Department of Pharmacology and Therapeutics, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA.
Department of Pharmacology and Toxicology, and Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA, 23298, USA.
J Exp Clin Cancer Res. 2022 Jun 2;41(1):184. doi: 10.1186/s13046-022-02389-z.
Epidermal growth factor receptor (EGFR) inhibitors, including cetuximab and panitumumab, are valuable therapeutics for colorectal cancer (CRC), but resistance to these inhibitors is common. The reason for such resistance is not well understood, which hampers development of better therapeutic strategies. Although activating mutations in KRAS, BRAF and PIK3CA are considered major drivers of CRC resistance to EGFR inhibitors, therapeutic targeting of these drug resistance drivers has not produced substantial clinical benefit.
We exploited cell lines and mouse tumor models (cell line xenografts and patient derived xenografts) for experiments of genetic and pharmacologic depletion of EGFR and/or its family member HER2, including EGFR mutants, inhibition of EGFR ligand shedding, and biochemical analysis of signaling proteins, to delineate the mechanism of CRC resistance to EGFR inhibitors and to assess the therapeutic activity of PEPD, which is a recombinant human protein that induces the degradation of both EGFR and HER2.
The sensitivity of CRC cells to cetuximab and panitumumab correlates with the ability of these drugs to induce EGFR downregulation. PEPD strongly inhibits oncogenic signaling and growth of CRC cells by causing profound depletion of EGFR and HER2, regardless of activating mutations of KRAS, BRAF and PIK3CA. siRNA knockdown of EGFR or HER2 also inhibits CRC cells resistant to EGFR inhibitors. Tumors harboring mutated KRAS, BRAF and/or PIK3CA also overexpress EGFR ligands, further suggesting that EGFR signaling remains important to the tumors. While excessive tumor-generated high-affinity EGFR ligands block target engagement by PEPD, aderbasib, an inhibitor of ADAM10 and ADAM17, enables PEPD to exert strong antitumor activity by inhibiting ligand shedding. Moreover, adding fluorouracil, which is commonly used in CRC treatment, to the combination of PEPD and aderbasib further enhances tumor inhibition.
Our study shows that CRC resistance to EGFR inhibitors results primarily from the inability of the inhibitors to downregulate their target and that a PEPD-based combination treatment overcomes the resistance.
表皮生长因子受体（EGFR）抑制剂，包括西妥昔单抗和帕尼单抗，是结直肠癌（CRC）的有效治疗方法，但对这些抑制剂的耐药性很常见。这种耐药性的原因尚不清楚，这阻碍了更好的治疗策略的发展。尽管 KRAS、BRAF 和 PIK3CA 的激活突变被认为是 CRC 对 EGFR 抑制剂耐药的主要驱动因素，但针对这些耐药驱动因素的治疗靶向并没有产生实质性的临床获益。
我们利用细胞系和小鼠肿瘤模型（细胞系异种移植和患者来源的异种移植）进行基因和药理学敲除 EGFR 和/或其家族成员 HER2 的实验，包括 EGFR 突变体、EGFR 配体脱落的抑制以及信号蛋白的生化分析，以描绘 CRC 对 EGFR 抑制剂耐药的机制，并评估 PEPD 的治疗活性，PEPD 是一种重组人蛋白，可诱导 EGFR 和 HER2 的降解。
CRC 细胞对西妥昔单抗和帕尼单抗的敏感性与这些药物诱导 EGFR 下调的能力相关。PEPD 通过强烈耗尽 EGFR 和 HER2，强烈抑制 CRC 细胞的致癌信号和生长，无论 KRAS、BRAF 和 PIK3CA 是否存在激活突变。EGFR 或 HER2 的 siRNA 敲低也抑制对 EGFR 抑制剂耐药的 CRC 细胞。携带突变型 KRAS、BRAF 和/或 PIK3CA 的肿瘤也过度表达 EGFR 配体，进一步表明 EGFR 信号仍然对肿瘤很重要。虽然肿瘤产生的高亲和力 EGFR 配体阻止了 PEPD 的靶标结合，但 ADAM10 和 ADAM17 的抑制剂 aderbasib 可通过抑制配体脱落使 PEPD 发挥强大的抗肿瘤活性。此外，将氟尿嘧啶（CRC 治疗中常用的药物）添加到 PEPD 和 aderbasib 的联合治疗中，进一步增强了肿瘤抑制作用。
我们的研究表明，CRC 对 EGFR 抑制剂的耐药性主要源于抑制剂不能下调其靶标，而基于 PEPD 的联合治疗克服了耐药性。
