Takamichi Hosaka

Phase II study of irinotecan and carboplatin in patients with the refractory or relapsed small cell lung cancer

We examined the safety and efficacy of the combination of irinotecan plus carboplatin in patients with refractory or relapsed small cell lung cancer (SCLC). Patients with previously treated SCLC were eligible. Patients were treated every 3 weeks with carboplatin (with a target area under the concentration versus time curve of 5 mg min/ml using the Calvert formula on day 1) plus irinotecan (50 mg/m(2) on days 1 and 8). From May 2000 to January 2002, 24 patients were eligible. None of the 22 patients achieved a complete response, but 15 achieved a partial response with an overall response rate of 68.2% (95% confidence interval, 45.1-86.1%). In 13 patients with sensitive disease, the response rate was 92.3% (95% confidence interval, 64.0-99.8%). The median survival time (MST) was 194 days (range 27-605 days). The MST did not differ significantly between patients with sensitive disease (245 days) and those with refractory disease (194 days, P=0.88). One patient died of treatment-related sepsis. Grade 3-4 hematologic toxicities included leukopenia in 58% of patients, neutropenia in 63%, thrombocytopenia in 58%, and anemia in 67%. Grade 3 diarrhea developed in 21% of patients and grade 3-4 infection in 13%. No patients had grade 4 diarrhea or grade 3-4 nausea and vomiting. This regimen is effective and well tolerated in patients with relapsed or refractory SCLC. However, the search for even more active regimens should be continued.

Enhancement of sensitivity to tumor necrosis factor α in non-small cell lung cancer cells with acquired resistance to gefitinib

Tumor cells that have acquired resistance to gefitinib through continuous drug administration may complicate future treatment. To investigate the mechanisms of acquired resistance, we established PC-9/ZD2001, a non-small-cell lung cancer cell line resistant to gefitinib, by continuous exposure of the parental cell line PC-9 to gefitinib. After 6 months of culture in gefitinib-free conditions, PC-9/ZD2001 cells reacquired sensitivity to gefitinib and were established as a revertant cell line, PC-9/ZD2001R. PC-9/ZD2001 cells showed collateral sensitivity to several anticancer drugs (vinorelbine, paclitaxel, camptothecin, and 5-fluorouracil) and to tumor necrosis factor α (TNF-α). Compared with PC-9 cells, PC-9/ZD2001 cells were 67-fold more sensitive to TNF-α and PC-9/ZD2001R cells were 1.3-fold more sensitive. Therefore, collateral sensitivity to TNF-α was correlated with gefitinib resistance. PC-9/ZD2001 cells expressed a lower level of epidermal growth factor receptor (EGFR) than did PC-9 cells; this down-regulation was partially reversed in PC-9/ZD2001R cells. TNF-α-induced autophosphorylation of EGFR (cross-talk signaling) was detected in all three cell lines. However, TNF-α-induced Akt phosphorylation and IκB degradation were observed much less often in PC-9/ZD2001 cells than in PC-9 cells or PC-9/ZD2001R cells. Expression of the inhibitor of apoptosis proteins c-IAP1 and c-IAP2 was induced by TNF-α in PC-9 and PC-9/ZD2001R cells but not in PC-9/ZD2001 cells. This weak effect of EGFR on Akt pathway might contribute to the TNF-α sensitivity of PC-9/ZD2001 cells. These results suggest that therapy with TNF-α would be effective in some cases of non-small-cell lung cancer that have acquired resistance to gefitinib.

A Molecular Mechanism of Diminished Binding Activity between 15 bp Deletion Mutant EGFR and c-Cbl Ubiquitin Ligase

Gefitinib sensitivity in non-small-cell lung cancer (NSCLC) is associated with activating mutations in epidermal growth factor receptor (EGFR). It has been reported that autophosphorylation of the mutant EGFR is prolonged as compared with wild type EGFR (Lynch et al NEJM 2004). Previously, we reported that the mutant EGFR underwent less protein degradation due to diminished binding to c-Cbl ubiquitin ligase as compared to wild type EGFR. To clarify the mechanism, we examined EGFR-induced site specific phosphorylation of c-Cbl. c-Cbl residues Y700, Y731, and Y774 were all phosphorylated by wild type EGFR, but the mutant EGFR could phosphorylate Y774 but Y700 and Y731. We speculated the alteration of phosphorylation status of c-Cbl might reduce its binding to EGFR. To confirm this hypothesis, we constructed mutant c-Cbl plasmids and established stable transfectants using wild type and the mutant EGFR transfectants. As the results, 1) the mutations of Y700F and Y73IF but Y774F reduced binding of wild type EGFR and c-Cbl. 2) all the three mutant c-Cbls showed less binding activity to the mutant EGFR. From these observations, it was suggested that the alteration of substrate specificity for c-Cbl and conformation change of the mutant EGFR might reduce its binding to c-Cb1.