Proapoptotic activity and ABCC1-related multidrug resistance reduction ability of semisynthetic oleanolic acid derivatives DIOXOL and HIMOXOL in human acute promyelocytic leukemia cells

Natural products as potential drug treatments for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL), which was once considered one of the deadliest types of leukemia, has become a curable malignancy since the introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) as clinical treatments. ATO, which has become the first-line therapeutic agent for APL, is derived from the natural mineral product arsenic, exemplifying an important role of natural products in the treatment of APL. Many other natural products, ranging from small-molecule compounds to herbal extracts, have also demonstrated great potential for the treatment and adjuvant therapy of APL. In this review, we summarize the natural products and representative components that have demonstrated biological activity for the treatment of APL. We also discuss future directions in better exploring their medicinal value, which may provide a reference for subsequent new drug development and combination therapy programs.

Recent advances in medicinal chemistry of oleanolic acid derivatives

Oleanolic acid (OA), a ubiquitous pentacyclic oleanane-type triterpene isolated from edible and medicinal plants, exhibits a wide spectrum of pharmacological activities and tremendous therapeutic potential. However, the undesirable pharmacokinetic properties limit its application and development. Numerous researches on structural modifications of OA have been carried out to overcome this limitation and improve its pharmacokinetic and therapeutic properties. This review aims to compile and summarize the recent progresses in the medicinal chemistry of OA derivatives, especially on structure-activity relationship in the last few years (2010-2021). It gives insights into the rational design of bioactive derivatives from OA scaffold as promising therapeutic agents.

Multivariate assessment of anticancer oleanane triterpenoids lipophilicity

Naturally occurring molecules are excellent sources of lead compounds. A series of oleanolic acid (OA) derivatives previously synthesized in our laboratory, which show promising antitumor activity, have been analyzed in terms of lipophilicity evaluation applying chromatographic and computational approaches. Retention data obtained on three reversed-phase liquid chromatography stationary phases (RP-HPLC) and immobilized artificial membrane chromatography (IAM-HPLC) were compared with computational methods using chemometric tools such as cluster analysis, principal component analysis and sum of ranking differences. To investigate the molecular mechanism of retention quantitive structure retention relationship analysis was performed, based on the genetic algorithm coupled with multiple linear regression (GA-MLR). The obtained results suggested that the ionization potential of studied molecules significantly affects their retention in classical RP-HPLC. In IAM-HPLC additionally, polarizability-related descriptors also play an essential role in that process. The lipophilicity indices comparison shows significant differences between the computational lipophilicity and chromatographically determined ones.

P. Cardoso D, U. Ferreira MJ. Overcoming Multidrug Resistance: Flavonoid and Terpenoid Nitrogen-Containing Derivatives as ABC Transporter Modulators

Multidrug resistance (MDR) in cancer is one of the main limitations for chemotherapy success. Numerous mechanisms are behind the MDR phenomenon wherein the overexpression of the ATP-binding cassette (ABC) transporter proteins P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance protein 1 (MRP1) is highlighted as a prime factor. Natural product-derived compounds are being addressed as promising ABC transporter modulators to tackle MDR. Flavonoids and terpenoids have been extensively explored in this field as mono or dual modulators of these efflux pumps. Nitrogen-bearing moieties on these scaffolds were proved to influence the modulation of ABC transporters efflux function. This review highlights the potential of semisynthetic nitrogen-containing flavonoid and terpenoid derivatives as candidates for the design of effective MDR reversers. A brief introduction concerning the major role of efflux pumps in multidrug resistance, the potential of natural product-derived compounds in MDR reversal, namely natural flavonoid and terpenoids, and the effect of the introduction of nitrogen-containing groups are provided. The main modifications that have been performed during last few years to generate flavonoid and terpenoid derivatives, bearing nitrogen moieties, such as aliphatic, aromatic and heterocycle amine, amide, and related functional groups, as well as their P-gp, MRP1 and BCRP inhibitory activities are reviewed and discussed.

Two new triterpenoids from the leaves and stems of Lantana camara

Two new oleanane-type triterpenoids with an epoxy bridge between C-3 and C-25, named lantacamaric acids A and B, were isolated from the leaves and stems of Lantana camara L. (Verbenaceae). In addition, seven known triterpenoids, two known iridoid glycosides, four known phenylethanoid glycosides, one known flavonoid glycoside, and one known cyanogenic glycoside were isolated. Their structures were determined based on the spectroscopic data. Furthermore, the cytotoxic activities of the isolated triterpenoids toward HL-60 cells were examined. The IC₅₀ values of all compounds were obtained and ranged from 1.16 to 68.4 μM, with three compounds exhibiting stronger activities than the positive control, cisplatin. In addition, the structure-activity relationship was investigated.

New uracil analog U-332 is an inhibitor of NF-κB in 5-fluorouracil-resistant human leukemia HL-60 cell line

BACKGROUND

5-Fluorouracil (5-FU) is an antimetabolite that interferes with DNA synthesis and has been widely used as a chemotherapeutic drug in various types of cancers. However, the development of drug resistance greatly limits its application. Overexpression of ATP-binding cassette (ABC) transporters in many types of cancer is responsible for the reduction of the cellular uptake of various anticancer drugs causing multidrug resistance (MDR), the major obstacle in cancer chemotherapy. Recently, we have obtained a novel synthetic 5-FU analog, U-332 [(R)-3-(4-bromophenyl)-1-ethyl-5-methylidene-6-phenyldihydrouracil], combining a uracil skeleton with an exo-cyclic methylidene group. U-332 was highly cytotoxic for HL-60 cells and showed similar cytotoxicity in the 5-FU resistant subclone (HL-60/5FU), in which this analog almost completely abolished expression of the ATP-binding cassette (ABC) transporter, multidrug resistance associate protein 1 (ABCC1). The expression of ABC transporters is usually correlated with NF-κB activation. The aim of this study was to determine the level of NF-κB subunits in the resistant HL-60/5-FU cells and to evaluate the potential of U-332 to inhibit activation of NF-κB family members in this cell line.

METHODS

Anti-proliferative activity of compound U-332 was assessed by the MTT assay. In order to disclose the mechanism of U-332 cytotoxicity, quantitative real-time PCR analysis of the NF-κB family genes, c-Rel, RelA, RelB, NF-κB1, and NF-κB2, was investigated. The ability of U-332 to reduce the activity of NF-κB members was studied by ELISA test.

RESULTS

In this report it was demonstrated, using RT-PCR and ELISA assay, that members of the NF-κB family c-Rel, RelA, RelB, NF-κB1, and NF-κB2 were all overexpressed in the 5-FU-resistant HL-60/5FU cells and that U-332 potently reduced the activity of c-Rel, RelA and NF-κB1 subunits in this cell line.

CONCLUSIONS

This finding indicates that c-Rel, RelA and NF-κB1 subunits are responsible for the resistance of HL-60/5FU cells to 5-FU and that U-332 is able to reverse this resistance. U-332 can be viewed as an important lead compound in the search for novel drug candidates that would not cause multidrug resistance in cancer cells.

New uracil analogs as downregulators of ABC transporters in 5-fluorouracil-resistant human leukemia HL-60 cell line

Overexpression of ATP-binding cassette (ABC) transporters causing multidrug resistance (MDR) in cancer cells is one of the major obstacles in cancer chemotherapy. The 5-FU resistant subclone (HL-60/5FU) of the human HL-60 promyelocytic leukemia cell line was selected by the conventional method of continuous exposure of the cells to the drug up to 0.08 mmol/L concentration. HL-60/5FU cells exhibited six-fold enhanced resistance to 5-FU than HL-60 cells. RT-PCR and ELISA assay showed significant overexpression of MDR-related ABC transporters, ABCB1, ABCG2 but especially ABCC1 in the HL-60/5FU as compared with the parental cell line. Three novel synthetic 5-methylidenedihydrouracil analogs, U-236, U-332 and U-359, selected as highly cytotoxic for HL-60 cells in MTT test, showed similar cytotoxicity in the resistant cell line. When co-incubated with 5-FU, these analogs were found to down-regulate the expression of all three transporters. However, the most pronounced effect was caused by U-332 which almost completely abolished ABCC1 expression in the resistant HL-60/5FU cells. Additionally, U-332 inhibited the activity of ATPase, an enzyme which catalyzes hydrolysis of ATP, providing energy to efflux drugs from the cells through the cellular membranes. Taken together, the obtained data suggest that acquired 5-FU resistance in HL-60/5FU cells results from overexpression of ABCC1 and that targeting ABCC1 expression could be a potential approach to re-sensitize resistant leukemia cells to 5-FU. The synthetic uracil analog U-332, which can potently down-regulate ABC transporter expression and therefore disturb drug efflux, can be considered an efficient ABCC1 regulator in cancer cells.

Cytotoxicity of oleanolic and ursolic acid derivatives toward hepatocellular carcinoma and evaluation of NF-κB involvement

Oleanolic and ursolic acids are two ubiquitous isomeric triterpene phytochemicals known for their anticancer activity. A set of derivatives of the two compounds with a modified oxidation state and lipophylicity at C-3 and C-28 positions, were prepared and tested as anticancer agents versus the lines HepG2, Hep3B and HA22T/VGH of hepatocarcinoma, a strongly aggressive tumor that is not responsive toward the standard therapies. New derivatives containing a three carbons side chain on the C-3 position were synthetized in both stereoisomeric forms by the Barbier-Grignard procedure and three of them were found to be active toward all of the three targets. The implication of the transcriptional nuclear factor NF-κB in the mechanism of action was assessed for the more active compounds in the set, as hepatocellular carcinoma (HCC) cyto-types are known to overexpress NF-κB.

The Effects of Synthetically Modified Natural Compounds on ABC Transporters

Multidrug resistance (MDR) is a major hurdle which must be overcome to effectively treat cancer. ATP-binding cassette transporters (ABC transporters) play pivotal roles in drug absorption and disposition, and overexpression of ABC transporters has been shown to attenuate cellular/tissue drug accumulation and thus increase MDR across a variety of cancers. Overcoming MDR is one desired approach to improving the survival rate of patients. To date, a number of modulators have been identified which block the function and/or decrease the expression of ABC transporters, thereby restoring the efficacy of a range of anticancer drugs. However, clinical MDR reversal agents have thus far proven ineffective and/or toxic. The need for new, effective, well-tolerated and nontoxic compounds has led to the development of natural compounds and their derivatives to ameliorate MDR. This review evaluates whether synthetically modifying natural compounds is a viable strategy to generate potent, nontoxic, ABC transporter inhibitors which may potentially reverse MDR.

Enhancing anticancer activity through the combination of bioreducing agents and triterpenes

AIM

Triterpenes are natural compounds, whose wide biological activity predestines them for application as promising new chemotherapeutics. In this paper, we report the results of our investigations into the substitution of oleanolic acid with aromatic and nitroaromatic moieties acting as bioreducing agents.

RESULTS

The process of reduction of nitro groups was investigated through cyclic voltammetry, UV-Vis and electron paramagnetic resonance spectroelectrochemistry. The cytotoxic activity against selected cancer cell lines was determined, showing a significant increase in cytotoxicity when the triterpene is equipped with a nitroaromatic moiety.

CONCLUSION

We believe this approach to the functionalization is promising in terms of enhancing anticancer activity. We also indicate electrochemical techniques as advantageous preclinical screening methods for the identification of cytotoxic agents.

Decreased expression of the augmenter of liver regeneration results in growth inhibition and increased chemosensitivity of acute T lymphoblastic leukemia cells

Augmenter of liver regeneration (ALR) plays crucial roles in cell survival and growth. Previous studies have demonstrated that ALR exerts a protective effect on toxic agent‑induced cell death in acute T lymphoblastic leukemia cells and ALR knockdown can sensitize cancer cells to radiation. However, the biological functions of ALR against drug resistance in T-cell acute lymphoblastic leukemia are mostly unknown. In the present study, we investigated the effect of small interfering RNA (siRNA)-induced ALR silencing on cell proliferation and sensitivity to vincristine (VCR) of Jurkat cells. We found that ALR siRNA effectively decreased the ALR expression, then inhibited cell growth and increased sensitivity to VCR in Jurkat cells. Flow cytometry assay revealed that the downregulation of ALR expression promoted cell apoptosis and regulated cell cycle distribution. Following incubation with VCR, apoptosis-related proteins, such as pro-PARP, pro-caspase 8, pro-caspase 3 and Bcl-2 were downregulated in the siRNA/ALR group. Pretreatment with siRNA/ALR in combination with VCR resulted in prolonged G2/M arrest, accompanied by downregulation of cdc25c and cdc2 expression and dissociation of cyclin B1. In conclusion, the results of this study demonstrated that targeted inhibition of the ALR expression in Jurkat cells triggered cell growth inhibition and sensitized cells to VCR via promoting apoptosis and regulating the cell cycle.

Semisynthetic oleanane triterpenoids inhibit migration and invasion of human breast cancer cells through downregulated expression of the ITGB1/PTK2/PXN pathway

This paper reports a study on the role of two synthetic derivatives of oleanolic acid (OA), HIMOXOL and Br-HIMOLID, in the regulation of cell migration and invasion and the underlying molecular mechanisms of breast cancer cells. The effect of the compounds on four breast cancer cell lines (MCF7, MDA-MB-231, MDA-MB-468, and T-47D) and also on noncancerous breast cells, MCF-12A, was reported. The compounds had no effect on the migration of MCF-12A cells. However, both the derivatives revealed a higher cytotoxicity than the maternal compound OA, and in sub-cytotoxic concentrations, they decreased the migration of MCF7, MDA-MB-231, and MDA-MB-468 breast cancer cells and also the invasion of MCF7 and MDA-MB-231 cells; although, the derivatives had no effect on the migration and invasion of T-47D cells. Both the derivatives of OA inhibited the cell migratory and invasive abilities of breast cancer cells by downregulating the expressions of ITGB1, PTK2, and PXN genes and by decreasing the phosphorylation status and the level of its respective proteins (integrin β1, FAK, and paxillin, respectively). This study is the first to report the antimigratory and anti-invasive activities of HIMOXOL and Br-HIMOLID in breast cancer cells.

Increased proapoptotic activity of electron beam irradiated doxorubicin and epirubicin in multidrug-resistant human leukemic cells

This study evaluated the effect of electron beam irradiation on the cytotoxic activity of anthracycline antibiotics such as doxorubicin (DOX), epirubicin (EPI), and dunorubicin (DAU) in human acute lymphoblastic leukemia cell line CCRF-CEM and its multidrug-resistant variant CCRF-VCR1000 cell line characterized by the overexpression of ABCB1 gene. Drugs were irradiated at doses of 10 and 25 kGy. Data from EPR studies proved that the highest concentration of free radicals was found in DOX and that the number of stable free radicals is always greater after irradiation. In in vitro studies, a higher cytotoxic activity of irradiated DOX and EPI in multidrug-resistant CCRF-VCR1000 cells was observed. This tendency was maintained during the storage at 4 °C for 90 days. Changes in CCRF-CEM cells' viability were not dependent on the irradiation status and its dose and were only drug-concentration dependent in all measurement time points. It was proved that increased potency of 25 kGy e-beam irradiated drugs results from their enhanced proapoptotic activity. Apoptotic cell death observed in CCRF-VCR1000 cells treated with irradiated drugs was caspase-8, -9, and -3 dependent and related to the increased Bax/Bcl-2 ratio. No significant differences in the effects of irradiated and non-irradiated drugs on p53 and NFκB transcription factor level and their translocation to the nucleus were noted. Increased activity of the irradiated drugs was not dependent on ABCB1 level.