Effects of epidermal growth factor on MDA-MB-468 breast cancer cells: alterations in polyamine biosynthesis and the expression of p21/CIP1/WAF1

Single cell lineage tracing reveals clonal dynamics of anti-EGFR therapy resistance in triple negative breast cancer

BACKGROUND

Most primary Triple Negative Breast Cancers (TNBCs) show amplification of the Epidermal Growth Factor Receptor (EGFR) gene, leading to increased protein expression. However, unlike other EGFR-driven cancers, targeting this receptor in TNBC yields inconsistent therapeutic responses.

METHODS

To elucidate the underlying mechanisms of this variability, we employ cellular barcoding and single-cell transcriptomics to reconstruct the subclonal dynamics of EGFR-amplified TNBC cells in response to afatinib, a tyrosine kinase inhibitor (TKI) that irreversibly inhibits EGFR.

RESULTS

Integrated lineage tracing analysis revealed a rare pre-existing subpopulation of cells with distinct biological signature, including elevated expression levels of Insulin-Like Growth Factor Binding Protein 2 (IGFBP2). We show that IGFBP2 overexpression is sufficient to render TNBC cells tolerant to afatinib treatment by activating the compensatory insulin-like growth factor I receptor (IGF1-R) signalling pathway. Finally, based on reconstructed mechanisms of resistance, we employ deep learning techniques to predict the afatinib sensitivity of TNBC cells.

CONCLUSIONS

Our strategy proved effective in reconstructing the complex signalling network driving EGFR-targeted therapy resistance, offering new insights for the development of individualized treatment strategies in TNBC.

Methionine Restriction and Cancer Biology

The essential amino acid, methionine, is important for cancer cell growth and metabolism. A growing body of evidence indicates that methionine restriction inhibits cancer cell growth and may enhance the efficacy of chemotherapeutic agents. This review summarizes the efficacy and mechanism of action of methionine restriction on hallmarks of cancer in vitro and in vivo. The review highlights the role of glutathione formation, polyamine synthesis, and methyl group donation as mediators of the effects of methionine restriction on cancer biology. The translational potential of the use of methionine restriction as a personalized nutritional approach for the treatment of patients with cancer is also discussed.

The functional role of polyamines in eukaryotic cells

Polyamines, consisting of putrescine, spermidine and spermine are essential for normal cell growth and viability in eukaryotic cells. Since polyamines are cations, they interact with DNA, ATP, phospholipids, specific kinds of proteins, and especially with RNA. Consequently, the functions of these acidic compounds and some proteins are modified by polyamines. In this review, the functional modifications of these molecules by polyamines are presented. Structural change of specific mRNAs by polyamines causes the stimulation of the synthesis of several different proteins, which are important for cell growth and viability. eIF5 A, the only known protein containing a spermidine derivative, i.e. hypusine, also functions at the level of translation. Experimental results thus far obtained strongly suggest that the most important function of polyamines is at the level of translation.

Photo-immobilized EGF chemical gradients differentially impact breast cancer cell invasion and drug response in defined 3D hydrogels

Breast cancer cell invasion is influenced by growth factor concentration gradients in the tumor microenvironment. However, studying the influence of growth factor gradients on breast cancer cell invasion is challenging due to both the complexities of in vivo models and the difficulties in recapitulating the tumor microenvironment with defined gradients using in vitro models. A defined hyaluronic acid (HA)-based hydrogel crosslinked with matrix metalloproteinase (MMP) cleavable peptides and modified with multiphoton labile nitrodibenzofuran (NDBF) was synthesized to photochemically immobilize epidermal growth factor (EGF) gradients. We demonstrate that EGF gradients can differentially influence breast cancer cell invasion and drug response in cell lines with different EGF receptor (EGFR) expression levels. Photopatterned EGF gradients increase the invasion of moderate EGFR expressing MDA-MB-231 cells, reduce invasion of high EGFR expressing MDA-MB-468 cells, and have no effect on invasion of low EGFR-expressing MCF-7 cells. We evaluate MDA-MB-231 and MDA-MB-468 cell response to the clinically tested EGFR inhibitor, cetuximab. Interestingly, the cellular response to cetuximab is completely different on the EGF gradient hydrogels: cetuximab decreases MDA-MB-231 cell invasion but increases MDA-MB-468 cell invasion and cell number, thus demonstrating the importance of including cell-microenvironment interactions when evaluating drug targets.

Spatio-temporal regulation of EGFR signaling by the Eps15 homology domain-containing protein 3 (EHD3)

The epidermal growth factor (EGF) receptor EGFR is a major receptor tyrosine kinase whose role in gliomagenesis is well established. We have recently identified EHD3 [Eps15 homology (EH) domain-containing protein 3], an endocytic trafficking regulatory protein, as a putative brain tumor suppressor. Here, we investigate the underlying mechanisms, by establishing a novel mechanistic and functional connection between EHD3 and the EGFR signaling pathway. We show that, in response to stimulation with the EGF ligand, EHD3 accelerates the rate of EGFR degradation by dramatically increasing its ubiquitination. As part of this process, EHD3 also regulates EGFR endosomal trafficking by diverting it away from the recycling route into the degradative pathway. Moreover, we found that upon EGF activation, rather than affecting the total MAPK and AKT downstream signaling, EHD3 decreases endosome-based signaling of these two pathways, thus suggesting the contribution of EHD3 in the spatial regulation of EGFR signaling. This function explains the higher sensitivity of EHD3-expressing cells to the growth-inhibitory effects of EGF. In summary, this is the first report supporting a mechanism of EHD3-mediated tumor suppression that involves the attenuation of endosomal signaling of the EGFR oncogene.

Targeting polyIC to EGFR over-expressing cells using a dsRNA binding protein domain tethered to EGF

Selective delivery of drugs to tumor cells can increase potency and reduce toxicity. In this study, we describe a novel recombinant chimeric protein, dsRBEC, which can bind polyIC and deliver it selectively into EGFR over-expressing tumor cells. dsRBEC, comprises the dsRNA binding domain (dsRBD) of human PKR (hPKR), which serves as the polyIC binding moiety, fused to human EGF (hEGF), the targeting moiety. dsRBEC shows high affinity towards EGFR and triggers ligand-induced endocytosis of the receptor, thus leading to the selective internalization of polyIC into EGFR over-expressing tumor cells. The targeted delivery of polyIC by dsRBEC induced cellular apoptosis and the secretion of IFN-β and other pro-inflammatory cytokines. dsRBEC-delivered polyIC is much more potent than naked polyIC and is expected to reduce the toxicity caused by systemic delivery of polyIC.

Modulation of cellular function by polyamines

Polyamines (putrescine, spermidine and spermine) are essential for normal cell growth. The polyamine levels in cells are regulated by biosynthesis, degradation, and transport. Polyamines can modulate the functions of DNA, nucleotide triphosphates, proteins, and especially RNA because most polyamines exist in a polyamine-RNA complex in cells. Thus, the major focus on this review is on the role of polyamines in protein synthesis. In addition, effects of polyamines on B to Z conversion of DNA, transcription, phosphorylation of proteins, cell cycle progression, apoptosis and ion channels, especially NMDA receptors, are outlined. The function of eIF5A is also briefly discussed. Finally, a correlation between acrolein, produced from polyamines by polyamine oxidases, and chronic renal failure or brain stroke is summarized. Increased levels of polyamine oxidases and acrolein are good markers of chronic renal failure and brain stroke.

Nuclear and membrane receptor-mediated signalling pathways modulate polyamine biosynthesis and interconversion

Polyamines play an important role in cell growth and differentiation, while their overproduction has potentially oncogenic consequences. Polyamine homoeostasis, a critical determinant of cell fate, is precisely tuned at the level of biosynthesis, degradation and transport. The enzymes ODC (ornithine decarboxylase), AdoMetDC (S-adenosylmethionine decarboxylase) and SSAT (spermidine/spermine N(1)-acetyltransferase) are critical for polyamine pool maintenance. Our experiments were designed to examine the expression of these enzymes in testosterone-induced hypertrophic and antifolate-induced hyperplastic mouse kidney, characterized by activation of AR (androgen receptor) and HGF (hepatocyte growth factor) membrane receptor c-Met respectively. The expression of these key enzymes was up-regulated by antifolate CB 3717 injury-evoked activation of HGF/c-Met signalling. In contrast, activation of the testosterone/AR pathway remarkably induced a selective increase in ODC expression without affecting other enzymes. Studies in catecholamine-depleted kidneys point to a synergistic interaction between the signalling pathways activated via cell membrane catecholamine receptors and AR, as well as c-Met. We found that this cross-talk modulated the expression of ODC and AdoMetDC, enzymes limiting polyamine biosynthesis, but not SSAT. This is in contrast with the antagonistic cross-talk between AR- and c-Met-mediated signalling which negatively regulated the expression of ODC, but affected neither AdoMetDC nor SSAT.

HIV-1 Tat peptide immunoconjugates differentially sensitize breast cancer cells to selected antiproliferative agents that induce the cyclin-dependent kinase inhibitor p21WAF-1/CIP-1

In this study, we evaluated the ability of anti-p21 antibodies conjugated to 17-mer peptides [GRKKRRQRRRPPQGYGC] harboring the membrane-translocating and nuclear import sequences [underlined] of HIV-1 tat protein to inhibit the cyclin-dependent kinase inhibitor, p21(WAF-1/Cip-1) (p21) and differentially sensitize MDA-MB-468 and MCF-7 human breast cancer (BC) cells to the antiproliferative effects of treatments that induce or do not induce p21. BC cells were treated with increasing concentrations of epidermal growth factor (EGF; 0.5-10 nM), the topoisomerase I inhibitor, camptothecin (CPT; 0.1-4 muM), or increasing doses of gamma-radiation (2-20 Gy). Western blot was used to evaluate p21 expression. The effect of treatment on cell cycle distribution was studied. Growth inhibition was measured by the WST-1 assay. Expression of p21 was increased in MDA-MB-468 cells treated with EGF or CPT but not by gamma-irradiation. MCF-7 cells exhibited p21 upregulation following exposure to CPT and gamma-radiation but not EGF. EGF caused cell cycle arrest in G(1) phase for MDA-MB-468 cells. CPT caused G(1)-phase arrest in MDA-MB-468 cells and prolonged S phase in MCF-7 cells. gamma-Radiation caused an increase in cells in G(2)/M phase for MDA-MB-468 and MCF-7. MDA-MB-468 cells were growth-inhibited by EGF, CPT, and gamma-radiation. MCF-7 cells were growth-stimulated by EGF and inhibited by CPT and gamma-radiation. Combining EGF with tat-anti-p21 immunoconjugates (ICs) amplified the growth-inhibitory effect on MDA-MB-468 cells 1.2-fold to 2.3-fold, but had no effect on the growth stimulation of MCF-7 cells by EGF. Tat-anti-p21 ICs sensitized MCF-7 cells 1.4-fold to gamma-radiation but had no effect on the growth of gamma-irradiated MDA-MB-468 cells. Tat-anti-p21 ICs sensitized both MDA-MB-468 and MCF-7 cells 1.7-fold to CPT. We conclude that tat-anti-p21 ICs are promising sensitizers for cytotoxic cancer therapies and that their sensitization is dependent on treatment-related p21 expression. This general approach could potentially be extended to other growth-regulatory molecules that are associated with tumor growth and progression.

STAT1 activation-induced apoptosis of esophageal squamous cell carcinoma cells in vivo

BACKGROUND

The induction of apoptosis might be a promising treatment for cancers refractory to conventional therapies, such as esophageal cancer. In this study, we examined whether epidermal growth factor-induced growth inhibition results from apoptosis of esophageal squamous cell carcinoma (SCC) cells as a result of STAT1 activation and evaluated whether interferon gamma (IFN-gamma) can induce apoptosis of cancer cells in vivo.

METHODS

To assess the function of STAT1, we established stable transfectants expressing dominant-negative STAT1. Apoptosis was assessed by several experimental techniques, including flow cytometry. Differentiation was evaluated by Western blot test with involucrin used as a marker. In vivo, cancer cells were injected into male BALB/c nu/nu mice. Two weeks later, the mice started to receive injections of IFN-gamma or saline into a tail vein four times per week. Concentrations of IFN-gamma in the tumors were analyzed by enzyme-linked immunosorbent assay. Apoptosis was evaluated by TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) staining.

RESULTS

Epidermal growth factor inhibited the growth of esophageal SCC cells by causing apoptosis through several pathways involving STAT1 activation. IFN-gamma induced the apoptosis of cancer cells, but it also promoted the differentiation (not apoptosis) of primary cultured cells derived from normal esophageal epithelium. IFN-gamma also inhibited the growth of xenograft tumors of esophageal SCC cells in vivo.

CONCLUSIONS

Our results suggest that IFN-gamma is one candidate for cytokine-based therapy of cancer. IFN-gamma-induced STAT1 activation might be involved in the apoptosis of esophageal SCC cells and in the terminal differentiation of normal squamous cells. Further studies of STAT1 signaling pathways may provide the basis for new targeted therapeutic strategies for esophageal SCC.

123I-labeled HIV-1 tat peptide radioimmunoconjugates are imported into the nucleus of human breast cancer cells and functionally interact in vitro and in vivo with the cyclin-dependent kinase inhibitor, p21WAF-1/Cip-1

PURPOSE

To evaluate the internalization and nuclear translocation of (123)I-tat-peptide radioimmunoconjugates in MDA-MB-468 breast cancer cells and their ability to interact with the cyclin-dependent kinase inhibitor, p21(WAF-1/Cip-1).

METHODS

Peptides [GRKKRRQRRRPPQGYGC] harboring the nuclear-localizing sequence from HIV tat domain were conjugated to anti-p21(WAF-1/Cip-1) antibodies. Immunoreactivity was assessed by Western blot using lysate from MDA-MB-468 cells exposed to EGF to induce p21(WAF-1/Cip-1). Internalization and nuclear translocation were measured. The ability of tat-anti-p21(WAF-1/Cip-1) to block G(1)-S phase arrest in MDA-MB-468 cells caused by EGF-induced p21(WAF-1/Cip-1) was evaluated. Tumor and normal tissue uptake were determined at 48 h p.i. in athymic mice implanted s.c. with MDA-MB-468 xenografts injected intratumorally with EGF.

RESULTS

There was 13.4+/-0.2% of radioactivity internalized by MDA-MB-468 cells incubated with (123)I-tat-anti-p21(WAF-1/Cip-1) and 34.6+/-3.1% imported into the nucleus. Tat-anti-p21(WAF-1/Cip-1)(8 muM) decreased the proportion of EGF-treated cells in G(1) phase from 81.9+/-0.7% to 46.1+/-0.7% (p<0.001), almost restoring the G(1) phase fraction to that of unexposed cells (25.8+/-0.2%). Non-specific tat-mouse IgG did not block EGF-induced G(1)-S phase arrest. Tumor uptake of radioactivity was higher in mice injected with EGF to induce p21(WAF-1/Cip-1) than in mice not receiving EGF (3.1+/-0.4% versus 1.8+/-0.2% ID/g; p=0.04). Western blot analysis of tumors revealed a threefold increase in the p21(WAF-1/Cip-1)/beta-actin ratio.

CONCLUSION

We conclude that intracellular and nuclear epitopes in cancer cells can be functionally targeted with tat-radioimmunoconjugates to exploit many more epitopes for imaging and radiotherapeutic applications than have previously been accessible.

Spermine oxidase SMO(PAOh1), Not N1-acetylpolyamine oxidase PAO, is the primary source of cytotoxic H2O2 in polyamine analogue-treated human breast cancer cell lines

The induction of polyamine catabolism and its production of H2O2 have been implicated in the response to specific antitumor polyamine analogues. The original hypothesis was that analogue induction of the rate-limiting spermidine/spermine N1-acetyltransferase (SSAT) provided substrate for the peroxisomal acetylpolyamine oxidase (PAO), resulting in a decrease in polyamine pools through catabolism, oxidation, and excretion of acetylated polyamines and the production of toxic aldehydes and H2O2. However, the recent discovery of the inducible spermine oxidase SMO(PAOh1) suggested the possibility that the original hypothesis may be incomplete. To examine the role of the catabolic enzymes in the response of breast cancer cells to the polyamine analogue N1,N1-bis(ethyl)norspermine (BENSpm), a stable knockdown small interfering RNA strategy was used. BENSpm differentially induced SSAT and SMO(PAOh1) mRNA and activity in several breast cancer cell lines, whereas no N1-acetylpolyamine oxidase PAO mRNA or activity was detected. BENSpm treatment inhibited cell growth, decreased intracellular polyamine levels, and decreased ornithine decarboxylase activity in all cell lines examined. The stable knockdown of either SSAT or SMO(PAOh1) reduced the sensitivity of MDA-MB-231 cells to BENSpm, whereas double knockdown MDA-MB-231 cells were almost entirely resistant to the growth inhibitory effects of the analogue. Furthermore, the H2O2 produced through BENSpm-induced polyamine catabolism was found to be derived exclusively from SMO(PAOh1) activity and not through PAO activity on acetylated polyamines. These data suggested that SSAT and SMO(PAOh1) activities are the major mediators of the cellular response of breast tumor cells to BENSpm and that PAO plays little or no role in this response.

Inhibition of Phosphatidylinositol 3-Kinase/Protein Kinase B Signaling Is Not Sufficient to Account for Indole-3-Carbinol–Induced Apoptosis in Some Breast and Prostate Tumor Cells

PURPOSE AND EXPERIMENTAL DESIGN

Indole-3-carbinol has been proposed to induce apoptosis via a mechanism involving inhibition of protein kinase B (PKB) signaling in breast and prostate tumor cell lines. However, no functional data exist, and the effect of indole-3-carbinol on viability is known to be highly cell type specific. Here, we examine any requirement for PKB inhibition in induction of apoptosis by indole-3-carbinol in the MDA MB468 cell line using in vitro kinase assays, transfection, Western blotting, and flow cytometry. Comparison is also made with MCF10CA1 breast and PC3 prostate tumor cells.

RESULTS

Indole-3-carbinol directly inhibited activity of phosphatidylinositol 3-kinase (PI3K) immunoprecipitated from HBL100 or MDA MB468 cells in vitro. Nonetheless, we present three lines of evidence that inhibition of PI3K/PKB signaling is not required for induction of apoptosis by indole-3-carbinol. First, 50% inhibition of PKB phosphorylation by LY294002 resulted in only 15% apoptosis after 72 hours, whereas similar PKB inhibition by indole-3-carbinol coincided with 30% apoptosis after only 24 hours. Second, induction of phospho-PKB (p-PKB) levels following stimulation with epidermal growth factor did not prevent indole-3-carbinol-induced apoptosis. Third, overexpression of active PKBalpha did not prevent induction of apoptosis by indole-3-carbinol. Inhibition of PKB phosphorylation by LY294002 in the PC3 and MCF10CA1 tumor cell lines similarly failed to result in a significant increase in apoptosis.

CONCLUSIONS

Our results show that inhibition of PI3K/PKB signaling by indole-3-carbinol or LY294002 is not directly correlated with induction of apoptosis in several breast or prostate cell lines.

Vascular smooth muscle cell-specific regulation of cyclin-dependent kinase inhibitor p21WAF1/Cip1 transcription by Sp1 is mediated via distinctcis-acting positive and negative regulatory elements in the proximal p21WAF1/Cip1 promoter

Smooth muscle cells (SMC) play a central role in common vascular pathologies such as atherosclerosis and restenosis. Understanding the molecular regulation of SMC proliferation at a transcriptional level may provide important clues for the targeted control of vascular hyperplasia. We recently reported the capacity of the transcription factor Sp1 to down-regulate p21(WAF1/Cip1) production thereby reducing p21(WAF1/Cip1)-cyclin D1-Cdk4 complex formation and inhibiting vascular SMC proliferation (Kavurma and Khachigian [2003] J. Biol. Chem. 278, 32537-32543). We have now localized the Sp1-response elements in the p21(WAF1/Cip1) promoter responsible for p21(WAF1/Cip1) repression in WKY12-22 SMCs. The proximal region of the p21(WAF1/Cip1) promoter contains five distinct Sp1-binding elements that we have termed A, B, C, D, and E. Electrophoretic mobility shift analysis revealed that SMC nuclear Sp1 interacts with all five Sp1-binding sites, and each of these sites is critical for Sp1 repression of the p21(WAF1/Cip1) promoter, since mutation in any one element ablates repression, and in some cases results in activation. In contrast, only elements C, D, and E are bound by Sp1 in endothelial cells. Sp1 overexpression activates the p21(WAF1/Cip1) promoter in this cell type. Furthermore, mutation in any of these five elements is not sufficient to prevent activation of the p21(WAF1/Cip1) promoter by Sp1 in endothelial cells. Surprisingly, double mutations of elements C and E facilitates superactivation by Sp1 in both cell types, whereas triple mutations of C, D, and E inactivate the promoter. These findings demonstrate cell type-specific regulation of p21(WAF1/Cip1) transcription by Sp1 via distinct cis-acting positive and negative regulatory elements in the proximal p21(WAF1/Cip1) promoter.

The role of tyrosine kinase Etk/Bmx in EGF-induced apoptosis of MDA-MB-468 breast cancer cells

Etk/Bmx, a member of the Tec family of tyrosine kinases, mediates various signaling pathways and confers several cellular functions. In the present study, we have explored the functional role of Etk in mediating EGF-induced apoptosis, using MDA-MB-468 cell line as a model. We first demonstrated that EGF treatment induces Etk tyrosine phosphorylation in both HeLa and MDA-MB-468 cells. Overexpression of Etk by recombinant adenovirus in MDA-MB-468 cells potentiates the extent of EGF-induced cell apoptosis. The observed Etk-enhanced MDA-MB-468 cell apoptosis is associated with the Stat1 activation, as demonstrated by electrophoresis mobility shift assays and reporter gene assays. By contrast, a kinase domain deletion mutant EtkDeltaK, functioning as a dominant-negative mutant, ameliorates EGF-induced Stat1 activation and apoptosis in MDA-MB-468 cells. To explore whether the activated Etk alone is sufficient for inducing apoptosis, a conditionally activated Etk (DeltaEtk-ER), a chimeric fusion protein of PH domain-truncated Etk and ligand-binding domain of estrogen receptor, was introduced into MDA-MB-468 cells. Upon beta-estradiol ligand activation, the DeltaEtk-ER could stimulate Stat1 activity and confer cell apoptosis independent of EGF treatment. Taken together, our findings indicate that Etk is a downstream signaling molecule of EGF receptor and suggest that Etk activation is essential for transducing the EGF-induced apoptotic signaling.

Antisense imaging of epidermal growth factor-induced p21(WAF-1/CIP-1) gene expression in MDA-MB-468 human breast cancer xenografts

Molecular imaging of the expression of key genes which determine the response to DNA damage following cancer treatment may predict the effectiveness of a particular treatment strategy. A prominent early response gene for DNA damage is the gene encoding p21(WAF-1/CIP-1), a cyclin-dependent kinase inhibitor that regulates progression through the cell cycle. In this study, we explored the feasibility of imaging p21(WAF-1/CIP-1) gene expression at the mRNA level using an 18-mer phosphorothioated antisense oligodeoxynucleotide (ODN) labeled with (111)In. The known induction of the p21(WAF-1/CIP-1) gene in MDA-MB-468 human breast cancer cells following exposure to epidermal growth factor (EGF) was used as an experimental tool. Treatment of MDA-MB-468 cells in vitro with EGF (20 n M) increased the ratio of p21(WAF-1/CIP-1) mRNA/beta-actin mRNA threefold within 2 h as measured by the reverse transcription polymerase chain reaction (RT-PCR). A concentration-dependent inhibition of EGF-induced p21(WAF-1/CIP-1) protein expression was achieved in MDA-MB-468 cells by treatment with antisense ODNs with up to a tenfold decrease observed at 1 microM. There was a fourfold lower inhibition of p21(WAF-1/CIP-1) protein expression by control sense or random sequence ODNs. Intratumoral injections of EGF (15 microg/dayx3 days) were employed to induce p21(WAF-1/CIP-1) gene expression in MDA-MB-468 xenografts implanted subcutaneously into athymic mice. RT-PCR of explanted tumors showed a threefold increased level of p21(WAF-1/CIP-1) mRNA compared with normal saline-treated tumors. Successful imaging of EGF-induced p21(WAF-1/CIP-1) gene expression in MDA-MB-468 xenografts was achieved at 48 h post injection of (111)In-labeled antisense ODNs (3.7 MBq; 2 microg). Tumors displaying basal levels of p21(WAF-1/CIP-1) gene expression in the absence of EGF treatment could not be visualized. Biodistribution studies showed a significantly higher tumor accumulation of (111)In-labeled antisense ODNs in the presence of EGF induction of the p21(WAF-1/CIP-1) gene (0.32%+/-0.06% injected dose/g) compared with normal saline-treated control mice (0.11%+/-0.07% injected dose/g). The tumor/blood ratio for antisense ODNs in the presence of EGF induction of the p21(WAF-1/CIP-1) gene (4.87+/-0.87) was also significantly higher than for control random sequence ODNs (2.14+/-0.69) or for mice receiving antisense ODNs but not treated with EGF (2.07+/-0.37). We conclude that antisense imaging of upregulated p21(WAF-1/CIP-1) gene expression is feasible and could represent a promising new molecular imaging strategy for monitoring tumor response in cancer patients. To our knowledge, this study also describes the first report of molecular imaging of the upregulated expression of a downstream gene target of the EGFR, a transmembrane tyrosine kinase receptor.

Caspase-8-mediated BID cleavage and release of mitochondrial cytochrome c during Nomega-hydroxy-L-arginine-induced apoptosis in MDA-MB-468 cells. Antagonistic effects of L-ornithine

We have previously reported that N(omega)-hydroxy-l-arginine (NOHA), a stable intermediate product formed during the conversion of l-arginine to nitric oxide, induced apoptosis in MDA-MB-468 cells, and this action was antagonized in the presence of l-ornithine. We also reported that apoptosis induced by NOHA in this cell line could not be explained on the basis of a reduction of intracellular polyamines. In the current study, we investigated other potential mechanism(s) by which NOHA may have induced apoptosis in this cell line. We observed that NOHA initially activated caspase-8 and induced cleavage of BH(3) interacting domain. This was followed by release of cytochrome c and subsequently, activation of downstream caspases-9 and -3 to cleave poly(ADP-ribose) polymerase. We also observed that NOHA induced a rapid and persistent hyperpolarization of the mitochondrial membrane potential rather than depolarization indicating that the release of cytochrome c by NOHA was by a mechanism independent of the mitochondrial transition pore. Exogenous l-ornithine did not inhibit NOHA-induced caspase-8 activation and cleavage of BH(3) interacting domain but acted at the mitochondrial level and inhibited the NOHA-induced cytochrome c release and apoptosis.

Comparative antiproliferative effects of (111)In-DTPA-hEGF, chemotherapeutic agents and gamma-radiation on EGFR-positive breast cancer cells

The antiproliferative effects of (111)In-DTPA-hEGF on breast cancer cells expressing high levels of EGFR were compared with those of chemotherapeutic agents or gamma-radiation. MDA-MB-468 cells were cultured with (111)In-DTPA-hEGF (30 MBq/microg, 1.8 x 10(5) MBq/micromol), DTPA-hEGF, methotrexate, doxorubicin, paclitaxel or 5-fluorouracil. Cell growth was measured colorimetrically. The IC(50) for 111In-DTPA-hEGF was < 70 pM (11 kBq/mL) versus 500 pM for DTPA-hEGF. The IC(50) for paclitaxel, methotrexate, doxorubicin and 5-fluorouracil was 6 nM, 15 nM, 20 nM and 4 microM respectively. (111)In-DTPA-hEGF (70 pM, 11 kBq/mL) delivered approx. 6 Gy to breast cancer cells producing growth inhibition equivalent to 4 Gy of gamma-radiation. We conclude that (111)In-DTPA-hEGF exhibited potent antiproliferative effects towards breast cancer cells at concentrations much lower than chemotherapeutic agents and equivalent to those produced by several Gy of high dose rate gamma-radiation.

Activation of caspase-3 activity and apoptosis in MDA-MB-468 cells by N(omega)-hydroxy-L-arginine, an inhibitor of arginase, is not solely dependent on reduction in intracellular polyamines

We have shown previously that (NOHA) an intermediate in the nitric oxide (NO) synthetic pathway and an inhibitor of arginase significantly reduced intracellular polyamines, activated caspase-3 and induced apoptosis in the human breast cancer cell line MDA-MB-468. These actions of NOHA were abolished in the presence of exogenous L-ornithine suggesting that a reduction in the intracellular polyamine content might be responsible for the activation of caspase-3 and apoptotic actions of NOHA. In order to further explore this possibility, we used SAM-486A and alpha-difluoromethylornithine (DFMO), which are inhibitors of S-adenosylmethionine decarboxylase (SAMDC), and ornithine decarboxylase (ODC), respectively, either alone or in combination to reduce the intracellular polyamine levels. We then assessed whether a reduction in polyamine levels by these two compounds to a similar degree to that produced by NOHA activated caspase-3 which occurs prior to the onset of apoptosis. We observed that both SAM-486A and DFMO, either alone or in combination, inhibited cell proliferation, induced p21 and arrested cells in the G(0)-G(1) phase of the cell cycle but failed to activate caspase-3 as assessed by enzymatic assay of caspase-3, western blot analysis of the proteolytic cleavage of caspase-3 protein as well as TUNEL assay. Furthermore, pre-incubation of the cells with SAM-486A and DFMO for 4 days, either alone or in combination significantly inhibited the activation of caspase-3 and apoptosis by NOHA when compared with that observed with cells treated with NOHA alone. Our results, therefore, indicate that the activation of caspase-3 and apoptosis observed with NOHA cannot be solely explained by a reduction in intracellular polyamine levels and that other mechanisms need to be also considered.

Growth inhibitory effect of green tea extract in Ehrlich ascites tumor cells involves cytochrome c release and caspase activation

We reported previously that the mechanism by which Green tea extract (GTE) elicited growth-inhibitory effects in Ehrlich ascites tumor cells involved a decrease in ornithine decarboxylase (ODC) activity and in cell viability. Decrease in ODC activity has been associated with apoptotic cell death and we therefore studied changes in cytochrome c release and caspase activation, which characterize apoptosis. GTE caused a dose- and time-dependent increase in caspase-3-like protease activation, preceded by a release of cytochrome c from the mitochondria. Inhibiting the activation of caspase-3 with acetyl-Asp-Glu-Val-Asp-alpha-aldehyde (caspase inhibitor) caused a reversal in the effect on cell viability.

Involvement of polyamines in B cell receptor-mediated apoptosis: spermine functions as a negative modulator

The B cell lymphoma WEHI231 has been used as a model for studying clonal deletion of B cells on the basis of its ability to undergo growth arrest and apoptosis by B cell antigen receptor (BCR) cross-linking. To comprehensively analyze the genes involved in BCR-mediated apoptosis, we applied the technique of serial analysis of gene expression (SAGE) to WEHI231. Comparison of expression patterns revealed that BCR cross-linking caused coordinate changes in the expression of genes involved in polyamine metabolism. Polyamines are ubiquitous compounds required for cell proliferation and homeostasis. The coordinate expression of the polyamine-related genes was confirmed by semiquantitative reverse transcriptase-polymerase chain reaction analysis. During apoptosis, the genes involved in polyamine biosynthesis were downregulated, whereas those involved in polyamine catabolism were upregulated, suggesting that intracellular polyamines play a role in BCR-mediated apoptosis. Levels of intracellular putrescine, spermidine, and spermine were reduced after BCR cross-linking. These effects were prevented by concurrent CD40 stimulation, which blocked BCR-mediated apoptosis. Furthermore, addition of spermine could repress the BCR-mediated apoptosis by attenuating the mitochondrial membrane potential (Deltapsim) loss and activation of caspase-7 induced by BCR signaling. These findings strongly suggest that polyamine regulation is involved in apoptosis during B cell clonal deletion.

Hepatocyte growth factor induces pro-apoptotic genes in HepG2 hepatoma but not in B16-F1 melanoma cells

Hepatocyte growth factor (HGF) exerts a cytostatic effect on HepG2 and B16-F1 cell lines. To evaluate the possible involvement of the apoptotic process in this effect, we performed studies at cellular and molecular levels. HGF induced apoptosis only in HepG2 hepatoma cells at day 3 in about 20% of the cells undergoing growth inhibition, while hallmarks of apoptosis did not occur in B16-F1 melanoma cells. During the first 24 h after HGF treatment, enhanced expression of the pro-apoptotic genes bax and c-Myc was observed at level of mRNA and protein. Concomitant induction of antizyme (AZ) might lower ornithine decarboxylase (ODC) protein level though a huge increase in ODC mRNA level took place. This was suggested as a signal for apoptosis decisional phase. The levels of the proteins examined except that of AZ fell down thereafter when HepG2 cells underwent apoptosis. In B16-F1 cells, only ODC and AZ protein levels were elevated probably in relation to the initial elevated growth rate and the absence of apoptosis involvement in the following cytostatic effect of HGF in melanoma cells. Consistent with this hypothesis, bax mRNA and protein levels were unchanged or even lower relative to control values.