Maria Rybczynska

Effects of miltefosine on various biochemical parameters in a panel of tumor cell lines with different sensitivities

We investigated endocytosis activity, uptake of miltefosine (hexadecylphosphocholine), phospholipid and cholesterol content, the cell cycle, and apoptosis in 13 tumor cell lines (MCF7, MCF7/ADR, KB-3-1, KB-8-5, KB-C1, HeLa, HeLa-MDR1-G185, HeLa-MDR1-V185, CCRF/CEM, CCRF/VCR1000, CCRF/ADR5000, HL-60, HL-60/AR) with different sensitivities to treatment with the antitumor phospholipid analogues miltefosine and D-21266 (octadecyl-(N,N-dimethyl-piperidino-4-yl)-phosphate). In this panel of cell lines, MDR1 (multidrug resistance gene 1)- and MRP1 (multidrug resistance-associated protein)-expressing cells were found to be slightly more resistant to both compounds than sensitive parental cells. No correlation was found between resistance to miltefosine and endocytosis, intracellular concentration of miltefosine, the phospholipid and cholesterol content, induction of apoptosis, or cell cycle alterations in all the cell lines tested. Wild-type p53 containing WMN Burkitts lymphoma cells and wild type p53-deficient CA46 exhibited similar sensitivities to miltefosine. The low percentage of apoptosis induced in MCF7 cells lacking caspase 3 indicated that caspase 3 seems to play an essential role in miltefosine-induced apoptosis.

Beneficial or harmful influence of phytosterols on human cells

So far, a protective influence of phytosterols on the human organism and atherogenesis has been suggested. Most studies have concentrated on the cytotoxic efficacy of phytosterols on cancer cells. However, there are only a few reports showing their influence on normal cells. The aim of the present study was to determine whether dietary plant sterols and their thermal processing products could influence the viability of normal, abdominal endothelial cells that play a crucial role in atherogenesis. Thus, we studied the effect of rapeseed oil-extract components, beta-sitosterol, cholesterol and their epoxy-derivatives, 5 alpha,6 alpha-epoxy-beta-sitosterol and 5 alpha,6 alpha-epoxycholesterol, on the proliferation and viability of human abdominal aorta endothelial cells HAAE-2 in vitro. We showed strong cytotoxic properties of beta-sitosterol in HAAE-2 cells (half maximal inhibitory concentration (IC50) = 1.99 (SEM 0.56) microm) and, interestingly, a weaker cytotoxic effect of 5 alpha,6 alpha-epoxy-beta-sitosterol (IC50>200 microm). Moreover, we observed a significantly stronger cytotoxic activity of beta-sitosterol than cholesterol (IC50 = 8.99 (SEM 2.74) microm). We also revealed that beta-sitosterol as well as cholesterol caused apoptosis, inducing caspase-3 activity in the cells (60 % increase compared with control cells) that corresponded to the DNA fragmentation analysis in a terminal uridine deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling (TUNEL) study. Although absorption of plant sterols is low compared with cholesterol, they can still influence other physiological functions. Since they effectively reduce serum LDL-cholesterol and atherosclerotic risk but also decrease the viability of cancer cells as well as normal cells in a time- and dose-dependent manner in vitro, their influence on other metabolic processes remains to be elucidated.

Protein kinase Cε as a cancer marker and target for anticancer therapy.

Protein kinase Cε (PKCε) is a representative member of a family of novel PKC isoforms that are independent of calcium, but can be activated by phorbol esters, diacylglycerol (DAG) and phosphatidylserine (PS). This kinase is capable of modulating crucial cell functions, including proliferation, differentiation and survival. These activities depend on enzyme translocation to subcellular compartments upon binding DAG, PS or exogenous stimulators. PKCε initiates malignant transformation of cells through its effects on the Ras/Raf/MAPK pathway and displays the greatest carcinogenic potential of all PKC isoforms. PKCε also promotes tumor metastatic capacity and resistance to anti-cancer therapy. Overexpression of PKCε is found in numerous cancers including colon, breast, stomach, prostate, thyroid and lung and is considered an important marker of negative disease outcome. Although overexpression of PKCε is observed in tumors, it is not found in healthy tissues hence it has been suggested as a diagnostic marker or a putative target for specific inhibitors used for treatment of cancer. Research on selective inhibition of PKCε is under way and diverse approaches may become clinically applicable anti-tumor strategies. Suppression of the PKCε-encoding gene achieved through the antisense cDNA, suppression of PKCε with RNAi and inhibition achieved with translocation-inhibitory peptides may provide novel treatment strategies for cancer.

Signal transduction of constitutively active protein kinase C epsilon

The protein kinase C (PKC) family is the most prominent target of tumor-promoting phorbol esters. For the PKCepsilon isozyme, different intracellular localizations and oncogenic potential in several but not all experimental systems have been reported. To obtain information about PKCepsilon-signaling, we investigated the effects of constitutively active rat PKCepsilon (PKCepsilonA/E, alanine 159 is replaced by glutamic acid) in HeLa cells in a doxycycline-inducible vector. Upon induction of PKCepsilonA/E expression by doxycycline, the major part of PKCepsilonA/E was localized to the Golgi. This led (i) to phosphorylations of PKCepsilon(S729), Elk-1(S383), PDK1(S241) and Rb(S807/S811), (ii) to elevated expression of receptor of activated C kinase 2 (RACK2) after 12 h, and (iii) increased colony formation in soft agar, increased cell migration and invasion, but not to decreased doubling time. Following induction of PKCepsilonA/E-expression by doxycycline for 24 h and additional short-term treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA), PKCepsilonA/E translocated to the plasma membrane and increased phosphorylation of MARCKS(S152/156). Treatment with doxycycline/TPA or TPA alone increased phosphorylations of Elk-1(S383), PDK1(S241), Rb(S807/S811), PKCdelta(T505), p38MAPK(T180/Y182), MEK1/2(S217/S221) and ERK2(T185/T187). MARCKS was not phosphorylated after treatment with TPA alone, demonstrating that in this system it is phosphorylated only by PKCepsilon localized to the plasma membrane but not by PKCalpha or delta, the other TPA-responsive PKC isozymes in HeLa cells. These results demonstrate that PKCepsilon can induce distinctly different signaling from the Golgi and from the plasma membrane.

Methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate (HIMOXOL), a synthetic oleanolic acid derivative, induces both apoptosis and autophagy in MDA-MB-231 breast cancer cells.

HIMOXOL (methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate) is a synthetic derivative of oleanolic acid (OA). HIMOXOL revealed the highest cytotoxic effect among tested synthetic OA analogs. In this study we focused on elucidating the cytotoxic mechanism of HIMOXOL in MDA-MB-231 breast cancer cells. HIMOXOL reduced MDA-MB-231 cell viability with an IC50 value of 21.08±0.24μM. In contrast to OA, the tested compound induced cell death by activating apoptosis and the autophagy pathways. More specifically, we found that HIMOXOL was able to activate the extrinsic apoptotic pathway, which was proven by observation of caspase-8, caspase-3 and PARP-1 protein activation in Western blot analysis. An increase in the ratio of Bax/Bcl-2 protein levels was also detected. Moreover, HIMOXOL triggered microtubule-associated protein LC3-II expression and upregulated beclin 1. This observed compound activity was modulated by mitogen-activated protein kinases and NFκB/p53 signaling pathways. Together, these data suggest that HIMOXOL, a synthetic oleanolic acid derivative which activates dual cell death machineries, could be a potential and novel chemotherapeutic agent.

Reversal of multidrug resistance by the staurosporine derivatives CGP 41251 and CGP 42700

It has been shown previously that the staurosporine derivative CGP 41251, a specific inhibitor of protein kinase C (IC50 = 50 nM), exhibits antitumor activity and reverses mdr1‐mediated multidrug resistance. At present, the compound is evaluated as an anticancer drug in clinical phase I trials. We compared the effects of CGP 41251 with CGP 42700, another staurosporine derivative, which exhibits low protein kinase C inhibiting activity (IC50 = >100 μM). We found that in contrast to CGP 41251, CGP 42700 does not show antiproliferative activity in HeLa and KB cells in tissue culture (up to a concentration of 10 μM). We compared both compounds for their ability to reverse mdr1‐mediated resistance in KB‐C1 and in HeLa‐MDR1 cells (transfected with the mdr1 gene). CGP 42700 is able to reverse mdr1‐mediated resistance to a similar extent as CGP 41251. The intracellular accumulation of rhodamine 123 in KB‐C1 cells following pretreatment with CGP 41251 for 30 min was higher than that following treatment with CGP 42700 if determined in medium without serum. However, quantitation of rhodamine efflux in an ex vivo assay using human CD8+ cells in serum showed that CGP 42700 is more effective in inhibiting the efflux of rhodamine 123 than CGP 41251. We conclude from our results that (1) CGP 42700 is more effective in reversal of multidrug resistance in serum than CGP 41251, indicating that the compound may be useful for treatment of patients, and (2) CGP 42700 does not inhibit protein kinase C and cell proliferation and, therefore, may be less toxic and elicit less side effects in humans than other chemosensitizers. Int. J. Cancer 77:64–69, 1998.© 1998 Wiley‐Liss, Inc.

Study of ABCB1 polymorphism frequency in breast cancer patients from Poland

BACKGROUND The accumulation of mutagenic substances in the human body may result in DNA metabolism disruption followed by carcinogenesis. As a consequence of mutations in the genes coding for transmembrane protein pumps, the intracellular concentration of xenobiotics may significantly increase. This, in turn, may provoke altered risk for cancer development. The gene known to be the most relevant in the transport of numerous compounds is ABCB1 (also known as MDR1). Numerous mutations and polymorphisms that affect the encoded proteins (PgP) function were identified in this gene. The aim of the study was to define the frequency of 2677G>A,T and 3435C>T polymorphisms in a population of Polish breast cancer patients and to estimate their contribution to cancer development. METHODS The polymorphism frequency analysis (209 patients vs. 202 control subjects) was performed either by allele-specific amplification (2677G>A,T) or by restriction fragment length polymorphism (RFLP) using the SAU3AI restriction enzyme (3435C>T) followed by verification with hybridization probe assays in a Real-Time system and sequencing. RESULTS In the control group the frequency of individual 2677 genotypes was: wild homozygous GG = 34%, heterozygous G/T or G/A = 52.5% and variant homozygous AA or TT = 13.5%, while the genotype frequency in the group of studied patients was 43.5, 44.5 and 12%, respectively. In the control group, the frequency of individual 3435 genotypes was: CC = 25.4%, CT = 50.2%, TT = 24.4%, while the genotype frequency in the group of studied patients was 23, 46 and 31%, respectively. CONCLUSION Thus, no significant differences in the studied polymorphism frequencies were observed. It is then suggested that the studied polymorphisms, although probably good candidates in other tissue cancer types, might not be good predictive factors in breast cancer risk or development in Caucasians.

Phytosterols in Physiological Concentrations Target Multidrug Resistant Cancer Cells

Phytosterols have been proposed to act as potent anticancer agents. However the mechanism of their action has not been elucidated yet. Thus, the aim of our study was to determine whether plant sterols and their thermal processing products (in physiological concentration range) could influence the viability of cancer cells and thus could be considered as positive diet complements. Additionally we decided to study potential specificity of those natural compounds against cells showing high multidrug resistance. In this study we show that the cytotoxic effect of β-sitosterol was observed in both, estrogen-dependent and estrogen-independent cells. It was also shown that the β-sitosterol was significantly more cytotoxic in cells with basal ABCB1 expression (MCF7) than in multidrug resistant NCI/ADR-RES. Surprisingly, 5a,6a-epoxysitosterol did not decrease the viability of any investigated cells but on the contrary, it provoked their increased proliferation. It was shown that oxyphytosterols blocked the cell cycle of MCF7 cells in G0/G1 phase while did not affect NCI/ADR-RES cell cycle in physiological concentration range. We also show that PgP activity (responsible for Multidrug Resistance phenomena) is inhibited by β-sitosterol. Thus, the phytosterols are supposed to act at various mechanisms but, what is most interesting, can target cells showing high multidrug resistance potential.

Ataxia telangiectasia heterozygotes and patients display increased fluidity and decrease in contents of sulfhydryl groups in red blood cell membranes.

In red blood cell membranes of ataxia telangiectasia mutated (ATM) homozygotes and heterozygotes, decreased values of the corrected fluorescence anisotropy and the anisotropy parameter were found, indicating increased fluidity and decreased microviscosity, respectively. These changes in membranes were accompanied by a decrease in SH-groups and an increase in malondialdehyde (MDA) contents. The content of MDA both in homozygotes and in heterozygotes exceeded roughly threefold the respective control values. Decreased content of GSH in red blood cells was found only in ATM homozygotes. The change most specific for the ATM gene appears to be the increase in fluidity, since only this parameter displays the proportionally greater changes in ATM homozygotes compared to ATM heterozygotes. The observations presented here may indicate that the ATM gene is expressed in precursors of red blood cells and deficiency of normal AT gene function may produce the changes which persist in circulating cells.

Critical temperatures for the interaction of free fatty acids with the erythrocyte membrane

Non-esterified long-chain fatty acids reduce the extent of hypotonic hemolysis at a certain low concentration range but cause hemolysis at higher concentrations. This biphasic behavior was investigated at different temperatures (0-37 degrees C) for lauric (12:0), myristic (14:0), palmitoleic (16:1), oleic (cis-18:1) and elaidic (trans-18:1) acids. The results are summarized as follows: (A) the fatty acids examined exhibit a high degree of specificity in their thermotropic behavior; (B) oleic acid protects against hypotonic hemolysis even at the highest concentrations, up to 15 degrees C, when it becomes hemolytic, but only in a limited concentration range; (C) elaidic acid does not affect the osmotic stability of erythrocytes up to 20 degrees C, when it starts protecting: above 30 degrees C, it becomes hemolytic at the highest concentrations; (D) palmitoleic acid is an excellent protecting agent at all temperatures in a certain concentration range, becoming hemolytic at higher concentrations; (E) lauric acid protects up to 30 degrees C and becomes hemolytic only above this temperature; (F) myristic acid exhibits an extremely unusual behavior at 30 and 37 degrees C by having alternating concentration ranges of protecting and hemolytic effects; (G) there is a common critical temperature for hemolysis at 30 degrees C for saturated and trans-unsaturated fatty acids; (H) the initial slope of Arrhenius plots of percent hemolysis at the concentration of maximum protection is negative for cis-unsaturated fatty acids and positive for saturated and trans-unsaturated fatty acids.