Iris L. K. Wong

Modulation of multidrug resistance protein 1 (MRP1/ABCC1)-mediated multidrug resistance by bivalent apigenin homodimers and their derivatives.

Here we showed that bivalency approach is effective in modulating multidrug resistance protein 1 (MRP1/ABCC1)-mediated doxorubicin (DOX) and etoposide (VP16) resistance in human 2008/MRP1 ovarian carcinoma cells. Flavonoid dimers bearing five or six ethylene glycol (EG) units with 6-methyl (4e, 4f) or 7-methyl (5e, 5f) substitution on the ring A of flavonoid dimers have the highest modulating activity for DOX against MRP1 with an EC(50) ranging from 73 to 133 nM. At 0.5 microM, the flavonoid dimer 4e was sufficient to restore DOX accumulation in 2008/MRP1 to parental 2008/P level. Lineweaver-Burk and Dixon plot suggested that it is likely a competitive inhibitor of DOX transport with a K(i) = 0.2 microM. Our data suggest that flavonoid dimers have a high affinity toward binding to DOX recognition site of MRP1. This results in inhibiting DOX transport, increasing intracellular DOX retention, and finally resensitizing 2008/MRP1 to DOX. The present study demonstrates that flavonoid dimers can be employed as an effective modulator of MRP1-mediated drug resistance in cancer cells.

Design and Syntheses of Permethyl Ningalin B Analogues: Potent Multidrug Resistance (MDR) Reversal Agents of Cancer Cells

A series of novel N-arylalkyl-3,4-diaryl-substituted pyrrole-2,5-diones were synthesized. They exhibited promising P-gp modulating activity in a P-gp overexpressing breast cancer cell line (LCC6MDR). Compound 6 (with three methoxy groups at D-ring) displayed the highest P-gp modulating activity. 6 at 1 microM can sensitize LCC6MDR cells toward paclitaxel by 18.2-fold. Interestingly, a synergy on modulating P-gp was noted when 6 and 25 were used together (fractional inhibitory concentration index FICI = 0.42). Combination of 6 (0.5 microM) and 25 (0.5 microM) resulted in a 66-fold sensitization of LCC6MDR cells toward paclitaxel. They also reversed P-gp mediated doxorubicin (DOX) and vincristine resistance. Kinetic characterization suggests that permethyl ningalin B analogues likely act as a noncompetitive inhibitor of P-gp-mediated DOX transport (K(i) = 5.4-5.8 microM). The present study demonstrates that synthetic analogues of permethyl ningalin B can be employed as effective and safe modulators of P-gp-mediated drug resistance in cancer cells.

Amine linked flavonoid dimers as modulators for P-glycoprotein-based multidrug resistance: structure-activity relationship and mechanism of modulation.

Here we report a great improvement in reversal potency of cancer drug resistance when flavonoid dimers possess a functionally substituted aminopolyethylene glycol linker. The most potent compound, 18, contains a N-benzyl group at the linker. It has many advantages including (1) high potencies in reversing P-glycoprotein (P-gp) mediated resistance in LCC6MDR cells to various anticancer drugs with EC(50) in the nanomolar range, (2) low toxicity and high therapeutic index, and (3) preferential inhibition of P-gp over multidrug resistance protein 1 and breast cancer resistance protein. Compound 18 stimulates P-gp-ATPase activity by 2.7-fold and mediates a dose-dependent inhibition of doxorubicin (DOX) transport activity. Lineweaver-Burk and Dixon plots suggest that 18 is a competitive inhibitor to DOX in binding to P-gp with a K(i) of 0.28-0.34 μM and a Hill coefficient of 1.17. Moreover, the LCC6MDR cell displays about 2.1-fold lower intracellular accumulation of 18 compared to the wild type, suggesting that 18 is a P-gp substrate as well.

Flavonoid Dimers as Bivalent Modulators for P-Glycoprotein-Based Multidrug Resistance: Structure–Activity Relationships

Bivalent modulators of P‐glycoprotein: A small library of flavonoid homodimers and heterodimers was synthesized, and their in vitro activity in reversing paclitaxel resistance was evaluated along with structure–activity relationships. SAR trends indicate that flavonoid dimers with nonpolar, hydrophobic, less bulky substituents generally show more potent reversing activity. This will help guide future efforts in the search for more potent compounds.

Flavonoid Dimers as Bivalent Modulators for Pentamidine and Sodium Stiboglucanate Resistance in Leishmania

ABSTRACT Drug resistance by overexpression of ATP-binding cassette (ABC) transporters is an impediment in the treatment of leishmaniasis. Flavonoids are known to reverse multidrug resistance (MDR) in Leishmania and mammalian cancers by inhibiting ABC transporters. Here, we found that synthetic flavonoid dimers with three (compound 9c) or four (compound 9d) ethylene glycol units exhibited a significantly higher reversing activity than other shorter or longer ethylene glycol-ligated dimers, with ∼3-fold sensitization of pentamidine and sodium stibogluconate (SSG) resistance in Leishmania, respectively. This modulatory effect was dosage dependent and not observed in apigenin monomers with the linker, suggesting that the modulatory effect is due to its bivalent nature. The mechanism of reversal activity was due to increased intracellular accumulation of pentamidine and total antimony in Leishmania. Compared to other MDR modulators such as verapamil, reserpine, quinine, quinacrine, and quinidine, compounds 9c and 9d were the only agents that can reverse SSG resistance. In terms of reversing pentamidine resistance, 9c and 9d have activities comparable to those of reserpine and quinacrine. Modulators 9c and 9d exhibited reversal activity on pentamidine resistance among LeMDR1−/−, LeMDR1+/+, and LeMDR1-overexpressed mutants, suggesting that these modulators are specific to a non-LeMDR1 pentamidine transporter. The LeMDR1 copy number is inversely related to pentamidine resistance, suggesting that it might be involved in importing pentamidine into the mitochondria. In summary, bivalency could be a useful strategy for the development of more potent ABC transporter modulators and flavonoid dimers represent a promising reversal agent for overcoming pentamidine and SSG resistance in parasite Leishmania.

Structure-activity relationship study of permethyl ningalin B analogues as P-glycoprotein chemosensitizers.

A novel series of permethyl ningalin B analogues were synthesized and evaluated for their P-glycoprotein (P-gp)-modulating activities in a P-gp-overexpressing breast cancer cell line (LCC6MDR). Compounds 35 and 37, which possess one methoxy group and one benzyloxy group at aryl ring C, displayed the most potent P-gp-modulating activity. A 1 μM concentration of 35 and 37 resensitized LCC6MDR cells toward paclitaxel by 42.7-fold, with respective EC50 values of 93.5 and 110.0 nM. Their mechanism of P-gp modulation is associated with an increase in intracellular drug accumulation. Their advantages also include low cytotoxicity (IC50 for L929 fibroblast >100 μM) and high therapeutic indexes (>909 after normalization with their EC50 values). 35 is not a substrate of P-gp. They are potentially dual-selective modulators for both P-gp and breast cancer resistance protein transporters. The present study demonstrates that these new compounds can be employed as effective and safe modulators of P-gp-mediated drug resistance in cancer cells.

Quinacrine and a novel apigenin dimer can synergistically increase the pentamidine susceptibility of the protozoan parasite Leishmania

OBJECTIVES The aim of this study was to investigate the synergistic effect of quinacrine and a novel apigenin dimer (compound 9d) on reversing pentamidine resistance of Leishmania parasites. METHODS Pentamidine-resistant cell lines, LePentR50 and LdAG83PentR50, were generated by gradually increasing pentamidine pressure on wild-type promastigotes. We tested the effects of different combinations of quinacrine and an apigenin dimer on modulating the pentamidine resistance levels of LePentR50 and LdAG83PentR50 using an MTS proliferation assay. We then measured the accumulation level of pentamidine using HPLC. The fractional inhibitory concentration index (FICI) method was used to evaluate the interaction between quinacrine and the apigenin dimer on reversing pentamidine resistance in Leishmania. RESULTS LePentR50 and LdAG83PentR50 promastigotes were approximately 8.6- and 4.6-fold more resistant to pentamidine than their wild-type parents. Amastigotes derived from LePentR50 and LdAG83PentR50 were also pentamidine-resistant. We found that quinacrine can increase the susceptibility of Leishmania to pentamidine. Quinacrine, when used at 6 microM, can increase the IC(50) of pentamidine by 3.8-, 3.4-, 3.5- and 6.3-fold in wild-type Leishmania enriettii Le, LePentR50, wild-type Leishmania donovani LdAG83 and LdAG83PentR50, respectively. Quinine, quinidine and verapamil did not show any sensitizing effect. The sensitizing effect of quinacrine was: (i) dose-dependent; (ii) not associated with an increase in pentamidine accumulation; and (iii) only observed in pentamidine-resistant but not sodium stibogluconate-resistant or vinblastine-resistant parasites. Other than quinacrine, we also found that an apigenin dimer (compound 9d), previously shown to be able to inhibit ABCB1-mediated cancer drug resistance in mammalian cells, can also increase the pentamidine susceptibility of Leishmania. 9d, when used at 6 microM, can increase the IC(50) of pentamidine by 2.5-, 4.2-, 1.6- and 1.9-fold in Le, LePentR50, LdAG83 and LdAG83PentR50, respectively. Unlike quinacrine, sensitization by 9d was accompanied by an increase in pentamidine accumulation, presumably due to the inhibition of an ABC transporter. Using the FICI method, we found that quinacrine and 9d can act synergistically. When they are used in a 1:1 ratio, they sensitize LePentR50 to pentamidine by 19-fold, with an FICI of 0.48 (P < 0.005), indicating that they might act synergistically. CONCLUSIONS Our findings support the notion that the pentamidine susceptibility of Leishmania is mediated by multiple targets. Quinacrine and apigenin dimer 9d, each inhibiting its own target, can have a synergistic effect when used together to sensitize Leishmania to pentamidine.

Flavonoid Dimers as Novel, Potent Antileishmanial Agents

The present study found that synthetic flavonoid dimers with either polyethylene glycol linker or amino ethyleneglycol linker have marked leishmanicidal activity. Compound 39 showed very consistent and promising leishmanicidal activity for both extracellular promastigotes (IC₅₀ ranging from 0.13 to 0.21 μM) and intracellular amastigotes (IC₅₀ = 0.63 μM) irrespective of the drug-sensitivity of parasites. Moreover, compound 39 displayed no toxicity toward macrophage RAW 264.7 cells (IC₅₀ > 100 μM) and primary mouse peritoneal elicited macrophages (IC₅₀ > 88 μM). Its high value of therapeutic index (>140) was better than other highly potent antileishmanials such as amphotericin B (therapeutic index = 119). Compound 39 is therefore a new, safe, and effective antileishmanial candidate compound which is even effective against drug-refractory parasites.

Potent and Nontoxic Chemosensitizer of P-Glycoprotein-Mediated Multidrug Resistance in Cancer: Synthesis and Evaluation of Methylated Epigallocatechin, Gallocatechin, and Dihydromyricetin Derivatives

We are interested in developing novel natural product-derived P-gp inhibitors to reverse cancer drug resistance. Here, we have synthesized 55 novel derivatives of methylated epigallocatechin (EGC), gallocatechin (GC), and dihydromyricetin (DHM). Three EGC derivatives (23, 35, and 36) and three GC derivatives (50, 51, and 53) are significantly better than epigallocatechin gallate (EGCG) with a relative fold (RF) ranging from 31.4 to 53.6. The effective concentration (EC50) of 23 and 51 ranges from 102 to 195 nM. Compounds 23 and 51 are noncytotoxic to fibroblasts with IC50 > 100 μM. Compound 23 is specific for P-gp without modulating activity toward MRP1 or BCRP. Compounds 23 and 51 are non-P-gp substrates. Important pharmacophores for P-gp modulation were identified. In summary, methylated EGC and GC derivatives represent a new class of potent, specific, noncytotoxic, and nonsubstrate P-gp modulators.

In Vitro and In Vivo Efficacy of Novel Flavonoid Dimers against Cutaneous Leishmaniasis

ABSTRACT Treatment of leishmaniasis by chemotherapy remains a challenge because of limited efficacy, toxic side effects, and drug resistance. We previously reported that synthetic flavonoid dimers have potent antipromastigote and antiamastigote activity against Leishmania donovani, the causative agent of visceral leishmaniasis. Here, we further investigate their leishmanicidal activities against cutaneous Leishmania species. One of the flavonoid dimers (compound 39) has marked antipromastigote (50% inhibitory concentrations [IC50s], 0.19 to 0.69 μM) and antiamastigote (IC50s, 0.17 to 2.2 μM) activities toward different species of Leishmania that cause cutaneous leishmaniasis, including Leishmania amazonensis, Leishmania braziliensis, Leishmania tropica, and Leishmania major. Compound 39 is not toxic to peritoneal elicited macrophages, with IC50 values higher than 88 μM. In the mouse model of cutaneous leishmaniasis induced by subcutaneous inoculation of L. amazonensis in mouse footpads, intralesional administration of 2.5 mg/kg of body weight of compound 39.HCl can reduce footpad thickness by 36%, compared with that of controls values. The amastigote load in the lesions was reduced 20-fold. The present study suggests that flavonoid dimer 39 represents a new class of safe and effective leishmanicidal agent against visceral and cutaneous leishmaniasis.