Two controls of cell proliferation underlie cancer relapse.

Much progress has been made in understanding the basis of cancer. Current therapies can effectively shrink tumors. But they frequently relapse, metastasize to other locations, and are lethal. Effective therapies are very much needed for preventing this relapse. Creation of a eukaryotic organism commences with one original stem cell, a fertilized egg, which multiplies and differentiates. Mutations of normal stem cells can produce cancer stem cells (CSC). These cells may resist chemotherapy, proliferate, and produce new tumors. Human chorionic gonadotrophin (hCG) is composed of two proteins (alpha and beta) that bind to the cell membrane and activate a number of intracellular pathways. hCG has been shown to activate the proliferation of cancer stem cells. Cyclin dependent regulation of the adult cells is created in normal differentiation and replaces the hCG regulation of stem cells. To selectively kill the cancer stem cells conventional cancer therapies could be followed with a therapy based on inactivating human chronic gonadotrophin (HCG). For example chemically modified prostaglandins like RU486 prevent binding of the unmodified steroid to hCG and inactivate hCG.

Bioregulation.

During the 20th century great progress was made in genetics and biochemistry, and these were combined into a molecular biological understanding of functions of macromolecules. Further great discoveries will be made about bioregulations, applicable to scientific problems such as cell development and evolution, and to illnesses including heart disease through defective control of cholesterol production, and to neurological cell-based diseases. The "War Against Cancer" is still far from won. The present generation of scientists can develop clinical applications from recent basic science discoveries.

Suppression of cancer relapse and metastasis by inhibiting cancer stemness.

Partial or even complete cancer regression can be achieved in some patients with current cancer treatments. However, such initial responses are almost always followed by relapse, with the recurrent cancer being resistant to further treatments. The discovery of therapeutic approaches that counteract relapse is, therefore, essential for advancing cancer medicine. Cancer cells are extremely heterogeneous, even in each individual patient, in terms of their malignant potential, drug sensitivity, and their potential to metastasize and cause relapse. Indeed, hypermalignant cancer cells, termed cancer stem cells or stemness-high cancer cells, that are highly tumorigenic and metastatic have been isolated from cancer patients with a variety of tumor types. Moreover, such stemness-high cancer cells are resistant to conventional chemotherapy and radiation. Here we show that BBI608, a small molecule identified by its ability to inhibit gene transcription driven by Stat3 and cancer stemness properties, can inhibit stemness gene expression and block spherogenesis of or kill stemness-high cancer cells isolated from a variety of cancer types. Moreover, cancer relapse and metastasis were effectively blocked by BBI608 in mice. These data demonstrate targeting cancer stemness as a novel approach to develop the next generation of cancer therapeutics to suppress cancer relapse and metastasis.

A need for basic research on fluid-based early detection biomarkers.

Cancer continues to be a major cause of mortality despite decades of effort and expense. The problem reviewed here is that before many cancers are discovered they have already progressed to become drug resistant or metastatic. Biomarkers found in blood or other body fluids could supplement current clinical indicators to permit earlier detection and thereby reduce cancer mortality.

Mst1 is an interacting protein that mediates PHLPPs' induced apoptosis.

PHLPP1 and PHLPP2 phosphatases exert their tumor-suppressing functions by dephosphorylation and inactivation of Akt in several breast cancer and glioblastoma cells. However, Akt, or other known targets of PHLPPs that include PKC and ERK, may not fully elucidate the physiological role of the multifunctional phosphatases, especially their powerful apoptosis induction function. Here, we show that PHLPPs induce apoptosis in cancer cells independent of the known targets of PHLPPs. We identified Mst1 as a binding partner that interacts with PHLPPs both in vivo and in vitro. PHLPPs dephosphorylate Mst1 on the T387 inhibitory site, which activate Mst1 and its downstream effectors p38 and JNK to induce apoptosis. The same T387 site can be phosphorylated by Akt. Thus, PHLPP, Akt, and Mst1 constitute an autoinhibitory triangle that controls the fine balance of apoptosis and proliferation that is cell type and context dependent.

The pursuit of oncotargets through understanding defective cell regulation.

More effective anticancer agents are essential, as has too often been demonstrated by the paucity of therapeutics which preserve life. Their discovery is very difficult. Many approaches are being applied, from testing folk medicines to automated high throughput screening of large chemical libraries. Mutations in cancer cells create dysfunctional regulatory systems. This Perspective summarizes an approach to applying defective molecular control mechanisms as oncotargets on which drug discoveries against cancer can be based.

Metastasis and AKT activation.

Metastasis, responsible for 90% of cancer patient deaths, is an inefficient process because many tumor cells die. The survival of metastatic tumor cells should be considered as a critical therapeutic target. This review provides a new perspective regarding the role of AKT in tumor survival, and the rationale to target AKT in anti-metastasis therapies.

Metastasis and AKT activation.

Metastasis is responsible for 90% of cancer patient deaths. More information is needed about the molecular basis for its potential detection and treatment. The activated AKT kinase is necessary for many events of the metastatic pathway including escape of cells from the tumor's environment, into and then out of the circulation, activation of proliferation, blockage of apoptosis, and activation of angiogenesis. A series of steps leading to metastatic properties can be initiated upon activation of AKT by phosphorylation on Ser-473. These findings lead to the question of how this activation is connected to metastasis. Activated AKT phosphorylates GSK-3beta causing its proteolytic removal. This increases stability of the negative transcription factor SNAIL, thereby decreasing transcription of the transmembrane protein E-cadherin that forms adhesions between adjacent cells, thereby permitting their detachment. How is AKT hyperactivated in metastatic cells? Increased PI3K or TORC2 kinase activity- or decreased PHLPP phosphatase could be responsible. Furthermore, a positive feedback mechanism is that the decrease of E-cadherin lowers PTEN and thereby increases PIP3, further activating AKT and metastasis.

Biomarkers, regerons, and pathways to lethal cancer.

Cancer is a disease of "outlaw" cells that become mutated in regulatory mechanisms. They have lost normal self controls and relationships to the whole organism. Cancers can progress by several pathways from a normal cell to malignant cancer, from bad to worse. Questions about advisability of treatment for some cancers arise from the possibility that they are arrested during progression and so never become lethal. Techniques could be developed to determine the degree of progression and possibility for successful treatment. This article is intended to suggest a way of looking at cancer. It is not a review so references to research articles are infrequent.

Nuclear factor-kappaB activation: a molecular therapeutic target for estrogen receptor-negative and epidermal growth factor receptor family receptor-positive human breast cancer.

Nuclear factor-kappaB (NF-kappaB), a transcription factor with pleotropic effects, is a downstream mediator of growth signaling in estrogen receptor (ER)-negative and erbB family particularly erbB2 (HER-2/neu) receptor-positive cancer. We previously reported activation of NF-kappaB in ER-negative breast cancer cells and breast tumor specimens, but the consequence of inhibiting NF-kappaB activation in this subclass of breast cancer has not been shown. In this study, we investigated the role of NF-kappaB activation by studying the tumorigenic potential of cells expressing genetically manipulated, inducible, dominant-negative inhibitory kappaB kinase (IKK) beta in xenograft tumor model. Conditional inhibition of NF-kappaB activation by the inducible expression of dominant-negative IKKbeta simultaneously blocked cell proliferation, reinstated apoptosis, and dramatically blocked xenograft tumor formation. Secondly, the humanized anti-erbB2 antibody trastuzumab (Herceptin) and the specific IKK inhibitor NF-kappaB essential modifier-binding domain peptide both blocked NF-kappaB activation and cell proliferation and reinstated apoptosis in two ER-negative and erbB2-positive human breast cancer cell lines that are used as representative model systems. Combinations of these two target-specific inhibitors synergistically blocked cell proliferation at concentrations that were singly ineffective. Inhibition of NF-kappaB activation with two other low molecular weight compounds, PS1145 and PS341, which inhibited IKK activity and proteasome-mediated phosphorylated inhibitory kappaB protein degradation, respectively, blocked erbB2-mediated cell growth and reversed antiapoptotic machinery. These results implicate NF-kappaB activation in the tumorigenesis and progression of ER-negative breast cancer. It is postulated that this transcription factor and its activation cascade offer therapeutic targets for erbB2-positive and ER-negative breast cancer.

Metastatic potential of 21T human breast cancer cells depends on Akt/protein kinase B activation.

Most cancer lethality is caused by metastasis. To gain insight into the molecular basis of tumor progression to metastasis, we used the 21T series of human mammary epithelial cells obtained by successive biopsies from one breast cancer patient. The c-erbB2 gene is amplified and overexpressed in each of three 21T tumor lines. The erbB receptor tyrosine kinase-activated phosphatidylinositol 3-kinase/Akt signaling cascade is crucial for the development and maintenance of epithelial cells, and dysregulation of this pathway is frequently associated with cellular transformation and cancer. For Akt to be fully activated, Ser(473) on its COOH terminus needs to be phosphorylated. We detected more Ser(473) Akt phosphorylation in MT cells, derived from a pleural effusion, compared with cells from the primary tumor. This phosphorylation has recently been shown to be catalyzed by mammalian target of rapamycin (mTOR)/rictor kinase. By using genetic and pharmacologic activators and inhibitors, we showed that Ser(473) Akt phosphorylation is more sensitive to mTOR/rictor inhibition in metastatic tumor cells than normal mammary epithelial and primary tumor cells. The mTOR/rictor kinase activity was indispensable for both Ser(473) Akt phosphorylation and migration of metastatic MT2 cells. In addition, a large decrease of protein phosphatase PH domain leucine-rich repeat protein phosphatase (PHLPP) was found, which could be responsible for the overexpression of Ser(473) Akt in MT cells. Our data indicate that these breast cancer cells acquire new vulnerabilities, rictor and PHLPP, which might provide an Achilles' heel for therapeutic intervention of breast cancer metastasis.

A protocol for differential display of mRNA expression using either fluorescent or radioactive labeling.

Since its invention in the early 1990s, differential display (DD) has become one of the most commonly used techniques for identifying differentially expressed genes at the mRNA level. Unlike other genomic approaches, such as DNA microarrays, DD systematically detects changes in mRNA profiles among multiple samples being compared without the need of any prior knowledge of genomic information of the living organism being studied. Here, we present an optimized DD protocol with a fluorescent digital readout as well as traditional radioactive labeling. The resulting streamlined fluorescent DD process offers an unprecedented accuracy, sensitivity and throughput in comprehensive and quantitative analysis of eukaryotic gene expression. Results usually can be obtained within days using a limited number of primer combinations, but a comprehensive DD screen may take weeks or months to accomplish, depending on gene coverage required and the number of differentially expressed genes present within a biological system being compared.

Identification of prostate cancer mRNA markers by averaged differential expression and their detection in biopsies, blood, and urine.

The advent of serum prostate-specific antigen (PSA) as a biomarker has enabled early detection of prostate cancer and, hence, improved clinical outcome. However, a low PSA is not a guarantee of disease-free status, and an elevated PSA is frequently associated with a negative biopsy. Therefore, our goal is to identify molecular markers that can detect prostate cancer with greater specificity in body fluids such as urine or blood. We used the RT-PCR differential display method to first identify mRNA transcripts differentially expressed in tumor vs. patient-matched nontumor prostate tissue. This analysis led to the identification of 44 mRNA transcripts that were expressed differentially in some but not all tumor specimens examined. To identify mRNA transcripts that are differentially expressed in most tumor specimens, we turned to differential display of pooled tissue samples, a technique we name averaged differential expression (ADE). We performed differential display of mRNA from patient-matched nontumor vs. tumor tissue, each pooled from 10 patients with various Gleason scores. Differentially expressed mRNA transcripts identified by ADE were fewer in number, but were expressed in a greater percentage of tumors (>75%) than those identified by differential display of mRNA from individual patient samples. Differential expression of these mRNA transcripts was also detected by RT-PCR in mRNA isolated from urine and blood samples of prostate cancer patients. Our findings demonstrate the principle that specific cDNA probes of frequently differentially expressed mRNA transcripts identified by ADE can be used for the detection of prostate cancer in urine and blood samples.

Tumor progression--targets for differential therapy.

Differential killing of the patient's cancer cells versus normal cells is a necessity for chemotherapy. Advantage can be taken of close regulations of gene expression and of enzyme activity that are essential for normal cell functioning, and that are altered during tumor progression. Summarized here is our research on four such progression changes of cancer cells; some deregulate proliferation control and others decrease programmed death (apoptosis). These processes will be illustrated with examples of potential chemotherapies based on them. Methods for discovery of such changes include Differential Display and microarrays.

Regulatory molecular biology.

Close regulations of molecular biological processes are essential for life. Defective controls cause diseases such as cancer and neurological malfunctions. We now are provided with a plethora of regulatory mechanisms exerted at many levels. Prominent are covalent protein modifications, non-covalent feedback inhibition that modifies enzyme activity, and enzyme induction. Non-covalent or covalent binding to them of either small molecules or proteins act on functional DNA, RNA, proteins and metabolites regulates their production and degradation rates, activities and intra-cell locations. Time frames differ greatly, from seconds to days or longer. A control at every level is balanced by an opposing mechanism: populations of organisms are balanced by birth vs. death, cell synthesis by apoptosis, mutation by DNA repair, macromolecular syntheses by their degradations, metabolite anabolism vs. catabolism, enzyme activation by inhibition, protein kinases by phosphatases. Any abnormal molecular condition is sensed when regulation is defective as in cancer, which leads to its rectification, to cell death, or to disease if this is not possible.

Targeting the NF-kappa B pathway in estrogen receptor negative MDA-MB-231 breast cancer cells using small inhibitory RNAs.

Cancer cells in order to survive are often mutated to block apoptosis. One chemotherapeutic option is the re-establishment of apoptosis. An example of such a therapy is the PKC inhibitor Gö6976, which activates apoptosis and shrinks in vivo tumors in estrogen receptor-negative breast cancers. We proposed as a mechanism blockage of activation of the transcription factor NF-kappaB, which is anti-apoptotic and often elevated in cancers. Over recent years, questions have arisen regarding the specificity of these "small-molecule inhibitors." We have therefore explored the role of NF-kappaB inhibition in MDA-MB-231 breast cancer cells using small inhibitory RNAs (siRNA). siRNAs designed against NF-kappaB protein p65 (RelA) and IKKalpha, IKKbeta, and IKKgamma, strongly decreased the target proteins. But, unlike Gö6976, they did not decrease basal NF-kappaB or cause apoptosis. In particular, the decrease in p65 protein had no effects on apoptosis or cell proliferation, thus questioning the importance of NF-kappaB alone in the maintenance of these cells. Furthermore, the proteasome inhibitor MG-132 caused loss of IkappaBalpha, and an increase of it is phosphorylated form, but basal NF-kappaB was unchanged, whilst activation of NF-kappaB by TNFalpha was completely inhibited, suggesting that MG-132 activity is independent of constitutive NF-kappaB activation. We ascribe these differences to the specificity of inhibition by siRNAs as compared to the well-known non-specificity of small-molecule inhibitors. We conclude that the mutations in these cancer cells made them resistant to apoptosis, by elevating their NF-kappaB and activating other basal pathways that are blocked by Gö6976 but not by IKK and p65 siRNAs.

Cancer chemotherapy by deoxynucleotide depletion and E2F-1 elevation.

We propose that the lethality of commonly used anticancer drugs, e.g., methotrexate and cis-platinum are due, at least in part, to an increase of the E2F-1-mediated apoptotic cascade. The drugs directly or indirectly decrease deoxynucleoside triphosphates. The E2F family acts to provide control of S phase by transcribing genes required for deoxynucleoside triphosphate and DNA synthesis. Thus, a mechanism for control of E2F-1 is essential, a signal safeguarding against aberrant or uncontrolled cell proliferation. We have proposed a feedback control by NTPs that down-regulates E2F-1. Here, we provide evidence in support of this hypothesis.

Crossroads of estrogen receptor and NF-kappaB signaling.

Cellular homeostasis in higher organisms is maintained by balancing cell growth, differentiation, and death. Two important systems that transmit extracellular signals into the machinery of the cell nucleus are the signaling pathways that activate nuclear factor kappaB (NF-kappaB) and estrogen receptor (ER). These two transcription factors induce expression of genes that control cell fates, including proliferation and cell death (apoptosis). However, ER has anti-inflammatory effects, whereas activated NF-kappaB initiates and maintains cellular inflammatory responses. Recent investigations elucidated a nonclassical and nongenomic effect of ER: inhibition of NF-kappaB activation and the inflammatory response. In breast cancer, antiestrogen therapy might cause reactivation of NF-kappaB, potentially rerouting a proliferative signal to breast cancer cells and contributing to hormone resistance. Thus, ER ligands that selectively block NF-kappaB activation could provide specific potential therapy for hormone-resistant ER-positive breast cancers.

Regulation in S phase by E2F.

The DNA synthetic S phase of the unperturbed cell cycle is a closed system, as compared to regulation of G(1) by external growth factors. The E2F family provides internal control in S phase by transcribing genes required for deoxynucleotide triphosphate (dNTP) and DNA synthesis. Furthermore, over expression of E2F-1 activates programmed cell death (apoptosis), a safeguarding signal of aberrant growth of cells that have become carcinogenic. Mechanisms for control of E2F-1 are thus essential. The hypothesis is proposed that deoxythymidine triphosphate (dTTP) allosterically feedback controls E2F-1 to regulate both DNA synthesis and apoptosis. This may act either upon production of E2F-1 or its degradation.