Biological considerations and clinical applications of new HER2-targeted agents

Over the past two decades, since the discovery of the human EGF receptor 2 (HER2) oncogene, the oncoprotein has become one of the best known and intensively studied tumor targets in oncology. In fact, laboratory findings were the basis for clinical proof-of-principle studies, whose results not only confirmed the relationship between gene amplification and an aggressive tumor phenotype but also demonstrated that the poor prognosis associated with receptor overexpression could be improved. Indeed, the success in treating patients with HER2-positive breast cancer extends to those with early as well as advanced disease. Nonetheless, not all tumors respond to treatment targeting the receptor; disease progression also occurs after initially responding to anti-HER2 therapy. This article focuses on the biology of HER2 and three novel agents currently in clinical trials that target HER2 beyond disease progression.     

YES1 activation induces acquired resistance to neratinib in HER2‐amplified breast and lung cancers

Molecular‐targeted therapies directed against human epidermal growth factor receptor 2 (HER2) are evolving for various cancers. Neratinib is an irreversible pan‐HER tyrosine kinase inhibitor and has been approved by the FDA as an effective drug for HER2‐positive breast cancer. However, acquired resistance of various cancers to molecular‐targeted drugs is an issue of clinical concern, and emergence of resistance to neratinib is also considered inevitable. In this study, we established various types of neratinib‐resistant cell lines from HER2‐amplified breast and lung cancer cell lines using several drug exposure conditions. We analyzed the mechanisms of emergence of the resistance in these cell lines and explored effective strategies to overcome the resistance. Our results revealed that amplification of YES1, which is a member of the SRC family, was amplified in two neratinib‐resistant breast cancer cell lines and one lung cancer cell line. Knockdown of YES1 by siRNA and pharmacological inhibition of YES1 by dasatinib restored the sensitivity of the YES1‐amplified cell lines to neratinib in vitro. Combined treatment with dasatinib and neratinib inhibited tumor growth in vivo. This combination also induced downregulation of signaling molecules such as HER2, AKT and MAPK. Our current results indicate that YES1 plays an important role in the emergence of resistance to HER2‐targeted drugs, and that dasatinib enables such acquired resistance to neratinib to be overcome.     

Pharmacokinetics of oral neratinib during co-administration of ketoconazole in healthy subjects

AIM

The primary objective was to evaluate the pharmacokinetics of a single dose of neratinib, a potent, low-molecular-weight, orally administered, irreversible pan-ErbB (ErbB-1, -2, -4) receptor tyrosine kinase inhibitor, during co-administration with ketoconazole, a potent CYP3A4 inhibitor.

METHODS

This was an open-label, randomized, two-period, crossover study. Fasting healthy adults received a single oral dose of neratinib 240 mg alone and with multiple oral doses of ketoconazole 400 mg. Blood samples were collected up to 72 h after each neratinib dose. Plasma concentration data were analyzed using a noncompartmental method. The least square geometric mean ratios [90% confidence interval (CI)] of C_max(neratinib+ketoconazole) : C_max(neratinib alone), and AUC(neratinib+ketoconazole) : AUC(neratinib alone) were assessed.

RESULTS

Twenty-four subjects were enrolled. Compared with neratinib administered alone, co-administration of ketoconazole increased neratinib C_max by 3.2-fold (90% CI: 2.4, 4.3) and AUC by 4.8-fold (3.6, 6.5). Median t_max was 6.0 h with both regimens. Ketoconazole decreased mean apparent oral clearance of neratinib from 346 l h⁻¹ to 87.1 l h⁻¹ and increased mean elimination half-life from 11.7 h to 18.0 h. The incidence of adverse events was comparable between the two regimens (50% neratinib alone, 65% co-administration with ketoconazole).

CONCLUSION

Co-administration of neratinib with ketoconazole, a potent CYP3A inhibitor, increased neratinib C_max by 3.2-fold and AUC by 4.8-fold compared with administration of neratinib alone. These results indicate that neratinib is a substrate of CYP3A and is susceptible to interaction with potent CYP3A inhibitors and, thus, dose adjustments may be needed if neratinib is administered with such compounds.     

Antitumor activity of pan‐HER inhibitors in HER2‐positive gastric cancer

Molecularly targeted therapy has enabled outstanding advances in cancer treatment. Whereas various anti‐human epidermal growth factor receptor 2 (HER2) drugs have been developed, trastuzumab is still the only anti‐HER2 drug presently available for gastric cancer. In this study, we propose novel treatment options for patients with HER2‐positive gastric cancer. First, we determined the molecular profiles of 12 gastric cancer cell lines, and examined the antitumor effect of the pan‐HER inhibitors afatinib and neratinib in those cell lines. Additionally, we analyzed HER2 alteration in 123 primary gastric cancers resected from Japanese patients to clarify possible candidates with the potential to respond to these drugs. In the drug sensitivity analysis, both afatinib and neratinib produced an antitumor effect in most of the HER2‐amplified cell lines. However, some cells were not sensitive to the drugs. When the molecular profiles of the cells were compared based on the drug sensitivities, we found that cancer cells with lower mRNA expression levels of IGFBP7, a tumor suppressor gene that inhibits the activation of insulin‐like growth factor‐1 receptor (IGF‐1R), were less sensitive to pan‐HER inhibitors. A combination therapy consisting of pan‐HER inhibitors and an IGF‐1R inhibitor, picropodophyllin, showed a notable synergistic effect. Among 123 clinical samples, we found 19 cases of HER2 amplification and three cases of oncogenic mutations. In conclusion, afatinib and neratinib are promising therapeutic options for the treatment of HER2‐amplified gastric cancer. In addition to HER2 amplification, IGFBP7 might be a biomarker of sensitivity to these drugs, and IGF‐1R‐targeting therapy can overcome drug insensitiveness in HER2‐amplified gastric cancer.     

Early clinical development of epidermal growth factor receptor targeted therapy in breast cancer

Introduction: Epidermal growth factor receptor (EGFR) targeted treatment has been evaluated but has not shown a clear clinical benefit for breast cancer. This review article aims to consider the knowledge of the biological background of EGFR pathways in dissecting clinical studies of EGFR targeted treatment in breast cancer.

Areas covered: This review focuses on the role of the EGFR pathway and the investigational drugs that target EGFR for breast cancer.

Expert opinion: Recent studies have indicated that EGFR targeted therapy for breast cancer has some promising effects for patients with triple-negative breast cancer, basal-like breast cancer, and inflammatory breast cancer. However, predictive and prognostic biomarkers for EGFR targeted therapy have not been identified. The overexpression or amplification of EGFR itself may not be the true factor of induction of the canonical pathway as an oncogenic driver of breast cancer. Instead, downstream, non-canonical pathways related to EGFR may contribute to some aspects of the biological behavior of breast cancer; therefore, the blockade of the receptor could result in sufficient suppression of downstream pathways to inhibit the aggressive behavior of breast cancer. Mechanistic studies to investigate the dynamic interaction between the EGFR pathway and non-canonical pathways are warranted.     

来那替尼对人乳腺癌细胞增殖、凋亡的影响及其作用机制

目的:探讨来那替尼对人乳腺癌细胞增殖、凋亡的影响及其作用机制。方法:以0,0.5,1和2 μmol·L^-1四种浓度的来那替尼处理人乳腺癌细胞BT474,MTT法检测其对细胞增殖的影响;流式细胞术检测其对细胞生长周期及凋亡的影响;蛋白免疫印迹法检测其对细胞凋亡信号通路相关蛋白的表达水平。结果:MTT实验结果表明来那替尼可显著抑制人乳腺癌细胞的增殖,2 μmol·L^-1来那替尼处理96 h后,其细胞存活率为31%;流式细胞分析结果表明来那替尼可将BT474细胞阻滞在G₀/G₁期,2 μmol·L^-1来那替尼阻滞效果最为明显,处于G₀/G₁期的细胞百分比为76%;来那替尼也可促进细胞凋亡,2 μmol·L^-1剂量时凋亡率为19.3%。蛋白免疫印迹结果表明来那替尼可减弱细胞内AKT、mTOR的磷酸化蛋白表达水平。结论:来那替尼可能通过抑制细胞内PI3K-AKT-mTOR信号通路促进乳腺癌细胞凋亡,为乳腺癌的治疗提供理论依据。     

The irreversible ERBB1/2/4 inhibitor neratinib interacts with the BCL-2 inhibitor venetoclax to kill mammary cancer cells

The irreversible ERBB1/2/4 inhibitor, neratinib, down-regulates the expression of ERBB1/2/4 as well as the levels of MCL-1 and BCL-XL. Venetoclax (ABT199) is a BCL-2 inhibitor. At physiologic concentrations neratinib interacted in a synergistic fashion with venetoclax to kill HER2 + and TNBC mammary carcinoma cells. This was associated with the drug-combination: reducing the expression and phosphorylation of ERBB1/2/3; in an eIF2α-dependent fashion reducing the expression of MCL-1 and BCL-XL and increasing the expression of Beclin1 and ATG5; and increasing the activity of the ATM-AMPKα-ULK1 S317 pathway which was causal in the formation of toxic autophagosomes. Although knock down of BAX or BAK reduced drug combination lethality, knock down of BAX and BAK did not prevent the drug combination from increasing autophagosome and autolysosome formation. Knock down of ATM, AMPKα, Beclin1 or over-expression of activated mTOR prevented the induction of autophagy and in parallel suppressed tumor cell killing. Knock down of ATM, AMPKα, Beclin1 or cathepsin B prevented the drug-induced activation of BAX and BAK whereas knock down of BID was only partially inhibitory. A 3-day transient exposure of established estrogen-independent HER2 + BT474 mammary tumors to neratinib or venetoclax did not significantly alter tumor growth whereas exposure to [neratinib + venetoclax] caused a significant 7-day suppression of growth by day 19. The drug combination neither altered animal body mass nor behavior. We conclude that venetoclax enhances neratinib lethality by facilitating toxic BH3 domain protein activation via autophagy which enhances the efficacy of neratinib to promote greater levels of cell killing.