Clinical Trials on Cellular Therapy for Children and Adolescents With Cancer: A 15-Year Trend in the United States

INTRODUCTION

Cellular therapies are frequently studied in clinical trials for pediatric patients with malignant disease. Characteristics of ongoing and completed cellular therapy clinical trials in the U.S. involving children and adolescents have not previously been reported.

METHODS

We searched ClinicalTrials.gov for clinical trials involving cellular therapies enrolling patients under 18 years of age in the U.S. Trials were initially stratified into child-only (maximum age of eligibility <18 years), child/adolescent and young adult (AYA) (maximum age of eligibility ≤21 years), and child/adult (maximum age of eligibility >21 years). Descriptive characteristics and trends over time were analyzed.

RESULTS

We included 202 trials posted 2007-2022. Of the 202 trials, only three trials were child-only; thus, our subsequent analysis focused on comparing child/AYA (≤21 years) and child/adult trials (>21 years). One hundred sixty-nine (84%) enrolled both child and adult populations. The vast majority of trials were early phase (phase 1, 1/2, and 2, 198/202, 98%). Chimeric antigen receptor T cell therapies were most commonly studied (88/202, 44%), while natural-killer cell therapies were most common in child/AYA trials (42% vs. 16%). Most trials were single institution-only (130/202, 64%) and did not receive industry funding (163/202, 81%). Studies with industry funding were more likely to be multicenter (64% vs. 29%) and international (31% vs. 0.6%). Notably, no central nervous system tumor-specific trials had industry funding. There was no difference in therapy type based on funding source. Yearly new trial activations increased over the time period studied (p=0.01).

CONCLUSION

The frequency of cellular therapy trial activations enrolling child/AYA patients with cancer in the U.S. has increased over time. Most studies were phase 1 or 2, single institution-only, and not industry-supported. Future opportunities for cell therapy for pediatric cancer should include multi-institutional approaches.

Guidelines for clinical evaluation of anti-cancer drugs

Clinical studies intended for regulatory approval must demonstrate the clinical benefits of the drug in a target population. Clinical development of a drug proceeds by stepwise clinical studies; after safety and pharmacokinetics are evaluated and the recommended dosage and administration are determined, efficacy and safety are evaluated in an exploratory manner, and finally clinical benefits are compared with conventional standard therapies. Guidelines for the clinical evaluation of anti‐cancer drugs in Japan were established in 1991 and amended in 2006 after molecular‐targeted drugs were introduced. Recent progress in the development of drugs acting on the immune system and cancer genomic medicine targeting rare but important molecular subtypes have altered the strategy for development of anti‐cancer drugs. It is often difficult to conduct a confirmatory randomized controlled study using overall survival as the primary endpoint in rare molecular subtypes, and the primary evaluation of the efficacy of some drugs and subsequent approval is based on the tumor response. As conducting clinical studies for rare subtypes solely within Japan is difficult, drug development needs to be conducted within a global study. However, this requires robust monitoring to detect possible ethnic differences in pharmacokinetics and drug efficacy. Development using the conditional approval system for drugs enforced in 2020 may be considered, when clinical utility is evaluated based on surrogate endpoints. Because of these changes, we have revised the guidelines for the clinical evaluation of anti‐cancer drugs in Japan. To promote global development of anti‐cancer drugs involving Japan, the guidelines have been translated into English.

Recent progress in development of drugs acting on the immune system and cancer genomic medicine targeting rare but important molecular subtypes have altered the strategy for development of anti‐cancer drugs. As conducting clinical studies for rare subtypes solely within Japan is difficult, drug development needs to be conducted within a global study with monitoring possible ethnic differences. Because of these changes, we have revised the guidelines for the clinical evaluation of anti‐cancer drugs in Japan.

Phase I trial of the mTOR inhibitor everolimus in combination with multi-agent chemotherapy in relapsed childhood acute lymphoblastic leukemia

BACKGROUND

We sought to determine the feasibility of co-administering everolimus with a four-drug reinduction in children and adolescents with acute lymphoblastic leukemia (ALL) experiencing a first marrow relapse.

PROCEDURE

This phase I study tested everolimus with vincristine, prednisone, pegaspargase and doxorubicin in patients with marrow relapse occurring >18 months after first complete remission (CR). The primary aim was to identify the maximum tolerated dose of everolimus. Three dose levels (DLs) were tested during dose escalation (2, 3, and 5 mg/m² /day). Additional patients were enrolled at the 3- and 5 mg/m² /day DLs to further evaluate toxicity (dose expansion).

RESULTS

Thirteen patients enrolled during dose escalation and nine during dose expansion. During dose escalation, one dose-limiting toxicity occurred (grade 4 hyperbilirubinemia) in six evaluable patients at DL3 (5 mg/m² /day). The most common grade ≥3 adverse events were febrile neutropenia, infections, transaminitis, hyperbilirubinemia, and hypophosphatemia. Two of the 12 patients treated at DL3 developed Rothia mucilaginosa meningitis. Nineteen patients (86%) achieved a second CR (CR2). Of those, 13 (68%) had a low end-reinduction minimal residual disease (MRD) level (≤10^-3 by polymerase chain reaction-based assay). The CR2 rate for patients with B-cell ALL treated at DL3 (n = 12) was 92%; 82% of these patients had low MRD.

CONCLUSIONS

Everolimus combined with four-drug reinduction chemotherapy was generally well tolerated and associated with favorable rates of CR2 and low end-reinduction MRD. The recommended phase 2 dose of everolimus given in combination with a four-drug reinduction is 5 mg/m² /day. This promising combination should be further evaluated in a larger patient cohort.

Clinical Outcome of Patients with Advanced Biliary Tract Cancer in a Dedicated Phase I Unit

AIMS

Advanced biliary tract carcinomas (ABC) are malignancies with limited effective therapies for advanced disease. There is little published evidence of outcomes of ABC patients participating in phase I clinical trials.

MATERIALS AND METHODS

Patient characteristics, treatment details and outcomes of ABC patients treated at a dedicated phase I unit were captured and analysed from case and trial records.

RESULTS

In total, 123 ABC patients were included in the study, of which 48 patients participated in 41 different phase I trials; 75 (61%) did not participate due to rapid disease progression or patient choice. Molecular characterisation of tumours using a targeted panel was conducted in 15 (31%), yielding several potentially actionable mutations, including BRCA, PIK3CA, FGFR, AKT and PTEN loss. Of the 39 evaluable patients there was one exceptional responder. Eighteen (46%) other patients achieved stable disease as their best response, with a clinical benefit rate at 4 months of 10%. Treatment was generally well tolerated with grade 3 or 4 adverse events only observed in eight patients (17 %), of which six were drug related and led to trial discontinuation in one (3%), with no toxicity-related deaths.

CONCLUSION

Carefully selected ABC patients have been found to tolerate experimental phase I clinical trials without excess toxicity. The aggressive nature of this disease warrants consideration of early referral to a phase I unit. Future work will require comprehensive molecular profiling in an attempt to understand the biology underlying the exceptional responders and to match patients in real-time to targeted therapies.

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.

Evaluation of patritumab with or without erlotinib in combination with standard cytotoxic agents against pediatric sarcoma xenograft models

BACKGROUND

Integrating molecularly targeted agents with cytotoxic drugs used in curative treatment of pediatric cancers is complex. An evaluation was undertaken with the ERBB3/Her3-specific antibody patritumab (P) either alone or with the ERBB1/epidermal growth factor receptor inhibitor erlotinib (E) in combination with standard cytotoxic agents, cisplatin, vincristine, and cyclophosphamide, in pediatric sarcoma xenograft models that express receptors and ligands targeted by these agents.

PROCEDURES

Tumor models were selected based upon ERBB3 expression and phosphorylation, and ligand (heregulin) expression. Patritumab, E, or these agents combined was evaluated without or with concomitant cytotoxic agents using procedures developed by the Pediatric Preclinical Testing Program.

RESULTS

Full doses of cytotoxic agents were tolerated when combined with P, whereas dose reductions of 25% (vincristine, cisplatin) or 50% (cyclophosphamide) were required when combined with P + E. Patritumab, E alone, or in combination did not significantly inhibit growth of any tumor model, except for Rh18 xenografts (E alone). Patritumab had no single-agent activity and marginally enhanced the activity of vincristine and cisplatin only in Ewing sarcoma ES-4. P + E did not increase the antitumor activity of vincristine or cisplatin, whereas dose-reduced cyclophosphamide was significantly less active than cyclophosphamide administered at its maximum tolerated dose when combined with P + E.

CONCLUSIONS

P had no single-agent activity, although it marginally potentiated the activity of vincristine and cisplatin in one of three models studied. However, the addition of E necessitated dose reduction of each cytotoxic agent, abrogating the enhancement observed with P alone.

Tolerability of oral sorafenib in pet dogs with a diagnosis of cancer

Sorafenib is a multi-target small molecule inhibitor of the RAF kinase family and VEGFR-2/PDGFR. The US Food and Drug Administration approved sorafenib in human patients with liver, thyroid, or renal carcinoma. The aim of this study was to help guide future pharmacokinetic (PK) studies of sorafenib in dogs with a cancer diagnosis. Client-owned dogs were eligible if they had a cytologic or histologic diagnosis of cancer. Patients were enrolled at escalating doses of sorafenib. Patients were evaluable for the study if they received at least one dose of sorafenib and presented 1 week later for a follow-up examination, blood work, and assessment of drug tolerability. The goal of this study was not to define a maximum tolerated dose as may be reasonable in conventional cytotoxic chemotherapy drugs, but rather to describe the tolerability of this drug in dogs with a cancer diagnosis, as a prequel to future sorafenib PK studies. No patients in the study had any evidence of adverse events that were attributable to sorafenib. Doses of 3 mg/kg were well tolerated and associated with a suggestion of clinical activity, supportive of future PK, and pharmacodynamic analysis. Such future studies are recommended at this dose to define the associated exposure achieved and determine a reasonable schedule for sorafenib administration.

A comprehensive review of heregulins, HER3, and HER4 as potential therapeutic targets in cancer

Heregulins (HRGs) bind to the receptors HER3 or HER4, induce receptor dimerization, and trigger downstream signaling that leads to tumor progression and resistance to targeted therapies. Increased expression of HRGs has been associated with worse clinical prognosis; therefore, attempts to block HRG-dependent tumor growth have been pursued. This manuscript summarizes the function and signaling of HRGs and review the preclinical evidence of its involvement in carcinogenesis, prognosis, and treatment resistance in several malignancies such as colorectal cancer, non-small cell lung cancer, ovarian cancer, and breast cancer. Agents in preclinical development and clinical trials of novel therapeutics targeting HRG-dependent signaling are also discussed, including anti-HER3 and -HER4 antibodies, anti-metalloproteinase agents, and HRG fusion proteins. Although several trials have indicated an acceptable safety profile, translating preclinical findings into clinical practice remains a challenge in this field, possibly due to the complexity of downstream signaling and patterns of HRG, HER3 and HER4 expression in different cancer subtypes. Improving patient selection through biomarkers and understanding the resistance mechanisms may translate into significant clinical benefits in the near future.

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.

A comparison of safety and efficacy of cytotoxic versus molecularly targeted drugs in pediatric phase I solid tumor oncology trials

BACKGROUND

Prior reviews of phase I pediatric oncology trials involving primarily cytotoxic agents have reported objective response rates (ORRs) and toxic death rates of 7.9-9.6% and 0.5%, respectively. These data may not reflect safety and efficacy in phase I trials of molecularly targeted (targeted) drugs.

METHODS

A systematic review of pediatric phase I solid tumor trials published in 1990-2013 was performed. The published reports were evaluated for patient characteristics, toxicity information, and response numbers.

RESULTS

A total of 143 phase I pediatric clinical trials enrolling 3,896 children involving 53 targeted and 48 cytotoxic drugs were identified. A meta-analysis demonstrated that the ORR is 2.1-fold higher with cytotoxic drugs (0.066 vs. 0.031 per subject; P = 0.007). By contrast, the pooled estimate of the stable disease rate (SDR) is similar for cytotoxic and targeted drugs (0.2 vs. 0.23 per subject; P = 0.27).  The pooled estimate of the dose-limiting toxicity rate is 1.8-fold larger with cytotoxic drugs (0.24 vs. 0.13 per subject; P = 0.0003). The hematologic grade 3-4 (G3/4) toxicity rate is 3.6-fold larger with cytotoxic drugs (0.43 vs. 0.12 per treatment course; P = 0.0001); however, the nonhematologic G3/4 toxicities and toxic deaths occur at similar rates for cytotoxic and targeted drugs.

CONCLUSIONS

In phase I pediatric solid tumor trials, ORRs were significantly higher for cytotoxic versus targeted agents. SDRs were similar in targeted and cytotoxic drug trials. Patients treated with cytotoxic agents were more likely to experience hematologic G3/4 toxicities than those patients receiving targeted drugs.

Initial testing (stage 1) of tazemetostat (EPZ-6438), a novel EZH2 inhibitor, by the Pediatric Preclinical Testing Program

BACKGROUND

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.

PROCEDURES

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 28 days. H3K27me3:H3 ratios were determined in control and treated tumors.

RESULTS

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.

CONCLUSIONS

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 (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.

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 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 tubulin binding agent nanoparticle albumin-bound (nab) paclitaxel (Abraxane(®)) by the Pediatric Preclinical Testing Program (PPTP)

BACKGROUND

Nanoparticle albumin-bound paclitaxel (nab-paclitaxel, Abraxane(®)) is FDA approved for the treatment of several adult cancers. Antimitotic agents are essential components for curative therapy of pediatric solid tumors, although taxanes have shown limited activity. Because of the novel formulation, nab-paclitaxel was evaluated against a limited series of Pediatric Preclinical Testing Program (PPTP) solid tumors.

PROCEDURES

Nab-paclitaxel was tested against a limited subset of PPTP solid tumor xenograft models at a dose of 50 mg/kg using a q4d × 3 schedule intravenously.

RESULTS

Nab-paclitaxel was well tolerated in vivo, producing maximum weight loss of approximately 10% with recovery to baseline weight in the week following the third dose. All 20 xenograft models tested were considered evaluable for efficacy. Nab-paclitaxel induced statistically significant differences in event-free survival (EFS) distribution compared to control in 19 of 20 (95%) of the solid tumors. Objective responses were observed in 12 of 20 (60%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in 5 of 8 Ewing sarcoma models and 6 of 8 rhabdomyosarcomas. There were no objective regressions in either neuroblastoma (n = 2) or osteosarcoma (n = 2) xenograft panels. At the dose tested, systemic exposures of nab-paclitaxel in mice were somewhat greater than those tolerated in humans.

CONCLUSIONS

The high level of activity observed against the rhabdomyosarcoma and Ewing sarcoma PPTP preclinical models makes nab-paclitaxel an interesting agent to consider for pediatric evaluation.

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.

Improving access to novel agents for childhood leukemia

Leukemia is the most common pediatric cancer. Despite great progress in the development of curative therapy, leukemia remains a leading cause of death from disease in childhood, and survivors are at life-long risk of complications of treatment. New agents are needed to further increase cure rates and decrease treatment-associated toxicities. The complex biology and aggressive nature of childhood leukemia, coupled with the relatively small patient population available for study, pose specific challenges to the development of new therapies. In this review, the authors discuss strategies and initiatives designed to improve access to new agents in the treatment of pediatric leukemia.

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 solid tumor testing (stage 1) of AZD1480, an inhibitor of Janus kinases 1 and 2 by the pediatric preclinical testing program

BACKGROUND

AZD1480 is an ATP competitive inhibitor of Janus kinases 1 and 2 (JAK1, 2) that has been shown to inhibit the growth of solid tumor models. This agent was selected for testing the putative role of JAK/STAT signaling in the standard PPTP solid tumor models.

PROCEDURES

AZD1480 was tested against the PPTP in vitro cell line panel at concentrations from 1.0 nM to 10 μM and against the PPTP in vivo solid tumor xenograft panels at (60 mg/kg once daily (SID) × 5) for three consecutive weeks. Additional studies evaluated 5 to 20 mg/kg BID × 5 with SID dosing at 7-30 mg/kg at weekends for three consecutive weeks.

RESULTS

In vitro the median relative IC50 (rIC50 ) for the PPTP cell lines was 1.5 µM, with a range from 0.3 µM to 5.9 µM. The two cell lines with rIC50 values of 0.3 µM both had ALK activating genomic alterations. AZD1480 demonstrated statistically significant differences (P < 0.05) in EFS distribution compared to control in 89% of the solid tumor xenografts. AZD1480 induced intermediate (EFS T/C > 2) or high-level growth inhibition in 15 of 30 (50%) solid tumor xenografts. Tumor regressions were observed in three of six Wilms tumor models at doses that induced inhibition of Stat3(Y705) phosphorylation.

CONCLUSIONS

AZD1480 demonstrated significant tumor growth inhibition against most PPTP solid tumor xenografts, similar to that observed for antiangiogenic agents tested by the PPTP. Tumor regressing activity was noted for Wilms tumor xenografts.

Initial testing (stage 1) of glembatumumab vedotin (CDX-011) by the pediatric preclinical testing program

BACKGROUND

Glembatumumab vedotin is an antibody-auristatin conjugate that targets cells expressing the transmembrane glycoprotein NMB (GPNMB, also known as osteoactivin). It has entered clinical evaluation for adult cancers that express GPNMB, including melanoma and breast cancer.

PROCEDURES

Glembatumumab vedotin was administered intravenously at a dose of 2.5 mg/kg using a weekly × 3 schedule, and its antitumor activity was evaluated against selected Pediatric Preclinical Testing Program (PPTP) solid tumor xenografts using standard PPTP response metrics.

RESULTS

Among PPTP xenografts, GPNMB was primarily expressed on the osteosarcoma xenografts, all of which expressed GPNMB at the RNA level, although at varying levels. Protein expression assessed by immunohistochemistry (IHC) showed variation across the osteosarcoma xenografts with one model showing no tumor cell expression. Glembatumumab vedotin induced statistically significant differences (P < 0.05) in event-free survival (EFS) distribution compared to control in each of the six osteosarcoma models studied. Three of six osteosarcoma xenografts demonstrated a maintained complete response (MCR). Two other xenografts showed progressive disease with growth delay, while the final xenograft showed progressive disease with no growth delay. Two of the osteosarcoma xenografts with MCRs showed the highest GPNMB expression at the RNA level. Conversely, the xenograft with the lowest GPNMB mRNA expression had the poorest response to glembatumumab vedotin. Two rhabdomyosarcoma xenografts that did not express GPNMB showed limited responses to glembatumumab vedotin.

CONCLUSIONS

Glembatumumab vedotin yielded high-level activity against three of six osteosarcoma xenografts, with evidence for response being related to GPNMB expression levels.

Initial testing (stage 1) of the notch inhibitor PF-03084014, by the pediatric preclinical testing program

PF-03084014, a γ-secretase inhibitor, was tested against the PPTP in vitro cell line panel (1.0 nM to 10 μM) and against the in vivo xenograft panels (administered orally twice daily on Days 1-7 and 15-21). PF-03084014 demonstrated limited in vitro activity, with no cell line achieving ≥50% inhibition. PF-03084014 induced significant differences in EFS distribution in 14 of 35 (40%) solid tumor xenografts, and 1 of 9 ALL xenografts (which lacked a NOTCH1 mutation), but objective responses were not observed. PF-03084014 demonstrated limited single agent activity in vitro and in vivo against the pediatric preclinical models studied.

Initial testing (stage 1) of the investigational mTOR kinase inhibitor MLN0128 by the pediatric preclinical testing program

MLN0128 is an investigational small molecule ATP-competitive inhibitor of the serine/threonine kinase mTOR. MLN0128 was tested against the in vitro panel at concentrations ranging from 0.1 nM to 1 μM and against the PPTP in vivo panels at a dose of 1 mg/kg administered orally daily × 28. In vitro the median relative IC(50) concentration was 19 nM. In vivo MLN0128 induced significant differences in EFS in 24/31 (77%) solid tumor models, but 0/7 ALL xenografts. The modest activity observed for MLN0128 against the PPTP preclinical models is similar to that previously reported for another TOR kinase inhibitor.

Initial testing (stage 1) of the topoisomerase II inhibitor pixantrone, by the pediatric preclinical testing program

Pixantrone, a novel aza-anthracenedione with cytotoxic activity, was tested against the PPTP in vitro panel (3.0 nM to 30.0 μM) and against a limited panel of PPTP Wilms tumors and sarcomas (7.5 mg/kg) administered intravenously using an every 4 day × 3 schedule. In vitro pixantrone showed a median relative IC50 value of 54 nM (range <3 nM to 1.03 μM). In vivo pixantrone induced significant differences in EFS distribution compared to controls in two of eight solid tumor xenografts at dose levels relevant to human drug exposure. A complete response was observed for one Wilms tumor xenograft.

Initial testing (Stage 1) of TAK-701, a humanized hepatocyte growth factor binding antibody, by the Pediatric Preclinical Testing Program

TAK-701 is a humanized antibody that binds hepatocyte growth factor (HGF), thus suppressing c-Met transduced signaling and c-Met dependent proliferation and migration of tumor cells. Six childhood solid tumor xenografts were selected for evaluating TAK-701 based on immunochemical detection of HGF/c-Met autocrine signaling [i.e., pMet(Tyr1349) and HGF positive]. TAK-701 was tested using a dose of 30 mg/kg administered by the intraperitoneal (IP) route twice weekly for 4 weeks. TAK-701 did not induce significant differences in EFS distribution in treated tumors compared to control tumors. Objective responses were not observed in any of the tested solid tumor xenografts.

Initial testing (stage 1) of the histone deacetylase inhibitor, quisinostat (JNJ-26481585), by the Pediatric Preclinical Testing Program

BACKGROUND

Quisinostat (JNJ-26481585) is a second-generation pyrimidyl-hydroxamic acid histone deacetylase (HDAC) inhibitor with high cellular potency towards Class I and II HDACs. Quisinostat was selected for clinical development as it showed prolonged pharmacodynamic effects in vivo and demonstrated improved single agent antitumoral efficacy compared to other analogs.

PROCEDURES

Quisinostat was tested against the PPTP in vitro panel at concentrations ranging from 1.0 nM to 10 μM and was tested against the PPTP in vivo panels at a dose of 5 mg/kg (solid tumors) or 2.5 mg/kg (ALL models) administered intraperitoneally daily × 21.

RESULTS

In vitro quisinostat demonstrated potent cytotoxic activity, with T/C% values approaching 0% for all of the cell lines at the highest concentration tested. The median relative IC50 value for the PPTP cell lines was 2.2 nM (range <1-19 nM). quisinostat induced significant differences in EFS distribution compared to control in 21 of 33 (64%) of the evaluable solid tumor xenografts and in 4 of 8 (50%) of the evaluable ALL xenografts. An objective response was observed in 1 of 33 solid tumor xenografts while for the ALL panel, two xenografts achieved complete response (CR) or maintained CR, and a third ALL xenograft achieved stable disease.

CONCLUSIONS

Quisinostat demonstrated broad activity in vitro, and retarded growth in the majority of solid tumor xenografts studied. The most consistent in vivo activity signals observed were for the glioblastoma xenografts and T-cell ALL xenografts.

Initial testing (stage 1) of the Polo-like kinase inhibitor volasertib (BI 6727), by the Pediatric Preclinical Testing Program

BACKGROUND

Volasertib (BI 6727) is a potent inhibitor of Polo-like kinase 1 (Plk1), that is overexpressed in several childhood cancers and cell lines. Because of its novel mechanism of action, volasertib was evaluated through the PPTP.

PROCEDURES

Volasertib was tested against the PPTP in vitro cell line panel at concentrations from 0.1 nM to 1.0 μM and against the PPTP in vivo xenograft panels administered IV at a dose of 30 mg/kg (solid tumors) or 15 mg/kg (ALL models) using a q7dx3 schedule.

RESULTS

In vitro volasertib demonstrated cytotoxic activity, with a median relative IC50 value of 14.1 nM, (range 6.0-135 nM). Volasertib induced significant differences in EFS in 19 of 32 (59%) of the evaluable solid tumor xenografts and in 2 of 4 (50%) of the evaluable ALL xenografts. Volasertib induced tumor growth inhibition meeting criteria for intermediate EFS T/C (>2) activity in 11 of 30 (37%) evaluable solid tumor xenografts, including neuroblastoma (4 of 6) and glioblastoma (2 of 3) panels, and 2 of 4 ALL models. Objective responses (CR's) were observed for 4 of 32 solid tumor (two neuroblastoma, one glioblastoma, and one rhabdomyosarcoma) and one of four ALL xenografts.

CONCLUSIONS

Volasertib shows potent in vitro activity against the PPTP cell lines with no histotype selectivity. In vivo, volasertib induced regressions in several xenograft models. However, pharmacokinetic data suggest that mice tolerate higher systemic exposure to volasertib than humans, suggesting that the current results may over-estimate potential clinical efficacy against the childhood cancers studied.

Initial testing (Stage 1) of the antibody-maytansinoid conjugate, IMGN901 (Lorvotuzumab mertansine), by the pediatric preclinical testing program

BACKGROUND

IMGN901 (lorvotuzumab mertansine) is an antibody-drug conjugate composed of a humanized antibody that specifically binds to CD56 (NCAM, neural cell adhesion molecule) and that is conjugated to the maytansinoid, DM1 (a microtubule targeting agent).

PROCEDURES

IMGN901 and DM1-SMe (unconjugated DM1 as a mixed disulfide with thiomethane to cap its sulfhydryl group) were tested in vitro at concentrations ranging from 0.01 nM to 0.1 µM and 0.3 pM to 3 nM, respectively. IMGN901 was tested against a subset of PPTP solid tumor xenografts focusing on those with high CD56 expression.The combination of IMGN901 with topotecan was also evaluated.

RESULTS

Neuroblastoma models expressed CD56 at or above the median expression level for all PPTP xenografts and cell lines. Neuroblastoma cell lines demonstrated relatively low sensitivity to DM1-SMe compared to other cell lines, but the sensitivity of neuroblastoma cell lines to IMGN901 was comparable to that of non-neuroblastoma cell lines. In vivo, objective responses were observed in 9 of 24 (38%) models including, three of seven neuroblastoma xenografts, and two of seven rhabdomyosarcoma xenografts. All xenografts with objective responses showed homogeneous high-level staining by IHC for CD56, but not all xenografts with homogenous high-level staining had objective responses. Combined with topotecan, IMGN901 demonstrated therapeutic enhancement against two of four neuroblastoma models.

CONCLUSIONS

IMGN901 has anti-tumor activity against some CD56 expressing pediatric cancer models. High expression of CD56 is a biomarker for in vivo response, but resistance mechanisms to IMGN901 in some high CD56 expressing lines need to be defined.

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

BACKGROUND

Antimitotic agents are essential components for curative therapy of pediatric acute leukemias and many solid tumors. Eribulin is a novel agent that differs from both Vinca alkaloids and taxanes in its mode of binding to tubulin polymers.

PROCEDURES

Eribulin was tested against the PPTP in vitro cell line panel at concentrations from 0.1 nM to 1.0 μM and against the PPTP in vivo xenograft panels at a dose of 1 mg/kg (solid tumors) or 1.5 mg/kg (ALL models) using a q4dx3 schedule repeated at Day 21.

RESULTS

In vitro eribulin demonstrated cytotoxic activity, with a median relative IC50 value of 0.27 nM, (range <0.1-14.8 nM). Eribulin was well tolerated in vivo, and all 43 xenograft models were considered evaluable for efficacy. Eribulin induced significant differences in event-free survival (EFS) distribution compared to control in 29 of 35 (83%) of the solid tumors and in 8 of 8 (100%) of the ALL xenografts. Objective responses were observed in 18 of 35 (51%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in panels of Wilms tumor, Ewing sarcoma, rhabdomyosarcoma, glioblastoma, and osteosarcoma xenografts. All eight ALL xenografts achieved CR or MCR.

CONCLUSIONS

The high level of activity observed for eribulin against the PPTP preclinical models makes this an interesting agent to consider for pediatric evaluation. The activity pattern observed for eribulin in the solid tumor panels is equal or superior to that observed previously for vincristine.

Initial testing (stage 1) of ganetespib, an Hsp90 inhibitor, by the Pediatric Preclinical Testing Program

Ganetespib, an Hsp90 inhibitor, was tested against the PPTP in vitro cell line panel and selected xenografts in vivo, including JAK2- and BRAF-mutated models. Ganetespib demonstrated potent in vitro cytotoxic activity (median rIC50 8.8 nM, range 4.4-27.1 nM). In vivo, ganetespib induced significant differences in EFS distribution for 4 of 11 xenografts. Intermediate activity (EFS T/C > 2) was noted only for the MV4;11 xenograft, and there were no objective responses. Administered as single agents, Hsp90 inhibitors examined by the PPTP have shown limited evidence for a therapeutic window against both solid tumor and leukemia pediatric preclinical models.

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

BACKGROUND

The DNA methylating agent temozolomide was developed primarily for treatment of glioblastoma. However, preclinical data have suggested a broader application for treatment of childhood cancer. Temozolomide was tested against the PPTP solid tumor and ALL models.

PROCEDURES

Temozolomide was tested against the PPTP in vitro panel at concentrations ranging from 0.1 to 1,000 µM and was tested against the PPTP in vivo panels at doses from 22 to 100 mg/kg administered orally daily for 5 days, repeated at day 21.

RESULTS

In vitro temozolomide showed cytotoxicity with a median relative IC50 (rIC50 ) value of 380 µM against the PPTP cell lines (range 1 to > 1,000 µM). The three lines with rIC50 values lesser than 10 µM had low MGMT expression compared to the remaining cell lines. In vivo temozolomide demonstrated significant toxicity at 100 mg/kg, but induced tumor regressions in 15 of 23 evaluable solid tumor models (13 maintained CR [MCR], 2 CR) and 5 of 8 ALL models (3 MCR, 2 CR). There was a steep dose response curve, with lower activity at 66 mg/kg temozolomide and with tumor regressions at 22 and 44 mg/kg restricted to models with low MGMT expression.

CONCLUSIONS

Temozolomide demonstrated high level antitumor activity against both solid tumor and leukemia models, but also elicited significant toxicity at the highest dose level. Lowering the dose of TMZ to more closely match clinical exposures markedly reduced the antitumor activity for many xenograft lines with responsiveness at lower doses closely related to low MGMT expression.

Initial testing (stage 1) of the phosphatidylinositol 3' kinase inhibitor, SAR245408 (XL147) by the pediatric preclinical testing program

BACKGROUND

Activation of the PI3 kinase pathway occurs frequently in many adult cancers and is implicated in tumor cell proliferation, survival, and resistance to chemotherapy and radiotherapy. However, less is known regarding the relevance of this pathway in pediatric cancers. Here we have evaluated SAR245408, a novel small molecule PI3K inhibitor, against childhood cancer cell lines and xenografts.

PROCEDURES

SAR245408 was tested against the PPTP in vitro cell line panel at concentrations from 10 to 100 µM and against the PPTP in vivo xenograft panels at a dose of 100 mg/kg administered orally daily × 14.

RESULTS

In vitro SAR245408 demonstrated cytotoxic activity, with a median relative IC50 value of 10.9 µM (range 2.7-24.5 µM). SAR245408 was well tolerated in vivo, and all 44 tested xenograft models were evaluable for efficacy. SAR245408 induced significant differences in EFS distribution compared to control in 29 of 37 (79%) of solid tumor xenografts and in two of seven (29%) ALL xenografts. SAR245408 induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity (EFS T/C > 2) in 4 of 37 (11%) solid tumor xenografts. Intermediate EFS T/C activity was also observed for two of seven (29%) evaluable ALL xenografts. Objective responses were not observed for solid tumor or for ALL xenografts.

CONCLUSIONS

Under the conditions evaluated in this study, SAR245408 achieved modest single-agent activity against most PPTP preclinical models. Further exploration of SAR245408 in combination with standard agents or with other signaling inhibitors could be considered.

Initial testing of the MDM2 inhibitor RG7112 by the Pediatric Preclinical Testing Program

BACKGROUND

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 was selected for evaluation by the Pediatric Preclinical Testing Program (PPTP) due to the relatively low incidence of p53 mutations in pediatric cancers compared with adult malignancies.

PROCEDURES

RG7112 and its inactive enantiomer RG7112i were evaluated against the 23 cell lines of the PPTP in vitro panel using 96 hours exposure (1 nM to 10 µM). It 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 of observation. Response outcomes were related to MDM2 and p53 expression datasets (http://pptp.nchresearch.org/data.html).

RESULTS

RG7112 demonstrated cytotoxic activity with a lower median IC(50) for p53 WT versus p53 mutant cell lines (approximately 0.4 µM vs. >10 µM, respectively). RG7112 induced tumor growth inhibition meeting criteria for intermediate activity (EFS T/C > 2) in 10 of 26 (38%) solid tumor xenografts. Objective responses included medulloblastoma, alveolar rhabdomyosarcoma, Wilms, rhabdoid and Ewing sarcoma xenografts. For the ALL panel, there was one partial response, five complete responses and one maintained complete response. The ALL xenografts expressed the highest levels of p53 among the PPTP panels.

CONCLUSIONS

RG7112 induced tumor regressions in solid tumors from different histotype panels, and exhibited consistent high-level activity against ALL xenografts. This high level of activity supports prioritization of RG7112 for further evaluation.

Initial testing (stage 1) of the cyclin dependent kinase inhibitor SCH 727965 (dinaciclib) by the pediatric preclinical testing program

BACKGROUND

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.

PROCEDURES

SCH 727965 was tested against the PPTP in vitro panel using 96 hours 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.

RESULTS

The median IC(50) value for the cell lines was 7.5 nM, with less than fourfold range between the minimum (3.4 nM) and maximum (11.2 nM) IC(50) 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.

CONCLUSIONS

SCH 727965 shows an interesting pattern of activity suggesting its potential applicability against selected childhood cancers, particularly leukemias.

Evaluation of arsenic trioxide by the pediatric preclinical testing program with a focus on Ewing sarcoma

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 IC(50) value of 0.9 µM, with Ewing sarcoma cell lines having IC(50) 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.

Initial testing (stage 1) of SGI-1776, a PIM1 kinase inhibitor, by the pediatric preclinical testing program

The PIM kinase inhibitor, SGI-1776, was tested against the PPTP in vitro (1.0 nM-10 µM) and in vivo panels (148 mg/kg daily × 5 days for 3 weeks). SGI-1776 exhibited cytotoxic activity in vitro with a median relative IC(50) 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).

Initial testing of the multitargeted kinase inhibitor pazopanib by the Pediatric Preclinical Testing Program

Pazopanib is an oral angiogenesis inhibitor targeting vascular growth factor receptor-1, -2, and -3, platelet derived growth factor receptor-α, platelet derived growth factor receptor-β, and KIT that has demonstrated activity against a variety of adult cancer xenografts. Pazopanib was tested against a panel of pediatric rhabdomyosarcoma and Ewing sarcoma xenografts at a dose of 108 mg/kg/day or 100 mg/kg twice daily, administered orally for 28 days. While no objective responses were observed, pazopanib induced statistically significant differences in event-free survival compared to controls in approximately one-half of the sarcoma xenograft models tested. Though well tolerated, pazopanib showed limited activity against the sarcoma models evaluated, with the best tumor responses being growth delay.

Testing of the Akt/PKB inhibitor MK-2206 by the Pediatric Preclinical Testing Program

BACKGROUND

MK-2206 is a small molecule allosteric inhibitor of Akt/PKB that is undergoing clinical trials for treatment of cancer.

PROCEDURES

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.

RESULTS

In vitro, the median relative IC(50) value for MK-2206 was 2.2 µM. Four cell lines with IC(50) 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 twofold 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.

CONCLUSIONS

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.

Initial testing of JNJ-26854165 (Serdemetan) by the pediatric preclinical testing program

JNJ-26854165 was originally developed as an activator of p53 capable of inducing apoptosis in cancer cell lines. In vitro, JNJ-26854165 demonstrated cytotoxic activity. The ALL cell line panel had a significantly lower median IC(50) (0.85 µM) than the remaining cell lines. In vivo JNJ-26854165 induced significant differences in EFS distribution compared to control in 18 of 37 solid tumors and in 5 of 7 of the evaluable ALL xenografts. Objective responses were observed in 4 of 37 solid tumor xenografts, and 2 of 7 ALL xenografts achieved PR or CR. Responses were noted in xenografts with both mutant and wild-type p53.

Initial testing of the investigational NEDD8-activating enzyme inhibitor MLN4924 by the pediatric preclinical testing program

BACKGROUND

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.

PROCEDURES

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.

RESULTS

The median relative IC(50) for MLN4924 against the PPTP cell lines was 143 nM, (range: 15-678 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 Wilm's 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.

CONCLUSIONS

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.

Initial testing (Stage 1) of AT13387, an HSP90 inhibitor, by the pediatric preclinical testing program

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 or 60 mg/kg) administered orally twice weekly. In vitro AT13387 showed a median EC(50) 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.

Initial testing of the CENP-E inhibitor GSK923295A by the pediatric preclinical testing program

BACKGROUND

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.

PROCEDURES

GSK923295A was evaluated against the 23 cell lines in the Pediatric Preclinical Testing Program (PPTP) in vitro panel using 96 hr 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 days 1-3 and 8-10 schedule that was repeated at day 21. The agent was administered via the intraperitoneal (i.p.) route at a daily dose of 125 mg/kg.

RESULTS

The median IC(50) for all PPTP cell lines was 27 nM, with the median IC(50) 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 event-free survival 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, and 3 with complete response (CR).

CONCLUSIONS

GSK923295A demonstrated significant antitumor activity against solid tumor models, inducing CRs in Ewing sarcoma, rhabdoid, and rhabdomyosarcoma xenografts. These results suggest that CENP-E may be a valuable therapeutic target in pediatric cancer.

Combination testing (Stage 2) of the Anti-IGF-1 receptor antibody IMC-A12 with rapamycin by the pediatric preclinical testing program

BACKGROUND

IMC-A12, a fully human antibody that blocks ligand binding to the Type 1 insulin-like growth factor receptor, and rapamycin, a selective inhibitor of mTORC1 signaling, have both demonstrated significant antitumor activity against PPTP solid tumor models. Here we have evaluated antitumor activity of each agent individually and in combination against nine tumor models.

PROCEDURES

IMC-A12 was administered twice weekly and rapamycin was administered daily for 5 days per week for a planned 4 weeks. The impact of combining IMC-A12 with rapamycin was evaluated using two measures: (1) the "therapeutic enhancement" measure, and (2) a linear regression model for time-to-event to formally evaluate for sub- and supra-additivity for the combination compared to the agents used alone.

RESULTS

Two osteosarcomas, and one Ewing sarcoma of the nine xenografts tested showed therapeutic enhancement. The combination effect was most dramatic for EW-5 for which PD2 responses of short duration were observed for both single agents and a prolonged PR response was observed for the combination. Both OS-2 and OS-9 showed significantly longer times to progression with the combination compared to either of the single agents, although objective response criteria were not met.

CONCLUSIONS

The combination of IMC-A12 with rapamycin was well tolerated, and induced tumor responses that were superior to either single agent alone in several models. These studies confirm reports using other antibodies that inhibit IGF-1 receptor-mediated signaling that indicate enhanced therapeutic effect for this combination, and extend the range of histotypes to encompass additional tumors expressing IGF-1R where this approach may be effective.

Initial testing (stage 1) by the pediatric preclinical testing program of RO4929097, a γ-secretase inhibitor targeting notch signaling

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.

Initial testing (stage 1) of LCL161, a SMAC mimetic, by the Pediatric Preclinical Testing Program

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 or 75 mg/kg [solid tumors] or 100 mg/kg [ALL]) administered orally twice in a week. LCL161 showed a median relative IC(50) 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 and glioblastoma), but not in ALL xenografts. No objective tumor responses were observed. In vivo LCL161 demonstrated limited single agent activity against the pediatric preclinical models studied.

Combination testing of cediranib (AZD2171) against childhood cancer models by the pediatric preclinical testing program

BACKGROUND

Cediranib (AZD2171) is a potent small molecule inhibitor of vascular endothelial growth factor (VEGF) receptors. Cediranib has demonstrated single agent activity in several adult cancers and is being studied in combination with standard cytotoxic agents in multiple disease settings.

PROCEDURES

Cediranib was tested in vivo against six childhood tumor xenograft models (four sarcomas, one glioblastoma, one neuroblastoma) alone or combined with cyclophosphamide (two models), vincristine (three models) or cisplatin (one model), each administered at its maximum tolerated dose, or rapamycin (six models).

RESULTS

The combination of cediranib with standard cytotoxic agents was superior to the cytotoxic agent used alone for a single xenograft (one of the three xenografts evaluated for the vincristine-cediranib combination). The cediranib-cyclophosphamide combination was inferior to single agent cyclophosphamide in time to event for both models studied and was significantly inferior for one of the models. Cediranib combined with rapamycin was superior to each of the agents used alone in two of the six models and was determined to be additive or supra-additive with rapamycin in four models, although the effects were not large.

CONCLUSIONS

Cediranib combined with cytotoxic chemotherapy agents demonstrated little or no benefit (and in one case was significantly inferior) compared to chemotherapy alone for the six pediatric cancer xenografts studied. By contrast, the combination of cediranib with rapamycin was additive or supra-additive in four of the six models in terms of prolongation of time to event, though tumor regressions were not observed for this combination.