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 β1-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 α-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.
suppression of anoikis; E-cadherin; ErbB4; EWS-FLI1; Ewing tumor
SCH 727965 is a novel drug in clinical development that potently and selectively inhibits CDK1, CDK2, CDK5, and CDK9. The activity of SCH 727965 was evaluated against the PPTP’s in vitro and in vivo panels.
SCH 727965 was tested against the PPTP in vitro panel using 96 hour exposure at concentrations ranging from 0.1 nM to 1.0 μM. It was tested against the PPTP in vivo panels at a dose of 40 mg/kg administered intraperitoneally twice weekly for 2 weeks and repeated at Day 21 with a total observation period of 6 weeks.
The median IC50 value for the cell lines was 7.5 nM, with less than 4-fold range between the minimum (3.4 nM) and maximum (11.2 nM) IC50 values. SCH 727965 demonstrated an activity pattern consistent with cytotoxicity for most of the cell lines. Forty-three xenograft models were studied and SCH 727965 induced significant delays in event free survival distribution compared to control in 23 of 36 (64%) evaluable solid tumor xenografts and in 3 of 7 ALL xenografts. SCH 727965 did not induce objective responses in the solid tumor panels and the best response observed was stable disease for one osteosarcoma xenograft. In the leukemia panel, there were two objective responses with a complete response observed in a single xenograft.
SCH 727965 shows an interesting pattern of activity suggesting its potential applicability against selected childhood cancers, particularly leukemias.
Preclinical Testing; Developmental Therapeutics; SCH 727965; Dinaciclib
Despite intensive treatment with chemotherapy, radiotherapy and surgery, over 70% of patients with metastatic Ewing's Sarcoma Family of Tumors (EFT) will die of their disease. We hypothesize that properly characterized laboratory models reflecting the drug resistance of clinical tumors will facilitate the application of new therapeutic agents to EFT. To determine resistance patterns, we studied newly established EFT cell lines derived from different points in therapy: two established at diagnosis (CHLA-9, CHLA-32), two after chemotherapy and progressive disease (CHLA-10, CHLA-25), and two at relapse after myeloablative therapy and autologous bone marrow transplantation (post-ABMT) (CHLA-258, COG-E-352). The new lines were compared to widely studied EFT lines TC-71, TC-32, SK-N-MC, and A-673. These lines were extensively characterized with regard to identity (short tandem repeat (STR) analysis), p53, p16/14 status, and EWS/ETS breakpoint and target gene expression profile. The DIMSCAN cytotoxicity assay was used to assess in vitro drug sensitivity to standard chemotherapy agents. No association was found between drug resistance and the expression of EWS/ETS regulated genes in the EFT cell lines. No consistent association was observed between drug sensitivity and p53 functionality or between drug sensitivity and p16/14 functionality across the cell lines. Exposure to chemotherapy prior to cell line initiation correlated with drug resistance of EFT cell lines in 5/8 tested agents at clinically achievable concentrations (CAC) or the lower tested concentration (LTC): (cyclophosphamide (as 4-HC) and doxorubicin at CAC, etoposide, irinotecan (as SN-38) and melphalan at LTC; P<0.1 for one agent, and P<0.05 for four agents. This panel of well-characterized drug-sensitive and drug-resistant cell lines will facilitate in vitro preclinical testing of new agents for EFT.
Sorafenib is an inhibitor of multiple kinases (e.g., VEGF receptors, PDGFR, FLT3, RET, BRAF, KIT) and is approved by FDA for treatment of two adult cancers. The activity of sorafenib was evaluated against the PPTP's in vitro and in vivo panels.
Sorafenib was evaluated against the PPTP in vitro panel using 96 hour exposure at concentrations ranging from 1.0 nM to 10.0 μM. It was tested against the PPTP in vivo panels at a dose of 60 mg/kg administered by oral gavage daily for 5 days per week, repeated for 6 weeks.
In vitro sorafenib demonstrated cytotoxic activity, with a median IC50 value of 4.3 μM. Twenty of 23 cell lines had IC50 values between 1.0 and 10.0 μM. A single cell line (Kasumi-1) with an activating KIT mutation had an IC50 value < 1.0 μM (IC50 = 0.02 μM). In vivo sorafenib induced significant differences in EFS distribution compared to control in 27 of 36 (75%) of the evaluable solid tumor xenografts and in 1 of 8 (12.5%) of the evaluable ALL xenografts. Sorafenib induced tumor growth inhibition meeting criteria for intermediate activity (EFS T/C) in 15 of 34 (44%) evaluable solid tumor xenografts. No xenografts achieved an objective response.
The primary in vitro activity of sorafenib was noted at concentrations above 1 μM, with the exception of a more sensitive cell line with an activating KIT mutation. The primary in vivo effect for sorafenib was tumor growth inhibition, which was observed across multiple histotypes.
Preclinical Testing; Developmental Therapeutics; tyrosine kinases
MLN4924 is an investigational first-in-class small molecule inhibitor of NEDD8-activating enzyme (NAE). NAE is an essential component of the NEDD8 conjugation pathway, controlling the activity of a subset of ubiquitin-proteasome system (UPS) E3 ligases, multiprotein complexes that transfer ubiquitin molecules to substrate proteins.
MLN4924 was tested against the PPTP in vitro panel using 96 hour exposure time at concentrations ranging from 1.0 nM to 10 μM. It was tested in vivo at a dose of 100 mg/kg [66 mg/kg for the acute lymphoblastic leukemia (ALL) xenografts] administered orally twice daily × 5 days. Treatment duration was 3 weeks.
The median relative IC50 for MLN4924 against the PPTP cell lines was 143 nM, (range 15 nM to 678 nM) with that for the Ewing panel being significantly lower (31 nM). MLN4924 induced significant differences in EFS distribution compared to control in 20 of 34 (59%) evaluable solid tumor xenografts. MLN4924 induced intermediate activity (EFS T/C values > 2) in 9 of the 33 evaluable xenografts (27%), including 4 of 4 glioblastoma xenografts, 2 of 3 Wilms tumor xenografts, 2 of 5 rhabdomyosarcoma xenografts, and 1 of 4 neuroblastoma xenografts. For the ALL panel, 5 of 8 evaluable xenografts showed intermediate activity for the EFS T/C measure. MLN4924 did not induce objective responses in the PPTP solid tumor or ALL panels.
MLN4924 showed potent activity in vitro and in vivo showed tumor growth inhibitory activity against a subset of the PPTP solid tumor and ALL xenografts.
Preclinical Testing; Developmental Therapeutics; MLN4924
The PIM kinase inhibitor, SGI-1776, was tested against the PPTP in vitro (1.0 nM to 10 μM) and in vivo panels (148 mg/kg daily x 5 days for 3 weeks). SGI-1776 exhibited cytotoxic activity in vitro with a median relative IC50 of 3.1 μM. SGI-1776 induced significant differences in EFS distribution in vivo in 9 of 31 solid tumor xenografts and in 1 of 8 of the evaluable ALL xenografts. SGI-1776 induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity in 1 of 39 evaluable models. In contrast, SGI-1776 induced complete responses of subcutaneous MV4;11 (B myeloid leukemia).
Preclinical Testing; Developmental Therapeutics; kinase inhibitors
Arsenic trioxide was tested against the PPTP in vitro panel (1.0 nM to 10 μM) and against the PPTP Ewing sarcoma in vivo panel administered intraperitoneally at a dose of 2.5 mg/kg daily × 5 per week for a planned treatment duration of 3 weeks. Arsenic trioxide showed a median relative IC50 value of 0.9 μM, with Ewing sarcoma cell lines having IC50 values similar to those of the remaining PPTP cell lines. Arsenic trioxide did not induce significant differences in EFS distribution compared to control in any of the Ewing sarcoma xenografts studied, and no objective responses were observed.
Preclinical Testing; Developmental Therapeutics; Arsenic trioxide; Ewing sarcoma
MK-2206 is a small molecule allosteric inhibitor of Akt/PKB that is undergoing clinical trials for treatment of cancer.
MK-2206 was tested against the PPTP in vitro panel using a 96 hour exposure (1.0 nM-10 μM), and in vivo using thrice weekly dosing for a planned 4 weeks at its maximum tolerated dose (MTD) of 180 mg/kg.
In vitro, the median relative IC50 value for MK-2206 was 2.2μM. Four cell lines with IC50 values < 200 nM included two ALL cell lines (COG-LL-317 and RS4;11), an AML cell line with an activating KIT mutation (Kasumi-1), and a Ewing sarcoma cell line (CHLA-10). In vivo, MK-2206 induced significant differences in EFS distribution compared to control in 12 of 29 (41%) of the evaluable solid tumor xenografts and in 2 of 8 (25%) of the evaluable ALL xenografts. Significant differences in EFS distribution were most frequently noted in the osteosarcoma panel (6 of 6). A single solid tumor xenograft (OS-31) had a greater than two-fold increase in time to event compared to control animals, with all other solid tumor xenografts showing lesser degrees of tumor growth inhibition. Objective responses were not observed for either the solid tumor or ALL xenografts.
MK-2206 showed its most consistent activity in vitro against ALL cell lines and in vivo against osteosarcoma xenografts. However, no objective responses were observed in solid tumor or ALL xenografts. Further preclinical work evaluating MK-2206 in pediatric models in the combination therapy setting may contribute to its pediatric development.
Preclinical Testing; Developmental Therapeutics; MK-2206
AT13387, a non-geldanamycin inhibitor of heat-shock protein 90 (HSP90), was tested against the PPTP in vitro panel (1.0 nM to 10 μM) and against the PPTP in vivo panels (40 mg/kg or 60 mg/kg) administered orally twice weekly. In vitro AT13387 showed a median EC50 value of 41 nM and exhibited activity consistent with a cytotoxic effect. In vivo AT13387 induced significant differences in EFS distribution compared to controls in 17% evaluable solid tumor xenografts, but in none of the ALL xenografts. No objective tumor responses were observed. In vivo AT13387 demonstrated only modest single agent activity.
Preclinical Testing; Developmental Therapeutics; HSP90 inhibitors
Neuroblastomas are tumors of peripheral sympathetic neurons and are the most common solid tumor in children. To determine the genetic basis for neuroblastoma we performed whole-genome sequencing (6 cases), exome sequencing (16 cases), genome-wide rearrangement analyses (32 cases), and targeted analyses of specific genomic loci (40 cases) using massively parallel sequencing. On average each tumor had 19 somatic alterations in coding genes (range, 3–70). Among genes not previously known to be involved in neuroblastoma, chromosomal deletions and sequence alterations of chromatin remodeling genes, ARID1A and ARID1B, were identified in 8 of 71 tumors (11%) and were associated with early treatment failure and decreased survival. Using tumor-specific structural alterations, we developed an approach to identify rearranged DNA fragments in sera, providing personalized biomarkers for minimal residual disease detection and monitoring. These results highlight dysregulation of chromatin remodeling in pediatric tumorigenesis and provide new approaches for the management of neuroblastoma patients.
The centromere kinesin motor protein CENP-E plays a crucial role in mitosis, and is an appealing molecular target in cancer. GSK923295A is an allosteric inhibitor of CENP-E that is undergoing clinical evaluation.
GSK923295A was evaluated against the 23 cell lines in the Pediatric Preclinical Testing Program (PPTP) in vitro panel using 96 hour exposures to concentrations ranging from 1.0 nM to 10.0 μM. GSK923295A was also tested in vivo against the PPTP acute lymphoblastic leukemia (ALL) and solid tumor xenograft panels using a Day 1–3 and Day 8–10 schedule that was repeated at Day 21. The agent was administered via the intraperitoneal (IP) route at a daily dose of 125 mg/kg.
The median IC50 for all PPTP cell lines was 27 nM, with the median IC50 for the ALL panel being the lowest (18 nM) and for the neuroblastoma panel the highest (39 nM). Excessive toxicity was observed for each of the 8 xenografts of the ALL panel in NOD/SCID mice. Thirty-five solid tumor xenograft models were considered evaluable. GSK923295A induced significant differences in EFS distribution compared to controls in 32 of 35 evaluable solid tumor xenografts tested. Objective responses were noted in 13 of 35 solid tumor xenografts, including 9 with maintained complete responses (MCR), and 3 with complete response (CR).
GSK923295A demonstrated significant antitumor activity against solid tumor models, inducing complete responses in Ewing sarcoma, rhabdoid and rhabdomyosarcoma xenografts. These results suggest that CENP-E may be a valuable therapeutic target in pediatric cancer.
Preclinical Testing; Developmental Therapeutics; GSK923295A
The primary objective of Children's Oncology Group study P9641 was to demonstrate that surgery alone would achieve 3-year overall survival (OS) ≥ 95% for patients with asymptomatic International Neuroblastoma Staging System stages 2a and 2b neuroblastoma (NBL). Secondary objectives focused on other low-risk patients with NBL and on those who required chemotherapy according to protocol-defined criteria.
Patients and Methods
Patients underwent maximally safe resection of tumor. Chemotherapy was reserved for patients with, or at risk for, symptomatic disease, with less than 50% tumor resection at diagnosis, or with unresectable progressive disease after surgery alone.
For all 915 eligible patients, 5-year event-free survival (EFS) and OS were 89% ± 1% and 97% ± 1%, respectively. For patients with asymptomatic stage 2a or 2b disease, 5-year EFS and OS were 87% ± 2% and 96% ± 1%, respectively. Among patients with stage 2b disease, EFS and OS were significantly lower for those with unfavorable histology or diploid tumors, and OS was significantly lower for those ≥ 18 months old. For patients with stage 1 and 4s NBL, 5-year OS rates were 99% ± 1% and 91% ± 1%, respectively. Patients who required chemotherapy at diagnosis achieved 5-year OS of 98% ± 1%. Of all patients observed after surgery, 11.1% experienced recurrence or progression of disease.
Excellent survival rates can be achieved in asymptomatic low-risk patients with stages 2a and 2b NBL after surgery alone. Immediate use of chemotherapy may be restricted to a minority of patients with low-risk NBL. Patients with stage 2b disease who are older or have diploid or unfavorable histology tumors fare less well. Future studies will seek to refine risk classification.
Neuroblastoma is a childhood tumor in which transient therapeutic responses are typically followed by recurrence with lethal chemoresistant disease. In this study, we characterized the apoptotic responses in diverse neuroblastomas using an unbiased mitochondrial functional assay. We defined the apoptotic set-point of neuroblastomas using responses to distinct BH3 death domains providing a BH3 response profile, and directly confirmed survival dependencies. We found that viable neuroblastoma cells and primary tumors are primed for death with tonic sequestration of Bim, a direct activator of apoptosis, by either Bcl-2 or Mcl-1, providing a survival dependency that predicts the activity of Bcl-2 antagonists. The Bcl-2/Bcl-xL/Bcl-w inhibitor ABT-737 showed single agent activity against only Bim:Bcl-2 primed tumor xenografts. Durable complete regressions were achieved in combination with non-curative chemotherapy even for highest-risk molecular subtypes with MYCN amplification and activating ALK mutations. Furthermore, the use of unique isogenic cell lines from patients at diagnosis and at the time of relapse showed that therapy resistance was not mediated by upregulation of Bcl-2 homologues or loss of Bim priming, but by repressed Bak/Bax activation. Together, our findings provide a classification system that identifies tumors with clinical responses to Bcl-2 antagonists, defines Mcl-1 as the principal mediator of Bcl-2 antagonist resistance at diagnosis, and isolates the therapy resistant phenotype to the mitochondria.
Bcl-2 homology proteins; mitochondrial profiling; animal models; Bcl-2 antagonist
RO4929097 is a potent and selective inhibitor of γ-secretase and as a result is able to inhibit Notch pathway signaling. The activity of RO4929097 was evaluated against the in vivo panels of the Pediatric Preclinical Testing Program (PPTP). RO4929097 induced significant differences in event-free survival (EFS) distribution compared to control in 6 of 26 (23%) of the evaluable solid tumor xenografts and in 0 of 8 (0%) of the evaluable ALL xenografts. The most consistent tumor growth delay effects were noted in the osteosarcoma panel. RO4929097 at the dose and schedule evaluated demonstrated little antitumor activity against childhood cancer xenografts.
Preclinical Testing; Developmental Therapeutics; Notch
LCL161, a SMAC mimetic, was tested against the PPTP in vitro panel (1.0 nM to 10.0 μM) and the PPTP in vivo panels (30 mg/kg or 75 mg/kg [solid tumors] or 100 mg/kg [ALL]) administered orally twice weekly. LCL161 showed a median relative IC50 value of >10 μM, being more potent against several leukemia and lymphoma lines. In vivo LCL161 induced significant differences in EFS distribution in approximately one-third of solid tumor xenografts (osteosarcoma, glioblastoma), but in no ALL xenografts. No objective tumor responses were observed. In vivo LCL161 demonstrated limited single agent activity against the pediatric preclinical models studied.
Preclinical Testing; Developmental Therapeutics; SMAC mimetic
Genz644282 is a novel non-camptothecin topoisomerase I poison that is in clinical development.
Genz644282 was tested against the PPTP in vitro panel (0.1 nM–1 μM), and in vivo using three times per week × 2 schedule repeated at day 21 at its maximum tolerated dose (MTD) of 4 mg/kg. Subsequently Genz644282 was tested at 4, 3, 2 and 1 mg/kg in 3 models to assess the dose response relationship. mRNA gene signatures predictive for Genz644282 response in vitro were applied to select 15 tumor models that were evaluated prospectively.
In vitro, Genz644282 demonstrated potent cytotoxic activity with a median IC50 of 1.2 nM (range 0.2–21.9 nM). In vivo, Genz644282 at its MTD (4 mg/kg) induced maintained complete responses (MCR) in 6/6 evaluable solid tumor models. At 2 mg/kg Genz644282 induced CR or MCR in 3/3 tumor models relatively insensitive to topotecan, but there were no objective responses at 1 mg/kg. Further testing at 2 mg/kg showed that Genz644282 induced objective regressions in 7 of 17 (41%) models. There was a significant correlation between predictive response scores based on Affymetrix U133Plus2 baseline tumor expression profiles and the observed in vivo responses to Genz644282.
Genz644282 was highly active within a narrow dose range (2–4 mg/kg), typical of other topoisomerase I poisons.. As with other topoisomerase I poisons, how accurately these data will translate to clinical activity will depend upon the drug exposures that can be achieved in children treated with this agent.
Preclinical Testing; Developmental Therapeutics; Genz644282
PG11047 is a novel conformationally restricted analog of the natural polyamine spermine that lowers cellular endogenous polyamine levels and competitively inhibits natural polyamine functions leading to cancer cell growth inhibition. The activity of PG11047 was evaluated against the PPTP’s in vitro and in vivo panels.
PG11047 was evaluated against the PPTP in vitro panel using 96 hour exposure at concentrations ranging from 10 nM to 100 μM. It was tested against the PPTP in vivo panels at a dose of 100 mg/kg administered by the intraperitoneal (IP) route weekly for 6 weeks.
In vitro PG11047 demonstrated a concentration-response pattern consistent with cytostatic activity. The median relative IC50 for PG11047 was 71 nM. Cell lines of the Ewing sarcoma panel had a lower median relative IC50 value compared to the remaining cell lines in the panel, while cell lines of the neuroblastoma panel had a higher median relative IC50 value. In vivo PG11047 induced significant differences in EFS distribution compared to control in 5 of 32 (15.6%) of the evaluable solid tumor xenografts and in 0 of 7 (0%) of the evaluable ALL xenografts. The single case of tumor regression occurred in an ependymoma xenograft.
Further pediatric development of PG11047 will require better defining a target population and identifying combinations for which there is a tumor-selective cytotoxic effect. The regression observed for an ependymoma xenograft and the exquisite sensitivity of some Ewing sarcoma cell lines to the antiproliferative effects of PG11047 provide leads for further preclinical investigations.
Preclinical Testing; Developmental Therapeutics; polyamine
BACKGROUND AND PURPOSE
High plasma levels of fenretinide [N-(4-hydroxyphenyl)retinamide (4-HPR)] were associated with improved outcome in a phase II clinical trial. Low bioavailability of 4-HPR has been limiting its therapeutic applications. This study characterized metabolism of 4-HPR in humans and mice, and to explore the effects of ketoconazole, an inhibitor of CYP3A4, as a modulator to increase 4-HPR plasma levels in mice and to increase the low bioavailability of 4-HPR.
4-HPR metabolites were identified by mass spectrometric analysis and levels of 4-HPR and its metabolites [N-(4-methoxyphenyl)retinamide (4-MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR)] were quantified by high-performance liquid chromatography (HPLC). Kinetic analysis of enzyme activities and the effects of enzyme inhibitors were performed in pooled human and pooled mouse liver microsomes, and in human cytochrome P450 (CYP) 3A4 isoenzyme microsomes. In vivo metabolism of 4-HPR was inhibited in mice.
Six 4-HPR metabolites were identified in the plasma of patients and mice. 4-HPR was oxidized to 4-oxo-4-HPR, at least in part via human CYP3A4. The CYP3A4 inhibitor ketoconazole significantly reduced 4-oxo-4-HPR formation in both human and mouse liver microsomes. In two strains of mice, co-administration of ketoconazole with 4-HPR in vivo significantly increased 4-HPR plasma concentrations by > twofold over 4-HPR alone and also increased 4-oxo-4-HPR levels.
CONCLUSIONS AND IMPLICATIONS
Mice may serve as an in vivo model of human 4-HPR pharmacokinetics. In vivo data suggest that the co-administration of ketoconazole at normal clinical doses with 4-HPR may increase systemic exposure to 4-HPR in humans.
fenretinide; metabolism; ketoconazole; paediatric cancers
Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and l-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.
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.
In vitro cytotoxicity testing employs a semi-automated fluorescence-based digital imaging cytotoxicity assay (DIMSCAN) that has a 4-log dynamic range of detection. Curve fitting of the fractional survival data of the cell lines in response to various concentrations of the agents was used to calculate relative IC50, absolute IC50, and Ymin values The panel of 23 pediatric cancer cell lines included leukemia (n=6), lymphoma (n=2), rhabdomyosarcoma (n=4), brain tumors (n=3), Ewing family of tumors (EFT, n=4), and neuroblastoma (n=4). The doubling times obtained using DIMSCAN were incorporated into data analyses to estimate the relationship between input cell numbers and final cell number.
We report in vitro activity data for three drugs (vincristine, melphalan, and etoposide) that are commonly used for pediatric cancer and for the mTOR inhibitor rapamycin, an agent that is currently under preclinical investigation for cancer. To date, the PPTP has completed in vitro testing of 39 investigational and approved agents for single drug activity and two investigational agents in combination with various “standard” chemotherapy drugs.
This robust in vitro cytotoxicity testing system for pediatric cancers will enable comparisons to response data for novel agents obtained from xenograft studies and from clinical trials.
Cell line models; childhood cancer; cytotoxicity; DIMSCAN; NCI PPTP
GSK690693 is a small molecule ATP-competitive inhibitor of the pro-survival kinase Akt. Since Akt regulates multiple downstream targets including transcription factors, glycogen synthase 3, the pro-apoptotic protein Bad, as well as MDM2 and mTORC1, it was tested against the in vitro and in vivo panels of the Pediatric Preclinical Testing Program (PPTP).
GSK690693 was tested in vitro at concentrations from 1 nM to 10 μM, and against the in vivo panel of xenografts at a dose of 30 mg/kg daily x 5 for 6 consecutive weeks. Three measures of in vivo antitumor activity were used: 1) an objective response measure modeled after the clinical setting; 2) a treated to control (T/C) tumor volume measure; and 3) a time to event measure based on the median event-free survival (EFS) of treated and control animals for each xenograft.
GSK690693 inhibited cell growth in vitro with IC50 values between 6.5 nM and >10 μM. In vivo, GSK690693 significantly increased EFS in 11 of 34 (32%) solid tumor xenografts, most notably in all 6 osteosarcoma models, but not in any of the 8 ALL xenografts tested. No objective responses were observed and only one solid tumor met EFS T/C criteria for intermediate activity.
GSK690693 demonstrated broad activity in vitro, however our results against both the solid tumor and ALL PPTP in vivo panels demonstrate that, as single agent at the dose and schedule used, GSK690693 has only modest antitumor activity.
Preclinical Testing; Developmental Therapeutics; Akt inhibitor
The hu14.18-IL2 fusion protein consists of interleukin-2 molecularly linked to a humanized monoclonal antibody that recognizes the GD2 disialoganglioside expressed on neuroblastoma cells. This phase II study assessed the antitumor activity of hu14.18-IL2 in two strata of patients with recurrent or refractory neuroblastoma.
Patients and Methods
Hu14.18-IL2 was given intravenously (12 mg/m2/daily) for 3 days every 4 weeks for patients with disease measurable by standard radiographic criteria (stratum 1) and for patients with disease evaluable only by [123I]metaiodobenzylguanidine (MIBG) scintigraphy and/or bone marrow (BM) histology (stratum 2). Response was established by independent radiology review as well as BM histology and immunocytology, and durability was assessed by repeat evaluation after more than 3 weeks.
Thirty-nine patients were enrolled (36 evaluable). No responses were seen in stratum 1 (n = 13). Of 23 evaluable patients in stratum 2, five patients (21.7%) responded; all had a complete response (CR) of 9, 13, 20, 30, and 35+ months duration. Grade 3 and 4 nonhematologic toxicities included capillary leak, hypoxia, pain, rash, allergic reaction, elevated transaminases, and hyperbilirubinemia. Two patients required dopamine for hypotension, and one patient required ventilatory support for hypoxia. Most toxicities were reversible within a few days of completing a treatment course and were expected based on phase I results.
Patients with disease evaluable only by MIBG and/or BM histology had a 21.7% CR rate to hu14.8-IL2, whereas patients with bulky disease did not respond. Hu14.18-IL2 warrants further testing in children with nonbulky high-risk neuroblastoma.
AZD6244 (ARRY-142886) is a potent small molecule inhibitor of MEK1/2 that is in phase 2 clinical development.
AZD6244 was tested against the PPTP in vitro panel (1 nM-10μM). In vivo AZD6244 was tested at a dose of 100 mg/kg administered orally twice daily five days per week for 6 weeks. Subsequently, AZD6244 was evaluated against two juvenile pilocytic astrocytoma (JPA) xenografts using once and twice daily dosing schedules. Phosphorylation of ERK1/2 was used as a surrogate for in vivo inhibition of MEK1/2 was determined by immunoblotting.
At the highest concentration used in vitro (10 μM) AZD6244 only inhibited growth by 50% in 5 of the 23 cell lines. Against the in vivo tumor panels, AZD6244 induced significant differences in EFS distribution in 10 of 37 (27%) solid tumor models and 0 of 6 acute lymphoblastic leukemia (ALL) models. There were no objective responses. Pharmacodynamic studies indicated at this dose and schedule AZD6244 completely inhibited ERK1/2 phosphorylation. AZD6244 was evaluated against two JPA xenografts, BT-35 (wild type BRAF) and BT-40 (mutant [V600E] BRAF). BT-40 xenografts were highly sensitive to AZD6244, whereas BT-35 xenografts progressed on AZD6244 treatment.
At the dose and schedule of administration used, AZD6244 as a single agent had limited in vitro and in vivo activity against the PPTP tumor panels despite inhibition of MEK1/2 activity. However, AZD6244 was highly active against BT-40 JPA xenografts that harbor constitutively activated BRAF, causing complete regressions.
Preclinical Testing; Developmental Therapeutics; AZD6244
Defects in apoptotic pathways can promote cancer cell survival and also confer resistance to antineoplastic drugs. One pathway being targeted for antineoplastic therapy is the anti-apoptotic B-cell lymphoma-2 (Bcl-2) family of proteins (Bcl-2, Bcl-XL, Bcl-w, Mcl-1, Bfl1/A-1, and Bcl-B) that bind to and inactivate BH3-domain pro-apoptotic proteins. Signals transmitted by cellular damage (including antineoplastic drugs) or cytokine deprivation can initiate apoptosis via the intrinsic apoptotic pathway. It is controversial whether some BH3-domain proteins (Bim or tBid) directly activate multidomain pro-apoptotic proteins (e.g., Bax and Bak) or act via inhibition of those anti-apoptotic Bcl-2 proteins (Bcl-2, Bcl-XL, Bcl-w, Mcl-1, Bfl1/A-1, and Bcl-B) that stabilize pro-apoptotic proteins. Overexpression of anti-apoptotic Bcl-2 family members has been associated with chemotherapy resistance in various human cancers, and preclinical studies have shown that agents targeting anti-apoptotic Bcl-2 family members have preclinical activity as single agents and in combination with other antineoplastic agents. Clinical trials of several investigational drugs targeting the Bcl-2 family (oblimersen sodium, AT-101, ABT-263, GX15-070) are ongoing. Here, we review the role of the Bcl-2 family in apoptotic pathways and those agents that are known and/or designed to inhibit the anti-apoptotic Bcl-2 family of proteins.