Mcl-1 Dependence Predicts Response To Vorinostat and Gemtuzumab Ozogamicin In Acute Myeloid Leukemia

The outcome of older adults with acute myeloid leukemia (AML) using standard curative-intent chemotherapeutics remains dismal because of increasing risks of treatment-related mortality and therapeutic resistance associated with advancing patient age, accumulation of medical comorbidities, and changing disease biology. As a result, current expert guidelines, e.g. by the National Comprehensive Cancer Network (NCCN), recommend that these patients should receive investigational therapies. Still, investigational therapeutics typically exhibit response in only a subset of patients, and factors such as age or cytogenetics are often insufficient to predict treatment success with high accuracy. Here, we utilized BH3 profiling, a method for assessing mitochondrial functionality in apoptosis signaling, as a biomarker strategy for identification of patients likely to exhibit clinical response to an investigational regimen of a histone deacetylase (HDAC) inhibitor, vorinostat, in combination with gemtuzumab ozogamicin (GO), an immunoconjugate consisting of an anti-CD33 antibody and a toxic calicheamicin moiety. Cytotoxic effects of these agents have been shown to involve mitochondrial pathways of apoptosis, providing the scientific rationale for our study.

Thirty-one adults aged 60 years or older received treatment with vorinostat and GO for newly diagnosed AML (NCT00673153). For 26 of these patients, pretreatment peripheral blood mononuclear cell (PBMC) or bone marrow (BM) aspirate specimens were available. Blinded to outcomes, we analyzed these specimens by flow cytometry-based BH3 profiling. This assay indirectly measures induction of mitochondrial outer membrane permeabilization in response to treatment with BH3-only peptides, including activators (e.g. BIM) and sensitizers (e.g. NOXA, PUMA, BAD, HRK, BMF) as a surrogate for the function of Bcl-2 family proteins. Findings from these profiling studies were then correlated with disease characteristics and treatment outcome.

BH3 profiling was technically successful in 23 of 26 tested specimens. Log regression analyses indicated a correlation between priming with NOXA, a selective modulator of the anti-apoptotic protein Mcl-1, and response to induction therapy (i.e. achievement of complete remission [CR]/CRp vs. resistance; p=.027). Using the area under the receiver operating curve (AUC) to quantify the accuracy of outcome prediction, the % priming achieved with NOXA yielded an AUC of 0.83 (95% CI: 0.65-1.00; p=.00042). After adjustment for age, the AUC associated with NOXA priming increased further (AUC=0.88 [0.75-1.00]). The % priming with NOXA was also statistically significantly associated with the duration of overall survival (OS; p=.027), with an AUC of 0.87 (0.64-1.00; p=.0017). Patients in the highest tertile of NOXA priming exhibited a median OS of 453.5 days vs. the other patients median OS of 132 days (p=.12 Mantel-Cox).

Our data show that the degree of priming indicated by NOXA identifies Mcl-1 dependence that is associated with response and outcome of vorinostat/GO in older adults with AML. This finding would be compatible with a pivotal role of Bcl-2 family protein-mediated mitochondrial depolarization for the clinical efficacy of GO and vorinostat, consistent with previous in vitro studies. Importantly, Mcl-1 -dependence as indicated by BH3 profiling of NOXA response may predict response to investigational therapeutic regimens for AML and, if integrated as predictive biomarker, may improve patient outcomes through identifying subsets of patients likely to respond to treatment with HDAC inhibitors and immunoconjugates including calicheamicins when given in combination.

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