The potential roles of retinoids in combating drug resistance in cancer: implications of ATP-binding cassette (ABC) transporters

Multidrug resistance (MDR) means that tumour cells become unresponsive during or after the course of treatment to one or more of chemotherapeutic drugs. Chemotherapeutic resistance critically limits the treatment outcomes and remains a key challenge for clinicians. The alternation in intracellular drug concentration through the modulation of its transport across the plasma membrane is the major cause for MDR and is adopted by various mediators, including ATP-requiring enzymes (ATPases). Among these ATPases, ABC transporters have been extensively studied, and found to be highly implicated in tumorigenesis and MDR. The present review sheds light on the documented effects of retinoids on ABC enzymes to understand their mechanism in combating cancer cell resistance. This would open the gate to test the mechanism and applicability of different new synthetic retinoids in literature and market as modulators of ATP-dependent efflux pumping activity, and promote their applicability in diminishing anti-cancer drug resistance.

Therapeutic effect of kaempferol on atopic dermatitis by attenuation of T cell activity via interaction with multidrug resistance-associated protein 1

BACKGROUND AND PURPOSE

Kaempferol is a natural flavonoid widely investigated in various fields due to its antioxidant, anti-cancer, and anti-inflammatory activities, but few studies have shown its inhibitory effect on T cell activation. This study examined the therapeutic potential of kaempferol in atopic dermatitis by modulating T cell activation.

EXPERIMENTAL APPROACH

Effects of kaempferol on T cell activation and the underlying mechanisms were investigated in Jurkat cells and mouse CD4⁺ T cells. A model of atopic dermatitis in mice was used to determine its therapeutic potential on T cell-mediated conditions in vivo. Western blots, RT-PCR, pulldown assays and ELISA were used, along with histological analysis of skin.

KEY RESULTS

Pretreatment with kaempferol reduced CD69 expression and production of inflammatory cytokines including IL-2 from activated Jurkat cells and murine CD4⁺ T cells without cytotoxicity. Pulldown assays revealed that kaempferol physically binds to MRP-1 in T cells, inhibiting the action of MRP-1. In activated T cells, kaempferol suppressed JNK phosphorylation and the TAK1-IKKα mediated NF-κB pathway. Oral administration of kaempferol to mice showed improved manifestation of atopic dermatitis, a T cell-mediated condition. Western blot results showed that, as in the in vitro studies, decreased phosphorylation of JNK was associated with down-regulated MRP-1 activity in vivo, in the kaempferol-treated mice in the atopic dermatitis model.

CONCLUSION AND IMPLICATIONS

Kaempferol regulates T cell activation by inhibiting MRP-1 activity in activated T cells, thus showing protective effects against T cell mediated disease in vivo.

Folic acid (FA)-conjugated mesoporous silica nanoparticles combined with MRP-1 siRNA improves the suppressive effects of myricetin on non-small cell lung cancer (NSCLC)

Non-small cell lung cancer (NSCLC) is a common diagnosed cancer disease worldwide and its management remains a challenge. Synergistic cancer therapeutic strategy is interesting for multiple advantages, such as excellent targeting accuracy, low side effects, and promoted therapeutic efficiency. In the present study, myricetin (Myr)-loaded mesoporous silica nanoparticles (MSN) combined with multidrug resistance protein (MRP-1) siRNA was prepared. The surface of the synthesized nanoparticles was modified with folic acid (FA) to promote the therapeutic efficiency of Myr for the treatment of NSCLC. The collected particles were nano-sized and showed a sustained release of Myr in the physiological conditions. FA-conjugated nanoformulations displayed a significant uptake in lung cancer cells compared with that of the non-targeted nanoparticles. The in vitro drug release results suggested a sustained release in FA-conjugated MSN with Myr and MRP-1 nanoparticles compared to the free Myr and MSN combined with MRP-1/Myr. Treatments with FA-conjugated MSN combined with Myr and MRP-1 markedly reduced the cell viability of lung cancer cell lines, including A549 and NCI-H1299, which was accompanied with the decreased number of colony formation. In addition, FA-conjugated MSN loaded with Myr and MRP-1 significantly induced apoptosis in lung cancer cells, along with up-regulated expression levels of cleaved Caspase-3 and PARP. In vivo fluorescence results demonstrated that FA-conjugated MSN with Myr and MRP-1 nanoparticles could specifically accumulate at tumor sites. Compared with free Myr and MSN combined with MRP-1/Myr nanoparticles, FA-conjugated MSN loaded with Myr and MRP-1 nanoparticles could more effectively suppress tumor growth with little side effects. Overall, FA-conjugated nanoparticulate system could provide a novel and effective platform for the treatment of NSCLC.

Hepatocyte SLAMF3 reduced specifically the multidrugs resistance protein MRP-1 and increases HCC cells sensitization to anti-cancer drugs

Multidrug resistance MDR proteins (MRPs) are members of the C family of a group of proteins named ATP binding cassette (ABC) transporters. MRPs can transport drugs including anticancer drugs, nucleoside analogs, antimetabolites and tyrosine kinase inhibitors. Drugs used in HCC therapy, such as tyrosine kinase inhibitor sorafenib, are substrates of uptake and/or efflux transporters. Variable expression of MRPs at the plasma membrane of tumor cells may contribute to drug resistance and subsequent clinical response. Recently, we reported that the hepatocyte SLAMF3 expression (Signaling Lymphocytic Activation Molecule Family member 3) was reduced in tumor cells from hepatocellular carcinoma (HCC) compared to its high expression in adjacent tissues. In the present study, we make a strong correlation between induced SLAMF3 overexpression and the specific loss of MRP-1 expression and its functionalities as a drugs resistance transporter. No changes were observed on expression of ABCG2 and MDR. More importantly, we highlight a strong inverse correlation between MRP-1 and SLAMF3 expression in patients with HCC. We propose that the SLAMF3 overexpression in cancerous cells could represent a potential therapeutic strategy to improve the drugs sensibility of resistant cells and thus control the therapeutic failure in HCC patients.

Effects of realgar on GSH synthesis in the mouse hippocampus: Involvement of system XAG(-), system XC(-), MRP-1 and Nrf2

Realgar is a type of mineral drug that contains arsenic and has neurotoxicity. Glutathione (GSH), which is the main antioxidant in the central nervous system, plays a key role in antioxidant defenses and the detoxification of arsenic. However, whether realgar interferes with the synthesis of GSH in the brain and the molecular mechanisms underlying its effects are largely unknown. Here, we used mouse models of exposure to realgar to show that realgar affects the synthesis of GSH in the hippocampus, leading to ultrastructural changes in hippocampal neurons and synapses and deficiencies in cognitive abilities, and that the mechanisms that cause this effect may be associated with alterations in the expression of system XAG(-), system XC(-), multidrug resistance-associated protein 1(MRP-1), nuclear factor E2-related factor 2 (Nrf2), γ-glutamylcysteine synthetase (γ-GCS), and the levels of glutamate (Glu) and cysteine (Cys) in the extracellular fluid. These findings provide a theoretical basis for preventing the drug-induced chronic arsenic poisoning in the nervous system that is triggered by realgar.

Tumor growth retardation and chemosensitizing action of fatty acid synthase inhibitor orlistat on T cell lymphoma: implication of reconstituted tumor microenvironment and multidrug resistance phenotype

BACKGROUND

Orlistat, a fatty acid synthase (FASN) inhibitor, has been demonstrated to inhibit tumor cell survival. However, the mechanism(s) of its tumor growth retarding action against malignancies of hematological origin remains unclear. It is also not understood if the antitumor action of orlistat implicates modulated susceptibility of tumor cell to anticancer drugs. Therefore, the present investigation focuses to study the antitumor and chemosensitizing action of orlistat in a murine host bearing a progressively growing T cell lymphoma.

METHODS

Tumor-bearing mice were administered with vehicle alone or containing orlistat followed by administration of PBS with or without cisplatin. Tumor progression and survival of tumor-bearing host were monitored along with analysis of tumor cell survival and apoptosis. Tumor ascitic fluid was examined for pH, NO and cytokines. Expression of genes and proteins was investigated by RT-PCR and western blot respectively. ROS was analyzed by DCFDA staining and FASN activity by spectrophotometry.

RESULTS

Orlistat administration to tumor-bearing mice resulted in tumor growth retardation, prolonged life span, declined tumor cell survival and chemosensitization to cisplatin. It was accompanied by increased osmotic fragility, modulated acidosis, expression of ROS, NO, cytokines, MCT-1 and VH(+) ATPase, Bcl2, Caspase-3, P53, inhibited FASN activity and declined expression of MDR and MRP-1 proteins.

CONCLUSION

Orlistat manifests antitumor and chemosensitizing action implicating modulated regulation of cell survival, reconstituted-tumor microenvironment and altered MDR phenotype.

GENERAL SIGNIFICANCE

These observations indicate that orlistat could be utilized as an adjunct regimen for improving antitumor efficacy of cisplatin.

The Effects of Crinum asiaticum on the Apoptosis Induction and the Reversal of Multidrug Resistance in HL-60/MX2

The present study investigated the anti-proliferative and chemosensitizing effects of Crinum asiaticum var. japonicum against multi-drug resistant (MDR) cancer cells. The 80% methanol extract, chloroform (CHCI₃) fraction and butanol (BuOH) fraction of C asiaticum inhibited the growth of mitoxantrone (MX) resistant HL-60 (HL-60/MX2) cells. When HL-60/MX2 cells were treated with the CHCI₃ and BuOH fractions, DNA ladder and sub-G1 hypodiploid cells were observed. Furthermore, the fractions reduced Bcl-2 mRNA levels, whereas Bax mRNA levels were increased. These results suggest that the inhibitory effect of C. asiaticum on the growth of the HL-60/MX2 cells might arise from the induction of apoptosis. Treatment of HL-60/MX2 cells with the fractions markedly decreased the mRNA levels of the multi-drug resistance protein-1 and breast cancer resistance protein. The CHCI3 fraction and hexane fraction increased MX accumulation in HL-60/MX2 cells. These results imply that the CHCI₃ fraction of C asiaticum plays a pivotal role as a chemosensitizer. We suggest that components of C asiaticum might have a therapeutic potential for the treatment of MDR leukemia.