A simple and rapid pre-clinical in vivo model reveals comparative cardiotoxicity profiles of kinase inhibitors

Despite significant success, targeted therapeutics such as kinase inhibitors (KIs) still pose adverse events such as the cardiotoxicity. There is a lot of variation in the type and intensity of cardiotoxicity caused by different KIs and current pre-clinical models are inadequate to predict it. Thus, there is a need to develop more simple and rapid models for screening of novel KIs at the pre-clinical step itself. We thus aimed to establish a rapid and robust pre-clinical animal model for predicting cardiotoxicity of KIs and identify comparative cardiotoxicity profiles of a panel of FDA-approved KIs. Heart rate measurement and survival analysis of Daphnia was performed at regular intervals following treatment with ten KIs that were approved for the treatment of various cancers. The heart rates of Daphnia as well as the survival varied between KIs in a dose and time dependent manner suggesting differential cardiotoxicity profiles of various KIs. Further, the correlation between the cardiotoxicity and survival also varied among the ten KIs. Importantly, sorafenib and vemurafenib displayed maximum and least cardiotoxicity, respectively. The comparative cardiotoxicity profiles also are in conformity with the previous studies indicating the utility of Daphnia as a valuable and relevant animal model to rapidly predict the cardiotoxicity of novel KIs at a pre-clinical stage.

AMPK-induced novel phosphorylation of RUNX1 inhibits STAT3 activation and overcome imatinib resistance in chronic myelogenous leukemia (CML) subjects

Imatinib resistance remains an unresolved problem in CML disease. Activation of JAK2/STAT3 pathway and increased expression of RUNX1 have become one reason for development of imatinib resistance in CML subjects. Metformin has gained attention as an antileukemic drug in recent times. However, the molecular mechanism remains elusive. The present study shows that RUNX1 is a novel substrate of AMP-activated kinase (AMPK), where AMPK phosphorylates RUNX1 at Ser 94 position. Activation of AMPK by metformin could lead to increased cytoplasmic retention of RUNX1 due to Ser 94 phosphorylation. RUNX1 Ser 94 phosphorylation resulted in increased interaction with STAT3, which was reflected in reduced transcriptional activity of both RUNX1 and STAT3 due to their cytoplasmic retention. The reduced transcriptional activity of STAT3 and RUNX1 resulted in the down-regulation of their signaling targets involved in proliferation and anti-apoptosis. Our cell proliferation assays using in vitro resistant cell line models and PBMCs isolated from CML clinical patients and normal subjects demonstrate that metformin treatment resulted in reduced growth and improved imatinib sensitivity of resistant subjects.

Metformin exerts antileukemic effects by modulating lactate metabolism and overcomes imatinib resistance in chronic myelogenous leukemia

Imatinib is the frontline treatment option in treating chronic myelogenous leukemia (CML). Hitherto, some patients relapse following treatment. Biochemical analysis of a panel of clonally derived imatinib-resistant cells revealed enhanced glucose uptake and ATP production, suggesting increased rates of glycolysis. Interestingly, increased lactate export was also observed in imatinib-resistant cell lines. Here, we show that metformin inhibits the growth of imatinib-resistant cell lines as well as peripheral blood mononuclear cells isolated from patients who relapsed following imatinib treatment. Metformin exerted these antiproliferative effects by inhibiting MCT1 and MCT4, leading to the inhibition of lactate export. Furthermore, glucose uptake and ATP production were also inhibited following metformin treatment due to the inhibition of GLUT1 and HK-II in an AMPK-dependent manner. Our results also confirmed that metformin-mediated inhibition of lactate export and glucose uptake occurs through the regulation of mTORC1 and HIF-1α. These results delineate the molecular mechanisms underlying metabolic reprogramming leading to secondary imatinib resistance and the potential of metformin as a therapeutic option in CML.

Large-scale pathogenicity prediction analysis of cancer-associated kinase mutations reveals variability in sensitivity and specificity of computational methods

BACKGROUND

Mutations in kinases are the most frequent genetic alterations in cancer; however, experimental evidence establishing their cancerous nature is available only for a small fraction of these mutants.

AIMS

Predicition analysis of kinome mutations is the primary aim of this study. Further objective is to compare the performance of various softwares in pathogenicity prediction of kinase mutations.

MATERIALS AND METHODS

We employed a set of computational tools to predict the pathogenicity of over forty-two thousand mutations and deposited the kinase-wise data in Mendeley database (Estimated Pathogenicity of Kinase Mutants [EPKiMu]).

RESULTS

Mutations are more likely to be drivers when being present in the kinase domain (vs. non-kinase domain) and belonging to hotspot residues (vs. non-hotspot residues). We identified that, while predictive tools have low specificity in general, PolyPhen-2 had the best accuracy. Further efforts to combine all four tools by consensus, voting, or other simple methods did not significantly improve accuracy.

DISCUSSION

The study provides a large dataset of kinase mutations along with their predicted pathogenicity that can be used as a training set for future studies. Furthermore, a comparative sensitivity and selectivity of commonly used computational tools is presented.

CONCLUSION

Primary-structure-based in silico tools identified more cancerous/deleterious mutations in the kinase domains and at the hot spot residues while having higher sensitivity than specificity in detecting deleterious mutations.

Applications of promiscuity of FDA-approved kinase inhibitors in drug repositioning and toxicity

Promiscuity of therapeutics has important implications in treatment and toxicity. So far, a comprehensive understanding of promiscuity related to kinase inhibitors is lacking and such an analysis may offer potential opportunities for drug repurposing. In the present study, profiling of inhibitor-specific kinases based on the available biochemical IC50s was performed, fold-change of IC50 values for additional targets were calculated by taking the primary target as the reference kinase, and finally the promiscuity degree (PD) for FDA-approved kinase inhibitors was calculated. Surprisingly, class II inhibitors showed more PD than that of the class I inhibitors. We further identified cancer types and sub-types in which additional kinase targets or off-targets of inhibitors were overexpressed for potential drug repurposing. In addition, the expression of these kinases in normal human tissues were also profiled to predict toxicity following drug repositioning. Taken together, the study offers opportunities for cancer treatment in a kinase-specific manner.

Molecular docking analysis reveals differential binding affinities of multiple classes of selective inhibitors towards cancer-associated KRAS mutants

KRAS is the most frequently mutated oncogene in solid cancers, and inhibitors that specifically target the KRAS-G12C mutant were recently approved for clinical use. The limited availability of experimental data pertaining to the sensitivity of KRAS-non-G12C mutants towards RAS inhibitors made it difficult to predict the response of KRAS-mutated cancers towards RAS-targeted therapies. The current study aims at evaluating sensitivity profiles of KRAS-non-G12C mutations towards clinically approved sotorasib and adagrasib, and experimental RAS inhibitors based on binding energies derived through molecular docking analysis. Computationally predicted sensitivities of KRAS mutants conformed with the available but limited experimental data, thus validating the usefulness of molecular docking approach in predicting clinical response towards RAS inhibitor treatment. Our results indicate differential sensitivity of KRAS mutants towards both clinical and experimental therapeutics; while certain mutants exhibited broad cross-resistance to most inhibitors, some mutants showed resistance towards specific inhibitors. These results thus suggest the potential of emergence of more resistance mutations in future towards RAS-targeted therapy and points to an urgent need to develop novel classes of inhibitors that are able to overcome both primary and secondary drug resistance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03407-9.

Squamous cell carcinoma of the lung: Improving the detection and management of immune-related adverse events

INTRODUCTION

Immune checkpoint inhibitors (ICIs) have revolutionized treatment for patients with non-small lung cancer (NSCLC). Currently approved ICIs are monoclonal antibodies that target programmed death receptor 1 (PD-1), its ligand PD-L1, or CTLA-4. With ICIs comes a novel collection of toxicities: immune-related adverse events (IRAEs). Management of IRAEs requires multidisciplinary expertise. We review the biology of IRAEs and their management in patients with squamous NSCLC.

AREAS COVERED

We review the pathophysiology of ICIs and IRAEs. For IRAEs related to squamous NSCLC, Cochrane Central, EMBASE, and PubMed were queried for trials with patients with squamous cell carcinoma or adenocarcinoma histology, who were assessed for incidence rates of IRAEs. Thirteen trials met inclusion criteria. National guidelines are reviewed to outline management strategies for IRAEs.

EXPERT OPINION

IRAEs are unique compared to standard chemotherapy. As the role of ICIs expand across all stages of squamous cell NSCLC and with different combinations of antineoplastics, management of IRAEs will become crucial. Optimal management of IRAEs requires multidisciplinary teamwork. Further investigation into the pathophysiology of IRAEs can enhance current management strategies.

Analysis of cellular models of clonal evolution reveals co-evolution of imatinib and HSP90 inhibitor resistances

Treatment relapse due to clonal evolution was shown to be an independent factor for poor prognosis in advanced stages of chronic myeloid leukemia. Overcoming secondary resistance arising due to clonal evolution is still an unmet need and lack of adequate pre-clinical models hampers the identification of underlying mechanisms and testing of alternate treatment strategies. The current study thus aimed to create cellular models to study molecular mechanisms underlying clonal evolution and identify strategies to overcome the secondary drug resistance. Analysis of cell lines derived from three independent cell-based screens revealed the co-evolution specifically of imatinib and HSP90 inhibitor (HSP90i) resistances despite their exposure to a single inhibitor alone. Molecular and biochemical characterization of these cell lines revealed additional cytogenetic abnormalities, differential activation of pro-survival signaling molecules and over expression of ABL kinase and HSP90 genes. Importantly, all the imatinib-HSP90i dual resistant cell lines remained sensitive to sorafenib and vorinostat suggesting their utility in treating patients who relapse upon imatinib treatment due to clonal evolution. In addition, we cite similar examples of dual resistance towards various kinase inhibitors and HSP90i in some cell lines that represent solid cancers suggesting co-evolution leading to secondary drug resistance as a pan-cancer phenomenon. Taken together, our results suggest the efficacy of HSP90i in overcoming drug resistance caused by point mutations in the target kinase but not in cases of clonal evolution.

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors in non-small cell lung cancer harboring uncommon EGFR mutations: Focus on afatinib

The development of first-, second-, and third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) has revolutionized the treatment of patients with non-small cell lung cancer (NSCLC) harboring mutations in the EGFR. However, limited data are available regarding the activity of available EGFR TKIs against uncommon EGFR mutations. This is an important question because improvements in screening techniques are facilitating the identification of patients with uncommon mutations for whom optimal treatment has not yet been clarified. This uncertainty reflects the fact that most prospective clinical trials of EGFR TKIs have been restricted to patients with tumor harboring common (Del19 or L858R) mutations. In this article, we discuss the nature of EGFR mutation heterogeneity in NSCLC and review recent preclinical and clinical data that have assessed the sensitivity of different mutations to different EGFR TKIs. Recent preclinical data indicate that second-generation ErbB family blockers, such as afatinib, have a broad activity profile across uncommon EGFR mutations. Emerging evidence indicates that the preclinical data for afatinib are reflected in the clinic. Subanalysis of clinical trials, and real-world data, demonstrate that EGFRs with defined, but uncommon mutations such as G719X, S768I, and L861Q are sensitive to afatinib, which is now approved for tumors harboring these mutations. A recent clinical trial has demonstrated that EGFRs harboring some of these less common mutations also appear to be sensitive to the third-generation EGFR TKI, osimertinib. Treatment options for tumors with other uncommon mutations, notably exon 20 insertion, remain an area of unmet need, although osimertinib has shown preclinical activity in this setting, and early clinical activity has been seen with the dual EGFR/HER2 TKIs, poziotinib and TAK-788. Further data are required to help drive appropriate treatment decisions in patients whose tumors harbor these uncommon EGFR mutations. To see an abstract video summarising the content of the paper, please visit http://usscicomms.com/oncology/masood/seminars-in-oncology/.

Evolvement of nutraceutical onion plants engineered for resveratrol biosynthetic pathway

Genetically engineered onion expressing codon-optimized VvSTS1 gene accumulated stilbenes and extended life span in yeast and can serve as potential nutraceutical. Resveratrol (RV) is a natural polyphenolic compound found in certain plant species including grapes. RV is well known for its nutraceutical properties and to assuage several disease conditions. Onion is the second most consumed vegetable worldwide and contains large quantities of precursor molecules, malonyl-CoA and para-coumaroyl-CoA that are needed for RV biosynthesis. The present study reports the development of nutraceutical onion by engineering RV biosynthetic pathway. A codon-optimized grapevine synthetic stilbene synthase gene (VvSTS1) was synthesized using native grapevine sequence. Six-week-old healthy yellowish compact nodular calli were co-cultivated with Agrobacterium tumefaciens harbouring pCAMBIA1300-hpt II-CaMV35S-VvSTS1-nos. PCR analysis revealed the presence of VvSTS1 and hpt II genes in putative transgenics. Southern blot analysis confirmed the integration of VvSTS1 gene and independent nature of transformants. LC-ESI-HRMS analysis revealed the accumulation of variable quantities of RV (24.98-50.18 µg/g FW) and its glycosylated form polydatin (33.6-67.15 µg/g FW) in both leaves and bulbs, respectively, indicating the successful engineering of RV biosynthetic pathway into onion. The transgenic onion bulb extracts extended the life span in haploid yeast. The transgenic onion accumulating RV and polydatin, developed for the first of its kind, may serve as a potential nutraceutical resource.

Emergence of ERBB2 Mutation as a Biomarker and an Actionable Target in Solid Cancers

The oncogenic role ERBB2 amplification is well established in breast and gastric cancers. This has led to the development of a well-known portfolio of monoclonal antibodies and kinase inhibitors targeting the ERBB2 kinase. More recently, activating mutations in the ERBB2 gene have been increasingly reported in multiple solid cancers and were shown to play an oncogenic role similar to that of ERBB2 amplification. Thus, ERBB2 mutations define a distinct molecular subtype of solid tumors and serve as actionable targets. However, efforts to target ERBB2 mutation has met with limited clinical success, possibly because of their low frequency, inadequate understanding of the biological activity of these mutations, and difficulty in separating the drivers from the passenger mutations. Given the current impetus to deliver molecularly targeted treatments for cancer, there is an important need to understand the therapeutic potential of ERBB2 mutations. Here we review the distribution of ERBB2 mutations in different tumor types, their potential as a novel biomarker that defines new subsets in many cancers, and current data on preclinical and clinical efforts to target these mutations. IMPLICATIONS FOR PRACTICE: A current trend in oncology is to identify novel genomic drivers of solid tumors and developing precision treatments that target them. ERBB2 amplification is an established therapeutic target in breast and gastric cancers, but efforts to translate this finding to other solid tumors with ERBB2 amplification have not been effective. Recently the focus has turned to targeting activating ERBB2 mutations. The year 2018 marked an important milestone in establishing ERBB2 mutation as an important actionable target in multiple cancer types. There have been several recent preclinical and clinical studies evaluating ERBB2 mutation as a therapeutic target with varying success. With increasing access to next-generation sequencing technologies in the clinic, oncologists are frequently identifying activating ERBB2 mutations in patients with cancer. There is a significant need both from the clinician and bench scientist perspectives to understand the current state of affairs for ERBB2 mutations.

Synthesis and cytotoxicity of novel 14α-O-(1,4-disubstituted-1,2,3-triazolyl) ester derivatives of andrographolide

A series of novel 14α-O-(1,4-disubstituted-1,2,3-triazolyl) ester derivatives of andrographolide (5a-n) were synthesized from andrographolide (1). For this endeavour, selective esterification at C-14 hydroxyl group of andrographolide (1) with propiolic acid via protection, deprotection strategy followed by 1,4-regioselective [1,3]dipolar cycloaddition of alkyne, azide using Cu(I) catalyzed Click chemistry. All the synthesized derivatives were screened for their cytotoxicity on HCT-15, HeLa and K562 cell lines. Compounds 5c and 5j showed highest activity against HCT-15 and K562 cell lines whereas compound 5a displayed activity in all the three cell lines. Loss of cell viability was not observed with the non-transformed cell line MRC-5 with compounds 5j, 5k, 5h and 2 indicating cytotoxic activity of these compounds towards cancer cell lines. Further, molecular docking analysis and SAR studies of highly active compounds 5c and 5j revealed enhanced binding affinity to the target NF-κB protein.

Molecular docking analysis of imine stilbene analogs and evaluation of their anti-aging activity using yeast and mammalian cell models

The NAD⁺-dependent histone deacetylase SIRT1 was shown to be associated with aging and longevity. A stilbene, resveratrol (RV) was shown to exert anti-aging activity by stimulating the SIRT1 activity. However, the utility of RV is limited by its low bioavailability and structural instability. It is thus envisaged to test imine stilbene (IMS) analogs of RV for their potential anti-aging activity. In the present study, molecular docking analysis of five IMS analogs (3a, 3b, 3c, 3d and 3e) against the SIRT1 protein has been carried out. All the five IMS analogs displayed enhanced binding affinity towards SIRT1; three out of five IMS analogs (3a, 3 b, 3e) showed significantly higher affinity with lower binding energies (-9.58, -9.54, and -9.82 kcal mol^-1) than RV (-8.11 kcal mol^-1). Further, experimental validation of anti-aging activity was performed by measuring the chronological life span in vitro using yeast and cellular replicative senescence (CRS) in mammalian cell line models. All IMS analogs extended the chronological life span in yeast as compared to untreated cells as well as RV treated cells. Enhanced anti-aging activity was also observed in an analogous mammalian cell line model upon treatment with either RV or IMS analogs. The results thus suggest that most of the IMS analogs tested may serve as potent drug lead molecules with anti-aging activity.

Elucidation of conformational diversity of druggable enzymes and classification of chemical modulators based on inhibitor-bound structures

Communicated by Ramaswamy H. Sarma.

Computational Analysis of Epidermal Growth Factor Receptor Mutations Predicts Differential Drug Sensitivity Profiles toward Kinase Inhibitors

INTRODUCTION

A significant proportion of patients with lung cancer carry mutations in the EGFR kinase domain. The presence of a deletion mutation in exon 19 or L858R point mutation in the EGFR kinase domain has been shown to cause enhanced efficacy of inhibitor treatment in patients with NSCLC. Several less frequent (uncommon) mutations in the EGFR kinase domain with potential implications in treatment response have also been reported. The role of a limited number of uncommon mutations in drug sensitivity was experimentally verified. However, a huge number of these mutations remain uncharacterized for inhibitor sensitivity or resistance.

METHODS

A large-scale computational analysis of clinically reported 298 point mutants of EGFR kinase domain has been performed, and drug sensitivity profiles for each mutant toward seven kinase inhibitors has been determined by molecular docking. In addition, the relative inhibitor binding affinity toward each drug as compared with that of adenosine triphosphate was calculated for each mutant.

RESULTS

The inhibitor sensitivity profiles predicted in this study for a set of previously characterized mutants correlated well with the published clinical, experimental, and computational data. Both the single and compound mutations displayed differential inhibitor sensitivity toward first- and next-generation kinase inhibitors.

CONCLUSIONS

The present study provides predicted drug sensitivity profiles for a large panel of uncommon EGFR mutations toward multiple inhibitors, which may help clinicians in deciding mutant-specific treatment strategies.

Silver-catalyzed synthesis of pyrrolopiperazine fused with oxazine/imidazole via a domino approach: evaluation of anti-cancer activity

Ag-Catalyzed synthesis of pyrrolopiperazine fused with oxazine/imidazole by the reaction of δ-alkynyl aldehydes and nucleophilic amines was performed. Several of these compounds were found to exhibit anti-cancer activity against cancer cell lines.

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.

FeCl3 catalysed 7-membered ring formation in a single pot: a new route to indole-fused oxepines/azepines and their cytotoxic activity

FeCl₃ catalysed construction of 7 membered ring, oxepine and azepine derivatives by the reaction of 2,3-dichloro N-heterocycles with 2-(1H-indol-2-yl)phenol/aniline. Several of these compounds were found anti-proliferative properties against cancer cell lines.

Targeting oncoprotein stability overcomes drug resistance caused by FLT3 kinase domain mutations

FLT3 is the most frequently mutated kinase in acute myeloid leukemia (AML). Internal tandem duplications (ITDs) in the juxta-membrane region constitute the majority of activating FLT3 mutations. Several FLT3 kinase inhibitors were developed and tested in the clinic with significant success. However, recent studies have reported the development of secondary drug resistance in patients treated with FLT3 inhibitors. Since FLT3-ITD is an HSP90 client kinase, we here explored if targeting the stability of drug-resistant FLT3 mutant protein could be a potential therapeutic option. We observed that HSP90 inhibitor treatment resulted in the degradation of inhibitor-resistant FLT3-ITD mutants and selectively induced toxicity in cells expressing FLT3-ITD mutants. Thus, HSP90 inhibitors provide a potential therapeutic choice to overcome secondary drug resistance following TKI treatment in FLT3-ITD positive AML.

Analysis of conformational determinants underlying HSP90-kinase interaction

The role of HSP90 in stabilization of oncogenic tyrosine kinases made it an attractive therapeutic target for treating cancer but the molecular basis underlying the interaction between the HSP90 chaperone and client kinases is not elucidated yet. Using kinase inhibitors we show that the inactive conformation of ERBB2 does not interact with HSP90 chaperone and is thus not amenable to degradation upon HSP90 inhibitor treatment, while active ERBB2 kinase conformation promotes interaction with the HSP90 machinery and thus is degraded upon HSP90 inhibitor treatment. Interestingly, the kinase-chaperone interaction is disrupted in case of BCR-ABL and FLT3-ITD when bound to inhibitors irrespective of whether they block the kinase in an active or inactive conformation and thus our results indicate that the stability of the active kinase conformation varies between different kinases.

Asymmetric kinase dimer formation is crucial for the activation of oncogenic EGFRvIII but not for ERBB3 phosphorylation

Background

Formation of asymmetric kinase dimers is required for wt-EGFR activation upon ligand stimulation. The role of receptor dimerization in oncogenic EGFRvIII mutant activation is not completely understood and the molecular details of EGFRvIII interactions within homo-dimers and hetero-dimers are not elucidated yet.

Findings

By employing mutations that disrupt the asymmetric kinase dimer interface in EGFRvIII, we demonstrate that the mechanism of oncogenic EGFRvIII mutant activation is similar to that of the full-length wild-type EGFR. Surprisingly, the monomeric EGFRvIII lacks autophosphorylation and the formation of asymmetric kinase dimers is indispensable for oncogenic kinase activation. In addition, we show that ERBB3 can act as an activator of EGFRvIII by forming asymmetric kinase dimer in a ligand-independent manner. Interestingly, we found that the formation of asymmetric kinase dimer is dispensable for ERBB3 phosphorylation by the activated EGFR kinase as well as the ERBB2 kinase thus revealing a novel model for receptor function.

Conclusions

Lateral signaling is a novel mechanism of signal propagation via ERBB3 upon activation by EGFR/ERBB2 kinase even in the absence of their ability to form asymmetric kinase dimers.

Abstract 1887: Targeting oncoprotein stability overcomes lapatinib-resistance due to ERBB2 kinase domain mutations

ERBB2 kinase domain mutations were recently reported in some solid cancers. Moreover, certain ERBB2 mutations were shown to cause lapatinib resistance in vitro thus predicting their emergence in treated patients. We have recently shown that ERBB2-L755S, ERBB2-L755P and ERBB2-T798M mutants cause lapatinib resistance by stabilizing the active kinase conformation (DFG-in), which is incompatible with lapatinib binding (DFG-out). Using an in vitro cell-based drug resistance screen we also showed that these lapatinib resistant mutations might cause secondary resistance in patients treated with lapatinb. Thus, it is important to search for alternate treatment strategies to overcome lapatinib resistance. ERBB2 kinase is a client for HSP90 and is degraded by HSP90 inhibitor treatment. We thus tested if targeting ERBB2 mutant stability by inhibiting HSP90 overcomes lapatinib resistance. Since the kinase domain is important for the ERBB2 interaction with HSP90, we tested whether ERBB2 kinase domain mutants retained their interaction with the chaperone. Co-immunoprecipitation analysis showed that the interaction of ERBB2 mutants with HSP90 is intact. Importantly, HSP90 inhibitor treatment resulted in the degradation of lapatinib-resistant ERBB2 mutants as observed with the wild type ERBB2 kinase. Thus, HSP90 inhibitors may offer an alternative treatment option to overcome primary or secondary lapatinib resistance in patients harbouring ERBB2 mutations. Moreover, combined targeting of different physiological aspects (enzyme activity and protein stability) may prevent the emergence of secondary drug resistance due to kinase domain mutations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1887. doi:1538-7445.AM2012-1887

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. IC(50) 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.

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

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.

Sensitivity toward sorafenib and sunitinib varies between different activating and drug-resistant FLT3-ITD mutations

OBJECTIVE

Activating mutations in FLT3 are known to be a frequent transforming event in acute myeloid leukemia. Small molecule-inhibitor therapy targeting the FLT3 kinase is, therefore, an attractive strategy. FLT3 kinase inhibitors, such as PKC412, have already entered clinical trials. Even though results are encouraging, emergence of primary and secondary resistance does occur in the majority of patients. Thus, it will be crucial to carefully characterize the activity of every single compound against different activating and resistance FLT3-internal tandem duplication (ITD) mutations. Here we tested the efficacy of sunitinib and sorafenib to inhibit primary FLT3 activating mutations (ITD and D835Y) and of secondary resistance mutations.

METHODS

Ba/F3 cell lines stably expressing oncogenic FLT3 mutations were used to calculate cellular IC(50) values for sunitinib and sorafenib using cell proliferation assays. Differential IC(50) values for sorafenib toward FLT3-ITD and FLT3-D835Y were confirmed by Western blotting. Cell death was measured by propidium-iodide staining and flow cytometry.

RESULTS

Sorafenib inhibits FLT3-ITD more potent than FLT3-D835Y, while sunitinib is equally effective against both mutant forms of FLT3. Importantly, sensitivity toward sorafenib and sunitinib varies between the different secondary FLT3-ITD resistance mutations.

CONCLUSIONS

These results establish sensitivity profiles for the FLT3 inhibitors sunitinib and sorafenib. This may help to develop rational treatment strategies for acute myeloid leukemia with these compounds.

Nickel is a specific antagonist for the catabolism of activated alpha 2-macroglobulin

The multifunctional low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP) binds and degrades several ligands involved in protease and lipoprotein metabolism. We previously reported that nickel (Ni2+) specifically inhibits the binding of activated alpha 2-macroglobulin (alpha 2 M*) at 4 degrees C to LRP and had no effect on the binding of other ligands to the receptor (Hussain et al. (1995) Biochem. 34, 16074-16081). In the current investigation, we have examined the effect of Ni2+ on the catabolism of 125 I-labeled alpha 2M*, receptor-associated protein (RAP) and lactoferrin at physiologic temperatures by fibroblasts. Nickel completely inhibited the degradation of alpha 2M* over a wide range of concentrations (0.3-2.4 nM); 50% inhibition for the degradation of 1.2 nM alpha 2M* was observed at 0.5 mM Ni2+. Furthermore, nickel inhibited the binding, internalization and degradation of 125I-alpha 2M* in a dose- and time-dependent manner. In contrast, the degradation of several concentrations of 125I-RAP by fibroblasts was not affected by different amounts of Ni2+ for various times. Similarly, Ni2+ did not inhibit the degradation of lactoferrin either before or after treating the cells with heparitinase to remove cell-surface proteoglycans. The degradation of lactoferrin was, however, inhibited by the RAP indicating that lactoferrin degradation was mediated by the LRP. These data suggest that Ni2+ is a specific inhibitor for the degradation of alpha 2M*.

Up-regulation of the low density lipoprotein receptor-related protein by dexamethasone in HepG2 cells

Dexamethasone has been shown to decrease the expression of the low density lipoprotein (LDL) receptor, but its effect on other members of the LDL receptor family is not known. We studied the effect of dexamethasone in HepG2 cells on the expression of the LDL receptor family members using radiolabeled receptor associated protein (RAP) which binds to all the members of the family. Treatment of HepG2 cells with increasing concentrations of dexamethasone resulted in a 2-fold increase in the binding and degradation of RAP. To identify the receptor responsible for the increased binding and degradation of RAP, we used specific ligands. For LDL receptor, we used LDL itself. For the LDL receptor-related protein/alpha 2-macroglobulin receptor, we used activated alpha 2-macroglobulin. The binding of LDL to HepG2 cells was decreased, whereas binding and degradation of activated alpha 2-macroglobulin was increased by 2-fold suggesting that dexamethasone increased LRP expression. Increased LRP expression was positively correlated with the increase in the steady-state levels and transcript numbers of the LRP mRNA; no changes in RAP or gamma-actin mRNA levels were observed. Increased mRNA levels were not due to an increased rate of transcription of the gene as assessed by nuclear run-on experiments. These studies indicate that dexamethasone increases cell-surface LRP activity in HepG2 cells by increasing the steady state mRNA levels and suggest that post-transcriptional mechanisms play a role in controlling LRP mRNA levels.

Chylomicron assembly and catabolism: role of apolipoproteins and receptors

Chylomicrons are lipoproteins synthesized exclusively by the intestine to transport dietary fat and fat-soluble vitamins. Synthesis of apoB48, a translational product of the apob gene, is required for the assembly of chylomicrons. The apob gene transcription in the intestine results in 14 and 7 kb mRNAs. These mRNAs are post-transcriptionally edited creating a stop codon. The edited mRNAs chylomicrons from the shorter apoB48 peptide remains to be elucidated. In addition, the roles of proteins involved in the assembly pathway, e.g. apobec-1, MTP and apoA-IV, needs to be studied. Cloning of enzymes involved in the intestinal biosynthesis of triglycerides will be crucial to fully appreciate the assembly of chylomicrons. There is a need for cell culture and transgenic animal models that can be used for intestinal lipoprotein assembly. The catabolism of chylomicrons is far more complex and efficient than the catabolism of VLDL. Even though the major steps involved in the catabolism of chylomicrons are now known, the determinants for apolipoprotein exchange, processing of remnants in the space of Disse, as well as the mechanism of uptake of these particles by extra-hepatic tissue needs further exploration.

Nickel is a specific inhibitor for the binding of activated alpha 2-macroglobulin to the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

The low density receptor-related protein/alpha 2-macroglobulin receptor (LRP/alpha 2-MR) binds to several ligands involved in lipoprotein and protease clearance. The receptor-associated protein (RAP) inhibits the binding of all known ligands. We studied the inhibition by Ni2+ of the binding of different ligands to cells and to the purified LRP/alpha 2-MR. Ni2+ inhibited all of the specific binding of radiolabeled methylamine-activated alpha 2-macroglobulin (125I-alpha 2-M*) to rabbit aortic smooth muscle cells (SMC), rat hepatoma Fu5AH, and mouse fibroblast L cells. Ni2+ also inhibited the binding of trypsin-activated alpha 2-macroglobulin to SMC but did not affect the binding of RAP, Pseudomonas exotoxin A, or low-density lipoproteins. The inhibition of alpha 2-M* binding by Ni2+ was not due to its interaction with alpha 2-M*. Preincubation of SMC with Ni2+ followed by ligand binding suggested that Ni2+ binds to cell-surface molecules and inhibits the binding of alpha 2-M* but does not affect RAP binding. Most of the binding of alpha 2-M* to SMC was due to its binding to the LRP/alpha 2-MR, as opposed to the recently described signaling receptor, as demonstrated by the inhibition of this binding by the RAP. Moreover, the inhibition of alpha 2-M* binding to the LRP/alpha 2-MR by Ni2+ was demonstrated using purified receptor immobilized on microtiter plates. Two to three molecules of 63Ni2+ bound to the immobilized receptor with equal affinity but not to alpha 2-M*. The specific binding of alpha 2-M* to the immobilized receptor was inhibited in the presence of nickel.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of recombinant human apoB-48-containing lipoproteins in rat hepatoma McA-RH7777 cells transfected with apoB-48 cDNA. Overexpression of apoB-48 decreases synthesis of endogenous apoB-100

We studied the effect of overexpression of apolipoprotein (apo) B-48 on the synthesis and secretion of endogenous apoB-100 in rat hepatoma McA-RH7777 cell lines stably transfected with human apoB-48 cDNA under the control of the cytomegalovirus promoter. Three cell lines that secrete 40 to 60 ng human apoB.mg cell protein-1.h-1 were used. The recombinant human apoB-48 exhibited physicochemical characteristics (buoyant density, 1.06 to 1.21 g/mL; beta-electrophoretic mobility and diameters, 16 to 20 nm) indistinguishable from those of endogenous rat apoB-48. Overexpression of the recombinant human apoB-48 resulted in a 50% decrease in the secretion of endogenous apoB-100 but did not affect the secretion of apoE or apoA-I. Several possible mechanisms for the decreased secretion of apoB-100 were evaluated. First, recruitment of lipids into lipoproteins was shown to be unaffected since no major changes in the physicochemical properties of apoB-100-containing lipoproteins were observed. Second, the intracellular degradation of apoB-100 was not altered as the intracellular retention half-time and secretion efficiency remained unaffected by apoB-48 overexpression. Third, the posttranslational regulatory mechanisms for apoB-100 remained normal, as demonstrated by a twofold increase in apoB-100 secretion after supplementation with oleic acid. Unexpectedly, a 35% to 50% decrease in the steady-state synthesis of endogenous apoB-100 was observed in apoB-48-transfected cells compared with control cells. These data suggested that decreased secretion of apoB-100 was secondary to decreased synthesis. The decreased apoB-100 synthesis was not due to decreased steady-state levels of rat apoB-100 mRNA. These results suggest that overexpression of recombinant human apoB-48 may interfere with posttranscriptional events, possibly at the translation-translocation level, and decrease translational yield of apoB-100. These posttranscriptional events prior to the complete synthesis of the apoB-100 polypeptide can be important in the control of apoB-100 secretion.

Contribution of vitamin A deficiency to calculogenic risk factors of urine: studies in children

Studies in experimental animals showed that vitamin A deficiency enhanced the severity of urinary calculi disease. In India, children with low socioeconomic status are the major victims of bladder stone disease, and vitamin A deficiency is also more prevalent among these children. However, no systematic study is available to correlate the vitamin A-deficient status of children with their predisposition to urinary calculi disease. Vitamin A-deficient and normal boys were the subjects of this study. Twenty-four-hour samples of urine were collected from all the children at the beginning of the study and after normalizing the vitamin A status of the deficient children. Important risk factors were estimated in urine. Plasma vitamin A levels were also measured in these children. Among the deficient group, only children with plasma vitamin A levels of 15 micrograms and lower exhibited calcium oxalate crystalluria. Most importantly, abnormal crystalluria was observed in all children whose plasma vitamin A levels were 13 micrograms/dl or less. Compared to normal children the urine of vitamin A-deficient children showed the following changes: (a) reduced concentration of crystal growth inhibitors, namely citrate and glycosaminoglycans; (b) a decline in inhibitory activity toward calcium oxalate crystal growth; and (c) enhanced excretion of high risk factors, namely calcium and oxalate. Correction of vitamin A status normalized the above abnormal properties of urine. The results of this study strongly support the hypothesis that the vitamin A-deficient state is one of the factors that can enhance the risk of urolithiasis in susceptible populations.