Previous studies have demonstrated the importance of energy metabolism as it relates to numerous aspects of leukemia stem cell (LSC) biology. Specifically, in acute myelogenous leukemia (AML), it has been shown that LSCs have a unique reliance on oxidative phosphorylation (OXPHOS), and that inhibition of B-cell lymphoma 2 (BCL-2) acts to down-regulate OXPHOS and eradicate LSCs in pre-clinical models. In the clinical setting, when BCL-2 inhibitor venetoclax is combined with azacitidine, high response rates (~80%) in elderly de novo AML patients have been observed (PMID: 29339097). Nonetheless, a significant portion of these patients ultimately experience disease progression. The mechanism of resistance and characteristics of these patients is poorly understood.

Our preliminary data shows that the venetoclax + azacitidine (ven/aza) regimen targets LSCs through alteration of energy metabolism. Specifically, the regimen disrupts the TCA cycle leading to decreases in ATP production and inhibition of OXPHOS. This metabolic targeting is central to ven/aza efficacy and we hypothesize that resistance and progression of AML patients is due to compensatory mechanisms that restore sufficient levels of OXPHOS (PMID:3333149). Investigation of such mechanisms led us to explore the potential activity of MCL1. Previous studies have shown MCL1 can influence venetoclax resistance, however little is known about MCL1's role in metabolism, although a report in breast cancer cells suggests MCL1 modulates OXPHOS (PMID: 28978427). In leukemia, MCL1 expression has been shown to be partially upregulated through mutations in protein tyrosine phosphatase non- receptor type 11 (PTPN11), and PTPN11 mutations have been shown to increase LSC frequency. Thus, we hypothesized that PTPN11 mutations may confer resistance to venetoclax-based regimens at least partially by up-regulation of MCL1.

To test this hypothesis, we investigated the relationship between PTPN11 mutations, MCL1, and the metabolic phenotype. In comparison to specimens with a wild type allele, LSCs isolated from PTPN11 mutant patient specimens showed increased levels of OXPHOS as well as glycolysis, amino acids, and fatty acids, suggesting an ability to utilize multiple energy sources for survival. PTPN11 mutant specimens also show decreased sensitivity to venetoclax, suggesting OXPHOS is not affected by venetoclax to the same degree as PTPN11 wild type specimens (fig. 1). Furthermore, when we introduced a mutated allele of PTPN11 into a primary AML specimen we observed increased oxidative phosphorylation and glycolysis, which correlated with decreased in vitro sensitivity to venetoclax (fig. 2).

To test the potential role of MCL1 in PTPN11 mutant specimens, we employed a small molecule MCL-1 inhibitor. Metabolic analysis of specimens treated with the MCL-1 inhibitor showed decreased OXPHOS in PTPN11 mutant specimens (fig 3). Further, PTPN11 mutant specimens exhibit increased sensitivity to the MCL-1 inhibitor (fig. 4).

To investigate a potential mechanistic link to clinical observations, we next examined 45 older, previously untreated AML patients from our institution who received ven/aza, both in the context of the multi-institutional study NCT02203773 (N=33) and with off-label use (N=12). Of 12 variables examined, only the presence of PTPN11 predicted shorter response duration (table 1). In addition, of the 9 patients who progressed ven/aza, 2 (22%) acquired PTPN11 mutations upon progression, further suggesting PTPN11 may represent a resistance mechanism to this regimen. Notably, PTPN11 is not preferentially detected in patients who progress after regimens other than ven/aza.

In conclusion, AML containing PTPN11 mutations exhibit a unique energy metabolism profile. These specimens also appear to have increased sensitivity to MCL-1 inhibitors. The presence of PTPN11 mutations represents both a novel method for predicting response to ven/aza and a potential strategy for targeting patients who progress. We propose that addition of an MCL-1 inhibitor for treatment of AML patients bearing PTPN11 or related mutations may increase therapeutic responses.

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Disclosures

Savona:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Consultancy. Fesik:Boehringer Ingelheim: Consultancy. Pollyea:Celyad: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Curis: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy.

Topics:
azacitidine, leukemia, myelocytic, acute, mutation, protein tyrosine phosphatase, non-receptor type 11, ptpn11 gene, venetoclax, leukemia, amino acids, breast cancer cells, disease progression

Author notes

*

Asterisk with author names denotes non-ASH members.

© 2018 by The American Society of Hematology
2018
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