsive drug delivery vehicles with high drug loading and controlled release properties for chemotherapeutics. An acid-labile poly(ethylene oxide)-block-polyphosphoester-graft-PTX drug conjugate (PEO-b-PPE-g-PTX G2) degradable, polymeric paclitaxel (PTX) conjugate containing ultra-high levels of PTX loading is improved significantly, in this second-generation development, which involves connection of each PTX molecule to the polymer backbone via a pH-sensitive β-thiopropionate linkage. The PEO-b-PPE-g-PTX G2 forms well-defined nanoparticles in an aqueous solution, by direct dissolution into water, with a number-averaged hydrodynamic diameter of 114 ± 31 nm, and exhibits a PTX loading capacity as high as 53 wt%, with a maximum PTX concentration of 0.68 mg mL(-1) in water (vs 1.7 μg mL(-1) for free PTX). The PEO-b-PPE-g-PTX G2 shows accelerated drug release under acidic conditions (≈50 wt% PTX released in 8 d) compared with neutral conditions (≈20 wt% PTX released in 8 d). Compared to previously reported polyphosphoester-based PTX drug conjugates, PEO-b-PPE-g-PTX G1 without the β-thiopropionate linker, the PEO-b-PPE-g-PTX G2 shows pH-triggered drug release property and 5- to 8-fold enhanced in vitro cytotoxicity against two cancer cell lines.

Synthesis and cytotoxicity evaluation of oleanolic acid derivatives

Twelve derivatives of oleanolic acid (1) have been synthesized and evaluated for their inhibitory activities against the growth of prostate PC3, breast MCF-7, lung A549, and gastric BGC-823 cancer cells by MTT assays. Within these series of derivatives, compound 17 exhibited the most potent cytotoxicity against PC3 cell line (IC50=0.39 μM) and compound 28 displayed the best activity against A549 cell line (IC50=0.22 μM). SAR analysis indicates that H-donor substitution at C-3 position of oleanolic acid may be advantageous for improvement of cytotoxicity against PC3, A549 and MCF-7 cell lines.

Well-defined degradable brush polymer-drug conjugates for sustained delivery of Paclitaxel

To achieve a conjugated drug delivery system with high drug loading but minimal long-term side effects, a degradable brush polymer-drug conjugate (BPDC) was synthesized through azide-alkyne click reaction of acetylene-functionalized polylactide (PLA) with azide-functionalized paclitaxel (PTXL) and poly(ethylene glycol) (PEG). Well-controlled structures of the resulting BPDC and its precursors were verified by (1)H NMR and gel permeation chromatography (GPC) characterizations. With nearly quantitative click efficiency, drug loading amount of the BPDC reached 23.2 wt %. Both dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM) imaging indicated that the BPDC had a nanoscopic size around 10-30 nm. The significant hydrolytic degradability of the PLA backbone of the BPDC was confirmed by GPC analysis of its incubated solution. Drug release study showed that PTXL moieties can be released through the cleavage of the hydrolyzable conjugation linkage in pH 7.4 at 37 °C, with 50% release in about 22 h. As illustrated by cytotoxicity study, while the polymeric scaffold of the BPDC is nontoxic, the BPDC exhibited higher therapeutic efficacy toward MCF-7 cancer cells than free PTXL at 0.1 and 1 μg/mL. Using Nile red as encapsulated fluorescence probe, cell uptake study showed effective internalization of the BPDC into the cells.

Analogue-based drug discovery: Contributions to medicinal chemistry principles and drug design strategies. Microtubule stabilizers as a case in point (Special Topic Article)

The benefits of utilizing marketed drugs as starting points to discover new therapeutic agents have been well documented within the IUPAC series of books that bear the title Analogue-based Drug Discovery (ABDD). Not as clearly demonstrated, however, is that ABDD also contributes to the elaboration of new basic principles and alternative drug design strategies that are useful to the field of medicinal chemistry in general. After reviewing the ABDD programs that have evolved around the area of microtubule-stabilizing chemo-therapeutic agents, the present article delineates the associated research activities that additionally contributed to general strategies that can be useful for prodrug design, identifying pharmacophores, circumventing multidrug resistance (MDR), and achieving targeted drug distribution.

pH-Sensitive brush polymer-drug conjugates by ring-opening metathesis copolymerization

Representing a new category of polymer-drug conjugates, brush polymer-drug conjugates were prepared by ring-opening metathesis copolymerization. Following judicious structural design, these conjugates exhibited well-shielded drug moieties, significant water solubility, well-defined nanostructures, and acid-triggered drug release.

Enhancement of docetaxel solubility via conjugation of formulation-compatible moieties

Computer-based theoretical calculations were employed to direct the design of docetaxel conjugates with enhanced solubility in the internal phase of a nano-emulsion formulation. The theoretically-identified optimal docetaxel conjugates were synthesized by direct attachment of lauroyl moieties through an ester linkage to docetaxel. In comparison to docetaxel, the conjugates exhibited significantly improved solubility in oil, as predicted by our theoretical calculations. This contributed to high drug entrapment efficiencies (up to 97%) and a high drug loading capacity (5.7% w/w) for the docetaxel conjugates. The mono-substitution of an acyl group at C-2' of docetaxel resulted in a conjugate with 37- to 46-fold lower cytotoxicity than that of the parent drug in two human cancer cell lines. Importantly, the activity exerted by the mono-substituted docetaxel on the cancer cells was due in part to the cytotoxicity of the parent drug that was released via hydrolysis of the ester bond between the lauroyl moiety and the drug under biologically relevant conditions. In contrast, di- and tri-substitution of acyl groups at C-2', C-7 and/or C-10 of docetaxel resulted in non-hydrolysable conjugates that were found to be inactive. Overall, our results show that computer-based theoretical calculation is a promising strategy for guiding the enhancement of material-drug compatibility in formulation development. Also, these studies confirm that chemical modification of docetaxel for enhancement of material-drug compatibility should be limited to mono-substitution at C-2' and result in a prodrug that is hydrolysable at a moderate rate under biologically relevant conditions.

In vivo antitumor activity of novel water-soluble taxoids

The antitumor activity of newly developed taxoids possessing a sugar moiety (glucose, galactose or mannose) to improve water solubility was evaluated. Galactose-bound taxoid (10-alpha-GAG-DT) proved superior to all other taxoids in both water solubility and antitumor activity. Therapeutic efficacy of 10-alpha-GAG-DT in terms of in vivo antitumor activity was found to be approximately equivalent to that of docetaxel, which is known to be superior to that of paclitaxel. The observation that the sugar moiety was gradually hydrolyzed in serum to release docetaxel indicates that 10-alpha-GAG-DT acts as a prodrug.

Synthesis and evaluation of water-soluble docetaxel prodrugs-docetaxel esters of malic acid

The synthesis of docetaxel esters of malic acid is described. These compounds were found to have greatly improved water solubility and are stable in solution at neutral pH. The C2' modified compounds 2a-c and 3a-c behave as prodrugs, that is, docetaxel is generated upon exposure to human plasma, whereas the C7 and C2',7,10- l modified derivatives do not. 2'-dl-Malyl docetaxel sodium salt demonstrated enhanced antitumor activity in vitro when compared to docetaxel and showed the inhibitory effect on tumor growth in vivo.

Improved biochemical strategies for targeted delivery of taxoids

Paclitaxel (Taxol) and docetaxel (Taxotere) are very important anti-tumor drugs in clinical use for cancer. However, their clinical utility is limited due to systemic toxicity, low solubility and inactivity against drug resistant tumors. To improve chemotherapeutic levels of these drugs, it would be highly desirable to design strategies which bypass the above limitations. In this respect various prodrug and drug targeting strategies have been envisioned either to improve oral bioavailability or tumor specific delivery of taxoids. Abnormal properties of cancer cells with respect to normal cells have guided in designing of these protocols. This review article records the designed biochemical strategies and their biological efficacies as potential taxoid chemotherapeutics.

Design, synthesis, and evaluation of novel thienopyrrolizinones as antitubulin agents

Herein, we describe the structure-activity relationship study of a new 3-aryl-8H-thieno[2,3-b]pyrrolizin-8-one series of antitubulin agents. The pharmacological results from the National Cancer Institute in vitro human disease oriented tumor cell line screening allowed us to identify compound 1d (NSC 676693) as a very efficient antitumoral drug in all cancer cell lines tested. This prompted us to define the structural requirements essential for this antiproliferative activity. Among all analogues synthesized in this study, compound 1o was the most promising, being 10-fold more potent than compound 1d. Its activity over a panel of nine tumoral cell lines was in the nanomolar range for all of the histological types tested, and surprisingly, the resistant KB-A1 cell line was also sensitive to this compound. Moreover, a flow cytometric study showed that L1210 cells treated by the most potent compounds were arrested in the G(2)/M phases of the cell cycle with a significant percentage of cells having reinitiated a cycle of DNA synthesis without cell division. This interesting pharmacological profile, resulting from inhibition of tubulin polymerization, encouraged us to perform preliminary in vivo studies that led to a new prodrug chemical approach.

O–N Intramolecular acyl migration strategy in water-soluble prodrugs of taxoids

We synthesized a highly water-soluble canadensol prodrug 6 that formed canadensol 3 by a simple pH-dependent chemical mechanism via the O-N intramolecular acyl migration of the isobutyryl group. This prodrug, a 2'-O-isobutyryl isoform of 3, has no additional functional auxiliaries released during the conversion to 3. This is a significant advantage in toxicology and medical economics, since the potential side effects of reported water-soluble auxiliaries and the use of detergent for solubilization can be avoided. The solubility of 6 was 2.26 mg mL(-1) and only the parent drug 3 was released under physiological conditions (pH=7.4) while, in acidic medium, the release of 3 slowed until migration was completely obstructed at pH=2. In further consideration of this strategy, we elucidated the use of an 'O-N acyl-like' migration reaction of the Boc group in the design of a docetaxel prodrug. Both O-N migration and undesired hydrolysis of the Boc group occurred under physiological conditions, although no oxazolidinone formation was observed, suggesting the limitation of our water-soluble prodrug strategy to docetaxel.

Controlled drug release: new water-soluble prodrugs of an HIV protease inhibitor

We designed and synthesized a series of highly water-soluble prodrugs of an HIV protease inhibitor, KNI-727 (1), containing tandem-linked two auxiliary units, a solubilizing moiety and a self-cleavable spacer. Prodrugs with an ionized amino group at the solubilizing moiety exhibited a remarkable increase of water-solubility (>10(4) fold) compared to the parent drug 1. These prodrugs released I not enzymatically, but chemically via an intramolecular cyclization-elimination reaction through an imide formation in physiological conditions. Diversified rates of parent drug release were observed when the chemical structure of both the solubilizing and the spacer moieties were modified. This new approach for water-soluble prodrugs will enable to control chemically the release of parent drug as well as to maintain high water-solubility.