ALVOCIDIB SYNERGIZES WITH CYTARABINE AND DAUNORUBICIN (7+3) IN PRECLINICAL MODELS OF ACUTE MYELOID LEUKEMIA
Author(s): ,
Wontak Kim
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Hillary Haws
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Ryan Mangelson
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Peter Peterson
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Clifford Whatcott
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Adam Siddiqui-Jain
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
Steven Weitman
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
,
David Bearss
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
Steven Warner
Affiliations:
Discovery Biology,Tolero Pharmaceuticals, Inc.,LEHI,United States
(Abstract release date: May 18, 2017) EHA Learning Center. Warner S. May 18, 2017; 180678
Dr. Steven Warner
Dr. Steven Warner

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Abstract
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Abstract: E902

Type: Eposter Presentation

Background
Although survival of patients with acute myeloid leukemia (AML) has increased in the years 1975-2011, the 5-year, overall survival of patients with AML remains unacceptably low at an estimated 26% (2011). ‘7+3’ treatment (cytarabine 100-200 mg/m2 + anthracycline [daunorubicin 60-90 mg/m2/day or idarubicin 12 mg/m2/day]) remains the standard induction therapy in AML patients, and has persisted largely unchanged for more than 30 years. There is a significant unmet clinical need for improved therapeutic options in patients with AML. Alvocidib is a CDK9 inhibitor currently in development for the treatment of patients with AML. Alvocidib has previously been studied as part of the ACM regimen, a combination regimen incorporating the time-sequential (TST) administration of alvocidib, cytarabine, and mitoxantrone, in multiple Phase 1 and 2 clinical trials. The ACM regimen has achieved significant improvements in complete response (CR) rates versus 7+3 in previously untreated intermediate and high-risk AML patients. The rationale for time-sequential administration of the ACM regimen was developed with an incomplete understanding of alvocidib’s mechanism of action. TST was based on the expectation that alvocidib would synchronize cells, capitalizing on the S-phase specific activity of cytarabine in the combination. However, rather than cell-cycle inhibition, alvocidib potently induces apoptosis by inhibiting the expression of key anti-apoptotic proteins via CDK9/RNA polymerase II, including MCL-1. With this understanding, we reasoned that alvocidib would also enhance the activity of the 7+3 regimen.

Aims
These studies sought to interrogate the preclinical activity of alvocidib in the context of the 7+3 regimen in models for AML.

Methods
CellTiter-Glo and Caspase-Glo was used for all cell viability and apoptosis assays interrogating alvocidib and 7+3 activity in cell lines, following manufacturer’s protocol. We used RT-PCR to measure mRNA expression of MCL-1 and other markers in response to drug treatment. Protein levels were interrogated using standard immunoblotting techniques. To determine the efficacy of an alvocidib/7+3 combination on tumor growth in vivo, we performed a MV4-11 xenograft mouse study.

Results
Single agent IC50 values of alvocidib, cytarabine, and daunorubicin range in AML cell lines from 2.2 nM to as high as 567 nM in viability assays. In apoptosis (Caspase-Glo) assays, however, we observed modest induction with single agent cytarabine, and good induction with single agent daunorubicin or alvocidib. In the combination, however, we observed very strong synergy with more than two-fold enhanced induction of apoptosis in some treatment groups. As has been previously described, we report here too that alvocidib treatment reduced the expression of MCL-1 protein and mRNA in a time and concentration-dependent fashion in AML cells. We observed this in the 7+3 treatment context as well. In an MV4-11 xenograft model, we observed 21.1 and 48.5% tumor growth inhibition (%TGI) following single agent treatment of daunorubicin or cytarabine, respectively. 1.25 mg/kg alvocidib yielded 60.0 %TGI. The combination of alvocidib, cytarabine, and daunorubicin, however, resulted in tumor regression, yielding a 116.2 %TGI.

Conclusion
Though multiple clinical studies have demonstrated the increased efficacy of the ACM regimen over 7+3 in AML, these studies cannot correctly capture the clinical contribution of alvocidib alone as they do not offer a direct comparison. The current study attempted to interrogate the contribution of alvocidib to the 7+3 induction regimen, in preclinical models. These results provide a clear rationale for a clinical study directly comparing the triple combination to 7+3 alone. Taken together, our results suggest that a combination of alvocidib, cytarabine, and daunorubicin might be a potential clinical regimen in treating frontline AML, offering patients additional treatment options in treating their disease.

Session topic: 3. Acute myeloid leukemia - Biology

Keyword(s): Apoptosis, AML

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