Rama Krishna Kancha

Functional Analysis of Epidermal Growth Factor Receptor (EGFR) Mutations and Potential Implications for EGFR Targeted Therapy

Purpose: Epidermal growth factor receptor (EGFR) mutations in non–small cell lung cancer (NSCLC) might be predictive for clinical response to EGFR inhibitor treatment. However, retrospective analyses of EGFR mutations in clinical trials have shown inconclusive results and the effect of EGFR sequencing in NSCLC is still controversial. Because the vast majority of EGFR mutations described have not been functionally characterized, simple correlation of mutational status and treatment response may not provide reliable information about the predictive value of EGFR mutations. Thus, we aimed to characterize a comprehensive panel of clinically observed EGFR mutations. Experimental Design and Results: A panel of 30 EGFR mutations was cloned and characterized for kinase activity and the ability to confer growth factor independence. Interestingly, 4 of 30 EGFR mutations showed no kinase activity even after ligand stimulation and were not able to confer growth factor independence. Ba/F3 cells expressing activating EGFR mutants were then used to test the efficacy of EGFR inhibitors in a cell proliferation assay. IC50 values were calculated for gefitinib, erlotinib, and AEE788. We show that the sensitivity of EGFR mutations toward different inhibitors varies significantly, thus establishing a comprehensive sensitivity profile for each inhibitor. Conclusions: EGFR mutations identified in NSCLC patients display distinct biological features. The variability in kinase activity, transforming potential, and sensitivity to EGFR inhibitors has to be considered in clinical studies aiming to correlate mutational status and drug response. The identification of comprehensive drug resistance profiles opens the opportunity to test alternative EGFR inhibitors in vitro.

Differential Sensitivity of ERBB2 Kinase Domain Mutations towards Lapatinib

Background Overexpression of the ERBB2 kinase is observed in about one-third of breast cancer patients and the dual ERBB1/ERBB2 kinase inhibitor lapatinib was recently approved for the treatment of advanced ERBB2-positive breast cancer. Mutations in the ERBB2 receptor have recently been reported in breast cancer at diagnosis and also in gastric, colorectal and lung cancer. These mutations may have an impact on the clinical responses achieved with lapatinib in breast cancer and may also have a potential impact on the use of lapatinib in other solid cancers. However, the sensitivity of lapatinib towards clinically observed ERBB2 mutations is not known. Methodology/Principal Findings We cloned a panel of 8 clinically observed ERBB2 mutations, established stable cell lines and characterized their sensitivity towards lapatinib and alternative ERBB2 inhibitors. Both lapatinib-sensitive and lapatinib-resistant ERBB2 mutations were observed. Interestingly, we were able to generate lapatinib resistance mutations in wt-ERBB2 cells incubated with lapatinib for prolonged periods of time. This indicates that these resistance mutations may also cause secondary resistance in lapatinib-treated patients. Lapatinib-resistant ERBB2 mutations were found to be highly resistant towards AEE788 treatment but remained sensitive towards the dual irreversible inhibitors CL-387785 and WZ-4002. Conclusions/Significance Patients harbouring certain ERBB2 kinase domain mutations at diagnosis may not benefit from lapatinib treatment. Moreover, secondary lapatinib resistance may develop due to kinase domain mutations. Irreversible ERBB2 inhibitors may offer alternative treatment options for breast cancer and other solid tumor patients harbouring lapatinib resistance mutations. In addition, these inhibitors may be of interest in the scenario of secondary lapatinib resistance.

The Epidermal Growth Factor Receptor-L861Q Mutation Increases Kinase Activity without Leading to Enhanced Sensitivity Toward Epidermal Growth Factor Receptor Kinase Inhibitors

Introduction: Mutations in the epidermal growth factor receptor (EGFR) kinase domain such as EGFR-L858R and EGFR-G719S have been reported to activate the kinase and also sensitize a subset of patients with non-small cell lung cancer to EGFR kinase inhibitor treatment. Nevertheless, for other common point mutations such as EGFR-L861Q, it is unclear whether and to what extent they sensitize toward gefitinib and erlotinib. Thus far, there is no reliable cellular assay to compare in a ligand-independent manner intrinsic kinase activity and drug sensitivity of the unmutated (wild type) and mutated EGFR kinase domain. Methods: To overcome this obstacle, we introduced L858R, G719S, and L861Q into the backbone of EGFRvIII. EGFRvIII has a wild type-kinase domain but is activated in a ligand-independent manner through a deletion in the extracellular domain. Results: Using this tool, we show that the L861Q mutation displays enhanced kinase activity and transforming potential compared with L858R, G719S, and also to the wild type-EGFR kinase domain. Interestingly, L861Q does not increase drug sensitivity toward clinically used EGFR kinase inhibitors in contrast to the L858R and G719S mutation. In addition, we demonstrate that EGFR-L861Q could be effectively inhibited with the irreversible second-generation EGFR inhibitor WZ-4002. Conclusions: Thus, in the common EGFR-L861Q mutation, activation of the kinase domain is uncoupled from a sensitizing effect toward clinically approved kinase inhibitors. Therefore, patients with EGFR-L861Q may not have the same clinical benefit from gefitinib/erlotinib treatment as patients with EGFR-L858R and EGFR-G719S mutations. Treatment with irreversible second-generation kinase inhibitors such as WZ-4002 may be an attractive option in the future for patients with EGFR-L861Q.

Imatinib and leptomycin B are effective in overcoming imatinib-resistance due to Bcr-Abl amplification and clonal evolution but not due to Bcr-Abl kinase domain mutation

The findings of this study indicate that the combination of imatinib and leptomycin B effectively induces cell death in imatinib-resistant Ba/F3 cells which display Bcr-Abl amplification or signs of clonal evolution. Treatment with imatinib is very effective in Bcr-Abl positive leukemia. However, development of resistance to this drug is a common phenomenon in late stage disease. The Bcr-Abl protein localizes to the cytoplasm in transformed cells but can enter the nucleus upon treatment with imatinib. Using leptomycin B, a nuclear export blocker, it has been shown that reactivated nuclear Bcr-Abl kinase activity can induce cell death, thus presenting an interesting potential treatment option for imatinib resistant disease. Here we show that the combination of imatinib and leptomycin B effectively induces cell death in imatinib-resistant Ba/F3 cells which display Bcr-Abl amplification or signs of clonal evolution. However, no such synergism is observed in imatinib-resistant Ba/F3 cells carrying the T315I mutation of Bcr-Abl or those which have lost Bcr-Abl expression. Thus, a partial inhibition of Bcr-Abl by imatinib is required for this approach in agreement with the proposed mode of action.

Bis(1H‐indol‐2‐yl)methanones are effective inhibitors of FLT3‐ITD tyrosine kinase and partially overcome resistance to PKC412A in vitro

Inhibition of the mutated fms‐like tyrosine kinase 3 (FLT3) receptor tyrosine kinase is a promising therapeutic strategy in acute myeloid leukaemia (AML). However, development of resistance to FLT3 tyrosine kinase inhibitors (TKI), such as PKC412A, has been described recently. This observation may have an increasing impact on the duration of response and relapse rates in upcoming clinical trials employing FLT3‐TKI. Herein we investigated two representatives of a novel class of FLT3‐TKI: Bis(1H‐indol‐2‐yl)methanones. Both compounds effectively induced apoptosis in FLT3‐internal tandem duplicate (ITD)‐transfected murine myeloid cells and in primary FLT3‐ITD positive blasts. Combination of both compounds with chemotherapy revealed synergistic effects in apoptosis assays. The compounds did not show significant toxicity in human bone marrow cells derived from healthy donors. Compound102 overcame resistance to PKC412 within a non‐myelotoxic dose‐range. Western Blotting experiments of 32D‐FLT3‐ITD cells showed dose‐dependent dephosphorylation of FLT3‐ITD and of its downstream targets STAT5, AKT and ERK upon incubation with either compound. In conclusion, bis(1H‐indol‐2‐yl)methanones overcome resistance mediated by FLT3‐ITD mutations at position N676 and show strong efficacy in FLT3‐ITD‐positive cells alone as well as in combination with chemotherapy. We propose that further development of methanone compounds overcoming resistance to currently established FLT3‐TKIs is an important step forward to an anticipated need within our future therapeutic algorithm in FLT3‐ITD‐positive AML.

Computational analysis of ABL kinase mutations allows predicting drug sensitivity against selective kinase inhibitors

The ABL kinase inhibitor imatinib has been used as front-line therapy for Philadelphia-positive chronic myeloid leukemia. However, a significant proportion of imatinib-treated patients relapse due to occurrence of mutations in the ABL kinase domain. Although inhibitor sensitivity for a set of mutations was reported, the role of less frequent ABL kinase mutations in drug sensitivity/resistance is not known. Moreover, recent reports indicate distinct resistance profiles for second-generation ABL inhibitors. We thus employed a computational approach to predict drug sensitivity of 234 point mutations that were reported in chronic myeloid leukemia patients. Initial validation analysis of our approach using a panel of previously studied frequent mutations indicated that the computational data generated in this study correlated well with the published experimental/clinical data. In addition, we present drug sensitivity profiles for remaining point mutations by computational docking analysis using imatinib as well as next generation ABL inhibitors nilotinib, dasatinib, bosutinib, axitinib, and ponatinib. Our results indicate distinct drug sensitivity profiles for ABL mutants toward kinase inhibitors. In addition, drug sensitivity profiles of a set of compound mutations in ABL kinase were also presented in this study. Thus, our large scale computational study provides comprehensive sensitivity/resistance profiles of ABL mutations toward specific kinase inhibitors.

Synthesis of Novel Imine Stilbene Analogs Exhibiting Potent Anticancer Activity

BACKGROUND Resveratrol (RV) and its analogues Aza-stilbenes were found effective in exhibiting anticancer activity. OBJECTIVE The present study mainly focused on the green synthesis of novel imine stilbene analogues and evaluation of their anticancer activity besides their influence on hypoxia-induced gene expression in cancer cells. METHOD Novel imine stilbenes, differing in number and/or position of hydroxyl and methoxy functional groups, have been synthesized using green chemistry mediated condensation reaction between aldehydes and amines in the ethanolic extract of Psoralea corylifolia hairy roots and tested for their anticancer potential. RESULTS Ethanol containing 1% hairy root extract facilitated instant reaction and yielded more than 99% product( s). MTT assay on HeLa cells treated with imine stilbene analogues revealed an increase in the inhibition of cell proliferation as compared to RV. Treatment of nontumor HEK293 cells with these compounds disclosed minimal toxicity implying the selective advantage of these compounds for cervical cancer therapy. Scratch assay on HeLa cells displayed inhibition of directional cell motility by these analogues and compound 3e [4-((E)-(4- hydroxyphenylimino)methyl)-2-methoxyphenol] recorded maximum inhibition. In reporter assay, as compared to untreated N-(2-Methoxy-2-oxoacetyl) glycine methyl ester (DMOG) induced cells, hypoxia response element- directed transcriptional activity has been significantly reduced in DMOG induced cells treated with imine stilbene analogues. CONCLUSION Overall results indicated that four of the five imine stilbene analogues exhibited enhanced anticancer activity than that of the RV. As such, the novel synthetic compounds 3d, 3e and 3b endowed with potent anticancer activity than RV can serve as drug lead molecules.