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Endoxifen is an active metabolite of tamoxifen, a drug used in the treatment of breast cancer. In order to be clinically effective, tamoxifen must be converted to endoxifen by cytochrome P450 2D6 (CYP2D6). A study involving single escalating oral doses was conducted in humans to evaluate the safety, tolerability, and pharmacokinetics (PK) of endoxifen. This is the first study demonstrating that single oral doses of endoxifen are safe and well tolerated and have sufficient bioavailability to reach systemically effective levels in human subjects. Furthermore, it was found that endoxifen is rapidly absorbed and systemically available and that it displays dose proportionality in peak drug concentrations in plasma (C(max)) and area under the concentration-time curve extrapolated from 0 to ∞ (AUC(0-∞)) over the dose range 0.5-4.0 mg.

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Purpose: Raf proteins are key elements of growth-related cellular signaling pathways and are a component of cancer cell resistance to radiation therapy. Antisense oligonucleotides to c-raf-1 permit highly selective inhibition of the gene product and offer a strategy for sensitizing cancer cells to radiation therapy. In this dose escalation study, we evaluated the safety of combined liposomal formulation of raf antisense oligonucleotide (LErafAON) and radiation therapy in patients with advanced malignancies. Experimental Design: Patients with advanced solid tumors were treated with LErafAON in a phase I dose escalation study while receiving palliative radiation therapy. Drug-related and radiation-related toxicities were monitored. Pharmacokinetics and expression of c-raf-1 mRNA and Raf-1protein were determined in peripheral blood mononuclear cells. Results: Seventeen patients with palliative indications for radiation therapy were entered into this study. Thirteen patients received daily infusions of LErafAON and four received twice-weekly infusions. Radiation therapy was delivered in daily 300-cGy fractions over 2 weeks. Patients tolerated radiation, and no unexpected radiation-related side effects were observed. Drug-related reactions (grade z2), such as back pain, chills, dyspnea, fatigue, fever, flushing, and hypertension, were observed in most patients and were managed by premedication with corticosteroids and antihistamines. Serious adverse events occurred in five patients, including acute infusion-related symptoms, abnormal liver function tests, hypoxia, dehydration, diarrhea, esophagitis, fever, hypokalemia, pharyngitis, and tachypnea.Twelve of17 patients were evaluable for tumor response at completion of treatment; four showed partial response, four showed stable disease, and four experienced progressive disease. The intact rafAON was detected in plasma for 30 minutes to several hours. Six patients with partial response or stable disease were evaluable for c-raf-1 mRNA and/or Raf-1protein expression. Inhibition of c-raf-1mRNA was observed in three of five patients. Raf-1protein was inhibited in four of five patients. Conclusion: This is the first report of the combined modality treatment using antisense oligonucleotides with radiation therapy in patients with advanced cancer. A dose of 2.0 mg/kg of LErafAON administered twice weekly is tolerated with premedication and does not enhance radiation toxicity in patients. The observation of dose-dependent, infusion-related reactions has led to further modification of the liposomal composition for use in future clinical trials.