Oral verapamil with chemotherapy for advanced non-small cell lung cancer: a randomised study

Lung cancer, comorbidities, and medication: the infernal trio

Most patients with lung cancer are smokers and are of advanced age. They are therefore at high risk of having age- and lifestyle-related comorbidities. These comorbidities are subject to treatment or even polypharmacy. There is growing evidence of a link between lung cancer, comorbidities and medications. The relationships between these entities are complex. The presence of comorbidities and their treatments influence the time of cancer diagnosis, as well as the diagnostic and treatment strategy. On the other hand, cancer treatment may have an impact on the patient's comorbidities such as renal failure, pneumonitis or endocrinopathies. This review highlights how some comorbidities may have an impact on lung cancer presentation and may require treatment adjustments. Reciprocal influences between the treatment of comorbidities and anticancer therapy will also be discussed.

Comprehensive Evaluation of Multiple Approaches Targeting ABCB1 to Resensitize Docetaxel-Resistant Prostate Cancer Cell Lines

Docetaxel (DTX) is a mainstay in the treatment of metastatic prostate cancer. Failure of DTX therapy is often associated with multidrug resistance caused by overexpression of efflux membrane transporters of the ABC family such as the glycoprotein ABCB1. This study investigated multiple approaches targeting ABCB1 to resensitize DTX-resistant (DTXR) prostate cancer cell lines. In DU145 DTXR and PC-3 DTXR cells as well as age-matched parental controls, the expression of selected ABC transporters was analyzed by quantitative PCR, Western blot, flow cytometry and immunofluorescence. ABCB1 effluxing activity was studied using the fluorescent ABCB1 substrate rhodamine 123. The influence of ABCB1 inhibitors (elacridar, tariquidar), ABCB1-specific siRNA and inhibition of post-translational glycosylation on DTX tolerance was assessed by cell viability and colony formation assays. In DTXR cells, only ABCB1 was highly upregulated, which was accompanied by a strong effluxing activity and additional post-translational glycosylation of ABCB1. Pharmacological inhibition and siRNA-mediated knockdown of ABCB1 completely resensitized DTXR cells to DTX. Inhibition of glycosylation with tunicamycin affected DTX resistance partially in DU145 DTXR cells, which was accompanied by a slight intracellular accumulation and decreased effluxing activity of ABCB1. In conclusion, DTX resistance can be reversed by various strategies with small molecule inhibitors representing the most promising and feasible approach.

Calcium signaling: A therapeutic target to overcome resistance to therapies in cancer

Innate and acquired resistances to therapeutic agents are responsible for the failure of cancer treatments. Due to the multifactorial nature of resistance, the identification of new therapeutic targets is required to improve cancer treatment. Calcium is a universal second messenger that regulates many cellular functions such as proliferation, migration, and survival. Calcium channels, pumps and exchangers tightly regulate the duration, location and magnitude of calcium signals. Many studies have implicated dysregulation of calcium signaling in several pathologies, including cancer. Abnormal calcium fluxes due to altered channel expression or activation contribute to carcinogenesis and promote tumor development. However, there is limited information on the role of calcium signaling in cancer resistance to therapeutic drugs. This review discusses the role of calcium signaling as a mediator of cancer resistance, and assesses the potential value of combining anticancer therapy with calcium signaling modulators to improve the effectiveness of current treatments.

Cancer chemotherapy: insights into cellular and tumor microenvironmental mechanisms of action

Chemotherapy has historically been the mainstay of cancer treatment, but our understanding of what drives a successful therapeutic response remains limited. The diverse response of cancer patients to chemotherapy has been attributed principally to differences in the proliferation rate of the tumor cells, but there is actually very little experimental data supporting this hypothesis. Instead, other mechanisms at the cellular level and the composition of the tumor microenvironment appear to drive chemotherapy sensitivity. In particular, the immune system is a critical determinant of chemotherapy response with the depletion or knock-out of key immune cell populations or immunological mediators completely abrogating the benefits of chemotherapy in pre-clinical models. In this perspective, we review the literature regarding the known mechanisms of action of cytotoxic chemotherapy agents and the determinants of response to chemotherapy from the level of individual cells to the composition of the tumor microenvironment. We then summarize current work toward the development of dynamic biomarkers for response and propose a model for a chemotherapy sensitive tumor microenvironment.

Down-regulation of ABCB1 by Collateral Sensitivity Drugs Reverses Multidrug Resistance and Up-regulates Enolase I

The emergence of drug resistance remains an obstacle in the clinical treatment of cancer. Recent developments in the studies of drug resistance have identified compounds such as verapamil and tamoxifen that specifically target ABCB1-expressing multidrug resistant (MDR) cells, through an ATP-dependent ROS-generating mechanism. In this report, we demonstrate that treatment of ABCB1-expressing multidrug resistant cells (CHORC5 or MDA-Doxo400) or individual clones of the latter with sub-lethal concentrations of tamoxifen or verapamil down-regulates ABCB1 protein and mRNA expression in surviving clones. Consequently, tamoxifen- and verapamil-treated cells show increased sensitivity to chemotherapeutic drugs (e.g., colchicine and doxorubicin) and decreased sensitivity to collateral sensitivity drugs (e.g., verapamil and tamoxifen). Importantly, we show for the first time that down-regulation of ABCB1 expression resulting from tamoxifen treatment and CRISPR-knockout of ABCB1 expression up-regulate α-enolase (enolase I) protein levels and activity. These findings demonstrate a possible effect of ABCB1 expression on the metabolic homeostasis of MDR cells. Moreover, given the use of tamoxifen to prevent the recurrence of estrogen receptor-positive breast cancer, the findings of this study may be clinically important in modulating activity of other drugs.

Predictive Value of MRP-1 in Localized High-Risk Soft Tissue Sarcomas: A Translational Research Associated to ISG-STS 1001 Randomized Phase III Trial

MRP-1 is implicated in multidrug resistance and was described as prognostic in high-risk patients with soft-tissue sarcoma (STS) in a previous study. The current research aimed to validate MRP-1 prognostic/predictive value in localized sarcomas treated with anthracyclines plus ifosfamide within the ISG-1001 phase III study. In addition, the inhibitory activity on MRP-1 was investigated in preclinical studies to identify new combinations able to increase the efficacy of standard chemotherapy in STS. MRP-1 expression was assessed by IHC in tissue microarrays from patients with STS and tested for correlation with disease-free survival (DFS) and overall survival (OS). In vitro studies tested the efficacy of MRP-1 inhibitors (nilotinib, ripretinib, selumetinib, and avapritinib) in sarcoma cell lines. The effect of combinations of the most active MRP-1 inhibitors and chemotherapy was measured on the basis of apoptosis. MRP-1 was evaluable in 231 of 264 cases who entered the study. MRP-1 expression (strong intensity) was independently associated with worse DFS [HR, 1.78; 95% confidence interval (CI), 1.11-2.83; P = 0.016], in the multivariate analysis, with a trend for a worse OS (HR, 1.78; 95% CI, 0.97-3.25; P = 0.062). In vitro studies showed that the addition of MRP-1 inhibitors (nilotinib or avapritinib) to doxorubicin plus palifosfamide, significantly increased cell death in SK-UT-1 and CP0024 cell lines. MRP-1 is an adverse predictive factor in localized high-risk patients with STS treated with neoadjuvant anthracyclines plus ifosfamide followed by surgery. In vitro findings support the clinical assessment of the combination of chemotherapy and MRP-1 inhibitors as a promising strategy to overcome the drug ceiling effect for chemotherapy.

Novel Therapeutic Approaches of Ion Channels and Transporters in Cancer

The expression and function of many ion channels and transporters in cancer cells display major differences in comparison to those from healthy cells. These differences provide the cancer cells with advantages for tumor development. Accordingly, targeting ion channels and transporters have beneficial anticancer effects including inhibition of cancer cell proliferation, migration, invasion, metastasis, tumor vascularization, and chemotherapy resistance, as well as promoting apoptosis. Some of the molecular mechanisms associating ion channels and transporters with cancer include the participation of oxidative stress, immune response, metabolic pathways, drug synergism, as well as noncanonical functions of ion channels. This diversity of mechanisms offers an exciting possibility to suggest novel and more effective therapeutic approaches to fight cancer. Here, we review and discuss most of the current knowledge suggesting novel therapeutic approaches for cancer therapy targeting ion channels and transporters. The role and regulation of ion channels and transporters in cancer provide a plethora of exceptional opportunities in drug design, as well as novel and promising therapeutic approaches that may be used for the benefit of cancer patients.

Repurposing of drugs: An attractive pharmacological strategy for cancer therapeutics

Human malignancies are one of the major health-related issues though out the world and anticipated to rise in the future. The development of novel drugs/agents requires a huge amount of cost and time that represents a major challenge for drug discovery. In the last three decades, the number of FDA approved drugs has dropped down and this led to increasing interest in drug reposition or repurposing. The present review focuses on recent concepts and therapeutic opportunities for the utilization of antidiabetics, antibiotics, antifungal, anti-inflammatory, antipsychotic, PDE inhibitors and estrogen receptor antagonist, Antabuse, antiparasitic and cardiovascular agents/drugs as an alternative approach against human malignancies. The repurposing of approved non-cancerous drugs is an effective strategy to develop new therapeutic options for the treatment of cancer patients at an affordable cost in clinics. In the current scenario, most of the countries throughout the globe are unable to meet the medical needs of cancer patients because of the high cost of the available cancerous drugs. Some of these drugs displayed potential anti-cancer activity in preclinic and clinical studies by regulating several key molecular mechanisms and oncogenic pathways in human malignancies. The emerging pieces of evidence indicate that repurposing of drugs is crucial to the faster and cheaper discovery of anti-cancerous drugs.

Anticancer Effects of Antihypertensive L-Type Calcium Channel Blockers on Chemoresistant Lung Cancer Cells via Autophagy and Apoptosis

Purpose

Hypertension and cancer are frequently found comorbidity occurring in same individual. This study was intended to evaluate the anticancer effects of commonly used antihypertensive medications and chemotherapy on chemoresistant lung cancer cells.

Methods

Calcium channel blockers (CCBs), including Verapamil, Diltiazem, and Nifedipine, either alone or combined with docetaxel (DOC) or vincristine (VCR) were used to treat A549 lung adenocarcinoma chemoresistant sublines. Cell viability was determined by MTT assay, and colony formation assay was used to demonstrate the long-term effect of CCBs on proliferation of the sublines. Apoptosis was evaluated by Annexin V assay and autophagy intensity was quantitated from acidic vesicular organelle formation. Pan-caspase inhibitor, shATG5 interference and chloroquine were applied to study the roles of Verapamil on apoptosis and autophagy, with related proteins verified by Western blot analysis.

Results

Results show that 10 μM of Verapamil and Diltiazem, but not Nifedipine, differentially induce autophagy in DOC-resistant or VCR-resistant A549 cells, respectively. When CCBs are combined with DOC or VCR to treat the sublines, 10 μM of Verapamil induces autophagy more significantly than Diltiazem and Nifedipine, respectively, in DOC-resistant (54.91±0.76, 18.03±0.69, 7.05±0.30) or VCR-resistant A549 (32.41±1.04, 21.51±0.63, 7.14±0.24) cells. Inhibition of apoptosis by pan-caspase inhibitor partly reduced cell death indicates association of caspase-dependent cell death but with persistence of autophagy. Inhibition of autophagy by interfering ATG5 expression reduced c-PARP level and apoptotic cells suggest a pro-death role of autophagy. Chloroquine treatment enhanced autophagosome accumulation and cell death but with reduced c-PARP level suggests that mechanism of caspase-independent cell death also contributes to Verapamil/chemotherapy-induced anticancer effects. 

Conclusion

Verapamil combined with DOC or VCR induces chemoresistant lung cancer cells to death through autophagy burst and apoptosis more strongly than Diltiazem and Nifedipine. Administering Verapamil or Diltiazem individually with chemotherapy, but not Nifedipine, can be considered in lung cancer patients with hypertension.

HERG channel and cancer: A mechanistic review of carcinogenic processes and therapeutic potential

The human ether-à-go-go related gene (HERG) encodes the alpha subunit of Kv11.1, which is a voltage-gated K⁺ channel protein mainly expressed in heart and brain tissue. HERG plays critical role in cardiac repolarization, and mutations in HERG can cause long QT syndrome. More recently, evidence has emerged that HERG channels are aberrantly expressed in many kinds of cancer cells and play important roles in cancer progression. HERG could therefore be a potential biomarker for cancer and a possible molecular target for anticancer drug design. HERG affects a number of cellular processes, including cell proliferation, apoptosis, angiogenesis and migration, any of which could be affected by dysregulation of HERG. This review provides an overview of available information on HERG channel as it relates to cancer, with focus on the mechanism by which HERG influences cancer progression. Molecular docking attempts suggest two possible protein-protein interactions of HERG with the ß1-integrin receptor and the transcription factor STAT-1 as novel HERG-directed therapeutic targeting which avoids possible cardiotoxicity. The role of epigenetics in regulating HERG channel expression and activity in cancer will also be discussed. Finally, given its inherent extracellular accessibility as an ion channel, we discuss regulatory roles of this molecule in cancer physiology and therapeutic potential. Future research should be directed to explore the possibilities of therapeutic interventions targeting HERG channels while minding possible complications.

Current progress and future perspectives of polypharmacology : From the view of non-small cell lung cancer

A pre-eminent subtype of lung carcinoma, Non-small cell lung cancer accounts for paramount causes of cancer-associated mortality worldwide. Undeterred by the endeavour in the treatment strategies, the overall cure and survival rates for NSCLC remain substandard, particularly in metastatic diseases. Moreover, the emergence of resistance to classic anticancer drugs further deteriorates the situation. These demanding circumstances culminate the need of extended and revamped research for the establishment of upcoming generation cancer therapeutics. Drug repositioning introduces an affordable and efficient strategy to discover novel drug action, especially when integrated with recent systems biology driven stratagem. This review illustrates the trendsetting approaches in repurposing along with their numerous success stories with an emphasize on the NSCLC therapeutics. Indeed, these novel hits, in combination with conventional anticancer agents, will ideally make their way the clinics and strengthen the therapeutic arsenal to combat drug resistance in the near future.

Cell Membrane Transport Mechanisms: Ion Channels and Electrical Properties of Cell Membranes

Cellular life strongly depends on the membrane ability to precisely control exchange of solutes between the internal and external (environmental) compartments. This barrier regulates which types of solutes can enter and leave the cell. Transmembrane transport involves complex mechanisms responsible for passive and active carriage of ions and small- and medium-size molecules. Transport mechanisms existing in the biological membranes highly determine proper cellular functions and contribute to drug transport. The present chapter deals with features and electrical properties of the cell membrane and addresses the questions how the cell membrane accomplishes transport functions and how transmembrane transport can be affected. Since dysfunctions of plasma membrane transporters very often are the cause of human diseases, we also report how specific transport mechanisms can be modulated or inhibited in order to enhance the therapeutic effect.

Disrupting P-glycoprotein function in clinical settings: what can we learn from the fundamental aspects of this transporter?

P-glycoprotein is one of the most well-studied drug transporters, significant for its role in cancer multiple drug resistance. However, using P-gp inhibitors with the aim of enhancing the therapeutic efficacy of anti-cancer drugs has led to disappointing outcomes. Furthermore, several lead compounds suggested by in vitro and pre-clinical studies have shown variable pharmacokinetics and therapeutic efficacies when applied in the clinical setting. This review will highlight the need to revisit a sound approach to better design and apply P-gp inhibitors in light of safety and efficacy. Challenges confronting the issue hinge upon myriad studies that do not necessarily represent the heterogeneous target population of this therapeutic approach. The application of P-gp modulators has also been complicated by the promiscuous substrate-binding behaviour of P-gp, as well as toxicities related to its intrinsic presence in healthy tissue. This review capitalizes on information spanning genetics, energetics, and pharmacology, bringing to light some fundamental aspects that ought to be reconsidered in order to improve upon and design the next generation of P-gp inhibitors.

P-glycoprotein Mediated Efflux Modulators of Plant Origin: A Short Review

Drug efflux transporters such as P-glycoprotein (P-gp) help maintain cellular homeostasis but are also major contributors to the development of multidrug resistance (MDR) phenomena. Since P-gp was associated with MDR, several compounds showing potential to inhibit this transporter have been identified. Particular attention has been given to natural products, namely those of plant origin, looking for highly effective and safe P-gp inhibitors with little to no interaction with other cellular or metabolic processes. Here we abridge several examples of plant compounds from distinct classes, polyketides, lignans, anthraquinones, coumarins, alkaloids, mono- and sesqui-terpenes, steroids and limonoids, which have shown the ability to modulate in vitro or in vivo the P-gp activity.

Usefulness of targeting lymphocyte Kv1.3-channels in the treatment of respiratory diseases

T lymphocytes predominantly express delayed rectifier K(+)-channels (Kv1.3) in their plasma membranes. Patch-clamp studies revealed that the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. Using selective channel inhibitors in experimental animal models, in vivo studies further revealed the clinically relevant relationship between the channel expression and the development of chronic respiratory diseases, in which chronic inflammation or the overstimulation of cellular immunity in the airways is responsible for the pathogenesis. In chronic respiratory diseases, such as chronic obstructive pulmonary disease, asthma, diffuse panbronchiolitis and cystic fibrosis, in addition to the supportive management for the symptoms, the anti-inflammatory effects of macrolide antibiotics were shown to be effective against the over-activation or proliferation of T lymphocytes. Recently, we provided physiological and pharmacological evidence that macrolide antibiotics, together with calcium channel blockers, HMG-CoA reductase inhibitors, and nonsteroidal anti-inflammatory drugs, effectively suppress the Kv1.3-channel currents in lymphocytes, and thus exert anti-inflammatory or immunomodulatory effects. In this review article, based on the findings obtained from recent in vivo and in vitro studies, we address the novel therapeutic implications of targeting the lymphocyte Kv1.3-channels for the treatment of chronic or acute respiratory diseases.

Voltage-gated ion channels in cancer cell proliferation

Changes of the electrical charges across the surface cell membrane are absolutely necessary to maintain cellular homeostasis in physiological as well as in pathological conditions. The opening of ion channels alter the charge distribution across the surface membrane as they allow the diffusion of ions such as K+, Ca++, Cl.

Targeting ion channels for cancer therapy by repurposing the approved drugs

Ion channels have been shown to be involved in oncogenesis and efforts are being poured in to target the ion channels. There are many clinically approved drugs with ion channels as "off" targets. The question is, can these drugs be repurposed to inhibit ion channels for cancer treatment? Repurposing of drugs will not only save investors' money but also result in safer drugs for cancer patients. Advanced bioinformatics techniques and availability of a plethora of open access data on FDA approved drugs for various indications and omics data of large number of cancer types give a ray of hope to look for possibility of repurposing those drugs for cancer treatment. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

A novel nanoparticle formulation overcomes multiple types of membrane efflux pumps in human breast cancer cells

Multidrug resistance (MDR) in cancer cells can involve overexpression of different types of membrane drug efflux pumps and other drug resistance mechanisms. Hence, inhibition of one resistance mechanism may not be therapeutically effective. Previously we demonstrated a new polymer lipid hybrid nanoparticle (PLN) system was able to circumvent drug resistance of P-glycoprotein (P-gp) overexpressing breast cancer cells. The objectives of the present study were 2-fold: (1) to evaluate the ability of the PLN system to overcome two other membrane efflux pumps-multidrug resistance protein 1 (MRP1+) and breast cancer resistance protein (BCRP+) overexpressed on human breast cancer cell lines MCF7 VP (MRP1+) and MCF7 MX (BCRP+); and (2) to evaluate possible synergistic effects of doxorubicin (Dox)-mitomycin C (MMC) in these cell lines. These objectives were accomplished by measuring in vitro cellular uptake, intracellular trafficking, and cytotoxicity (using a clonogenic assay and median effect analysis), of Dox, MMC, or Dox-MMC co-loaded PLN. Treatment of MDR cells with PLN encapsulating single anticancer agents significantly enhanced cell kill compared to free Dox or MMC solutions. Dox-MMC co-loaded PLN were 20-30-folds more effective in killing MDR cells than free drugs. Co-encapsulated Dox-MMC was more effective in killing MDR cells than single agent-encapsulated PLN. Microscopic images showed perinuclear localization of fluorescently labelled PLN in all cell lines. These results are consistent with our previous results for P-gp overexpressing breast cancer cells suggesting the PLN system can overcome multiple types of membrane efflux pumps increasing the cytotoxicity of Dox-MMC at significantly lower doses than free drugs.

Role of ion channels in regulating Ca²⁺ homeostasis during the interplay between immune and cancer cells

Ion channels are abundantly expressed in both excitable and non-excitable cells, thereby regulating the Ca²⁺ influx and downstream signaling pathways of physiological processes. The immune system is specialized in the process of cancer cell recognition and elimination, and is regulated by different ion channels. In comparison with the immune cells, ion channels behave differently in cancer cells by making the tumor cells more hyperpolarized and influence cancer cell proliferation and metastasis. Therefore, ion channels comprise an important therapeutic target in anti-cancer treatment. In this review, we discuss the implication of ion channels in regulation of Ca²⁺ homeostasis during the crosstalk between immune and cancer cell as well as their role in cancer progression.

Salutary effect of calcium channel blockade following hypoxic and septic insult

BACKGROUND

Intestinal ischemia and reperfusion is a major problem associated with a high morbidity and mortality following trauma and hemorrhagic shock. Apoptosis is the major mode of cell death following reperfusion. The cytoskeleton damage precedes the apoptotic final microscopic features. Calcium plays a central role in apoptosis. Therefore, we studied whether verapamil could preserve the function of the cytoskeleton in an in vitro intestinal model following hypoxia-reoxygenation (H/R). Our goal was to assess mainly the cytoskeleton functions, which includes IgA transport and the cell monolayer barrier integrity.

METHODS

Confluent HT29 intestinal monolayers grown in a two-chamber cell culture system were held under hypoxic (5% CO2) conditions for 90 minutes followed by normoxia (21% O2) (H/R). Cell subsets were exposed to lipopolysaccharide (10 μg/mL) before H/R. Verapamil (8 μM) was added to HT29 cell subsets after H/R treatment. Dimeric IgA was added to the basal compartment, and apical media were sampled at intervals to quantitate IgA transcytosis using enzyme-linked immunosorbent assay. HT29 cells held under normoxic conditions served as controls. HT29 permeability to FD4 was assessed at the end of each experiment. In a separate experiment, HT29 cells were stained for F actin using rhodamine-labeled phalloidin.

RESULTS

Intestinal monolayer permeability was increased following treatment with H/R and/or lipopolysaccharide. Verapamil treatment prevented increased permeability in HT29 cells and led to an increase in IgA transport. Disruption of actin microfilaments was demonstrated following H/R insult but was abrogated by the addition of verapamil following H/R insult.

CONCLUSION

Reperfusion can lead to both physical and immune derangement of epithelial cell barrier function. Verapamil may be important in preserving gut barrier function. Additional studies including in vivo confirmation in animal shock models are needed to validate these findings.

A tamoxifen derivative, N,N-diethyl-2-[4-(phenylmethyl) phenoxy] ethanamine, selectively targets P-glycoprotein-positive multidrug resistant Chinese hamster cells

DPPE, a tamoxifen derivative with antihistamine activity, was previously shown to potentiate the toxicity of chemotherapeutic drugs. Recently, a Phase III clinical study using doxorubicin with DPPE demonstrated significant increase in the overall survival of breast cancer patients. In this study we examined the effects of DPPE alone on the growth of drug sensitive and P-gp positive CHO cell line. Our results demonstrate DPPE is selectively toxic to P-gp positive cells and the sensitivity to DPPE alone correlated with the levels of P-gp expression. Moreover, in MDR cells, DPPE-induced apoptosis was significantly reduced with Bcl2 overexpression and in the presence of P-gp ATPase inhibitor, PSC833. Furthermore, knockdown of P-gp expression in MDR cells with P-gp-siRNA reversed DPPE sensitivity and increased their sensitivity to doxorubicin and taxol but not to cisplatin. The addition of DPPE to membrane fractions led to dose-dependent increase in P-gp ATPase that was inhibited with PSC833. Moreover, incubation of P-gp positive cells with DPPE led to a significant increase in superoxide levels and a drop in cellular ATP and GSH pools that were reversible with inhibitors of P-gp ATPase. The combined presence of DPPE and the mitochondria electron transport complex III inhibitor, antimycin A, synergized in their effects on the growth of MDR cells but had no effect on the growth of parental drug sensitive cells. Collectively, the results of this study provide a possible mechanism that may be relevant to the clinical results of DPPE in breast cancer trial and demonstrates DPPE as P-gp collateral sensitivity drug.

Priming cancer cells for drug resistance: role of the fibroblast niche

Conventional and targeted chemotherapies remain integral strategies to treat solid tumors. Despite the large number of anti-cancer drugs available, chemotherapy does not completely eradicate disease. Disease recurrence and the growth of drug resistant tumors remain significant problems in anti-cancer treatment. To develop more effective treatment strategies, it is important to understand the underlying cellular and molecular mechanisms of drug resistance. It is generally accepted that cancer cells do not function alone, but evolve through interactions with the surrounding tumor microenvironment. As key cellular components of the tumor microenvironment, fibroblasts regulate the growth and progression of many solid tumors. Emerging studies demonstrate that fibroblasts secrete a multitude of factors that enable cancer cells to become drug resistant. This review will explore how fibroblast secretion of soluble factors act on cancer cells to enhance cancer cell survival and cancer stem cell renewal, contributing to the development of drug resistant cancer.

Reversal of ATP-binding cassette drug transporter activity to modulate chemoresistance: why has it failed to provide clinical benefit?

Enhanced drug extrusion from cells due to the overexpression of the ATP-binding cassette (ABC) drug transporters inhibits the cytotoxic effects of structurally diverse and mechanistically unrelated anticancer agents and is a major cause of multidrug resistance (MDR) of human malignancies. Multiple compounds can suppress the activity of these efflux transporters and sensitize resistant tumor cells, but despite promising preclinical and early clinical data, they have yet to find a role in oncologic practice. Based on the knowledge of the structure, function, and distribution of MDR-related ABC transporters and the results of their preclinical and clinical evaluation, we discuss probable reasons why these inhibitors have not improved the outcome of therapy for cancer patients. We also outline new MDR-reversing strategies that directly target ABC transporters or circumvent relevant signaling pathways.

Verapamil enhances the antitumoral efficacy of oncolytic adenoviruses

The therapeutic potential of oncolytic adenoviruses is limited by the rate of adenovirus release. Based on the observation that several viruses induce cell death and progeny release by disrupting intracellular calcium homeostasis, we hypothesized that the alteration in intracellular calcium concentration induced by verapamil could improve the rate of virus release and spread, eventually enhancing the antitumoral activity of oncolytic adenoviruses. Our results indicate that verapamil substantially enhanced the release of adenovirus from a variety of cell types resulting in an improved cell-to-cell spread and cytotoxicity. Furthermore, the combination of the systemic administration of an oncolytic adenovirus (ICOVIR-5) with verapamil in vivo greatly improved its antitumoral activity in two different tumor xenograft models without affecting the selectivity of this virus. Overall, our findings indicate that verapamil provides a new, safe, and versatile way to improve the antitumoral potency of oncolytic adenoviruses in the clinical setting.

NSC23925, identified in a high-throughput cell-based screen, reverses multidrug resistance

Background

Multidrug resistance (MDR) is a major factor which contributes to the failure of cancer chemotherapy, and numerous efforts have been attempted to overcome MDR. To date, none of these attempts have yielded a tolerable and effective therapy to reverse MDR; thus, identification of new agents would be useful both clinically and scientifically.

Methodology/Principal Findings

To identify small molecule compounds that can reverse chemoresistance, we developed a 96-well plate high-throughput cell-based screening assay in a paclitaxel resistant ovarian cancer cell line. Coincubating cells with a sublethal concentration of paclitaxel in combination with each of 2,000 small molecule compounds from the National Cancer Institute Diversity Set Library, we identified a previously uncharacterized molecule, NSC23925, that inhibits Pgp1 and reverses MDR1 (Pgp1) but does not inhibit MRP or BCRP-mediated MDR. The cytotoxic activity of NSC23925 was further evaluated using a panel of cancer cell lines expressing Pgp1, MRP, and BCRP. We found that at a concentration of >10 µM NSC23925 moderately inhibits the proliferation of both sensitive and resistant cell lines with almost equal activity, but its inhibitory effect was not altered by co-incubation with the Pgp1 inhibitor, verapamil, suggesting that NSC23925 itself is not a substrate of Pgp1. Additionally, NSC23925 increases the intracellular accumulation of Pgp1 substrates: calcein AM, Rhodamine-123, paclitaxel, mitoxantrone, and doxorubicin. Interestingly, we further observed that, although NSC23925 directly inhibits the function of Pgp1 in a dose-dependent manner without altering the total expression level of Pgp1, NSC23925 actually stimulates ATPase activity of Pgp, a phenomenon seen in other Pgp inhibitors.

Conclusions/Significance

The ability of NSC23925 to restore sensitivity to the cytotoxic effects of chemotherapy or to prevent resistance could significantly benefit cancer patients.

Modulation of Oral Drug Bioavailability: From Preclinical Mechanism to Therapeutic Application

Currently, more than one fourth of all anticancer drugs are developed as oral formulations, and it is expected that this number will increase substantially in the near future. To enable oral drug therapy, adequate oral bioavailability must be achieved. Factors that have proved to be important in limiting the oral bioavailability are the presence of ATP-binding cassette drug transporters (ABC transporters) and the cytochrome P450 enzymes. We discuss the tissues distribution and physiological function of the ABC transporters in the human body, their expression in tumors, currently known polymorphisms and drugs that are able to inhibit their function as transporter. Furthermore, the role of the ABC transporters and drug-metabolizing enzymes as mechanisms to modulate the pharmacokinetics of anticancer agents, will be reviewed. Finally, some clinical examples of oral drug modulation are discussed. Among these examples are the coadministration of paclitaxel with CsA, a CYP3A4 substrate with P-glycoprotein (P-gp) modulating activity, and topotecan combined with the BCRP/P-gp transport inhibitor elacridar. Both are good examples of improvement of oral drug bioavailability by temporary inhibition of drug transporters in the gut epithelium.

The prince and the pauper. A tale of anticancer targeted agents

Cancer rates are set to increase at an alarming rate, from 10 million new cases globally in 2000 to 15 million in 2020. Regarding the pharmacological treatment of cancer, we currently are in the interphase of two treatment eras. The so-called pregenomic therapy which names the traditional cancer drugs, mainly cytotoxic drug types, and post-genomic era-type drugs referring to rationally-based designed. Although there are successful examples of this newer drug discovery approach, most target-specific agents only provide small gains in symptom control and/or survival, whereas others have consistently failed in the clinical testing. There is however, a characteristic shared by these agents: -their high cost-. This is expected as drug discovery and development is generally carried out within the commercial rather than the academic realm. Given the extraordinarily high therapeutic drug discovery-associated costs and risks, it is highly unlikely that any single public-sector research group will see a novel chemical "probe" become a "drug". An alternative drug development strategy is the exploitation of established drugs that have already been approved for treatment of non-cancerous diseases and whose cancer target has already been discovered. This strategy is also denominated drug repositioning, drug repurposing, or indication switch. Although traditionally development of these drugs was unlikely to be pursued by Big Pharma due to their limited commercial value, biopharmaceutical companies attempting to increase productivity at present are pursuing drug repositioning. More and more companies are scanning the existing pharmacopoeia for repositioning candidates, and the number of repositioning success stories is increasing. Here we provide noteworthy examples of known drugs whose potential anticancer activities have been highlighted, to encourage further research on these known drugs as a means to foster their translation into clinical trials utilizing the more limited public-sector resources. If these drug types eventually result in being effective, it follows that they could be much more affordable for patients with cancer; therefore, their contribution in terms of reducing cancer mortality at the global level would be greater.

Concise Review: Clinical Relevance of Drug–Drug and Herb–Drug Interactions Mediated by the ABC Transporter ABCB1 (MDR1, P‐glycoprotein)

The importance of P-glycoprotein (P-gp) in drug-drug interactions is increasingly being identified. P-gp has been reported to affect the pharmacokinetics of numerous structurally and pharmacologically diverse substrate drugs. Furthermore, genetic variability in the multidrug resistance 1 gene influences absorption and tissue distribution of drugs transported. Inhibition or induction of P-gp by coadministered drugs or food as well as herbal constituents may result in pharmacokinetic interactions leading to unexpected toxicities or undertreatment. On the other hand, modulation of P-gp expression and/or activity may be a useful strategy to improve the pharmacological profile of anticancer P-gp substrate drugs. In recent years, the use of complementary and alternative medicine (CAM), like herbs, food, and vitamins, by cancer patients has increased significantly. CAM use substantially increases the risk for interactions with anticancer drugs, especially because of the narrow therapeutic window of these compounds. However, for most CAMs, it is unknown whether they affect metabolizing enzymes and/or drug transporter activity. Clinically relevant interactions are reported between St John's wort or grapefruit juice and anticancer as well as nonanticancer drugs. CAM-drug interactions could explain, at least in part, the large interindividual variation in efficacy and toxicity associated with drug therapy in both cancer and noncancer patients. The study of drug-drug, food-drug, and herb-drug interactions and of genetic factors affecting pharmacokinetics and pharmacodynamics is expected to improve drug safety and will enable individualized drug therapy. Disclosure of potential conflicts of interest is found at the end of this article.

Future perspectives for the development of P-glycoprotein modulators

Resistance to chemotherapeutic agents constitutes one of the major obstacles to the successful treatment of cancer. While several mechanisms underlying drug resistance have been elucidated, the most widely studied mechanism involves the efflux of antineoplastic drugs from cancer cells by P-glycoprotein, the 170 kD glycoprotein product of the MDR-I gene. The observation that several compounds are able to inhibit P-glycoprotein in vitro created optimism that the problem of multidrug resistance in cancer could be quickly resolved by moving these compounds into the clinic. However, despite a large number of clinical trials with several different putative Pgp modulators, the value of Pgp modulation in clinical oncologic practice remains unresolved. While these initial trials have not answered the question of whether Pgp is an important mechanism of resistance in human cancers, or whether modulation of Pgp is likely to positively impact on the treatment of cancer, they have provided insights regarding the problems inherent in conducting trials of this nature. These clinical insights, along with knowledge gained from continued basic research on drug resistance mediated by Pgp and related transporters, will form a strong foundation for future research into the role of Pgp and Pgp modulation in the treatment of cancer. The ubiquitous nature of transporters and the high prevalence of transporter substrates among antineoplastic drugs, compel the development of modulators that can be used to prevent or reverse drug resistance.

Tariquidar (XR9576): a P-glycoprotein drug efflux pump inhibitor

P-glycoprotein actively transports structurally unrelated compounds out of cells, conferring the multidrug resistance phenotype in cancer. Tariquidar is a potent, specific, noncompetitive inhibitor of P-glycoprotein. Tariquidar inhibits the ATPase activity of P-glycoprotein, suggesting that the modulating effect is derived from the inhibition of substrate binding, inhibition of ATP hydrolysis or both. In clinical trials, tariquidar is tolerable and does not have significant pharmacokinetic interaction with chemotherapy. In patients, inhibition of P-glycoprotein has been demonstrated for 48 h after a single dose of tariquidar. Studies to assess a possible increase in toxicity of chemotherapy and the impact of P-glycoprotein inhibition on tumor response and patient outcome are ongoing. Tariquidar can be considered an ideal agent for testing the role of P-glycoprotein inhibition in cancer.

3-(3,4,5-Trimethoxyphenyl)-1-oxo-2-propene: A novel pharmacophore displaying potent multidrug resistance reversal and selective cytotoxicity

This study revealed that various alicyclic and acyclic compounds containing the 3-(3,4,5-trimethoxyphenyl)-2-propenoyl group displayed potent MDR reversal properties. In particular, a concentration of 4 microg/ml of 2,5-bis(3,4,5-trimethoxyphenylmethylene)cyclopentanone was 31 times more potent than verapamil as a MDR revertant. In general, they were selectively toxic to malignant rather than normal cells. Two representative compounds induced apoptosis in human HL-60 cells and markedly activated caspase-3.

Implications of cancer stem cells in the treatment of cancer

Identification of cancer stem cells (CSCs) in both hematological and solid malignancies suggests that CSCs may be a common phenomenon for most malignancies. Similarly to normal stem cells, CSCs can self-renew and differentiate into progeny cancer cells. Almost all current therapy against cancer targets differentiated cancer cells. CSCs are more resistant to therapy secondary to quiescence, increased expression of antiapoptotic proteins and drug efflux transporters. In this article, we review the current status of CSC research and propose the targeting of CSC cell-surface molecules, signal transduction pathways, the stem cell niche, stem cell differentiation and drug resistance.

Targeting multidrug resistance in cancer

Effective treatment of metastatic cancers usually requires the use of toxic chemotherapy. In most cases, multiple drugs are used, as resistance to single agents occurs almost universally. For this reason, elucidation of mechanisms that confer simultaneous resistance to different drugs with different targets and chemical structures - multidrug resistance - has been a major goal of cancer biologists during the past 35 years. Here, we review the most common of these mechanisms, one that relies on drug efflux from cancer cells mediated by ATP-binding cassette (ABC) transporters. We describe various approaches to combating multidrug-resistant cancer, including the development of drugs that engage, evade or exploit efflux by ABC transporters.

Changes in P-glycoprotein activity are mediated by the growth of a tumour cell line as multicellular spheroids

BACKGROUND

Expression of P-glycoprotein (P-gp), the multidrug resistance (MDR) 1 gene product, can lead to multidrug resistance in tumours. However, the physiological role of P-gp in tumours growing as multicellular spheroids is not well understood. Recent evidence suggests that P-gp activity may be modulated by cellular components such as membrane proteins, membrane-anchoring proteins or membrane-lipid composition. Since, multicellular spheroids studies have evidenced alterations in numerous cellular components, including those related to the plasma membrane function, result plausible that some of these changes might modulate P-gp function and be responsible for the acquisition of multicellular drug resistance. In the present study, we asked if a human lung cancer cell line (INER-51) grown as multicellular spheroids can modify the P-gp activity to decrease the levels of doxorubicin (DXR) retained and increase their drug resistance.

RESULTS

Our results showed that INER-51 spheroids retain 3-folds lower doxorubicin than the same cells as monolayers however; differences in retention were not observed when the P-gp substrate Rho-123 was used. Interestingly, neither the use of the P-gp-modulating agent cyclosporin-A (Cs-A) nor a decrease in ATP-pools were able to increase DXR retention in the multicellular spheroids. Only the lack of P-gp expression throughout the pharmacological selection of a P-gp negative (P-gpneg) mutant clone (PSC-1) derived from INER-51 cells, allow increase of DXR retention in spheroids.

CONCLUSION

Thus, multicellular arrangement appears to alter the P-gp activity to maintain lower levels of DXR. However, the non expression of P-gp by cells forming multicellular spheroids has only a minor impact in the resistance to chemotherapeutic agents.

Tumour stem cells and drug resistance

The contribution of tumorigenic stem cells to haematopoietic cancers has been established for some time, and cells possessing stem-cell properties have been described in several solid tumours. Although chemotherapy kills most cells in a tumour, it is believed to leave tumour stem cells behind, which might be an important mechanism of resistance. For example, the ATP-binding cassette (ABC) drug transporters have been shown to protect cancer stem cells from chemotherapeutic agents. Gaining a better insight into the mechanisms of stem-cell resistance to chemotherapy might therefore lead to new therapeutic targets and better anticancer strategies.

The role of ABC transporters in clinical practice

Drug resistance remains one of the primary causes of suboptimal outcomes in cancer therapy. ATP-binding cassette (ABC) transporters are a family of transporter proteins that contribute to drug resistance via ATP-dependent drug efflux pumps. P-glycoprotein (P-gp), encoded by the MDR1 gene, is an ABC transporter normally involved in the excretion of toxins from cells. It also confers resistance to certain chemotherapeutic agents. P-gp is overexpressed at baseline in chemotherapy-resistant tumors, such as colon and kidney cancers, and is upregulated after disease progression following chemotherapy in malignancies such as leukemia and breast cancer. Other transporter proteins mediating drug resistance include those in the multidrug-resistance-associated protein (MRP) family, notably MRP1, and ABCG2. These transporters are also involved in normal physiologic functions. The expressions of MRP family members and ABCG2 have not been well worked out in cancer. Increased drug accumulation and drug resistance reversal with P-gp inhibitors have been well documented in vitro, but only suggested in clinical trials. Limitations in the design of early resistance reversal trials contributed to disappointing results. Despite this, three randomized trials have shown statistically significant benefits with the use of a P-gp inhibitor in combination with chemotherapy. Improved diagnostic techniques aimed at the selection of patients with tumors that express P-gp should result in more successful outcomes. Further optimism is warranted with the advent of potent, nontoxic inhibitors and new treatment strategies, including the combination of new targeted therapies with therapies aimed at the prevention of drug resistance.

Strategies for reversing drug resistance

Drug resistance, intrinsic or acquired, is a problem for all chemotherapeutic agents. In this review, we examine numerous strategies that have been tested or proposed to reverse drug resistance. Included among these strategies are approaches targeting the apoptosis pathway. Although the process of apoptosis is complex, it provides several potential sites for therapeutic intervention. A variety of targets and approaches are being pursued, including the suppression of proteins inhibiting apoptosis using antisense oligonucleotides (ASOs), and small molecules targeted at proteins that modulate apoptosis. An alternate strategy is based on numerous studies that have documented methylation of critical regions in the genome in human cancers. Consequently, efforts have been directed at re-expressing genes, including genes that affect drug sensitivity, using 5-azacytidine and 2'-deoxy-5-azacytidine (DAC, decitabine) as demethylating agents. While this strategy may be effective as a single modality, success will most likely be achieved if it is used to modulate gene expression in combination with other modalities such as chemotherapy. At a more basic level, attempts have been made to modulate glutathione (GSH) levels. Owing to its reactivity and high intracellular concentrations, GSH has been implicated in resistance to several chemotherapeutic agents. Several approaches designed to deplete intracellular GSH levels have been pursued including the use of buthionine-(S,R)-sulfoxime (BSO), a potent and specific inhibitor of gamma-glutamyl cysteine synthetase (gamma-GCS), the rate-limiting step in the synthesis of GSH, a hammerhead ribozyme against gamma-GCS mRNA to downregulate specifically its levels and targeting cJun expression to reduce GSH levels. Alternate strategies have targeted p53. The frequent occurrence of p53 mutations in human cancer has led to the development of numerous approaches to restore wild-type (wt) p53. The goals of these interventions are to either revert the malignant phenotype or enhance drug sensitivity. The approach most extensively investigated has utilized one of several viral vectors. An alternate approach, the use of small molecules to restore wt function to mutant p53, remains an option. Finally, the conceptually simplest mechanism of resistance is one that reduces intracellular drug accumulation. Such reduction can be effected by a variety of drug efflux pumps, of which the most widely studied is P-glycoprotein (Pgp). The first strategy utilized to inhibit Pgp function relied on the identification of non-chemotherapeutic agents as competitors. Other approaches have included the use of hammerhead ribozymes against the MDR-1 gene and MDR-1-targeted ASOs. Although modulation of drug resistance has not yet been proven to be an effective clinical tool, we have learned an enormous amount about drug resistance. Should we succeed, these pioneering basic and clinical studies will have paved the road for future developments.

Overview of the clinical efficacy of investigational anticancer drugs

The purpose of this overview was to make a broad inventory of investigational drugs for medicinal cancer treatment and, specifically, to indicate the evidence of clinical efficacy. Information was retrieved from electronic database searches in Medline and CANCERLIT and relevant published reviews. As the most recent findings are first reported as conference abstracts, an important basis for identification of new drugs and clinical results was a hand search of 13,392 abstracts from five major recent cancer conferences. A total of 209 investigational approaches or drugs were identified and classified into one of eight groups according to proposed mechanism of action. For 28 drugs/approaches survival data were available from randomized controlled trials. Statistically significant benefit was observed for only 12. In earlier phases no or modest anticancer activity was reported. It is speculated that the expanding knowledge in tumour biology might not easily translate into new substantially better anticancer drugs.

Multidrug resistance in cancer: role of ATP-dependent transporters

Chemotherapeutics are the most effective treatment for metastatic tumours. However, the ability of cancer cells to become simultaneously resistant to different drugs--a trait known as multidrug resistance--remains a significant impediment to successful chemotherapy. Three decades of multidrug-resistance research have identified a myriad of ways in which cancer cells can elude chemotherapy, and it has become apparent that resistance exists against every effective drug, even our newest agents. Therefore, the ability to predict and circumvent drug resistance is likely to improve chemotherapy.