A phase I study of EKB-569 in combination with capecitabine in patients with advanced colorectal cancer

Synthesis and biological evaluation of 2-styrylquinolines as antitumour agents and EGFR kinase inhibitors: molecular docking study

A new series of 4,6-disubstituted 2-(4-(dimethylamino)styryl)quinoline 4a,b–9a,b was synthesized by the reaction of 2-(4-(dimethylamino)styryl)-6-substituted quinoline-4-carboxylic acids 3a,b with thiosemicarbazide, p-hydroxybenzaldehyde, ethylcyanoacetate, and 2,4-pentandione. In addition, the antitumour activity of all synthesized compounds 3a,b–9a,b was studied via MTT assay against two cancer cell lines (HepG2 and HCT116). Furthermore, epidermal growth factor receptor (EGFR) inhibition, using the most potent antitumour compounds, 3a, 3b, 4a, 4b, and 8a, was evaluated. The interpretation of the results showed clearly that the derivatives 3a, 4a, and 4b exhibited the highest antitumour activities against the tested cell lines HepG2 and HCT116 with IC₅₀ range of 7.7–14.2 µg/ml, in comparison with the reference drugs 5-fluorouracil (IC₅₀ = 7.9 and 5.3 µg/ml, respectively) and afatinib (IC₅₀ = 5.4 and 11.4 µg/ml, respectively). In vitro EGFR screening showed that compounds 3a, 3b, 4a, 4b, and 8a exhibited moderate inhibition towards EGFR with IC₅₀ values at micromolar levels (IC₅₀ range of 16.01–1.11 µM) compared with the reference drugs sorafenib (IC₅₀ = 1.14 µM) and erlotinib (IC₅₀ = 0.1 µM). Molecular docking was performed to study the mode of interaction of compounds 3a and 4b with EGFR kinase.

Fighting cancer drug resistance: Opportunities and challenges for mutation-specific EGFR inhibitors

Multiple mutations in the EGFR gene are a major cause for the failure of Erlotinib and Gefitinib in the treatment of patients harboring non-small-cell lung cancer (NSCLC) who initially responded to this therapy. The development of these tyrosine kinase inhibitors (TKIs) is going back to the early 90s, where cancer was widely considered and fully treated as a disease of an organ. Fundamental gain of knowledge in cell biology in general and cancer genetics in particular led us to where we currently stand: cancer is a disease that originates in the genome. Fast and affordable gene sequencing paved the way and opened our eyes for the genetic instability of many cancers, particularly EGFR driven NSCLC. This might allow highly rational and personal therapies by aiming at a very particular wild type and mutant kinase pattern. However, the paradigm "one disease - one target - one drug" is currently challenged. Both activating and deactivating EGFR mutations are known to render the development of novel targeted drugs difficult. Among all lung adenocarcinomas, only 20% are driven by EGFR and only a subpopulation has an activating mutation (e.g. L858R), making them sensitive to first generation EGFR inhibitors. Unfortunately, most of them acquire second deactivating mutations (e.g. T790M) during treatment, leading to a complete loss of response. Are specific inhibitors of the double EGFR mutant L858R/T790M the magic bullet? Much scientific evidence but also high expectations justify this approach. Structural biology of EGFR mutants constitutes the basis for highly rational approaches. Second generation pan EGFR inhibitors inhibiting wild type (WT) and mutant EGFR like Afatinib suffer from dose-limiting adverse effects. Inhibition of WT EGFR is considered to be the culprit. Third generation EGFR inhibitors follow two strategies. Mutant selectivity and improved target residential time. These inhibitors display high mutant selectivity and irreversible binding patterns while sparing WT EGFR activity, hence enhancing tumor selectivity while minimizing adverse effects. Third generation EGFR inhibitors are still undergoing preclinical and clinical evaluation. The most advanced are Rociletinib and AZD9291 which displayed encouraging preliminary clinical phase II data regarding response and adverse effects. In the current review we show both a medicinal chemists' approach toward the design of third generation EGFR inhibitors as well as a detailed overview of the development of EGFR inhibitors over the last decade. High interdisciplinary approaches, such as structural biology and time-resolved tumor genetics pave the way toward the development of drugs that target EGFR mutants. This might lead to highly effective targeted and personalized therapies with enhanced response rates for a minor cohort of patients which have to undergo continuous gene sequencing, hence enabling therapies with tailor-made TKIs.

Blockade of glioma proliferation through allosteric inhibition of JAK2

The gene that encodes the epidermal growth factor receptor (EGFR) is frequently overexpressed or mutated in human cancers, including glioblastoma. However, the efficacy of EGFR-targeted small-molecule inhibitors or monoclonal antibodies in glioblastomas that also have mutation or deletion of the gene encoding phosphatase and tensin homolog (PTEN) has been modest. We found that EGFR signaling was blocked by a small molecule (G5-7) that selectively inhibited Janus kinase 2 (JAK2)-mediated phosphorylation and activation of EGFR and STAT3 (signal transducer and activator of transcription 3) by binding to JAK2, thereby decreasing the activity of downstream signaling by mTOR (mammalian target of rapamycin) and inducing cell cycle arrest. G5-7 inhibited the proliferation of PTEN-deficient glioblastoma cell lines harboring a constitutively active variant of EGFR (U87MG/EGFRvIII) and human glioblastoma explant neurosphere cultures, but the drug only weakly inhibited the proliferation of either glioblastoma cell lines that were wild type for EGFR and stably transfected with PTEN (U87MG/PTEN) or normal neural progenitor cells and astrocytes. Additionally, G5-7 reduced vascular endothelial growth factor (VEGF) secretion and endothelial cell migration and induced apoptosis in glioblastoma xenografts, thereby suppressing glioblastoma growth in vivo. Furthermore, G5-7 was more potent than EGFR or JAK2 inhibitors that interfere with either ligand or adenosine 5'-triphosphate (ATP) binding at impeding glioblastoma cell proliferation, demonstrating that this allosteric JAK2 inhibitor may be an effective clinical strategy.

Fixed-dose capecitabine is feasible: results from a pharmacokinetic and pharmacogenetic study in metastatic breast cancer

The pro-drug capecitabine is approved for treatment of anthracycline- and paclitaxel-resistant metastatic breast cancer. However, toxicity and large interpatient pharmacokinetic variability occur despite body surface area (BSA)-dosing. We hypothesized that a fixed-dose schedule would simplify dosing and provide an effective and safe alternative to BSA-based dosing. We conducted an open label, single-arm, two-stage study of oral capecitabine with fixed starting dose (3,000 mg total daily dose in two divided doses × 14 days q21 days) in patients with metastatic breast cancer. We correlated pharmacodynamic endpoints [e.g., efficacy (response) per RECIST and toxicity], adherence and pharmacokinetics/pharmacogenetics. Sample size of 45 patients was required to detect a 25 % response rate from null response rate of 10 % using a Simon two-stage design. Twenty-six patients were enrolled in the first-stage and 21 were evaluable after a median of four cycles of capecitabine. Two thirds of patients received either the same dose or a dose 500 mg lower than what would have been administered with a commonly used 2,000 mg/m(2) BSA-dosing schedule. Eight patients had stable disease but progressed after a median of seven cycles. Despite a clinical benefit rate of 19 %, no RECIST responses were observed following the first stage and the study was closed. Dose-reductions were required for grade 2 hand-foot syndrome (28 %) and vomiting (5 %). Adherence was similar when using both patient-reported and Medication Event Monitoring System methods. High interpatient variability was observed for capecitabine and metabolite pharmacokinetics, but was not attributed to observed pharmacogenetic or BSA differences. Single agent activity of capecitabine was modest in our patients with estrogen receptor-positive or -negative metastatic breast cancer and comparable to recent studies. BSA was not the main source of pharmacokinetic variability. Fixed-dose capecitabine is feasible, and simplifies dosing.

Phase I study of axitinib combined with paclitaxel, docetaxel or capecitabine in patients with advanced solid tumours

Background:

Axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors, enhanced the efficacy of chemotherapy in human xenograft tumour models. This phase I study investigated the safety, tolerability, pharmacokinetics and antitumour activity of axitinib combined with chemotherapy.

Methods:

A total of 42 patients with advanced solid tumours received a continuous axitinib starting dose of 5 mg twice daily (b.i.d.) plus paclitaxel (90 mg m^–2 weekly), docetaxel (100 mg m^–2 every 3 weeks) or capecitabine (1000 or 1250 mg m^–2 b.i.d., days 1–14).

Results:

Common treatment-related adverse events across all cohorts were nausea (45.2%), hypertension (45.2%), fatigue (42.9%), diarrhoea (38.1%), decreased appetite (33.3%) and hand–foot syndrome (31.0%). There was one complete response, nine partial responses and seven patients with stable disease. Ten patients (23.8%) remained on therapy for >8 months. Paclitaxel and capecitabine pharmacokinetics were similar in the absence or presence of axitinib, but docetaxel exposure was increased in the presence of axitinib. Axitinib pharmacokinetics were similar in the absence or presence of co-administered agents.

Conclusions:

Axitinib combined with paclitaxel or capecitabine was well tolerated; no additive increase in toxicities was observed. Antitumour activity was observed for each treatment regimen and across multiple tumour types.

Clinical perspectives for irreversible tyrosine kinase inhibitors in cancer

Irreversible inhibitors provide potent and selective inhibition of tyrosine kinase enzymes. Use of such inhibitors has proved promising in overcoming the tumor resistance encountered with reversible tyrosine kinase inhibitors. Irreversible inhibitors inactivate their protein target through covalent interaction with a nucleophilic cysteine residue within the nucleotide binding pocket of the kinase domain. Different irreversible tyrosin kinase inhibitors directed against epidermal growth factor receptor (EGFR), Bruton's tyrosine kinase (BTK), vascular endothelial growth factor receptor (VEGFR) and fibroblast growth factor receptor tyrosine kinase (FGFR) have been developed and some of them have been employed clinically as anticancer agents. This review focuses on recent preclinical and clinical progress with currently available irreversible tyrosine kinase inhibitors. The chemical structures of the candidates, structure-activity relationships, biological activities and results of current clinical investigations are described.

Phase I study of temsirolimus in combination with EKB-569 in patients with advanced solid tumors

Purpose Activation of EGFR can stimulate proliferative and survival signaling through mTOR. Preclinical data demonstrates synergistic activity of combined EGFR and mTOR inhibition. We undertook a phase I trial of temsirolimus (T, an mTOR inhibitor) and EKB-569 (E, an EGFR inhibitor) to determine the safety and tolerability. Methods The primary aim was to determine the maximally tolerated dose (MTD) of this combination in adults with solid tumors. Following the dose-escalation phase, (Cohort A), two subsequent cohorts were used to assess any pharmacokinetic (PK) interaction between the agents. Results Forty eight patients were enrolled. The MTD of this combination was E, 35 mg daily and T, 30 mg on days 1-3 and 15-17 using a 28-day cycle. The most common toxicities were nausea, diarrhea, fatigue, anorexia, stomatitis, rash, anemia, neutropenia, thrombocytopenia, and hypertriglyceridemia. Sixteen patients (36%) had at least one grade 3 toxicity. The most frequent grade 3/4 toxicities were diarrhea, dehydration, and nausea and vomiting (19% each). No grade 5 events were seen. Four patients had a partial response and 15 had stable disease. Clinical benefit was seen across a range of tumor types and in all cohorts. PK analysis revealed no significant interaction between E and T. Conclusions This combination of agents is associated with tolerable toxicities at doses that induced responses. PK studies revealed no interaction between the drugs. Further investigations of this targeting strategy may be attractive in renal cell carcinoma, non-small cell lung cancer, alveolar sarcoma, and carcinoid tumor.

Protein kinase biochemistry and drug discovery

Protein kinases are fascinating biological catalysts with a rapidly expanding knowledge base, a growing appreciation in cell regulatory control, and an ascendant role in successful therapeutic intervention. To better understand protein kinases, the molecular underpinnings of phosphoryl group transfer, protein phosphorylation, and inhibitor interactions are examined. This analysis begins with a survey of phosphate group and phosphoprotein properties which provide context to the evolutionary selection of phosphorylation as a central mechanism for biological regulation of most cellular processes. Next, the kinetic and catalytic mechanisms of protein kinases are examined with respect to model aqueous systems to define the elements of catalysis. A brief structural biology overview further delves into the molecular basis of catalysis and regulation of catalytic activity. Concomitant with a prominent role in normal physiology, protein kinases have important roles in the disease state. To facilitate effective kinase drug discovery, classic and emerging approaches for characterizing kinase inhibitors are evaluated including biochemical assay design, inhibitor mechanism of action analysis, and proper kinetic treatment of irreversible inhibitors. As the resulting protein kinase inhibitors can modulate intended and unintended targets, profiling methods are discussed which can illuminate a more complete range of an inhibitor's biological activities to enable more meaningful cellular studies and more effective clinical studies. Taken as a whole, a wealth of protein kinase biochemistry knowledge is available, yet it is clear that a substantial extent of our understanding in this field remains to be discovered which should yield many new opportunities for therapeutic intervention.

AST1306, a novel irreversible inhibitor of the epidermal growth factor receptor 1 and 2, exhibits antitumor activity both in vitro and in vivo

Despite the initial response to the reversible, ATP-competitive quinazoline inhibitors that target ErbB-family, such a subset of cancer patients almost invariably develop resistance. Recent studies have provided compelling evidence that irreversible ErbB inhibitors have the potential to override this resistance. Here, we found that AST1306, a novel anilino-quinazoline compound, inhibited the enzymatic activities of wild-type epidermal growth factor receptor (EGFR) and ErbB2 as well as EGFR resistant mutant in both cell-free and cell-based systems. Importantly, AST1306 functions as an irreversible inhibitor, most likely through covalent interaction with Cys797 and Cys805 in the catalytic domains of EGFR and ErbB2, respectively. Further studies showed that AST1306 inactivated pathways downstream of these receptors and thereby inhibited the proliferation of a panel of cancer cell lines. Although the activities of EGFR and ErbB2 were similarly sensitive to AST1306, ErbB2-overexpressing cell lines consistently exhibited more sensitivity to AST1306 antiproliferative effects. Consistent with this, knockdown of ErbB2, but not EGFR, decreased the sensitivity of SK-OV-3 cells to AST1306. In vivo, AST1306 potently suppressed tumor growth in ErbB2-overexpressing adenocarcinoma xenograft and FVB-2/N(neu) transgenic breast cancer mouse models, but weakly inhibited the growth of EGFR-overexpressing tumor xenografts. Tumor growth inhibition induced by a single dose of AST1306 in the SK-OV-3 xenograft model was accompanied by a rapid (within 2 h) and sustained (≥24 h) inhibition of both EGFR and ErbB2, consistent with an irreversible inhibition mechanism. Taken together, these results establish AST1306 as a selective, irreversible ErbB2 and EGFR inhibitor whose growth-inhibitory effects are more potent in ErbB2-overexpressing cells.

Cysteine mapping in conformationally distinct kinase nucleotide binding sites: application to the design of selective covalent inhibitors

Kinases have emerged as one of the most prolific therapeutic targets. An important criterion in the therapeutic success of inhibitors targeting the nucleotide binding pocket of kinases is the inhibitor residence time. Recently, covalent kinase inhibitors have attracted attention since they confer terminal inhibition and should thus be more effective than reversible inhibitors with transient inhibition. The most robust approach to design irreversible inhibitors is to capitalize on the nucleophilicity of a cysteine thiol group present in the target protein. Herein, we report a systematic analysis of cysteine residues present in the nucleotide binding site of kinases, which could be harnessed for irreversible inhibition, taking into consideration the different kinase conformations. We demonstrate the predictive power of this analysis with the design and validation of an irreversible inhibitor of KIT/PDGFR kinases. This is the first example of a covalent kinase inhibitor that combines a pharmacophore addressing the DFG-out conformation with a covalent trap.

A tolerability and pharmacokinetic study of adjuvant erlotinib and capecitabine with concurrent radiation in resected pancreatic cancer

BACKGROUND

Erlotinib is approved for the treatment of advanced pancreas cancer. We conducted a prospective trial to determine the safety profile and recommended phase 2 dose of erlotinib and capecitabine given concurrently with intensity-modulated radiation therapy (IMRT) in resected pancreatic cancer patients. The pharmacokinetic profile of this combination was also evaluated.

METHODS

Patients with resected pancreatic adenocarcinoma received erlotinib and capecitabine concurrently with IMRT delivered at 1.8 Gy daily in 28 fractions (total = 50.4 Gy). The starting dose level (DL 1) was erlotinib 150mgdaily and capecitabine 800 mg/m(2) twice daily without interruption. The next lower dose level (DL -1) was erlotinib 100 mg daily and capecitabine 800 mg/m(2) twice daily (Monday to Friday). Plasma samples were obtained for pharmacokinetic analysis.

RESULTS

Thirteen patients were enrolled in total. At DL 1, six of the seven treated patients were evaluable for toxicities. Four completed planned treatment, but all required treatment interruption or dose reduction. The dose-limiting toxicities were neutropenia, diarrhea, and rash. Six patients were subsequently enrolled to and completed planned treatment in DL-1. Themost common toxicities were fatigue, elevated liver enzymes, and anorexia. The pharmacokinetic parameters of erlotinib and OSI-420 were not significantly different in the presence or absence of capecitabine and were consistent with historical controls.

CONCLUSIONS

When administered concurrently with IMRT, erlotinib 100 mg daily and capecitabine 800 mg/m(2) twice daily (Monday to Friday) can be administered safely in resected pancreas cancer patients, and is the recommended regimen for efficacy studies using this regimen.

The PI3 kinase/mTOR blocker NVP-BEZ235 overrides resistance against irreversible ErbB inhibitors in breast cancer cells

Resistance against first and second generation (irreversible) ErbB inhibitors is an unsolved problem in clinical oncology. The purpose of this study was to examine the effects of the irreversible ErbB inhibitors pelitinib and canertinib on growth of breast and ovarian cancer cells. Although in vitro growth-inhibitory effects of both drugs exceeded by far the effects of all reversible ErbB blockers tested (lapatinib, erlotinib, and gefitinib), complete growth inhibition was usually not reached. To define the mechanism of resistance, we examined downstream signaling pathways in drug-exposed cells by Western blot analysis. Although ErbB phosphorylation was reduced by pelitinib and canertinib, activation of the AKT/mTOR pathway remained essentially unaltered in drug-resistant cells. Correspondingly, transfection of tumor cells with constitutively activated AKT was found to promote resistance against all ErbB inhibitors tested, whereas dominant negative AKT reinstalled sensitivity in drug-resistant cells. In a next step, we applied PI3K/AKT/mTOR blockers including the dual PI3K/mTOR kinase inhibitor NVP-BEZ235. These agents were found to cooperate with pelitinib and canertinib in producing in vitro growth inhibition in cancer cells resistant against ErbB-targeting drugs. In conclusion, our data show that ErbB drug-refractory activation of the PI3K/AKT/mTOR pathway plays a crucial role in resistance against classical and second-generation irreversible ErbB inhibitors, and NVP-BEZ235 can override this form of resistance against pelitinib and canertinib.

Development of a new epidermal growth factor receptor positron emission tomography imaging agent based on the 3-cyanoquinoline core: synthesis and biological evaluation

The epidermal growth factor receptor (EGFR/c-ErbB1/HER1) is overexpressed in many cancers including breast, ovarian, endometrial, and non-small cell lung cancer. An EGFR specific imaging agent could facilitate clinical evaluation of primary tumors and/or metastases. To achieve this goal we designed and synthesized a small array of fluorine containing compounds based on a 3-cyanoquinoline core. A lead compound, 16, incorporating 2'-fluoroethyl-1,2,3-triazole was selected for evaluation as a radioligand based on its high affinity for EGFR kinase (IC50=1.81+/-0.18 nM), good cellular potency (IC50=21.97+/-9.06 nM), low lipophilicity and good metabolic stability. 'Click' labeling afforded [18F]16 in 37.0+/-3.6% decay corrected radiochemical yield based on azide [18F]14 and 7% end of synthesis (EOS) yield from aqueous fluoride. Compound [18F]16 was obtained with >99% radiochemical purity in a total synthesis time of 3 h. The compound showed good stability in vivo and a fourfold higher uptake in high EGFR expressing A431 tumor xenografts compared to low EGFR expressing HCT116 tumor xenografts. Furthermore, the radiotracer could be visualized in A431 tumor bearing mice by small animal PET imaging. Compound [18F]16 therefore constitutes a promising radiotracer for further evaluation for imaging of EGFR status.

Thymidylate synthase (TYMS) enhancer region genotype-directed phase II trial of oral capecitabine for 2nd line treatment of advanced pancreatic cancer

PURPOSE

The primary aim of this study was to characterize the 6-month overall survival and toxicity associated with second-line capecitabine treatment of advanced pancreatic cancer patients harboring the TYMS *2/*2 allele. The secondary aim was to analyze the response rate and pharmacokinetics of capecitabine-based therapy in this patient population. Lastly, TYMS, ATM and RecQ1 single nucleotide polymorphism were analyzed relative to overall survival in patients screened for study participation.

METHODS

Eighty patients with stage IV pancreatic cancer were screened for the *2/*2 TYMS allele. Patients with the *2/*2 TYMS polymorphism were treated with capecitabine, 1,000 mg/m2 twice daily for 14 consecutive days of a 21 day cycle. Screened patients not possessing TYMS *2/*2 were monitored for survival. Pharmacokinetic analysis was done during Cycle 1 of the therapy.

RESULTS

Sixteen of the 80 screened patients tested positive for *2/*2 TYMS variant. Four out of the 16 eligible patients were treated on study. The study was terminated early due to poor accrual and increased toxicity. Three patients experienced grade 3 non-hematologic toxicities of palmer-plantar erythrodysesthesia, diarrhea, nausea and vomiting. Grade 2 toxicities were similar and occurred in all patients. Only one patient was evaluable for response after completion of three cycles of therapy. The presence of the *2/*2 TYMS genotype in all of the screened patients trended toward a decreased overall survival.

CONCLUSION

To our knowledge, this study represents the first genotype-directed clinical trial for patients with pancreatic adenocarcinoma. Although the study was closed early, it appears capecitabine therapy in pancreatic cancer patients harboring the TYMS *2/*2 variant may be associated with increased non-hematologic toxicity. This study also demonstrates the challenges performing a genotype-directed study in the second-line setting for patients with advanced pancreatic cancer.

Mechanisms of tumor resistance to EGFR-targeted therapies

BACKGROUND

Much effort has been devoted to development of cancer therapies targeting EGFR, based on its role in regulating cell growth. Small-molecule and antibody EGFR inhibitors have clinical roles based on their efficacy in a subset of cancers, generally as components of combination therapies. Many cancers are either initially resistant to EGFR inhibitors or become resistant during treatment, limiting the efficacy of these reagents.

OBJECTIVE/METHODS

To review cellular resistance mechanisms to EGFR-targeted therapies.

RESULTS/CONCLUSIONS

The best validated of these mechanisms include activation of classic ATP-binding casette (ABC) multidrug transporters; activation or mutation of EGFR; and overexpression or activation of signaling proteins operating in relation to EGFR. We discuss current efforts and potential strategies to override these sources of resistance. We describe emerging systems-biology-based concepts of alternative resistance to EGFR-targeted therapies, and discuss their implications for use of EGFR-targeted and other targeted therapies.