Event-free Survival Distribution Research Articles

Treatment Strategies and Long-Term Outcomes in Silent Corticotroph Adenomas: A Single-Center Retrospective Study of 367 Cases.

Silent corticotroph adenoma (SCA) is a high-risk pituitary neuroendocrine tumor (PitNET) which exhibits more aggressive behavior than other nonfunctioning PitNETs. Some SCAs are observed to recur after total resection (TR). We aim to discuss the long-term outcomes after endoscopic endonasal surgery for SCAs and explore optimal treatment after operation. Clinical data and intraoperative videos from 367 SCAs who underwent endoscopic endonasal surgery were retrospectively collected. Patients were categorized into TR and subtotal resection (STR) groups according to 3-month postoperative MRIs. Based on close-up intraoperative observation of the relationship between tumor and pituitary gland, diaphragm, and medial wall cavernous sinus, patients in the TR group were further subdivided into gross total resection (GTR) and near total resection (NTR) groups. Patients in the STR group were subdivided as STR followed by observation (STR + ob) and STR followed by adjuvant stereotactic radiosurgery (SRS) (STR + SRS). Kaplan-Meier analysis was used to compare the event-free survival among these subgroups. Headache (27.5%) and vision loss (55.3%) were the most common presenting symptoms. Cavernous sinus (CS) invasion was confirmed intraoperatively in 167 (45.5%) patients. After operation, 175 (47.7%), 83 (22.6%), 32 (8.7%), and 77 (21%) patients were divided into GTR, NTR, STR + ob, and STR + SRS groups, respectively. The mean follow-up time was 40.9 ± 25.8 months. There were 0, 17 (20.5%), 9 (28.1%), and 4 (5.2%) patients noted to have PitNET recurrence or progression in GTR, NTR, STR + ob, and STR + SRS groups, respectively. Event-free survival distribution in the NTR group was similar to that in the STR + ob group (P = .696), which was significantly lower than that in the STR + SRS group (P = .008). Adrenocorticotropic hormone (ACTH)-negative SCAs have lower preoperative ACTH levels and were more likely to invade CS than ACTH-positive SCAs. CS invasion was commonly seen in SCAs, often precluding GTR. Radical surgery and close follow-up were proposed. Early postoperative adjuvant SRS for remnant tumor should be considered.

Outcome of patients with relapsed or refractory nonrhabdomyosarcoma soft tissue sarcomas enrolled in phase 2 cooperative group clinical trials: A report from the Children's Oncology Group.

The aim of this study was to estimate the event-free survival (EFS) of children and young adults with relapsed or refractory nonrhabdomyosarcoma soft tissue sarcoma (NRSTS) treated in nonrandomized phase 2 studies conducted by the Children's Oncology Group (COG) and predecessor groups to establish a benchmark EFS for future phase 2 NRSTS trials evaluating the activity of novel agents. A retrospective analysis of patients with recurrent or refractory NRSTS prospectively enrolled in nonrandomized phase 2 COG and predecessor group trials between 1994 and 2015 was conducted. EFS was defined as disease progression/relapse or death and calculated via the Kaplan-Meier method. The log-rank test and relative risk regression were used to compare EFS distribution by age at enrollment, sex, race, NRSTS histology, prior lines of therapy, calendar year of trial, and type of radiographic response. In total, 137 patients were enrolled in 13 phase 2 trials. All trials used radiographic response rate as a primary outcome, and none of the agents used were considered active on the basis of trial-specified thresholds. The estimated median EFS and 6-month EFS of the entire study cohort was 1.5 months (95% confidence interval [CI], 1.3-1.8 months) and 19.4% (95% CI, 12.7%-26%), respectively. No difference in EFS was observed by age at enrollment, sex, race, NRSTS histology subtype, prior lines of therapies, and trial initiation year. EFS significantly differed by radiographic response. The EFS for children and young adults with relapsed or refractory NRSTS remains suboptimal. Established EFS can be referenced as a benchmark for future single-agent phase 2 trials incorporating potentially active novel agents in this population.

Abstract 4820: Pediatric preclinical testing consortium evaluation of the CD123 antibody drug conjugate, IMGN632, against xenograft models of pediatric acute lymphoblastic leukemia

Abstract Introduction: The characteristic expression of CD123 (the alpha subunit of the IL-3 receptor) in multiple hematological malignancies, including acute myeloid leukemia (AML), blastic plasmacytoid dendritic cell neoplasm and acute lymphoblastic leukemia (ALL) has made this antigen an attractive target for the development of new therapeutics. IMGN632 is a CD123 targeting antibody drug conjugate (ADC) comprised of a novel humanized antiCD123 antibody, G4723A, linked to a DNA monoalkylating payload of the indolindobenzodiazepine pseudodimer (IGN) class of cytotoxic compounds. IMGN632 demonstrates potent activity in AML samples at low concentrations with minimal impact on normal bone marrow progenitors, and antileukemia effects in AML xenograft models. A phase I clinical trial of IMGN632 in CD123 positive malignancies is ongoing (NCT033865). Therefore, it was of interest to test the in vivoefficacy of IMGN632 against preclinical models of pediatric ALL. Methods: Pediatric ALL patient-derived xenografts (PDXs) grew in an orthotopic manner in NSG mice. Engraftment was assessed by the % human leukemic blasts in the peripheral blood (%huCD45+). Treatment commenced when the median %huCD45+exceeded 1%, and mice received IMGN632 or non-binding control ADC (240 µg/kg IV weekly x 3) or vehicle. An event was defined as the %huCD45+>25% or leukemia-related morbidity. The Kaplan-Meier method was used to compare event-free survival (EFS) between treated (T) and control (C) groups. Stringent objective response measures were assigned to each mouse and reported as group medians. Cell surface CD123 levels were expressed as specific antibody binding capacity (sABC). IMGN632 was provided by ImmunoGen, Inc. Results: IMGN632 was tested against 8 pediatric ALL PDXs (3 B-ALL; 3 MLLr-ALL; 2 Ph+-ALL) in which median cell surface CD123 expression ranged from 510-3375 sABC. NSG mice tolerated IMGN632 well with maximum average weight losses of 0.0-7.7% across treatment groups compared to 0.0-8.1% in vehicle controls. IMGN632 induced significant differences in EFS distribution compared to control in 8 of 8 PDXs. T-C values ranged from 9.8 to 64.8 days (T/C 3.0-9.4) and Maintained Complete Responses were observed in 6 of 8 PDXs. In 6 of 8 PDXs the median EFS of the IMGN632-treated groups extended >5 weeks beyond the end of treatment. The control ADC did not significantly delay the progression of any PDX. There was no apparent correlation between CD123 sABC levels and in vivo activity with IMGN632 efficacy being observed across all CD123 expression levels. Conclusions: IMGN632 exerted profound in vivo efficacy against PDXs derived from a broad range of ALL subtypes and with a broad range of CD123 antigen levels. These data strongly support the clinical investigation of IMGN632 in acute lymphoblastic leukemia. (Supported by NCI Grants CA199222 & CA199000) Citation Format: Kathryn Evans, Narimanne El-Zein, Connor Jones, Stephen W. Erickson, Yuelong Guo, Beverly A. Teicher, Sharlene Adams, Patrick A. Zweidler-McKay, Malcolm A. Smith, Richard B. Lock. Pediatric preclinical testing consortium evaluation of the CD123 antibody drug conjugate, IMGN632, against xenograft models of pediatric acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4820.

Abstract 3187: Pediatric Preclinical Testing Consortium evaluation of the menin inhibitor, VTP-50469, against xenograft models of MLL-rearranged infant acute lymphoblastic leukemia

Abstract Introduction: Rearrangements involving the MLL (mixed lineage leukemia, KMT2A) gene (MLLr) occur broadly in acute leukemia, in ~80% of infant acute lymphoblastic leukemia (ALL) cases, and are associated with poor outcome. Menin is a ubiquitously expressed nuclear protein, and the MLLr-menin interaction is the key impetus for transformation of MLLr-expressing cells. VTP-50469 is a potent, orally available, small molecule inhibitor of the MLL-menin interaction with pM binding affinity for menin. Therefore, it was of interest to test the in vivo efficacy of VTP-50469 against preclinical models of infant MLLr-ALL. Methods: Infant MLLr-ALL patient-derived xenografts (PDXs) grew in an orthotopic manner in NSG mice. Engraftment and response to treatment were assessed by enumeration of the % human leukemic blasts in the murine peripheral blood (%huCD45+). Treatment commenced when the median %huCD45+ exceeded 1%, and mice received VTP-50469 (120 mg/kg by oral gavage twice daily x 28) or vehicle. An event was defined as the %huCD45+ >25% or leukemia-related morbidity. The Kaplan-Meier method was used to compare event-free survival (EFS) between treated (T) and control (C) groups. Stringent objective response measures were assigned to each mouse and reported as group medians (Houghton et al, Pediatr. Blood Cancer, 2007;49:928-40). Leukemia infiltration into the femoral bone marrow was also assessed at Day 28 following treatment initiation. VTP-50469 was provided by Vitae Pharmaceuticals. Results: VTP-50469 was well tolerated, with maximum average weight losses of 1.6-6.4% across treatment groups compared to 0-2.0% in vehicle control treated groups. VTP-50469 induced significant differences in EFS distribution compared to control in 6 of 6 (100%) of the evaluable MLLr-ALL PDXs. VTP-50469 T-C values in MLLr-ALL PDXs ranged from 1.2 to 100 days (T/C 1.3-21.1), and Maintained Complete Responses (MCRs) were observed in 5 of 6 PDXs. Two of 8 mice engrafted with an MLLr-ALL harboring the MLL-AFF1 (t4;11) translocation had not reached event >230 days following treatment initiation. A significant reduction (P<0.001) in bone marrow infiltration at Day 28 was observed in 2 of 4 evaluable MLLr-ALL PDXs. VTP-50469 at 30 mg/kg (4-fold lower than its maximum tolerated dose) also elicited MCRs in 8 of 8 mice engrafted with an MLL-AFF1 PDX. The on-target activity of VTP-50469 was verified by its lack of efficacy against an ALL PDX harboring the BCR-ABL1 translocation. Conclusions: VTP-50469 exerted profound in vivo efficacy against ALL PDXs derived from infants harboring MLL-AFF1, MLL-GAS7, and MLL-ENL translocations, and significantly reduced leukemia infiltration in the bone marrow. VTP-50469 was also effective across a broad dose range, indicating that it may represent a novel treatment for MLLr leukemia. (Supported by NCI Grants CA199222 & CA199000) Citation Format: Richard B. Lock, Kathryn Evans, Tara Pritchard, Stephen W. Erickson, Yuelong Guo, David A. Claremon, Gerard M. McGeehan, Beverly A. Teicher, Malcolm A. Smith. Pediatric Preclinical Testing Consortium evaluation of the menin inhibitor, VTP-50469, against xenograft models of MLL-rearranged infant acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3187.

Abstract LB-B16: The AKR1C3-Activated Prodrug OBI-3424 Exerts Profound In Vivo Efficacy Against Preclinical Models of T-Cell Acute Lymphoblastic Leukemia (T-ALL); a Pediatric Preclinical Testing Consortium Study

Abstract Introduction: Aldo-keto reductase family 1 member C3 (AKR1C3) belongs to a superfamily of oxidoreductases that are broadly expressed in human tissues. AKR1C3 catalyzes the reduction of a diverse group of substrates, and is expressed at high levels in several human cancers including T-ALL. We previously showed that AKR1C3 is a biomarker of T-ALL sensitivity to the hypoxia-activated pre-prodrug PR-104, which is also activated under aerobic conditions by AKR1C3 (Manesh et al, Blood, 2015;126:1193-202). Therefore, it was of interest to test the in vivo efficacy of OBI-3424 against preclinical models of T-ALL, since OBI-3424 is a highly selective prodrug that is converted by AKR1C3 to a DNA alkylating agent. Methods: ALL patient-derived xenografts (PDXs) grew in an orthotopic manner following intravenous inoculation into NSG mice. Engraftment and response to treatment were assessed by enumeration of the % human leukemic blasts in the murine peripheral blood (%huCD45+). Treatment commenced when the %huCD45+ exceeded a median of 1%, and mice received OBI-3424 (2.5 mg/kg by the intraperitoneal route once weekly x 3) or vehicle. An event was defined as the %huCD45+ exceeding 25% or leukemia-related morbidity. The Kaplan-Meier method was used to compare event-free survival (EFS) between treated (T) and control (C) groups. Stringent objective response measures were assigned to each mouse and reported as group medians (Houghton et al, PBC, 2007;49:928-40). Leukemia infiltration into the femoral bone marrow was also assessed at Day 28 following treatment initiation. OBI-3424 was provided by Threshold Pharmaceutical and is being developed by OBI Pharma, Inc. (ex-Asia) and Ascenta Pharma (Asia). Results: OBI-3424 was well tolerated, with only a 2.8% toxicity rate in the drug-treated groups. OBI-3424 induced significant differences in EFS distribution compared to control in 9 of 9 (100%) of the evaluable PDXs. T-C values ranged from 17.1 to 65.2 days (T/C 2.3-14.0), and objective responses were observed in 8 of 9 PDXs (2 complete responses, CRs; 6 maintained CRs, MCRs). A significant reduction (P<0.0001) in bone marrow infiltration at Day 28 was observed in 4 of 6 evaluable T-ALL PDXs. The importance of AKR1C3 in the in vivo responses of ALL PDXs to OBI-3424 was verified using a B-cell precursor ALL PDX (ALL-11) that had been lentivirally transduced to stably overexpress AKR1C3 (ALL-11/1C3) compared with empty vector control (ALL-11/EV). Mice engrafted with ALL-11/1C3 exhibited an MCR (T-C >37.3 days, T/C >3) compared with a CR for ALL-11/EV (T-C 21.1 days, T/C 2.5). Infiltration of ALL-11/1C3 cells into the murine bone marrow was significantly reduced at Day 28 in OBI-3424-treated compared with vehicle-treated mice (P<0.0001) but not in mice engrafted with ALL-11/EV. Conclusions: At a dose of 2.5 mg/kg, which is estimated to achieve exposure levels in mice that will be readily attainable in humans, OBI-3424 exerted profound in vivo efficacy against a broad range of T-ALL PDXs and significantly reduced leukemia infiltration in the bone marrow. Since these PDXs were derived predominantly from aggressive and fatal disease, OBI-3424 may represent a novel treatment for aggressive and chemoresistant T-ALL in an AKR1C3 biomarker-driven clinical trial. (Supported by NCI Grants CA199222 & CA199000) Citation Format: Richard B. Lock, Kathryn Evans, Raymond Yung, Tara Pritchard, Beverly A. Teicher, JianXin Duan, Yuelong Guo, Stephen W. Erickson, Malcolm A. Smith. The AKR1C3-Activated Prodrug OBI-3424 Exerts Profound In Vivo Efficacy Against Preclinical Models of T-Cell Acute Lymphoblastic Leukemia (T-ALL); a Pediatric Preclinical Testing Consortium Study [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B16.

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.

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. M6620 was tested in vitro at concentrations ranging from 1.0nM to 10.0 μM and at 75nM 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 5mg/kg. M6620 was administered intravenously on days 2 and 9 at 20mg/m2 approximately 16hr after cisplatin. 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. 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.

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

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. 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. 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. 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 (stage 1) of tazemetostat (EPZ‐6438), a novel EZH2 inhibitor, by the Pediatric Preclinical Testing Program

Tazemetostat (EPZ-6438) is a selective inhibitor of the histone methyltransferase EZH2 and currently in clinical development for non-Hodgkin lymphoma and genetically defined tumors. Tazemetostat was tested against the Pediatric Preclinical Testing Program (PPTP) solid tumor xenografts using a dose of 400 mg/kg administered twice daily by oral gavage for 28days. H3K27me3:H3 ratios were determined in control and treated tumors. Tazemetostat induced significant differences in event-free survival (EFS) distribution compared with control in nine of 30 (30%) of the xenografts studied. Significant differences in EFS distribution were observed in five of seven (71%) rhabdoid tumor xenograft lines compared with four of 23 (17%) nonrhabdoid xenograft lines (chi-square [χ2 ] test P = 0.006). Tazemetostat induced tumor growth inhibition meeting criteria for intermediate and high EFS treated-to-control (T/C) activity in two of 25 (8%) and one of 25 (4%) xenografts, respectively. Intermediate and high activity for the EFS T/C metric was observed exclusively among rhabdoid tumor xenografts (three of five rhabdoid tumor vs 0 of 22 nonrhabdoid tumors (χ² test P < 0.001). One rhabdoid tumor xenograft (G401) showed stable disease. For one rhabdoid tumor (G401), delayed tumor regression to tazemetostat was noted following 1 week of tumor growth. Tazemetostat induced significant reduction of H3K27me3 levels in the majority of tumors compared with controls. Tazemetostat demonstrated significant antitumor activity in rhabdoid tumor models but showed no consistent activity against any other histology. Tazemetostat reduced H3K27me3 levels irrespective of tumor response. Further preclinical testing to evaluate tazemetostat in combination with other anticancer agents is warranted.

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

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. 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. 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. 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.

Benefit from prolonged dose-intensive chemotherapy for infants with malignant brain tumors is restricted to patients with ependymoma: a report of the Pediatric Oncology Group randomized controlled trial 9233/34

The randomized controlled Pediatric Oncology Group study 9233 tested the hypothesis that dose-intensive (DI) chemotherapy would improve event-free survival (EFS) for children <3 years of age with newly diagnosed malignant brain tumors. Of 328 enrolled eligible patients, diagnoses were medulloblastoma (n = 112), ependymoma (n = 82), supratentorial primitive neuroectodermal tumor (sPNET, n = 38) and other malignant brain tumors (n = 96), and were randomized to 72 weeks of standard dose chemotherapy (Regimen A, n = 162) or DI chemotherapy (Regimen B, n = 166). Radiation therapy (RT) was recommended for patients with evidence of disease at completion of chemotherapy or who relapsed within 6 months of chemotherapy completion. Distributions of EFS for Regimens A and B were not significantly different (P = 0.32) with 2- and 10-year rates of 22.8% ± 3.3% and 15.4% ± 3.7%, and 27.1% ± 3.4% and 20.8% ± 3.8%, respectively. Thus, the study hypothesis was rejected. While distributions of EFS and OS were not significantly different between Regimens A and B for patients with medulloblastoma and sPNET, DI chemotherapy resulted in significantly improved EFS distribution (P = .0011) (2-year EFS rates of 42.1% vs. 19.6% with SD chemotherapy), but not OS distribution, for patients with centrally confirmed ependymoma. The degree of surgical resection affected EFS, OS or both for most tumor groups. Approximately 20%, 40% and 20% of patients with medulloblastoma, ependymoma treated with DI chemotherapy, and sPNET, respectively appear to have been cured without RT. Of 11 toxic deaths on study, 10 occurred on the DI chemotherapy arm. Prolonged dose-intensive chemotherapy given to infants with malignant brain tumors resulted in increased EFS only for patients with ependymoma.

Abstract LB-317: Pediatric Preclinical Testing Program (PPTP) evaluation of volasertib (BI 6727), a Polo-like kinase (PLK) inhibitor

Abstract Background: Volasertib is a first in class, selective and potent cell cycle kinase inhibitor that induces mitotic arrest and apoptosis by targeting PLK. Genomic screens have identified PLK1 as a potential therapeutic target for several pediatric cancers, including rhabdomyosarcoma and neuroblastoma. Methods: Volasertib (provided by Boehringer Ingelheim) was tested in vitro at concentrations from 0.1 nM to 1.0 µM. Volasertib was tested against the PPTP solid tumor xenografts using a dose of 30 mg/kg administered intravenously weekly x 3. For the ALL panel (using NOD-SCID mice), the MTD was 15 mg/kg, and this dose was used for efficacy testing. The total planned treatment period was 3 weeks with an additional 3 weeks observation. Two measures of antitumor activity were primarily used: 1) an objective response measure modeled after the clinical setting; and 2) a time to event (4-fold increase in tumor volume) measure based on the median event-free survival (EFS) of treated (T) and control (C) animals for each xenograft. Intermediate activity requires EFS T/C &amp;gt; 2, with high activity additionally requiring regression at the end of the observation period. Results: The median relative IC50 (rIC50) value for the PPTP cell lines was 14.1 nM, with a range from 6.0 nM to 135 nM. The median rIC50 values were lowest for the ALL cell line panel compared to the remaining cell lines (11.9 versus 16.0 nM, respectively), but this difference was not significant, and overall there were no differences in rIC50 by histotype. Against the PPTP in vivo panels volasertib induced significant differences in EFS distribution compared to control in 19 of 32 (59%) evaluable solid tumor xenografts and in 2 of 4 (50%) evaluable ALL xenografts. Volasertib induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity in 11 of 30 (37%) evaluable solid tumor xenografts. Intermediate activity for the EFS T/C metric was most consistently observed in the neuroblastoma (4 of 6) and glioblastoma (2 of 3) panels. For the ALL panel, 2 of 4 (50%) xenografts met criteria for intermediate activity. Objective responses were observed for 4 of 32 solid tumor and 1 of 4 ALL xenografts. Two of 6 neuroblastoma xenografts demonstrated CRs, as did 1 of 3 glioblastoma and 1 of 5 rhabdomyosarcoma xenografts evaluable for this response measure. Conclusions: Volasertib showed low nanomolar in vitro potency against the PPTP cell lines with no histotype selectivity. Volasertib induced regressions in 5 of 36 evaluable PPTP xenografts with the neuroblastoma panel showing the most consistent pattern of responsiveness to volasertib. Given available pharmacokinetic data showing that mice tolerate higher systemic exposure to volasertib than humans, it is unlikely that the PPTP in vivo results are under-estimating the potential clinical activity of volasertib against the childhood cancer types evaluated here. (Supported by NCI NO1CM42216) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-317. doi:1538-7445.AM2012-LB-317

Abstract C103: Pediatric Preclinical Testing Program (PPTP) Stage 1 evaluation of the p53-MDM2 antagonist RG7112: Early evidence for high activity against MLL-rearranged leukemias.

Abstract Introduction: Tumor suppressor p53 is a pro-apoptotic molecule frequently inactivated in cancer by gene mutations or defective signaling. Mutated p53 is uncommon in many childhood cancers and hence agents able to free p53 from inhibitory mechanisms may have therapeutic benefit in the pediatric setting. RG7112 is a selective inhibitor of p53-MDM2 binding that frees p53 from negative control, activating the p53 pathway in cancer cells leading to cell cycle arrest and apoptosis. RG7112 is a member of the Nutlin family of MDM2 antagonists that has improved potency and pharmacological properties. Methods: RG7112 and its inactive enantiomer RG7112i were evaluated against the 23 cell lines of the PPTP in vitro panel using 96 hour exposure at concentrations from 1 nM to 10 μM. RG7112 was tested against the PPTP in vivo panel focusing on p53 wild type (WT) xenografts at a dose of 100 mg/kg daily for 14 days followed by 4 weeks observation. MDM2 and p53 expression for the PPTP models tested were available through Affymetrix U133 Plus 2.0 arrays (Clin Cancer Res 2008:14:4572–83). Results: In vitro, RG7112 produced treated to control (T/C) ratios approaching 0% for most p53 WT cell lines at the highest concentration tested. The median IC50 for RG7112 was ∼0.4 μM on p53 WT cell lines versus &amp;gt; 10 μM on p53 mutant cell lines. RG7112 was well tolerated in vivo, with 44 of 45 xenograft models evaluable for efficacy. RG7112 induced significant differences in EFS (event-free survival) distribution compared to control in 15 of 27 (56%) evaluable p53 WT solid tumor xenografts. RG7112 induced a twofold or greater delay in time to event in 10 of 25 (40%) p53 WT solid tumor xenografts, including: 2/2 rhabdoid tumor, 2/2 Wilms tumor, 2/3 Ewing, 3/6 rhabdomyosarcoma models, but no neuroblastoma (n=5) or osteosarcoma (n=6) models. Objective responses were observed in 5 solid tumor xenografts: maintained complete response (MCR) or complete response (CR) for a medulloblastoma and an alveolar rhabdomyosarcoma, respectively, and partial responses (PR) for a Wilms tumor, rhabdoid tumor, and Ewing tumor xenograft. For the systemic-disease ALL panel, among 13 xenografts there were 11 CR, 1 MCR and 1 PR. Each of the 7 ALL xenografts with MLL rearrangement was sensitive to RG7112 with 6 CR and 1 MCR. Two additional MLL-rearranged xenografts (MV4;11 and RS4;11) grown subcutaneously were also tested, with the former showing MCR and the latter tumor growth delay. Solid tumor xenografts with mutant p53 (Rh30R and EW5) showed no in vivo response to RG7112 as expected. The osteosarcoma xenografts were p53 WT, but had very low p53 expression and low MDM2 expression, and they failed to respond to RG7112. The ALL xenografts expressed the highest levels of p53 and MDM2 among the PPTP panels and showed the most consistent responses to RG7112. Conclusions: RG7112 induced tumor regressions in one xenograft line from the rhabdomyosarcoma, medulloblastoma, Wilms tumor, Ewing and rhabdoid tumor panels and induced CRs or MCRs for most ALL xenografts. The consistent high level activity of RG7112 against leukemia models with MLL-rearrangement was particularly notable. This high level of activity supports prioritization of RG7112 for further evaluation. Preclinical evaluations of RG7112 with standard agents are planned. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C103.

Abstract 740: Pediatric Preclinical Testing Program (PPTP) evaluation of the NEDD8-activating enzyme (NAE) inhibitor MLN4924

Abstract Background: MLN4924 is a potent and selective small molecule NAE inhibitor. In most cancer cells tested, inhibition of NAE leads to induction of DNA rereplication, resulting in DNA damage and cell death. NEDD8-activating enzyme (NAE) is an essential component of the NEDD8 conjugation pathway that controls the activity of the cullin-RING subtype of ubiquitin ligases, thereby regulating the turnover of a subset of proteins upstream of the proteasome. Substrates of cullin-RING ligases have important roles in cellular processes associated with cancer cell growth and survival pathways. The activity of MLN4924 was evaluated against the PPTP's in vitro and in vivo panels. Methods: The PPTP includes a molecularly characterized in vitro panel of cell lines (n=27) and in vivo panel of xenografts (n=61) representing most of the common types of childhood solid tumors and childhood acute lymphoblastic leukemia (ALL). MLN4294 (provided by Millennium Pharmaceuticals) was tested in vitro at concentrations from 1.0 nM to 10.0 µM and was tested against the PPTP in vivo panel using a 100 mg/kg dose (66mg/kg for ALL panel) BID administered SQ daily × 5 for 3 weeks, with observation for 6 weeks. Three measures of 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 (4-fold increase in tumor volume) measure based on the median event-free survival (EFS) of treated and control animals for each xenograft. Results: The median relative IC50 for MLN4924 against the PPTP cell lines was 143 nM, with a range from 15 nM to 678 nM. The median relative IC50 value for the Ewing panel (31 nM) was significantly lower than that of the remaining PPTP cell lines. MLN4924 demonstrated an activity pattern consistent with cytotoxic activity. MLN4924 was well tolerated, with a toxicity rate of 4.6%. 42 of 45 xenograft models were considered evaluable for efficacy. MLN4924 induced significant differences in EFS distribution compared to control in 20 of 34 (59%) solid tumor xenografts. MLN4924 induced intermediate activity (EFS T/C values &amp;gt; 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. The maximum shift in time to event for treated animals was 3.8-fold (ALL-3), and two other xenografts had shifts in time to event of 3.0-fold (ALL-2 and ALL-17). MLN4924 did not induce objective responses in the PPTP solid tumor or ALL panels, with the best response being stable disease for 1 ALL xenograft. Conclusions: MLN4924 potently inhibits the cell lines of the PPTP in vitro panel and shows an interesting pattern of in vivo activity. Pharmacokinetic and pharmacodynamic studies are ongoing. (Supported by NCI NO1CM42216) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 740. doi:10.1158/1538-7445.AM2011-740

Abstract 5266: Pediatric Preclinical Testing Program (PPTP) evaluation of the CDK inhibitor SCH 727965

Abstract Background: SCH 727965 is a potent inhibitor of CDK1, CDK2 and CDK9 activities in vitro and has been shown to be effective as a single agent against a wide-spectrum of adult tumor xenograft models including lung, prostate, breast, ovarian and multiple myeloma, with tumor growth inhibition from 12% to 150% (regression) noted. The activity of SCH 727965 was evaluated against the PPTP's in vitro and in vivo panels. Methods: The PPTP includes a molecularly characterized in vitro panel of cell lines (n=27) and in vivo panel of xenografts (n=61) representing most of the common types of childhood solid tumors and childhood acute lymphoblastic leukemia (ALL). SCH 727965 (provided by Schering-Plough) was tested in vitro at concentrations from 0.1 nM to 1.0 μM and was tested against the PPTP in vivo panel using a 40 mg/kg dose administered IP twice-weekly for 2 weeks, repeated at Day 21 with a total planned treatment and observation period of 6 weeks. Three measures of 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 (4-fold increase in tumor volume) measure based on the median event-free survival (EFS) of treated and control animals for each xenograft. Results: The median IC50 value for the PPTP cell lines was 7.5 nM, with a 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 cytotoxic activity for most of the PPTP cell lines with minimum (Ymin) T/C% values approaching 0% for most cell lines. SCH 727965 was well tolerated in vivo, with a toxicity rate &amp;lt; 5%. All 43 (36 solid tumor and 7 ALL) xenograft models studied were evaluable for efficacy. SCH 727965 induced significant differences in EFS distribution compared to control in 23 of 36 (64%) evaluable solid tumor xenografts. Seven of 33 solid tumor xenografts evaluable for the EFS T/C activity measure showed a 2-fold or greater increase in time to event for the SCH 727965 treated group. SCH 727965 did not induce objective responses in the PPTP solid tumor panels. The best response in these panels was stable disease (SD) which was observed for the osteosarcoma xenograft OS-1. PD2 (progressive disease with growth delay) was observed in 15 of 36 xenografts, being most commonly observed in the rhabdomyosarcoma (4 of 6), rhabdoid tumor (2 of 2) and the Ewing sarcoma (3 of 5) tumor panels. In the ALL panel, the best response was a complete response (CR), which was observed in a single xenograft (ALL-17). A T-cell ALL xenograft (ALL-16) attained a partial response (PR). The remaining 5 ALL xenografts showed progressive disease. Conclusions: SCH 727965 potently inhibits the cell lines of the PPTP in vitro panel and shows an interesting pattern of in vivo activity suggesting its potential applicability against selected childhood cancer subtypes. (Supported by NCI NO1CM42216) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5266.

Pediatric Preclinical Testing Program (PPTP) testing of the CENP-E inhibitor GSK923295A

10015 Background: GSK923295A is a small molecule inhibitor of centromere-associated protein E (CENP-E), a mitotic kinesin that is required for metaphase chromosome alignment and integration of mitotic spindle mechanics with mitotic checkpoint signaling. An initial phase I clinical trial in adults is ongoing. Methods: The PPTP includes a molecularly characterized in vitro panel of cell lines (n = 27) and in vivo panel of xenografts (n = 60) representing most of the common types of childhood solid tumors and childhood acute lymphoblastic leukemia (ALL). GSK923295A was tested in vitro at concentrations from 1.0 nM to 10.0 μM (96 hour exposure) and was tested in vivo using a daily × 3 for 2 weeks schedule, repeated at day 21. GSK923295A was administered IP at a dose of 125 mg/kg. Three measures of antitumor activity were used: 1) an objective response measure modeled after the clinical setting; 2) a time to event measure based on the median event-free survival (EFS); and 3) a treated to control (T/C) tumor volume measure. Results: GSK923295A demonstrated potent in vitro activity against the PPTP cell line panel with a median IC50 of 27 nM (range 12 nM to &gt; 10 μM). 35 of 37 solid tumor xenograft models were evaluable. GSK923295A induced significant differences in EFS distribution compared to controls in 32 of 35 evaluable models. Objective responses were noted in 13 of 35 xenografts, including 9 with maintained complete responses (MCR), 3 with complete response (CR), and 1 with partial response (PR). Three of 5 Ewing sarcoma xenografts achieved MCR or CR, as did 2 of 3 rhabdoid tumor, and 2 of 5 rhabdomyosarcoma models. For the neuroblastoma panel, the best response was progressive disease (PD) with growth delay compared to controls (PD2 response), which was observed in 5 of 6 xenografts. GSK923295A showed activity against the ALL panel, but unexplained toxicity (generally on or after day 21) precluded formal analysis. Conclusions: GSK923295A has substantial in vitro and in vivo activity against the PPTP's preclinical models. The observed high level of preclinical activity for GSK923295A will need to be evaluated in the context of systemic exposures achieved in the xenograft models and those achievable in humans at tolerable doses. (Supported by NCI NO1CM42216) [Table: see text]