Drug Evaluation: Oncologic, Endocrine & Metabolic: Docetaxel (Taxotere®): current status and clinical prospects

Combination of Docetaxel and Doxorubicin as First-Line Chemotherapy in Metastatic Breast Cancer

Docetaxel (Taxotere®) and doxorubicin have previously demonstrated a significant antitumor activity in patients with metastatic breast cancer. Furthermore, a lack of cross resistance and overlapping toxicities between the two agents have been reported. In a prospective study, docetaxel (80 mg/m2, 1-hr iv infusion) and doxorubicin (60 mg/m2, 1-hr iv infusion) were administered as first-line chemotherapy in metastatic breast cancer patients to evaluate the clinical efficacy and toxicity of the combination. Forty-three patients were enrolled in the study. The median age was 47 years (range, 30-69). The docetaxel-doxorubicin combination was applied with 3-week intervals until progression. Complete response was achieved in 9 (21.4%) of 42 assessable patients and partial response in 24 (57.2%) patients, for an overall response rate of 78.6%. Median response duration was 8 months (3-18 months). Nausea and vomiting (76%), alopecia (64%), neutropenia (35.7%) and mucositis (33%) were the major side effects of the combination. There was one case of cardiac toxicity. In conclusion, the docetaxel-doxorubicin protocol can be considered as an active regimen for the treatment of patients with metastatic breast cancer with acceptable toxicity and a fairly high response rate.

Phosphatidylcholine-derived phosphatidic acid and diacylglycerol are involved in the signaling pathways activated by docetaxel

Taxanes are known to activate several cellular signals including mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-kappa B), tyrosine phosphorylation of Shc, and serine phosphorylation of Bcl-2. However, the mediators of these signaling pathways are unknown. Using U937 leukemic cells, we evaluated the effect of docetaxel on phosphatidylcholine (PC) and its metabolites, phosphatidic acid (PA) and diacylglycerol (DAG), and their impact on MAPK and NF-kappa B activation, as well as on Raf-1 and Bcl-2 phosphorylation. Metabolic labeling studies showed that docetaxel (10 nM) induced two waves of PA production (130-140%), which were detected at 1 and 10 min. Docetaxel also stimulated DAG production (130%), which followed the first PA wave. The initial PA burst was due to phospholipase D (PLD)-mediated PC hydrolysis. Subsequent DAG production was inhibited by the phosphatidate phosphohydrolase (PAP) inhibitor, propranolol. R59949, a DAG kinase inhibitor, increased DAG accumulation and blocked the second PA wave. These results suggest that docetaxel triggers a metabolic cascade consisting in PLD-mediated PC hydrolysis, PA release, PAP-dependent DAG production, and DAG kinase stimulation, leading to DAG conversion back to PA. Neither R59949 nor propranolol influenced docetaxel-induced Raf-1/ERK activation. However, R59949 abrogated both NF-kappa B activation and Bcl-2 phosphorylation, suggesting that DAG and/or DAG-derived PA contribute in regulating these events.