Platelet activation in patients with colorectal cancer.

Aspirin may reduce the risk of colorectal neoplasia at doses similar to those recommended for the prevention of cardiovascular disease. Thus, we aimed to address whether enhanced platelet activation, as assessed by the measurement of the urinary excretion of 11-dehydro-TXB(2) (a major enzymatic metabolite of TXB(2)), occurs in patients with colorectal cancer. In 10 patients with colorectal cancer, the urinary excretion of 11-dehydro-TXB(2) was significantly higher than in 10 controls, matched for sex, age and cardiovascular risk factors [1001(205-5571) versus 409(113-984) pg/mg creatinine, respectively, median (range), P<0.05]. The administration of aspirin 50 mg daily for 5 consecutive days to colorectal cancer patients caused a cumulative inhibition of platelet cyclooxygenase (COX)-1 activity either ex vivo, as assessed by the measurement of serum TXB(2) levels, or in vivo, as assessed by urinary 11-dehydro-TXB(2) excretion. In conclusion, enhanced platelet activation occurs in colorectal cancer patients. Permanent inactivation of platelet COX-1 by low-dose aspirin might restore anti-tumor reactivity.

Clinical pharmacology of novel selective COX-2 inhibitors.

Novel coxibs (i.e. etoricoxib, valdecoxib, parecoxib and lumiracoxib) with enhanced biochemical cyclooxygenase (COX)-2 selectivity over that of rofecoxib and celecoxib have been recently developed. They have the potential advantage to spare COX-1 activity, thus reducing gastrointestinal toxicity, even when administered at high doses to improve efficacy. They are characterized by different pharmacodynamic and pharmacokinetics features. The higher biochemical selectivity of valdecoxib than celecoxib, evidenced in vitro, may be clinically relevant leading to an improved gastrointestinal safety. Interestingly, parecoxib, a pro-drug of valdecoxib, is the only injectable coxib. Etoricoxib shows only a slightly improved COX-2 selectivity than rofecoxib, a highly selective COX-2 inhibitor that has been reported to halve the incidence of serious gastrointestinal toxicity compared to nonselective nonsteroidal antiinflammatory drugs (NSAIDs). Lumiracoxib, the most selective COX-2 inhibitor in vitro, is the only acidic coxib. The hypothesis that this chemical property may lead to an increased and persistent drug accumulation in inflammatory sites and consequently to an improved clinical efficacy, however, remains to be verified. Several randomized clinical studies suggest that the novel coxibs have comparable efficacy to nonselective NSAIDs in the treatment of osteoarthritis, rheumatoid arthritis and acute pain, but they share similar renal side-effects. The apparent dose-dependence of renal toxicity may limit the use of higher doses of the novel coxibs for improved efficacy. Large-size randomized clinical trials are ongoing to define the gastrointestinal and cardiovascular safety of the novel coxibs.

Clinical pharmacology of selective COX-2 inhibitors.

The discovery of cyclooxygenase (COX)-2 has provided the rationale for the development of a new class of nonsteroidal antiinflammatory drugs (NSAIDs), the selective COX-2 inhibitors (denominated coxibs), with the aim of reducing the gastrointestinal (GI) toxicity associated with the administration of NSAIDs by virtue of COX-1 sparing. Rofecoxib and celecoxib are the first selective COX-2 inhibitors approved by the FDA and EMEA for the treatment of rheumatoid arthritis (RA), osteoarthritis (OA) and for relief of acute pain. Rofecoxib has been shown to spare COX-1 activity ex vivo, in platelets and gastric mucosa, when administered at therapeutic doses or above. In a large clinical trial, COX-2 inhibitors have been demonstrated to halve the incidence of serious upper GI events vs a nonselective NSAID. Recently, other selective COX-2 inhibitors with different COX-1/COX-2 selectivity and pharmacokinetic features have been developed, i.e. valdecoxib, parecoxib, etoricoxib and lumiracoxib. The improved biochemical selectivity of valdecoxib vs celecoxib in vitro (COX-1/COX-2 ratio: 60 vs 30, respectively) may be clinically relevant leading to an improved GI safety. Interestingly, parecoxib, a pro-drug of valdecoxib, is the only injectable coxib. Etoricoxib, showing only a slightly higher COX-2 selectivity than rofecoxib in vitro (COX-1/COX-2 ratio: 344 vs 272, respectively), has been reported to cause a similar specific COX-2 inhibition ex vivo that should translate into comparable GI safety. Lumiracoxib, the most selective COX-2 inhibitor in vitro (COX-1/COX-2 ratio: 400), is the only acidic coxib. It has been hypothesized that this pecular chemical feature may lead to an enhanced concentration in inflammatory sites that may translate into an improved clinical efficacy. The results of clinical trials have shown that coxibs have a comparable clinical efficacy and renal toxicity and an improved GI safety vs nonselective NSAIDs. Whether the different pharmacodynamic and pharmacokinetics features of the various coxibs will produce detectable differences in efficacy and toxicity remains to be evaluated in appropriate comparative randomized clinical studies.

The human pharmacology of monocyte cyclooxygenase 2 inhibition by cortisol and synthetic glucocorticoids.

BACKGROUND: We studied the concentration dependence of the inhibitory effects of cortisol, 6-methylprednisolone, and dexamethasone on cyclooxygenase-2 (COX-2) expression and activity in human monocytes in response to lipopolysaccharide (LPS) in vitro. Moreover, we characterized the time and dose dependence of the inhibitory effects of 6-methylprednisolone, administered to healthy subjects, on LPS-inducible prostaglandin E2 (PGE2) biosynthesis in whole blood ex vivo. METHODS: Heparinized whole-blood samples obtained from healthy subjects and patients with rheumatoid arthritis were incubated with LPS (10 microg/ml) for 24 hours at 37 degrees C, and PGE2 was measured in plasma as an index of monocyte COX-2 activity. Comparative experiments were performed in LPS-stimulated isolated monocytes. The levels of COX-2-like immunoreactivity in monocyte lysates were measured by a specific Western blot technique. PGE2 was evaluated by radioimmunoassay. RESULTS: Nanomolar concentrations of cortisol, 6-methylprednisolone, and dexamethasone suppressed LPS-induced PGE2 biosynthesis both in whole blood and in isolated monocytes in vitro with relative potencies similar to those reported for their anti-inflammatory effects in vivo. The administration of single oral doses (4, 8, or 16 mg) of 6-methylprednisolone caused a dose- and time-dependent inhibition of whole-blood COX-2 activity. Whole-blood samples obtained from patients with rheumatoid arthritis treated with comparable maintenance doses of glucocorticoids produced significantly lower levels of LPS-inducible PGE2 than were found in untreated patients. CONCLUSIONS: Therapeutic plasma levels of synthetic glucocorticoids down-regulate inducible prostanoid biosynthesis in circulating monocytes. This effect may represent a readily measurable surrogate marker of their clinical efficacy for dose-finding studies.