Endocytic recycling compartments altered in cisplatin-resistant cancer cells

Innovative nanochemotherapy for overcoming cancer multidrug resistance

Tumor multidrug resistance (MDR) is a phenomenon in which drug-resistant tumor cells are resistant to multiple other unexposed antitumor drugs with different structures and targets. MDR of cancer is a primary cause of clinical chemotherapy failure. With the progress of nanotechnology in the medical field, more and more research works have developed many nanotechnology-based strategies to challenge drug resistance. This review details the recent studies at the National Center for Nanoscience and Technology utilizing various nanochemotherapy strategies for overcoming chemotherapy resistance of tumor. We discuss the benefits and limitations of the diverse strategies, as well as possible ways to overcome these limitations. Importantly, in order to combat cancer chemotherapy resistance with nanomedicine, the mechanisms of drug endocytosis and subsequent fate need to be explored and focused on. In the meanwhile, due to the complexity and diversity of chemotherapy resistance mechanisms, the development of more intelligent and controllable nanodrugs may have greater scope for clinical application.

Different Ability of Multidrug-Resistant and -Sensitive Counterpart Cells to Release and Capture Extracellular Vesicles

Cancer multidrug resistance (MDR) is one of the main challenges for cancer treatment efficacy. MDR is a phenomenon by which tumor cells become resistant to several unrelated drugs. Some studies have previously described the important role of extracellular vesicles (EVs) in the dissemination of a MDR phenotype. EVs’ cargo may include different players of MDR, such as microRNAS and drug-efflux pumps, which may be transferred from donor MDR cells to recipient drug-sensitive counterparts. The present work aimed to: (i) compare the ability of drug-sensitive and their MDR counterpart cells to release and capture EVs and (ii) study and relate those differences with possible distinct fate of the endocytic pathway in these counterpart cells. Our results showed that MDR cells released more EVs than their drug-sensitive counterparts and also that the drug-sensitive cells captured more EVs than their MDR counterparts. This difference in the release and capture of EVs may be associated with differences in the endocytic pathway between drug-sensitive and MDR cells. Importantly, manipulation of the recycling pathway influenced the response of drug-sensitive cells to doxorubicin treatment.

Tumor-intrinsic and -extrinsic (immune) gene signatures robustly predict overall survival and treatment response in high grade serous ovarian cancer patients

In the present study, we developed a transcriptomic signature capable of predicting prognosis and response to primary therapy in high grade serous ovarian cancer (HGSOC). Proportional hazard analysis was performed on individual genes in the TCGA RNAseq data set containing 229 HGSOC patients. Ridge regression analysis was performed to select genes and develop multigenic models. Survival analysis identified 120 genes whose expression levels were associated with overall survival (OS) (HR = 1.49-2.46 or HR = 0.48-0.63). Ridge regression modeling selected 38 of the 120 genes for development of the final Ridge regression models. The consensus model based on plurality voting by 68 individual Ridge regression models classified 102 (45%) as low, 23 (10%) as moderate and 104 patients (45%) as high risk. The median OS was 31 months (HR = 7.63, 95% CI = 4.85-12.0, P < 1.0-10) and 77 months (HR = ref) in the high and low risk groups, respectively. The gene signature had two components: intrinsic (proliferation, metastasis, autophagy) and extrinsic (immune evasion). Moderate/high risk patients had more partial and non-responses to primary therapy than low risk patients (odds ratio = 4.54, P < 0.001). We concluded that the overall survival and response to primary therapy in ovarian cancer is best assessed using a combination of gene signatures. A combination of genes which combines both tumor intrinsic and extrinsic functions has the best prediction. Validation studies are warranted in the future.

Autophagy modulating agents as chemosensitizers for cisplatin therapy in cancer

Although cisplatin is one of the most common antineoplastic drug, its successful utilisation in cancer treatment is limited by the drug resistance. Multiple attempts have been made to find potential cisplatin chemosensitisers which would overcome cancer cells resistance thus improving antineoplastic efficacy. Autophagy modulation has become an important area of interest regarding the aforementioned topic. Autophagy is a highly conservative cellular self-digestive process implicated in response to multiple environmental stressors. The high basal level of autophagy is a common phenomenon in cisplatin-resistant cancer cells which is thought to grant survival benefit. However current evidence supports the role of autophagy in either promoting or limiting carcinogenesis depending on the context. This encourages the search of substances modulating the process to alleviate cisplatin resistance. Such a strategy encompasses not only simple autophagy inhibition but also harnessing the process to induce autophagy-dependent cell death. In this paper, we briefly describe the mechanism of cisplatin resistance with a special emphasis on autophagy and we give an extensive literature review of potential substances with cisplatin chemosensitising properties related to autophagy modulation.

Cancer stem cells and their niche in the progression of squamous cell carcinoma

Most cancers harbor a small population of highly tumorigenic cells known as cancer stem cells (CSCs). Because of their stem cell-like properties and resistance to conventional therapies, CSCs are considered to be a rational target for curable cancer treatment. However, despite recent advances in CSC research, CSC-targeted therapies are not as successful as was initially hoped. The proliferative, invasive, and drug-resistant properties of CSCs are regulated by the tumor microenvironment associated with them, the so-called CSC niche. Thus, targeting tumor-promoting cellular crosstalk between CSCs and their niches is an attractive avenue for developing durable therapies. Using mouse models of squamous cell carcinoma (SCC), we have demonstrated that tumor cells responding to transforming growth factor β (TGF-β) function as drug-resistant CSCs. The gene expression signature of TGF-β-responding tumor cells has accelerated the identification of novel pathways that drive invasive tumor progression. Moreover, by focusing on the cytokine milieu and macrophages in the proximity of TGF-β-responding tumor cells, we recently uncovered the molecular basis of a CSC-niche interaction that emerges during early tumor development. This review article summarizes the specialized tumor microenvironment associated with CSCs and discusses mechanisms by which malignant properties of CSCs are maintained and promoted.

Drug uptake-based chemoresistance in breast cancer treatment

Breast cancer is the most prevalent type of tumor and the second leading cause of death due to cancer among women. Although screening methods, diagnosis and therapeutic options have improved in the last decade, chemoresistance remains an important challenge. There is evidence relating breast cancer resistance with signaling pathways involving hormone and growth receptors, survival, apoptosis and the activation of efflux pumps. However, the resistance mechanisms linked to drug uptake are poorly understood, despite it often being observed that the drug content is lower in resistant cancer cells and that the entry of the drug into these cells is a limiting process for the subsequent therapeutic effect.In this review, we provide an overview of drug uptake-based resistance mechanisms developed by cancer cells in the four main types of chemotherapy used in breast cancer: anthracyclines, taxanes, oxazaphosphorines and platinum-based drugs. The contribution of tumor microenvironment to reduced drug-uptake and multidrug resistance is also analyzed. As a developing field, nanomedicine-based approaches provide promising opportunities to improve drug specific targeting, cell interaction and uptake into cancer cells. The endocytic-mediated pathways attributed to the different types of nanoformulations as well as the contribution of nanotherapeutics to overcoming chemoresistance affecting drug uptake in breast cancer will be described. New approaches focusing on drug uptake mechanisms could improve breast cancer chemotherapy, obtaining better dose-response outcomes and reducing toxic side effects.

Chemotherapy-induced apoptosis, autophagy and cell cycle arrest are key drivers of synergy in chemo-immunotherapy of epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is the most lethal of all gynecological malignancies in the UK. Recent evidence has shown that there is potential for immunotherapies to be successful in treating this cancer. We have previously shown the effective application of combinations of traditional chemotherapy and CAR (chimeric antigen receptor) T cell immunotherapy in in vitro and in vivo models of EOC. Platinum-based chemotherapy synergizes with ErbB-targeted CAR T cells (named T4), significantly reducing tumor burden in mice. Here, we show that paclitaxel synergizes with T4 as well, and look into the mechanisms behind the effectiveness of chemo-immunotherapy in our system. Impairment of caspase activity using pan-caspase inhibitor Z-VAD reveals this chemotherapy-induced apoptotic pathway as an essential factor in driving synergy. Mannose-6-phosphate receptor-mediated autophagy and the arrest of cell cycle in G2/M are also shown to be induced by chemotherapy and significantly contributing to the synergy. Increased expression of PD-1 on T4 CAR T cells occurred when these were in culture with ovarian tumor cells; on the other hand, EOC cell lines showed increased PD-L1 expression following chemotherapy treatment. These findings provided a rationale to look into testing PD-1 blockade in combination with paclitaxel and T4 immunotherapy. Combination of these three agents in mice resulted in significant reduction of tumor burden, compared to each treatment alone. In conclusion, the mechanism driving synergy in chemo-immunotherapy of EOC is multifactorial. A deeper understanding of such process is needed to better design combination therapies and carefully stratify patients.

Suppression of chloride voltage-gated channel 3 expression increases sensitivity of human glioma U251 cells to cisplatin through lysosomal dysfunction

The mechanism of cisplatin resistance is complex. Previous studies have indicated that chloride voltage-gated channel 3 (CLCN3) is associated with drug resistance; however, the mechanisms are not fully understood. Therefore, the present study explored the involvement of CLCN3 in cisplatin resistance in human glioma U251 cells. The effects of combined cisplatin treatment and CLCN3 suppression on cultured U251 cells were investigated. The decreased viability of cisplatin-treated U251 cells indicated the cytotoxic effects of CLCN3 silencing. Expression of the apoptosis-related gene TP53 and caspase 3 activation were enhanced in cisplatin-treated U251 cells. Furthermore, the ratio of BCL2/BAX expression was decreased. Notably, CLCN3 suppression promoted cisplatin-induced cell damage in U251 cells. Thus, the combined use of cisplatin and CLCN3 antisense had additive effects in U251 cells. In addition, the present results indicated that CLCN3 suppression decreased lysosome stabilization in U251 cells treated with cisplatin. To conclude, the present results indicated that CLCN3 suppression can sensitize glioma cells to cisplatin through lysosomal dysfunction.

Lower expression of miR-218 in human breast cancer is associated with lymph node metastases, higher grades, and poorer prognosis

Breast cancer is considered as the most prevalent malignancy in women worldwide. Despite emergence of several prognosticators for better management of patients, there are still limitations for their clinical application due to the complexity of breast tumors, and therefore, new biomarkers for better prognosis of clinical outcomes would be of the great essence. MicroRNAs are highly conserved small non-coding regulatory RNAs involved in post-transcriptional regulating of gene expression during different cellular mechanisms. Accumulating studies suggest that miR-218 plays a multifunctional role in various cancer types and different stages. Here, to address prognostic significance of miR-218 in breast cancer, we investigate the expression profile of miR-218 and B-cell-specific Moloney murine leukemia virus integration site 1 ( BMI1) gene, as one of the putative targets of miR-218, in 33 paired breast tumors and their adjacent normal tissues with respect to the clinicopathological features of patients using quantitative real-time polymerase chain reaction. The correlation of both miR-218 and BMI1 gene expression with overall survival of breast cancer patients was also examined recruiting OncoLNC data portal. Finally, to better understand biological function of miR-218 in breast cancer, we performed in silico Gene Ontology and signaling pathway enrichment analysis on miR-218 targetome. According to our data, significant elevation of the expression of miR-218 and downregulation of BMI1 were observed in clinical breast cancer specimens compared with normal tissues ( p < 0.0001). The lower expression of miR-218 was associated with lymph node metastases, higher grades, and poorer prognosis (logrank p = 0.00988), whereas no significant difference in overall survival was observed between patients with higher and lower expression of BMI1 (logrank p = 0.254). These findings suggest that miR-218 expression profiling might be clinically applicable as a prognostic biomarker in breast cancer. In addition, our in silico enrichment analyses revealed that the association of miR-218 expression with breast cancer prognosis might be through its involvement in endocytosis and gap junction biological pathways.

The counterflow transport of sterols and PI4P

Cholesterol levels in intracellular membranes are constantly adjusted to match with specific organelle functions. Cholesterol is kept high in the plasma membrane (PM) because it is essential for its barrier function, while low levels are found in the endoplasmic reticulum (ER) where cholesterol mediates feedback control of its own synthesis by sterol-sensor proteins. The ER→Golgi→PM concentration gradient of cholesterol in mammalian cells, and ergosterol in yeast, appears to be sustained by specific intracellular transport processes, which are mostly mediated by lipid transfer proteins (LTPs). Here we review a recently described function of two LTPs, OSBP and its yeast homolog Osh4p, which consists in creating a sterol gradient between membranes by vectorial transport. OSBP also contributes to the formation of ER/Golgi membrane contact sites, which are important hubs for the transfer of several lipid species. OSBP and Osh4p organize a counterflow transport of lipids whereby sterols are exchanged for the phosphoinositide PI4P, which is used as a fuel to drive sterol transport. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.

Toward a Better Understanding of the Complexity of Cancer Drug Resistance

Resistance to anticancer drugs is a complex process that results from alterations in drug targets; development of alternative pathways for growth activation; changes in cellular pharmacology, including increased drug efflux; regulatory changes that alter differentiation pathways or pathways for response to environmental adversity; and/or changes in the local physiology of the cancer, such as blood supply, tissue hydrodynamics, behavior of neighboring cells, and immune system response. All of these specific mechanisms are facilitated by the intrinsic hallmarks of cancer, such as tumor cell heterogeneity, redundancy of growth-promoting pathways, increased mutation rate and/or epigenetic alterations, and the dynamic variation of tumor behavior in time and space. Understanding the relative contribution of each of these factors is further complicated by the lack of adequate in vitro models that mimic clinical cancers. Several strategies to use current knowledge of drug resistance to improve treatment of cancer are suggested.

Evaluation of fluorophore-tethered platinum complexes to monitor the fate of cisplatin analogs

The platinum drugs cisplatin, carboplatin, and oxaliplatin are highly utilized in the clinic and as a consequence have been extensively studied in the laboratory setting, sometimes by generating fluorophore-tagged analogs. Here, we synthesized two Pt(II) complexes containing ethane-1,2-diamine ligands linked to a BODIPY fluorophore, and compared their biological activity with previously reported Pt(II) complexes conjugated to carboxyfluorescein and carboxyfluorescein diacetate. The cytotoxicity and DNA damage capacity of Pt-fluorophore complexes was compared to cisplatin, and the Pt-BODIPY complexes were found to be more cytotoxic with reduced cytotoxicity in cisplatin-resistant cells. Microscopy revealed a predominately cytosolic localization, with nuclear distribution at higher concentrations. Spheroids grown from parent and resistant cells revealed penetration of Pt-BODIPY into spheroids, and retention of the cisplatin-resistant spheroid phenotype. While most activity profiles were retained for the Pt-BODIPY complexes, accumulation in resistant cells was only slightly affected, suggesting that some aspects of Pt-fluorophore cellular pharmacology deviate from cisplatin.

New mechanisms for old drugs: Insights into DNA-unrelated effects of platinum compounds and drug resistance determinants

Platinum drugs have been widely used for the treatment of several solid tumors. Although DNA has been recognized as the primary cellular target for these agents, there are unresolved issues concerning their effects and the molecular mechanisms underlying the antitumor efficacy. These cytotoxic agents interact with sub-cellular compartments other than the nucleus. Here, we review how such emerging phenomena contribute to the pharmacologic activity as well as to drug resistance phenotypes. DNA-unrelated effects of platinum drugs involve alterations at the plasma membrane and in endo-lysosomal compartments. A direct interaction with the mitochondria also appears to be implicated in drug-induced cell death. Moreover, the pioneering work of a few groups has shown that platinum drugs can act on the tumor microenvironment as well, and potentiate antitumor activity of the immune system. These poorly understood aspects of platinum drug activity sites may be harnessed to enhance their antitumor efficacy. A complete understanding of DNA-unrelated effects of platinum compounds might reveal new aspects of drug resistance allowing the implementation of the antitumor therapeutic efficacy of platinum compound-based regimens and minimization of their toxic side effects.

A polymer–(multifunctional single-drug) conjugate for combination therapy

A single-drug integrating three different drug functions (platinum, azidyl radical and DMC) and two types of therapies (chemotherapy and radiation therapy) was synthesized and attached onto a carrier to prepare a polymer–(multifunctional single-drug) conjugate.

Reduced Intracellular Drug Accumulation in Drug-Resistant Leukemia Cells is Not Only Solely Due to MDR-Mediated Efflux but also to Decreased Uptake

Expression of ABC family transporter proteins that promote drug efflux from cancer cells is a widely observed mechanism of multi-drug resistance of cancer cells. Cell adaptation in long-term culture of HL60 leukemic cells in the presence of chemotherapy leads to induction and maintenance of the ABC transporters expression, preventing further accumulation of drugs. However, we found that decreased accumulation of drugs and fluorescent dyes also contributed by a reduced uptake by the resistant cells. Confocal time-lapse microscopy and flow cytometry revealed that fluid-phase endocytosis was diminished in drug-resistant cells compared to drug-sensitive cells. Drug uptake was increased by insulin co-treatment when cells were grown in methylcellulose and monitored under the microscope, but not when cultured in suspension. We propose that multi-drug resistance is not only solely achieved by enhanced efflux capacity but also by supressed intake of the drug, offering an alternative target to overcome drug resistance or potentiate chemotherapy.

Biophysics of cell membrane lipids in cancer drug resistance: Implications for drug transport and drug delivery with nanoparticles

In this review, we focus on the biophysics of cell membrane lipids, particularly when cancers develop acquired drug resistance, and how biophysical changes in resistant cell membrane influence drug transport and nanoparticle-mediated drug delivery. Recent advances in membrane lipid research show the varied roles of lipids in regulating membrane P-glycoprotein function, membrane trafficking, apoptotic pathways, drug transport, and endocytic functions, particularly endocytosis, the primary mechanism of cellular uptake of nanoparticle-based drug delivery systems. Since acquired drug resistance alters lipid biosynthesis, understanding the role of lipids in cell membrane biophysics and its effect on drug transport is critical for developing effective therapeutic and drug delivery approaches to overcome drug resistance. Here we discuss novel strategies for (a) modulating the biophysical properties of membrane lipids of resistant cells to facilitate drug transport and regain endocytic function and (b) developing effective nanoparticles based on their biophysical interactions with membrane lipids to enhance drug delivery and overcome drug resistance.

The antibody-drug conjugate: an enabling modality for natural product-based cancer therapeutics

The Antibody Drug Conjugate (ADC) is a therapeutic modality consisting of a monoclonal antibody attached to a cytotoxic, small-molecule payload. The antibody portion of the ADC serves as a transport vehicle that recognizes and binds to a protein antigen expressed in tumor tissues. The localized delivery and release of the payload within or near malignant cells allows for targeted delivery of a potent cytotoxic agent to diseased tissue, while reducing damage to antigen-negative, normal tissues. Recent years have witnessed an explosive increase in ADC-based therapies, due mainly to clinical reports of activity in both hematologic and epithelial cancers. Accompanying this upsurge in ADC development is a renewed interest in natural product cytotoxins, which are typically highly potent cell-killing agents, but suffer from poor drug-like properties and narrow safety margins when systemically administered as conventional chemotherapeutics. In this review, we discuss recent advances related to the construction of ADCs, the optimization of ADC safety and efficacy, and the increasingly pivotal roles of natural product payloads in the current and future landscape of ADC therapy.

Overcoming chemotherapy resistance of ovarian cancer cells by liposomal cisplatin: molecular mechanisms unveiled by gene expression profiling

Previously we reported that liposomal cisplatin (CDDP) overcomes CDDP resistance of ovarian A2780cis cancer cells (Krieger et al., Int. J. Pharm. 389, 2010, 10-17). Here we find that the cytotoxic activity of liposomal CDDP is not associated with detectable DNA platination in resistant ovarian cancer cells. This suggests that the mode of action of liposomal CDDP is different from the free drug. To gain insight into mechanisms of liposomal CDDP activity, we performed a transcriptome analysis of untreated A2780cis cells, and A2780cis cells in response to exposure with IC50 values of free or liposomal CDDP. A process network analysis of upregulated genes showed that liposomal CDDP induced a highly different gene expression profile in comparison to the free drug. p53 was identified as a key player directing transcriptional responses to free or liposomal CDDP. The free drug induced expression of essential genes of the intrinsic (mitochondrial) apoptosis pathway (BAX, BID, CASP9) most likely through p38MAPK activation. In contrast, liposomal CDDP induced expression of genes from DNA damage pathways and several genes of the extrinsic pathway of apoptosis (TNFRSF10B-DR5, CD70-TNFSF7). It thus appears that liposomal CDDP overcomes CDDP resistance by inducing DNA damage and in consequence programmed cell death by the extrinsic pathway. Predictions from gene expression data with respect to apoptosis activation were confirmed at the protein level by an apoptosis antibody array. This sheds new light on liposomal drug carrier approaches in cancer and suggests liposomal CDDP as promising strategy for the treatment of CDDP resistant ovarian carcinomas.

Cisplatin resistance: a cellular self-defense mechanism resulting from multiple epigenetic and genetic changes

Cisplatin is one of the most effective broad-spectrum anticancer drugs. Its effectiveness seems to be due to the unique properties of cisplatin, which enters cells via multiple pathways and forms multiple different DNA-platinum adducts while initiating a cellular self-defense system by activating or silencing a variety of different genes, resulting in dramatic epigenetic and/or genetic alternations. As a result, the development of cisplatin resistance in human cancer cells in vivo and in vitro by necessity stems from bewilderingly complex genetic and epigenetic changes in gene expression and alterations in protein localization. Extensive published evidence has demonstrated that pleiotropic alterations are frequently detected during development of resistance to this toxic metal compound. Changes occur in almost every mechanism supporting cell survival, including cell growth-promoting pathways, apoptosis, developmental pathways, DNA damage repair, and endocytosis. In general, dozens of genes are affected in cisplatin-resistant cells, including pathways involved in copper metabolism as well as transcription pathways that alter the cytoskeleton, change cell surface presentation of proteins, and regulate epithelial-to-mesenchymal transition. Decreased accumulation is one of the most common features resulting in cisplatin resistance. This seems to be a consequence of numerous epigenetic and genetic changes leading to the loss of cell-surface binding sites and/or transporters for cisplatin, and decreased fluid phase endocytosis.

Impact of cisplatin administration on protein expression levels in renal cell carcinoma: a proteomic analysis

Renal cell carcinoma (RCC) is the most common renal neoplasm in adults. Considering that chemoresistance is a typical feature of RCC, every effort should be made in order to identify mechanisms of drug resistance. We used two-dimensional gel electrophoresis and mass spectrometry to study changes in protein expression levels that occur in primary resistant LN78 RCC cells when treated with therapeutic concentrations of cisplatin. Expression differences of selected proteins were confirmed by immunoblot. Up-regulation of heat-shock proteins can block apoptosis indirectly by altered protein folding and by direct interaction with apoptosis regulatory proteins. Cyclophilin A and stratifin can modify cell cycle control and enable tumor cells to escape and further proliferate despite DNA damage caused by cisplatin. Increased activity of glycolytic enzymes reflect metabolic adaptations to increased energy requirements as well as converting to alternative energy sources because of cisplatin-induced disturbed mitochondrial oxidation. Changes in cytoskeletal proteins may change the handling of cisplatin by altering transport and increasing cellular efflux of the drug. Repression of vimentin and disturbance of antioxidative mechanisms may represent vulnerable points in tumor cellular defense against cisplatin. The involvement of these proteins in cisplatin resistance and their potential as therapeutic targets requires further evaluation.

Extensive disease small cell lung cancer dose-response relationships: implications for resistance mechanisms

BACKGROUND

Some studies (but not others) suggested that high doses are beneficial in small cell lung cancer (SCLC). We hypothesized that dose-response curve (DRC) shape reflects resistance mechanisms.

METHODS

We reviewed published SCLC clinical trials and converted response rates into estimated mean tumor cell kill, assuming killing is proportional to reduction in tumor volume. Mean % cell survival was plotted versus planned dose intensity. Nonlinear and linear meta-regression analyses (weighted according to the number of patients in each study) were used to assess DRC characteristics.

RESULTS

Although associations between dose and cell survival were not statistically significant, DRCs sloped downward for five of seven agents across all doses and for all seven when lowest doses were excluded. Maximum mean cell kill across all drugs and doses was approximately 90%, suggesting that there may be a maximum achievable tumor cell kill irrespective of number of agents or drug doses.

CONCLUSIONS

Downward DRC slopes suggest that maintaining relatively high doses may possibly maximize palliation, although the associations between dose and slope did not achieve statistical significance, and slopes for most drugs tended to be shallow. DRC flattening at higher doses would preclude cure and would suggest that "saturable passive resistance" (deficiency of factors required for cell killing) limits maximum achievable cell kill. An example of factors that could flatten the DRC at higher doses and lead to saturable passive resistance would be presence of quiescent, noncycling cells.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

Intrinsic differences in cisplatin sensitivity of head and neck cancer cell lines: Correlation to lysosomal pH

BACKGROUND

Cisplatin treatment is beneficial for approximately 20% of patients with head and neck squamous cell carcinoma (HNSCC). Tools to predict the clinical outcome and evaluate intrinsic cisplatin sensitivity are, therefore, required.

METHODS

Cisplatin sensitivity, lysosomal pH, and cell death pathway was studied in 5 HNSCC lines and compared with normal oral keratinocytes.

RESULTS

We identified a linear relationship between lysosomal pH and cisplatin sensitivity. Reduced lysosomal acidification was correlated to decreased expression of the V(0)V(1)-ATPase B2 subunit, which is part of the lysosomal acidifying complex. Cisplatin caused apoptosis accompanied by lysosomal membrane permeabilization, and inhibition of lysosomal proteases (cathepsins) partly prevented cell death.

CONCLUSION

Cisplatin-induced apoptosis of HNSCC is more efficient in cell lines with low lysosomal pH and is mediated by the release of lysosomal content. Lysosomal pH and expression of V(0)V(1)-ATPase subunits are possible future markers of intrinsic cisplatin sensitivity.

Role of the RNA-binding protein IMP-2 in muscle cell motility

Insulin-like growth factor 2 (IGF-2) mRNA-binding proteins (IMPs) are a family of posttranscriptional regulatory factors with well-understood roles in embryonic development and cancer but with poorly characterized functions in normal adult cells and tissues. We now show that IMP-2, the most ubiquitously expressed member of the family, is abundant in human and mouse adult skeletal myoblasts, where it is indispensable for cell motility and for stabilization of microtubules. To explore the functions of IMP-2, we analyzed the transcripts that were differentially regulated in IMP-2-depleted myoblasts and bound to IMP-2 in normal myoblasts. Among them were the mRNAs of PINCH-2, an important mediator of cell adhesion and motility, and MURF-3, a microtubule-stabilizing protein. By gain- and loss-of-function assays and gel shift experiments, we show that IMP-2 regulates the expression of PINCH-2 and MURF-3 proteins via direct binding to their mRNAs. Upregulation of PINCH-2 in IMP-2-depleted myoblasts is the key event responsible for their decreased motility. Our data reveal how the posttranscriptional regulation of gene expression by IMP-2 contributes to the control of adhesion structures and stable microtubules and demonstrate an important function for IMP-2 in cellular motility.

Copper transporter 2 regulates endocytosis and controls tumor growth and sensitivity to cisplatin in vivo

Copper transporter 2 (CTR2) is one of the four copper transporters in mammalian cells that influence the cellular pharmacology of cisplatin and carboplatin. CTR2 was knocked down using a short hairpin RNA interference. Robust expression of CTR2 was observed in parental tumors grown in vivo, whereas no staining was found in the tumors formed from cells in which CTR2 had been knocked down. Knockdown of CTR2 reduced growth rate by 5.8-fold, increased the frequency of apoptotic cells, and decreased the vascular density, but it did not change copper content. Knockdown of CTR2 increased the tumor accumulation of cis-diamminedichloroplatinum(II) [cisplatin (cDDP)] by 9.1-fold and greatly increased its therapeutic efficacy. Because altered endocytosis has been implicated in cDDP resistance, uptake of dextran was used to quantify the rate of macropinocytosis. Knockdown of CTR2 increased dextran uptake 2.5-fold without reducing exocytosis. Inhibition of macropinocytosis with either amiloride or wortmannin blocked the increase in macropinocytosis mediated by CTR2 knockdown. Stimulation of macropinocytosis by platelet-derived growth factor coordinately increased dextran and cDDP uptake. Knockdown of CTR2 was associated with activation of the Rac1 and cdc42 GTPases that control macropinocytosis but not activation of the phosphoinositide-3 kinase pathway. We conclude that CTR2 is required for optimal tumor growth and that it is an unusually strong regulator of cisplatin accumulation and cytotoxicity. CTR2 regulates the transport of cDDP in part through control of the rate of macropinocytosis via activation of Rac1 and cdc42. Selective knockdown of CTR2 in tumors offers a strategy for enhancing the efficacy of cDDP.

Metallofullerene nanoparticles circumvent tumor resistance to cisplatin by reactivating endocytosis

Cisplatin is a chemotherapeutic drug commonly used in clinics. However, acquired resistance confines its application in chemotherapeutics. To overcome the acquired resistance to cisplatin, it is reasoned, based on our previous findings of mediation of cellular responses by [Gd@C(82)(OH)(22)](n) nanoparticles, that [Gd@C(82)(OH)(22)](n) may reverse tumor resistance to cisplatin by reactivating the impaired endocytosis of cisplatin-resistant human prostate cancer (CP-r) cells. Here we report that exposure of the CP-r PC-3-luc cells to cisplatin in the presence of nontoxic [Gd@C(82)(OH)(22)](n) not only decreased the number of surviving CP-r cells but also inhibited growth of the CP-r tumors in athymic nude mice as measured by both optical and MRI. Labeling the CP-r PC-3 cells with transferrin, an endocytotic marker, demonstrated that pretreatment of the CP-r PC-3-luc cells with [Gd@C(82)(OH)(22)](n) enhanced intracellular accumulation of cisplatin and formation of cisplatin-DNA adducts by restoring the defective endocytosis of the CP-r cancer cells. The results suggest that [Gd@C(82)(OH)(22)](n) nanoparticles overcome tumor resistance to cisplatin by increasing its intracellular accumulation through the mechanism of restoring defective endocytosis. The technology can be extended to other challenges related to multidrug resistance often found in cancer treatments.

Involvement of vacuolar sequestration and active transport in tolerance of Saccharomyces cerevisiae to hop iso-alpha-acids

The hop plant, Humulus lupulus L., has an exceptionally high content of secondary metabolites, the hop alpha-acids, which possess a range of beneficial properties, including antiseptic action. Studies performed on the mode of action of hop iso-alpha-acids have hitherto been restricted to lactic acid bacteria. The present study investigated molecular mechanisms of hop iso-alpha-acid resistance in the model eukaryote Saccharomyces cerevisiae. Growth inhibition occurred at concentrations of hop iso-alpha-acids that were an order of magnitude higher than those found with hop-tolerant prokaryotes. Chemostat-based transcriptome analysis and phenotype screening of the S. cerevisiae haploid gene deletion collection were used as complementary methods to screen for genes involved in hop iso-alpha-acid detoxification and tolerance. This screening and further analysis of deletion mutants confirmed that yeast tolerance to hop iso-alpha-acids involves three major processes, active proton pumping into the vacuole by the vacuolar-type ATPase to enable vacuolar sequestration of iso-alpha-acids and alteration of cell wall structure and, to a lesser extent, active export of iso-alpha-acids across the plasma membrane. Furthermore, iso-alpha-acids were shown to affect cellular metal homeostasis by acting as strong zinc and iron chelators.

Mechanisms of multidrug resistance in cancer

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Resistance exists against every effective anticancer drug and can develop by numerous mechanisms including decreased drug uptake, increased drug efflux, activation of detoxifying systems, activation of DNA repair mechanisms, evasion of drug-induced apoptosis, etc. In the first part of this chapter, we briefly summarize the current knowledge on individual cellular mechanisms responsible for MDR, with a special emphasis on ATP-binding cassette transporters, perhaps the main theme of this textbook. Although extensive work has been done to characterize MDR mechanisms in vitro, the translation of this knowledge to the clinic has not been crowned with success. Therefore, identifying genes and mechanisms critical to the development of MDR in vivo and establishing a reliable method for analyzing clinical samples could help to predict the development of resistance and lead to treatments designed to circumvent it. Our thoughts about translational research needed to achieve significant progress in the understanding of this complex phenomenon are therefore discussed in a third section. The pleotropic response of cancer cells to chemotherapy is summarized in a concluding diagram.

Fractal analysis and ionic dependence of endocytotic membrane activity of human breast cancer cells

The endocytic membrane activities of two human breast cancer cell lines (MDA-MB-231 and MCF-7) of strong and weak metastatic potential, respectively, were studied in a comparative approach. Uptake of horseradish peroxidase was used to follow endocytosis. Dependence on ionic conditions and voltage-gated sodium channel (VGSC) activity were characterized. Fractal methods were used to analyze quantitative differences in vesicular patterning. Digital quantification showed that MDA-MB-231 cells took up more tracer (i.e., were more endocytic) than MCF-7 cells. For the former, uptake was totally dependent on extracellular Na(+) and partially dependent on extracellular and intracellular Ca(2+) and protein kinase activity. Analyzing the generalized fractal dimension (D(q )) and its Legendre transform f(alpha) revealed that under control conditions, all multifractal parameters determined had values greater for MDA-MB-231 compared with MCF-7 cells, consistent with endocytic/vesicular activity being more developed in the strongly metastatic cells. All fractal parameters studied were sensitive to the VGSC blocker tetrodotoxin (TTX). Some of the parameters had a "simple" dependence on VGSC activity, if present, whereby pretreatment with TTX reduced the values for the MDA-MB-231 cells and eliminated the differences between the two cell lines. For other parameters, however, there was a "complex" dependence on VGSC activity. The possible physical/physiological meaning of the mathematical parameters studied and the nature of involvement of VGSC activity in control of endocytosis/secretion are discussed.

Multidrug resistance decreases with mutations of melanosomal regulatory genes

Whereas resistance to chemotherapy has long impeded effective treatment of metastatic melanoma, the mechanistic basis of this resistance remains unknown. One possible mechanism of drug resistance is alteration of intracellular drug distribution either by drug efflux or sequestration into intracellular organelles. Melanomas, as well as primary melanocytes from which they arise, have intracellular organelles, called melanosomes, wherein the synthesis and storage of the pigment melanin takes place. In this study, comparisons of congenic cells with and without functional molecules regulating melanosome formation show that sensitivity to the chemotherapeutic agent cis-diaminedichloroplatinum II (cis-platin) significantly increases with the mutation of genes regulating melanosome formation, concomitant disruption of melanosome morphology, and loss of mature melanosomes. Absence of the melanosomal structural protein gp100/Pmel17 causes increased cis-platin sensitivity. Independent mutations in three separate genes that regulate melanosome biogenesis (Dtnbp1, Pldn, Vps33a) also result in increased cis-platin sensitivity. In addition, a mutation of the gene encoding the integral melanosomal protein tyrosinase, resulting in aberrant melanosome formation, also causes increased cis-platin sensitivity. Furthermore, sensitivity to agents in other chemotherapeutic classes (e.g., vinblastine and etoposide) also increased with the mutation of Pldn. In contrast, a mutation in another melanosomal regulatory gene, Hps1, minimally affects melanosome biogenesis, preserves the formation of mature melanosomes, and has no effect on cis-platin or vinblastine response. Together, these data provide the first direct evidence that melanosomal regulatory genes influence drug sensitivity and that the presence of mature melanosomes likely contributes to melanoma resistance to therapy.

SIRT1 contributes in part to cisplatin resistance in cancer cells by altering mitochondrial metabolism

Tumors frequently develop resistance to cisplatin, a platinum drug used as a cornerstone of present-day chemotherapy regimens, significantly decreasing its usefulness in the clinic. Although it is known that cisplatin-resistant (CP-r) cancer cells commonly grow more slowly and exhibit reduced uptake of various compounds, including nutrients, the effect of tumor metabolism on cisplatin resistance is unclear. It was found that in CP-r cells, uptake of 2-deoxyglucose was reduced due to dysfunction and altered morphology of mitochondria compared with cisplatin-sensitive parental cancer cells. The CP-r cells overexpressed SIRT1, a histone deacetylase that plays a central role in DNA damage response and transcriptional silencing. Incubation of drug-sensitive cells in low glucose medium induced the expression of SIRT1 and increased cellular resistance to cisplatin. Reduced SIRT1 expression by a SIRT1 SMART small interfering RNA duplex sensitized the >20-fold resistant CP-r cells to cisplatin treatment 1.5- to 2-fold, and SIRT1 overexpression by SIRT1 cDNA transfection increased cisplatin resistance in cisplatin-sensitive cells by 2- to 3-fold. Our findings therefore suggest that reduced glucose use and altered mitochondrial metabolism mediated by SIRT1 is one of several alterations that contribute to cellular resistance to cisplatin.

A combined treatment of HeLa cells with the farnesyl protein transferase inhibitor L-744,832 and cisplatin significantly increases the therapeutic effect as compared to cisplatin monotherapy

Activating mutations of Ras that frequently occur during malignant transformation, enhance growth-promoting signal transduction, allowing cells to bypass stringent control of cell cycle progression, thereby rendering them highly proliferative. Abundantly expressed c-Ha-ras protein in human cervical HeLa cells is farnesylated and attached to the plasma membrane, inducing enhanced signal transduction. Exposure of HeLa cells to cisplatin very efficiently inhibits cell proliferation and induces apoptosis. Unfortunately, high doses of cisplatin are strongly cytotoxic, therefore, an alternative therapeutic strategy allowing dose reduction of cisplatin by inhibition of farnesylation could increase the curative effects of cisplatin, thereby benefiting cancer patients. We used two inhibitors of farnesyl protein transferase (FPTase), FTI, and L-744,832, to sensitize HeLa cells to the action of cisplatin. The combined administration of cisplatin and inhibitors of FPTase increased the cytostatic potency of cisplatin. L-744,832 exhibited a stronger synergistic effect in combination with cisplatin than FTI. Moreover, the efficiency of the combined therapy strongly depended on the treatment regimen: The highest efficiency was achieved after combined treatment for 24 h and post-incubation with an inhibitor of FPTase for 48 h. Following this optimized treatment, apoptosis was induced in approximately 50% of HeLa cells treated with 1 microM cisplatin, representing approximately a threefold increase as compared to cisplatin monotherapy. Combined treatment of HeLa cells with cisplatin and inhibitors of FPTase significantly increases the efficacy of the therapy and allows to reduce the dose of cisplatin. Importantly, best therapeutic effects can be achieved by post-treatment with inhibitors of FPTase.

The chemical genomic portrait of yeast: uncovering a phenotype for all genes

Genetics aims to understand the relation between genotype and phenotype. However, because complete deletion of most yeast genes ( approximately 80%) has no obvious phenotypic consequence in rich medium, it is difficult to study their functions. To uncover phenotypes for this nonessential fraction of the genome, we performed 1144 chemical genomic assays on the yeast whole-genome heterozygous and homozygous deletion collections and quantified the growth fitness of each deletion strain in the presence of chemical or environmental stress conditions. We found that 97% of gene deletions exhibited a measurable growth phenotype, suggesting that nearly all genes are essential for optimal growth in at least one condition.

The role of cellular accumulation in determining sensitivity to platinum-based chemotherapy

The platinum (Pt) drugs cisplatin and carboplatin are heavily employed in chemotherapy regimens; however, similar to other classes of drugs, a number of intrinsic and acquired resistance mechanisms hamper their effectiveness. The method by which Pt drugs enter cells has traditionally been attributed to simple passive diffusion. However, recent evidence suggests a number of active uptake and efflux mechanisms are at play, and altered regulation of these transporters is responsible for the reduced accumulation of drug in resistant cells. This review suggests a model that helps reconcile the disparate literature by describing multiple pathways for Pt-containing drugs into and out of the cell.

The inhibitory effect of (-)-epigallocatechin gallate on activation of the epidermal growth factor receptor is associated with altered lipid order in HT29 colon cancer cells

(-)-Epigallocatechin gallate (EGCG), a major biologically active constituent of green tea, inhibits activation of the epidermal growth factor (EGF) receptor (EGFR) and downstream signaling pathways in several types of human cancer cells, but the precise mechanism is not known. Because several plasma membrane-associated receptor tyrosine kinases (RTK) including EGFR are localized in detergent-insoluble ordered membrane domains, so-called "lipid rafts," we examined whether the inhibitory effect of EGCG on activation of the EGFR is associated with changes in membrane lipid order in HT29 colon cancer cells. First, we did cold Triton X-100 solubility assays. Phosphorylated (activated) EGFR was found only in the Triton X-100-insoluble (lipid raft) fraction, whereas total cellular EGFR was present in the Triton X-100-soluble fraction. Pretreatment with EGCG inhibited the binding of Alexa Fluor 488-labeled EGF to the cells and also inhibited EGF-induced dimerization of the EGFR. To examine possible effects of EGCG on membrane lipid organization, we labeled the cells with the fluorescent lipid analogue 1, 1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate, which preferentially incorporates into ordered membrane domains in cells and found that subsequent treatment with EGCG caused a marked reduction in the Triton X-100-resistant membrane fraction. Polyphenon E, a mixture of green tea catechins, had a similar effect but (-)-epicatechin (EC), the biologically inactive compound, did not significantly alter the Triton X-100 solubility properties of the membrane. Furthermore, we found that EGCG but not EC caused dramatic changes in the function of bilayer-incorporated gramicidin channels. Taken together, these findings suggest that EGCG inhibits the binding of EGF to the EGFR and the subsequent dimerization and activation of the EGFR by altering membrane organization. These effects may also explain the ability of EGCG to inhibit activation of other membrane-associated RTKs, and they may play a critical role in the anticancer effects of this and related compounds.

Mechanisms of resistance to cisplatin and carboplatin

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.

The roles of copper transporters in cisplatin resistance

Platinum-based antitumor agents have been effective in the treatments of many human malignancies but the ultimate success of these agents is often compromised by development of drug resistance. One mechanism associated with resistance to platinum drugs is reduced intracellular accumulation owing to impaired drug intake, enhanced outward transport, or both. Mechanisms for transporting platinum drugs were not known until recent demonstrations that import and export transporters involved in maintenance copper homeostasis are also involved in the transport of these drugs. Ctr1, the major copper influx transporter, has been convincingly demonstrated to transport cisplatin and its analogues, carboplatin, and oxaliplatin. Evidence also suggests that the two copper efflux transporters ATP7A and ATP7B regulate the efflux of cisplatin. These observations are intriguing, because conventional thinking of the inorganic physiologic chemistry of cisplatin and copper is quite different. Hence, understanding the underlying mechanistic aspects of these transporters is critically important. While the mechanisms by which hCtr1, ATP7A and ATP7B transport copper ions have been studied extensively, very little is known about the mechanisms by which these transporters shuffle platinum-based antitumor agents. This review discusses the identification of copper transporters as platinum drug transporters, the structural-functional and mechanistic aspects of these transporters, the mechanisms that regulate their expression, and future research directions that may eventually lead to improved efficacy of platinum-based-based drugs in cancer chemotherapy through modulation of their transporters' activities.

Mass Spectrometry Analysis of the Native Protein Complex Containing Actinin-4 in Prostate Cancer Cells

Actinin-4 was originally identified as an actin-binding protein associated with cell motility and cancer invasion and metastasis. However, actinin-4 forms complexes with a large number of different partner proteins and is speculated to have several distinct functions depending on its partner. The level of actinin-4 expression was found to be significantly lower in prostate cancer cells than in non-cancerous basal cells, and restoration of actinin-4 expression inhibited cell proliferation by prostate cancer cell line 22RV1. Immunoprecipitation and mass spectrometry analysis revealed that actinin-4 forms native complexes with several partner proteins in 22RV1 cells, including with beta/gamma-actin, calmodulin, the clathrin heavy chain, non-muscular myosin heavy chain, heterogeneous nuclear ribonucleoprotein A1, and Ras-GTPase-activating protein SH3 domain-binding protein. Clathrin is a coat protein that covers the internalized membrane pit that forms during early endocytosis. We found that other clathrin-related and unrelated cargo proteins, including dynamin, adaptin-delta, beta subunit of neuronal adaptin-like protein, and p47A, also interact with actinin-4. Immunofluorescence microscopy revealed that dynamin and clathrin co-localized with actinin-4 at the sites of membrane ruffling, and transfection of actinin-4 cDNA facilitated the transport of transferrin into perinuclear endosomes. Endocytosis terminates signaling evoked by cell surface receptors and regulates the recycling of receptors and ligands. We identified a panel of proteins whose expression and/or subcellular localization was regulated by actinin-4 by performing organelle fractionation and ICAT-LC-MS/MS. The decreased expression of actinin-4 protein in prostate cancer cells may cause aberrations in the intracellular trafficking of various cell surface molecules and contribute to carcinogenesis.