Junji Tsurutani

Loss of PTEN/MMAC1/TEP in EGF receptor-expressing tumor cells counteracts the antitumor action of EGFR tyrosine kinase inhibitors

We have examined the possible mechanisms of resistance to the epidermal growth factor receptor (EGFR) inhibitors in tumor cells with variable levels of EGFR. ZD1839 (Iressa) is a small-molecular-weight, ATP-mimetic that specifically inhibits the EGFR tyrosine kinase. A431 cell growth was markedly inhibited by ZD1839 (IC50⩽0.1 μM) whereas the MDA-468 cells were relatively resistant (IC502 μM). Low doses of ZD1839 delayed cell cycle progression and induced apoptosis in A431 cells but not in MDA-468 cells. In both cell lines, 0.1 μM ZD1839 eliminated EGFR phosphorylation. However, the basal activity of the phosphatidylinositol-3 kinase (PI3 K) target Akt was eliminated in A431 but not in MDA-468 cells, implying that their Akt activity is independent of EGFR signals. A431 cells express PTEN/MMAC1/TEP, a phosphatase that can dephosphorylate position D3 of phosphatidylinositol-3,4,5 trisphosphate, the site that recruits the plecstrin-homology domain of Akt to the cell membrane. On the contrary, MDA-468 cells lack the phosphatase and tensin homolog (PTEN), potentially setting Akt activity at a high threshold that is unresponsive to EGFR inhibition alone. Therefore, we reintroduced (PTEN) by retroviral infection in MDA-468 cells. In MDA-468/PTEN but not in vector controls, treatment with ZD1839 inhibited P-Akt levels, induced relocalization of the Forkhead factor FKHRL1 to the cell nucleus, and increased FKHRL1-dependent transcriptional activity. ZD1839 induced a greater degree of apoptosis and cell cycle delay in PTEN-reconstituted than in control cells. These data suggest that loss of PTEN, by permitting a high level of Akt activity independent of receptor tyrosine kinase inputs, can temporally dissociate the inhibition of the EGFR with that of Akt induced by EGFR inhibitors. Thus, in EGFR-expressing tumor cells with concomitant amplification(s) of PI3K-Akt signaling, combined blockade of the EGFR tyrosine kinase and Akt should be considered as a therapeutic approach.

Nelfinavir, A lead HIV protease inhibitor, is a broad-spectrum, anticancer agent that induces endoplasmic reticulum stress, autophagy, and apoptosis in vitro and in vivo

Purpose: The development of new cancer drugs is slow and costly. HIV protease inhibitors are Food and Drug Administration approved for HIV patients. Because these drugs cause toxicities that can be associated with inhibition of Akt, an emerging target in cancer, we assessed the potential of HIV protease inhibitors as anticancer agents. Experimental Design: HIV protease inhibitors were screened in vitro using assays that measure cellular proliferation, apoptotic and nonapoptotic cell death, endoplasmic reticulum (ER) stress, autophagy, and activation of Akt. Nelfinavir was tested in non–small cell lung carcinoma (NSCLC) xenografts with biomarker assessment. Results: Three of six HIV protease inhibitors, nelfinavir, ritonavir, and saquinavir, inhibited proliferation of NSCLC cells, as well as every cell line in the NCI60 cell line panel. Nelfinavir was most potent with a mean 50% growth inhibition of 5.2 μmol/L, a concentration achievable in HIV patients. Nelfinavir caused two types of cell death, caspase-dependent apoptosis and caspase-independent death that was characterized by induction of ER stress and autophagy. Autophagy was protective because an inhibitor of autophagy increased nelfinavir-induced death. Akt was variably inhibited by HIV protease inhibitors, but nelfinavir caused the greatest inhibition of endogenous and growth factor–induced Akt activation. Nelfinavir decreased the viability of a panel of drug-resistant breast cancer cell lines and inhibited the growth of NSCLC xenografts that was associated with induction of ER stress, autophagy, and apoptosis. Conclusions: Nelfinavir is a lead HIV protease inhibitor with pleiotropic effects in cancer cells. Given its wide spectrum of activity, oral availability, and familiarity of administration, nelfinavir is a Food and Drug Administration–approved drug that could be repositioned as a cancer therapeutic.

Preferential Inhibition of Akt and Killing of Akt-Dependent Cancer Cells by Rationally Designed Phosphatidylinositol Ether Lipid Analogues

Activation of the PI3k/Akt pathway controls key cellular processes and contributes to tumorigenesis in vivo, but investigation of the PI3k/Akt pathway has been limited by the lack of specific inhibitors directed against Akt. To develop Akt inhibitors, we used molecular modeling of the pleckstrin homology (PH) domain of Akt to guide synthesis of structurally modified phosphatidylinositol ether lipid analogues (PIAs). Here, we characterize the biochemical and cellular effects of PIAs. Of 24 compounds tested, five PIAs with modifications at two sites on the inositol ring inhibited Akt with IC(50)s < 5 micro M. Molecular modeling identified putative interactions of PIAs with the phosphoinositide-binding site in the PH domain of Akt, and growth factor-induced translocation of Akt to the plasma membrane was inhibited by PIA administration. Inhibition of Akt occurred rapidly and was maintained for hours. PIAs decreased phosphorylation of many downstream targets of Akt without affecting upstream kinases, such as PI3k or phosphoinositide-dependent kinase-1, or members of other kinase pathways such as extracellular signal-regulated kinase. Importantly, PIAs increased apoptosis 20-30-fold in cancer cell lines with high levels of endogenous Akt activity but only 4-5-fold in cancer cell lines with low levels of Akt activity. These studies identify PIAs as effective Akt inhibitors, and provide proof of principle for targeting the PH domain of Akt.

FOXQ1 is overexpressed in colorectal cancer and enhances tumorigenicity and tumor growth.

Forkhead box Q1 (FOXQ1) is a member of the forkhead transcription factor family, and it has recently been proposed to participate in gastric acid secretion and mucin gene expression in mice. However, the role of FOXQ1 in humans and especially in cancer cells remains unknown. We found that FOXQ1 mRNA is overexpressed in clinical specimens of colorectal cancer (CRC; 28-fold/colonic mucosa). A microarray analysis revealed that the knockdown of FOXQ1 using small interfering RNA resulted in a decrease in p21(CIP1/WAF1) expression, and a reporter assay and a chromatin immunoprecipitation assay showed that p21 was one of the target genes of FOXQ1. Stable FOXQ1-overexpressing cells (H1299/FOXQ1) exhibited elevated levels of p21 expression and inhibition of apoptosis induced by doxorubicin or camptothecin. Although cellular proliferation was decreased in H1299/FOXQ1 cells in vitro, H1299/FOXQ1 cells significantly increased tumorigenicity [enhanced green fluorescent protein (EGFP): 2/15, FOXQ1: 7/15] and enhanced tumor growth (437 +/- 301 versus 1735 +/- 769 mm3, P < 0.001) in vivo. Meanwhile, stable p21 knockdown of H1299/FOXQ1 cells increased tumor growth, suggesting that FOXQ1 promotes tumor growth independent of p21. Microarray analysis of H1299/EGFP and H1299/FOXQ1 revealed that FOXQ1 overexpression upregulated several genes that have positive roles for tumor growth, including VEGFA, WNT3A, RSPO2, and BCL11A. CD31 and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining of the tumor specimens showed that FOXQ1 overexpression mediated the angiogenic and antiapoptotic effect in vivo. In conclusion, FOXQ1 is overexpressed in CRC and enhances tumorigenicity and tumor growth presumably through its angiogenic and antiapoptotic effects. Our findings show that FOXQ1 is a new member of the cancer-related FOX family.

Reversal of breast cancer resistance protein (BCRP/ABCG2)-mediated drug resistance by novobiocin, a coumermycin antibiotic

Breast cancer resistance protein (BCRP/ABCG2) of an ATP‐binding cassette half‐transporter confers resistance against mitoxantrone and camptothecin derivatives of topotecan and irinotecan. Novobiocin, a coumermycin antibiotic, is known to enhance anticancer drug sensitivity of cancer cells in vitro and in vivo, the mechanism of which remains undetermined. Here we focused on drug efflux pump and examined whether novobiocin reversed drug resistance in multidrug‐resistant cells highly expressing BCRP. To explore the reversal mechanisms, intracellular drug accumulation was measured by flow cytometry, and a topotecan transport study using plasma membrane vesicles was performed. We used PC‐6/SN2‐5H2 small cell lung cancer and MCF‐7/MX breast cancer cells selected with SN‐38 of the active irinotecan metabolite and mitoxantrone, respectively, and the BCRP cDNA transfectant MCF‐7/clone 8 cells. These cells expressed high levels of BCRP mRNA but not other known transporters. Compared to the parental PC‐6 cells, PC‐6/SN2‐5H2 cells were 141‐, 173‐ and 57.2‐fold resistant to topotecan, SN‐38 and mitoxantrone, respectively. Novobiocin at 60 μM decreased the degree of the above resistance by approximately 26‐fold in PC‐6/SN2‐5H2 cells, and similarly reversed resistance in MCF‐7/MX, MCF‐7/clone 8 and un‐selected NCI‐H460 cells highly expressing BCRP. Furthermore, novobiocin increased the intracellular topotecan accumulation in these cells and inhibited the topotecan transport into the membrane vesicles of PC‐6/SN2‐5H2 cells. No effects of novobiocin in these assay were observed in the parental PC‐6 and MCF‐7 cells. The kinetic parameters in the transport study indicated that novobiocin was a inhibitor for BCRP, resulting in competitive inhibition of BCRP‐mediated topotecan transport. These findings suggest that novobiocin effectively overcomes BCRP‐mediated drug resistance at acceptable concentrations.

Inhibition of the Phosphatidylinositol 3-Kinase/Akt/Mammalian Target of Rapamycin Pathway but not the MEK/ERK Pathway Attenuates Laminin-Mediated Small Cell Lung Cancer Cellular Survival and Resistance to Imatinib Mesylate or Chemotherapy

The fact that small cell lung cancer (SCLC) is commonly incurable despite being initially responsive to chemotherapy, combined with disappointing results from a recent SCLC clinical trial with imatinib, has intensified efforts to identify mechanisms of SCLC resistance. Adhesion to extracellular matrix (ECM) is one mechanism that can increase therapeutic resistance in SCLC cells. To address whether adhesion to ECM increases resistance through modulation of signaling pathways, a series of SCLC cell lines were plated on various ECM components, and activation of two signaling pathways that promote cellular survival, the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway and the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) pathway, was assessed. Although differential activation was observed, adhesion to laminin increased Akt activation, increased cellular survival after serum starvation, and caused the cells to assume a flattened, epithelial morphology. Inhibitors of the PI3K/Akt/mTOR pathway (LY294002, rapamycin) but not the MEK/ERK pathway (U0126) abrogated laminin-mediated survival. SCLC cells plated on laminin were not only resistant to serum starvation-induced apoptosis but were also resistant to apoptosis caused by imatinib. Combining imatinib with LY294002 or rapamycin but not U0126 caused greater than additive increases in apoptosis compared with apoptosis caused by the inhibitor or imatinib alone. Similar results were observed when adenoviruses expressing mutant Akt were combined with imatinib, or when LY294002 was combined with cisplatin or etoposide. These studies identify laminin-mediated activation of the PI3K/Akt/mTOR pathway as a mechanism of cellular survival and therapeutic resistance in SCLC cells and suggest that inhibition of the PI3K/Akt/mTOR pathway is one strategy to overcome SCLC resistance mediated by ECM.

Mect1-Maml2 Fusion Oncogene Linked to the Aberrant Activation of Cyclic AMP/CREB Regulated Genes

Malignant salivary gland tumors can arise from a t(11;19) translocation that fuses 42 residues from Mect1/Torc1, a cyclic AMP (cAMP)/cAMP-responsive element binding protein (CREB)-dependent transcriptional coactivator, with 982 residues from Maml2, a NOTCH receptor coactivator. To determine if the Mect1-Maml2 fusion oncogene mediates tumorigenicity by disrupting cAMP/CREB signaling, we have generated in-frame deletions within the CREB-binding domain of Mect1/Torc1 for testing transformation activity and have also developed a doxycycline-regulated Mect1-Maml2 mammalian expression vector for global gene expression profiling. We observed that small deletions within the CREB-binding domain completely abolished transforming activity in RK3E epithelial cells. Further, we have shown that the ectopic induction of Mect1-Maml2 in HeLa cells strongly activated the expression of a group of known cAMP/CREB-regulated genes. In addition, we detected candidate cAMP-responsive element sites within 100 nucleotides of the transcriptional start sites of other genes activated by Mect1-Maml2 expression. In contrast, we did not observe alterations of known Notch-regulated target genes in these expression array profile experiments. We validated the results by reverse transcription-PCR in transfected HeLa, RK3E, and H2009 lung tumor cells and in mucoepidermoid cancer cells that endogenously express the fusion oncopeptide. Whereas overexpression of components of the cAMP pathway has been associated with a subset of human carcinomas, these data provide a direct genetic link between deregulation of cAMP/CREB pathways and epithelial tumorigenesis and suggest future therapeutic strategies for this group of salivary gland tumors.

Identification of a Highly Effective Rapamycin Schedule that Markedly Reduces the Size, Multiplicity, and Phenotypic Progression of Tobacco Carcinogen–Induced Murine Lung Tumors

Purpose: Human and murine preneoplastic lung lesions induced by tobacco exposure are characterized by increased activation of the Akt/mammalian target of rapamycin (mTOR) pathway, suggesting a role for this pathway in lung cancer development. To test this, we did studies with rapamycin, an inhibitor of mTOR, in A/J mice that had been exposed to the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Experimental Design: Tumorigenesis was induced by i.p. injection of NNK, and rapamycin was administered 1 or 26 weeks after NNK administration. Biomarkers associated with mTOR inhibition were assessed in lung and/or surrogate tissues using immunohistochemistry and immunoblotting. Rapamycin levels were measured using mass spectroscopy. Results: Rapamycin was administered on a daily (5 of 7 days) regimen beginning 26 weeks after NNK decreased tumor size, proliferative rate, and mTOR activity. Multiplicity was not affected. Comparing this regimen with an every-other-day (qod) regimen revealed that rapamycin levels were better maintained with qod administration, reaching a nadir of 16.4 ng/mL, a level relevant in humans. When begun 1 week after NNK, this regimen was well tolerated and decreased tumor multiplicity by 90%. Tumors that did develop showed decreased phenotypic progression and a 74% decrease in size that correlated with decreased proliferation and inhibition of mTOR. Conclusions: Tobacco carcinogen–induced lung tumors in A/J mice are dependent upon mTOR activity because rapamycin markedly reduced the development and growth of tumors. Combined with the Food and Drug Administration approval of rapamycin and broad clinical experience, these studies provide a rationale to assess rapamycin in trials with smokers at high risk to develop lung cancer.

Mutational analysis of the β-tubulin gene in lung cancer

Recently, several studies have suggested that a major mechanism of resistance to paclitaxel might involve mutations in the β-tubulin gene in tumor cells. To investigate the frequency of β-tubulin mutations in Japanese patients with small and non-small cell lung cancer, direct sequence analysis following reverse transcription-polymerase chain reaction (RT-PCR) of the β-tubulin gene was performed using total RNA from 20 lung cancer cell lines and 22 specimens from lung cancer patients. First-strand cDNA sequence analysis of the 42 samples showed silent mutations at codon 180 of the β-tubulin gene, which encodes the GTP-binding site of the protein, and codons 195 and 217. However, neither missense nor non-sense mutations affecting microtubule dynamics, within or near the GTP-binding site of the β-tubulin gene, were detected. These results indicate that β-tubulin gene mutations might not play a major role in the mechanism of resistance to paclitaxel in Japanese lung cancer patients. Further investigations are needed to clarify the mechanism of drug resistance.

Risk Factors for Cisplatin-Induced Nephrotoxicity and Potential of Magnesium Supplementation for Renal Protection

Background Nephrotoxicity remains a problem for patients who receive cisplatin chemotherapy. We retrospectively evaluated potential risk factors for cisplatin-induced nephrotoxicity as well as the potential impact of intravenous magnesium supplementation on such toxicity. Patients and Methods We reviewed clinical data for 401 patients who underwent chemotherapy including a high dose (≥60 mg/m2) of cisplatin in the first-line setting. Nephrotoxicity was defined as an increase in the serum creatinine concentration of at least grade 2 during the first course of cisplatin chemotherapy, as assessed on the basis of National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. The severity of nephrotoxicity was evaluated on the basis of the mean change in the serum creatinine level. Magnesium was administered intravenously to 67 patients (17%). Results Cisplatin-induced nephrotoxicity was observed in 127 patients (32%). Multivariable analysis revealed that an Eastern Cooperative Oncology Group performance status of 2 (risk ratio, 1.876; P = 0.004) and the regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) (risk ratio, 1.357; P = 0.047) were significantly associated with an increased risk for cisplatin nephrotoxicity, whereas intravenous magnesium supplementation was associated with a significantly reduced risk for such toxicity (risk ratio, 0.175; P = 0.0004). The development of hypomagnesemia during cisplatin treatment was significantly associated with a greater increase in serum creatinine level (P = 0.0025). Magnesium supplementation therapy was also associated with a significantly reduced severity of renal toxicity (P = 0.012). Conclusions A relatively poor performance status and the regular use of NSAIDs were significantly associated with cisplatin-induced nephrotoxicity, although the latter association was marginal. Our findings also suggest that the ability of magnesium supplementation to protect against the renal toxicity of cisplatin warrants further investigation in a prospective trial.