Nino Keshelava

E-cadherin cell-cell adhesion in ewing tumor cells mediates suppression of anoikis through activation of the ErbB4 tyrosine kinase.

Ability to grow under anchorage-independent conditions is one of the major hallmarks of transformed cells. Key to this is the capacity of cells to suppress anoikis, or programmed cell death induced by detachment from the extracellular matrix. To model this phenomenon in vitro, we plated Ewing tumor cells under anchorage-independent conditions by transferring them to dishes coated with agar to prevent attachment to underlying plastic. This resulted in marked up-regulation of E-cadherin and rapid formation of multicellular spheroids in suspension. Addition of calcium chelators, antibodies to E-cadherin (but not to other cadherins or beta(1)-integrin), or expression of dominant negative E-cadherin led to massive apoptosis of spheroid cultures whereas adherent cultures were unaffected. This correlated with reduced activation of the phosphatidylinositol 3-kinase-Akt pathway but not the Ras-extracellular signal-regulated kinase 1/2 cascade. Furthermore, spheroid cultures showed profound chemoresistance to multiple cytotoxic agents compared with adherent cultures, which could be reversed by alpha-E-cadherin antibodies or dominant negative E-cadherin. In a screen for potential downstream effectors of spheroid cell survival, we detected E-cadherin-dependent activation of the ErbB4 receptor tyrosine kinase but not of other ErbB family members. Reduction of ErbB4 levels by RNA interference blocked Akt activation and spheroid cell survival and restored chemosensitivity to Ewing sarcoma spheroids. Our results indicate that anchorage-independent Ewing sarcoma cells suppress anoikis through a pathway involving E-cadherin cell-cell adhesion, which leads to ErbB4 activation of the phosphatidylinositol 3-kinase-Akt pathway, and that this is associated with increased resistance of cells to cytotoxic agents.

Interleukin-6 in the Bone Marrow Microenvironment Promotes the Growth and Survival of Neuroblastoma Cells

Neuroblastoma, the second most common solid tumor in children, frequently metastasizes to the bone marrow and the bone. Neuroblastoma cells present in the bone marrow stimulate the expression of interleukin-6 (IL-6) by bone marrow stromal cells (BMSC) to activate osteoclasts. Here we have examined whether stromal-derived IL-6 also has a paracrine effect on neuroblastoma cells. An analysis of the expression of IL-6 and its receptor, IL-6R, in 11 neuroblastoma cell lines indicated the expression of IL-6 in 4 cell lines and of IL-6R in 9 cell lines. Treatment of IL-6R-positive cells with recombinant human IL-6 resulted in signal transducer and activator of transcription-3 and extracellular signal-regulated kinase-1/2 activation. Culturing IL-6R-positive neuroblastoma cells in the presence of BMSC or recombinant human IL-6 increased proliferation and protected tumor cells from etoposide-induced apoptosis, whereas it had no effect on IL-6R-negative tumor cells. In vivo, neuroblastoma tumors grew faster in the presence of a paracrine source of IL-6. IL-6 induced the expression of cyclooxygenase-2 in neuroblastoma cells with concomitant release of prostaglandin-E2, which increased the expression of IL-6 by BMSC. Supporting a role for stromal-derived IL-6 in patients with neuroblastoma bone metastasis, we observed elevated levels of IL-6 in the serum and bone marrow of 16 patients with neuroblastoma bone metastasis and in BMSC derived from these patients. Altogether, the data indicate that stromal-derived IL-6 contributes to the formation of a bone marrow microenvironment favorable to the progression of metastatic neuroblastoma.

Initial testing (stage 1) of the proteasome inhibitor bortezomib by the pediatric preclinical testing program

Bortezomib is a proteasome inhibitor that has been approved by FDA for the treatment of multiple myeloma and that has completed phase 1 testing in children. The purpose of the current study was to evaluate the antitumor activity of bortezomib against the in vitro and in vivo childhood cancer preclinical models of the Pediatric Preclinical Testing Program (PPTP).

National Cancer Institute Pediatric Preclinical Testing Program: Model Description for In Vitro Cytotoxicity Testing

The National Cancer Institute (NCI) has established the Pediatric Preclinical Testing Program (PPTP) for testing drugs against in vitro and in vivo childhood cancer models to aid in the prioritization of drugs considered for early phase pediatric clinical trials.

p53 mutations and loss of p53 function confer multidrug resistance in neuroblastoma

BACKGROUND Neuroblastomas often acquire sustained drug resistance during therapy. Sensitivities to carboplatin, etoposide, or melphalan were determined for 18 neuroblastoma cell lines; eight were sensitive and ten were resistant. As p53 mutations are rare in neuroblastomas studied at diagnosis, we determined if acquired p53 mutations and loss of function conferred multidrug resistance. RESULTS Loss of p53 function (p53-LOF), defined as a failure to induce p21 and/or MDM2 in response to melphalan, was seen in 1/8 drug-sensitive and 6/10 drug-resistant cell lines. In four cell lines p53-LOF was associated with mutations in the DNA binding region of p53, while three cell lines with LOF and four cell lines with functional p53 had no evidence of p53 muta-tions. Nonfunctional and mutated p53 was detected in one resistant cell line, while a sensitive cell line derived from the same patient prior to treatment had functional and wild type (wt) p53. We transfected HPV 16 E6 (which mediates degradation of p53, causing LOF) into two drug-sensitive neuroblastoma cell lines with functional p53. LC(90) values of HPV 16 E6 transfected cell lines were 3-7-fold (melphalan), 8-109-fold (carboplatin), and 2-158-fold (etoposide) greater than that of LXSN-transfected controls. CONCLUSIONS These data suggest that some neuroblastomas acquire p53 mutations during therapy, which is associated with a loss of p53 function, and can confer high-level multidrug resistance.

Cross-resistance of topoisomerase I and II inhibitors in neuroblastoma cell lines.

Purpose: We have previously shown that neuroblastoma cell lines established from patients after intensive chemotherapy show sustained resistance to various drugs and especially high resistance to etoposide (up to 51 times higher than a clinically achievable level). To determine whether topoisomerase I inhibitors (topotecan and CPT-11) are effective against etoposide-resistant neuroblastomas, we studied the response to topotecan and the active metabolite of CPT-11 (SN-38) in 19 cell lines with a spectrum of sensitivities to etoposide. Materials and methods: The panel included cell lines established at diagnosis and after disease progression either during induction chemotherapy or after myeloablative therapy supported with bone marrow transplantation. Cytotoxicities of topotecan, SN-38, and etoposide were determined using a microplate digital image microscopy (DIMSCAN) assay with a 4-log dynamic range. Results: All six etoposide-resistant cell lines were resistant to topotecan and SN-38 (resistance defined as LC90 higher then clinically achievable levels for the drug). Significant cross-resistance by Pearsons correlation analysis (r ≥ 0.6) occurred between topotecan + etoposide, topotecan + SN-38, and etoposide + SN-38. Conclusions: Topotecan and CPT-11 do not have significant activity against most etoposide-resistant neuroblastoma cell lines and this suggests that agents other than topoisomerase inhibitors should be explored for the treatment of recurrent neuroblastomas.

Initial testing (stage 1) of vorinostat (SAHA) by the pediatric preclinical testing program

Vorinostat, a histone deacetylase inhibitor, was evaluated against the in vitro and in vivo childhood solid tumor and leukemia models in the Pediatric Preclinical Testing Program (PPTP). In vitro testing was performed by the DIMSCAN cytotoxicity assay. In vivo, vorinostat was administered intraperitoneally to mice bearing xenografts. Vorinostat demonstrated 2‐log cell growth inhibitory activity in vitro, but generally at concentrations not sustainable in the clinic. No objective responses were observed for any of the solid tumor or acute lymphoblastic leukemia xenografts. Preclinical studies with appropriate drug combinations may provide direction for further clinical evaluations of vorinostat against selected pediatric cancers. Pediatr Blood Cancer 2009;53:505–508.

Buthionine sulfoximine and myeloablative concentrations of melphalan overcome resistance in a melphalan-resistant neuroblastoma cell line.

Background Alkylator resistance contributes to treatment failure in high-risk neuroblastoma. Buthionine sulfoximine (BSO) can deplete glutathione and synergistically enhance in vitro sensitivity to the alkylating agent melphalan (L-PAM) for many neuroblastoma cell lines, but optimal use of this combination needs to be defined because clinical responses have been less frequent and not durable. Patients and Methods The authors established and characterized a neuroblastoma cell line (CHLA-171) from a patient who died of progressive disease after treatment with BSO and low-dose L-PAM. Results CHLA-171 lacks MYCN amplification, expresses PGP (P-glycoprotein) 9.5 RNA, and shows cell surface antigen expression (human leukocyte antigen class I weakly positive, but HSAN 1.2 (hybridoma, SAN 1.2) and anti-GD2 (anti-ganglioside GD2 antibody) strongly positive) characteristic of neuroblastoma cell lines. Twenty-four hours of BSO treatment (0–1,000 &mgr;mol/L) maximally depleted CHLA-171 glutathione to 36% of baseline. The cytotoxic response of CHLA-171 to BSO and L-PAM, alone and in combination, was measured by digital image microscopy (DIMSCAN) over a range of drug concentrations and compared with drug levels obtained in the patient during BSO/L-PAM therapy. As single agents, CHLA-171 was highly resistant to L-PAM (LD 90 = 42 &mgr;mol/L; peak plasma concentration in the patient equals 3.9 &mgr;mol/L) and moderately resistant to BSO (LD 90 = 509 &mgr;mol/L; steady-state concentration in the patient equals 397 &mgr;mol/L). Treatment with a 10:1 (BSO:L-PAM) fixed ratio combination synergistically overcame resistance (3–4 logs of cell kill, combination index <1) at clinically achievable levels of BSO (100–400 &mgr;mol/L) and levels of L-PAM (10–40 &mgr;mol/L) clinically achievable only with hematopoietic stem cell support. Conclusions The in vitro results obtained for CHLA-171 suggest that BSO/L-PAM therapy may be optimally effective for drug-resistant neuroblastoma using myeloablative doses of L-PAM.

Drug resistance in human neuroblastoma cell lines correlates with clinical therapy

To determine if neuroblastoma acquires a sustained drug-resistant phenotype from patient exposure to therapy, we studied neuroblastoma cell lines established at different points of therapy: at diagnosis prior to therapy, at progressive disease after induction therapy and at relapse after intensive chemoradiotherapy and bone marrow transplantation (post-BMT). Melphalan, cisplatin, carboplatin, doxorubicin, and etoposide cytotoxicities were determined by DIMSCAN assay. Drug resistance progressively increased with therapy and 3/5 post-BMT lines showed high resistance to most drugs. IC 90s 37, 78, 719 and 256 times higher than clinically achievable drug levels were obtained in post-BMT cell lines for melphalan, cisplatin, doxorubicin and etoposide, respectively. Resistance correlated with the therapies patients received: considerable etoposide and doxorubicin resistance (> 1000-fold resistance) was seen in cell lines obtained from patients treated with these drugs. These cell lines indicate that neuroblastoma acquires resistance to cytotoxic drugs that is probably due to stable genetic alterations occurring during therapy.

Synergism of buthionine sulfoximine and melphalan against neuroblastoma cell lines derived after disease progression

BACKGROUND Despite intensive-alkylator based regimens, >50% of patients with high-risk neuroblastoma (NB) die from recurrent disease that is probably due, in part, to acquired alkylator resistance. PROCEDURE Using buthionine sulfoximine (BSO)-mediated, glutathione (GSH) depletion to modulate melphalan (L-PAM) resistance, we examined six NB cell lines established after progressive disease following either standard chemotherapy, BSO/L-PAM therapy, or myeloablative therapy and autologous hematopoietic stem cell transplant (AHSCT). RESULTS Four of the six cell lines (three p53-nonfunctional and one p53-functional) showed high-level L-PAM resistance. CONCLUSIONS Fixed ratio analysis demonstrated BSO/L-PAM synergy (combination index >1) for all cell lines tested. In L-PAM-resistant cell lines, the minimal cytotoxicity observed for BSO combined with nonmyeloablative concentrations of L-PAM was markedly enhanced (>4 logs total cell kill) when BSO was combined with myeloablative concentrations of L-PAM. In alkylator-resistant NB, the optimal use of BSO may require dose escalation of L-PAM to levels requiring AHSCT.