Yunus Luqmani

Mechanisms of Drug Resistance in Cancer Chemotherapy

The management of cancer involves procedures, which include surgery, radiotherapy and chemotherapy. Development of chemoresistance is a persistent problem during the treatment of local and disseminated disease. A plethora of cytotoxic drugs that selectively, but not exclusively, target actively proliferating cells include such diverse groups as DNA alkylating agents, antimetabolites, intercalating agents and mitotic inhibitors. Resistance constitutes a lack of response to drug-induced tumour growth inhibition; it may be inherent in a subpopulation of heterogeneous cancer cells or be acquired as a cellular response to drug exposure. Resistance varies. Although regulatory approval may require efficacy in as few as 20% of trial cohorts, a drug may subsequently be used in unselected patients displaying resistance to the treatment. Principal mechanisms may include altered membrane transport involving the P-glycoprotein product of the multidrug resistance (MDR) gene as well as other associated proteins, altered target enzyme (e.g. mutated topoisomerase II), decreased drug activation, increased drug degradation due to altered expression of drug-metabolising enzymes, drug inactivation due to conjugation with increased glutathione, subcellular redistribution, drug interaction, enhanced DNA repair and failure to apoptose as a result of mutated cell cycle proteins such as p53. Attempts to overcome resistance mainly involve the use of combination drug therapy using different classes of drugs with minimally overlapping toxicities to allow maximal dosages and with narrowest cycle intervals, necessary for bone marrow recovery. Adjuvant therapy with P-glycoprotein inhibitors and, in specific instances, the use of growth factor and protein kinase C inhibitors are newer experimental approaches that may also prove effective in abrogating or delaying onset of resistance. Gene knockout using antisense molecules may be another effective way of blocking drug resistance genes. Conversely, drug resistance may also be used to good purpose by transplanting retrovirally transformed CD34 cells expressing the MDR gene to protect the bone marrow during high-dose chemotherapy.

Signalling pathways involved in endocrine resistance in breast cancer and associations with epithelial to mesenchymal transition (Review)

Both de novo and acquired endocrine resistance constitute a major therapeutic problem for treatment of hormone-positive breast cancer. Multiple explanatory mechanisms have been proposed through the study of cellular models which focus principally on receptor tyrosine kinase mediated signalling pathways utilizing src, PI3K, MAPK and Smads. Many of the transducing molecules, particularly nuclear transcription factors such as Snail, Twist, Snail2, ZEB, FOXC2, TCF/LEF and Goosecoid are participants in proliferation as well as invasion and metastasis, involving a process of orchestrated cellular remodeling which is being likened to the process of epithelial to mesenchymal transition that takes place during embryonic development. We review the accumulating evidence that points towards the occurrence of this phenomenon as a consequence of the loss of endocrine control, with both processes being similarly characterized by depletion of cell adhesion proteins, E-cadherin, catenins and cytokeratins, increased association with the extracellular matrix through induction of metalloproteinases, fibronectin and collagen, and a switch to a mobile vimentin-based cytoskeletal structure with loss of apical basal polarity.

Estrogen Receptor Silencing Induces Epithelial to Mesenchymal Transition in Human Breast Cancer Cells

We propose the hypothesis that loss of estrogen receptor function which leads to endocrine resistance in breast cancer, also results in trans-differentiation from an epithelial to a mesenchymal phenotype that is responsible for increased aggressiveness and metastatic propensity. siRNA mediated silencing of the estrogen receptor in MCF7 breast cancer cells resulted in estrogen/tamoxifen resistant cells (pII) with altered morphology, increased motility with rearrangement and switch from a keratin/actin to a vimentin based cytoskeleton, and ability to invade simulated components of the extracellular matrix. Phenotypic profiling using an Affymetrix Human Genome U133 plus 2.0 GeneChip indicated geometric fold changes ≥3 in approximately 2500 identifiable unique sequences, with about 1270 of these being up-regulated in pII cells. Changes were associated with genes whose products are involved in cell motility, loss of cellular adhesion and interaction with the extracellular matrix. Selective analysis of the data also showed a shift from luminal to basal cell markers and increased expression of a wide spectrum of genes normally associated with mesenchymal characteristics, with consequent loss of epithelial specific markers. Over-expression of several peptide growth factors and their receptors are indicative of an increased contribution to the higher proliferative rates of pII cells as well as aiding their potential for metastatic activity. Signalling molecules that have been identified as key transcriptional drivers of epithelial to mesenchymal transition were also found to be elevated in pII cells. These data support our hypothesis that induced loss of estrogen receptor in previously estrogen/antiestrogen sensitive cells is a trigger for the concomitant loss of endocrine dependence and onset of a series of possibly parallel events that changes the cell from an epithelial to a mesenchymal type. Inhibition of this transition through targeting of specific mediators may offer a useful supplementary strategy to circumvent the effects of loss of endocrine sensitivity.

Phosphofructokinase: A mediator of glycolytic flux in cancer progression

In view of the current limitations of cancer chemotherapy, there has been resurgent interest in re-visiting glycolysis to determine whether tumors could be killed by energy deprivation rather than solely by strategies to inhibit proliferation. Cancer cells exhibit a uniquely high rate of glucose utilization, converting it into lactate whose export subsequently creates an acidic extracellular environment that is thought to promote invasion and metastasis, in preference to its complete oxidation even in the presence of adequate oxygen supply. Reductive analysis of each step of glycolysis shows that, of the three rate limiting enzymes of the pathway, isoforms of phosphofructokinase may afford the greatest opportunity as targets to deprive cancer cells from essential energy and substrates for macromolecular synthesis for proliferation while allowing normal cells to survive. Strategies discussed include restricting the substrate for this enzyme. While prospects for monotherapy with glycolytic inhibitors are poor, combination therapy may be productive.

Differential Effect of Growth Factors on Invasion and Proliferation of Endocrine Resistant Breast Cancer Cells

We have established several breast cancer cell lines that exhibit a permanent ER-depleted phenotype, induced by shRNA transfection of MCF-7 cells, which afford a useful model for studying acquired endocrine resistance. Previously we showed that MDA-231 as well as ER-silenced cells could invade through simulated extracellular matrix components. However, the contribution of individual serum components responsible for cell invasion was not determined. In the present study, an under-agarose gel assay was used to quantitatively assess the invasive movement of two ER-silenced cell lines (pII and YS2.5) in comparison to the parental MCF-7, the ER negative MDA-231, and normal HBL100 cells, as well as a line that was ER-shRNA transfected but failed to exhibit ER down-regulation (YS1.2). We also examined the effect of the growth factors EGF, IGF-1, TGFβ, PDGFC and RANTES on pII cell invasion and proliferation. All breast cancer cell lines which had reduced ER expression exhibited a serum-dependent invasive ability related to the degree of induced ER loss. TGFβ treatment inhibited pII cell proliferation and enhanced their invasive ability but at a relatively high dose. IGF-1 and EGF enhanced pII cell proliferation, with the latter playing the major role in promoting cell invasion. PDGFC did not affect either process although it is highly expressed in pII cells. Differential effects were observed on activation of Akt and ERK1/2 suggesting their involvement as intracellular mediators of EGF induced invasion, in part through the regulation of matrix metalloproteinase activity. Targeting EGF receptor tyrosine kinase activity by erlotinib resulted in significant inhibition of both pII cell proliferation and directional invasion towards EGF suggesting that this drug has potential therapeutic usefulness for preventing spread of particularly endocrine resistant breast cancer.

The influence of pH and hypoxia on tumor metastasis

Rapid malignant proliferation, prior to effective tumor neoangiogenesis, creates a microenvironment around solid cancers, which is predominantly hypoxic and characterized by a high interstitial fluid pressure. Presumably as an adaptive response, tumor cells favor metabolic activity with apparently inefficient energy output, and production of intermediates that promote cellular replication, preferentially through anaerobic glycolysis, a phenomenon that persists even in re-established normoxic conditions (anomalously referred to as ‘aerobic glycolysis’). Extrusion of the consequently excessive accumulation of lactate and protons decreases extracellular pH, leading to a microenvironment considered conducive to promotion of tumor motility, invasion and metastasis, and one that will invariably influence response to drug treatment. This review will critically assess the evidence forming the basis of current understanding of the precise pH conditions in the extracellular tumor matrix, its regulation by cancer cells and relationship with hypoxia, its relevance to malignant progression and its exploitation for therapeutic advantage.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

ABO blood group in Kuwaitis : detailed allele frequency distribution and identification of novel alleles

BACKGROUND:  The ABO blood group is clinically the most important blood group system and can now be genotyped easily by DNA‐based methods without family studies.

Anti-Inflammatory Action of Angiotensin 1-7 in Experimental Colitis.

Background There is evidence to support a role for angiotensin (Ang) 1–7 in reducing the activity of inflammatory signaling molecules such as MAPK, PKC and SRC. Enhanced angiotensin converting enzyme 2 (ACE2) expression has been observed in patients with inflammatory bowel disease (IBD) suggesting a role in its pathogenesis, prompting this study. Methods The colonic expression/activity profile of ACE2, Ang 1–7, MAS1-receptor (MAS1-R), MAPK family and Akt were determined by western blot and immunofluorescence. The effect of either exogenous administration of Ang 1–7 or pharmacological inhibition of its function (by A779 treatment) was determined using the mouse dextran sulfate sodium model. Results Enhanced colonic expression of ACE2, Ang1-7 and MAS1-R was observed post-colitis induction. Daily Ang 1–7 treatment (0.01–0.06 mg/kg) resulted in significant amelioration of DSS-induced colitis. In contrast, daily administration of A779 significantly worsened features of colitis. Colitis-associated phosphorylation of p38, ERK1/2 and Akt was reduced by Ang 1–7 treatment. Conclusion Our results indicate important anti-inflammatory actions of Ang 1–7 in the pathogenesis of IBD, which may provide a future therapeutic strategy to control the disease progression.

Blockade of voltage-gated sodium channels inhibits invasion of endocrine-resistant breast cancer cells.

Voltage-gated Na+ channels (VGSCs) are membrane proteins which are normally expressed in excitable cells but have also been detected in cancer cells, where they are thought to be involved in malignancy progression. In this study we examined the ion current and expression profile of VGSC (Nav1.5) in estrogen receptor (ER)-positive (MCF-7) and silenced (pII) breast cancer cells and its possible influence on their proliferation, motility and invasion. VGSC currents were analysed by whole cell patch clamp recording. Nav1.5 expression and localization, in response to EGF stimulation, was examined by western blotting and immunofluorescence respectively. Cell invasion (under-agarose and Matrigel assays), motility (wound healing assay) and proliferation (MTT assay) were assessed in pII cells in response to VGSC blockers, phenytoin (PHT) and tetrodotoxin (TTX), or by siRNA knockdown of Nav1.5. The effect of PHT and TTX on modulating EGF-induced phosphorylation of Akt and ERK1/2 was determined by western blotting. Total matrix metalloproteinase (MMP) was determined using a fluorometric-based activity assay. The level of various human proteases was detected by using proteome profiler array kit. VGSC currents were detected in pII cells, but were absent in MCF-7. Nav1.5 showed cytoplasmic and perinuclear expression in both MCF-7 and pII cells, with enhanced expression upon EGF stimulation. Treatment of pII cells with PHT, TTX or siRNA significantly reduced invasion towards serum components and EGF, in part through reduction of P-ERK1/2 and proteases such as cathepsin E, kallikrein-10 and MMP-7, as well as total MMP activity. At high concentrations, PHT inhibited motility while TTX reduced cell proliferation. Pharmacological or genetic blockade of Nav1.5 may serve as a potential anti-metastatic therapy for breast cancer.