In vitro metabolism of the phosphatidylinositol 3-kinase inhibitor, wortmannin, by carbonyl reductase

Impregnation of mesenchymal stem cell conditioned media with wortmannin enhanced its antiproliferative effect in breast cancer cells via PI3K/Akt/mTOR pathway

BACKGROUND/AIM

Conditioned media derived from Mesenchymal stem cells (MSC-CM) was suggested as a promising alternative cell-free regenerative therapy. It is hypothesized that the synergistic effect of MSC-CM with anticancer drugs may improve their antiproliferative and antimetastatic effects against cancer cells. Herein, the MSC-CM was impregnated with Wortmannin, a pan-PI3K/Akt/mTOR inhibitor, and their combined effect was investigated against breast cancer cells.

MATERIALS AND METHODS

To explore this, the cytotoxic, apoptotic, and autophagic potentials were assessed in luminal-A breast cancer cells (MCF-7).

RESULTS

We found that incubation of MCF-7 to Wort-containing-CM induced apoptosis- and autophagy-mediated cell death, meanwhile prolonged exposure caused massive necrotic cell death. The involvement of MSC-CM effectively reduced Wortmannin IC50 observed in Wort-treated cells. Also, Wort-loaded-CM induced nuclear DNA fragmentation and reduced in vitro cell migration. These findings were associated with a Wort-dependent reduction in cell viability, the formation of the phosphorylated Akt and mTOR proteins, reduced the expression of mRNA, and downregulated the expression of the catalytic domain of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K-Ca).

CONCLUSION

These findings revealed the promising antiproliferative and antimetastasis effects of combining pan-PI3K/Akt/mTOR inhibitors with MSC-derived-CM in breast cancer via the downregulation of PI3K/AKT/mTOR signaling pathways. Further studies are required to validate this chem-regenerative strategy in cancer treatment.

Recent progress in the synthesis of the furanosteroid family of natural products

This review focuses on an overview of recent advances in the synthesis of furanosteroids and illustrates their applications in medicinal chemistry over the period of 2005–present.

Inhibition of Phosphatidylinositol 3-kinease suppresses formation and progression of experimental abdominal aortic aneurysms

Accumulating evidence suggests an important role of Phosphatidylinositol 3-kinease (PI3K) pathway in inflammatory cells infiltration. Given  the essential role of inflammatory cells infiltration during the formation and progression of abdominal aortic aneurysm (AAA), to investigate the possibility of preventing AAA formation and progression via targeting PI3K is anticipated. Here, experimental AAAs was created in rats by transient intraluminal porcine pancreatic elastase (PPE) infusion into the infrarenal aorta firstly. AAAs rats were administrated with vehicle or Wortmannin during the period of day 0 to day 28 after PPE infusion. The aortic diameter of rats treated with Wortmannin was significantly smaller than those treated with vehicle. Meanwhile, Elastin destruction score and SMC destruction score were significantly decreased in rats treated with Wortmannin. Furthermore, histological analysis revealed infiltration of inflammatory cells were significantly reduced in rats treated with Wortmannin. Finally, the mRNA expression of PI3K and protein expression of pAKT in human abdominal aneurismal aorta tissues was elevated as compare to normal aorta. Our study revealed that PI3K inhibitor suppresses experimental AAAs formation and progression, through mechanisms likely related to impairing inflammation cells infiltration and median elastin degradation. These findings indicated that PI3K inhibitor may hold substantial translation value for AAA diseases.

In vitro metabolism of pyripyropene A and ACAT inhibitory activity of its metabolites

Pyripyropene A (PPPA, 1) of fungal origin, a selective inhibitor of acyl-CoA:cholesterol acyltransferase 2 (ACAT2), proved orally active in atherogenic mouse models. The in vitro metabolites of 1 in liver microsomes and plasma of human, rabbit, rat and mouse were analyzed by ultra fast liquid chromatography and liquid chromatography/tandem mass spectrometry. In the liver microsomes from all species, successive hydrolysis occurred at the 1-O-acetyl residue, then at the 11-O-acetyl residue of 1, while the 7-O-acetyl residue was resistant to hydrolysis. Furthermore, dehydrogenation of the newly generated 11-alcoholic hydroxyl residue occurred in human and mouse-liver microsomes, while oxidation of the pyridine ring occurred in human and rabbit liver microsomes. On the other hand, hydrolysis of the 7-O-acetyl residue proceeded only in the mouse plasma. These data indicated that the in vitro metabolic profiles of 1 have subtle differences among animal species. All of the PPPA metabolites observed in liver microsomes and plasma markedly decreased ACAT2 inhibitory activity. These findings will help us to synthesize new PPPA derivatives more effective in in vivo study than 1.

Calcium-induced apoptosis is delayed by HER1 receptor signalling through the Akt and PLCγ pathways in bladder cancer cells

The level of extracellular calcium has been demonstrated to regulate important physiological processes like cell growth and apoptosis. We demonstrate that in the bladder cancer cell line RT4, an increased extracellular calcium level induces apoptosis and that the HER1 receptor functions as a cell survival factor and delays apoptosis. After 12 h of calcium treatment (10 mM) apoptosis was detected in the RT4 cells. Increased activation of the HER1 receptor was detected as soon as 30 min after calcium addition, and the activation decreased again after 12 h of incubation, coinciding with the time when apoptosis was detectable. Inhibition of HER1 with Gefitinib (5 μM) or Tyrphostin (AG1478) (20 μM) augmented the calcium-induced apoptosis, and with HER1 inhibition apoptosis was detectable after 6 h. Analysis of downstream signalling molecules showed an increased activation of Akt, PLCγ and MAPK in response to calcium treatment. The activation of Akt and PLCγ was abolished by inhibition of HER1 with Gefitinib (5 μM), whereas this had no effect on the activity of MAPK. In addition, incubation with inhibitors of Akt and PLCγ significantly augmented calcium-induced apoptosis, whereas this was not seen with MAPK inhibition. Finally a significant increase in PKCδ activity was observed with calcium treatment alone and was augmented further with HER1 inhibition. In conclusion we show that calcium-induced apoptosis in bladder cancer cells is delayed by HER1 receptor activation involving the Akt and PLCγ signalling pathways.

Doxorubicinolone formation and efflux: a salvage pathway against epirubicin accumulation in human heart

Secondary alcohol metabolites and reactive oxygen species mediate cardiomyopathy induced by cumulative doses of antitumor anthracyclines, such as doxorubicin and epirubicin. Epirubicin exhibits a defective conversion to both toxic species, thereby inducing cardiotoxicity at doses higher than equiactive to doxorubicin; however, the gain in cardiac tolerability seems to be marginal compared with the magnitude of the metabolic defects of epirubicin. Cardiomyopathy may occur independent of toxic metabolites if a given anthracycline tends to accumulate in the heart; therefore, we characterized whether epirubicin showed an unusual accumulation in human myocardial strips incubated in plasma. Epirubicin exhibited a higher uptake and reached myocardial levels 2 times higher than those of doxorubicin. Epirubicin also showed a unique metabolization to doxorubicinolone, the product of epirubicin deglycosidation and carbonyl reduction. In diffusing from the strips to plasma, doxorubicinolone caused membrane permeation effects that augmented epirubicin elimination. Experiments with purified doxorubicinolone showed that the efflux of 1 mol doxorubicinolone promoted the concomitant elimination of as many as approximately 40 mol epirubicin. Doxorubicinolone could also diffuse from plasma back to the strips, causing a permeation effect that promoted epirubicin reuptake; however, this reverse process was slower and less potent. On balance, doxorubicinolone efflux diminished the epirubicin to doxorubicin accumulation ratio to approximately 1.5. These results suggest that the cardiac tolerability of epirubicin is limited by its accumulation in the heart and that such accumulation would be even higher in the absence of doxorubicinolone formation and efflux. These results may also serve guidelines for developing noncardiotoxic anthracyclines.

Fexofenadine brain exposure and the influence of blood-brain barrier P-glycoprotein after fexofenadine and terfenadine administration

P-glycoprotein (P-gp) plays an important role in determining net brain uptake of fexofenadine. Initial in vivo experiments with 24-h subcutaneous osmotic minipump administration demonstrated that fexofenadine brain penetration was 48-fold higher in mdr1a(-/-) mice than in mdr1a(+/+) mice. In contrast, the P-gp efflux ratio at the blood-brain barrier (BBB) for fexofenadine was only approximately 4 using an in situ brain perfusion technique. Pharmacokinetic modeling based on the experimental results indicated that the apparent fexofenadine P-gp efflux ratio is time-dependent due to low passive permeability at the BBB. Fexofenadine brain penetration after terfenadine administration was approximately 25- to 27-fold higher than after fexofenadine administration in both mdr1a(+/+) and mdr1a(-/-) mice, consistent with terfenadine metabolism to fexofenadine in murine brain tissue. The fexofenadine formation rate after terfenadine in situ brain perfusion was comparable with that in a 2-h brain tissue homogenate in vitro incubation. The fexofenadine formation rate increased approximately 5-fold during a 2-h brain tissue homogenate incubation with hydroxyl-terfenadine, suggesting that the hydroxylation of terfenadine is the rate-limiting step in fexofenadine formation. Moreover, regional brain metabolism seems to be an important factor in terfenadine brain disposition and, consequently, fexofenadine brain exposure. Taken together, these results indicate that the fexofenadine BBB P-gp efflux ratio has been underestimated previously due to the lack of complete equilibration of fexofenadine across the blood-brain interface under typical experimental paradigms.

Targeting phosphoinositide 3-kinase: moving towards therapy

Phosphoinositide 3-kinases (PI3K) orchestrate cell responses including mitogenic signaling, cell survival and growth, metabolic control, vesicular trafficking, degranulation, cytoskeletal rearrangement and migration. Deregulation of the PI3K pathway occurs by activating mutations in growth factor receptors or the PIK3CA locus coding for PI3Kalpha, by loss of function of the lipid phosphatase and tensin homolog deleted in chromosome ten (PTEN/MMAC/TEP1), by the up-regulation of protein kinase B (PKB/Akt), or the impairment of the tuberous sclerosis complex (TSC1/2). All these events are linked to growth and proliferation, and have thus prompted a significant interest in the pharmaceutical targeting of the PI3K pathway in cancer. Genetic targeting of PI3Kgamma (p110gamma) and PI3Kdelta (p110delta) in mice has underlined a central role of these PI3K isoforms in inflammation and allergy, as they modulate chemotaxis of leukocytes and degranulation in mast cells. Proof-of-concept molecules selective for PI3Kgamma have already successfully alleviated disease progress in murine models of rheumatoid arthritis and lupus erythematosus. As targeting PI3K moves forward to therapy of chronic, non-fatal disease, safety concerns for PI3K inhibitors increase. Many of the present inhibitor series interfere with target of rapamycin (TOR), DNA-dependent protein kinase (DNA-PK(cs)) and activity of the ataxia telangiectasia mutated gene product (ATM). Here we review the current disease-relevant knowledge for isoform-specific PI3K function in the above mentioned diseases, and review the progress of >400 recent patents covering pharmaceutical targeting of PI3K. Currently, several drugs targeting the PI3K pathway have entered clinical trials (phase I) for solid tumors and suppression of tissue damage after myocardial infarction (phases I,II).

Defective taxane stimulation of epirubicinol formation in the human heart: insight into the cardiac tolerability of epirubicin-taxane chemotherapies

The antitumor anthracycline doxorubicin induces a dose-related cardiotoxicity that correlates with the myocardial levels of its secondary alcohol metabolite doxorubicinol. Combining doxorubicin with taxanes such as paclitaxel or docetaxel may aggravate cardiotoxicity, presumably because the taxanes cause an allosteric-like stimulation of cytoplasmic aldehyde reductases that convert doxorubicin to doxorubicinol in the heart. A less severe aggravation of cardiotoxicity was observed on combining taxanes with epirubicin, a closely related analog of doxorubicin; therefore, we characterized whether the cardiac tolerability of epirubicin-taxane therapies could be due to a defective taxane stimulation of the conversion of epirubicin to its secondary alcohol metabolite epirubicinol. Comparisons between doxorubicin and epirubicin in isolated human heart cytosol showed that epirubicin exhibited a lower V(max)/K(m) value for reaction with aldehyde reductases and a defective stimulation of epirubicinol formation by paclitaxel or docetaxel. A similar pattern occurred in the soluble fraction of human myocardial strips incubated in plasma with anthracyclines and paclitaxel or docetaxel, formulated in their clinical vehicles Cremophor EL or polysorbate 80. Doxorubicin, but not epirubicin, was also able to generate reactive oxygen species in the membrane fraction of myocardial strips; however, the levels of doxorubicin-derived reactive oxygen species were not further augmented by paclitaxel. These results support the notion that taxanes might aggravate the cardiotoxicity of doxorubicin through a specific stimulation of doxorubicinol formation. The failure of paclitaxel or docetaxel to stimulate epirubicinol formation therefore uncovers an important determinant of the improved cardiac tolerability of epirubicin-taxane combinations.

Multiplicity of mammalian reductases for xenobiotic carbonyl compounds

A variety of carbonyl compounds are present in foods, environmental pollutants, and drugs. These xenobiotic carbonyl compounds are metabolized into the corresponding alcohols by many mammalian NAD(P)H-dependent reductases, which belong to the short-chain dehydrogenase/reductase (SDR) and aldo-keto reductase superfamilies. Recent genomic analysis, cDNA isolation and characterization of the recombinant enzymes suggested that, in humans, the six members of each of the two superfamilies, i.e., total of 12 enzymes, are involved in the reductive metabolism of xenobiotic carbonyl compounds. They comprise three types of carbonyl reductase, dehydrogenase/reductase (SDR family) member 4, 11beta-hydroxysteroid dehydrogenase type 1, L-xylulose reductase, two types of aflatoxin B1 aldehyde reductase, 20alpha-hydroxysteroid dehydrogenase, and three types of 3alpha-hydroxysteroid dehydrogenase. Accumulating data on the human enzymes provide new insights into their roles in cellular and molecular reactions including xenobiotic metabolism. On the other hand, mice and rats lack the gene for a protein corresponding to human 3alpha-hydroxysteroid dehydrogenase type 3, but instead possess additional five or six genes encoding proteins that are structurally related to human hydroxysteroid dehydrogenases. Characterization of the additional enzymes suggested their involvement in species-specific biological events and species differences in the metabolism of xenobiotic carbonyl compounds.

Chemistry and biology of wortmannin

Recent synthetic and biological studies of the viridin class of steroidal furans have revealed multiple opportunities for fundamental discoveries as well as advanced drug design. Wortmannin is a potent enzyme inhibitor that binds to the ATP site of important regulatory kinases such as PI-3 kinase and Polo-like kinase. The natural product shares a unique mechanism-based biological activation pathway with other viridins. Furthermore, while there have been several encouraging approaches toward the total synthesis of these compounds, there is still ample room for improvements in synthetic strategies and tactics, and the development of structurally simplified analogs that exert more specific biological effects and are devoid of toxicity issues that have thwarted the clinical development of the parent compounds.

Measurement of xenobiotic carbonyl reduction in human liver fractions

Carbonyl reducing enzymes are involved in the metabolism of endogenous as well as xenobiotic molecules. Enzymes that catalyze the reversible oxidoreduction of aldehyde and ketone moieties include alcohol dehydrogenases, aldo-keto reductases, quinone reductases, and short-chain dehydrogenases/reductases. These enzymes differ with respect to subcellular location, cofactor dependence, and susceptibility to chemical inhibitors. Thus, it is possible to assess the relative contributions of these enzyme systems in the hepatic metabolism of a particular xenobiotic through simple in vitro experiments with commercially available reagents. The approaches described in this unit assume the availability of analytical procedures for measuring the parent compound and metabolites, such as HPLC with radiochemical, UV, or MS detection. Thus, the purpose of this unit is to outline methods for the study of the enzymatic carbonyl reduction of a drug development candidate or other xenobiotic molecule of interest.