Multidrug resistance proteins: role of P-glycoprotein, MRP1, MRP2, and BCRP (ABCG2) in tissue defense

Curcumin and cancer: An “old-age” disease with an “age-old” solution

Understanding the molecular mechanisms underlying synergistic, potentiative and antagonistic effects of drug combinations could facilitate the discovery of novel efficacious combinations and multi-targeted agents. In this article, we describe an extensive investigation of the published literature on drug combinations for which the combination effect has been evaluated by rigorous analysis methods and for which relevant molecular interaction profiles of the drugs involved are available. Analysis of the 117 drug combinations identified reveals general and specific modes of action, and highlights the potential value of molecular interaction profiles in the discovery of novel multicomponent therapies.

Mechanisms of drug combinations: interaction and network perspectives.

MGMT: key node in the battle against genotoxicity, carcinogenicity and apoptosis induced by alkylating agents.

While cisplatin and carboplatin are active versus most common cancers, epithelial malignancies are incurable when metastatic. Even if an initial response occurs, acquired resistance due to mutations and epigenetic events limits efficacy. Resistance may be due to excess of a resistance factor, to saturation of factors required for tumor cell killing, or to mutation or alteration of a factor required for tumor cell killing. Platinum resistance could arise from decreased tumor blood flow, extracellular conditions, reduced platinum uptake, increased efflux, intracellular detoxification by glutathione, etc., decreased binding (e.g., due to high intracellular pH), DNA repair, decreased mismatch repair, defective apoptosis, antiapoptotic factors, effects of several signaling pathways, or presence of quiescent non-cycling cells. In lung cancer, flattening of dose-response curves at higher doses suggests that efficacy is limited by exhaustion of something required for cell killing, and several clinical observations suggest epigenetic events may play a major role in resistance.

Mechanisms of resistance to cisplatin and carboplatin

Previous studies have shown that glutathione S-transferases (GSTs) can operate in synergy with efflux transporters, multi-drug resistance proteins (MRPs), to confer resistance to several carcinogens, mutagens and anticancer drugs. To address the poorly documented role of the GSTM1 in cancer chemoresistance, we used CAL1 human melanoma cells expressing no endogenous GSTM1 and a high level of MRP1. Cells were transfected with an expression vector containing the GSTM1 cDNA, and different clones were selected expressing different levels of GSTM1 (RT-PCR, Western blot, and enzyme activity). Cells overexpressing GSTM1 displayed a 3- to 4-fold increase in resistance to anticancer drugs vincristine (VCR) and chlorambucil (CHB) in proliferation, cytotoxic, and clonogenic survival assays. Inhibitors of MRP1 (sulfinpyrazone, verapamil) and GST (dicumarol, curcumin) completely reversed the GSTM1-associated resistance to VCR, indicating that a MRP efflux function is necessary to potentiate GSTM1-mediated resistance to VCR. Conversely, MRP1 inhibitors had no effect on the sensitivity to CHB. Using immunofluorescence assay, GSTM1 was also shown to protect microtubule network integrity from VCR-induced inhibition of microtubule polymerization. In conclusion, these results show that GSTM1 alone is involved in melanoma resistance to CHB, whereas it can act in synergy with MRP1 to protect cells from toxic effects of VCR.

Glutathione S-transferase M1 and multidrug resistance protein 1 act in synergy to protect melanoma cells from vincristine effects.

Transferring a gene into cancer cells in order to sensitize them to drugs is an important approach in human cancer gene-therapy research. Thymidine phosphorylase (TP) is the first enzyme in the metabolic activation pathway of 5-fluorouracil (5-FU) to fluorodeoxyribonucleotides, thus, it could be used to increase the sensitivity of cancer cells to this anti-pyrimidine agent. In this study, an expression vector containing the human TP cDNA was transfected into C26 murine colon-carcinoma cells. Stable transfectants were selected; all showed increased TP activity, ranging from 2- to 10-fold when compared with wild-type cells. The in vitro sensitivity of transfectants to 5-FU and 5'-deoxy-5-fluorouridine (5'-DFUR) was enhanced, in agreement with the observed increase in TP activity. Then, tumors were generated by s.c. injection of TP-transfected or wild-type C26 cells in syngeneic BALB/c mice. 5-FU (25 mg/kg, i.p.) induced a growth delay of TP-transfected C26 tumors as compared with C26 wild-type tumors. These data suggest that TP could be transfected in tumor cells to increase the sensitivity to 5-FU for subsequent cancer gene therapy.

Enhancement of 5-fluorouracil cytotoxicity by human thymidine-phosphorylase expression in cancer cells: In vitro and In vivo study

Thymidine phosphorylase (TP) is markedly upregulated in many solid tumors such as colorectal, breast and kidney cancers. Because TP is identical to platelet-derived endothelial cell growth factor, this enzyme is believed to have angiogenic properties, although the precise mechanisms through which it promotes neoangiogenesis are still not fully elucidated. TP is involved as well in the tumoral activation of widely prescribed pyrimidine-derived antimetabolites such as 5-FU, 5'-dFUR and newly marketed capecitabine, and, in this respect, has been presented as a determinant to fluoropyrimidine efficacy in various in vitro and in vivo models. This dual and apparently contradictory role that TP plays yields inconsistent results in the study of relationships between this enzyme expression and clinical outcome in patients treated with fluoropyrimidine analogs. Some studies have shown that high tumoral TP expression was associated indeed with poor clinical response and tumor aggressiveness. Conversely, other reports demonstrated that tumoral TP could be considered as a good response factor in patients exposed to fluoropyrimidine drugs. TP exhibits then its more favorable profile, probably in converting 5-FU to active metabolites responsible for its efficacy as antitumor agent. As a result, TP-targeting as a rationale for anticancer therapy remains unclear. TP inhibitors are being synthesized as an attempt to fight neoangiogenesis, whereas promising new strategies such as taxotere/capecitabine or radiotherapy/fluoropyrimidines associations aim at nothing but boosting TP activity to optimize drug activation in tumors. Such a discrepancy illustrates the complexity of understanding and predicting the exact role of TP in the clinical outcome of patients exposed to fluoropyrimidines, a group of major drugs extensively used in oncology.

Thymidine phosphorylase and fluoropyrimidines efficacy: a Jekyll and Hyde story.

We
investigated the effects of 2′-deoxyinosine (d-Ino), a modulator
yielding thymidine phosphorylase activity, on cellular pharmacology of
5-fluorouracil (FUra) in various human colorectal cell lines and its
antitumoral activity when combined with FUra in human xenografts.
Associating d-Ino with FUra increased by 38 up to 700 times the
sensitivity of HT29 and FUra-resistant SW620 lines, respectively, but
not of CaCo2 cells, although high levels of intracellular FdUMP and
subsequent higher thymidylate synthase inhibition were observed. Cell
death studies confirmed the ability of d-Ino to enhance both early and
late apoptosis induced by FUra in HT29 and SW620 but not in CaCo2.
Similarly, we showed that associating d-Ino increased by 68 up to 101%
the Fas overexpression induced by FUra in HT29 and SW620 but not in
CaCo2 cells. Anti-Fas and anti-FasL antibodies both partly reversed
this increase of cell sensitivity, thus confirming the role Fas plays
in the modulation of FUra toxicity by d-Ino. This Fas component could
explain the discrepancy between the lines because CaCo2 has been
described as insensitive to Fas-mediated apoptosis. Antitumor activity
of the combination was next investigated in nude mice transplanted with
SW620. Results showed that although FUra alone has little effect on
SW620 xenografts ( P > 0.05), associating d-Ino
significantly reduced the tumor growth by 57% ( P < 0.05). This study suggests that it is possible to reduce both
 in vitro and in vivo resistance to FUra
by modulating the way the drug is converted after cellular uptake.

https://clincancerres.aacrjournals.org/content/clincanres/6/4/1529.full.pdf

Enhanced Antitumor Activity of 5-Fluorouracil in Combination with 2′-Deoxyinosine in Human Colorectal Cell Lines and Human Colon Tumor Xenografts

We reported previously that 5-fluorouracil (FUra) efficacy could be enhanced by increasing tumoral thymidine phosphorylase (TP) activity Potentiated TP yield was achieved by either transfecting cells with human TP gene (A Evrard et al , Br J Cancer, 80: 1726–1733, 1999) or associating FUra with 2′-deoxyinosine (d-Ino), a modulator providing the tumors with TP cofactor deoxyribose 1-phosphate (J Ciccolini et al, Clin Cancer Res, 6: 1529–1535, 2000) The purpose of the present work was to study the effects of a combined modulation (TP gene transfer + use of d-Ino) on the sensitivity to FUra of the LS174T human colorectal cell line Results showed a near 4000 times increase of cell sensitivity in vitro after double (genetic + biochemical) modulation This potentiation of tumor response was accompanied by a total change in the FUra anabolic pathway with a 5000% increase of cytosolic fluorodeoxyuridine monophosphate, a stronger and longer inhibition of thymidylate synthase, and 300% augmentation of DNA damage Besides, whereas thymidine failed to inhibit FUra cytotoxicity in LS174T wild-type cells, the potentiation of the antitumor activity observed in the modulating regimen was partly reversed by thymidine, indicative of thymidylate synthase as the main drug target The impact of this double modulation was next investigated in xenograft-bearing nude mice Results showed that whereas FUra alone was completely ineffective on wild-type tumor growth, the size of TP-transfected tumors in animals treated with the FUra/d-Ino combination was reduced by 80% ( P < 005) Our results suggest that FUra exhibits stronger antiproliferative activity when activated via TP through the DNA pathway and that high tumoral TP activity therefore leads to enhanced sensitivity to fluoropyrimidines

https://mct.aacrjournals.org/content/molcanther/1/2/133.full.pdf

Combination of thymidine phosphorylase gene transfer and deoxyinosine treatment greatly enhances 5-fluorouracil antitumor activity in vitro and in vivo.

Pierre Cuq

Papers

Glutathione S-transferase M1 and multidrug resistance protein 1 act in synergy to protect melanoma cells from vincristine effects.

Enhancement of 5-fluorouracil cytotoxicity by human thymidine-phosphorylase expression in cancer cells: In vitro and In vivo study

Thymidine phosphorylase and fluoropyrimidines efficacy: a Jekyll and Hyde story.

Enhanced Antitumor Activity of 5-Fluorouracil in Combination with 2′-Deoxyinosine in Human Colorectal Cell Lines and Human Colon Tumor Xenografts

Combination of thymidine phosphorylase gene transfer and deoxyinosine treatment greatly enhances 5-fluorouracil antitumor activity in vitro and in vivo.