Reduced ER-mitochondria connectivity promotes neuroblastoma multidrug resistance.

Most cancer deaths result from progression of therapy resistant disease, yet our understanding of this phenotype is limited. Cancer therapies generate stress signals that act upon mitochondria to initiate apoptosis. Mitochondria isolated from neuroblastoma cells were exposed to tBid or Bim, death effectors activated by therapeutic stress. Multidrug-resistant tumor cells obtained from children at relapse had markedly attenuated Bak and Bax oligomerization and cytochrome c release (surrogates for apoptotic commitment) in comparison with patient-matched tumor cells obtained at diagnosis. Electron microscopy identified reduced ER-mitochondria-associated membranes (MAMs; ER-mitochondria contacts, ERMCs) in therapy-resistant cells, and genetically or biochemically reducing MAMs in therapy-sensitive tumors phenocopied resistance. MAMs serve as platforms to transfer Ca2+ and bioactive lipids to mitochondria. Reduced Ca2+ transfer was found in some but not all resistant cells, and inhibiting transfer did not attenuate apoptotic signaling. In contrast, reduced ceramide synthesis and transfer was common to resistant cells and its inhibition induced stress resistance. We identify ER-mitochondria-associated membranes as physiologic regulators of apoptosis via ceramide transfer and uncover a previously unrecognized mechanism for cancer multidrug resistance.

Non-synonymous, synonymous, and non-coding nucleotide variants contribute to recurrently altered biological processes during retinoblastoma progression.

Retinoblastomas form in response to biallelic RB1 mutations or MYCN amplification and progress to more aggressive and therapy-resistant phenotypes through accumulation of secondary genomic changes. Progression-related changes include recurrent somatic copy number alterations and typically non-recurrent nucleotide variants, including synonymous and non-coding variants, whose significance has been unclear. To determine if nucleotide variants recurrently affect specific biological processes, we identified altered genes and over-represented variant gene ontologies in 168 exome or whole-genome-sequenced retinoblastomas and 12 tumor-matched cell lines. In addition to RB1 mutations, MYCN amplification, and established retinoblastoma somatic copy number alterations, the analyses revealed enrichment of variant genes related to diverse biological processes including histone monoubiquitination, mRNA processing (P) body assembly, and mitotic sister chromatid segregation and cytokinesis. Importantly, non-coding and synonymous variants increased the enrichment significance of each over-represented biological process term. To assess the effects of such mutations, we examined the consequences of a 3' UTR variant of PCGF3 (a BCOR-binding component of Polycomb repressive complex I), dual 3' UTR variants of CDC14B (a regulator of sister chromatid segregation), and a synonymous variant of DYNC1H1 (a regulator of P-body assembly). One PCGF3 and one of two CDC14B 3' UTR variants impaired gene expression whereas a base-edited DYNC1H1 synonymous variant altered protease sensitivity and stability. Retinoblastoma cell lines retained only ~50% of variants detected in tumors and enriched for new variants affecting p53 signaling. These findings reveal potentially important differences in retinoblastoma cell lines and tumors and implicate synonymous and non-coding variants, along with non-synonymous variants, in retinoblastoma oncogenesis.

The O6-methyguanine-DNA methyltransferase inhibitor O6-benzylguanine enhanced activity of temozolomide + irinotecan against models of high-risk neuroblastoma.

DNA-damaging chemotherapy is a major component of therapy for high-risk neuroblastoma, and patients often relapse with treatment-refractory disease. We hypothesized that DNA repair genes with increased expression in alkylating agent resistant models would provide therapeutic targets for enhancing chemotherapy. In-vitro cytotoxicity of alkylating agents for 12 patient-derived neuroblastoma cell lines was assayed using DIMSCAN, and mRNA expression of 57 DNA repair, three transporter, and two glutathione synthesis genes was assessed by TaqMan low-density array (TLDA) with further validation by qRT-PCR in 26 cell lines. O6-methylguanine-DNA methyltransferase (MGMT) mRNA was upregulated in cell lines with greater melphalan and temozolomide (TMZ) resistance. MGMT expression also correlated significantly with resistance to TMZ+irinotecan (IRN) (in-vitro as the SN38 active metabolite). Forced overexpression of MGMT (lentiviral transduction) in MGMT non-expressing cell lines significantly increased TMZ+SN38 resistance. The MGMT inhibitor O6-benzylguanine (O6BG) enhanced TMZ+SN38 in-vitro cytotoxicity, H2AX phosphorylation, caspase-3 cleavage, and apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling. TMZ+IRN+O6BG delayed tumor growth and increased survival relative to TMZ+IRN in two of seven patient-derived xenografts established at time of death from progressive neuroblastoma. We demonstrated that high MGMT expression was associated with resistance to alkylating agents and TMZ+IRN in preclinical neuroblastoma models. The MGMT inhibitor O6BG enhanced the anticancer effect of TMZ+IRN in vitro and in vivo. These results support further preclinical studies exploring MGMT as a therapeutic target and biomarker of TMZ+IRN resistance in high-risk neuroblastoma.

Vorinostat and fenretinide synergize in preclinical models of T-cell lymphoid malignancies.

T-cell lymphoid malignancies (TCLMs) are in need of novel and more effective therapies. The histone deacetylase (HDAC) inhibitors and the synthetic cytotoxic retinoid fenretinide have achieved durable clinical responses in T-cell lymphomas as single agents, and patients who failed prior HDAC inhibitor treatment have responded to fenretinide. We have previously shown fenretinide synergized with the class I HDAC inhibitor romidepsin in preclinical models of TCLMs. There exist some key differences between HDAC inhibitors. Therefore, we determined if the pan-HDAC inhibitor vorinostat synergizes with fenretinide. We demonstrated cytotoxic synergy between vorinostat and fenretinide in nine TCLM cell lines at clinically achievable concentrations that lacked cytotoxicity for non-malignant cells (fibroblasts and blood mononuclear cells). In vivo, vorinostat + fenretinide + ketoconazole (enhances fenretinide exposures by inhibiting fenretinide metabolism) showed greater activity in subcutaneous TCLM xenograft models than other groups. Fenretinide + vorinostat increased reactive oxygen species (ROS, measured by 2',7'-dichlorodihydrofluorescein diacetate dye), resulting in increased apoptosis (via transferase dUTP nick end labeling assay) and histone acetylation (by immunoblotting). The synergistic cytotoxicity, apoptosis, and histone acetylation of fenretinide + vorinostat was abrogated by the antioxidant vitamin C. Like romidepsin, vorinostat combined with fenretinide achieved synergistic cytotoxic activity and increased histone acetylation in preclinical models of TCLMs, but not in non-malignant cells. As vorinostat is an oral agent and not a P-glycoprotein substrate it may have advantages in such combination therapy. These data support conducting a clinical trial of vorinostat combined with fenretinide in relapsed and refractory TCLMs.

Cytotoxicity and molecular activity of fenretinide and metabolites in T-cell lymphoid malignancy, neuroblastoma, and ovarian cancer cell lines in physiological hypoxia.

OBJECTIVE: All-trans-N-(4-hydroxyphenyl)retinamide or fenretinide (4-HPR) acts by reactive oxygen species (ROS) and dihydroceramides (DHCers). In early-phase clinical trials 4-HPR has achieved complete responses in T-cell lymphomas (TCL) and neuroblastoma (NB) and signals of activity in ovarian cancer (OV). We defined the activity of 4-HPR metabolites in N-(4-methoxyphenyl)retinamide (MPR), 4-oxo-N-(4-hydroxyphenyl)retinamide (oxoHPR), and the 4-HPR isomer 13-cis-fenretinide (cis-HPR) in NB, OV, and TCL cell lines cultured in physiological hypoxia. METHODS: We compared the effect of 4-HPR, cis-HPR, oxoHPR, and MPR on cytotoxicity, ROS, and DHCers in a panel of TCL, NB, and OV cell lines cultured in bone marrow level physiological hypoxia (5% O2), utilizing a fluorescence-based cytotoxicity assay (DIMSCAN), flow cytometry, and quantitative mass spectrometry. RESULTS: 4-HPR (10 µmol/l) achieved more than three logs of cell kill in nine of 15 cell lines. Cytotoxicity of 4-HPR and oxoHPR was comparable; in some cell lines, cis-HPR cytotoxicity was lower than 4-HPR, but additive when combined with 4-HPR. MPR was not cytotoxic. ROS and DHCers were equivalently increased by 4-HPR and oxoHPR in all cell lines (P<0.01), to a lesser extent by cis-HPR (P<0.01), and not increased in response to MPR (P>0.05). Mitochondrial membrane depolarization, caspase-3 cleavage, and apoptosis (TUNEL) were all significantly increased by 4-HPR and oxoHPR (P<0.01). CONCLUSION: Cytotoxic and pharmacodynamic activity was comparable with 4-HPR and oxoHPR, lower with cis-HPR, and MPR was inactive. Neither MPR or cis-HPR antagonized 4-HPR activity. These data support focusing on achieving high 4-HPR exposures for maximizing antineoplastic activity.

Initial testing (stage 1) of M6620 (formerly VX-970), a novel ATR inhibitor, alone and combined with cisplatin and melphalan, by the Pediatric Preclinical Testing Program.

BACKGROUND: M6620 is a novel inhibitor of the DNA damage repair enzyme ATR, and has potentiated the activity of cisplatin and irinotecan in non-small cell lung cancer and colon cancer xenografts, respectively. PROCEDURES: M6620 was tested in vitro at concentrations ranging from 1.0 nM to 10.0 µM and at 75 nM in combination with cisplatin or melphalan. M6620 was tested against 24 solid tumor xenografts alone and in combination with cisplatin. Cisplatin was administered intraperitoneally on days 1 and 8 at a dose of 5 mg/kg. M6620 was administered intravenously on days 2 and 9 at 20 mg/m2 approximately 16 hr after cisplatin. RESULTS: The median relative IC50 (rIC50 ) value for M6620 was 0.19 µM (range 0.03-1.38 µM). M6620 reduced the mean IC50 of cisplatin and melphalan by 1.48- and 1.95-fold, respectively. M6620 as a single agent in vivo induced significant differences in event-free survival (EFS) distribution in 5 of 24 (21%) solid tumor xenografts, but induced no objective responses. Cisplatin as a single agent induced significant differences in EFS distribution compared to control in 18 of 24 (75%) solid tumor xenografts. Three objective responses to cisplatin were observed. The M6620 and cisplatin combination induced significant differences in EFS distribution compared to control in 21 of 24 (88%), with four objective responses. CONCLUSIONS: M6620 showed modest potentiation of cisplatin and melphalan activity for some cell lines. M6620 showed little single-agent activity and the addition of M6620 to cisplatin significantly prolonged time to event for a minority of tested xenografts across several histologies.

Cytotoxic activity of difluoromethylornithine compared with fenretinide in neuroblastoma cell lines.

BACKGROUND: Maintenance therapy with 13-cis-retinoic acid and immunotherapy (given after completion of intensive cytotoxic therapy) improves outcome for high-risk neuroblastoma patients. The synthetic retinoid fenretinide (4-HPR) achieved multiple complete responses in relapse/refractory neuroblastoma in early-phase clinical trials, has low systemic toxicity, and has been considered for maintenance therapy clinical trials. Difluoromethylornithine (DFMO, an irreversible inhibitor of ornithine decarboxylase with minimal single-agent clinical response data) is being used for maintenance therapy of neuroblastoma. We evaluated the cytotoxic activity of DFMO and fenretinide in neuroblastoma cell lines. PROCEDURE: We tested 16 neuroblastoma cell lines in bone marrow-level hypoxia (5% O2 ) using the DIMSCAN cytotoxicity assay. Polyamines were measured by HPLC-mass spectrometry and apoptosis by transferase dUTP nick end labeling (TUNEL) using flow cytometry. RESULTS: At clinically achievable levels (100 µM), DFMO significantly decreased (P < 0.05) polyamine putrescine and achieved modest cytotoxicity (<1 log (90% cytotoxicity). Prolonged exposures (7 days) or culture in 2% and 20% O2 did not enhance DFMO cytotoxicity. However, fenretinide (10 µM) even at a concentration lower than clinically achievable in neuroblastoma patients (20 µM) induced ≥ 1 log cell kill in 14 cell lines. The average IC90 and IC99 of fenretinide was 4.7 ± 1 µM and 9.9 ± 1.8 µM, respectively. DFMO did not induce a significant increase (P > 0.05) in apoptosis (TUNEL assay). Apoptosis by fenretinide was significantly higher (P < 0.001) compared with DFMO or controls. CONCLUSIONS: DFMO as a single agent has minimal cytotoxic activity for neuroblastoma cell lines.

Phase I study of vorinostat in combination with isotretinoin in patients with refractory/recurrent neuroblastoma: A new approaches to Neuroblastoma Therapy (NANT) trial.

BACKGROUND: Vorinostat combined with retinoids produces additive antitumor effects in preclinical studies of neuroblastoma. Higher systemic exposures of vorinostat than achieved in pediatric phase I trials with continuous daily dosing are necessary for in vivo increased histone acetylation and cytotoxic activity. We conducted a phase I trial in children with relapsed/refractory neuroblastoma to determine the maximum tolerated dose (MTD) of vorinostat on an interrupted schedule, escalating beyond the previously identified pediatric MTD. METHODS: Isotretinoin (cis-13-retinoic acid) 80 mg/m2 /dose was administered by mouth twice daily on days 1-14 in combination with escalating doses of daily vorinostat up to 430 mg/m2 /dose (days 1-4; 8-11) in each 28-day cycle using the standard 3 + 3 design. Vorinostat pharmacokinetic testing and histone acetylation assays were performed. RESULTS: Twenty-nine patients with refractory or relapsed neuroblastoma were enrolled and 28 were evaluable for dose escalation decisions. Median number of cycles completed was two (range 1-15); 11 patients received four or more cycles. Three patients experienced cycle 1 dose-limiting toxicities. A total of 18 patients experienced grade 3/4 toxicities related to study therapy. The maximum intended dose of vorinostat (430 mg/m2 /day, days 1-4; 8-11) was tolerable and led to increased histone acetylation in surrogate tissues when compared to lower doses of vorinostat (P = 0.009). No objective responses were seen. CONCLUSIONS: Increased dose vorinostat (430 mg/m2 /day) on an interrupted schedule is tolerable in combination with isotretinoin. This dose led to increased vorinostat exposures and demonstrated increased histone acetylation. Prolonged stable disease in patients with minimal residual disease warrants further investigation.

P450 inhibitor ketoconazole increased the intratumor drug levels and antitumor activity of fenretinide in human neuroblastoma xenograft models.

We previously reported that concurrent ketoconazole, an oral anti-fungal agent and P450 enzyme inhibitor, increased plasma levels of the cytotoxic retinoid, fenretinide (4-HPR) in mice. We have now determined the effects of concurrent ketoconazole on 4-HPR cytotoxic dose-response in four neuroblastoma (NB) cell lines in vitro and on 4-HPR activity against two cell line-derived, subcutaneous NB xenografts (CDX) and three patient-derived NB xenografts (PDX). Cytotoxicity in vitro was assessed by DIMSCAN assay. Xenografted animals were treated with 4-HPR/LXS (240 mg/kg/day) + ketoconazole (38 mg/kg/day) in divided oral doses in cycles of five continuous days a week. In one model, intratumoral levels of 4-HPR and metabolites were assessed by HPLC assay, and in two models intratumoral apoptosis was assessed by TUNEL assay, on Day 5 of the first cycle. Antitumor activity was assessed by Kaplan-Meier event-free survival (EFS). The in vitro cytotoxicity of 4-HPR was not affected by ketoconazole (p ≥ 0.06). Ketoconazole increased intratumoral levels of 4-HPR (p = 0.02), of the active 4-oxo-4-HPR metabolite (p = 0.04), and intratumoral apoptosis (p ≤ 0.0006), compared to 4-HPR/LXS-alone. Concurrent ketoconazole increased EFS in both CDX models compared to 4-HPR/LXS-alone (p ≤ 0.008). 4-HPR + ketoconazole also increased EFS in PDX models compared to controls (p ≤ 0.03). Thus, concurrent ketoconazole decreased 4-HPR metabolism with resultant increases of plasma and intratumoral drug levels and antitumor effects in neuroblastoma murine xenografts. These results support the clinical testing of concurrent ketoconazole and oral fenretinide in neuroblastoma.

Microfluidic Separation of Lymphoblasts for the Isolation of Acute Lymphoblastic Leukemia Using the Human Transferrin Receptor as a Capture Target.

Acute lymphocytic leukemia (ALL) is the most prevalent pediatric cancer, and the peripheral blood lymphoblast percentage is an important index for ALL diagnosis and prognosis. We describe a microfluidic device that isolates and enumerates peripheral blood lymphoblasts using affinity separations. The innovative use of a nonspecific ligand allows a widespread "net" for cancer cells, without a priori knowledge of the cancer type. Using lymphoblasts spiked into blood, we simulated leukemia cases with lymphoblast concentrations ranging from 1 to 30% of total leukocytes. Lymphoblasts were isolated using monoclonal antibodies for the Human Transferring Receptor (CD71). Anti-CD71 antibodies were found to be more effective for capturing lymphoblasts than commonly used, ALL-specific antibodies for CD7 and CD10. CCRF-CEM lymphoblasts were isolated in the chip with 82-97% purity, with lower concentrations tested (7%) still showing >80% purity for cell capture. Patient-derived ALL cell lines COG-LL-332 and COG-LL-317 were isolated in the chip with 80%-97% and 57% -92% of purity, respectively, with the initial spike concentrations as low as 1%. The ability to capture ALL lymphoblasts present in blood at low concentrations provides a novel approach for characterization of ALL cells, including patients with low leukemic burdens during and after therapy.

Initial testing of VS-4718, a novel inhibitor of focal adhesion kinase (FAK), against pediatric tumor models by the Pediatric Preclinical Testing Program.

VS-4718, a novel inhibitor of focal adhesion kinase (FAK), was tested against the Pediatric Preclinical Testing Program's (PPTP's) in vitro cell line panel and showed a median relative IC50 of 1.22 µM. VS-4718 was tested in vivo against the PPTP xenograft models using a dose of 50 mg/kg administered by the oral route twice daily for 21 days. VS-4718 induced significant differences in an event-free survival distribution compared with control in 18 of 36 of the evaluable solid tumor xenografts and in 0 of 8 acute lymphoblastic leukemia (ALL) xenografts, but no xenograft lines showed tumor regression. Future plans include further evaluation of the role of FAK inhibition in combination with ABL kinase inhibitors for Ph+ ALL.

Initial testing (stage 1) of the curaxin CBL0137 by the pediatric preclinical testing program.

BACKGROUND: CBL0137 is a novel drug that modulates FAcilitates Chromatin Transcription (FACT), resulting in simultaneous nuclear factor-κB suppression, heat shock factor 1 suppression and p53 activation. CBL0137 has demonstrated antitumor effects in animal models of several adult cancers and neuroblastoma. PROCEDURES: CBL0137 was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations ranging from 1.0 nM to 10.0 µM and against the PPTP in vivo solid tumor xenograft and acute lymphocytic leukemia (ALL) panels at 50 mg/kg administered intravenously weekly for 4 weeks. RESULTS: The median relative IC50 (rIC50 ) value for the PPTP cell lines was 0.28 µM (range: 0.13-0.80 µM). There were no significant differences in rIC50 values by histotype. CBL0137 induced significant differences in event-free survival (EFS) distribution compared to control in 10 of 31 (32%) evaluable solid tumor xenografts and in eight of eight (100%) evaluable ALL xenografts. Significance differences in EFS distribution were observed in four of six osteosarcoma lines, three of three rhabdoid tumor lines and two of six rhabdomyosarcoma lines. No objective responses were observed among the solid tumor xenografts. For the ALL panel, one xenograft achieved complete response and four achieved partial response. CONCLUSIONS: The most consistent in vivo activity for CBL0137 was observed against ALL xenografts, with some solid tumor xenograft lines showing tumor growth delay. It will be important to relate the drug levels in mice at 50 mg/kg to those in humans at the recommended phase 2 dose.

Initial Testing of NSC 750854, a Novel Purine Analog, Against Pediatric Tumor Models by the Pediatric Preclinical Testing Program.

BACKGROUND: NSC 750854 is a purine analog with an antitumor activity profile distinctive from that of other anticancer purines. It has shown significant activity against adult cancer preclinical models. PROCEDURE: NSC 750854 was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations from 1.0 nM to 10 µM and against the PPTP in vivo xenograft panels administered intraperitoneally at a dose of 5 mg/kg daily for 5 days repeated at day 15. RESULTS: The median relative IC50 (rIC50 ) value for the PPTP cell lines was 32 nM (range from 11 to 124 nM), with consistent cytotoxicity across all cell lines. Acute lymphoblastic leukemia (ALL) cell lines were more sensitive to NSC 750854 than non-ALL cell lines. NSC 750854 induced significant differences in EFS distribution compared to control in 31 of 35 (89%) solid tumor xenografts. It induced tumor growth inhibition meeting criteria for intermediate or high event free survival (EFS) T/C activity in 17 of 32 (53%) evaluable solid tumor xenografts (most consistently in the rhabdomyosarcoma panel). Objective responses were observed in 15 of 37 (41%) solid tumor xenografts and in all eight leukemia models with complete response (CR) or maintained complete response (MCR) in seven of eight leukemia models. CONCLUSIONS: NSC 750854 has a unique spectrum of antitumor activity compared with other agents tested by the PPTP as it induces regression in tumor models with limited sensitivity to most agents tested to date. Given the promising level of activity observed for NSC 750854 against PPTP preclinical models, further exploration of its mechanism of action is warranted.

Pharmacodynamic and genomic markers associated with response to the XPO1/CRM1 inhibitor selinexor (KPT-330): A report from the pediatric preclinical testing program.

BACKGROUND: Selinexor (KPT-330) is an inhibitor of the major nuclear export receptor, exportin 1 (XPO1, also termed chromosome region maintenance 1, CRM1) that has demonstrated activity in preclinical models and clinical activity against several solid and hematological cancers. PROCEDURES: Selinexor was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations from 1.0 nM to 10 µM and against the PPTP in vivo xenograft panels administered orally at a dose of 10 mg/kg thrice weekly for 4 weeks. RESULTS: Selinexor demonstrated cytotoxic activity in vitro, with a median relative IC50 value of 123 nM (range 13.0 nM to >10 µM). Selinexor induced significant differences in event-free survival (EFS) distribution in 29 of 38 (76%) of the evaluable solid tumor xenografts and in five of eight (63%) of the evaluable ALL xenografts. Objective responses (partial or complete responses, PR/CR) were observed for 4 of 38 solid tumor xenografts including Wilms tumor, medulloblastoma (n = 2), and ependymoma models. For the ALL panel, two of eight (25%) xenografts achieved either CR or maintained CR. Two responding xenografts had FBXW7 mutations at R465 and two had SMARCA4 mutations. Selinexor induced p53, p21, and cleaved PARP in several solid tumor models. CONCLUSIONS: Selinexor induced regression against several solid tumor and ALL xenografts and slowed tumor growth in a larger number of models. Pharmacodynamic effects for XPO1 inhibition were noted. Defining the relationship between selinexor systemic exposures in mice and humans will be important in assessing the clinical relevance of these results.

Initial Testing (Stage 1) of MK-8242-A Novel MDM2 Inhibitor-by the Pediatric Preclinical Testing Program.

BACKGROUND: MK-8242 is an inhibitor of MDM2 that stabilizes the tumor suppressor TP53 and induces growth arrest or apoptosis downstream of TP53 induction. PROCEDURES: MK-8242 was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations from 1.0 nM to 10.0 µM and against the PPTP in vivo xenograft panels using oral gavage on Days 1-5 and Day 15-19 at a dose of 125 mg/kg (solid tumors) or 75 mg/kg (acute lymphoblastic leukemia [ALL] models). RESULTS: The median IC50 for MK-8242 was 0.07 µM for TP53 wild-type cell lines versus >10 µM for TP53 mutant cell lines. MK-8242 induced a twofold or greater delay in time to event in 10 of 17 (59%) of TP53 wild-type solid tumor xenografts, excluding osteosarcoma xenografts that have very low TP53 expression. Objective responses were observed in seven solid tumor xenografts representing multiple histotypes. For the systemic-disease ALL panel, among eight xenografts there were two complete responses (CRs) and six partial responses (PRs). Two additional MLL-rearranged xenografts (MV4;11 and RS4;11) grown subcutaneously showed maintained CR and PR, respectively. The expected pharmacodynamic responses to TP53 activation were observed in TP53 wild-type models treated with MK-8242. Pharmacokinetic analysis showed that MK-8242 drug exposure in SCID mice appears to exceed that was observed in adult phase 1 trials. CONCLUSIONS: MK-8242-induced tumor regressions across multiple solid tumor histotypes and induced CRs or PRs for most ALL xenografts. This activity was observed at MK-8242 drug exposures that appear to exceed those observed in human phase 1 trials.

Preservation of high glycolytic phenotype by establishing new acute lymphoblastic leukemia cell lines at physiologic oxygen concentration.

Cancer cells typically exhibit increased glycolysis and decreased mitochondrial oxidative phosphorylation, and they continue to exhibit some elevation in glycolysis even under aerobic conditions. However, it is unclear whether cancer cell lines employ a high level of glycolysis comparable to that of the original cancers from which they were derived, even if their culture conditions are changed to physiologically relevant oxygen concentrations. From three childhood acute lymphoblastic leukemia (ALL) patients we established three new pairs of cell lines in both atmospheric (20%) and physiologic (bone marrow level, 5%) oxygen concentrations. Cell lines established in 20% oxygen exhibited lower proliferation, survival, expression of glycolysis genes, glucose consumption, and lactate production. Interestingly, the effects of oxygen concentration used during cell line initiation were only partially reversible when established cell cultures were switched from one oxygen concentration to another for eight weeks. These observations indicate that ALL cell lines established at atmospheric oxygen concentration can exhibit relatively low levels of glycolysis and these levels are semi-permanent, suggesting that physiologic oxygen concentrations may be needed from the time of cell line initiation to preserve the high level of glycolysis commonly exhibited by leukemias in vivo.

Disialoganglioside-specific human natural killer cells are effective against drug-resistant neuroblastoma.

The disialoganglioside GD2 is a well-established target antigen for passive immunotherapy in neuroblastoma (NB). Despite the recent success of passive immunotherapy with the anti-GD2 antibody ch14.18 and cytokines, treatment of high-risk NB remains challenging. We expanded the approach of GD2-specific, antibody-based immunotherapy to an application of a GD2-specific natural killer (NK) cell line, NK-92-scFv(ch14.18)-zeta. NK-92-scFv(ch14.18)-zeta is genetically engineered to express a GD2-specific chimeric antigen receptor generated from ch14.18. Here, we show that chimeric receptor expression enables NK-92-scFv(ch14.18)-zeta to effectively lyse GD2(+) NB cells also including partially or multidrug-resistant lines. Our data suggest that recognition of GD2 by the chimeric receptor is the primary mechanism involved in NK-92-scFv(ch14.18)-zeta-mediated lysis and is independent of activating NK cell receptor/ligand interactions. Furthermore, we demonstrate that NK-92-scFv(ch14.18)-zeta is able to mediate a significant anti-tumor response in vivo in a drug-resistant GD2(+) NB xenograft mouse model. NK-92-scFv(ch14.18)-zeta is an NB-specific NK cell line that has potential for future clinical development due to its high stability and activity toward GD2(+) NB cell lines.

Initial testing (stage 1) of the anti-microtubule agents cabazitaxel and docetaxel, by the pediatric preclinical testing program.

BACKGROUND: Although microtubule-destabilizing agents (principally vincristine) are in common use in pediatric oncology, the microtubule-stabilizing taxanes are uncommonly used to treat childhood cancers. Cabazitaxel has been reported to have activity superior to that of docetaxel in preclinical models of multidrug-resistant adult cancers, and it was active in patients who had progressed on or after docetaxel. The PPTP conducted a comparison of these two agents against the PPTP in vitro panel and against a limited panel of solid tumor xenografts. PROCEDURES: Cabazitaxel and docetaxel were tested against the PPTP in vitro cell line panel at concentrations from 0.01 to 0.1 µM and in vivo against a subset of the PPTP solid tumor xenograft models at a dose of 10 or 7.5 mg/kg on an every 4 days × 3 I.V. schedule. RESULTS: In vitro, both cabazitaxel and docetaxel had similar potency (median rIC50 0.47 nM and 0.88 nM, respectively) and a similar activity profile, with Ewing sarcoma cells being significantly more sensitive to both agents. In vitro sensitivity to docetaxel inversely correlated with mRNA expression for ABCB1, but the correlation with ABCB1 expression was weaker for cabazitaxel. In vivo cabazitaxel demonstrated significantly greater activity than docetaxel in five of 12 tumor models, inducing regressions in six models compared with three models for docetaxel. CONCLUSIONS: Cabazitaxel demonstrated superior activity compared to docetaxel. The lower cabazitaxel systemic exposure tolerated in humans compared to mice needs to be considered when extrapolating these results to the clinical setting.

Initial testing (stage 1) of the PARP inhibitor BMN 673 by the pediatric preclinical testing program: PALB2 mutation predicts exceptional in vivo response to BMN 673.

BACKGROUND: BMN 673 is a potent inhibitor of poly-ADP ribose polymerase (PARP) that is in clinical testing with a primary focus on BRCA-mutated cancers. BMN 673 is active both through inhibiting PARP catalytic activity and by tightly trapping PARP to DNA at sites of single strand breaks. PROCEDURE: BMN 673 was tested in vitro at concentrations ranging from 0.1 nM to 1 µM and in vivo at a daily dose of 0.33 mg/kg administered orally twice daily (Mon-Fri) and once daily on weekends (solid tumors) for 28 days. RESULTS: The median relative IC50 (rIC50 ) concentration against the PPTP cell lines was 25.8 nM. The median rIC50 for the Ewing cell lines was lower than for the remaining cell lines (6.4 vs. 31.1 nM, respectively). In vivo BMN 673 induced statistically significant differences in EFS distribution in 17/43 (39.5%) xenograft models. Three objective regressions were observed: a complete response (CR) in a medulloblastoma line (BT-45), a maintained CR in a Wilms tumor line (KT-10), and a maintained CR in an ependymoma line (BT-41). BMN 673 maintained its high level of activity against KT-10 with a threefold reduction in dose. KT-10 possesses a truncating mutation in PALB2 analogous to PALB2 mutations associated with hereditary breast and ovarian cancer that abrogate homologous recombination (HR) repair. CONCLUSIONS: The PPTP results suggest that single agent BMN 673 may have limited clinical activity against pediatric cancers. Single agent activity is more likely for patients whose tumors have defects in HR repair.

Initial testing (stage 1) of BAL101553, a novel tubulin binding agent, by the pediatric preclinical testing program.

BAL101553 is a highly water soluble prodrug of BAL27862 that arrests tumor cell proliferation and induces cell death in cancer cells through disruption of the microtubule network. In vitro BAL27862 demonstrated potent activity, with the median relative IC50 (rIC50 ) of 13.8 nM (range 5.4-25.2 nM). The in vitro activity of BAL27862 against the PPTP cell lines is distinctive from that previously described for vincristine. BAL101553 induced significant differences in EFS distribution compared to control in 16 of 30 (53%) solid tumor xenografts and in two of four (67%) of the evaluable ALL xenografts. No objective responses were observed.