Formula optimization and in vivo study of poly(L-glutamic acid)-g-methoxy poly(ethylene glycol)/combretastatin A4/BLZ945 nanoparticles for cancer therapy

Poly(L-glutamic acid)-g-methoxy poly(ethylene glycol)/Combretastatin A4 (CA4)/BLZ945 nanoparticles (CB-NPs) have shown great potential in synergistic cancer therapy. However, it is still unclear how the nanoparticles' formula, such as injection dose, active agent ratio, and drug loading content, affects the side effects and in vivo efficacy of CB-NPs. In this study, a series of CB-NPs with different BLZ945/CA4 (B/C) ratios and drug loading contents were synthesized and evaluated on a hepatoma (H22) tumor-bearing mice model. The injection dose and B/C ratio were found to have a significant influence on the in vivo anticancer efficacy. The CB-NPs 20 with B/C weight ratio of 0.45/1, and total drug loading content (B + C) of 20.7 wt%, showed the highest potential for clinical application. Systematic pharmacokinetics, biodistribution, and in vivo efficacy evaluation for CB-NPs 20 have been finished, which may provide significant instruction for medicine screening and clinical application.

Recent advances in combretastatin A-4 codrugs for cancer therapy

CA4 is a potent microtubule polymerization inhibitor and vascular disrupting agent. However, the in vivo efficiency of CA4 is limited owing to its poor pharmacokinetics resulting from its high lipophilicity and low water solubility. To improve the water solubility, CA4 phosphate (CA4P) has been developed and shows potent antivascular and antitumor effects. CA4P had been evaluated as a vascular disrupting agent in previousc linical trials. However, it had been discontinued due to the lack of a meaningful improvement in progression-free survival and unfavorable partial response data. Codrug is a drug design approach to chemically bind two or more drugs to improve therapeutic efficiency or decrease adverse effects. This review describes the progress made over the last twenty years in developing CA4-based codrugs to improve the therapeutic profile and achieve targeted delivery to cancer tissues. It also discusses the existing problems and the developmental prospects of CA4 codrugs.

Combretastatin A4-loaded Poly (Lactic-co-glycolic Acid)/Soybean Lecithin Nanoparticles with Enhanced Drug Dissolution Rate and Antiproliferation Activity

OBJECTIVE

This study aimed to prepare combretastatin A4 (CA4)-loaded nanoparticles (CA4 NPs) using poly(lactic-co-glycolic acid) (PLGA) and soybean lecithin (Lipoid S100) as carriers, and further evaluate the physicochemical properties and cytotoxicities of CA4 NPs against cancer cells.

METHODS

CA4 NPs were prepared using a solvent evaporation technique. The effects of formulations on CA4 NPs were investigated in terms of particle size, zeta potential, encapsulation efficacy, and drug loading. The physicochemical properties of CA4 NPs were characterized using transmission electron microscopy, X-ray powder diffraction, differential scanning calorimetry, and Fourier transform infrared spectra. The drug release from CA4NPs was performed using a dialysis method. In addition, the cytotoxicity of CA4NPs against human alveolar basal epithelial (A549) cells was also evaluated.

RESULTS

CA4 NPs prepared with a low organic/water phase ratio (1:20) and high drug/PLGA mass ratio (1:2.5) exhibited a uniform hydrodynamic particle size of 142 nm, the zeta potential of -1.66 mV, and encapsulation efficacy and drug loading of 92.1% and 28.3%, respectively. CA4 NPs showed a significantly higher release rate than pure CA4 in pH 7.4 phosphate-buffered solution with 0.5% Tween 80. It was found that the drug molecules could change from the crystal state to an amorphous form when loaded into the PLGA/Lipoid S100 matrix, and some molecular interactions could also occur between the drug and PLGA. Importantly, CA4 NPs showed a remarkably higher antiproliferation activity against A549 cancer cells compared to pure CA4.

CONCLUSION

These results suggested the promising potential of PLGA/Lipoid S100 nanoparticles as the drug delivery system of CA4 for effective cancer therapy.

Dual-functional antitumor conjugates improving the anti-metastasis effect of combretastatin A4 by targeting tubulin polymerization and matrix metalloproteinases

This study prepared different novel conjugates containing tubulin and MMP inhibitors and assessed their anticancer effects. Typically, the conjugate 15g, which contained combretastatin A4 (CA4) and 2-(4-((diethoxyphosphono)(o-tolyl)methylamino)phenyl)acetic acid (19g) connected by an ester bond, showed the maximum effect against proliferation. Particularly, the conjugate yielded a reduced IC₅₀ value of 0.05 μM in controlling the proliferation of HepG2 cells compared to CA4 alone (0.09 μM). Systematic research indicated that 15g suppressed tubulin polymerization, induced cell cycle arrest at the G2/M phase, led to reactive oxidative stress (ROS) generation of HepG2 cells, and resulted in apoptosis by the mitochondrial-dependent apoptotic pathway. Moreover, 15g showed a potent effect on resistant metastasis by decreasing the levels of the proteins MMP2 and MMP9 in the HepG2 cells. Therefore, this conjugate is a potentially effective approach to improve the anti-metastatic effect of CA4 with high safety.

Pegylated liposomal encapsulation improves the antitumor efficacy of combretastatin A4 in murine 4T1 triple-negative breast cancer model

Combretastatin A4 (CA4), a vascular disrupting agent has been recently proposed as an anticancer agent. However, its low water solubility and low bioavailability limited its clinical efficacy. Overcomingthis issue requires developing new delivery strategies to enhance its anticancer effects. Here, we prepared various PEGylated liposomal formulations containing CA4 composed of different molar ratios of HSPC/DSPE-mPEG₂₀₀₀/Cholesterol/CA4 (F1: 80:5:10:5; F2: 75:5:15:5; F3: 70:5:20:5; F4: 60:5:30:5 and F5: 50:5:40:5) by the thin-film hydration method plus sonication and extrusion. All formulations had a particle diameter of 100-150 nm, a monomodal distribution with low polydispersity index and a negative zeta potential. Among the formulations only F1, F2, and F3 showed a high CA4 encapsulation efficiency; so their anticancer effects on triple-negative breast cancer (TNBC) were investigated in vitro and in vivo. The release study showed that F3 liposomes had significantly lower CA4 release compared to the F1 and F2 liposomes in different pH of 5.5, 6.5, and 7.4. We found that, CA4-loaded liposomes effectively inhibited both proliferation and migration of 4T1 and MDA-MB-231 TNBC cell lines by inducing cell cycle arrest at the G2/M phase and decreasing MMP-2 and MMP-9 expression and activity. In vivo studies revealed that F3 liposomes were highly accumulated at the tumor site and more effectively delayed tumor growth andprolonged the overall survival than other groups in 4T1 breast tumor-bearing mice. Taken together, encapsulation of CA4 in PEGylated F3 liposomes enhances its anti-tumor activity and may be serve as a promising approach for TNBC treatment and merits further investigation.

Targeted microbubbles carrying lipid-oil-nanodroplets for ultrasound-triggered delivery of the hydrophobic drug, combretastatin A4

The hydrophobicity of a drug can be a major challenge in its development and prevents the clinical translation of highly potent anti-cancer agents. We have used a lipid-based nanoemulsion termed Lipid-Oil-Nanodroplets (LONDs) for the encapsulation and in vivo delivery of the poorly bioavailable combretastatin A4 (CA4). Drug delivery with CA4 LONDs was assessed in a xenograft model of colorectal cancer. LC-MS/MS analysis revealed that CA4 LONDs, administered at a drug dose four times lower than drug control, achieved equivalent concentrations of CA4 intratumorally. We then attached CA4 LONDs to microbubbles (MBs) and targeted this construct to VEGFR2. A reduction in tumor perfusion was observed in CA4 LONDs-MBs treated tumors. A combination study with irinotecan demonstrated a greater reduction in tumor growth and perfusion (P = 0.01) compared to irinotecan alone. This study suggests that LONDs, either alone or attached to targeted MBs, have the potential to significantly enhance tumor-specific hydrophobic drug delivery.

Combretastatin A4/poly(L-glutamic acid)-graft-PEG conjugates self-assembled to nanoparticles

Combretastatin A4 (CA4) possesses varying ability to cause vascular disruption in tumors, while the short half-life, low water solubility and deactivation of many CA4 analogs during storage limited its antitumor efficacy and drug stability. A novel macromolecular conjugate of CA4 (CA4-PL) was synthesized by covalent bonding of CA4 onto poly(L-glutamic acid)-graft-polyethylene glycol (PLG-g-PEG) via Yamaguchi reaction. The obtained CA4-PL was characterized by ¹H NMR, GPC, and UV methods, and the properties of the nanoparticles composed of CA4-PL, including critical aggregation concentration, size and size distribution, and morphology, were investigated. CA4-PL can self-assemble to form micelle-like nanoparticles of 80~120 nm in diameter, which may have potential to improve the blood circulation period as well as the targetability of CA4, and find applications to treat various tumors when combined with traditional chemotherapy or radio therapy.

A poly(l-glutamic acid)-combretastatin A4 conjugate for solid tumor therapy: Markedly improved therapeutic efficiency through its low tissue penetration in solid tumor

Combretastatin A4 (CA4) is a leading agent in vascular disrupting strategies for tumor therapy. Although many small-molecule prodrugs of CA4 have been developed to improve its solubility, the overall therapeutic efficiency is moderate. A key reason for this is the reversible effect that CA4 has on tubulin as well as its rapid clearance from plasma and tissues. In this study, we proposed a poly(l-glutamic acid)-CA4 conjugate (PLG-CA4) nanomedicine to fulfill the requirements for fully liberating the potential of CA4 on tumor therapy. Enhanced accumulation and retention of CA4 in tumor tissue, especially, high distribution and gradual release around tumor blood vessels resulted in prolonged vascular disruption and markedly enhanced therapeutic efficiency. We examined and compared the therapeutic effect of PLG-CA4 and commercial combretastatin-A4 phosphate (CA4P) in a murine colon C26 tumor. PLG-CA4 showed significantly prolonged retention in plasma and tumor tissue. Most importantly, the PLG-CA4 was mainly distributed around the tumor vessels because of its low tissue penetration in solid tumor. Pathology tests showed that PLG-CA4 treatment resulted in persistent vascular disruption and tumor damage 72h after a single injection, this in contrast to CA4P treatment, which showed quick relapse at an equal dose. Tumor suppression tests showed that PLG-CA4 treatment resulted in a tumor suppression rate of 74%, which indicates a significant advantage when compared to tumor suppression rate of the CA4P group, which was 24%. This is the first time that an advantage of the polymeric CA4 nanomedicine with low tissue penetration for solid tumor therapy has been shown. Thus, the results presented in this study provide a new idea for enhancing the tumor therapeutic effect of vascular disrupting agents.

STATEMENT OF SIGNIFICANCE

Nanomedicine usually has low tissue penetration in solid tumors, which limits the efficacy of nanomedicine in most cases. But herein, we demonstrate a nanosized vascular disruptive agent (VDA) PLG-CA4 has supper advantages over small molecular combretastatin-A4 phosphate (CA4P) because the PLG-CA4 was mainly distributed around the tumor vessels due to its low tissue penetration in solid tumor.

Synthesis and cytotoxic activity of certain trisubstituted azetidin-2-one derivatives as a cis-restricted combretastatin A-4 analogues

Novel series of 1,3,4-trisubstituted azetidin-2-one derivatives 8a-p were synthesized and proposed as cytotoxic agents acting via inhibition of tubulin at the colchicine binding site. The design of the target compounds was based upon modification in the structure of the vascular targeting agent combretastatin A-4 (CA-4). The cis double bond linker in CA-4 was replaced with the azetidin-2-one ring aiming to prevent the cis/trans isomerization that suppresses the activity of CA-4, thereby enhancing its antiproliferative activity. All new compounds were investigated in vitro against MCF-7 and HCT-116 cell lines. The inhibition of tubulin polymerization by four most potent compounds 8g, 8j, 8n and 8o was also evaluated. The synthesis of the final targets was achieved adopting Staudinger reaction. Molecular modeling studies were performed to rationalize the biological results.

Anti-Microtubule Drugs

Small molecule drugs that target microtubules (MTs), many of them natural products, have long been important tools in the MT field. Indeed, tubulin (Tb) was discovered, in part, as the protein binding partner of colchicine. Several anti-MT drug classes also have important medical uses, notably colchicine, which is used to treat gout, familial Mediterranean fever (FMF), and pericarditis, and the vinca alkaloids and taxanes, which are used to treat cancer. Anti-MT drugs have in common that they bind specifically to Tb in the dimer, MT or some other form. However, their effects on polymerization dynamics and on the human body differ markedly. Here we briefly review the most-studied molecules, and comment on their uses in basic research and medicine. Our focus is on practical applications of different anti-MT drugs in the laboratory, and key points that users should be aware of when designing experiments. We also touch on interesting unsolved problems, particularly in the area of medical applications. In our opinion, the mechanism by which any MT drug cures or treats any disease is still unsolved, despite decades of research. Solving this problem for particular drug-disease combinations might open new uses for old drugs, or provide insights into novel routes for treatment.

Synthesis of combretastatin A4 analogues on steroidal framework and their anti-breast cancer activity

Combretastatin A4 analogues were synthesized on steroidal framework from gallic acid with a possibility of anti-breast cancer agents. Twenty two analogues were synthesized and evaluated for cytotoxicity against human breast cancer cell lines (MCF-7 & MDA-MB 231). The best analogue 22 showed potent antitubulin effect. Docking experiments also supported strong binding affinity of 22 to microtubule polymerase. In cell cycle analysis, 22 induced apoptosis in MCF-7 cells significantly. It was found to be non-toxic up to 300 mg/kg dose in Swiss albino mice in acute oral toxicity. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".