Cell and molecular determinants of in vivo efficacy of the BH3 mimetic ABT-263 against pediatric acute lymphoblastic leukemia xenografts

PURPOSE

Predictive biomarkers are required to identify patients who may benefit from the use of BH3 mimetics such as ABT-263. This study investigated the efficacy of ABT-263 against a panel of patient-derived pediatric acute lymphoblastic leukemia (ALL) xenografts and utilized cell and molecular approaches to identify biomarkers that predict in vivo ABT-263 sensitivity.

EXPERIMENTAL DESIGN

The in vivo efficacy of ABT-263 was tested against a panel of 31 patient-derived ALL xenografts composed of MLL-, BCP-, and T-ALL subtypes. Basal gene expression profiles of ALL xenografts were analyzed and confirmed by quantitative RT-PCR, protein expression and BH3 profiling. An in vitro coculture assay with immortalized human mesenchymal cells was utilized to build a predictive model of in vivo ABT-263 sensitivity.

RESULTS

ABT-263 demonstrated impressive activity against pediatric ALL xenografts, with 19 of 31 achieving objective responses. Among BCL2 family members, in vivo ABT-263 sensitivity correlated best with low MCL1 mRNA expression levels. BH3 profiling revealed that resistance to ABT-263 correlated with mitochondrial priming by NOXA peptide, suggesting a functional role for MCL1 protein. Using an in vitro coculture assay, a predictive model of in vivo ABT-263 sensitivity was built. Testing this model against 11 xenografts predicted in vivo ABT-263 responses with high sensitivity (50%) and specificity (100%).

CONCLUSION

These results highlight the in vivo efficacy of ABT-263 against a broad range of pediatric ALL subtypes and shows that a combination of in vitro functional assays can be used to predict its in vivo efficacy.

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.

Abstract 2745: AKR1C3 is a potential biomarker of T-cell acute lymphoblastic leukemia sensitivity to the pre-prodrug PR-104

Despite the success of current therapies for childhood acute lymphoblastic leukemia (ALL), novel treatments are required to treat high-risk or relapsed patients. PR-104 is a pre-prodrug hydrolyzed in vivo to PR-104A, which is then metabolized under hypoxia by one-electron reductases to DNA cross-linking metabolites. PR-104A is also activated under aerobic conditions by aldo-keto reductase 1C3 (AKR1C3). We previously showed profound in vivo efficacy of PR-104 (550 mg/kg IP weekly x 6) against a panel of T- and B-ALL xenografts derived from direct patient explants in immune-deficient mice. However, testing at doses as low as 10% of the MTD (50-200 mg/kg) showed retention of efficacy against a T-ALL but not a B-ALL xenograft. This study aimed to further evaluate PR-104 as a novel treatment for high-risk T-ALL by testing its in vivo efficacy against a large panel of pediatric ALL xenografts both as a single agent and in combination with established drugs. We also aimed to evaluate AKR1C3 as a biomarker of in vivo PR-104 sensitivity in T-ALL. PR-104A was significantly more cytotoxic in vitro against 8 T-ALL compared to 8 B-ALL xenografts (median IC50 value 9-fold higher in B-ALL; P&lt;0.0001), indicating that the difference in sensitivity is a cell-intrinsic phenomenon. Microarray analysis of gene expression, qRT-PCR and immunoblotting showed that AKR1C3 expression was significantly higher in T-ALL compared with B-ALL xenografts (P&lt;0.01). We also observed a strong correlation between AKR1C3 mRNA and protein expression and enzymatic activity (P&lt;0.0001). Moreover, AKR1C3 protein expression significantly correlated with in vitro sensitivity of xenografts to PR104A as assessed by Alamar blue cytotoxicity assay (P=0.0003). The in vivo efficacy of PR-104 was assessed using stringent objective response criteria modeled after the clinical setting, as well as time to event measurements. PR-104 administered as a single agent at a dose that provides pharmacokinetics that are readily achievable in adult leukemia patients (200 mg/kg weekly x 2) was more effective in inducing regression and progression delay of 3/3 chemoresistant T-ALL xenografts compared with an induction-type regimen of vincristine (0.15 mg/kg weekly x 2), dexamethasone (5 mg/kg daily x 5 x 2) and L-asparaginase (1,000 KU/kg daily x 5 x 2) (VXL). However, no therapeutic enhancement was observed in the combination of PR-104 with VXL. These results indicate that PR-104 shows promise as a novel therapy for the treatment of aggressive and chemoresistant T-ALL, and that AKR1C3 is a potential biomarker of in vivo PR-104 efficacy. The optimal combinations of PR-104 that result in therapeutic synergy with established drugs remain to be defined. Our findings have implications for the clinical development of PR-104, since patients with T-ALL may represent a particularly responsive population. This study was supported by NCI NO1CM42216 and Proacta, Inc.

Citation Format: Donya Moradi Manesh, Hernan Carol, Kathryn Evans, Jennifer Richmond, Stephen Jamieson, William R. Wilson, Peter J. Houghton, Malcolm A. Smith, Richard B. Lock. AKR1C3 is a potential biomarker of T-cell acute lymphoblastic leukemia sensitivity to the pre-prodrug PR-104. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2745. doi:10.1158/1538-7445.AM2013-2745