Overcoming Drug Resistance in HER2-positive Breast Cancer

HER2是一种致癌受体酪氨酸激酶(RTK)。它在大约20%的乳腺癌(BC)中过度表达。 由于基因扩增，称为HER2阳性BC(HER2+BC)。有几种HER2抑制剂可用 临床应用，并显著改善疾病结局。然而，原发和获得性耐药 是很常见的。大多数晚期疾病患者在接受治疗一段时间后会出现疾病进展。 耐药性是HER2+BC的一大悬而未决的问题，我们的长期目标是找到解决方案 这个问题。在这个项目中，我们建议研究一种重组人蛋白，即PEPDG278D，用于 克服HER2+BC的耐药性。PEPDG278D是多肽酶D的酶失活突变体 (也称为Prolidase)。外源性PEPDG278D与HER2及其家族成员的结合 在过度表达RTK的癌细胞中，PEPDG278D干扰它们的信号单位，引导它们 用于溶酶体的降解，并在体外和体内抑制细胞的生长。PEPDG278D抑制HER2+ 在体外和体内对目前的HER2抑制剂具有耐药性的BC细胞。然而，PEPDG278D在 小鼠研究表明，在RTKs表达的正常组织中，HER2和EGFR几乎没有影响 非常低。缺乏HER2和EGFR的癌细胞对PEPDG278D也不敏感。的目标 1)确定PEPDG278D在HER2+中的治疗活性和作用机制 2)评估PEPDG278D的安全性，并了解PEPDG278D如何替代HER2和EGFR 正常细胞。中心假设是PEPDG278D特异性地针对HER2和EGFR，并且其独特的 结合模式使其能够强烈和选择性地靶向过度表达的HER2和EGFR，从而 抑制耐药的HER2+BC而不会产生毒性。这项提议的理由是完成 这项研究可能会推动PEPDG278D进入临床评估。我们提出了三个具体目标来测试 假设：1)阐明PEPDG278D的靶向性，2)评估其治疗活性和 作用机制，以及3)确定其靶向选择性以及如何在正常情况下避免HER2和EGFR 细胞。将使用创新的实验方法组合，包括但不限于等基因 携带临床证实的分子变化的细胞、细胞和肿瘤对当前的HER2具有抵抗力 抑制剂，原代正常人类细胞和人源化小鼠。这项拟议的研究意义重大，因为 它解决了HER2+BC的一个主要问题，即耐药性。这项工作的预期成果包括： 1)显示HER2和EGFR是PEPDG278D的唯一治疗靶点；2)显示PEPDG278D 抑制HER2+BC对现有HER2抑制剂的耐药性及其机制；3)显示 HER2仍然是耐药的HER2+BC的关键治疗靶点；以及4)显示PEPDG278D是 对正常细胞和组织无毒，并了解其分子基础。我们的发现将会有一个 重要的积极影响，因为它们将产生对PEPDG278D临床研究的强烈热情。

HER2 is an oncogenic receptor tyrosine kinase (RTK). It is overexpressed in about 20% breast cancer (BC) due to gene amplification, known as HER2-positive BC (HER2+ BC). Several HER2 inhibitors are available clinically and have significantly improved disease outcome. However, primary and acquired drug resistance is common. Most patients with advanced disease show disease progression after some time on treatment. Drug resistance is a major unresolved problem in HER2+ BC, and our long-term goal is to find a solution to this problem. In this project, we propose to investigate a recombinant human protein, i.e., PEPDG278D, for overcoming drug resistance in HER2+ BC. PEPDG278D is an enzymatically inactive mutant of peptidase D (also known as prolidase). Exogenously-administered PEPDG278D binds to HER2 and its family member EGFR, and in cancer cells overexpressing the RTKs, PEPDG278D disrupts their signaling units, directs them for lysosomal degradation, and inhibits the growth of the cells in vitro and in vivo. PEPDG278D inhibits HER2+ BC cells that are resistant to current HER2 inhibitors in vitro and in vivo. Yet, PEPDG278D is well tolerated in mouse studies and shows little effect on HER2 and EGFR in normal tissues where expression of the RTKs is very low. Cancer cells lacking HER2 and EGFR are insensitive to PEPDG278D as well. The objectives of this proposal are: 1) to determine the therapeutic activity and mechanism of action of PEPDG278D in HER2+ BC, and 2) to assess PEPDG278D safety and to understand how PEPDG278D spares HER2 and EGFR in normal cells. The central hypothesis is that PEPDG278D targets HER2 and EGFR specifically and its unique binding mode enables it to target overexpressed HER2 and EGFR strongly and selectively, thereby inhibiting drug-resistant HER2+ BC without causing toxicity. The rationale for the proposal is that completion of the research may propel PEPDG278D into clinical evaluation. We propose three specific aims to test the hypothesis: 1) to elucidate the target specificity of PEPDG278D, 2) to assess its therapeutic activity and mechanism of action, and 3) to determine its target selectivity and how it spares HER2 and EGFR in normal cells. An innovative combination of experimental methods will be used, including but not limited to isogenic cells, cells and tumors carrying clinically verified molecular changes that confer resistance to current HER2 inhibitors, primary normal human cells and humanized mice. The proposed research is significant, because it addresses a major problem in HER2+ BC, i.e., drug resistance. Expected outcome of this work includes: 1) showing that HER2 and EGFR are the sole therapeutic targets of PEPDG278D; 2) showing that PEPDG278D inhibits HER2+ BC resistant to current HER2 inhibitors and the underlying mechanisms; 3) showing that HER2 remains a critical therapeutic target in drug-resistant HER2+ BC; and 4) showing that PEPDG278D is non-toxic to normal cells and tissues and understanding the molecular basis. Our findings will have an important positive impact, because they will generate strong enthusiasm for clinical study of PEPDG278D.