Recent clinical trials and optical control as a potential strategy to develop microtubule-targeting drugs in colorectal cancer management

Colorectal cancer (CRC) has remained the second and the third leading cause of cancer-related death worldwide and in the United States, respectively. Although significant improvement in overall survival has been achieved, death in adult populations under the age of 55 appears to have increased in the past decades. Although new classes of therapeutic strategies such as immunotherapy have emerged, their application is very limited in CRC so far. Microtubule (MT) inhibitors such as taxanes, are not generally successful in CRC. There may be some way to make MT inhibitors work effectively in CRC. One potential advantage that we can take to treat CRC may be the combination of optical techniques coupled to an endoscope or other fiber optics-based devices. A combination of optical devices and photo-activatable drugs may allow us to locally target advanced CRC cells with highly potent MT-targeting drugs. In this Editorial review, we would like to discuss the potential of optogenetic approaches in CRC management.

Anti-angiogenic effect of nano-formulated water soluble kaempferol and combretastatin in an in vivo chick chorioallantoic membrane model and HUVEC cells

The present study evaluated the efficacy of nano-formulated water-soluble kaempferol and combretastatin alone and combined against the native kaempferol and combretastatin on angiogenesis. The solvent evaporation method was used to synthesize the nano-formulated water-soluble kaempferol and combretastatin and characterized using various analyses such as dynamic light scattering (DLS) and Fourier-transform infrared (FT-IR) spectroscopy.The anti-angiogenic activity of native, nano-formulated water-soluble kaempferol and combretastatin was investigated by cell viability on HUVEC and A498 cell lines, while chick chorioallantoic membrane (CAM) assay was utilized to assess morphometric and histopathological changes, and mRNA expressions of VEGF-A and FGF2 using qRT-PCR. MTT assay results revealed that the combination of nano-formulated water-soluble kaempferol and combretastatin significantly reduced the cell viability compared to control, individual treatments of native, nano-formulated water-soluble kaempferol, and combretastatin. Morphometric analysis of CAM showed that treatment with nano-formulated water-soluble kaempferol and combretastatin caused a substantial decrease in density, vessel network, branch points, and nets of CAM blood vessels. The histopathological results of CAM showed the irregular shape of blood vessels at the thin stratum of chronic endoderm, and blood capillaries were diminished compared to the control. In addition, the mRNA expression levels of VEGF-A and FGF2 were significantly decreased compared with native forms. Therefore, the findings of this study indicate that nano-formulated water-soluble combretastatin and kaempferol suppress angiogenesis by preventing the activation of endothelial cells and suppressing factors of angiogenesis. Moreover, a combination of nano-formulated water-soluble kaempferol and combretastatin worked much better than individual treatments.

Time-course monitoring of in vitro biotransformation reaction via solid-phase microextraction-ambient mass spectrometry approaches

The solid-phase microextraction technique quantifies analytes without considerably affecting the sample composition. Herein, a proof-of-concept study was conducted to demonstrate the use of coated probe electrospray ionization (coated-PESI) and coated blade spray (CBS) as ambient mass spectrometry approaches for monitoring drug biotransformation. The ability of these methods was investigated for monitoring the dephosphorylation of a prodrug, combretastatin A4 phosphate (CA4P), into its active form, combretastatin A4 (CA4), in a cell culture medium supplemented with fetal bovine serum. The CBS spot analysis was modified to achieve the same extraction efficiency as protein precipitation and obtained results in 7 min. Because coated-PESI performs extraction without consuming any samples, it is the preferred technique in the case of a limited sample volume. Although coated-PESI only extracts small quantities of analytes, it uses the desorption solvent volume of 5-10 pL, resulting in high sensitivity, thus allowing the detection of compounds after only 1 min of extraction. The biotransformation of CA4P into CA4 via phosphatases occurs within the simple matrix, and the proposed sample preparation techniques are suitable for monitoring the biotransformation.

Novel molecules as the emerging trends in cancer treatment: an update

As per World Health Organization cancer remains as a leading killer disease causing nearly 10 million deaths in 2020. Since the burden of cancer increases worldwide, warranting an urgent search for anti-cancer compounds from natural sources. Secondary metabolites from plants, marine organisms exhibit a novel chemical and structural diversity holding a great promise as therapeutics in cancer treatment. These natural metabolites target only the cancer cells and the normal healthy cells are left unharmed. In the emerging trends of cancer treatment, the natural bioactive compounds have long become a part of cancer chemotherapy. In this review, we have tried to compile about eight bioactive compounds from plant origin viz. combretastatin, ginsenoside, lycopene, quercetin, resveratrol, silymarin, sulforaphane and withaferin A, four marine-derived compounds viz. bryostatins, dolastatins, eribulin, plitidepsin and three microorganisms viz. Clostridium, Mycobacterium bovis and Streptococcus pyogenes with their well-established anticancer potential, mechanism of action and clinical establishments are presented.

Design and synthesis of β-carboline and combretastatin derivatives as anti-neutrophilic inflammatory agents

A series of β-carboline derivatives was synthesized by the Pictet-Spengler reaction with or without the combretastatin skeleton. The structures of these derivatives were elucidated by spectroscopic techniques. All synthesized compounds were evaluated for their anti-inflammatory activity in human neutrophils. Among them, two compounds, NTU-228 and HK-72, showed significant inhibitory effects on N-formyl-Met-Leu-Phe (fMLF)-induced superoxide anion generation in human neutrophils with IC₅₀ values of 5.58 ± 0.56 and 2.81 ± 0.07 μM, respectively. Neither NTU-228 nor HK-72 caused cytotoxicity in human neutrophils. NTU-228 inhibited the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and intracellular Ca²⁺ levels ([Ca²⁺]_i) in fMLF-activated human neutrophils. Additionally, HK-72 selectively inhibited the fMLF-induced phosphorylation of p38 and [Ca²⁺]_i in human neutrophils. Molecular docking analysis showed a favorable binding affinity of HK-72 toward p38 MAPK. The proposed synthetic strategy opens up new opportunities for the synthesis of novel potential candidates against neutrophilic inflammation.

Anti-proliferative potential of triphenyl substituted pyrimidines against MDA-MB-231, HCT-116 and HT-29 cancer cell lines

A series of triphenyl substituted pyrimidines as analogous of colchicine and combretastatin A-4 was synthesized and evaluated for the antiproliferative potential. The compounds were screened against MDA-MB-231, HCT-116 and HT-29 cell lines using MTT assay. Most of the compounds displayed antiproliferative activity in low to sub micro molar concentration. Amongst the synthesized derivatives, compounds HK-2, HK-10 and HK-13 were found to be effective against all the three cancer cell lines. HK-2 exhibited IC₅₀ values of 3.39 µM, 4.78 µM and 4.23 µM, HK-10 showed IC₅₀ values of 0.81 µM, 5.89 µM, 4.96 µM and HK-13 showed IC₅₀ values 3.24 µM, 4.93 µM and 4.73 µM against MDA-MB-231, HCT-116 and HT-29 cancer cell lines, respectively. HK-10 was found to be the most potent compound in the series with IC₅₀ values of 0.81 µM against MDA-MB-231. In the cell cycle analysis, HK-2 and HK-10 showed cell arrest at G2/M phase of the cell cycle while HK-13 inhibited cell growth at the G1/G0 phase. All the three compounds showed cell death induced through apoptosis. In the docking studies, HK-2, HK-10 and HK-13 were found to fit well in the colchicine binding site of the tubulin. Some of the compounds in the current series were found to be promising against all the three cancer cell lines and may act as potent leads for further development.

Synthesis, biological evaluation, and modeling studies of 1,3-disubstituted cyclobutane-containing analogs of combretastatin A4

With the aim of circumventing the adverse cis/trans-isomerization of combretastatin A4 (CA4), a naturally occurring tumor-vascular disrupting agent, we designed novel CA4 analogs bearing 1,3-cyclobutane moiety instead of the cis-stilbene unit of the parent compound. The corresponding cis and trans cyclobutane-containing derivatives were prepared as pure diastereomers. The structure of the target compounds was confirmed by X-ray diffraction study. The title compounds were evaluated for their cytotoxic properties in human cancer cell lines HepG2 (hepatocarcinoma) and SK-N-DZ (neuroblastoma), and the overall activity was found in micromolar range. Molecular docking studies and molecular dynamics simulation within the colchicine binding site of tubulin were in good agreement with the obtained cytotoxicity data.

Evaluation of lipid-stabilised tripropionin nanodroplets as a delivery route for combretastatin A4

Lipid-based nanoemulsions are a cheap and elegant route for improving the delivery of hydrophobic drugs. Easy and quick to prepare, nanoemulsions have promise for the delivery of different therapeutic agents. Although multiple studies have investigated the effects of the oil and preparation conditions on the size of the nanoemulsion nanodroplets for food applications, analogous studies for nanoemulsions for therapeutic applications are limited. Here we present a study on the production of lipid-stabilised oil nanodroplets (LONDs) towards medical applications. A number of biocompatible oils were used to form LONDs with phospholipid coatings, and among these, squalane and tripropionin were chosen as model oils for subsequent studies. LONDs were formed by high pressure homogenisation, and their size was found to decrease with increasing production pressure. When produced at 175MPa, all LONDs samples exhibited sizes between 100 and 300nm, with polydispersity index PI between 0.1 and 0.3. The LONDs were stable for over six weeks, at 4°C, and also under physiological conditions, showing modest changes in size (<10%). The hydrophobic drug combretastatin A4 (CA4) was encapsulated in tripropionin LONDs with an efficiency of approximately 76%, achieving drug concentration of approximately 1.3mg/ml. SVR mouse endothelial cells treated with CA4 tripropionin LONDs showed the microtubule disruption, characteristic of drug uptake for all tested doses, which suggests successful release of the CA4 from the LONDs.

Enhanced anticancer effect of Combretastatin A-4 phosphate when combined with vincristine in the treatment of hepatocellular carcinoma

Tubulin targeting agents have received considerable interest as a potential tumor-selective vascular disrupting agents, which represent another avenue for cancer growing therapeutic opportunities. Hence, the present study was conducted to investigate the anti-tumor activity of Combretastatin A-4 phosphate (CA4-P) and vincristine against hepatocellular carcinoma in rats, by individual administration and in combination. In vitro study was conducted using human hepatocellular carcinoma cell lines, showed that CA4-P and vincristine have a potent cell cytotoxic and tubulin inhibitory effect. In addition, a remarkable synergistic effect was observed by the simultaneous application of both drugs. Whereas in vivo study was conducted using model of rat liver cancer initiated with DENA and promoted by CCl₄, showed that CA4-P and vincristine were significantly decreased liver relative weight, number of hepatic nodules and there relative volumes, tubulin content of the hepatic tissue, GSH and AFP. On the other hand, co-administration of both drugs exhibited significant further decrements in these parameters. Whereas a marked increase in MDA, carbonyl content and TNF-α inside hepatic tissue were observed in the treated groups and these increments were more prominent by co-administration of both drugs. In conclusion CA4-P showed a potential anti-cancer activity against hepatocellular carcinoma and this effect was greatly enhanced by co-administration with vincristine. Additionally, our new findings provided an important evidence that the anticancer activity of drugs with a narrow therapeutic window such as vincristine can be greatly improved by its co-administration with CA4-P providing more enhanced activity with less side effects.

Combretastatins: In vitro structure-activity relationship, mode of action and current clinical status

For the first time combretastatins were isolated from African willow tree Combretum Caffrum. Subsequent studies have shown the impact of combretastatin A4 phosphate, a water-soluble prodrug, on endothelial cells in tumor vascular system. The same effect was not observed in the vascular system. This selectivity is associated with combretastatins mechanism of action: binding to colchicine domain of microtubules, which affects the cytoskeleton functionality of immature endothelial cells. At the same time, combretastatins directly induce cell death via apoptosis and/or mitotic catastrophe pathways. The combination of both elements makes combretastatin an anticancer compound of high efficiency. The cis-configuration is crucial for its biological activity. To date, many derivatives were synthesized. The attempts to resolve spontaneous isomerization to less active trans-stilbene derivative are still in progress. This issue seems to be overcome by incorporation of the ethene bridge with heterocyclic moiety in combretastatins structure. This modification retains the cis-configuration and prevents isomerization. Nevertheless, combretastatin A4 phosphate disodium is still the most potent compound of this group. The combination therapy, which is the most effective treatment, includes combretastatin A4 phosphate (CA4P) and conventional chemotherapeutics and/or radiotherapy. CA4P is relatively well tolerated giving adverse events of moderate severity, which includes: nausea, vomiting, headache, and tumor pain. The aforementioned effects subside on the day of drug administration or on the following day.

Uniform Combretastatin-induced Effect on Monocytes and Neutrophils in Peripheral Blood but Not in Tumors

BACKGROUND/AIM

Combretastatin A-4 phosphate (CA4P) is a vascular-disrupting agent which affects the level of circulating neutrophils. Since tumor-associated macrophages and neutrophils may collaborate, we compared the effect of CA4P treatment on monocytes/macrophages and neutrophils.

MATERIAL AND METHODS

CDF1 mice with a C3H mammary carcinoma foot tumor were injected intraperitoneally with CA4P. Blood samples were taken and tumors excised at various time-points after treatment. Circulating monocytes and granulocytes were detected by flow cytometry and the tumor levels of these cell types was estimated immunohistochemically.

RESULTS

CA4P induced similar oscillating effects on the level of circulating monocytes and of neutrophils, with an initial decrease followed by an increase and a return to control levels at 6-h and 24-h, respectively. In tumors, only the macrophage level decreased significantly after treatment.

CONCLUSION

CA4P induced similar changes in the level of circulating monocytes and neutrophils, but only affected the fraction of macrophages significantly.

A series of flexible design adaptations to the Nikon E-C1 and E-C2 confocal microscope systems for UV, multiphoton and FLIM imaging

Multiphoton microscopy is widely employed in the life sciences using extrinsic fluorescence of low- and high-molecular weight labels with excitation and emission spectra in the visible and near infrared regions. For imaging of intrinsic and extrinsic fluorophores with excitation spectra in the ultraviolet region, multiphoton excitation with one- or two-colour lasers avoids the need for ultraviolet-transmitting excitation optics and has advantages in terms of optical penetration in the sample and reduced phototoxicity. Excitation and detection of ultraviolet emission around 300 nm and below in a typical inverted confocal microscope is more difficult and requires the use of expensive quartz optics including the objective. In this technical note we describe the adaptation of a commercial confocal microscope (Nikon, Japan E-C1 or E-C2) for versatile use with Ti-sapphire and OPO laser sources and the addition of a second detection channel that enables detection of ultraviolet fluorescence and increases detection sensitivity in a typical fluorescence lifetime imaging microscopy experiment. Results from some experiments with this setup illustrate the resulting capabilities.

Synthesis and biological evaluation of indole-based, anti-cancer agents inspired by the vascular disrupting agent 2-(3'-hydroxy-4'-methoxyphenyl)-3-(3″,4″,5″-trimethoxybenzoyl)-6-methoxyindole (OXi8006)

The discovery of a 2-aryl-3-aroyl indole-based small-molecule inhibitor of tubulin assembly (referred to as OXi8006) inspired the design, synthesis, and biological evaluation of a series of diversely functionalized analogues. In the majority of examples, the pendant 2-aryl ring contained a 3-hydroxy-4-methoxy substitution pattern, and the fused aryl ring featured a 6-methoxy group. Most of the variability was in the 3-aroyl moiety, which was modified to incorporate methoxy (33-36), nitro (25-27), halogen (28-29), trifluoromethyl (30), or trifluoromethoxy (31-32) functionalities. In two analogues (34 and 36), the methoxy substitution pattern in the fused aryl ring varied, while in another derivative (35) the phenolic moiety was translocated from the pendant 2-aryl ring to position-7 of the fused aryl ring. Each of the compounds were evaluated for their cytotoxicity (in vitro) against the SK-OV-3 (ovarian), NCI-H460 (lung), and DU-145 (prostate) human cancer cell lines and for their ability to inhibit tubulin assembly. Four of the compounds (30, 31, 35, 36) proved to be potent inhibitors of tubulin assembly (IC50 <5μM), and three of these compounds (31, 35, 36) were strongly cytotoxic against the three cancer cell lines. The most active compound (36) in this series, which incorporated a methoxy group at position-7, was comparable in terms of inhibition of tubulin assembly and cytotoxicity to the lead compound OXi8006.

Correlation of hydrogen-bonding propensity and anticancer profile of tetrazole-tethered combretastatin analogues

A series of 1,5-disubstituted tetrazole-tethered combretastatin analogues with extended hydrogen-bond donors at the ortho-positions of the aryl A and B rings were developed and evaluated for their antitubulin and antiproliferative activity. We wanted to test whether intramolecular hydrogen-bonding used as a conformational locking element in these analogues would improve their activity. The correlation of crystal structures with the antitubulin and antiproliferative profiles of the modified analogues suggested that hydrogen-bond-mediated conformational control of the A ring is deleterious to the bioactivity. In contrast, although there was no clear evidence that intramolecular hydrogen bonding to the B ring enhanced activity, we found that increased substitution on the B ring had a positive effect on antitubulin and antiproliferative activity. Among the various analogues synthesized, compounds 5d and 5e, having hydrogen-bonding donor groups at the ortho and meta-positions on the 4-methoxy phenyl B ring, are strong inhibitors of tubulin polymerization and antiproliferative agents having IC50 value in micromolar concentrations.

A-ring dihalogenation increases the cellular activity of combretastatin-templated tetrazoles

The combretastatins have been investigated for their antimitotic and antivascular properties, and it is widely postulated that a 3,4,5-trimethoxyaryl A-ring is essential to maintain potent activity. We have synthesized new tetrazole analogues (32-34), demonstrating that 3,5-dihalogenation can consistently increase potency by up to 5-fold when compared to the equivalent trimethoxy compound on human umbilical vein endothelial cells (HUVECs) and a range of cancer cells. Moreover, this increased potency offsets that lost by installing the tetrazole bridge into combretastatin A-4 (1), giving crystalline, soluble compounds that have low nanomolar activity, arrest cells in G2/M phase, and retain microtubule inhibitory activity. Molecular modeling has shown that optimized packing within the binding site resulting in increased Coulombic interaction may be responsible for this improved activity.