Inhibitors of phospholipid intracellular signaling as antiproliferative agents

The PI3K Pathway: Background and Treatment Approaches

Two-thirds of all breast cancer patients with metastases have a hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative subtype. Endocrine therapy is the treatment of choice in these patients since in addition to its effectiveness it can also maintain the patients' quality of life over a longer term. However, 44-62% of postmenopausal patients with metastatic breast carcinoma have primary tamoxifen resistance. After 3-5 years, 30-40% of the patients receiving tamoxifen treatment develop secondary resistance. Understanding the way in which resistance develops is therefore essential for developing treatment approaches that can prevent or reverse endocrine resistance. The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway plays a central role here. As a result of the numerous interactions involved, complex issues arise that need to be taken into account in the development and use of therapeutic agents. In addition, this signaling pathway is the one that most frequently undergoes mutations in breast cancer. The prognostic and predictive significance of individual mutations has not yet been fully explained, but it might provide a basis for patient selection in clinical studies. Initial research results on the use of PI3K inhibitors suggest that this may be a highly promising therapeutic approach, with an acceptable side effect profile.

Genistein potentiates the effect of 17-beta estradiol on human hepatocellular carcinoma cell line

Background:

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors. This cancer may be due to a multistep process with an accumulation of epigenetic alterations in tumor suppressor genes (TSGs), leading to hypermethylation of the genes. Hypermethylation of TSGs is associated with silencing and inactivation of them. It is well-known that DNA hypomethylation is the initial epigenetic abnormality recognized in human tumors. Estrogen receptor alpha (ERα) is one of the TSGs which modulates gene transcription and its hypermethylation is because of overactivity of DNA methyltransferases. Fortunately, epigenetic changes especially hypermethylation can be reversed by pharmacological compounds such as genistein (GE) and 17-beta estradiol (E2) which involve in preventing the development of certain cancers by maintaining a protective DNA methylation. The aim of the present study was to analyze the effects of GE on ERα and DNMT1 genes expression and also apoptotic and antiproliferative effects of GE and E2 on HCC.

Materials and Methods:

Cells were treated with various concentrations of GE and E2 and the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay was used. Furthermore, cells were treated with single dose of GE and E2 (25 μM) and flow cytometry assay was performed. The expression level of the genes was determined by quantitative real-time reverse transcription polymerase chain reaction.

Results:

GE increased ERα and decreased DNMT1 genes expression, GE and E2 inhibited cell viability and induced apoptosis significantly.

Conclusion:

GE can epigenetically increase ERα expression by inhibition of DNMT1 expression which in turn increases apoptotic effect of E2. Furthermore, a combination of GE and E2 can induce apoptosis more significantly.

Inhibitory Effect of Genistein on PLC/PRF5 Hepatocellular Carcinoma Cell Line

BACKGROUND

Natural compounds including flavonoids like genistein (GE) are able to inhibit cell proliferation and induce apoptosis. GE is the main representative of these groups. GE inhibits carcinogenic tumors such as colon, stomach, lung, and pancreas tumors. The aim of the present study was to analyze the apoptotic effect of GE in the hepatocellular carcinoma (HCC) PLC/PRF5 cell line.

METHODS

Cells were treated with various doses of GE (1, 5, 10, 25, 50, 75, and 100 μM/L) at different times (24, 48, and 72 h) and the MTT assay was commonly used. Furthermore, cells were treated with single dose of GE (25 μM) at different times and flow cytometry was performed.

RESULTS

GE inhibited the growth of liver cancer cells significantly with a time- and dose-dependent manner. The percentage of living cells in GE treatment groups with a concentration of 25 μM at different times were 53, 48 and 47%, respectively (P < 0.001). Result of flow cytometry demonstrated that GE at a 25 μM concentration induces apoptosis significantly in a time-dependent manner. The percentage of apoptotic cells at different times were 44, 56, and 60%, respectively (P < 0.001).

CONCLUSIONS

GE can significantly inhibit the growth of HCC cells and plays a significant role in apoptosis of this cell line.

The PI3K/AKT/mTOR pathway in breast cancer: targets, trials and biomarkers

The phosphoinositide 3 kinase (PI3K)/Akt/mammalian (or mechanistic) target of rapamycin (mTOR) pathway is a complicated intracellular pathway, which leads to cell growth and tumor proliferation and plays a significant role in endocrine resistance in breast cancer. Multiple compounds targeting this pathway are being evaluated in clinical trials. These agents are generally well tolerated and can be used in combination with targeted therapies, endocrine therapy or cytotoxic agents. The identification of subtypes of tumors more likely to respond to these therapeutics cannot be overemphasized, since breast cancer is a very heterogeneous malignancy. Activation of pathways such as KRAS and MEK can act as escape mechanisms that lead to resistance, thus a combination of agents targeting multiple steps of the intracellular machinery is promising. There is evidence that tumors with PIK3CA mutations are more sensitive to inhibitors of the PI3K pathway but this has yet to be validated. Large clinical trials with correlative studies are necessary to identify reliable biomarkers of efficacy.

Structural insights into phospholipase C-β function

Phospholipase C (PLC) enzymes convert phosphatidylinositol-4,5-bisphosphate into the second messengers diacylglycerol and inositol-1,4,5-triphosphate. The production of these molecules promotes the release of intracellular calcium and activation of protein kinase C, which results in profound cellular changes. The PLCβ subfamily is of particular interest given its prominent role in cardiovascular and neuronal signaling and its regulation by G protein-coupled receptors, as PLCβ is the canonical downstream target of the heterotrimeric G protein Gαq. However, this is not the only mechanism regulating PLCβ activity. Extensive structural and biochemical evidence has revealed regulatory roles for autoinhibitory elements within PLCβ, Gβγ, small molecular weight G proteins, and the lipid membrane itself. Such complex regulation highlights the central role that this enzyme plays in cell signaling. A better understanding of the molecular mechanisms underlying the control of its activity will greatly facilitate the search for selective small molecule modulators of PLCβ.

Relaxation effect of synthetic ceramide analogues in cat esophageal smooth muscle cells

Ceramide has emerged as a novel second messenger for intracellular signalling. It is produced from sphingomyelin and is involved in the control of cell differntiation, proliferation, and apoptosis. C(2)-ceramide, short chain ceramide, plays a role in mediating contraction of cat esophageal smooth muscle cells. We examined the effect of synthesized ceramide analogues on the C(2)-ceramide and ACh-induced contraction in esophageal smooth muscle cells isolated with collagenase. CY3523, CY3525, or CY3723 inhibited C(2)-ceramide induced contraction, in a time dependent manne. Each analogue also inhibited the contraction in concentration dependent manners. CY 3523, CY 3525, and CY 3723 had no effect to the contraction induced by PMA. The inhibition with CY3523, CY3525 and CY3723 on the C(2)-ceramide induced contraction was recovered by PMA. These analogues decreased the density of MAPK bands (p44/42 or p38) in the western blot. These results suggest that ceramide analogues can inhibit C(2)-ceramide induced contraction via PKC and MAPK dependent pathway.

Covalent reactions of wortmannin under physiological conditions

Wortmannin (Wm), a steroid-like molecule of 428.4 Da, appears to be unstable in biological fluids (apparent chemical instability), yet it exhibits an antiproliferative activity in assays employing a 48 hr incubation period (prolonged bioactivity), a situation we refer to as the "wortmannin paradox." Under physiological conditions, Wm covalently reacts with nucleophiles such as the side chains of cysteine, N-methyl hexanoic acid, lysine, or proline at the C20 position on the furan ring. Like Wm, WmC20 amino acid derivatives had significant antiproliferative activities. Three Wm derivatives, WmC20-proline, WmC20-cysteine, and a WmC20-N-methyl hexanoic acid, generated Wm that then reacted with lysine in an exchange-type reaction. This unusual, reversible, covalent reaction of Wm with nucleophiles under physiological conditions provides an explanation for the wortmannin paradox.

Genistein inhibits invasive potential of human hepatocellular carcinoma by altering cell cycle, apoptosis, and angiogenesis

AIM: To study the in vitro and in vivo inhibitory effects of genistein on invasive potential of Bel 7402 hepatocellular carcinoma (HCC) cells and to explore the underlying mechanism.

METHODS: Bel 7402 HCC cells were exposed to genistein. The invasive activity of tumor cells was assayed in transwell cell culture chamber. p125^FAK expression and cell cycle were evaluated by a functional assay. Cell apoptosis analysis was performed with TUNEL method. In addition, bilateral subrenal capsule xenograft transplantation of HCC was performed in 10 nude mice. Genistein was injected and the invasion of HCC into the renal parenchyma was observed. Microvessels with immunohistochemical staining were detected.

RESULTS: Genistein significantly inhibited the growth of Bel 7402 cells, the inhibitory rate of tumor cells was 26–42%. The invasive potential of Bel 7402 cells in vitro was significantly inhibited, the inhibitory rate was 11–28%. Genistein caused G2/M cell cycle arrest, S phase decreased significantly. The occurrence of apoptosis in genistein group increased significantly. The expression of p125^FAK in 5 μg/mL genistein group (15.26±0.16%) and 10 μg/mL genistein group (12.89±0.36%) was significantly lower than that in the control group (19.75±1.12%, P<0.05). Tumor growth in genistein-treated nude mice was significantly retarded in comparison to control mice, the inhibitory rate of tumor growth was about 20%. Genistein also significantly inhibited the invasion of Bel 7402 cells into the renal parenchyma of nude mice with xenograft transplant. The positive unit value of microvessels in genistein-treated group (10.422 ± 0.807) was significantly lower than that in control group (22.330 ± 5.696, P < 0.01).

CONCLUSION: Genistein can effectively inhibit the invasive potential of Bel 7402 HCC cells by altering cell cycle, apoptosis and angiogenesis, inhibition of focal adhesion kinase may play a significant role in this process.

Synthesis and biological evaluation of L-alpha-phosphatidyl-D-3-deoxy-3-heteromethyl-myo-inositols as phosphoinositide 3-kinase inhibitors

We have synthesized a series of 3-deoxy-3-heteromethyl derivatives of L-alpha-phosphatidyl-D-myo-inositol as part of our effort to develop specific, reversible inhibitors of phosphoinositide (PI) 3-kinase. Among various derivatives examined, phosphatidyl-D-3-deoxy-3-aminomethyl-myo-inositol displays the highest potency in inhibiting PI 3-kinase both in vitro and in cells. It effectively suppressed antigen-stimulated degranulation in mast cells (IC(50), 17 microM), suggesting a potential application of this PI 3-kinase inhibitor as a mast cell-stabilizing agent.

Modulation of phospholipase D by hexadecylphosphorylcholine: a putative novel mechanism for its antitumoral activity

Hexadecylphosphorylcholine (HePC, D-18506, INN: Mitelfosine) belongs to the family of alkylphosphocholines with anticancer activity. Previous reports have related its antitumoral activity to their ability to interfere with phospholipid metabolism. However a clear mechanism of action has not been established yet. We have investigated the effect of HePC on two enzymes recently reported to play a role in cell growth proliferation, phospholipase D (PLD) and choline kinase (ChoK). Our results demonstrate that treatment with HePC induces a rapid stimulation of PLD, that may be achieved by PKC dependent or independent mechanisms, depending on the cell line investigated. Both PLD1 and PLD2 isoenzymes are sensitive to HePC activation. By contrast, no effect was observed by HePC on ChoK, a new target for anticancer drug development. Furthermore, in all cell lines tested, a chronic exposure of the cells to HePC abrogates PLD activation by either phorbol esters or HePC itself with no effect on total cellular PLD levels. This is reflected in a strong inhibition of PLD activity. We suggest that the inhibitory effects on PLD by HePC may be related to its antitumoral action.

Opposite effects on cytosolic Ca2+ of antitumor phospholipids by induction of calcium influx and activation of endoplasmic reticulum Ca(2+)-ATPase

The ability of four different antitumor phospholipids, 1-O-hexadecyl-2-chloro-2-deoxyglycero-3-phosphocholine (ET16CIPC), hexadecylphosphocholine (C16OPC), hexadecylphospho-L-serine analogs (C16OPS, C16OPS-N-Ac) and cytidine-5'-hexadecylphosphonophosphate (C16PCMP) to modulate the cytosolic Ca2+ concentration [Ca2+]i was studied in an immortalized human mammary epithelial cell line H184 A1N4. The compounds induced different modes of activity depending on their structure and concentration. ET16CIPC induced between 0.31 and 5 microM a concentration dependent transient increase which was followed by a sustained increase at 10 microM. Studies using LaCl3 and Mn2+ quench of the Fura-2 fluorescence indicated that both effects are the result of an extracellular Ca2+ influx. Low concentrations of C16OPC, C16OPS and C16OPS-N-Ac induced no, or only a small, transient increase, whereas C16PCMP caused a decrease in [Ca2+]i. Thapsigargin and cyclopiazonic acid, specific inhibitors of the endoplasmic reticulum Ca(2+)-ATPase, prolonged the transient [Ca2+]i increase following ET16CIPC concentration dependently, increased markedly the small transient increase following C16OPC and the C16-phosphoserine analogs and converted the decrease in the basal [Ca2+]i level induced by C16PCMP to an increase. The identical effects with thapsigargin and cyclopiazonic acid provide evidence that the [Ca2+]i response observed is an expression of the balance between the ability of an analog to raise [Ca2+]i and to remove Ca2+ by activation of the endoplasmic reticulum Ca(2+)-ATPase. This behaviour might contribute to the antiproliferative effectiveness of antitumor phospholipids.

Modulation of the cytosolic Ca++ concentration by alkylphospho-L-serine analogs: relation to their antiproliferative action

Antiproliferative alkyllysophospholipid (ALP) analogs produced multiple effects on the cytosolic Ca++ concentration ([Ca++]i) in an immortalized human breast epithelial cell line (H 184). The addition of small concentrations resulted in a short transient [Ca++]i response. With higher concentrations the transient rise was followed by a sustained increase. Pretreatment of cells with the ALP analogs for two minutes inhibited the transient [Ca++] response. Increases in [Ca++]i and inhibition of the transient increase were studied in relation to the dose and structure of several ALP analogs. In a series of alkylphospho-L-serine analogs with different lengths of the alkyl chain we found different dependencies of the stimulatory and inhibitory effects on the dose and the structure. The ability to increase [Ca++]i is absent with the C14 and C15 analogs, is low with the C16 and high with the C18 analog. With the exception of the C12 analog, a dose-related inhibition was observed with all derivatives but the effective concentrations differed very strongly and the maximal potency was reached with the C15 and C16 analogs. The antiproliferative action seems to correlate rather with the potency to inhibit the transient [Ca++]i response than with its stimulation.

The level of pancreatic PLA2 receptor is closely associated with the proliferative state of rat uterine stromal cells

Rat uterine stromal cells (U(III)) express pancreatic type PLA2 (PLA2-I) receptor and internalize the enzyme bound to receptors. Here, we investigate the proliferating effect and alterations in binding of PLA2-I. There is a dramatic decline in PLA2-I binding in U(III) cells as they progress from a non-confluent proliferating state (40,000 sites/cell) to a confluent state (1300 sites/cell). Intracellular concentration of PLA2-I changed with the alteration in binding, suggesting that regulation in the PLA2 binding capacity may have important implications in growth control mechanisms.