Rosa Caputo

Antitumor Activity of ZD6474, a Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitor, in Human Cancer Cells with Acquired Resistance to Antiepidermal Growth Factor Receptor Therapy

Purpose: The epidermal growth factor receptor (EGFR) autocrine signaling pathway is involved in cancer development and progression. EGFR inhibitors such as C225 (cetuximab), a chimeric human-mouse anti-EGFR monoclonal antibody, and ZD1839 (gefitinib), a small molecule EGFR-selective tyrosine kinase inhibitor, are in advanced clinical development. The potential emergence of cancer cell resistance in EGFR-expressing cancers treated with EGFR inhibitors could determine lack of activity of these drugs in some cancer patients. Vascular endothelial growth factor (VEGF) is secreted by cancer cells and plays a key role in the regulation of tumor-induced endothelial cell proliferation and permeability. ZD6474 is a small molecule VEGF flk-1/KDR (VEGFR-2) tyrosine kinase inhibitor that also demonstrates inhibitory activity against EGFR tyrosine kinase. Experimental Design: The antitumor activity of ZD1839, C225, and ZD6474 was tested in athymic mice bearing human GEO colon cancer xenografts. GEO cell lines resistant to EGFR inhibitors were established from GEO xenografts growing in mice treated chronically with ZD1839 or C225. Expression of EGFR was evaluated by flow cytometry. Expression of various proteins involved in intracellular cell signaling was assessed by Western blotting. Tumor growth data were evaluated for statistical significance using the Student’s t test. All Ps were two-sided. Results: Although chronic administration of optimal doses of C225 or ZD1839 efficiently blocked GEO tumor growth in the majority of mice, tumors slowly started to grow within 80–90 days, despite continuous treatment. In contrast, continuous treatment of mice bearing established GEO xenografts with ZD6474 resulted in efficient tumor growth inhibition for the entire duration of dosing (up to 150 days). ZD6474 activity was also determined in mice pretreated with ZD1839 or C225. When GEO growth was apparent after 4 weeks of treatment with EGFR inhibitors, mice were either re-treated with EGFR inhibitors or treated with ZD6474. GEO tumor growth was blocked only in mice treated with ZD6474, whereas tumor progression was observed in mice re-treated with C225 or ZD1839. GEO tumors growing during treatment with C225 or with ZD1839 were established as cell lines (GEO-C225-RES and GEO-ZD1839-RES, respectively). Cell membrane-associated EGFR expression was only slightly reduced in these cell lines compared with parental GEO cells. Western blotting revealed no major change in the expression of the EGFR ligand transforming growth factor α of bcl-2, bcl-xL, p53, p27, MDM-2, akt, activated phospho-akt, or mitogen-activated protein kinase. However, both GEO-C225-RES and GEO-ZD1839-RES cells exhibited a 5–10-fold increase in activated phospho-mitogen-activated protein kinase and in the expression of cyclooxygenase-2 and of VEGF compared with GEO cells. GEO-C225-RES and GEO-ZD1839-RES growth as xenografts in nude mice was not significantly affected by treatment with either C225 or ZD1839 but was efficiently inhibited by ZD6474. Conclusions: Long-term treatment of GEO xenografts with selective EGFR inhibitors results in the development of EGFR inhibitor-resistant cancer cells. Growth of EGFR inhibitor-resistant tumors can be inhibited by ZD6474. These data indicate that inhibition of VEGF signaling has potential as an anticancer strategy, even in tumors that are resistant to EGF inhibitors.

ZD1839 (IRESSA), an EGFR-selective tyrosine kinase inhibitor, enhances taxane activity in bcl-2 overexpressing, multidrug-resistant MCF-7 ADR human breast cancer cells.

Constitutive bcl‐2 overexpression increases the tumorigenic and metastatic potential of doxorubicin‐resistant, estrogen‐independent, MCF‐7 ADR human breast cancer cells. We evaluated the sensitivity to taxanes (paclitaxel, docetaxel and IDN 5109) of 2 bcl‐2‐overexpressing MCF‐7 ADR clones and control neomycin‐transfected MCF‐7 ADR neo cells. The 2 bcl‐2‐overexpressing MCF‐7 ADR clones were relatively resistant to all 3 taxanes, whereas the MCF‐7 ADR neo cells were relatively resistant to paclitaxel and docetaxel, but sensitive to IDN 5109. We found that both MCF‐7 ADR neo and bcl‐2‐overexpressing MCF‐7 ADR clones express high levels of the epidermal growth factor receptor (EGFR) and its ligand, transforming growth factor‐α (TGF‐α). Therefore, we tested the growth inhibitory effect of ZD1839 (Iressa™, AstraZeneca, Macclesfield, UK), an orally active, selective EGFR tyrosine kinase inhibitor (EGFR‐TKI) that is in clinical development. ZD1839 inhibited the growth in soft agar of all 3 clones in a dose‐dependent manner (IC50 of approximately 0.1 μM). This effect was accompanied by a dose‐dependent inhibition of EGFR tyrosine autophosphorylation and of the production of TGF‐α, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). To determine whether the blockade of EGFR signaling might affect the sensitivity of bcl‐2‐overexpressing MCF‐7 ADR cells to taxanes, cells were treated with ZD1839 in combination with paclitaxel, docetaxel or IDN 5109, and dose‐dependent cooperative growth inhibition as well as apoptosis potentiation were observed. Combined treatment with IDN 5109 and ZD1839 also resulted in a significant inhibition of bcl‐2 expression in bcl‐2‐overexpressing MCF‐7 ADR cells. These results demonstrate the ability of ZD1839 to overcome taxane resistance in a model of hormone‐independent, multidrug‐resistant, human breast cancer.

Antisense oligonucleotides targeting the epidermal growth factor receptor inhibit proliferation, induce apoptosis and cooperate with cytotoxic drugs in human cancer cell lines

We have constructed a series of 22 phosphorothioate 20‐mer antisense oligonucleotides directed against different regions of the human (EGFR) mRNA. Treatment with EGFR antisense oligonucleotides showed a dose‐dependent inhibition of human GEO colon cancer cell growth in soft agar. Western blot analysis demonstrated a significant reduction in EGFR expression after treatment with each EGFR antisense oligonucleotide. The ability to inhibit GEO anchorage‐independent growth, however, varied among the EGFR antisense sequences with an IC50 ranging between 0.5 and 3.5 μM. Two of these antisense oligonucleotides targeting the regions between 2457–2476 and 614–4633 bases of the human EGFR mRNA have been modified as hybrid DNA/RNA mixed backbone oligonucleotides (MBO) to examine their anticancer properties in vivo. The 2 EGFR antisense MBOs retained the same biological properties of the fully phosphorothioate EGFR antisense oligonucleotides targeting the same EGFR mRNA sequences, such as blocking EGFR synthesis, inhibiting cell growth and enhancing programmed cell death in human cancer cell lines that express functional EGFRs. Furthermore, a potentiation in the growth inhibitory effect on GEO cancer cells was observed after treatment with these EGFR antisense MBOs in combination with cytotoxic drugs, including cisplatin, doxorubicin, paclitaxel, or topotecan. These results show the antiproliferative activity of specific EGFR antisense oligonucleotides and allow to identify novel EGFR antisense MBOs that deserve further evaluation as potential selective anticancer agents alone or in combination with cytotoxic drugs in human carcinomas that express functional EGFRs.

Cooperative Antitumor Effect of Multitargeted Kinase Inhibitor ZD6474 and Ionizing Radiation in Glioblastoma

Purpose: Glioblastoma multiforme is an aggressive disease in which vascular endothelial growth factor (VEGF) and the EGF receptor (EGFR) are implicated in tumor growth, relapse, and resistance to radiotherapy and chemotherapy. The VEGF receptors VEGFR-1 (flt-1) and VEGFR-2 (KDR), typically present on endothelial cells, have also been identified in human glioblastoma tissues and cell lines. In addition, EGFR is dysregulated in the majority of human glioblastomas and EGFR overexpression correlates with shorter survival. We have investigated the antitumor and antiangiogenic effect of ZD6474, an inhibitor of both VEGFR and EGFR signaling as a single agent and in combination with ionizing radiation. Experimental Design: We have used ZD6474 and/or ionizing radiation in human glioblastoma cell lines D54 and U251 in vitro and in nude mice bearing established xenografts. The effects of treatment on tumor blood vessels and protein expression were evaluated by Western blot and immunohistochemistry. Results: As single agents, ionizing radiation and ZD6474 caused a dose-dependent inhibition of soft agar growth in D54 and U251 cell lines, whereas a cooperative effect was obtained in combination. Treatment of mice bearing D54 xenografts with either ZD6474 or radiotherapy alone caused tumor growth inhibition that was reversible upon treatment cessation. A cooperative and long-lasting inhibition of tumor growth was obtained with ZD6474 in combination with concomitant radiotherapy. The antiproliferative effect was accompanied by inhibition of VEGF protein expression and inhibition of angiogenesis as measured by vessel counting. Conclusion: This study shows the antitumor activity of ZD6474 in combination with ionizing radiation in glioblastoma both in vitro and in vivo, and provides a scientific rationale to evaluate ZD6474 alone or in combination with radiotherapy in patients affected by this disease.

Novel Toll-Like Receptor 9 Agonist Induces Epidermal Growth Factor Receptor (EGFR) Inhibition and Synergistic Antitumor Activity with EGFR Inhibitors

Purpose: Immunostimulating Toll-like receptor 9 (TLR9) agonists cause antitumor activity interfering also with cancer proliferation and angiogenesis by mechanisms still incompletely understood. We hypothesized that modified TLR9 agonists could impair epidermal growth factor receptor (EGFR) signaling and, by this means, greatly enhance EGFR inhibitors effect, acting on both the receptor targeting and the immunologic arm. Experimental Design: We used a novel second-generation, modified, immunomodulatory TLR9 agonist (IMO), alone and in combination with the anti-EGFR monoclonal antibody cetuximab or tyrosine kinase inhibitor gefitinib, on the growth of GEO and cetuximab-resistant derivatives GEO-CR colon cancer xenografts. We have also evaluated the expression of several proteins critical for cell proliferation, apoptosis, and angiogenesis, including EGFR, mitogen-activated protein kinase, Akt, bcl-2, cyclooxygenase-2, vascular endothelial growth factor, and nuclear factor-κB. Results: IMO inhibited GEO growth and signaling by EGFR and the other proteins critical for cell proliferation and angiogenesis. IMO plus the anti-EGFR antibody cetuximab synergistically inhibited tumor growth, signaling proteins, and microvessel formation. EGFR signaling inhibition by IMO is relevant because IMO cooperated also with EGFR tyrosine kinase inhibitor gefitinib in GEO tumors, while it was inactive against GEO-CR xenografts. On the other hand, IMO boosted the non-EGFR-dependent cetuximab activity, causing a cooperative antitumor effect in GEO-CR cells. Finally, combination of IMO, cetuximab and chemotherapeutic irinotecan eradicated the tumors in 90% of mice. Conclusion: IMO interferes with EGFR-related signaling and angiogenesis and has a synergistic antitumor effect with EGFR inhibitors, especially with cetuximab, boosting both the EGFR dependent and independent activity of this agent. Moreover, this therapeutic strategy could be translated in patients affected by colorectal cancer.

A novel MDM2 anti-sense oligonucleotide has anti-tumor activity and potentiates cytotoxic drugs acting by different mechanisms in human colon cancer

MDM2 is over‐expressed in several human tumors. Its product is a negative‐feedback regulator of p53, which interferes with the control of cell proliferation and apoptosis, interacting not only with p53 but also with retinoblastoma (Rb) and E2F. Moreover, mutations in the ARF‐Ink4a locus may also allow MDM2 to override p53 functions. In this study, we have used a novel oligonucleotide anti‐sense MDM2, with mixed‐backbone structure and demonstrate that it causes inhibition of MDM2 expression, induction of both p53 and p21/WAF1 expression and a dose‐dependent, growth‐inhibitory effect in human GEO colon‐cancer cells. We also show that anti‐sense MDM2 has a co‐operative growth‐inhibitory effect with different classes of cytotoxic drugs acting by different mechanisms. Moreover, anti‐sense MDM2 induces apoptosis and markedly enhances the apoptotic activity of different cytotoxic drugs. Finally, we show that anti‐sense MDM2 has anti‐tumor activity in vivo in nude mice bearing GEO xenografts and potentiates the anti‐tumor effect of cytotoxic drugs. Indeed, despite the short treatment period, the combination of anti‐sense MDM2 and cytotoxic drugs causes a marked delay in tumor growth and prolongation of mice survival, lasting several months after treatment cessation. The anti‐tumor effect is associated with inhibition of MDM2 expression in tumor specimens of animals treated with anti‐sense MDM2, alone or in combination with a cytotoxic drug. Our results provide the rationale for development of a novel mixed‐backbone anti‐sense MDM2 into a clinical setting in therapeutic combination strategies with conventional cytotoxic drugs. Int. J. Cancer 88:804–809, 2000.

TLR9 agonist acts by different mechanisms synergizing with bevacizumab in sensitive and cetuximab-resistant colon cancer xenografts

Synthetic agonists of Toll-like receptor 9 (TLR9), a class of agents that induce specific immune response, exhibit antitumor activity and are currently being investigated in cancer patients. Intriguingly, their mechanisms of action on tumor growth and angiogenesis are still incompletely understood. We recently discovered that a synthetic agonist of TLR9, immune modulatory oligonucleotide (IMO), acts by impairing epidermal growth factor receptor (EGFR) signaling and potently synergizes with anti-EGFR antibody cetuximab in GEO human colon cancer xenografts, whereas it is ineffective in VEGF-overexpressing cetuximab-resistant GEO cetuximab-resistant (GEO-CR) tumors. VEGF is activated by EGFR, and its overexpression causes resistance to EGFR inhibitors. Therefore, we used IMO and the anti-VEGF antibody bevacizumab as tools to study IMOs role on EGFR and angiogenesis and to explore its therapeutic potential in GEO, LS174T, and GEO-CR cancer xenografts. We found that IMO enhances the antibody-dependent cell-mediated cytotoxicity (ADCC) activity of cetuximab, that bevacizumab has no ADCC, and IMO is unable to enhance it. Nevertheless, the IMO-plus-bevacizumab combination synergistically inhibits the growth of GEO and LS174T as well as of GEO-CR tumors, preceded by inhibition of signaling protein expression, microvessel formation, and human, but not murine, VEGF secretion. Moreover, IMO inhibited the growth, adhesion, migration, and capillary formation of VEGF-stimulated endothelial cells. The antitumor activity was irrespective of the TLR9 expression on tumor cells. These studies demonstrate that synthetic agonists of TLR9 interfere with growth and angiogenesis also by EGFR- and ADCC-independent mechanisms affecting endothelial cell functions and provide a strong rationale to combine IMO with bevacizumab and EGFR inhibitory drugs in colon cancer patients.

Combined targeting of epidermal growth factor receptor and MDM2 by gefitinib and antisense MDM2 cooperatively inhibit hormone-independent prostate cancer.

Purpose: The epidermal growth factor receptor (EGFR) may play a relevant role in the progression, hormone therapy resistance, and prognosis of prostate cancer patients. Also MDM2, a negative p53 regulator that interacts with retinoblastoma (Rb), E2F, p19arf and the ras-mitogen-activated protein kinase(MAPK) cascade plays an important role in prostate cancer progression and prognosis. On the basis of the EGFR and MDM2 role in integrating signaling pathways critical for prostate cancer progression, we investigated whether their selective combined blockade may have a cooperative antitumor effect in prostate cancer. For this purpose, we have used the EGFR tyrosine kinase inhibitor gefitinib (ZD1839, Iressa) and a second generation hybrid oligonucleotide antisense MDM2 (AS-MDM2), respectively. Experimental Design: Gefitinib and AS-MDM2 were administered to hormone-refractory and hormone-dependent human prostate cancer cells in vitro and to mice bearing tumor xenografts, evaluating the effects on growth, apoptosis, and protein expression, in vitro and in vivo. Results: We demonstrated that the combination of gefitinib and AS-MDM2 synergistically inhibits the growth of hormone-independent prostate cancer cells in vitro. This effect is accompanied by the inhibition of MDM2, phosphorylated Akt (pAkt), phosphorylated MAPK (pMAPK), and vascular endothelial growth factor (VEGF) expression and by Rb hypophosphorylation. The combination of the two agents in nude mice bearing the same hormone-independent tumors caused a potent cooperative antitumor effect. Tumor samples analysis confirmed the inhibition of MDM2, pAkt, pMAPK, VEGF, and basic fibroblast growth factor expression. Conclusions: This study shows that EGFR and MDM2 play a critical role in the growth of prostate cancer, especially hormone-dependent, and that their combined blockade by gefitinib and AS-MDM2 causes a cooperative antitumor effect, supporting the clinical development of this therapeutic strategy.

Resistance to taxanes is induced by c‐erbB‐2 overexpression in human MCF‐10A mammary epithelial cells and is blocked by combined treatment with an antisense oligonucleotide targeting type I protein kinase A

We have tested the sensitivity of human MCF‐10A mammary epithelial cells and of their transformed derivatives overexpressing an activated c‐Ha‐ras gene (MCF‐10A Ha‐ras cells), the c‐erbB‐2 gene (MCF‐10A c‐erbB‐2 cells) or both genes (MCF‐10A HE cells) to different cytotoxic drugs. As compared with parental MCF‐10A cells, the transformed cells exhibited an increased sensitivity to topoisomerase I‐ and topoisomerase II‐inhibitors, and to platinum‐derivatives with a 2‐ to 10‐fold reduction in IC50 values. A remarkable difference in sensitivity was observed following treatment with taxanes. While MCF‐10A Ha‐ras cells showed an increased sensitivity, MCF‐10A c‐erbB‐2 and MCF‐10A HE cells exhibited a relative resistance to taxol and taxotere, with an approximately 3.5‐ to 6.5‐fold higher IC50 as compared with MCF‐10A cells suggesting that c‐erbB‐2 overexpression has a dominant effect compared with an activated c‐Ha‐ras gene. The type I cAMP‐dependent protein kinase (PKAI) is overexpressed in cancer cells. Inhibition of PKAI by antisense oligonucleotides targeting its RIα regulatory subunit results in cancer cell growth inhibition. To evaluate the effect of blocking PKAI on MCF‐10A cell sensitivity to taxanes, we treated these cells with taxol or taxotere in combination with a PKAI antisense oligonucleotide. Treatment with this agent, but not with a control scramble sequence, was able to overcome the effect of c‐erbB‐2 overexpression on MCF‐10A cell sensitivity to taxol and taxotere, with a 20‐ to 40‐fold shift in the IC50 values for the 2 drugs. Int. J. Cancer 85:710–715, 2000.

A Novel Toll-Like Receptor 9 Agonist Cooperates with Trastuzumab in Trastuzumab-Resistant Breast Tumors through Multiple Mechanisms of Action

Purpose: Resistance to anti-HER2 monoclonal antibody trastuzumab is a relevant issue in breast cancer patients. Among the mechanisms implicated in trastuzumab resistance, increasing evidence supports a role of tumor microenvironment. We previously found that a novel toll-like receptor 9 agonist, referred to as immune modulatory oligonucleotide (IMO) and currently under clinical investigation, acts through epidermal growth factor receptor (EGFR) and shows direct antiangiogenic effects by cooperating with anti-EGFR or anti-VEGF drugs, thus interfering with cancer cells and microenvironment. Experimental Design: In this study, we used KPL-4 and JIMT-1 trastuzumab-resistant breast cancer cells to evaluate the combination IMO plus trastuzumab as a therapeutic option for trastuzumab-resistant breast cancers. Results: IMO inhibits KPL-4 and JIMT-1 xenografts growth and potentiates trastuzumab antitumor effect, with complete suppression of tumor growth, potent enhancement of trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity, and strong inhibition of EGFR/HER2-related signaling. In KPL-4 xenografts, IMO alone interferes with HER signal transduction, whereas trastuzumab is ineffective. IMO induces an HER-dependent signal inhibition also in vitro by modulating a functional interaction between toll-like receptor 9 and HER receptors occurring at membrane level. Finally, IMO plus trastuzumab produces a cooperative antiangiogenic effect related to suppression of endothelial HER-related signaling. Conclusions: We showed a cooperative effect of IMO plus trastuzumab in trastuzumab-resistant breast cancers due to IMO direct antitumor and antiangiogenic activity and antibody-dependent cell-mediated cytotoxicity enhancement. Moreover, we provided first evidence of a toll-like receptor 9/HER interaction at membrane level as novel mechanism of action. Altogether, we propose IMO plus trastuzumab as an effective strategy in trastuzumab-resistant breast cancers. (Clin Cancer Res 2009;15(22):692130)