Brk is coamplified with ErbB2 to promote proliferation in breast cancer

Amplification of the receptor tyrosine kinase ErbB2 is frequently observed in breast cancer. Amplification of erbB2 is also associated with multiple genomic gains and losses; however, the importance of these associated changes is largely unknown. We demonstrate that Brk, a cytoplasmic tyrosine kinase, is coamplified and coexpressed with ErbB2 in human breast cancers. ErbB2 interacts with Brk and increases its intrinsic kinase activity. Expression of Brk enhances the ErbB2-induced activation of Ras/MAPK signaling and cyclin E/cdk2 activity to induce cell proliferation of mammary 3-dimensional acini in culture. In a murine model of breast cancer, expression of Brk was found to shorten the latency of ErbB2-induced tumors by promoting cell proliferation, with no effect on protection from apoptosis. Furthermore, overexpression of Brk conferred resistance to the ability of Lapatinib, an ErbB2 kinase inhibitor, to inhibit ErbB2-induced proliferation. Thus, we identified Brk as a drug target for ErbB2-positive cancers.     

A phase I and pharmacokinetic study of lapatinib in combination with infusional 5-fluorouracil, leucovorin and irinotecan.

BACKGROUND: This study determined the optimally tolerated regimen (OTR) of oral lapatinib administered in combination with infusional 5-fluorouracil (5-FU), leucovorin and irinotecan (FOLFIRI) and assessed the safety, tolerability and pharmacokinetics of the combination. PATIENTS AND METHODS: Twenty-five patients were enrolled; 12 patients were treated at three dose levels to determine OTR; then 13 patients were treated at OTR to evaluate the pharmacokinetics of the combination. RESULTS: The 2-weekly OTR comprised lapatinib 1250 mg/day with irinotecan 108 mg/m(2) (day 1) and leucovorin 200 mg/m(2), 5-FU bolus 240 mg/m(2) and 5-FU infusion 360 mg/m(2) (days 1 and 2); doses of 5-FU and irinotecan represent a 40% reduction in dose compared to conventional FOLFIRI. Dose-limiting toxicities were grade 3 diarrhoea and grade 4 neutropenia. Co-administration of lapatinib increased the area under the plasma concentration-time curve of SN-38, the active metabolite of irinotecan, by an average of 41%; no other pharmacokinetic interactions were observed. Of 19 patients evaluable for disease response assessment, four patients had partial response and nine patients had stable disease. CONCLUSION: The combination of lapatinib and FOLFIRI is safe and demonstrates clinical activity; the documented PK interaction can effectively be compensated by lowering the doses of 5-FU and irinotecan. This regime may be further tested in a phase II trial.     

EGFR/HER-2双受体酪氨酸激酶抑制剂拉帕替尼的研究进展

EGFR/HER-2是理想的抗肿瘤分子靶点。拉帕替尼(lapatinib)是口服的小分子EGFR/HER-2双受体酪氨酸激酶抑制剂,体内外的临床前试验证实了lapatinib的抗肿瘤活性,Ⅰ期临床研究显示了它的安全性,治疗侵袭、复发、炎性、脑转移乳癌的Ⅱ、Ⅲ期临床研究取得了可喜的成绩。随着对乳癌生物特性的理解,选择特异的肿瘤亚型(HER-2过表达),进行分子靶向治疗(例如lapatinib)正成为一种新的辅助治疗方案。     

Prospective study of positron emission tomography for evaluation of the activity of lapatinib, a dual inhibitor of the ErbB1 and ErbB2 tyrosine kinases, in patients with advanced tumors

BACKGROUND: To evaluate the role of FDG-PET in assessing anti-tumor efficacy of molecular targeted drugs, we prospectively performed FDG-PET and CT for response evaluation in patients treated with lapatinib, a dual inhibitor of ErbB1 and ErbB2 tyrosine kinases. METHODS: Lapatinib was given orally once a day at doses ranging from 1200 to 1800 mg in a phase I study. CT and FDG-PET were performed before treatment, and at 1, 2 and 3 months after the initiation of the treatment and every 2 months thereafter. RESULTS: A total of 29 FDG-PET examinations were performed in eight patients with various solid tumors and the metabolic activity in the tumor was evaluated as SUVmax. The best responses, as assessed by CT, were as follows; one partial response, four stable disease and three disease progression. The partial response was observed in a patient with trastuzumab-resistant breast cancer, whose SUVmax was decreased by 60% from baseline. In all of the four patients whose best response was stable disease, the SUVmax was decreased by 6-42% one month after the start of treatment. Prolonged stable disease (10 months) was observed in a patient with colon cancer, whose SUVmax was decreased by 42%. In the patient group with disease progression, SUVmax was increased in two out of three patients. CONCLUSIONS: FDG-PET detected decreases in the metabolic activity of the tumors in patients who experienced clinical benefits on treatment with lapatinib. Thus, FDG-PET may be useful for the evaluation of molecular targeted drugs, such as lapatinib.     

Second-generation epidermal growth factor tyrosine kinase inhibitors in non-small cell lung cancer

Inhibiting the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) has an established role in the treatment of advanced non-small cell lung cancer. The first-generation EGFR inhibitors erlotinib and gefitinib have been approved for treatment in the second- and third-line setting. Second-generation EGFR tyrosine kinase inhibitors are now in development aiming to improve efficacy and overcome primary and secondary resistance to the first-generation drugs. The two most common strategies being used to achieve these aims are irreversible binding of drug to target and kinase multi-targeting. This is an overview of the early clinical development of selected second-generation tyrosine kinase inhibitors focusing on the treatment of non-small cell lung cancer.     

A phase II study of dose-dense temozolomide and lapatinib for recurrent low-grade and anaplastic supratentorial,infratentorial, and spinal cord ependymoma

BackgroundNo standard medical treatment exists for adult patients with recurrent ependymoma, and prospective clinical trials in this population have not succeeded because of its rarity and challenges in accruing patients. The Collaborative Ependymoma Research Network conducted a prospective phase II clinical trial of dose-dense temozolomide (TMZ) and lapatinib, targeting the unmethylated O⁶-methylguanine-DNA methyltransferase (MGMT) promoter status and increased expression of ErbB2 (human epidermal growth factor receptor 2) and ErbB1 (epidermal growth factor receptor) in ependymomas.MethodsPatients age 18 or older with histologically proven and progressive ependymoma or anaplastic ependymoma were eligible and received dose-dense TMZ and daily lapatinib. The primary outcome measure was median progression-free survival (PFS). Landmark 6- and 12-month PFS and objective response were measured. Serial assessments of symptom burden using the MD Anderson Symptom Inventory Brain Tumor (MDASI-BT)/MDASI–Spine Tumor modules were collected.ResultsThe 50 patients enrolled had a median age of 43.5 years, median Karnofsky performance status of 90, and a median of 2 prior relapses. Twenty patients had grade III, 16 grade II, and 8 grade I ependymoma. Half had spinal cord tumors; 15 had a supratentorial tumor, 8 infratentorial, and 2 had disseminated disease. Treatment was well tolerated. The median PFS was 7.8 months (95% CI: 5.5,12.2); the 6- and 12-month PFS rates were 55% and 38%, with 2 complete and 6 partial responses. Measures of symptom burden showed reduction in moderate-severe pain and other disease-related symptoms in most patients.ConclusionsThis treatment, with demonstrated clinical activity with objective responses and prolonged disease control associated with disease-related symptom improvements, is an option as a salvage regimen for adult patients with recurrent ependymoma.     

Lapatinib increases motility of triple-negative breast cancer cells by decreasing miRNA-7 and inducing Raf-1/MAPK-dependent interleukin-6

Lapatinib, a dual epidermal growth factor receptor (EGFR) and HER2 tyrosine kinase inhibitor (TKI), has been approved for HER2-positive breast cancer patients. Nevertheless, its inhibitory effect on EGFR did not deliver clinical benefits for triple-negative breast cancer (TNBC) patients even EGFR overexpression was frequently found in this disease. Moreover, lapatinib was unexpectedly found to enhance metastasis of TNBC cells, but the underlying mechanisms are not fully understood. In this study, we explored that the level of interleukin-6 (IL-6) was elevated in lapatinib-treated TNBC cells. Treatment with IL-6 antibody abolished the lapatinib-induced migration. Mechanistically, the signaling axis of Raf-1/mitogen-activated protein kinases (MAPKs), c-Jun N-terminal kinases (JNKs), p38 MAPK, and activator protein 1 (AP-1) was activated in response to lapatinib treatment to induce IL-6 expression. Furthermore, our data showed that microRNA-7 directly binds and inhibits Raf-1 3′UTR activity, and that down-regulation of miR-7 by lapatinib contributes to the activation of Raf-1 signaling pathway and the induction of IL-6 expression. Our results not only revealed IL-6 as a key regulator of lapatinib-induced metastasis, but also explored the requirement of miR7/Raf-1/MAPK/AP-1 axis in lapatinib-induced IL-6 expression.     

From the Cover: PNAS Plus: Mechanism for activation of mutated epidermal growth factor receptors in lung cancer

The initiation of epidermal growth factor receptor (EGFR) kinase activity proceeds via an asymmetric dimerization mechanism in which a “donor” tyrosine kinase domain (TKD) contacts an “acceptor” TKD, leading to its activation. In the context of a ligand-induced dimer, identical wild-type EGFR TKDs are thought to assume the donor or acceptor roles in a random manner. Here, we present biochemical reconstitution data demonstrating that activated EGFR mutants found in lung cancer preferentially assume the acceptor role when coexpressed with WT EGFR. Mutated EGFRs show enhanced association with WT EGFR, leading to hyperphosphorylation of the WT counterpart. Mutated EGFRs also hyperphosphorylate the related erythroblastic leukemia viral oncogene (ErbB) family member, ErbB-2, in a similar manner. This directional “superacceptor activity” is particularly pronounced in the drug-resistant L834R/T766M mutant. A 4-Å crystal structure of this mutant in the active conformation reveals an asymmetric dimer interface that is essentially the same as that in WT EGFR. Asymmetric dimer formation induces an allosteric conformational change in the acceptor subunit. Thus, superacceptor activity likely arises simply from a lower energetic cost associated with this conformational change in the mutant EGFR compared with WT, rather than from any structural alteration that impairs the donor role of the mutant. Collectively, these findings define a previously unrecognized mode of mutant-specific intermolecular regulation for ErbB receptors, knowledge of which could potentially be exploited for therapeutic benefit.The gene encoding the epidermal growth factor receptor (EGFR) tyrosine kinase is somatically mutated in a substantial fraction of patients with lung cancer. The majority of primary activating EGFR mutations occur within the tyrosine kinase domain (TKD). The most frequent of these, which occur with a combined frequency of 90% (1), are exon 19 deletions that eliminate four amino acids (LREA) from the TKD and exon 21 missense mutations that substitute arginine for leucine at position 834 (L834R) (also identified as L858R in an alternative numbering of the human EGFR sequence that includes the 24 residue signal sequence) (2).Exon 19 deletions and L834R substitutions are associated with increased sensitivity to EGFR tyrosine kinase inhibitors (TKIs), such as gefitinib and erlotinib, translating to a 70% radiographic response rate in patients (3–5). Unfortunately, all individuals with metastatic disease eventually develop progressive disease after 10–16 mo of treatment with EGFR TKIs. The most common mechanism of acquired resistance is mutation at a second site in the EGFR TKD (the gatekeeper residue), T766M (T790M). This mutation confers resistance by increasing affinity for ATP, with which inhibitors must compete for binding, and also by modestly decreasing intrinsic affinity for TKIs (6).Biochemical and crystallographic studies have shown that activation of the wild-type (WT) EGFR TKD involves formation of an asymmetric dimer in which one molecule allosterically activates its neighbor by promoting the reversal of intramolecular autoinhibitory interactions—acting as a “donor” or “activator” TKD that activates the “acceptor” or “receiver” TKD (7, 8). Crystal structures of individual L834R and T766M EGFR-TKD mutants show that these variants also form asymmetric dimers (6, 9), but whether the double mutant L834R/T766M adheres to the same configuration in the active state is unclear. Biochemical data indicate that the oligomerization potential of mutated EGFRs is enhanced relative to WT. For example, native gel and multiangle light scattering studies showed that the L834R substitution promotes formation of dimers and higher order oligomers of the EGFR TKD (10). Consistent with this observation, cell-based studies have demonstrated a reduced dependence on ligand stimulation for activation of mutated EGFRs. All mutated EGFR TKDs seen in lung cancer show an increase in catalytic efficiency over WT (6, 9, 11, 12). Interestingly, the doubly mutated L834R/T766M EGFR TKD has a two-to fivefold higher catalytic efficiency (k_cat/K_m) than either the singly mutated L834R or T766M mutant TKDs (6).Here, using a biochemical and structural approach, we sought to determine whether mutated EGFRs most commonly associated with primary drug sensitivity and acquired resistance in lung cancer adhere to the well-established asymmetric dimer model. Our biochemical reconstitution data demonstrate that these EGFR mutations do in fact adhere to this model, but with the striking difference that the oncogenic mutants preferentially assume the receiver role when expressed together with WT EGFR. Our crystal structure of active EGFR-L834R/T766M reveals an asymmetric dimer interface essentially the same as that in WT EGFR. We further show that mutated EGFRs can hyperphosphorylate WT EGFR as well as the related family member erythroblastic leukemia viral oncogene (ErbB)2 as a result of their preferential adoption of the acceptor or receiver position in the asymmetric dimer. These findings have important implications for understanding mechanisms of drug sensitivity and resistance in EGFR mutant lung cancers and shed light on the distinct properties of different mutated forms of EGFR.     

Recent progress in the discovery of Akt inhibitors as anticancer agents

Akt, also referred to as protein kinase B (PKB) or Related to A and C (RAC), is one of the major direct downstream targets of phosphoinositide 3-kinase (PI3K). As it plays a central role in promoting cancer cell proliferation and survival through a growing list of key substrates, intense efforts are underway to find inhibitors of Akt for the treatment of cancer. Discovery of potent and novel inhibitors of Akt has been facilitated greatly by the availability of the X-ray structure of the active form of Akt and by its structural similarity with other serine/threonine kinases. In this review, new Akt inhibitors for the treatment of cancer are comprehensively reviewed, with emphasis on small molecule inhibitors that bind to the ATP-binding site, allosteric sites and the PH domains. Inhibitors of pseudosubstrates and antisense oligonucleotides, as well as Akt inhibitors with unknown mechanism of actions, are also reviewed. Results of clinical trials of several Akt drug candidates are briefly discussed. A brief summary of Akt structure and regulation and the evidences supporting Akt as a cancer target is provided as well. The patent literature is surveyed through July 2007.