Mohamadi A. Sarkar

2‐Methoxyestradiol, a Promising Anticancer Agent

Estrogens occurring naturally in the body are metabolized to catecholestrogens (2‐ and 4‐hydroxyestradiol) by the cytochrome P450 enzymes. 2‐Hydroxy catecholestrogens are further metabolized by catechol‐O‐methyltransferase to 2‐methoxyestradiol, which is known to be protective against tumor formation. 2‐Methoxyestradiol exhibits potent apoptotic activity against rapidly growing tumor cells. It also possesses antiangiogenic activity through a direct apoptotic effect on endothelial cells. Other molecular mechanisms, including microtubule stabilization by inhibition of the colchicine‐binding site, have been reported. The exact mechanism of action of 2‐methoxyestradiol is still unclear, but it has been shown to be effective in preventing tumor growth in a variety of cell lines. 2‐Methoxyestradiol also possesses cardioprotective activity by inhibiting vascular smooth muscle cell growth in arteries. It has a lower binding affinity for estrogen receptor α compared with that of estradiol, and its affinity for estrogen receptor β is even lower than that of estrogen receptor α, thus it has minimal estrogenic activity. 2‐Methoxyestradiol is distinct because of its inability to engage estrogen receptors as an agonist, and its unique antiproliferative and apoptotic activities are mediated independently of estrogen receptors α and β. A phase I clinical trial of 2‐methoxyestradiol 200, 400, 600, 800, and 1000 mg/day in 15 patients with breast cancer showed significant reduction in bone pain and analgesic intake in some patients, with no significant adverse effects. Another phase I study of 2‐methoxyestradiol 200–1000 mg/day in combination with docetaxel 35 mg/m2/week for 4–6 weeks performed in 15 patients with advanced refractory metastatic breast cancer showed no serious drug‐related adverse effects. A phase II randomized, double‐blind trial of 2‐methoxyestradiol 400 and 1200 mg/day in 33 patients with hormone‐refractory prostate cancer showed that it was well tolerated and showed prostate specific antigen stabilizations and declines. We have started a phase I clinical trial to explore dosages greater than 1000 mg/day.

Drug Metabolism in the Nasal Mucosa

Nasal delivery is a potential alternative for systemic availability of drugs restricted to intravenous administration, such as peptide and protein drugs. Although nasal delivery avoids the hepatic first-pass effect, the enzymatic barrier of the nasal mucosa creates a pseudo-first-pass effect. The xenobiotic metabolic activity in the nasal epithelium has been investigated in several species including humans. The Phase I, cytochrome P-450 enzymes have been studied extensively for their toxicological significance, since these enzymes metabolize inhaled pollutants into reactive metabolites which may induce nasal tumors. The cytochrome P-450 activity in the olfactory region of the nasal epithelium is higher even than in the liver, mainly because of a three- to fourfold higher NADPH–cytochrome P-450 reductase content. Phase II activity has also been found in the nasal epithelium. The delivery of peptides and proteins has been hindered by the peptidase and protease activity in the nasal mucosa. The predominant enzyme appears to be aminopeptidase among other exopeptidases and endopeptidases. The absorption of peptide drugs can be improved by using aminoboronic acid derivatives, amastatin, and other enzyme inhibitors as absorption enhancers. It is possible that some of the surfactants, e.g., bile salts, increase absorption by inhibiting the proteolytic enzymes. Thus, in addition to the permeation barriers, there also exists an enzymatic barrier to nasal drug delivery, which is created by metabolic enzymes in the nasal epithelium.

Regiospecific expression of cytochrome P4501A1 and 1B1 in human uterine tissue

The goal of this study was to investigate the expression of these isoforms in different regions of the human uterus. Expression was determined in the endometrium (ENDO), endocervix (CERV) and squamous region (SR) from six non-smoking women by using RT-PCR. The transcripts encoding for CYP1A1 were significantly higher (P < 0.05) in the SR compared to the other areas. However, the expression of CYP1B1 was significantly higher (P < 0.05) in the ENDO. CYP1B1 expression appeared to be extremely low in a woman in the secretory stage of the menstrual phase, relative to the ENDO of the other patients who were all in the proliferative stage at hysterectomy. CYP1B1 mRNA was expressed in only two out of six patients in the SR and in three out of five patients in the CERV. CYP1A1 was also uniformly expressed in the ENDO of all except one patient, whereas expression was minimal in the other regions. It is likely that variability in the expression of these isoforms may be responsible for the differential susceptibility to cancer in women.

EFFECT OF CHRONIC RENAL INSUFFICIENCY ON HEPATIC AND RENAL UDP- GLUCURONYLTRANSFERASES IN RATS

Significant evidence exists regarding altered CYP450 enzymes in chronic renal insufficiency (CRI), although none exists for the phase II enzymes. The objective of this study was to investigate the effect of CRI on hepatic and renal UDP-glucuronyltransferase (UGT) enzymes. Three groups of rats were included: CRI induced by the 5/6th nephrectomy model, control, and control pair-fed (CPF) rats. UGT activities were determined in liver and kidney microsomes by the 3- and 17-glucuronidation of β-estradiol (E2-3G and E2-17G), glucuronidation of 4-methylumbelliferone (4-MUG), and 3-glucuronidation of morphine (M3G). UGT isoforms responsible for these catalytic activities were screened using recombinant rat UGT1A1, UGT1A2, UGT1A3, UGT1A7, UGT2B2, UGT2B3, and UGT2B8. UGT protein levels were examined by Western blot analysis using polyclonal antibodies. There was no significant difference between CRI and CPF rats in hepatic and/or renal E2-3G (UGT1A1), E2-17G (UGT2B3), 4-MUG (UGT1A6), and M3G (UGT2B1) formation. Formation of E2-17G and 4-MUG in the liver and E2-3G and 4-MUG in the kidney was significantly reduced (p < 0.05) in CPF and CRI rats compared with control rats. The down-regulated glucuronidation activities were accompanied by corresponding reductions in protein content of specific UGT isoforms. These results suggest that CRI does not seem to influence the protein levels or catalytic activity of most of the major hepatic or renal UGT enzymes. The observed down-regulation of hepatic and renal UGTs in CRI and CPF rats could be caused by restricted food intake in these groups of rats.

Quercetin not only inhibits P-glycoprotein efflux activity but also inhibits CYP3A isozymes

I have found the paper by Scambia et al. [1] describing the effect of quercetin, a plant-derived flavonoid, on the reversal of the multidrug resistance type 1 (MDR1)-associated Adriamycin resistance in MCF-7 human breast-cancer cell lines to be very interesting. The authors have shown that quercetin and other flavonoid derivatives inhibit P-glycoprotein (Pgp) pump-effiux activity in a dose-dependent manner. Moreover, 10 mM of quercetin appears to reduce the expression of immunoreactive Pgp in MCF-7 Adriamycin-resistant (AdrR) cells. These results indicate that quercetin may be capable of reversing MDR and synergizing the inhibitory activity of Adriamycin on the growth of MCF-7 AdrR cells. The authors conclude by stating that quercetin and related flavonoids may have therapeutic application in cancer therapy, particularly when used in combination with other conventional cytotoxic drugs. However, I would like to caution the anthors and others considering the use of quercetin and other flavonoids for such therapeutic applications. Flavonoids have been well established as inhibitors of a very important class of cytochrome P-450 isozymes, the CYP3A subfamily (the CYP450 are phase I oxidative enzymes found mainly in the liver). The CYP3A isozymes not only are abundant in the liver but are also expressed at significant levels in the gastrointestinal mucosa [2]. The CYP3A family of enzymes account for up to 25% of the total hepatic CYP450 and mediate the metabolism of a large variety of compounds, including cyclosporin A, erythromycin, lidocaine, quinidine, midazolam, triazolam, lovastatin, and tamoxifen. Grapefruit juice, which contains several flavonoids, of which naringin is the most common one, has been reported to increase significantly the bioavailability of nifedipine [3], felodipine [4], nitrendipine [5], and other dihydropyridine calcium channel antagonists. Enhanced hemodynamic and adverse experiences have been observed in patients with borderline hypertension for some of these agents [3]. This interaction appears to occur due to inhibition of presystemic metabolism and subsequent metabolic steps in the liver. Therefore, inhibition of these isozymes by the flavonoids is probably the reason for the > 3-fold increase in the peak serum concentration and the (Cmax) 2-fold increase in the area under the plasma concentration-time curve (AUC) reported for nisoldipine [6] and other dihydropyridines. In mechanistic in vitro studies with human liver microsomes, quercetin has been shown to be the most potent inhibitor of nifedipine and felodipine metabolism [7]. A 50-gmol/1 concentration of quercetin inhibited approximately 70% of felodipine and 50% of nifedipine metabolism. Most importantly, if therapeutic application of quercetin is considered, it would be given with cytotoxic agents, e. g., vinca alkaloids, etoposide, and teniposide, for tumors that are nonresponsive to these drugs. However, it has been reported that these cytotoxic agents could be metabolised by the CYP3A isozymes [8]. Therefore, it is possible that coadministration of quercetin (the most potent inhibitor of CYP3A isozymes) could inhibit the metabolism of these agents, thereby augmenting the hematologic toxicity due to accumulation of the parent compound. Although the clinical significance of the inhibitory effects of quercetin have not been fully elucidated, it is clear that quercetin and other flavonoids should be used judiciously. Significant potential exists for drug interactions due to coadministration of quercetin with other drugs, such as dihydropyridines, that are metabolized by the CYP3A isozymes. Furthermore, inhibition of the CYP3A isozymes may also interfere with the metabolism of cytotoxic agents, the effect of which quercetin is supposed to enhance due to reversal of Pgp efflux.

Pharmacodynamic profile of prolonged etoposide administration in patients with small cell lung cancer and non-Hodgkin's lymphoma.

Study Objective. To determine whether therapeutic drug monitoring can enhance administration of etoposide in patients with drug‐responsive neoplasms.

Pharmacodynamic and Pharmacokinetic Comparisons to Evaluate Bioequtvalence of Atenolol

AbstractFor some drugs, particularly chiral compounds, differential potencies of the enantiomers may lead to variable pharmacologic effects which cannot be identified just by comparing pharmacokinetics of the racemic mixture. Therefore true “bioequivalence” may be established by measuring pharmacologic response along with the pharmacokinetics. Atenolol was used as a model compound because only (S)-atenolol contributes to the β-blocking effect. Bioequivalency of atenolol, was studied in 31 healthy volunteers as a randomized, two treatment single dose crossover study. Following oral administration of Mylan (Trt A) and Reference (Trt B) atenolol tablets (100mg), 15 serial blood samples were drawn up to 24 hours, including a predose sample and plasma atenolol was analyzed by HPLC. Resting Systolic (SBP) and Diastolic (DBP) blood pressures and heart rates (HR) were measured at each blood sampling time. The Cpeak, Tpeak, AUC(0-tlast), AUC(O-inf), Kel and half-life were not statistically different and within 80%...

Glutathione S-transferase π-isoform is not altered in bladder tissue from smokers

Glutathione S-transferase π (GSTπ)-isoform is a cytosolic enzyme involved in the detoxification of reactive metabolites generated from environmental pollutants and cigarette smoke. Although cigarette smoking has been implicated in the etiology of bladder cancer, no information yet exists regarding GSTπ in smokers and nonsmokers. This study was carried out to evaluate the immunohistochemical localization and to measure levels of immunoreactive GSTπ in bladder tissue from smokers and nonsmokers. Tissues from patients diagnosed with transitional cell carcinoma (TCC) were obtained from paraffin embedded blocks fixed in formalin. Bladder tissues from smokers (n = 7) and nonsmokers (n = 8), and histologically confirmed cancerous and noncancerous areas of the same patients (n = 10) were studied. The immunoreactive GSTπ was quantified by calculating its optical density with a computerized Olympus BH-2 microscope connected to a DAGE camera. Immunohistochemical staining for GSTπ appeared to be evenly distributed in the cytosol of the transitional epithelium (TE) of the noncancerous regions. In the TE from patients with advanced TCC, the staining intensity appeared to be stronger in the nuclei relative to cytoplasm, an effect that was even more pronounced in poorly differentiated cancers and in cancers with squamoid features. The immunoreactive levels of GSTπ in the superficial TE cells was approximately 1.7-fold higher compared with the rest of the TE layer (p < 0.05) in smokers and nonsmokers. No significant differences (p > 0.05) were observed between smokers and nonsmokers in either of these regions. The higher concentration of GSTπ in the TE is suggestive of the protective role of this enzyme, serving to prevent any potentially harmful xenobiotics from entering the bladder tissue. The lack of differences in the detoxifying enzymes between smokers and nonsmokers suggests that the increased susceptibility of bladder cancer in smokers is probably mediated by other mechanisms.