Project 2 (Goetz)

他莫昔芬（TAM）仍然是治疗雌激素受体阳性（ER+）乳腺癌的重要药物。我们已经证明，内氧芬是一种有效的代谢物，部分来自细胞色素P450 2D6 （CYP2D6）的代谢，对TAM的抗增殖作用至关重要。我们观察到CYP2D6活性降低与tam治疗的乳腺癌复发风险升高相关，因此我们将研究重点放在了endoxifen上，为这一建议提供了初步数据。在荷瘤动物中，endoxifen优于TAM。此外，我们的体外数据表明，内氧芬可以克服与人表皮生长因子受体2 （HER2）表达相关的TAM耐药，因为内氧芬不像TAM那样刺激ER/HER2串扰。我们将这些数据提交给NCI，他们决定继续进行endoxifen药物的开发，包括临床级盐酸endoxifen的生产和IND提交的临床前毒理学/药理学。我们的初步数据表明，以下问题需要解决：1)内毒素的代谢途径是什么，内毒素相关的毒性是否与TAM相似（如子宫刺激）？2) endoxifen的体内抗肿瘤活性是否与芳香酶抑制剂（Al's）相似或更高，endoxifen是否在TAM或Al's耐药的细胞中表现出抗肿瘤活性？3)在人类中，我们能否确定一个可耐受的内氧芬剂量及其毒性特征是什么？4)通过体内增殖（Ki-67）和生长因子信号传导的减少以及临床反应来评估，内氧芬的耐受剂量是否具有生物学相关性？针对这些问题，我们提出了以下目标。目的1：进一步表征内氧芬的药代动力学、代谢和毒理学特征；目的2：研究endoxifen在小鼠异种移植瘤模型中的抗肿瘤活性及其对细胞信号传导的影响，并与TAM和来曲唑进行比较，描述endoxifen在TAM和来曲唑耐药肿瘤中的抗肿瘤活性；目标3：开展endoxifen人体I期研究，以确定最大耐受剂量（MTD），并描述其毒性特征。在此确定之后，我们将招募更多的患者来探索两种不同剂量的endoxifen: a) MTD和b)与1pm稳态浓度相关的endoxifen剂量。在这些剂量下，我们将检查endoxifen对子宫厚度、潮热频率和严重程度的影响，并进行配对肿瘤活检，以确定endoxifen对生长因子信号传导和增殖中重要蛋白质的影响。

Tamoxifen (TAM) continues to be an important drug for the treatment of estrogen receptor positive (ER+) breast cancer. We have demonstrated that endoxifen, a potent metabolite resulting in part from Cytochrome P450 2D6 (CYP2D6) metabolism, is critical for TAM's antiproliferative effects. Our observation that reductions in CYP2D6 activity were associated with a higher risk of recurrence in TAM-treated breast cancer led us to focus our studies on endoxifen, providing the preliminary data for this proposal. In tumor bearing animals, endoxifen is superior to TAM. Furthermore, our in vitro data indicate that endoxifen can overcome TAM resistance associated with Human Epidermal growth factor Receptor 2 (HER2) expression because endoxifen does not stimulate ER/HER2 cross-talk as TAM does. We presented these data to NCI and they decided to proceed with endoxifen drug development, including production of clinical grade endoxifen hydrochloride and preclinical toxicology/pharmacology for IND submission. Our preliminary data indicate that the following questions should be addressed: 1) What are the metabolic pathways responsible for elimination of endoxifen, and are endoxifen-related toxicities similar to TAM (e.g. uterine stimulation)? 2) Does endoxifen have in vivo anti-tumor activity similar or greater than aromatase inhibitors (Al's) and does endoxifen exhibit anti-tumor activity in cells resistant to TAM or Al's? 3) In humans, can we identify a tolerable endoxifen dose and what is its toxicity profile? and, 4) Is this tolerable dose of endoxifen biologically relevant, as assessed by reductions in proliferation (Ki-67) and growth factor signaling in vivo, as well as clinical responses? To address these questions, we have proposed the following aims. Aim 1: to further characterize the pharmacokinetics, metabolism and toxicology of endoxifen; Aim 2: to study endoxifen antitumor activity and its effects on cell signaling in a murine xenograft model in comparison to TAM and letrozole and to describe the anti-tumor activity of endoxifen in TAM and letrozole resistant tumors; and Aim 3: to conduct a phase I study of endoxifen in humans to determine the maximum tolerated dose (MTD), and describe its toxicity profile. Following this determination, we will enroll additional patients to explore 2 different doses of endoxifen: a) the MTD and b) the endoxifen dose associated with steady state concentrations of 1 pM. At these doses, we will examine the impact of endoxifen on uterine thickness, frequency and severity of hot flashes, and perform paired tumor biopsies to determine endoxifen's effect on proteins important in growth factor signaling and proliferation.