ALBERT

Description: Introduction. Despite considerable efforts towards novel therapeutics research and discovery, outcomes in AML remain poor. Although composite Complete Remission (cCR; CR, CRp, CRi) is routinely used as a measure of therapeutic clinical activity, cCR frequently does not translate to survival benefit. On this basis, the characterization and tracking of minimal residual disease (MRD) has emerged as a tool to help better define the depth of such cCR to offer prognostic utility on AML patients likely to experience survival benefit from a given experimental therapeutic. The MDM2 antagonist idasanutlin has shown promising clinical activity in AML. Idasanutlin enhances p53 activity through antagonism of the MDM2:p53 interaction. Disruption of this protein:protein interaction inhibits MDM2 targeting of p53 for ubiquitination and degradation, thus stabilizing p53 protein to exert tumor suppressor transcriptional regulation and induction of apoptotic pathways. Patients and Methods. Trial NP28679 (NCT01773408) is a Phase 1/1b study evaluating idasanutlin as monotherapy or in combination with cytarabine in relapsed or refractory AML patients with safety as primary and complete remission as secondary endpoints, respectively (Martinelli, EHA, 2016.) Duration of response was available as exploratory clinical data for a subset of patient. Patients' pre-treatment bone marrow aspirate specimens were evaluated by multiparametric flow cytometry using an 18 marker surface antigen-based panel. MRD assessment occurred per protocol recommendation at the time of hematological malignancy response assessment (HMRA) at Day 28 and for those patients initially experiencing cCR at each subsequent HMRA. Further flow cytometry analyses were conducted for expression changes of known p53 regulated proteins in CD45+(dim) blasts correlating with drug exposure, consistent with mechanistic engagement. Results. PFS analyses for cCR patients versus non-CR Kaplan-Meier plots indicate the median for responders is 315d (95%CI: 282, NA) versus non-responders is 43.5d (95%CI: 30, NA). When MRD1% is applied as a cut-point, analytics show a statistical association with median PFS (log-rank p-value 〈 .001) at 367d (95%CI: 219, NA) for 1% is 84d (95%CI: 30, NA.) Median MRD values for CR/CRp/CRi vs PR/HI vs PD are 0.42%, 1.79%, and 19.16%, respectively, again consistent with MRD serving as a surrogate for clinical activity (log rank test for trend p-value = .001) Additionally, multiparametric flow cytometry analysis of idasanutlin pharmacodynamic (PD) protein expression changes comparing pretreatment patient blood specimens to 24 hours following first dose administration indicates that increases in both p53 and MDM2 in CD45+(dim) blasts is associated with steady state drug exposure levels ([Spearman's Correlation =0.27; p=.013] and [Spearman's Correlation=0.24; p=.026,] respectively.) Interestingly, these changes in protein expression for p53 and MDM2 are associated with orthologous PD changes in serum protein macrophage inhibitory cytokine 1 (MIC-1) ([Spearman's Correlation=0.23; p=.035] and [Spearman's Correlation=0.22; p=.042,] respectively.) These PD changes are mechanistically consistent with enhanced p53 resulting from diminished MDM2 ubiquitination and degradation of p53. Conclusions. In summary, the results presented here are consistent with multiparametric flow cytometry MRD assessment as an early indication aligning with cCR in relapsed/refractory AML patients treated with idasanutlin. Further, assessment for association with progression-free survival indicates that the lowest quartile patients by MRD flow cytometry measurement (1%). As such, the data presented here support inclusion of MRD assessment by flow cytometry as a prognostic indicator to provide guiding information for assignment of depth of AML patient response. We will continue to monitor this biomarker for diagnostic potential as a prognostic indicator of survival-based outcomes in future randomized clinical studies of idasanutlin. Disclosures Lanza: Roche-Genentech: Employment. Martinelli:Pfizer: Consultancy, Speakers Bureau; MSD: Consultancy; Novartis: Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Genentech: Consultancy; Celgene: Consultancy, Speakers Bureau; Ariad: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; BMS: Speakers Bureau. Yee:Novartis Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding. Jukofsky:Roche Pharma: Employment. Reis:Roche Pharma: Employment. Blotner:Roche Pharma: Employment. Drummond:Pfizer: Honoraria, Speakers Bureau; celgene: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Roche: Honoraria, Speakers Bureau. Vey:Sunesis: Honoraria. Dickinson:GlaxoSmithKline: Consultancy, Research Funding. Kelly:Novartis: Consultancy, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Consultancy, Speakers Bureau. Theron:Roche Pharma: Employment. Venstrom:Roche-Genentech: Employment. Middleton:Roche Pharma: Employment. Chen:Roche Pharma: Employment. Kinnersley:Roche-Genentech: Employment, Equity Ownership. Nichols:Roche Pharma: Employment. Pierceall:Roche Pharma: Employment.

Description: Introduction. Despite years of translational research and discovery, outcomes in Acute Myeloid Leukemia remain poor. The MDM2 antagonist idasanutlin has shown promising clinical activity in solid tumors and acute leukemias. Idasanutlin enhances the activity of the tumor suppressor, p53, through antagonism of MDM2:p53 interaction. Such protein:protein disruption abolishes MDM2 targeting of p53 for ubiquitination and degradation. Subsequent stabilization of the p53 protein allows it to exert tumor suppressor transcriptional regulation and induction of apoptotic pathways. Identification of patients in whom functional p53 activation drives efficacy may translate into improved outcomes for patients treated with idasanutlin. Patients and Methods. Trial NP28679 (NCT01773408) is a Phase 1/1b study evaluating idasanutlin (as monotherapy or in combination with cytarabine) in relapsed or refractory AML patients, with clinical response as the primary endpoint. To identify biomarkers of response, patients' pre-treatment peripheral blood specimens were evaluated for MDM2 protein expression levels in leukemic blasts and leukemic stem cells. Association of MDM2 percent cell positivity with clinical outcomes was evaluated using intracellular flow cytometry gated on CD45dim leukemic blasts and CD45dim/CD117+/CD34+ leukemic stem cells. Results. We observed in a proof-of-principle training data set that MDM2 expression in leukemic blasts was associated with patients more likely to exhibit Complete Remission (CR, CRp, CRi) versus Progressive Disease (PD, HI, PR) [n=61; Wilcoxon p = .0041 (AUC = .74; 95%CI[.57, .91])] TP53 mutational status alone was not tightly associated with patient response (Fisher's Exact Test p = .19 [AUC = .60; 95%CI [.52,.67.])] When MDM2 protein expression and TP53 mutational status were analyzed as co-variates, an enhanced association with patient CR was observed (AUC = .76; 95% CI [.59, .93.]) A separate group of patients treated with an optimized idasanutlin formulation was utilized as a validation set. Association of CR with MDM2 expression in blasts was also shown in this separate patient population [n=24; Wilcoxon p = .0052 (AUC = .82; 95% CI [.64, 1.00.]) Comparable results were observed for proof-of-principle and validation set analyses of response association with MDM2 protein expression in AML patients CD45dim/CD117+/CD34+ stem cell subpopulations. Conclusions. In summary, training and validation sets reveal that MDM2 protein expression in leukemic blasts and stem cells are associated with idasanutlin-induced CR in patients with AML. We will continue to monitor this potentially predictive biomarker in future randomized clinical studies of idasanutlin. On a broader level, the data presented here support the concept that leukemic blasts may be "oncogene-addicted" to MDM2 in AML, i.e. that AML tumor cells may rely on a dominant oncogene for growth and survival, such that inhibition of the function of this specific oncogene is sufficient to halt the neoplastic phenotype. Thus, the concept of oncogene addiction may apply not only to mutated kinases but also to ubiquitin ligases such as MDM2. Disclosures Reis: Roche Pharma: Employment, Equity Ownership. Jukofsky:Roche Pharma: Employment, Equity Ownership. Chen:Roche Pharma: Employment, Equity Ownership. Martinelli:BMS: Speakers Bureau; MSD: Consultancy; Roche: Consultancy; ARIAD: Consultancy; Novartis: Speakers Bureau; Pfizer: Consultancy. Zhong:Roche Pharma: Employment, Equity Ownership. So:Roche Pharma: Employment, Equity Ownership. Drummond:Baxalta: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees. Assouline:Pfizer: Consultancy; BMS: Consultancy; Novartis: Consultancy. Hashemyan:Roche Pharma: Employment, Equity Ownership. Theron:Roche Pharma: Employment, Equity Ownership. Blotner:Roche Pharma: Employment, Equity Ownership. Rueger:Roche Pharma: Employment, Equity Ownership. Middleton:Roche Pharma: Employment, Equity Ownership. Vey:Celgene: Honoraria; Roche: Honoraria; Janssen: Honoraria. Nichols:Roche Pharma: Employment, Equity Ownership. Chen:Roche Pharma: Employment, Equity Ownership. Pierceall:Roche Pharma: Employment, Equity Ownership.