Activation of the AMPK regulated metabolic stress response by a small molecule HER2/EGFR tyrosine kinase inhibitor protects cardiac myocytes from apoptotic stimuli

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Background: The HER2 receptor tyrosine kinase is a survival factor for human cardiomyocytes, providing a potential explanation for the increased incidence of cardiomyopathy associated with anti-HER2 monoclonal antibody trastuzumab. Here we show that GW2974, a HER2/EGFR TKI, but not trastuzumab activates AMP kinase (AMPK), initiating a metabolic stress response in human cardiomyocytes that protects against TNFa induced cell death. GW2974 stimulates calcium dependent fatty acid oxidation in vitro resulting in upregulation of ATP and in myocardium of GW2974 treated rodents. Methods: Western blot: p-Akt, p-Erk1/2, p-AMPKa and p- eEF2 (Cell Signaling); ERRa, ERR? (R&D Systems); PGC-1 (Chemicon); MCAD (Cayman Chemicals); Heregulin, NF?B, and Actin (Sigma). ATP was performed utilizing a bioluminescence assay kit H52 (Roche). Lipid staining was done with Oil Red O (Sigma). Cells: Au565 breast cancer and primary human cardiomyocytes (HMC) were grown in RPMI supplemented with 15% BFS treatments. BAPTA/AM and Compound C (Calbiochem); GW2974 and TNFa (Sigma); trastuzumab (Genentech). Results: Our results show that treatment with GW2974 activates catabolic pathways by activation of AMPK. AMPK is a key regulator in mitochondrial energy producing pathways in human cardiac cells. Phosphorylation of AMPK resulted in phosphorylation of eEF2, upregulation of ERRa and PGC-1 and upregulation of ATP levels. AMPK activation depends on Ca++ as the calcium chelation abolished it. Trastuzumab and Gleevec failed to activate AMPK survival pathways. In addition, GW2974 protected cardiac cells from TNFa killing, whereas treatment with TNFa and trastuzumab resulted in pervasive cellular death. Inhibition of AMPK by Compound C or siRNA resulted in cardiomyocyte killing. Conclusion: Activation of AMPK and its effects on metabolic pathways and energy production in HMC may explain the apparent reduced risk of cardiotoxicity associated with HER2 TKI compared with trastuzumab in treating patients with HER2 overexpressing breast cancers. Although activation of AMPK protected normal cardiac myocytes, this effect appears to be lethal to sensitive HER2 overexpressing breast cancer cells, which are “addicted” to glycolysis.

No significant financial relationships to disclose.

EGF103009, a phase II trial of lapatinib monotherapy in patients with relapsed/refractory inflammatory breast cancer (IBC): Clinical activity and biologic predictors of response

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Background: Data from preclinical studies and small numbers of IBC patients inPhase I clinical trials suggest that IBC may be particularly sensitive to the anti-tumor effects of lapatinib, an inhibitor of ErbB1/ErbB2 tyrosine kinases. EGF103009 was initiated to confirm and expand these initial observations and identify a tumor profile predicting for the sensitivity of IBC to lapatinib. Methods: Patients with relapsed/refractory IBC based on clinical criteria, were assigned to Cohort A (ErbB2 overexpressors: 2/3+ IHC/FISH+) or B (ErbB1 +/ErbB2 non-overexpressors) after analysis of a fresh tumor biopsy in a central reference lab. Patients received lapatinib daily (1500mg/d). Clinical response was documented at day 56 and in the case of CR/PR, confirmed on day 84 and every 8 weeks thereafter. Target lesions were assessed according to RECIST criteria and response in skin disease documented by digital photography. Tumor expression of ErbB2, p-ErbB2, ErbB1, p-ErbB3, IGF-IR, PTEN, ER/PR, E-cadherin, β-catenin, and Rho B/C was analyzed by quantitative IHC from a fresh, pre-treatment biopsy. Results: Of 34 patients enrolled, clinical response data is available from 22 patients of which 17 had biopsies analyzed at a reference lab and assigned to Cohorts A (N=11) and B (N=6). Eight of 11 patients (72%) in Cohort A had a clinical response (CR/PR) to lapatinib documented by RECIST, skin disease, or both. There were no responders in Cohort B. All responders (i) overexpressed ErbB2 (2/3+ IHC or FISH+), (ii) increased p-ErbB2 (2/3+), (iii) co-expressed IGF-IR, and (iv) expressed activated, p-ErbB3. PTEN status did not affect response to lapatinib. Toxicity was generally grade I/II skin and G.I. with one grade III cardiotoxicity necessitating withdrawal from study. Conclusions: ErbB2 overexpression but not ErbB1 expression alone, predicts for sensitivity to lapatinib in IBC. High ErbB2, p-ErbB2 and IGF-IR co-expression predict for clinical response to lapatinib monotherapy in patients with relapsed/refractory IBC, illustrating the importance of selecting patients based on biology rather than histology alone, to maximize the clinical efficacy of ErbB kinase inhibitors in breast carcinomas.

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Tumor selective G2/M cell cycle arrest and apoptosis of epithelial and hematological malignancies by BBL22, a benzazepine

Two distinct benzodiazepine binding sites have been identified, (i) a central site restricted to brain and (ii) a ubiquitously expressed mitochondrial binding site, the so-called peripheral-type benzodiazepine receptor (PBR). In this paper, we show that a benzazepine referred to as BBL22 (2-amino 9-chloro-7-(2-fluorophenyl)-5H-pyrimidol[5,4-d][2]benzazepine), which is classified as a PBR ligand based on structure, induces arrest in G(2)/M phase of the cell cycle in human tumor cell lines of both epithelial and hematopoietic cellular origin. After G(2)/M arrest, several tumor types, notably prostate and certain breast cancer lines exhibited significant apoptosis. Ideally, cancer therapies should selectively target tumor cells while sparing normal cell counterparts. BBL22 exhibited such selectivity, as it did not affect the growth and survival of nonmalignant breast and prostate epithelial lines. Moreover, BBL22 demonstrated structural requirements for this selective antitumor activity as 11 structurally related PBR ligands, including high-affinity ligands Ro5-4864 and PK11195, failed to induce tumor cell growth arrest or apoptosis. The in vivo antitumor activity of BBL22 was examined in a human xenograft model of androgen-independent prostate cancer where BBL22 significantly reduced the growth of PC3 prostate tumors without eliciting overt toxicity. Identification of BBL22 represents a tumor selective therapeutic strategy for a variety of human tumors.

Sensitization of tumor cells to fas killing through overexpression of heat-shock transcription factor 1

Activation of the heat-shock or stress response is generally considered a cytoprotective response to heat or other proteotoxic stresses. In mammalian cells, stress-induced transcription of heat-shock genes is regulated by heat-shock transcription factor 1 (HSF1). We now show that activation of the Fas death receptor transactivates HSF1 in HeLa cells, a Fas-expressing cervical carcinoma line. Whereas HSF1 is constitutively expressed in a non-DNA-binding, transcriptionally inactive state, activation of Fas leads to enhanced transcription of a heat-shock reporter gene. The effects of Fas on heat-shock-gene transcription do not appear to be a consequence of cell death as they (1) precede apoptotic changes and (2) are not abrogated by YVAD-CMK, an inhibitor of Fas apoptosis that acts by blocking downstream effector proteases. Despite expressing Fas, HeLa cells are relatively insensitive to Fas-mediated killing, indicating that Fas expression alone, although necessary, is not sufficient for apoptosis. By overexpressing a constitutively activated form of HSF1, we sensitize HeLa cells to Fas-mediated killing. These findings shed new light on the interaction between two of the most evolutionarily conserved cell programs in nature, the Fas death pathway and the heat-shock response. Strategies designed to upregulate HSF1 in tumor cells, either through pharmacologic or gene-therapy approaches will hopefully provide a means with which to sensitize tumors to the killing effects of cancer therapies operating through the Fas receptor.

Truncation of Sp1 transcription factor by myeloblastin in undifferentiated HL60 cells

When HL60 cells are exposed to 1,25-dihydroxyvitamin D3 (1,25D3), they undergo changes approximating the phenotype of the monocyte. Little is known, however, about the regulation and the mechanisms of this transition. It was previously noted that DNA binding by the Sp1 transcription factor in nuclear extracts of HL60 cells is profoundly altered when these cells are induced to differentiate by 1,25D3. In the present study, we show that in untreated HL60 cells only a truncated, approximately 30-kDa Sp1 fragment, encompassing the C-terminal region, binds to the GC element-containing DNA. Full-length 105-kDa Sp1 protein cannot be detected in these cells, although reverse transriptase-polymerase chain reaction reveals the presence of both 5' and 3' ends of Sp1 mRNA. Following treatment with 10(7) M 1,25D3 for 96 hr or in cells made resistant to 1,25D3 or to 1-beta-D-arabinocytosine, the Sp1 protein can be demonstrated. After an exposure to purified myeloblastin, a serine protease, purified recombinant Sp1 protein and extracts of 1,25D3-treated cells show a pattern of DNA binding similar to the pattern seen using extracts of untreated HL60 cells, indicating that the Sp1 protein is a target for myeloblastin. Because myeloblastin is present in naive HL60 cells and is downregulated during their differentiation, inhibition of proteolysis of these transcription factors seems to provide a mechanism through which differentiating HL60 cells can acquire a new repertoire of gene expression, perhaps for the maintenance of the differentiated phenotype.

Activation signals regulate heat shock transcription factor 1 in human B lymphocytes

We previously showed that the ability of human B lymphocytes to elicit a cytoprotective heat shock response when confronted by heat or other stresses was dependent upon the state of cell activation. This was unexpected, considering the highly conserved nature of the heat shock response and the widely held belief that all nonmutated mature cells were capable of eliciting a heat shock response when stressed. To elucidate the mechanism by which activation primes B cells to respond to stresses, we examined heat shock transcription factor 1 (hHSF1) in B cells since this factor appears to be solely responsible for stress-induced transcription of heat shock genes in human cells. In the current report, we show that hHSF1-DNA binding complexes are undetectable in extracts of unactivated B cells. In fact, hHSF1 protein is not constitutively expressed in unactivated B cells, nor is its synthesis stress-inducible. However, following activation, hHSF1 can be found in either a transcriptionally active or an inactive state, depending upon whether the cell has been stressed or not. Thus, activation pathways play an important role in enabling B cells to survive and function properly in the context of physiologic stresses by regulating hHSF1.

28-kDa mammalian heat shock protein, a novel substrate of a growth regulatory protease involved in differentiation of human leukemia cells

Because of their differentiating effects in neoplastic cells in vitro, the use of retinoids in the treatment of various malignant and premalignant conditions is under investigation. To date, signal transduction pathways involved in retinoid-induced differentiation remain poorly understood. Differentiation of HL-60 cells by all-trans-retinoic acid (tRA) is directly mediated by down-regulation of the serine protease myeloblastin (mbn). In this report, we investigate the possibility that the 28-kDa heat shock protein (hsp28), previously linked to differentiation of normal and neoplastic cells including HL-60, may be regulated by mbn. Using NB4 promyelocytic leukemic cells as a differentiative model, we show that tRA induces initial suppression and subsequent up-regulation of hsp28 protein, mirroring tRA-induced changes in mbn protein. The progressive reduction in hsp28 mRNA levels in response to tRA suggests that changes in hsp28 protein levels might be posttranscriptionally mediated, raising the possibility that hsp28 may be targeted by mbn. To address this, we developed an assay using purified mbn and recombinant hsp28 and now show that hsp28 is hydrolyzed by mbn but not its homologue, human neutrophil elastase. Moreover, mbn does not indiscriminately hydrolyze other proteins. Identifying hsp28 as a substrate of mbn strongly suggests that hsp28 may be a key component of the tRA signaling pathway involved in regulating cell differentiation.

Regulation of the 28 kDa heat shock protein by retinoic acid during differentiation of human leukemic HL-60 cells

Dysregulation of hematopoietic cellular differentiation contributes to leukemogenesis. Unfortunately, relatively little is known about how cell differentiation is regulated. Considering that heat shock proteins (hsp) and specifically the small hsps have been increasingly linked to growth regulation, we sought to determine whether the mammalian small hsp (hsp28) is a growth-regulatory candidate during hematopoietic cell differentiation. Because of its effects on cell growth and differentiation and its increasing clinical use as a differentiating agent, we examined the effect of retinoic acid (RA) on hsp28 during differentiation of the human leukemic HL-60 cell line. Although hsp28 was constitutively expressed at low levels in untreated HL-60 cells, steady state hsp28 protein increased transiently, concomitant with the onset of G1 cell cycle arrest. Furthermore, hsp28 phosphorylation transiently increased within one hour following treatment with RA. Interestingly, in contrast to other differentiating agents the induction of hsp28 by RA was post-transcriptionally mediated with hsp28 protein and mRNA being discordantly regulated. These observations underscore the complex regulation of hsp28 by RA during granulocytic differentiation of human leukemic cells and indicate hsp28 as an intermediary in the pathway through which retinoids exert their growth and differentiative effects.

Heat shock protein is a unique marker of growth arrest during macrophage differentiation of HL-60 cells

Prior to morphologic and functional maturation, terminally differentiating hematopoietic cells first exit the cell cycle and undergo growth arrest. Relatively little is known about which molecules regulate differentiation-induced growth arrest. In the present report, we sought to determine whether the mammalian low molecular weight heat shock protein (hsp28) was a candidate growth-regulatory molecule during human hematopoiesis. To this end, hsp28 protein expression was examined during phorbol ester (PMA)-induced macrophage differentiation of the human HL-60 promyelocytic leukemic cell line. Whereas hsp28 was constitutively expressed at relatively low levels in an unphosphorylated state, hsp28 was rapidly phosphorylated within 4 hr following PMA-induced differentiation, preceding increased hsp28 protein levels at 24-48 h. In contrast to other differentiative agents, hsp28 steady state mRNA and protein were regulated concordantly in response to macrophage differentiation. More importantly, these changes were transient, and occurred concomitant with the down-regulation of cellular proliferation and the onset of G1 phase cell cycle arrest. In total, these observations implicate hsp28 as an intermediary in the myelomonocytic differentiative pathway of promyelocytic leukemic cells, and will shed light on the events regulating this process.

Anti-B4-blocked ricin: a phase I trial of 7-day continuous infusion in patients with B-cell neoplasms

PURPOSE

This phase I trial was undertaken to determine the maximum-tolerated dose (MTD) and dose-limiting toxicities (DLTs) of the B-cell-restricted immunotoxin anti-B4-blocked ricin (anti-B4-bR) when it is administered by 7-day continuous infusion.

PATIENTS AND METHODS

Thirty-four patients with relapsed and refractory B-cell neoplasms (26 non-Hodgkin's lymphoma [NHL], four chronic lymphocytic leukemia [CLL], four acute lymphoblastic leukemia [ALL]) received 7-day continuous infusion anti-B4-bR. Successive cohorts of at least three patients were treated at doses of 10 to 70 micrograms/kg/d for 7 days with the dose increased by 10 micrograms/kg/d for each cohort. The initial three cohorts of patients (10, 20, and 30 micrograms/kg/d x 7 days) also received a bolus infusion of 20 micrograms/kg before beginning the continuous infusion.

RESULTS

The MTD was reached at 50 micrograms/kg/d x 7 days. The DLTs were National Cancer Institute Common Toxicity Criteria (NCI CTC) grade IV reversible increases in AST and ALT, and grade IV decreases in platelet counts. Adverse reactions included fevers, nausea, headaches, myalgias, hypoalbuminemia, dyspnea, edema, and capillary leak syndrome. Potentially therapeutic serum levels of anti-B4-bR could be sustained for 4 days in patients treated at the MTD. Two complete responses (CRs), three partial responses (PRs), and 11 transient responses (TRs) were observed.

CONCLUSION

Anti-B4-bR can be administered safely by 7-day continuous infusion with tolerable, reversible toxicities to patients with relapsed B-cell neoplasms. Although occasional responses were seen, future trials will use anti-B4-bR in patients with lower tumor burdens to circumvent the obstacle of immunotoxin delivery to bulk disease.

Growth arrest of human B lymphocytes is accompanied by induction of the low molecular weight mammalian heat shock protein (Hsp28)

A large number of protein and molecular markers have been identified that delineate the early stages of human B cell activation and proliferation. In contrast, few if any molecules are transiently expressed precisely as activated B cells stop proliferating and undergo growth arrest. We demonstrate that the low molecular weight heat shock protein (hsp28) exhibits unique induction kinetics that specifically demarcates this interval. After mitogenic activation of unstimulated splenic B cells, hsp28 protein and phosphorylation transiently increase coinciding precisely with the peak of cellular proliferation and the onset of growth arrest. Although most neoplastic B cells constitutively express hsp28, three cell lines were identified that were hsp28-. No differences in phenotype or growth kinetics were detected between hsp28+ and hsp28- neoplastic B cells demonstrating that hsp28 expression is not essential for cell growth. However, when treated with phorbol ester or heat shock, these hsp28- cell lines synthesize hsp28 followed by the onset growth arrest. The consistency with which hsp28 induction transiently delineates the interval from peak proliferation to the onset of growth arrest suggests hsp28 itself is likely to be involved in regulating this process.

Growth arrest of human B lymphocytes is accompanied by induction of the low molecular weight mammalian heat shock protein (Hsp28)

A large number of protein and molecular markers have been identified that delineate the early stages of human B cell activation and proliferation. In contrast, few if any molecules are transiently expressed precisely as activated B cells stop proliferating and undergo growth arrest. We demonstrate that the low molecular weight heat shock protein (hsp28) exhibits unique induction kinetics that specifically demarcates this interval. After mitogenic activation of unstimulated splenic B cells, hsp28 protein and phosphorylation transiently increase coinciding precisely with the peak of cellular proliferation and the onset of growth arrest. Although most neoplastic B cells constitutively express hsp28, three cell lines were identified that were hsp28-. No differences in phenotype or growth kinetics were detected between hsp28+ and hsp28- neoplastic B cells demonstrating that hsp28 expression is not essential for cell growth. However, when treated with phorbol ester or heat shock, these hsp28- cell lines synthesize hsp28 followed by the onset growth arrest. The consistency with which hsp28 induction transiently delineates the interval from peak proliferation to the onset of growth arrest suggests hsp28 itself is likely to be involved in regulating this process.

Activation primes human B lymphocytes to respond to heat shock

Crosslinkage of the B cell antigen receptor by anti-mu beads or SAC results in the selective induction of hsp70. We have observed that activated cells, having enhanced expression of hsp70, survive lethal stimuli much better than their unactivated counterparts. These results are in accordance with the proposal that hsp70 is essential for cells to survive lethal environmental stresses. Moreover, the activation event itself primes B cells thereby enabling them to increase the expression of both hsp70 mRNA and protein. This is the first demonstration that triggering of B cells via crosslinkage of sIg is accompanied by the induction of thermotolerance without the need for a prior sublethal heat treatment.