Hernan Carol

The pediatric preclinical testing program: description of models and early testing results.

The Pediatric Preclinical Testing Program (PPTP) is an initiative supported by the National Cancer Institute (NCI) to identify novel therapeutic agents that may have significant activity against childhood cancers. The PPTP has established panels of childhood cancer xenografts and cell lines to be used for in vivo and in vitro testing. These include panels for Wilms tumor, sarcomas (rhabdomyosarcoma, Ewing sarcoma, and osteosarcoma), neuroblastoma, brain tumors (glioblastoma, ependymoma, and medulloblastoma), rhabdoid tumors (CNS and renal), and acute lymphoblastic leukemia (ALL). Here, we describe the characteristics of the in vivo tumor panels and report results for the in vivo evaluation of two standard agents, vincristine and cyclophosphamide.

Initial Testing of the Aurora Kinase A Inhibitor MLN8237 by the Pediatric Preclinical Testing Program (PPTP)

MLN8237 is a small molecule inhibitor of Aurora Kinase A (AURKA) that is currently in early phase clinical testing. AURKA plays a pivotal role in centrosome maturation and spindle formation during mitosis.

Initial testing (stage 1) of a monoclonal antibody (SCH 717454) against the IGF-1 receptor by the pediatric preclinical testing program

SCH 717454 (19D12) is a fully human antibody directed against the insulin‐like growth factor 1 receptor (IGF‐1R), which is implicated in the growth and metastatic phenotype of a broad range of malignancies. The activity of SCH 717454 was evaluated against the in vitro and in vivo panels of the Pediatric Preclinical Testing Program (PPTP).

Initial testing (stage 1) of the mTOR inhibitor rapamycin by the pediatric preclinical testing program

Rapamycin is a highly specific inhibitor of mTOR, a serine/threonine kinase that controls cap‐dependent translation. Here we report the activity of rapamycin against the in vitro and in vivo panels of the Pediatric Preclinical Testing Program (PPTP).

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

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

Initial testing (stage 1) of the BH3 mimetic ABT-263 by the pediatric preclinical testing program.

ABT‐263 is a potent (Ki < 1 nM) small‐molecule BH3 mimetic that inhibits the antiapoptotic proteins Bcl‐2, Bcl‐xL and Bcl‐w. The structurally related Bcl‐2 inhibitor ABT‐737 exhibits single‐agent preclinical activity against lymphoma, small‐cell lung carcinoma, and chronic lymphocytic leukemia and displays synergistic cytotoxicity with chemotherapeutics and radiation.

Pronounced hypoxia in models of murine and human leukemia: high efficacy of hypoxia-activated prodrug PR-104.

Recent studies indicate that interactions between leukemia cells and the bone marrow (BM) microenvironment promote leukemia cell survival and confer resistance to anti-leukemic drugs. There is evidence that BM microenvironment contains hypoxic areas that confer survival advantage to hematopoietic cells. In the present study we investigated whether hypoxia in leukemic BM contributes to the protective role of the BM microenvironment. We observed a marked expansion of hypoxic BM areas in immunodeficient mice engrafted with acute lymphoblastic leukemia (ALL) cells. Consistent with this finding, we found that hypoxia promotes chemoresistance in various ALL derived cell lines. These findings suggest to employ hypoxia-activated prodrugs to eliminate leukemia cells within hypoxic niches. Using several xenograft models, we demonstrated that administration of the hypoxia-activated dinitrobenzamide mustard, PR-104 prolonged survival and decreased leukemia burden of immune-deficient mice injected with primary acute lymphoblastic leukemia cells. Together, these findings strongly suggest that targeting hypoxia in leukemic BM is feasible and may significantly improve leukemia therapy.

Stage 2 combination testing of rapamycin with cytotoxic agents by the pediatric preclinical testing program

Rapamycin demonstrated broad-spectrum tumor growth inhibition activity against the in vivo panels of childhood tumors used in the Pediatric Preclinical Testing Program (PPTP). Here we have evaluated rapamycin combined with agents used frequently in the treatment of childhood malignancies. Rapamycin was tested in vitro against 23 cell lines alone or in combination with melphalan, cisplatin, vincristine, or dexamethasone (leukemic models only). In vivo, the impact of combining rapamycin with a cytotoxic agent 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 supraadditivity for the combination compared to the agents used alone. Combining rapamycin with cytotoxic agents in vitro gave predominantly subadditive or additive effects, except for dexamethasone in leukemia models for which supra-additive activity was observed. In vivo testing demonstrated that therapeutic enhancement was common for rapamycin in combination with cyclophosphamide and occurred for 4 of 11 evaluable xenografts for the rapamycin and vincristine combination. The combinations of rapamycin with either cyclophosphamide or vincristine were significantly more effective than the respective standard agents used alone at their maximum tolerated doses (MTD) for most evaluable xenografts. The combination of rapamycin and cisplatin produced excessive toxicity requiring cisplatin dose reductions, and therapeutic enhancement was not observed for this combination. Addition of rapamycin to either cyclophosphamide or vincristine at their respective MTDs appears promising, as these combinations are relatively well tolerated and as many of the pediatric preclinical models evaluated demonstrated therapeutic enhancement for these combinations. Mol Cancer Ther; 9(1); 101–12

Initial testing (stage 1) of AZD6244 (ARRY‐142886) by the pediatric preclinical testing program

AZD6244 (ARRY‐142886) is a potent small molecule inhibitor of MEK1/2 that is in phase 2 clinical development.

The Anti-CD19 Antibody–Drug Conjugate SAR3419 Prevents Hematolymphoid Relapse Postinduction Therapy in Preclinical Models of Pediatric Acute Lymphoblastic Leukemia

Purpose: Relapsed or refractory pediatric acute lymphoblastic leukemia (ALL) remains a major cause of death from cancer in children. In this study, we evaluated the efficacy of SAR3419, an antibody–drug conjugate of the maytansinoid DM4 and a humanized anti-CD19 antibody, against B-cell precursor (BCP)-ALL and infant mixed lineage leukemia (MLL) xenografts. Experimental Design: ALL xenografts were established as systemic disease in immunodeficient (NOD/SCID) mice from direct patient explants. SAR3419 was administered as a single agent and in combination with an induction-type regimen of vincristine/dexamethasone/l-asparaginase (VXL). Leukemia progression and response to treatment were assessed in real-time, and responses were evaluated using strict criteria modeled after the clinical setting. Results: SAR3419 significantly delayed the progression of 4 of 4 CD19+ BCP-ALL and 3 of 3 MLL-ALL xenografts, induced objective responses in all but one xenograft but was ineffective against T-lineage ALL xenografts. Relative surface CD19 expression across the xenograft panel significantly correlated with leukemia progression delay and objective response measure scores. SAR3419 also exerted significant efficacy against chemoresistant BCP-ALL xenografts over a large (10-fold) dose range and significantly enhanced VXL-induced leukemia progression delay in two highly chemoresistant xenografts by up to 82 days. When administered as protracted therapy following remission induction with VXL, SAR3419 prevented disease recurrence into hematolymphoid and other major organs with the notable exception of central nervous system involvement. Conclusion: These results suggest that incorporation of SAR3419 into remission induction protocols may improve the outcome for high-risk pediatric and adult CD19+ ALL. Clin Cancer Res; 19(7); 1795–805. ©2013 AACR.