Drug Resistance in Lung Cancer

描述（由申请人提供）：表皮生长因子受体（EGFR）酪氨酸激酶抑制剂（TKIs）吉非替尼和厄洛替尼是治疗表皮生长因子受体（EGFR）体细胞激活突变的非小细胞肺癌（NSCLC）的有效药物。然而，所有最初出现显著临床反应的患者在接受吉非替尼或厄洛替尼治疗时，最终会发展为肺癌的进行性生长。已经确定了两种已知的获得性（或继发性）耐药机制。其中包括50%的患者发生EGFR本身的继发性突变（EGFR T790M）， 20%的患者发生MET癌基因扩增。包括不可逆EGFR抑制剂和EGFR/MET抑制剂联合治疗以克服这些继发性耐药机制的治疗策略已经在临床前进行了评估，目前正在进入临床开发阶段。然而，关于耐药性发展的几个基本问题仍未得到解答。首先，特异性吉非替尼耐药克隆是否预先存在并因此在治疗过程中被选择，或者它们是否在吉非替尼治疗过程中出现？其次，虽然第二代激酶抑制剂可能具有治疗益处，但完全可以预期对这些药物也会产生耐药性（第三次耐药性）。我们利用EGFR突变的非小细胞肺癌细胞系在体外模拟了对EGFR激酶抑制剂的耐药性。重要的是，这些对吉非替尼耐药的EGFR突变NSCLC细胞系与临床产生吉非替尼或厄洛替尼耐药的EGFR突变NSCLC患者的肿瘤产生相同的耐药机制，我们已经使用这种体外模型系统来确定以前未被怀疑的吉非替尼耐药新机制（MET扩增）。因此，这些细胞系提供了一个强大的体外系统，用于研究吉非替尼耐药的起源，并确定第二代治疗是否可能改变或延迟吉非替尼耐药的发生。此外，它们可用于进一步确定对不可逆EGFR抑制剂和/或对EGFR/MET抑制剂联合的三级耐药机制。细胞系模型的发现将用于检查EGFR突变患者的肿瘤标本，这些患者正在接受吉非替尼、厄洛替尼或第二代激酶抑制剂的临床试验。这些研究将通过以下具体目的完成：目的1：确定吉非替尼耐药克隆是否预先存在或在药物治疗期间从头产生。目的2：确定治疗药物如何中和已知的吉非替尼耐药机制影响耐药性的出现。目的3：确定EGFR突变体NSCLC的三级耐药机制。临床前研究可能会为EGFR突变NSCLC患者带来新的治疗模式，这将有望使EGFR靶向治疗的获益时间比目前所能达到的更长。表皮生长因子受体（EGFR）酪氨酸激酶抑制剂（TKIs）吉非替尼和厄洛替尼是治疗表皮生长因子受体基因改变（突变）肺癌患者亚群的有效疗法。不幸的是，所有患者最终都会对这些药物产生耐药性。然而，针对特定吉非替尼耐药机制的第二代治疗药物已经开发出来。本提案的目的是研究体外耐药机制，并利用EGFR突变肺癌患者的肿瘤。公共卫生相关性：概述的研究将侧重于吉非替尼/厄洛替尼耐药的基本机制，制定最有效的策略来延迟或防止吉非替尼/厄洛替尼耐药的出现，以及确定对第二代治疗剂的耐药机制。这些研究的结果有望带来新的治疗方法，使EGFR靶向治疗的获益持续时间比目前所能达到的更长。本研究结果将对EGFR突变型非小细胞肺癌的治疗产生重大影响。

DESCRIPTION (provided by applicant): The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib are effective therapeutic agents for patients with non-small cell lung cancer (NSCLC) whose tumors harbor somatic activating mutations in EGFR. However, all patients who initially develop dramatic clinical responses will ultimately develop progressive growth of their lung cancer while being treated with gefitinib or erlotinib. Two known mechanisms of acquired (or secondary) resistance have been identified. These include a secondary mutation in EGFR itself (EGFR T790M) occurring in 50% of patients and amplification of the MET oncogene in 20% of patients. Therapeutic strategies including irreversible EGFR inhibitors and the combination of EGFR/MET inhibitors to overcome these secondary resistance mechanisms have been evaluated pre-clinically and are now entering clinical development. However, several fundamental questions regarding the development of resistance remain unanswered. First, do specific gefitinib resistant clones pre-exist and are thus selected for during the course of therapy or do they arise during the course of gefitinib treatment? Second, while second generation kinase inhibitors are likely to have a therapeutic benefit, it is fully anticipated that resistance (tertiary resistance) will also develop to these agents. We have modeled resistance to EGFR kinase inhibitors in vitro using EGFR mutant NSCLC cell lines. Importantly, these gefitinib resistant EGFR mutant NSCLC cell lines develop the same mechanisms of resistance as do tumors from NSCLC patients with EGFR mutations who clinically develop gefitinib or erlotinib resistance and we have used this in vitro model system to identify a previously unsuspected novel mechanism of gefitinib resistance (MET amplification). Thus these cell lines provide a powerful in vitro system in which to study the origins of gefitinib resistance and to determine whether second generation therapies might alter or delay the onset of gefitinib resistance. In addition, they can be used to further determine the mechanisms of tertiary resistance to irreversible EGFR inhibitors and/or to the combination of EGFR/MET inhibitors. Findings from the cell line models will then be used to examine tumor specimens from patients with EGFR mutations who are being treated in clinical trials with gefitinib, erlotinib or second generation kinase inhibitors. These studies will be accomplished through the following specific aims: Aim 1: To determine whether gefitinib resistant clones pre-exist or arise de novo during drug treatment. Aim 2: To determine how therapeutic agents that neutralize known gefitinib resistance mechanisms impact the emergence of drug resistance. Aim 3: To determine mechanisms of tertiary drug resistance in EGFR mutant NSCLC. The pre-clinical studies will likely lead to new treatment paradigms for patients with EGFR mutant NSCLC which will hopefully be associated with an even longer duration of benefit from EGFR targeted therapy than currently achievable. Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib are effective therapies for subsets of lung cancer patients whose cancers harbor genetic alterations (mutations) in EGFR. Unfortunately, all patients ultimately develop resistance to these drugs. However, second generation therapeutic agents have been developed against specific gefitinib resistance mechanisms. The goal of this proposal is to study drug resistance mechanisms in vitro and using tumors from lung cancer patients with EGFR mutations. PUBLIC HEALTH RELEVANCE: The outlined studies will focus on fundamental mechanisms of gefitinib/erlotinib resistance, on developing the most effective strategy to delay or prevent the emergence of gefitinib/erlotinib resistance and on identifying the mechanisms of resistance to second generation therapeutic agents. The findings from these studies will hopefully lead to treatment approaches that will be associated with an even longer duration of benefit from EGFR targeted therapy than currently achievable. Together findings from this proposal will have major impact in the treatment of EGFR mutant NSCLC.