Hypoxia-induced metastasis of human melanoma cells: involvement of vascular endothelial growth factor-mediated angiogenesis

Cancer chemotherapy resistance: Mechanisms and recent breakthrough in targeted drug delivery

Conventional chemotherapy, one of the most widely used cancer treatment methods, has serious side effects, and usually results in cancer treatment failure. Drug resistance is one of the primary reasons for this failure. The most significant drawbacks of systemic chemotherapy are rapid clearance from the circulation, the drug's low concentration in the tumor site, and considerable adverse effects outside the tumor. Several ways have been developed to boost neoplasm treatment efficacy and overcome medication resistance. In recent years, targeted drug delivery has become an essential therapeutic application. As more mechanisms of tumor treatment resistance are discovered, nanoparticles (NPs) are designed to target these pathways. Therefore, understanding the limitations and challenges of this technology is critical for nanocarrier evaluation. Nano-drugs have been increasingly employed in medicine, incorporating therapeutic applications for more precise and effective tumor diagnosis, therapy, and targeting. Many benefits of NP-based drug delivery systems in cancer treatment have been proven, including good pharmacokinetics, tumor cell-specific targeting, decreased side effects, and lessened drug resistance. As more mechanisms of tumor treatment resistance are discovered, NPs are designed to target these pathways. At the moment, this innovative technology has the potential to bring fresh insights into cancer therapy. Therefore, understanding the limitations and challenges of this technology is critical for nanocarrier evaluation.

Psychologic Stress Drives Progression of Malignant Tumors via DRD2/HIF1α Signaling

Although it is established that the sustained psychologic stress conditions under which patients with tumors often reside accelerates malignant progression of tumors, the molecular mechanism behind this association is unclear. In this work, the effect of psychologic stress on tumor progression was verified using a stress-stimulated tumor-bearing mouse model (Str-tumor). Both D2 dopamine receptor (DRD2) and hypoxia-inducible factor-1α (HIF1α) were highly expressed in the nucleus of Str-tumors. Treatment with trifluoperazine (TFP), a DRD2 inhibitor, elicited better antitumor effects in Str-tumors than the control group. These results indicate that DRD2 may mediate stress-induced malignant tumor progression. DRD2 interacted with von Hippel-Lindau (VHL) in the nucleus, and competitive binding of DRD2 and HIF1α to VHL resulted in reduced ubiquitination-mediated degradation of HIF1α, enhancing the epithelial-mesenchymal transition of tumor cells. TFP acted as an interface inhibitor between DRD2 and VHL to promote the degradation of HIF1α. In conclusion, DRD2 may promote the progression of malignant tumors induced by psychologic stress via activation of the oxygen-independent HIF1α pathway, and TFP may serve as a therapeutic strategy for stress management in patients with cancer. SIGNIFICANCE: This work identifies DRD2 regulation of HIF1α as a mechanism underlying the progression of malignant tumors stimulated by psychologic stress and suggests that DRD2 inhibition can mitigate these stress conditions in patients.See related commentary by Bernabé, p. 5144.

Selective modulation by PARP-1 of HIF-1α-recruitment to chromatin during hypoxia is required for tumor adaptation to hypoxic conditions

BACKGROUND

The adaptation to hypoxia is mainly controlled by the HIF transcription factors. Increased expression/activity of HIF-1α correlates with poor prognosis in cancer patients. PARP-1 inhibitors are used in the clinic to treat BRCAness breast/ovarian cancer and have been shown to regulate the hypoxic response; therefore, their use could be expanded.

METHODS

In this work by integrating molecular/cell biology approaches, genome-wide ChIP-seq, and patient samples, we elucidate the extent to which PARP-1 exerts control over HIF-1-regulated genes.

RESULTS

In human melanoma, PARP-1 and HIF-1α expression are strongly associated. In response to a hypoxic challenge poly(ADP-ribose) (PAR) is synthesized, HIF-1α is post-transcriptionally modified (PTM) and stabilized by PARylation at specific K/R residues located at its C-terminus. Using an unbiased ChIP-seq approach we demonstrate that PARP-1 dictates hypoxia-dependent HIF-recruitment to chromatin in a range of HIF-regulated genes while analysis of HIF-binding motifs (RCGTG) reveals a restriction on the recognition of hypoxia responsive elements in the absence of PARP-1. Consequently, the cells are poorly adapted to hypoxia, showing a reduced fitness during hypoxic induction.

CONCLUSIONS

These data characterize the fine-tuning regulation by PARP-1/PARylation of HIF activation and suggest that PARP inhibitors might have therapeutic potential against cancer types displaying HIF-1α over-activation.

Tumor Hypoxia as a Barrier in Cancer Therapy: Why Levels Matter

Simple Summary

Hypoxia is a common feature of solid tumors and associated with poor outcome in most cancer types and treatment modalities, including radiotherapy, chemotherapy, surgery and, most likely, immunotherapy. Emerging strategies, such as proton therapy and combination therapies with radiation and hypoxia targeted drugs, provide new opportunities to overcome the hypoxia barrier and improve therapeutic outcome. Hypoxia is heterogeneously distributed both between and within tumors and shows large variations across patients not only in prevalence, but importantly, also in level. To best exploit the emerging strategies, a better understanding of how individual hypoxia levels from mild to severe affect tumor biology is vital. Here, we discuss our current knowledge on this topic and how we should proceed to gain more insight into the field.

Abstract

Hypoxia arises in tumor regions with insufficient oxygen supply and is a major barrier in cancer treatment. The distribution of hypoxia levels is highly heterogeneous, ranging from mild, almost non-hypoxic, to severe and anoxic levels. The individual hypoxia levels induce a variety of biological responses that impair the treatment effect. A stronger focus on hypoxia levels rather than the absence or presence of hypoxia in our investigations will help development of improved strategies to treat patients with hypoxic tumors. Current knowledge on how hypoxia levels are sensed by cancer cells and mediate cellular responses that promote treatment resistance is comprehensive. Recently, it has become evident that hypoxia also has an important, more unexplored role in the interaction between cancer cells, stroma and immune cells, influencing the composition and structure of the tumor microenvironment. Establishment of how such processes depend on the hypoxia level requires more advanced tumor models and methodology. In this review, we describe promising model systems and tools for investigations of hypoxia levels in tumors. We further present current knowledge and emerging research on cellular responses to individual levels, and discuss their impact in novel therapeutic approaches to overcome the hypoxia barrier.

Retooling Cancer Nanotherapeutics' Entry into Tumors to Alleviate Tumoral Hypoxia

Anti-hypoxia cancer nanomedicine (AHCN) holds exciting potential in improving oxygen-dependent therapeutic efficiencies of malignant tumors. However, most studies regarding AHCN focus on optimizing structure and function of nanomaterials with presupposed successful entry into tumor cells. From such a traditional perspective, the main barrier that AHCN needs to overcome is mainly the tumor cell membrane. However, such an oversimplified perspective would neglect that real tumors have many biological, physiological, physical, and chemical defenses preventing the current state-of-the-art AHCNs from even reaching the targeted tumor cells. Fortunately, in recent years, some studies are beginning to intentionally focus on overcoming physiological barriers to alleviate hypoxia. In this Review, the limitations behind the traditional AHCN delivery mindset are addressed and the key barriers that need to be surmounted before delivery to cancer cells and some good ways to improve cell membrane attachment, internalization, and intracellular retention are summarized. It is aimed to contribute to Review literature on this emerging topic through refreshing perspectives based on this work and what is also learnt from others. This Review would therefore assist AHCNs researchers to have a quick overview of the essential information and glean thought-provoking ideas to advance this sub-field in cancer nanomedicine.

The Multifactorial Role of PARP-1 in Tumor Microenvironment

Poly(ADP-ribose) polymerases (PARPs), represent a family of 17 proteins implicated in a variety of cell functions; some of them possess the enzymatic ability to synthesize and attach poly (ADP-ribose) (also known as PAR) to different protein substrates by a post-translational modification; PARPs are key components in the cellular response to stress with consequences for different physiological and pathological events, especially during neoplasia. In recent years, using PARP inhibitors as antitumor agents has raised new challenges in understanding their role in tumor biology. Notably, the function of PARPs and PAR in the dynamic of tumor microenvironment is only starting to be understood. In this review, we summarized the conclusions arising from recent studies on the interaction between PARPs, PAR and key features of tumor microenvironment such as hypoxia, autophagy, tumor initiating cells, angiogenesis and cancer-associated immune response.

Clinical implications of ALDH1A1 and ALDH1A3 mRNA expression in melanoma subtypes

Aldehyde dehydrogenase (ALDH) activity is not only a valuable marker for cancer cells with stem-like features, but also plays a vital role in drug resistance and disease progression in many tumors including melanoma. However, the precise role of ALDH activity in patient prognosis remains unclear. In this study, using the Cancer Genome Atlas (TCGA) RNA-sequencing expression data, we analyzed gene expression of ALDH isozymes in melanoma tumors to define the expression patterns and the prognostic and predictive values of these enzymes. We found that ALDH1A1 and ALDH1A3 had both higher and broader expression ranges in melanoma patients, and that ALDH1A3 expression correlated with better overall survival in metastatic melanoma. Further, stratification of the TCGA cohorts by the mutational subtypes of melanoma specifically revealed that expression of ALDH1A3 correlated with better prognosis in metastatic BRAF-mutant melanoma while expression of ALDH1A1 correlated with better prognosis in BRAF wild-type melanoma. Gene set enrichment analysis (GSEA) of these cohorts identified upregulation in oxidative phosphorylation, adipogenesis, and fatty acid metabolism signaling in ALDH1A^lo patients, suggesting BRAF/MEK inhibitor resistance in that subset of patients. On the other hand, GSEA of ALDH1A3^hi cohorts revealed upregulation in glycolysis, hypoxia and angiogenesis, suggesting BRAF/MEK inhibitor sensitivity in that subset of patients. Gene expression analysis using pre-treatment tumor samples supports high ALDH1A3 expression before BRAF/MEK inhibitor treatment as predictive of better treatment response in BRAF-mutant melanoma patients. Our study provides evidence that high ALDH1A3 mRNA expression is not only a prognostic marker but also a predictive marker for BRAF/MEK inhibitor treatment response in BRAF-mutant metastatic melanoma patients.

Modulating Hypoxia via Nanomaterials Chemistry for Efficient Treatment of Solid Tumors

The common existence of hypoxia in solid tumors has been heavily researched because it renders tumors more resistant to most standard therapeutic methods, such as radiotherapy (RT), chemotherapy, and photodynamic therapy (PDT), and is associated with a more malignant phenotype and poor survival in patients with tumors. The development of hypoxia modulation methods for advanced therapeutic activity is therefore of great interest but remains a considerable challenge. Since the significant development of nanotechnology and nanomedicine, functionalized nanomaterials can be exploited as adjuvant "drugs" for these oxygen-dependent standard therapies or as hypoxia initiators for advanced new therapies to solid tumors. In this Account, we summarize our recent studies on the design and synthesis of nanomaterials with a set of desired chemistry benefits achievable by modulating hypoxia, suggesting a valid therapeutic option for tumors. The investigated strategies can be categorized into three groups: The first strategy is based on countering hypoxia. Considering that O₂ deficiency is the major obstacle for the oxygen-dependent therapies, we initially developed methods to supply O₂ by taking advantage of the hypoxia-responsive properties of nano-MnO₂ or nanomaterials' photothermal effects for increased intratumoral blood flow. The second approach is to disregard hypoxia. Possible benefits of nanoagents include reducing/eliminating reliance on O₂ or making O₂ replacements as adjuvants to standard therapies. To this end, we investigated a nano-upconversion/scintillator with the capacity toup-/down-convert near-infrared light (NIR)/X-ray to luminescence in the ultraviolet/visible region fortype-I PDT with minimized oxygen-tension dependency or developed Fe-based nanomaterials for chemodynamic therapy (CDT) without external energy and oxygen participation for efficient free radical killing of deep tumors. The third strategy involves exploiting hypoxia. The unique biological characteristics of hypoxia are exploited to activate nanoagents for new therapies. To address the discrepancy between the nanoagents' demand and supply within the hypoxia region, a smart "molecule-nano" medicine that stays small-molecule-like in the bloodstream and turns into self-assembled nanovesicles after entry into the hypoxia region was constructed for hypoxia-adaptive photothermal therapy (PTT). In addition to traditional anti-angiogenesis therapy, we prepared Mg₂Si nanoparticles by a special self-propagating high-temperature synthesis approach. These nanoparticles can directly remove the intratumoral oxygen via the oxidation reactions of Mg₂Si and later efficiently block the rapid reoxygenation via tumor blood vessels by the resultant SiO₂ microsheets for cancer starvation therapy. Taken together, these findings indicate that nanomaterials will assume a valuable role for anticancer exploration based on either their properties to make up oxygen deficiency or the use of hypoxia for therapeutic applications.

Phosphorylated Akt Protein at Ser473 Enables HeLa Cells to Tolerate Nutrient-Deprived Conditions

Background:

Despite angiogenesis, many tumours remain hypovascular and starved of nutrients while continuing to grow rapidly. The specific biochemical mechanisms associated with starvation resistance, austerity, may be new biological characters of cancer that are critical for cancer progression.

Objective:

This study aim was to investigate the effect of nutrient starvation on HeLa cells and the possible mechanism by which the cells are able to tolerate nutrient-deprived conditions.

Methods:

Nutrient starvation was achieved by culturing HeLa cells in nutrient-deprived medium (NDM) and cell survival was estimated by using cell counting kit-8. The effect of starvation on cell cycle distribution and the quantitative analysis of apoptotic cells were investigated by flow cytometry using propidium iodide staining. Western blotting was used to detect the expression levels of Akt and phosphorylated Akt at Ser473 (Ser⁴⁷³p-Akt) proteins.

Results:

HeLa cells displayed extremely long survival when cultured in NDM. The percentage of apoptotic HeLa cells was significantly increased by starvation in a time-dependent manner. A significant increase in the expression of Ser⁴⁷³p-Akt protein after starvation was also observed. Furthermore, it was found that Akt inhibitor III molecule inhibited the cells proliferation in a concentration- and time-dependent manner.

Conclusion:

Results of the present study provide evidence that Akt activation may be implicated in the tolerance of HeLa cells for nutrient starvation and may help to suggest new therapeutic strategies designed to prevent austerity of cervical cancer cells through inhibition of Akt activation.

Long-Lived Epidermal Cancer-Initiating Cells

Non-melanomatous skin cancers (NMSCs), which include basal and squamous cell carcinoma (BCC and SCC respectively), represent a significant burden on the population, as well as an economic load to the health care system; yet treatments of these preventable cancers remain ineffective. Studies estimate that there has been a 2-fold increase in the incidence of NMSCs between the 1960s and 1980s. The increase in cases of NMSCs, as well as the lack of effective treatments, makes the need for novel therapeutic approaches all the more necessary. To rationally develop more targeted treatments for NMSCs, a better understanding of the cell of origin, in addition to the underlying pathophysiological mechanisms that govern the development of these cancers, is urgently required. Research over the past few years has provided data supporting both a "bottom up" and "top down" mechanism of tumourigenesis. The "bottom up" concept involves a cancer stem cell originating in the basal compartment of the skin, which ordinarily houses the progenitor cells that contribute towards wound healing and normal cell turnover of overlying epidermal skin layers. The "top down" concept involves a more differentiated cell undergoing genetic modifications leading to dedifferentiation, giving rise to cancer initiating cells (CICs). This review explores both concepts, to paint a picture of the skin SCC cell of origin, the underlying biology, and also how this knowledge might be exploited to develop novel therapies.

Inhibitory role of TRIP-Br1 oncoprotein in hypoxia-induced apoptosis in breast cancer cell lines

TRIP-Br1 oncoprotein is known to be involved in many vital cellular functions. In this study, we examined the role of TRIP-Br1 in hypoxia-induced cell death. Exposure to the overcrowded and CoCl2-induced hypoxic conditions increased TRIP-Br1 expression at the protein level in six breast cancer cell lines (MCF7, MDA-MB-231, T47D, Hs578D, BT549, and MDA-MB-435) but resulted in no significant change in three normal cell lines (MCF10A, MEF and NIH3T3). Our result revealed that CoCl2-induced hypoxia stimulated apoptosis and autophagy, in which TRIP-Br1 expression was found to be upregulated. Interestingly, TRIP-Br1 silencing in the MCF7 and MDA-MB-231 cancer cells accelerated apoptosis and destabilization of XIAP under the CoCl2-induced hypoxic condition, implying that TRIP-Br1 may render cancer cells resistant to apoptosis through the stabilization of XIAP. We also propose that TRIP-Br1 seems to be upregulated at least partly as a result of the inhibition of PI3K/AKT signaling pathway and the overexpression of HIF-1α. In conclusion, our findings suggest that TRIP-Br1 functions as an oncogenic protein by providing cancer cells resistance to the hypoxia-induced cell death.

Intermittent induction of HIF-1α produces lasting effects on malignant progression independent of its continued expression

Dysregulation of hypoxia-inducible transcription factors HIF-1α and HIF-2α correlates with poor prognosis in human cancers; yet, divergent and sometimes opposing activities of these factors in cancer biology have been observed. Adding to this complexity is that HIF-1α apparently possesses tumor-suppressing activities, as indicated by the loss-of-function mutations or even homozygous deletion of HIF1A in certain human cancers. As a step towards understanding this complexity, we employed 8-week intermittent induction of a stable HIF-1α variant, HIF1α(PP), in various cancer cell lines and examined the effects on malignant progression in xenografts of immunocompromised mice in comparison to those of HIF2α(PP). Although 8-week treatment led to eventual loss of HIF1α(PP) expression, treated osteosarcoma U-2 OS cells acquired tumorigenicity in the subcutaneous tissue. Furthermore, the prior treatment resulted in widespread invasion of malignant glioma U-87 MG cells in the mouse brain and sustained growth of U-118 MG glioma cells. The lasting effects of HIF-1α on malignant progression are specific because neither HIF2α(PP) nor β-galactosidase yielded similar effects. By contrast, transient expression of HIF1α(PP) in U-87 MG cells or constitutive expression of HIF1α(PP) but not HIF2α(PP) in a patient-derived glioma sphere culture inhibited tumor growth and spread. Our results indicate that intermittent induction of HIF-1α produces lasting effects on malignant progression even at its own expense.

Deciphering the insights of poly(ADP-ribosylation) in tumor progression

Poly (ADP-ribose) polymerase (PARP) inhibitors are particularly efficient against tumors with defects in the homologous recombination repair pathway. Nonetheless poly(ADP-ribosylation) (PARylation) modulates prometastasic activities and adaptation of tumor to a hostile microenvironment. Modulation of metastasis-promoting traits is possible through the alteration of key transcription factors involved in the regulation of the hypoxic response, the recruitment of new vessels (or angiogenesis), and the stimulation of epithelial to mesenchymal transition (EMT). In this review, we summarized some of the findings that focalize on PARP-1's action on tumor aggressiveness, suggesting new therapeutic opportunities against an assembly of tumors not necessarily bearing DNA repair defects. Metastasis accounts for the vast majority of mortality derived from solid cancer. PARP-1 is an active player in tumor adaptation to metastasis and PARP inhibitors, recognized as promising therapeutic agents against homologous recombination deficient tumors, has novel properties responsible for the antimetastatic actions in different tumor settings.

An investigation on new ruthenium(II) hydrazone complexes as anticancer agents and their interaction with biomolecules

A new set of ruthenium(II) hydrazone complexes [Ru(H)(CO)(PPh3)2(L)] (1) and [RuCl2(DMSO)2(HL)] (2), with triphenyl phosphine or DMSO as co-ligands was synthesized by reacting benzoyl pyridine furoic acid hydrazone (HL) with [Ru(H)(Cl)(CO)(PPh3)3] and [RuCl2(DMSO)4]. The single crystal X-ray data of complexes 1 and 2 revealed an octahedral geometry around the ruthenium ion in which the hydrazone is coordinated through ON and NN atoms in complexes 1 and 2 respectively. The interaction of the compounds with calf thymus DNA (CT-DNA) has been estimated by absorption and emission titration methods which indicated that the ligand and the complexes interacted with CT-DNA through intercalation. In addition, the DNA cleavage ability of these newly synthesized ruthenium complexes assessed by an agarose gel electrophoresis method demonstrated that complex 2 has a higher DNA cleavage activity than that of complex 1. The binding properties of the free ligand and its complexes with bovine serum albumin (BSA) protein have been investigated using UV-visible, fluorescence and synchronous fluorescence spectroscopic methods which indicated the stronger binding nature of the ruthenium complexes to BSA than the free hydrazone ligand. Furthermore, the cytotoxicity of the compounds examined in vitro on a human cervical cancer cell line (HeLa) and a normal mouse embryonic fibroblasts cell line (NIH 3T3) revealed that complex 2 exhibited a superior cytotoxicity than complex 1 to the cancer cells but was less toxic to the normal mouse embryonic fibroblasts under identical conditions.

Mechanisms of tumour vascularization in cutaneous malignant melanoma: clinical implications

Malignant melanoma represents < 10% of all skin cancers but is responsible for the majority of skin-cancer-related deaths. Metastatic melanoma has historically been considered as one of the most therapeutically challenging malignancies. Fortunately, for the first time after decades of basic research and clinical investigation, new drugs have produced major clinical responses. Angiogenesis has been considered an important target for cancer treatment. Initial efforts have focused primarily on targeting endothelial and tumour-related vascular endothelial growth factor signalling. Here, we review different mechanisms of tumour vascularization described in melanoma and discuss the potential clinical implications.

The Warburg effect in tumor progression: mitochondrial oxidative metabolism as an anti-metastasis mechanism

Compared to normal cells, cancer cells strongly upregulate glucose uptake and glycolysis to give rise to increased yield of intermediate glycolytic metabolites and the end product pyruvate. Moreover, glycolysis is uncoupled from the mitochondrial tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) in cancer cells. Consequently, the majority of glycolysis-derived pyruvate is diverted to lactate fermentation and kept away from mitochondrial oxidative metabolism. This metabolic phenotype is known as the Warburg effect. While it has become widely accepted that the glycolytic intermediates provide essential anabolic support for cell proliferation and tumor growth, it remains largely elusive whether and how the Warburg metabolic phenotype may play a role in tumor progression. We hereby review the cause and consequence of the restrained oxidative metabolism, in particular in the context of tumor metastasis. Cells change or lose their extracellular matrix during the metastatic process. Inadequate/inappropriate matrix attachment generates reactive oxygen species (ROS) and causes a specific type of cell death, termed anoikis, in normal cells. Although anoikis is a barrier to metastasis, cancer cells have often acquired elevated threshold for anoikis and hence heightened metastatic potential. As ROS are inherent byproducts of oxidative metabolism, forced stimulation of glucose oxidation in cancer cells raises oxidative stress and restores cells' sensitivity to anoikis. Therefore, by limiting the pyruvate flux into mitochondrial oxidative metabolism, the Warburg effect enables cancer cells to avoid excess ROS generation from mitochondrial respiration and thus gain increased anoikis resistance and survival advantage for metastasis. Consistent with this notion, pro-metastatic transcription factors HIF and Snail attenuate oxidative metabolism, whereas tumor suppressor p53 and metastasis suppressor KISS1 promote mitochondrial oxidation. Collectively, these findings reveal mitochondrial oxidative metabolism as a critical suppressor of metastasis and justify metabolic therapies for potential prevention/intervention of tumor metastasis.

Hypoxic activation of the PERK/eIF2α arm of the unfolded protein response promotes metastasis through induction of LAMP3

PURPOSE

Conditions of poor oxygenation (hypoxia) are present in many human tumors, including cervix cancer, and are associated with increased risk of metastasis and poor prognosis. Hypoxia is a potent activator of the PERK/eIF2α signaling pathway, a component of the unfolded protein response (UPR) and an important mediator of hypoxia tolerance and tumor growth. Here, the importance of this pathway in the metastasis of human cervix carcinoma was investigated.

EXPERIMENTAL DESIGN

Amplification and expression of LAMP3, a UPR metastasis-associated gene, was examined using FISH and immunofluorescence in a cohort of human cervix tumors from patients who had received oxygen needle electrode tumor oxygenation measurements. To evaluate the importance of this pathway in metastasis in vivo, we constructed a series of inducible cell lines to interfere with PERK signaling during hypoxia and used these in an orthotopic cervix cancer model of hypoxia-driven metastasis.

RESULTS

We show that LAMP3 expression in human cervix tumors is augmented both by gene copy number alterations and by hypoxia. Induced disruption of PERK signaling in established orthotopic xenografts resulted in complete inhibition of hypoxia-induced metastasis to the lymph nodes. This is due, in part, to a direct influence of the UPR pathway on hypoxia tolerance. However, we also find that LAMP3 is a key mediator of hypoxia-driven nodal metastasis, through its ability to promote metastatic properties including cell migration.

CONCLUSION

These data suggest that the association between hypoxia, metastasis, and poor prognosis is due, in part, to hypoxic activation of the UPR and expression of LAMP3. Clin Cancer Res; 19(22); 6126-37. ©2013 AACR.

Is cancer a metabolic disease?

Although cancer has historically been viewed as a disorder of proliferation, recent evidence has suggested that it should also be considered a metabolic disease. Growing tumors rewire their metabolic programs to meet and even exceed the bioenergetic and biosynthetic demands of continuous cell growth. The metabolic profile observed in cancer cells often includes increased consumption of glucose and glutamine, increased glycolysis, changes in the use of metabolic enzyme isoforms, and increased secretion of lactate. Oncogenes and tumor suppressors have been discovered to have roles in cancer-associated changes in metabolism as well. The metabolic profile of tumor cells has been suggested to reflect the rapid proliferative rate. Cancer-associated metabolic changes may also reveal the importance of protection against reactive oxygen species or a role for secreted lactate in the tumor microenvironment. This article reviews recent research in the field of cancer metabolism, raising the following questions: Why do cancer cells shift their metabolism in this way? Are the changes in metabolism in cancer cells a consequence of the changes in proliferation or a driver of cancer progression? Can cancer metabolism be targeted to benefit patients?

A microfabricated platform for establishing oxygen gradients in 3-D constructs

Oxygen gradients are increasingly implicated in a number of biological processes, including stem cell differentiation and cancer metastasis. Unfortunately, the current in vitro tools designed to mimic conditions found in vivo lack application flexibility, simplicity in operation, and precise spatial control that most researchers require for widespread dissemination. The novel microfluidic-based device presented here addresses all the above concerns, offering a simple platform for enhanced control over the oxygen microenvironment exposed to three-dimensional cell-seeded constructs. The device utilizes an oxygen diffusion membrane approach to establish a gradient across a construct sandwiched between two continually perfused microfluidic networks. The device is capable of forming steady-state gradients at both the conditions tested-0 % to 5 % O₂ and 0 % to 21 % O₂-but a wide variety of profiles within the construct are possible. Cell viability with two model cell lines was also tested, with no adverse effects relative to the control.

Hypoxia-inducing factors as master regulators of stemness properties and altered metabolism of cancer- and metastasis-initiating cells

Accumulating lines of experimental evidence have revealed that hypoxia-inducible factors, HIF-1α and HIF-2α, are key regulators of the adaptation of cancer- and metastasis-initiating cells and their differentiated progenies to oxygen and nutrient deprivation during cancer progression under normoxic and hypoxic conditions. Particularly, the sustained stimulation of epidermal growth factor receptor (EGFR), insulin-like growth factor-1 receptor (IGF-1R), stem cell factor (SCF) receptor KIT, transforming growth factor-β receptors (TGF-βRs) and Notch and their downstream signalling elements such as phosphatidylinositol 3′-kinase (PI3K)/Akt/molecular target of rapamycin (mTOR) may lead to an enhanced activity of HIFs. Moreover, the up-regulation of HIFs in cancer cells may also occur in the hypoxic intratumoral regions formed within primary and secondary neoplasms as well as in leukaemic cells and metastatic prostate and breast cancer cells homing in the hypoxic endosteal niche of bone marrow. The activated HIFs may induce the expression of numerous gene products such as induced pluripotency-associated transcription factors (Oct-3/4, Nanog and Sox-2), glycolysis- and epithelial-mesenchymal transition (EMT) programme-associated molecules, including CXC chemokine receptor 4 (CXCR4), snail and twist, microRNAs and angiogenic factors such as vascular endothelial growth factor (VEGF). These gene products in turn can play critical roles for high self-renewal ability, survival, altered energy metabolism, invasion and metastases of cancer cells, angiogenic switch and treatment resistance. Consequently, the targeting of HIF signalling network and altered metabolic pathways represents new promising strategies to eradicate the total mass of cancer cells and improve the efficacy of current therapies against aggressive and metastatic cancers and prevent disease relapse.

Effect of culture at low oxygen tension on the expression of heat shock proteins in a panel of melanoma cell lines

OBJECTIVE

Tumours are commonly hypoxic and this can be associated with aggressive tumour type, metastasis and resistance to therapy. Heat shock proteins (hsps) are induced in response to hypoxia, provide cancer cells with protection against tumour-associated stressors and chaperone oncoproteins that drive tumour proliferation. This study examined the effect of different oxygen concentrations on the expression of hsps in melanoma cell lines.

METHODS

Melanoma cell lines were cultured in 2% and 20% O(2). Expression of Hsp90, Hsp70, Hsp60, Hsp40 and Hsp32 proteins were determined by flow cytometry.

RESULTS

Growth rates and viability were reduced in the majority of cell lines by culture in 2% O(2). Hsp expression was different in 2% compared to 20% O(2) and changes in Hsp90 expression correlated with cell line generation time (P<0.005) and viability (P<0.01). Greater total hsp expression correlated with improved viability in 2% but not 20% O(2) (P<0.05). Relative expression of the different hsps was consistent across cell lines and each correlated with the others (P = 0.0001) but not with Hsp32. Hsp expression was inversely correlated with cell line adhesion to laminin as well as collagen type IV and Breslow depth of the original primary tumour tissue (P<0.05), but not with Clark level or patient survival. All five hsps were identified on the cell surface.

CONCLUSION

Culture in 2% O(2) variably altered hsp expression in a panel of melanoma cell lines. Hsp expression was associated with certain cell line characteristics and clinical parameters of the originating tumour.

Vascular density and endothelial cell expression of integrin alpha v beta 3 and E-selectin in murine tumours

The endothelial cell adhesion molecules, including the integrin alpha v beta 3 (αvβ3) and E-selectin, are involved in the process of angiogenesis required for tumour growth, cell migration and metastasis. The purpose of this study was to assess and compare widely used tumour models to select the ones most suitable for angiogenesis research. Fifteen murine tumours were selected including melanoma (B16), colon (C26, C38, C51), mammary (MA13, MA16, MA16/Adr, MA17, MA17/Adr, MA25, MA44), pancreatic (PO2, PO3), Glasgow osteogenic sarcoma (GOS) and Lewis lung carcinoma (LLC). The tumour vascular density, assessed using the platelet endothelial cell adhesion molecule 1 (PECAM-1; CD31) immunostaining, revealed that B16 melanoma was poorly vascularized (<5 %), whereas the colon and mammary tumours were well vascularized (5-15 %). The most vascularized tumours (>15 %) were the pancreatic tumours (PO2 and PO3), the sarcoma (GOS) and the lung tumour (LLC). The integrin αvβ3 and E-selectin, evaluated by immunohistology, showed that 7/15 tumours expressed the αvβ3 integrin which was homogeneously distributed on all tumour sections (B16, C26, MA17/Adr, MA25, MA44, PO2, LLC). E-selectin was expressed in 4/15 tumours and its expression was restricted to the tumour periphery. Only 2/15 tumours (B16 and C26) were shown to express both integrin αvβ3 and E-selectin. In conclusion, these data not only contribute to a better understanding of the tumour biology of murine tumours but can also guide the choice of appropriate models for antiangiogenic therapy, for selective drug delivery to tumours and the validation of tumour imaging modalities targeting these endothelial cell adhesion molecules.

Endothelial cell HIF-1α and HIF-2α differentially regulate metastatic success

The hypoxia inducible transcription factors (HIFs) control many mediators of vascular response, including both angiogenic factors and small molecules such as nitric oxide (NO). In studying how endothelial HIF response itself affects metastasis, we found that loss of HIF-1α in endothelial cells reduces NO synthesis, retards tumor cell migration through endothelial layers, and restricts tumor cell metastasis, and that loss of HIF-2α has in each case the opposite effect. This results from differential regulation of NO homeostasis that in turn regulates vascular endothelial growth factor expression in an NO-dependent feedback loop. These opposing roles for the two HIF factors indicate that both they and endothelial cells regulate metastasis as malignancy progresses.

Snail1 mediates hypoxia-induced melanoma progression

Tumor hypoxia is a known adverse prognostic factor, and the hypoxic dermal microenvironment participates in melanomagenesis. High levels of hypoxia inducible factor (HIF) expression in melanoma cells, particularly HIF-2α, is associated with poor prognosis. The mechanism underlying the effect of hypoxia on melanoma progression, however, is not fully understood. We report evidence that the effects of hypoxia on melanoma cells are mediated through activation of Snail1. Hypoxia increased melanoma cell migration and drug resistance, and these changes were accompanied by increased Snail1 and decreased E-cadherin expression. Snail1 expression was regulated by HIF-2α in melanoma. Snail1 overexpression led to more aggressive tumor phenotypes and features associated with stem-like melanoma cells in vitro and increased metastatic capacity in vivo. In addition, we found that knockdown of endogenous Snail1 reduced melanoma proliferation and migratory capacity. Snail1 knockdown also prevented melanoma metastasis in vivo. In summary, hypoxia up-regulates Snail1 expression and leads to increased metastatic capacity and drug resistance in melanoma cells. Our findings support that the effects of hypoxia on melanoma are mediated through Snail1 gene activation and suggest that Snail1 is a potential therapeutic target for the treatment of melanoma.

Tumor necrosis factor blocking therapy alters joint inflammation and hypoxia

OBJECTIVE

To examine the effect of tumor necrosis factor (TNF) blocking therapy on hypoxia in vivo, macroscopic and microscopic inflammation, and magnetic resonance imaging (MRI) results in patients with inflammatory arthritis.

METHODS

Patients with inflammatory arthritis (n = 20) underwent full clinical assessment, arthroscopy, synovial biopsy, and MRI before and after initiation of biologic therapy. Macroscopic synovitis/vascularity was assessed with a visual analog scale, and tissue PO(2) (tPO(2) ) was measured at arthroscopy using a Licox probe. Cell-specific markers (CD4, CD8, CD68, CD20, and CD19) and blood vessel maturity were quantified by immunohistologic analysis and dual-immunofluorescence factor VIII/α-smooth muscle actin staining, respectively. Contiguous gadoteric acid-enhanced MRI of the target knee was used to assess synovial enhancement.

RESULTS

Biologic therapy responders showed a significant increase of tPO(2) in vivo (P < 0.05). This response was associated with significant reductions in 28-joint Disease Activity Score using the C-reactive protein level (DAS28-CRP) (P = 0.012), macroscopic synovitis (P = 0.017), macroscopic vascularity (P = 0.05), CD4+ T cells (P < 0.041), and CD68+ macrophages (P < 0.011). Blood vessel numbers were also reduced in responders; however, this did not reach statistical significance. Strong inverse correlations were demonstrated between changes in tPo(2) levels and changes in DAS28-CRP (r = -0.53, P < 0.001), CD4 (r = -0.44, P < 0.026), CD68 (r = -0.46, P < 0.003), and macroscopic vascularity (r = -0.314, P = 0.049) after therapy. Furthermore, changes in inflammation as measured by MRI showed a strong inverse correlation with tPO(2) levels (r = -0.688, P < 0.002) and positive correlations with CRP levels (r = 0.707, P = 0.001), macroscopic synovitis (r = 0.457, P = 0.056), macroscopic vascularity (r = 0.528, P= 0.017), CD4 (r = 0.553, P < 0.032), and CD68 (r = 0.670, P < 0.002) after therapy.

CONCLUSION

This is the first study to show that successful biologic therapy significantly improves in vivo synovial hypoxia. Changes are strongly associated with changes in macroscopic and microscopic measures of joint inflammation and MRI improvement. These data further strengthen the concept that hypoxia is an important event driving synovial inflammation.

Tumors exposed to acute cyclic hypoxic stress show enhanced angiogenesis, perfusion and metastatic dissemination

Clinical studies have shown that patients with highly hypoxic primary tumors may have poor disease-free and overall survival rates. Studies of experimental tumors have revealed that acutely hypoxic cells may be more metastatic than normoxic or chronically hypoxic cells. In the present work, causal relations between acute cyclic hypoxia and metastasis were studied by periodically exposing BALB/c nu/nu mice bearing A-07 human melanoma xenografts to a low oxygen atmosphere. The hypoxia treatment consisted of 12 cycles of 10 min of 8% O(2) in N(2) followed by 10 min of air for a total of 4 hr, began on the first day after tumor cell inoculation and was given daily until the tumors reached a volume of 100 mm(3). Twenty-four hours after the last hypoxia exposure, the primary tumors were subjected to dynamic contrast-enhanced magnetic resonance imaging for assessment of blood perfusion before being resected and processed for immunohistochemical examinations of microvascular density and expression of proangiogenic factors. Mice exposed to acute cyclic hypoxia showed increased incidence of pulmonary metastases, and the primary tumors of these mice showed increased blood perfusion, microvascular density and vascular endothelial growth factor-A (VEGF-A) expression; whereas, the expression of interleukin-8, platelet-derived endothelial cell growth factor and basic fibroblast growth factor was unchanged. The increased pulmonary metastasis was most likely a consequence of hypoxia-induced VEGF-A upregulation, which resulted in increased angiogenic activity and blood perfusion in the primary tumor and thus facilitated tumor cell intravasation and hematogenous transport into the general circulation.

Photobiological activity of Ru(II) dyads based on (pyren-1-yl)ethynyl derivatives of 1,10-phenanthroline

Several mononuclear Ru(II) dyads possessing 1,10-phenanthroline-appended pyrenylethynylene ligands were synthesized, characterized, and evaluated for their potential in photobiological applications such as photodynamic therapy (PDT). These complexes interact with DNA via intercalation and photocleave DNA in vitro at submicromolar concentrations when irradiated with visible light (lambda(irr) > or = 400 nm). Such properties are remarkably sensitive to the position of the ethynylpyrenyl substituent on the 1,10-phenanthroline ring, with 3-substitution showing the strongest binding under all conditions and causing the most deleterious DNA damage. Both dyads photocleave DNA under hypoxic conditions, and this photoactivity translates well to cytotoxicity and photocytotoxicity models using human leukemia cells, where the 5- and 3-substituted dyads show photocytotoxicity at 5-10 microM and 10-20 microM, respectively, with minimal, or essentially no, dark toxicity at these concentrations. This lack of dark cytotoxicity at concentrations where significant photoactivity is observed emphasizes that agents with strong intercalating units, previously thought to be too toxic for phototherapeutic applications, should not be excluded from the arsenal of potential photochemotherapeutic agents under investigation.

HIF-1α Promotes A Hypoxia-Independent Cell Migration

Hypoxia-inducible factor-1α (HIF-1α) is known as a transactivator for VEGF gene promoter. It can be induced by hypoxia. However, no study has been done so far to dissect HIF-1α-mediated effects from hypoxia or VEGF-mediated effects. By using a HIF-1α knockout (HIF-1α KO) cell system in mouse embryonic fibroblast (MEF) cells, this study analyzes cell migration and HIF-1α, hypoxia and VEGF activation. A hypoxia-mediated HIF-1α induction and VEGF transactivation were observed: both HIF-1α WT lines had significantly increased VEGF transactivation, as an indicator for HIF-1α induction, in hypoxia compared to normoxia; in contrast, HIF-1α KO line had no increased VEGF transactivation under hypoxia. HIF-1α promotes cell migration: HIF-1α-KO cells had a significantly reduced migration compared to that of the HIF-1α WT cells under both normoxia and hypoxia. The significantly reduced cell migration in HIF-1α KO cells can be partially rescued by the restoration of WT HIF-1α expression mediated by adenoviral-mediated gene transfer. Interestingly, hypoxia has no effect on cell migration: the cells had a similar cell migration rate under hypoxic and normoxic conditions for both HIF-1α WT and HIF-1α KO lines, respectively. Collectively, these data suggest that HIF-1α plays a role in MEF cell migration that is independent from hypoxia-mediated effects.

Antimetastatic activity of MONCPT in preclinical melanoma mice model

Previous study demonstrated that MONCPT, a topoisomerase I inhibitor, exhibited potent anti-proliferation and anti-angiogenesis activity in vitro and in vivo. In this study, we report the efficacy of MONCPT against the development of melanoma metastasis by an intravenous injection of green fluorescent protein-transfected mice melanoma carcinoma (B16F10-GFP) cells in C57BL/6 mice. MONCPT (2.0, 5.0 and 12.5 mg/kg/2 days) markedly decreased B16F10-GFP pulmonary metastases by 12.8%, 53.1% and 76.3%, respectively; whereas higher doses of MONCPT (31.0 mg/kg/2 days) significantly inhibited the tumor growth of B16F10 xenograft model. In the in vitro experiment, MONCPT suppressed the B16F10-GFP cell invasion and migration without affecting cell survival. Further studies demonstrated that MONCPT decreased the secretion of matrix metalloproteinase (MMP)-9 and VEGF, and reduced the protein expression of HIF-1α as well as the phosphorylation level of ERK in B16F10-GFP cells. These in vivo and in vitro results indicate that MONCPT possesses both the potent antimetastatic ability and the tumor growth-inhibition activity, and the dual function promises MONCPT as a potential therapeutic agent for tumor metastasis and tumor growth of melanoma carcinoma.

Transcriptionally regulated, prostate-targeted gene therapy for prostate cancer

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in American males today. Novel and effective treatment such as gene therapy is greatly desired. The early viral based gene therapy uses tissue-nonspecific promoters, which causes unintended toxicity to other normal tissues. In this chapter, we will review the transcriptionally regulated gene therapy strategy for prostate cancer treatment. We will describe the development of transcriptionally regulated prostate cancer gene therapy in the following areas: (1) Comparison of different routes for best viral delivery to the prostate; (2) Study of transcriptionally regulated, prostate-targeted viral vectors: specificity and activity of the transgene under several different prostate-specific promoters were compared in vitro and in vivo; (3) Selection of therapeutic transgenes and strategies for prostate cancer gene therapy (4) Oncolytic virotherapy for prostate cancer. In addition, the current challenges and future directions in this field are also discussed.

Tumor-immune interaction, surgical treatment, and cancer recurrence in a mathematical model of melanoma

Malignant melanoma is a cancer of the skin arising in the melanocytes. We present a mathematical model of melanoma invasion into healthy tissue with an immune response. We use this model as a framework with which to investigate primary tumor invasion and treatment by surgical excision. We observe that the presence of immune cells can destroy tumors, hold them to minimal expansion, or, through the production of angiogenic factors, induce tumorigenic expansion. We also find that the tumor–immune system dynamic is critically important in determining the likelihood and extent of tumor regrowth following resection. We find that small metastatic lesions distal to the primary tumor mass can be held to a minimal size via the immune interaction with the larger primary tumor. Numerical experiments further suggest that metastatic disease is optimally suppressed by immune activation when the primary tumor is moderately, rather than minimally, metastatic. Furthermore, satellite lesions can become aggressively tumorigenic upon removal of the primary tumor and its associated immune tissue. This can lead to recurrence where total cancer mass increases more quickly than in primary tumor invasion, representing a clinically more dangerous disease state. These results are in line with clinical case studies involving resection of a primary melanoma followed by recurrence in local metastases.

Melanoma is a deadly skin cancer that invades into the dermis and metastasizes into the surrounding tissue. In clinical cases, surgical excision of the primary tumor has led to widespread and accelerated growth in metastases. We develop a mathematical model describing the basic process of melanoma invasion, metastatic spread, and the anti-tumor immune response. This model is formulated using partial differential equations that describe the spatial and temporal evolution of a number of different cellular populations, and it uses a realistic skin geometry. Using simulations, we examine the importance of the immune response when a primary tumor is spawning satellite metastases. We find that local metastases can be suppressed by the immune response directed against the primary tumor, but grow aggressively following surgical treatment. We also find that moderately metastatic tumors optimally activate the local immune response against disseminated disease, and in this case tumor excision may have profound effects on metastatic growth. We conclude that surgical perturbation of the immune response controlling local metastases is one mechanism by which cancer can recur. This could have implications as to the appropriate clinical management of melanomas and other solid tumors.

Immunohistochemical detection of changes in tumor hypoxia

PURPOSE

Although hypoxia is a known prognostic factor, its effect will be modified by the rate of reoxygenation and the extent to which the cells are acutely hypoxic. We tested the ability of exogenous and endogenous markers to detect reoxygenation in a xenograft model. Our technique might be applicable to stored patient samples.

METHODS AND MATERIALS

The human colorectal carcinoma line, HT29, was grown in nude mice. Changes in tumor hypoxia were examined by injection of pimonidazole, followed 24 hours later by EF5. Cryosections were stained for these markers and for carbonic anhydrase IX (CAIX) and hypoxia-inducible factor 1alpha (HIF1alpha). Tumor hypoxia was artificially manipulated by carbogen exposure.

RESULTS

In unstressed tumors, all four markers showed very similar spatial distributions. After carbogen treatment, pimonidazole and EF5 could detect decreased hypoxia. HIF1alpha staining was also decreased relative to CAIX, although the effect was less pronounced than for EF5. Control tumors displayed small regions that had undergone spontaneous changes in tumor hypoxia, as judged by pimonidazole relative to EF5; most of these changes were reflected by CAIX and HIF1alpha.

CONCLUSION

HIF1alpha can be compared with either CAIX or a previously administered nitroimidazole to provide an estimate of reoxygenation.

Revisiting the seed and soil in cancer metastasis

Metastasis remains the overwhelming cause of death for cancer patients. During metastasis, cancer cells will leave the primary tumor, intravasate into the bloodstream, arrest at a distant organ, and eventually develop into gross lesions at the secondary sites. This intricate process is influenced by innumerable factors and complex cellular interactions described in 1889 by Stephen Paget as the seed and soil hypothesis. In this review, we revisit this seed and soil hypothesis with an emerging understanding of the cancer cell (i.e. seed) and its microenvironment (i.e. soil). We will provide background to suggest that a critical outcome of the seed-soil interaction is resistance of the stresses that would otherwise impede metastasis.

18F-EF5: a new PET tracer for imaging hypoxia in head and neck cancer

The aim of this study was to evaluate 2-(2-nitro-(1)H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) labeled with (18)F-fluorine to image hypoxia in patients with squamous cell carcinoma of the head and neck (HNSCC).

METHODS

Fifteen patients with HNSCC were studied. Measurement of tumor blood flow was followed by an (18)F-EF5 PET/CT scan. On a separate day, (18)F-FDG PET/CT was performed to determine the metabolically active tumor volume. In 6 patients, dynamic (18)F-EF5 images of the head and neck area were acquired, followed by static images acquired at 1, 2, and 3 h after injection. In the remaining 9 patients, only static images were obtained. (18)F-EF5 uptake in tumors was compared with that in neck muscle, and the (18)F-EF5 findings were correlated with the (18)F-FDG PET/CT studies.

RESULTS

A total of 13 primary tumors and 5 lymph node metastases were evaluated for their uptake of (18)F-EF5. The median tumor-to-muscle (18)F-EF5 uptake ratio (T/M) increased over time and was 1.38 (range, 1.1-3.2) 3 h after tracer injection. The median blood flow in tumors was 36.7 mL/100 g/min (range, 23.3-78.6 mL/100 g/min). Voxel-by-voxel analysis of coregistered blood flow and (18)F-EF5 images revealed a distinct pattern, resulting in a T/M of 1.5 at 3 h to be chosen as a cutoff for clinically significant hypoxia. Fourteen of 18 tumors (78%) had subvolumes within the metabolically active tumor volumes with T/M greater than or equal to 1.5.

CONCLUSION

On the basis of these data, the potential of (18)F-EF5 to detect hypoxia in HNSCC is encouraging. Further development of (18)F-EF5 for eventual targeting of antihypoxia therapies is warranted.

Hypoxia markers in human osteosarcoma: an exploratory study

Neoplastic cells growing under hypoxic conditions exhibit a more aggressive phenotype by activating a cascade of molecular events partly mediated by hypoxia-inducible transcription factor (HIF-1alpha) and vascular endothelial growth factor (VEGF). The roles of these markers have been studied previously in several cancer lines. We ascertained the frequency of HIF-1alpha expression, VEGF expression, the degree of neovascularization, and cell proliferation in osteosarcoma samples. Samples from osteosarcoma patients were assessed for HIF-1alpha and VEGF protein expression using immunohistochemistry, neovascularization using antibodies for Factor VIII, and cell proliferation using the Ki-67 labeling index. Associations between these parameters and clinical features were examined. HIF-1alpha staining was positive in 35% of patients and metastases were present in 61% of these HIF-1alpha-positive patients. VEGF protein expression was detected in 69% of patients, 92% of whom were female. We observed an insignificant trend for a higher frequency of VEGF expression in the high-grade as compared to low-grade osteosarcoma. We observed no association between vascular density and proliferation index and any clinical parameters. We found an association between HIF-1alpha expression and metastatic disease and between VEGF expression and female gender.

The tumor microenvironment and metastatic disease

The microenvironment of solid tumors is a heterogeneous, complex milieu for tumor growth and survival that includes features such as acidic pH, low nutrient levels, elevated interstitial fluid pressure (IFP) and chronic and fluctuating levels of oxygenation that relate to the abnormal vascular network that exists in tumors. The metastatic potential of tumor cells is believed to be regulated by interactions between the tumor cells and their extracellular environment (extracellular matrix (ECM)). These interactions can be modified by the accumulation of genetic changes and by the transient alterations in gene expression induced by the local tumor microenvironment. Clinical and experimental evidence suggests that altered gene expression in response to the hypoxic microenvironment is a contributing factor to increased metastatic efficiency. A number of genes that have been implicated in the metastatic process, involving angiogenesis, intra/extravasation, survival and growth, have been found to be hypoxia-responsive. The various metastatic determinants, genetic and epigenetic, somatic and inherited may serve as precedents for the future identification of more genes that are involved in metastasis. Much research has focused on genetic and molecular properties of the tumor cells themselves. In the present review we discuss the epigenetic and physiological regulation of metastasis and emphasize the need for further studies on the interactions between the pathophysiologic tumor microenvironment and the tumor extracellular matrix.

Graded hypoxia modulates the invasive potential of HT1080 fibrosarcoma and MDA MB231 carcinoma cells

Spatial and temporal oxygen heterogeneity exists in most solid tumour microenvironments due to an inadequate vascular network supplying a dense population of tumour cells. An imbalance between oxygen supply and demand leads to hypoxia within a significant proportion of a tumour, which has been correlated to the likelihood of metastatic dissemination in both rodent tumour models and human patients. Experimentally, it has been demonstrated that near-anoxic in vitro exposure results in transiently increased metastatic potential in some tumour cell lines. The purpose of this study was to examine the effect of graded low oxygen conditions on the invasive phenotype of human tumour cells using an in vitro model of basement membrane invasion, in which we measured oxygen availability directly at the invasion surface of the transwell chamber. Our results show a relationship between culture vessel geometry and time to achieve hypoxia which may affect the interpretation of low oxygen experiments. We exposed the human tumour cell lines, HT1080 and MDA MB231, to graded normobaric oxygen (5% O(2)-0.2% O(2)) either during or prior to in vitro basement membrane invasion to simulate conditions of intravasation and extravasation. A secondary aim was to investigate the potential regulation of matrix metalloproteinase activity by oxygen availability. We identified significant reductions in invasive ability under low oxygen conditions for the HT1080 cell line and an increase in invasion at intermediate oxygen conditions for the MDA MB231 cell line. There were differences in the absolute activity of the individual matrix metalloproteinases, MMP-2, -9, -14, between the two cell lines, however there were no significant changes following exposure to hypoxic conditions. This study demonstrates cell line specific effects of graded oxygen levels on invasive potential and suggests that intermediate levels of low oxygen may increase metastatic dissemination.

Interstitial fluid pressure, vascularity and metastasis in ectopic, orthotopic and spontaneous tumours

Background

High tumour interstitial fluid pressure (IFP) has been adversely linked to poor drug uptake in patients, and to treatment response following radiotherapy in cervix cancer patients. In this study we measured IFP values in a selection of murine and xenograft models, spontaneously arising or transplanted either intramuscularly (i/m) or orthotopically and analysed their relationship to tumour vascularity and metastatic spread.

Methods

KHT-C murine fibrosarcoma, ME180 and SiHa human cervix carcinoma were grown either intramuscularly (i/m), sub-cutaneously (s/c) or orthotopically. Polyoma middle-T (MMTV-PyMT) transgenic spontaneous mammary tumours were studied either as spontaneous tumours or following orthotopic or i/m transplantation. IFP was measured in all tumours using the wick-in-needle method. Spontaneous metastasis formation in the lungs or lymph nodes was assessed in all models. An immunohistochemical analysis of tumour hypoxia, vascular density, lymphatic vascular density and proliferation was carried out in ME180 tumours grown both i/m and orthotopically. Blood flow was also assessed in the ME180 model using high-frequency micro-ultrasound functional imaging.

Results

Tumour IFP was heterogeneous in all the models irrespective of growth site: KHT-C i/m: 2–42 mmHg, s/c: 1–14 mmHg, ME180: i/m 5–68 mmHg, cervix 4–21 mmHg, SiHa: i/m 20–56 mmHg, cervix 2–26 mmHg, MMTV-PyMT: i/m: 13–45 mmHg, spontaneous 2–20 mmHg and transplanted 2–22 mmHg. Additionally, there was significant variation between individual tumours growing in the same mouse, and there was no correlation between donor and recipient tumour IFP values. Metastatic dissemination to the lungs or lymph nodes demonstrated no correlation with tumour IFP. Tumour hypoxia, proliferation, and lymphatic or blood vessel density also showed no relationship with tumour IFP. Speckle variance analysis of ultrasound images showed no differences in vascular perfusion between ME180 tumours grown i/m versus orthotopically despite differences in IFP.

Conclusion

Our studies across a range of different tumour models showed substantial heterogeneity in tumour IFP, suggesting differences in the vascular development and interstitial fluid dynamics in the individual tumours. The results demonstrate a strong stochastic aspect to tumour IFP development, notably the variation apparent between different tumours within the same animal and the lack of correlation between donor and recipient tumours.

Immunosuppressive mechanisms in human tumors: why we still cannot cure cancer

Tumor cells often evoke specific immune responses that, however, fail to eliminate all the tumor cells. The development of cancer immunotherapies is, therefore, mostly focused on the generation of large numbers of activated anti-tumor effector cells by vaccination or adoptive T cell transfer. These developments are built on an ever-extended list of identified tumor-associated antigens and corresponding T cell epitopes, and a steady flow of reports from proof-of-principle animal model experiments demonstrating cure from disease by immune interventions. However, the promises have not translated into clinical successes for cancer patients. Even where tumor regression or complete responses were achieved there is usually relapse of the disease. Increasing numbers of reports over recent years highlight potential immunosuppressive mechanisms that act in tumors and systemically in cancer patients to block effective anti-tumor immune responses. They account in large parts for the failures of cancer immunotherapy and need to be overcome before progress can be expected. We review here the current state of the research on immunosuppressive networks in human cancer.

Hypoxia enhances metastatic efficiency in HT1080 fibrosarcoma cells by increasing cell survival in lungs, not cell adhesion and invasion

This study examined possible mechanisms for hypoxia-increased metastasis in a green fluorescent protein-labeled human fibrosarcoma cell line (HT1080). The efficiency of the lung arrest of tumor cells, which can be dependent on the adhesive potential of the tumor cells, was assessed by measuring the level of integrin alpha3beta1 protein and by adhesion assays, whereas the extravasation potential was examined by an invasion assay. These properties were not changed by exposure to hypoxia, indicating that lung arrest and extravasation are unlikely to play a major role in the effect of hypoxia on metastasis in this model. The main effect of hypoxic exposure was found to be increased survival after lung arrest as determined by clonogenic assay of tumor cells recovered from mouse lungs after i.v. injection. Concomitantly, apoptosis was identified as responsible for the death of lung-arrested cells, suggesting the involvement of an altered apoptotic response following hypoxic exposure of these cells. Consistent with this finding, we found that the effect of hypoxia on both increased metastasis and survival of arrested cells was inhibited by treatment with farnesylthiosalicylic acid. However, this effect was not due to down-regulation of hypoxia-inducible factor-1alpha, a mechanism of action of this drug reported by previous studies. Further detailed studies of the mechanisms of action of the drug are needed.

Predictive oncology: a review of multidisciplinary, multiscale in silico modeling linking phenotype, morphology and growth

Empirical evidence and theoretical studies suggest that the phenotype, i.e., cellular- and molecular-scale dynamics, including proliferation rate and adhesiveness due to microenvironmental factors and gene expression that govern tumor growth and invasiveness, also determine gross tumor-scale morphology. It has been difficult to quantify the relative effect of these links on disease progression and prognosis using conventional clinical and experimental methods and observables. As a result, successful individualized treatment of highly malignant and invasive cancers, such as glioblastoma, via surgical resection and chemotherapy cannot be offered and outcomes are generally poor. What is needed is a deterministic, quantifiable method to enable understanding of the connections between phenotype and tumor morphology. Here, we critically assess advantages and disadvantages of recent computational modeling efforts (e.g., continuum, discrete, and cellular automata models) that have pursued this understanding. Based on this assessment, we review a multiscale, i.e., from the molecular to the gross tumor scale, mathematical and computational "first-principle" approach based on mass conservation and other physical laws, such as employed in reaction-diffusion systems. Model variables describe known characteristics of tumor behavior, and parameters and functional relationships across scales are informed from in vitro, in vivo and ex vivo biology. We review the feasibility of this methodology that, once coupled to tumor imaging and tumor biopsy or cell culture data, should enable prediction of tumor growth and therapy outcome through quantification of the relation between the underlying dynamics and morphological characteristics. In particular, morphologic stability analysis of this mathematical model reveals that tumor cell patterning at the tumor-host interface is regulated by cell proliferation, adhesion and other phenotypic characteristics: histopathology information of tumor boundary can be inputted to the mathematical model and used as a phenotype-diagnostic tool to predict collective and individual tumor cell invasion of surrounding tissue. This approach further provides a means to deterministically test effects of novel and hypothetical therapy strategies on tumor behavior.

Hypoxia-driven selection of the metastatic phenotype

Intratumoral hypoxia is an independent indicator of poor patient outcome and increasing evidence supports a role for hypoxia in the development of metastatic disease. Studies suggest that the acquisition of the metastatic phenotype is not simply the result of dysregulated signal transduction pathways, but instead is achieved through a stepwise selection process driven by hypoxia. Hypoxia facilitates disruption of tissue integrity through repression of E-cadherin expression, with concomitant gain of N-cadherin expression which allows cells to escape anoikis. Through upregulation of urokinase-type plasminogen activator receptor (uPAR) expression, hypoxia enhances proteolytic activity at the invasive front and alters the interactions between integrins and components of the extracellular matrix, thereby enabling cellular invasion through the basement membrane and the underlying stroma. Cell motility is increased through hypoxia-induced hepatocyte growth factor (HGF)-MET receptor signaling, resulting in cell migration towards the blood or lymphatic microcirculation. Hypoxia-induced vascular endothelial growth factor (VEGF) activity also plays a critical role in the dynamic tumor-stromal interactions required for the subsequent stages of metastasis. VEGF promotes angiogenesis and lymphangiogenesis in the primary tumor, providing the necessary routes for dissemination. VEGF-induced changes in vascular integrity and permeability promote both intravasation and extravasation, while VEGF-induced angiogenesis in the secondary tissue is essential for cell proliferation and establishment of metastatic lesions. Through regulation of these critical molecular targets, hypoxia promotes each step of the metastatic cascade and selects tumor cell populations that are able to escape the unfavorable microenvironment of the primary tumor.

Preferential DNA cleavage under anaerobic conditions by a DNA-binding ruthenium dimer

In the absence of dioxygen, the cationic complex [(phen)2Ru(tatpp)Ru(phen)2]4+ (P4+) undergoes in situ reduction by glutathione (GSH) to form a species that induces DNA cleavage. Exposure to air strongly attenuates the cleavage activity, even in the presence of a large excess of reducing agent (e.g., 40 equiv of GSH per P4+), suggesting that the complex may be useful in targeting cells with a low-oxygen microenvironment (hypoxia) for destruction via DNA cleavage. The active species is identified as the doubly reduced, doubly protonated complex H2P4+, and a carbon-based radical species is implicated in the cleavage action. We postulate that the dioxygen concentration regulates the degree to which the carbon radical forms and thus regulates the DNA cleavage activity.

Acidic extracellular pH promotes experimental metastasis of human melanoma cells in athymic nude mice

Extracellular pH (pH(e)) is lower in many tumors than in the corresponding normal tissue. The significance of acidic pH(e) in the development of metastatic disease was investigated in the present work. Human melanoma cells (A-07, D-12, and T-22) were cultured in vitro at pH(e) 6.8 or 7.4 (control) before being inoculated into the tail vein of BALB/c nu/nu mice for formation of experimental pulmonary metastases. Cell invasiveness was studied in vitro by using Matrigel invasion chambers and angiogenesis was studied in vivo by using an intradermal assay. Protein secretion was measured by ELISA and immunocapture assays. Cells cultured at acidic pH(e) showed increased secretion of proteinases and proangiogenic factors, enhanced invasive and angiogenic potential, and enhanced potential to develop experimental metastases. Acidity-induced metastasis was inhibited by treatment with the general matrix metalloproteinase (MMP) inhibitor GM6001, the general cysteine proteinase inhibitor E-64, or blocking antibody against vascular endothelial growth factor-A (VEGF-A) or interleukin-8 (IL-8). Our study indicates that acidic pH(e) promotes experimental pulmonary metastasis in A-07, D-12, and T-22 human melanoma cells by a common mechanism involving acidity-induced up-regulation of the proteolytic enzymes MMP-2, MMP-9, cathepsin B, and cathepsin L and acidity-induced up-regulation of the proangiogenic factors VEGF-A and IL-8. One consequence of this observation is that treatment strategies involving deliberate tumor acidification to improve the efficacy of chemotherapy, photodynamic therapy, and hyperthermia should be avoided. Moreover, the possibility that the pH(e) of the primary tumor may be an important prognostic parameter for melanoma patients merits clinical investigation.

uPAR expression under hypoxic conditions depends on iNOS modulated ERK phosphorylation in the MDA-MB-231 breast carcinoma cell line

Urokinase plasminogen activator receptor (uPAR) plays a major role in cancer invasion and metastasis and uPAR expression is correlated with a poor prognosis in various cancer types. Moreover, the expression of uPAR is increased under hypoxic conditions. Nitric oxide (NO) and its metabolites produced by inducible nitric oxide synthase (iNOS) are important products of hypoxic stress, and NO may activate or modulate extracellular signal regulated kinase (ERK). Here, we evaluated uPA, uPAR, and activated ERK levels under hypoxic conditions, and the modulatory effects of iNOS and NO in the MDA-MB-231 human breast cancer cell line. Cells were incubated in a hypoxic or normoxic incubator and treated with PD98059 (a MEK 1/2 inhibitor, which abrogates ERK phosphorylation) and aminoguanidine (a selective iNOS inhibitor). uPAR expression, ERK phosphorylation, and uPA activity were found to be increased under hypoxic conditions. Moreover, when cells were treated with PD98059 under hypoxic conditions, uPAR was downregulated, whereas aminoguanidine markedly increased ERK phosphorylation in a dose dependent manner. Furthermore, aminoguanidine increased uPAR expression and prevented the inhibition of uPAR expression by PD98059. These results demonstrated that uPAR is induced by hypoxia and that increased uPAR expression is mediated by ERK phosphorylation, which in turn is modulated by iNOS/NO in MDA-MB-231 cells. We conclude that iNOS/NO downregulates the expression of uPAR under hypoxic conditions via ERK pathway modulation.

Analysis of Protein Redox Modification by Hypoxia

We examined hypoxia-induced changes in global thiol proteome profile in human prostate cancer cells using a BIAM-based display method. We analyzed the kinetics of protein thiol modification by using a pattern recognition algorithm, self-organizing maps (SOM) clustering, and identified the BIAM-labeled proteins by MALDI-TOF and ESI-tandem mass spectrometry. We found 99 out of 215 of total BIAM-labeled proteins were affected by hypoxia treatment and, yet, with diverse patterns and kinetics of redox modification. Our study proved that proteomics analysis employing the BIAM-labeling method can provide valuable information pertaining to global changes in the redox status of proteins in response to hypoxia.