Combination efficacy of pertuzumab and trastuzumab for trastuzumab emtansine-resistant cells exhibiting attenuated lysosomal trafficking or efflux pumps upregulation.

PURPOSE: Trastuzumab emtansine (T-DM1) is the standard treatment in the current second-line therapy of human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer. However, a useful therapy after T-DM1 resistance has not been established. In this study, we established two different HER2-positive T-DM1-resistant cancer cells and evaluated the antitumor effect of trastuzumab in combination with pertuzumab (TRAS + PER). METHODS: Single-cell-cloned OE19 and BT-474 cells were cultured with increasing concentrations of T-DM1 to generate T-DM1-resistant OE19bTDR and BT-474bTDR cells, respectively. HER2 expression was assessed by immunohistochemistry. Multidrug resistance proteins (MDR1 and MRP1) were evaluated by real-time polymerase chain reaction and western blotting. Intracellular trafficking of T-DM1 was examined by flow cytometry and immunofluorescence staining. Efficacy of TRAS + PER was evaluated by cell proliferation assay, HER3 and AKT phosphorylation, caspase 3/7 activity, and antitumor activity. RESULTS: HER2 expression of both resistant cells was equivalent to that of the parent cells. Overexpression of MDR1 and MRP1 was observed and affected the T-DM1 sensitivity in the OE19bTDR cells. Abnormal localization of T-DM1 into the lysosomes was observed in the BT-474bTDR cells. In BT-474bTDR cells, TRAS + PER inhibited the phosphorylation of AKT involved in HER2-HER3 signaling, and apoptosis induction and cell proliferation inhibition were significantly higher with TRAS + PER than with the individual drugs. TRAS + PER significantly suppressed tumor growth in the OE19bTDR xenograft model compared with each single agent. CONCLUSIONS: The results suggest that the TRAS + PER combination may be effective in T-DM1-resistant cancer cells where HER2 overexpression is maintained.

Trastuzumab in combination with paclitaxel enhances antitumor activity by promoting apoptosis in human epidermal growth factor receptor 2-positive trastuzumab-resistant gastric cancer xenograft models.

Trastuzumab, a humanized anti-human epidermal growth factor receptor 2 antibody drug, is the first-line therapy for human epidermal growth factor receptor 2-positive breast and gastric cancer. For breast cancer, the benefit of continuous treatment with trastuzumab after it becomes refractory to first-line therapy has been demonstrated. However, it is unclear whether trastuzumab can show similar efficacy as a second-line treatment for gastric cancer. Here, we report that trastuzumab in combination with paclitaxel exhibits increased antitumor efficacy even for trastuzumab-resistant xenografted tumors. We derived the trastuzumab-resistant models from previously established human epidermal growth factor receptor 2-positive gastric cancer patient-derived cells. Human epidermal growth factor receptor 2 expression, PIK3CA mutation, and phosphatase and tensin homolog expression in these resistant models was equivalent to those in the trastuzumab-sensitive parental model, whereas cyclin-dependent kinase inhibitors, such as p16, p15, and p21, were downregulated. Trastuzumab in combination with paclitaxel enhanced antitumor activity in both the sensitive and resistant models. In the trastuzumab-sensitive model, the combination of trastuzumab and paclitaxel resulted in suppression of the AKT-p27-retinoblastoma protein pathway and induction of apoptosis. Although this combination did not suppress retinoblastoma protein phosphorylation in the trastuzumab-resistant model, it did markedly decrease epidermal growth factor receptor and human epidermal growth factor receptor 2 phosphorylation and further enhance paclitaxel-mediated apoptosis. These results suggested that trastuzumab in combination with paclitaxel can still exert more potent antitumor efficacy than each agent alone in trastuzumab-resistant models, providing evidence that trastuzumab remains beneficial in the treatment of trastuzumab-resistant tumors.

The balance of forces generated by kinesins controls spindle polarity and chromosomal heterogeneity in tetraploid cells.

Chromosomal instability, one of the most prominent features of tumour cells, causes aneuploidy. Tetraploidy is thought to be an intermediate on the path to aneuploidy, but the mechanistic relationship between the two states is poorly understood. Here, we show that spindle polarity (e.g. bipolarity or multipolarity) in tetraploid cells depends on the level of functional phosphorylated Eg5, a mitotic kinesin, localised to the spindle. Multipolar spindles are formed in cells with high levels of phosphorylated Eg5. This process is suppressed by inhibition of Eg5 or expression of a non-phosphorylatable Eg5 mutant, as well as by changing the balance between opposing forces required for centrosome separation. Tetraploid cells with high levels of functional Eg5 give rise to a heterogeneous aneuploid population through multipolar division, whereas cells with low levels of functional Eg5 continue to undergo bipolar division and remain tetraploid. Furthermore, Eg5 protein levels correlate with ploidy status in tumour specimens. We provide a novel explanation for the tetraploid intermediate model, i.e. spindle polarity and subsequent tetraploid cell behaviour are determined by the balance of forces generated by mitotic kinesins at the spindle.

Expression of C-terminal ALK, RET, or ROS1 in lung cancer cells with or without fusion.

BACKGROUND: Genetic alterations, including mutation of epidermal growth factor receptor or v-Ki-ras2 kirsten rat sarcoma viral oncogene homolog and fusion of anaplastic lymphoma kinase (ALK), RET proto-oncogene (RET), or v-ros UR2 sarcoma virus oncogene homolog 1 (ROS1), occur in non-small cell lung cancers, and these oncogenic drivers are important biomarkers for targeted therapies. A useful technique to screen for these fusions is the detection of native carboxy-terminal (C-terminal) protein by immunohistochemistry; however, the effects of other genetic alterations on C-terminal expression is not fully understood. In this study, we evaluated whether C-terminal expression is specifically elevated by fusion with or without typical genetic alterations of lung cancer. METHODS: In 37 human lung cancer cell lines and four tissue specimens, protein and mRNA levels were measured by capillary western blotting and reverse transcription-PCR, respectively. RESULTS: Compared with the median of all 37 cell lines, mRNA levels at the C-terminus of all five of the fusion-positive cell lines tested (three ALK, one RET, and one ROS1) were elevated at least 2000-, 300-, or 2000-fold, respectively, and high C-terminal protein expression was detected. In an ALK fusion-positive tissue specimen, the mRNA and protein levels of C-terminal ALK were also markedly elevated. Meanwhile, in one of 36 RET fusion-negative cell lines, RET mRNA levels at the C-terminus were elevated at least 500-fold compared with the median of all 37 cell lines, and high C-terminal protein expression was detected despite the absence of RET fusion. CONCLUSIONS: This study of 37 cell lines and four tissue specimens shows the detection of C-terminal ALK or ROS1 proteins could be a comprehensive method to determine ALK or ROS1 fusion, whereas not only the detection of C-terminal RET protein but also other methods would be needed to determine RET fusion.

Molecular targeting of HER2-overexpressing biliary tract cancer cells with trastuzumab emtansine, an antibody-cytotoxic drug conjugate.

PURPOSE: Trastuzumab emtansine (T-DM1) provides clinical benefit in breast cancers overexpressing human epidermal growth factor receptor 2 (HER2). However, its efficacy against biliary tract cancers (BTC) has not been evaluated. In this study, the effectiveness of T-DM1 in various BTC cell lines and xenograft models with different levels of HER2 expression was investigated. METHODS: HER2 expression status in xenografts and patient tissue microarrays was assessed by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH). Cell-surface HER2 expression levels and cell growth inhibition in response to T-DM1 were examined in 17 BTC cell lines. The antitumor activity of T-DM1 was evaluated in four xenograft mouse models with different levels of HER2 expression. The effects of T-DM1 on HER2 signaling, antibody-dependent cell-mediated cytotoxicity (ADCC), cell cycle, and apoptosis were assessed in vitro. RESULTS: Cell-surface expression of HER2 was observed in both gallbladder carcinoma and cholangiocarcinoma tissues. The anti-proliferative activity of T-DM1 was higher in BTC cell lines and breast cancer cell lines with higher levels of HER2 expression. The HER2 status (IHC score|HER2-to-CEP17 ratio by FISH testing) of each BTC xenograft was 3 +|8.3 for KMCH-1, 2 +|4.7 for Mz-ChA-1, 1 +/0|1.4 for OCUG-1, and 0|1.1 for KKU-100, and T-DM1 showed antitumor activity in proportion to the HER2 status. T-DM1 inhibited HER2 signaling and induced ADCC, mitotic arrest, and apoptosis in KMCH-1 cells. CONCLUSIONS: T-DM1 exhibited preclinical activity in HER2-overexpressing BTC. Further evaluation in clinical studies is warranted.

Changes in HER2 Expression and Amplification Status Following Preoperative Chemotherapy for Gastric Cancer.

BACKGROUND: It is essential to establish a strategy for second-line treatment for human epidermal growth factor receptor 2 (HER2)-positive gastric cancer; however, HER2 expression status after chemotherapy treatment is not routinely determined. MATERIALS AND METHODS: We analyzed 25 cases of gastric cancer that received preoperative chemotherapy and selected the six pre-treatment samples that were HER2-positive. Pre- and post-treatment tumor samples were examined for HER2 expression, and for HER2, epidermal growth factor receptor (EGFR), and hepatocyte growth factor receptor (MET) gene amplification. RESULTS: Three patients had been treated with trastuzumab plus chemotherapy, and three patients with cytotoxic chemotherapy alone. Only one case that had an initial HER2 score of 3+ and had received trastuzumab plus chemotherapy remained HER2-positive after treatment. Decrease or loss of HER2 expression and amplification was observed in the other five patients. Amplification of EGFR or MET was not observed in any pre- or post-treatment specimens. CONCLUSION: Our data suggest that trastuzumab plus chemotherapy or chemotherapy alone may induce loss of HER2 positivity.

Mode of action of pertuzumab in combination with trastuzumab plus docetaxel therapy in a HER2-positive breast cancer xenograft model.

In a Phase III trial for HER2-positive breast cancer (the CLEOPATRA study), the triple-drug combination arm of pertuzumab plus trastuzumab plus docetaxel showed significantly longer progression-free survival and overall survival than did the trastuzumab plus docetaxel arm. In this study, we investigated the mechanism of action of the triple-drug combination therapy in vivo. For this purpose, we established a mouse xenograft model using KPL-4, a HER2-positive human breast cancer cell line, in which the triple-drug combination treatment dramatically induced tumor regression compared with double-drug combinations (trastuzumab plus docetaxel, pertuzumab plus docetaxel, or pertuzumab plus trastuzumab). Four days after the triple-drug treatment was started, strong reduction in the phosphorylation of HER2, epidermal growth factor receptor (EGFR), HER3, extracellular signal-regulated kinase (ERK), and AKT in tumor tissues was seen, despite only weak suppression of phosphorylation seen with the single- or double-drug treatments. Histopathological analysis and flow cytometric analysis showed that the triple-drug treatment enhanced apoptosis after mitotic arrest induced by docetaxel. Furthermore, infiltration of mononuclear cells around the tumor cells was strongly induced by the triple-drug combination treatment. These results suggested that the mechanism underlying the synergistic efficacy of the triple-drug combination was attributable, at least in part, to the docetaxel-mediated apoptosis being promoted by enhanced inhibition of HER2-HER3-AKT signaling as well to the intratumor infiltration of mononuclear cells induced by anti-HER2 antibodies being enhanced by docetaxel.

Overexpression and gene amplification of EGFR, HER2, and HER3 in biliary tract carcinomas, and the possibility for therapy with the HER2-targeting antibody pertuzumab.

BACKGROUND: Pertuzumab is a humanized monoclonal antibody that binds to HER2 at an epitope that prevents HER2 from dimerizing with ligand-activated HER-family receptors. To assess the potential of pertuzumab as a new therapy, the expression status of HER family members was determined in biliary tract carcinoma (BTC), and the antitumor activity of pertuzumab was investigated by assessing the inhibition of BTC cell growth. METHODS: The expression status of HER family members in 113 archival specimens of BTC was analyzed by using immunohistochemistry and fluorescence in situ hybridization. Using ten BTC cell lines, heregulin-alpha (HRG-α) stimulated cell proliferation and its inhibition by pertuzumab was tested in vitro. The phosphorylated HER family proteins and their respective downstream molecules were analyzed. In vivo antitumor activity of pertuzumab was evaluated in a xenograft model. RESULTS: Protein overexpression of HER2 and/or HER3 was observed in 23-34 % of the specimens and gene amplification in 17-27 %. Seven of the ten cell lines showed HER2 and/or HER3 protein overexpression and gene amplification, and HRG-α stimulated cell proliferation was observed in four of the ten cell lines. In a BTC cell line co-overexpressing HER2 and HER3, pertuzumab potently inhibited the HRG-α stimulated cell proliferation in a dose-dependent manner, and completely blocked the phosphorylation of HER3. Suppression of downstream pathway molecules including p-AKT was also observed. Pertuzumab inhibited the in vivo growth of subcutaneous tumors, and increased the number of apoptotic cancer cells. CONCLUSIONS: Pertuzumab exerts potent antitumor activity in BTC cells co-overexpressing HER2 and HER3. Pertuzumab provides a new therapeutic option against BTC.

Importance of formalin fixing conditions for HER2 testing in gastric cancer: immunohistochemical staining and fluorescence in situ hybridization.

BACKGROUND: Accurate and reliable assessment of human epidermal growth factor receptor type 2 (HER2) status is important for selecting patients with gastric cancer who may benefit from trastuzumab treatment. Here we examined the impact of formalin fixing conditions on HER2 immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in xenografted tumor tissues. METHODS: Xenografted tumor tissues of the human gastric cancer cell lines NCI-N87, SCH, and SNU-16 were collected and kept at room temperature for 0, 6, or 24 h before being fixed with 10 % neutral buffered formalin (NBF) for 24 h or 5, 7, or 10 days and embedded in paraffin. Use of 10 % NBF, 20 % NBF, or nonbuffered formalin as fixative was investigated. RESULTS: The HER2 IHC scores for NCI-N87, SCH, and SNU-16 tumors were 3+, 2+, and 1+, respectively, when specimens were fixed with 10 % NBF for 24 h immediately after resection of the tumors. Specimens left for longer than 6 h before fixation had shrinkage of the tumor periphery and decreased immunostaining intensity in this region in all specimens. In SCH and SNU-16 specimens, starting fixation 24 h after tumor tissue collection induced autolysis and reduction of the number of stained cells, and 10-day-fixation lowered the HER2 score. Prolongation of fixation time did not affect FISH results, but if samples were left for more than 6 h before fixation, the FISH score was strongly reduced in SCH specimens (2.3 to 1.3). Reduced IHC staining intensity was observed with 20 % NBF and nonbuffered formalin compared to 10 % NBF. CONCLUSIONS: The time to and length of fixation of tumor specimens can affect HER2 IHC and FISH scores. The fixative used can affect IHC results.

Enhanced antitumor activity of trastuzumab emtansine (T-DM1) in combination with pertuzumab in a HER2-positive gastric cancer model.

Human epidermal growth factor receptor 2 (HER2)-targeted therapy by trastuzumab has become increasingly important for treating HER2-positive cancers, and trastuzumab emtansine (T-DM1) is expected to serve as an effective alternative to trastuzumab. Pertuzumab, a HER2 dimerization inhibitor, showed prolonged progression-free survival when used with trastuzumab for HER2-positive breast cancer. In this study, we investigated the effect of combining T-DM1 and pertuzumab on xenografted gastric tumors. T-DM1 as a single agent showed significant antitumor activity in all the three HER2-high expression tumor models tested (NCI-N87, SCH and 4-1ST) but was ineffective against two HER2-low expression tumors (SNU-16 and MKN-28). Using the T-DM1-sensitive NCI-N87 model, the combination efficacy of T-DM1 and pertuzumab was elucidated. The combination induced significant tumor regression, whereas T-DM1 or pertuzumab alone did not. In cultured NCI-N87 cells stimulated with epidermal growth factor (EGF) or heregulin-α, concomitant treatment of T-DM1 and pertuzumab significantly inhibited proliferation and increased caspase 3/7 activity compared to either agent alone. Only the combination significantly inhibited the phosphorylation of EGFR or HER3, and its downstream factor AKT. Suppressed HER3 phosphorylation by the combination was also seen in the NCI-N87 xenografted tumors. Compared to single agent treatments, the combination treatment significantly enhanced antibody-dependent cellular cytotoxicity (ADCC) against NCI-N87 cells. These findings suggest that T-DM1 in combination with pertuzumab shows significant antitumor activity by increasing AKT signal inhibition and ADCC in HER2-positive gastric cancers.