Afatinib in the treatment of head and neck squamous cell carcinoma

Tumor Microenvironment Modifications Induced by Afatinib in Squamous Cell Carcinoma of the Head and Neck: A Window-of-Opportunity Study (EORTC-90111-24111)

PURPOSE

The EORTC-90111-24111 phase II window study evaluated afatinib versus no preoperative treatment in patients with primary squamous cell carcinoma of the head and neck (HNSCC). We investigated afatinib-induced tumor and microenvironment modifications by comparing pre- and posttreatment tumor biopsies.

PATIENTS AND METHODS

Thirty treatment-naïve patients with primary HNSCC were randomized. Twenty-five patients received afatinib for 14 days before surgery (40 mg 1×/day) and 5 patients were attributed to the control arm. Biopsies were taken at work-up and during surgery. Good quality RNA samples were used for omics analyses. The control arm was enlarged by samples coming from our previous similar window study.

RESULTS

IHC analyses of afatinib-treated tumor biopsies showed a decrease in pEGFR (P ≤ 0.05) and pERK (P ≤ 0.05); and an increase in CD3+ (P ≤ 0.01) and CD8+ (P ≤ 0.01) T-cell infiltration, and in CD3+ (P ≤ 0.05) T-cell density. RNA sequencing analyses of afatinib-treated tumor samples showed upregulation of inflammatory genes and increased expression scores of signatures predictive of response to programmed cell death protein 1 blockade (P ≤ 0.05). In posttreatment biopsies of afatinib-treated patients, two clusters were observed. Cluster 1 showed a higher expression of markers and gene sets implicated in epithelial-to-mesenchymal transition (EMT) and activation of cancer-associated fibroblasts (CAF) compared with cluster 2 and controls.

CONCLUSIONS

Short-term treatment with afatinib in primary HNSCC induces CD3+ and CD8+ tumor infiltration and, in some patients, EMT and CAF activation. These results open perspectives to overcome resistance mechanisms to anti-HER therapy and to potentiate the activity of immune checkpoint inhibitors.

The laterodorsal tegmentum-ventral tegmental area circuit controls depression-like behaviors by activating ErbB4 in DA neurons

Dopamine (DA) neurons in the ventral tegmental area (VTA) are critical to coping with stress. However, molecular mechanisms regulating their activity and stress-induced depression were not well understood. We found that the receptor tyrosine kinase ErbB4 in VTA was activated in stress-susceptible mice. Deleting ErbB4 in VTA or in DA neurons, or chemical genetic inhibition of ErbB4 kinase activity in VTA suppressed the development of chronic social defeat stress (CSDS)-induced depression-like behaviors. ErbB4 activation required the expression of NRG1 in the laterodorsal tegmentum (LDTg); LDTg-specific deletion of NRG1 inhibited depression-like behaviors. NRG1 and ErbB4 suppressed potassium currents of VTA DA neurons and increased their firing activity. Finally, we showed that acute inhibition of ErbB4 after stress attenuated DA neuron hyperactivity and expression of depression-like behaviors. Together, these observations demonstrate a critical role of NRG1-ErbB4 signaling in regulating depression-like behaviors and identify an unexpected mechanism by which the LDTg-VTA circuit regulates the activity of DA neurons.

Molecular and immune targets in cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer and often confers a good prognosis. Though surgery is the gold standard of treatment, unresectable or metastatic disease can necessitate systemic therapy. Of systemic agents, there is increasing interest in the use of immunotherapies and targeted therapy. Further study into the driver mutations in cSCC has identified opportunities for targeted therapy. In this review, we discuss both current and investigational immune and molecular targets of therapy for cSCC.

3D cell culture alters signal transduction and drug response in head and neck squamous cell carcinoma

Epidermal growth factor receptor (EGFR) upregulation is a typical characteristic of head and neck squamous cell carcinoma (HNSCC). However, tyrosine kinase inhibitors have not yet been able to achieve enough therapeutic benefit in clinical trials to justify their use in standard therapy regimens. At present, little is known about the reasons for this treatment failure. In the present study, the HNSCC cell lines UM-SCC-11B and UM-SCC-22B were tested for their response to tyrosine kinase inhibitors (TKI) under 2D and 3D cell culture conditions. Absorption and luciferase-based viability assays were used for this, as well as optical evaluation via fluorescence microscopy. In addition, EGFR and HER3 expression as well as the downstream signalling pathways PI3K/AKT/mTOR and RAS/RAF/MEK/ERK were investigated using western blotting. Cell line UM-SCC-11B revealed a strong resistance to lapatinib under 3D cell culture conditions, while a good response to TKI therapy was observed under 2D cell culture conditions. An associated overexpression of phosphorylated HER3 under 3D cell culture conditions offered a plausible explanation for the altered treatment response. The results of the present study represent an idea of how signalling mechanisms of cancer cells can be changed using different cell culture methods. Overall, 3D cell culture could be an important component in the analysis of resistance mechanisms in cancer therapy.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Evaluation of anti-EGFR potential of quinazoline derivatives using molecular docking: An in silico approach

Overexpression of epidermal growth factor receptor (EGFR) is commonly reported in epithelial malignancies such as oral squamous cell carcinoma. Inhibition of EGFR is, therefore, considered a potential therapeutic strategy. Among various anti-EGFR drugs, quinazoline-based tyrosine kinase inhibitors (TKIs) have gained increasing attention. Present study focused to investigate anti-EGFR potential of quinazoline-based compounds using in silico approach. Two widely used docking programs GOLD and AutoDock Vina were used for the study. Four drugs were docked on the X-ray crystallographic EGFR structure (1XKK). GOLD and AutoDock Vina produced results in terms of fitness score and binding affinity, respectively. GOLD prioritized varlitinib and AutoDock Vina preferred imatinib over other drugs. To reach the consensus from both software, all four drugs coupled with EGFR were studied rigorously. GOLD demonstrated varlitinib to be the best inhibitor with highest fitness score of 109, whereas AutoDock Vina revealed imatinib as the potent ligand with least binding energy of -10.9 kcal/mol. Most stable hydrogen bonds observed by GOLD and maximum number of hydrophobic contacts along with strong ionic interaction exhibited by varlitinib through both software have led us to conclude varlitinib as the most potent EGFR inhibitor in the studied group.

Efficacy of Afatinib in the Treatment of Patients with Non-Small Cell Lung Cancer and Head and Neck Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis

Simple Summary

Evidence from randomized controlled trials about the efficacy of monotherapy of afatinib on survival of patients with advanced non-small cell lung cancer (NSCLC) and recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC) has been not yet rigorously reviewed, which needs to be systemically reviewed and meta-analyzed in terms of overall survival and progression-free survival endpoints. The evidence from randomized controlled trials indicated that first- or second-line afatinib monotherapy has improved the survival of patients with NSCLC. Second-line monotherapy afatinib is well-tolerated and could be a promising monotherapy for recurrent/metastatic HNSCCs; however, further randomized controlled trials should be conducted to collect extra survival data regarding the efficacy of afatinib in R/M HNSCC.

Abstract

Several randomized controlled trials (RCTs) evaluated the afatinib efficacy in patients with advanced non-small cell lung cancer (NSCLC) and recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC). This review systemically outlined and meta-analyzed the afatinib efficacy in NSCLC and R/M HNSCC in terms of overall survival (OS) and progression-free survival (PFS) endpoints. Records were retrieved from PubMed, Web of Science, and ScienceDirect from 2011 to 2020. Eight afatinib RCTs were included and assessed for the risk of bias. In meta-analysis, overall pooled effect size (ES) of OS in afatinib group (AG) significantly improved in all RCTs and NSCLC-RCTs [hazard ratios (HRs): 0.89 (95% CI: 0.81–0.98, p = 0.02); I² = 0%, p = 0.71/ 0.86 (95% CI: 0.76–0.97; p = 0.02); I² = 0%, p = 0.50, respectively]. ES of PFS in AG significantly improved in all RCTs, NSCLC-RCTs, and HNSCC-RCTs [HRs: 0.75 (95% CI: 0.68–0.83; p < 0.00001); I² = 26%, p = 0.24; 0.75 (95% CI: 0.66–0.84; p < 0.00001); I² = 47%, p = 0.15/0.76 (95% CI: 0.65–88; p = 0.0004); I² = 34%, p = 0.0004, respectively]. From a clinical viewpoint of severity, interstitial lung disease, dyspnea, pneumonia, acute renal failure, and renal injury were rarely incident adverse events in the afatinib group. In conclusion, first- and second-line afatinib monotherapy improved the survival of patients with NSCLC, while second-line afatinib monotherapy could be promising for R/M HNSCC. The prospective protocol is in PROSPERO (ID = CRD42020204547).

Beyond tradition and convention: benefits of non-traditional model organisms in cancer research

Traditional laboratory model organisms are indispensable for cancer research and have provided insight into numerous mechanisms that contribute to cancer development and progression in humans. However, these models do have some limitations, most notably related to successful drug translation, because traditional model organisms are often short-lived, small-bodied, genetically homogeneous, often immunocompromised, are not exposed to natural environments shared with humans, and usually do not develop cancer spontaneously. We propose that assimilating information from a variety of long-lived, large, genetically diverse, and immunocompetent species that live in natural environments and do develop cancer spontaneously (or do not develop cancer at all) will lead to a more comprehensive understanding of human cancers. These non-traditional model organisms can also serve as sentinels for environmental risk factors that contribute to human cancers. Ultimately, expanding the range of animal models that can be used to study cancer will lead to improved insights into cancer development, progression and metastasis, tumor microenvironment, as well as improved therapies and diagnostics, and will consequently reduce the negative impacts of the wide variety of cancers afflicting humans overall.

Erlotinib overcomes paclitaxel-resistant cancer stem cells by blocking the EGFR-CREB/GRβ-IL-6 axis in MUC1-positive cervical cancer

Cancer stem cells (CSCs) are often enriched after chemotherapy and contribute to tumor relapse. While epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are widely used for the treatment of diverse types of cancer, whether EGFR-TKIs are effective against chemoresistant CSCs in cervical cancer is largely unknown. Here, we reveal that EGFR correlates with reduced disease-free survival in cervical cancer patients with chemotherapy. Erlotinib, an EGFR-TKI, effectively impedes CSCs enrichment in paclitaxel-resistant cells through inhibiting IL-6. In this context, MUC1 induces CSCs enrichment in paclitaxel-resistant cells via activation of EGFR, which directly enhances IL-6 transcription through cAMP response element-binding protein (CREB) and glucocorticoid receptor β (GRβ). Treatment with erlotinib sensitizes CSCs to paclitaxel therapy both in vitro and in vivo. More importantly, positive correlations between the expressions of MUC1, EGFR, and IL-6 were found in 20 cervical cancer patients after chemotherapy. Mining TCGA data sets also uncovered the expressions of MUC1-EGFR-IL-6 correlates with poor disease-free survival in chemo-treated cervical cancer patients. Collectively, our work has demonstrated that the MUC1-EGFR-CREB/GRβ axis stimulates IL-6 expression to induce CSCs enrichment and importantly, this effect can be abrogated by erlotinib, uncovering a novel strategy to treat paclitaxel-resistant cervical cancer.

Aberrant HER3 ligand heregulin-expressing head and neck squamous cell carcinoma is resistant to anti-EGFR antibody cetuximab, but not second-generation EGFR-TKI

The anti-epidermal growth factor receptor (EGFR) antibody cetuximab is standard therapy for head and neck squamous cell carcinoma (HNSCC). However, most HNSCC tumors are resistant to it and require alternative treatments. Here, we explored the mechanism of cetuximab resistance and evaluated its clinical relevance in HNSCC. An unbiased comprehensive transcriptome analysis was performed on cetuximab-resistant HNSCC FaDuCR cells. The causative resistance genome was knocked down with siRNA, cell signaling was immunologically analyzed, and drug efficacy was evaluated in vitro and in vivo. The mRNA in situ hybridization (ISH) of the causative genome was performed using 28 excised HNSCC tumors and its relationship with cetuximab efficacy was analyzed. FaDuCR cells were resistant to cetuximab, whereas parental FaDu cells were susceptible to it. FaDuCR cells expressed consistently higher levels of phosphorylated Akt than FaDu cells despite cetuximab exposure. A comprehensive transcriptome analysis revealed that the HER3-ligand heregulin was upregulated in FaDuCR cells compared to FaDu cells. Heregulin knockdown in FaDuCR cells repressed HER3 and Akt phosphorylation and recovered cetuximab anticancer efficacy. In contrast, pan-HER family tyrosine kinase inhibitors such as afatinib decreased HER3 and Akt phosphorylation in FaDuCR cells and inhibited FaDuCR tumor growth. Two of the 28 HNSCC tumor samples presented aberrant heregulin expression comparable to that of FaDuCR cells and were resistant to cetuximab therapy. In HNSCC, heregulin-mediated HER3-Akt activation causes resistance to cetuximab but not to second-generation EGFR-tyrosine kinase inhibitors. Subpopulations with aberrant heregulin-expressing HNSCC might be resistant to cetuximab.

Afatinib reverses ceritinib resistance (CR) in ALK/ROS1-positive non-small-cell lung cancer cell (NSCLC) via suppression of NRG1 pathway

BACKGROUND

Lung cancer (LC) is the most prevalent malignancy worldwide, and non-small-cell LC (NSCLC) cell is associated with high mortality. As a member of the second generation of anaplastic lymphoma kinase (ALK) suppressors, ceritinib has considerable therapeutic effects for ALK and c-ros oncogene 1 (ROS1)-positive NSCLC cell. Nevertheless, patients inevitably develop resistance to the drug. Our research focused on the exploration of whether afatinib was able to counteract ceritinib resistance (CR) in NSCLC cells with positive ALK or ROS1.

MATERIALS AND METHODS

Acquired CR cell sublines (HCC78R and H1299R) were induced by stepwise escalation of ceritinib exposure. MTT assay was used to validate cell proliferation. Fluorescence assay was performed for apoptosis analysis. Quantitative real-time PCR and Western blot assays were used to assess the alterations of signaling pathway-related mRNA and proteins, respectively.

RESULTS

We found that prolonged treatment of HCC78 and H1299 with ceritinib brought about 10 times weaker ceritinib sensitivity (CS) in comparison with parent cells. Additionally, the results showed that afatinib efficiently promoted CS, which was evidenced as reduced proliferation and cell death promotion, in NSCLC cells, irrespective of their previous sensitivity or resistance to ceritinib. Moreover, afatinib decreased neuregulin-1 (NRG1) signaling stimulation in CR as well as CS cells. Furthermore, supplementing NRG1 in H1299 and HCC78 cells triggered CR, which was attenuated by afatinib.

CONCLUSION

These results demonstrated that afatinib overcame CR in NSCLC cells with positive ALK or ROS1 by inhibiting the NRG1 signaling pathway, which might be a promising therapeutic approach.

Toward the use of precision medicine for the treatment of head and neck squamous cell carcinoma

Precision medicine is a new strategy that aims at preventing and treating human diseases by focusing on individual variations in people's genes, environment and lifestyle. Precision medicine has been used for cancer diagnosis and treatment and shows evident clinical efficacy. Rapid developments in molecular biology, genetics and sequencing technologies, as well as computational technology, has enabled the establishment of "big data", such as the Human Genome Project, which provides a basis for precision medicine. Head and neck squamous cell carcinoma (HNSCC) is an aggressive cancer with a high incidence rate and low survival rate. Current therapies are often aggressive and carry considerable side effects. Much research now indicates that precision medicine can be used for HNSCC and may achieve improved results. From this perspective, we present an overview of the current status, potential strategies, and challenges of precision medicine in HNSCC. We focus on targeted therapy based on cell the surface signaling receptors epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF) and human epidermal growth factor receptor-2 (HER2), and on the PI3K/AKT/mTOR, JAK/STAT3 and RAS/RAF/MEK/ERK cellular signaling pathways. Gene therapy for the treatment of HNSCC is also discussed.

Afatinib radiosensitizes head and neck squamous cell carcinoma cells by targeting cancer stem cells

The dismal prognosis of locally advanced and metastatic squamous cell carcinoma of the head and neck (HNSCC) is primarily due to the development of resistance to chemoradiation therapy (CRT). Deregulation of Epidermal Growth Factor Receptor (EGFR) signaling is involved in HNSCC pathogenesis by regulating cell survival, cancer stem cells (CSCs), and resistance to CRT. Here we investigated the radiosensitizing activity of the pan-EGFR inhibitor afatinib in HNSCC in vitro and in vivo. Our results showed strong antiproliferative effects of afatinib in HNSCC SCC1 and SCC10B cells, compared to immortalized normal oral epithelial cells MOE1a and MOE1b. Comparative analysis revealed stronger antitumor effects with afatinib than observed with erlotinib. Furthermore, afatinib enhanced in vitro radiosensitivity of SCC1 and SCC10B cells by inducing mesenchymal to epithelial transition, G1 cell cycle arrest, and the attenuating ionizing radiation (IR)-induced activation of DNA double strand break repair (DSB) ATM/ATR/CHK2/BRCA1 pathway. Our studies also revealed the effect of afatinib on tumor sphere- and colony-forming capabilities of cancer stem cells (CSCs), and decreased IR-induced CSC population in SCC1 and SCC10B cells. Furthermore, we observed that a combination of afatinib with IR significantly reduced SCC1 xenograft tumors (median weight of 168.25 ± 20.85 mg; p = 0.05) compared to afatinib (280.07 ± 20.54 mg) or IR alone (324.91 ± 28.08 mg). Immunohistochemical analysis of SCC1 tumor xenografts demonstrated downregulation of the expression of IR-induced pEGFR1, ALDH1 and upregulation of phosphorylated γH2AX by afatinib. Overall, afatinib reduces tumorigenicity and radiosensitizes HNSCC cells. It holds promise for future clinical development as a novel radiosensitizer by improving CSC eradication.

Animal models of head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the most common oral cancer worldwide. Local bone invasion into the maxilla or mandible and metastasis to regional lymph nodes often result in a poor prognosis, decreased quality of life and shortened survival time for HNSCC patients. Poor response to treatment and clinical outcomes are the major concerns in this aggressive cancer. Multiple animal models have been developed to replicate spontaneous HNSCC and investigate genetic alterations and novel therapeutic targets. This review provides an overview of HNSCC as well as the traditional animal models used in HNSCC preclinical research. The value and challenges of each in vivo model are discussed. Similarity between HNSCC in humans and cats and the possibility of using spontaneous feline oral squamous cell carcinoma (FOSCC) as a model for HNSCC in translational research are highlighted.

Increased Expression of HER2, HER3, and HER2:HER3 Heterodimers in HPV-Positive HNSCC Using a Novel Proximity-Based Assay: Implications for Targeted Therapies

PURPOSE

In other cancer types, HPV infection has been reported to coincide with overexpression of HER2 (ERBB2) and HER3 (ERBB3); however, the association between HER2 or HER3 expression and dimer formation in HNSCC has not been reported. Overexpression of HER2 and HER3 may contribute to resistance to EGFR inhibitors, including cetuximab, although the contribution of HPV in modulating cetuximab response remains unknown. Determination of heterodimerization of HER receptors is challenging and has not been reported in HNSCC. The present study aimed to determine the expression of HER proteins in HPV(+) versus HPV(-) HNSCC tumors using a proximity-based protein expression assay (VeraTag), and to determine the efficacy of HER-targeting agents in HPV(+) and HPV(-) HNSCC cell lines.

EXPERIMENTAL DESIGN

Expression of total HER1, HER2, and HER3, p95HER2, p-HER3, HER1:HER1 homodimers, HER2:HER3 heterodimers, and the HER3-PI3K complex in 88 HNSCC was determined using VeraTag, including 33 baseline tumors from individuals treated in a trial including cetuximab. Inhibition of cell growth and protein activation with cetuximab and afatinib was compared in HPV(+) and HPV(-) cetuximab-resistant cell lines.

RESULTS

Expression of total HER2, total HER3, HER2:HER3 heterodimers, and the HER3:PI3K complex were significantly elevated in HPV(+) HNSCC. Total EGFR was significantly increased in HPV(-) HNSCC where VeraTag assay results correlated with IHC. Afatinib significantly inhibited cell growth when compared with cetuximab in the HPV(+) and HPV(-) cetuximab-resistant HNSCC cell lines.

CONCLUSIONS

These findings suggest that agents targeting multiple HER proteins may be effective in the setting of HPV(+) HNSCC and/or cetuximab resistance.

Quantum mechanics/molecular mechanics modeling of covalent addition between EGFR-cysteine 797 and N-(4-anilinoquinazolin-6-yl) acrylamide

Irreversible epidermal growth factor receptor (EGFR) inhibitors can circumvent resistance to first-generation ATP-competitive inhibitors in the treatment of nonsmall-cell lung cancer. They covalently bind a noncatalytic cysteine (Cys797) at the surface of EGFR active site by an acrylamide warhead. Herein, we used a hybrid quantum mechanics/molecular mechanics (QM/MM) potential in combination with umbrella sampling in the path-collective variable space to investigate the mechanism of alkylation of Cys797 by the prototypical covalent inhibitor N-(4-anilinoquinazolin-6-yl) acrylamide. Calculations show that Cys797 reacts with the acrylamide group of the inhibitor through a direct addition mechanism, with Asp800 acting as a general base/general acid in distinct steps of the reaction. The obtained reaction free energy is negative (ΔA = -12 kcal/mol) consistent with the spontaneous and irreversible alkylation of Cys797 by N-(4-anilinoquinazolin-6-yl) acrylamide. Our calculations identify desolvation of Cys797 thiolate anion as a key step of the alkylation process, indicating that changes in the intrinsic reactivity of the acrylamide would have only a minor impact on the inhibitor potency.

Translational genomics and head and neck cancer: toward precision medicine

Head and neck squamous cell carcinoma (HNSCC) comprise a wide spectrum of neoplasms with different tumor biologies, prognosis and response to therapies. Current tumor classification and traditional diagnostic methods (e.g. clinical assessment, histopathology) are limited in their capacity to determine prognosis and clinical decision-making. Despite recent improvements in treatment, the outcome for patients with HNSCC remains poor. Similar to most tumors, several patient-related factors, (e.g. genetics and environment) and disease-related factors (e.g. tumor location, TMN staging) play a significant role on survival. Thus, the problem in defining the prognosis is that the clinical course and response to treatment differ considerably among patients. Such interindividual variability is related to the heterogeneity of the tumor, genetic and epigenetic variations, thus reflecting the interaction of multiple biological components that result in a unique phenotype. Integrative genomics are developed to identify the molecular pathways leading to cancer at the individual level and find novel prognostic markers for HNSCC, hence tailoring a treatment accordingly. Such genetic-based personalized diagnosis allows tumor stratification and implementation of targeted therapy. Modern medicine includes new drugs that disrupt the implicated molecules and their signaling pathways. Here, we summarize the current state of knowledge that elucidates the translation of genetic data into clinical benefit.

Afatinib enhances the efficacy of conventional chemotherapeutic agents by eradicating cancer stem-like cells

Cancer stem cells (CSC) have garnered significant attention as a therapeutic focus, based on evidence that they may represent an etiologic root of treatment-resistant cells. Indeed, expression of the multidrug resistance protein ATP-binding cassette subfamily G member 2 (ABCG2) confers chemoresistance to CSCs, where it serves as a potential biomarker and therapeutic target. Here, we show that afatinib, a small-molecule inhibitor of the tyrosine kinases EGFR, HER2, and HER4, preferentially eliminated side population cells with CSC character, in both cell lines and patient-derived leukemia cells, by decreasing ABCG2 expression. In these cells, afatinib also acted in parallel to suppress self-renewal capacity and tumorigenicity. Combining afatinib with the DNA-damaging drug topotecan enhanced the antitumor effect of topotecan in vitro and in vivo. Mechanistic investigations suggested that ABCG2 suppression by afatinib did not proceed by proteolysis through the ubiquitin-dependent proteosome, lysosome, or calpain. Instead, we found that afatinib increased DNA methyltransferase activity, thereby leading to methylation of the ABCG2 promoter and to a decrease in ABCG2 message level. Taken together, our results advocate the use of afatinib in combination with conventional chemotherapeutic drugs to improve efficacy by improving CSC eradication.