Recurrent mutations at R140 and R172 in isocitrate dehydrogenase 2 (IDH2) occur in many cancers, including ∼12% of acute myeloid leukemia (AML). In preclinical models these mutations cause ...accumulation of the oncogenic metabolite R-2-hydroxyglutarate (2-HG) and induce hematopoietic differentiation block. Single-agent enasidenib (AG-221/CC-90007), a selective mutant IDH2 (mIDH2) inhibitor, produced an overall response rate of 40.3% in relapsed/refractory AML (rrAML) patients with mIDH2 in a phase 1 trial. However, its mechanism of action and biomarkers associated with response remain unclear. Here, we measured 2-HG, mIDH2 allele burden, and co-occurring somatic mutations in sequential patient samples from the clinical trial and correlated these with clinical response. Furthermore, we used flow cytometry to assess inhibition of mIDH2 on hematopoietic differentiation. We observed potent 2-HG suppression in both R140 and R172 mIDH2 AML subtypes, with different kinetics, which preceded clinical response. Suppression of 2-HG alone did not predict response, because most nonresponding patients also exhibited 2-HG suppression. Complete remission (CR) with persistence of mIDH2 and normalization of hematopoietic stem and progenitor compartments with emergence of functional mIDH2 neutrophils were observed. In a subset of CR patients, mIDH2 allele burden was reduced and remained undetectable with response. Co-occurring mutations in NRAS and other MAPK pathway effectors were enriched in nonresponding patients, consistent with RAS signaling contributing to primary therapeutic resistance. Together, these data support differentiation as the main mechanism of enasidenib efficacy in relapsed/refractory AML patients and provide insight into resistance mechanisms to inform future mechanism-based combination treatment studies.
•Enasidenib inhibits mIDH2, leading to leukemic cell differentiation with emergence of functional mIDH2 neutrophils in rrAML patients.•RAS pathway mutations and increased mutational burden overall are associated with a decreased response rate to mIDH2 inhibition.
Data concerning the treatment approach and clinical outcomes in younger patients with myelodysplastic syndromes (MDS) are lacking. Furthermore, published results from genomic profiling in the young ...adult MDS population are few. We identified patients aged 20–50 at diagnosis evaluated for de novo MDS at our institution over a 32-year period. Clinical information and results from sequencing panels were extracted for analysis. 68 eligible patients were found, including 32% with multilineage dysplasia and 29% with excess blasts-2 WHO subtypes. Revised International Prognostic Scoring System for MDS (IPSS-R) categorization had 47% high/very high-risk, and this classification held prognostic significance. The median overall survival was 59 months, and most patients (75%) underwent allogeneic hematopoietic cell transplantation (alloHCT). Thirty-four patients had mutational profiling; the most commonly mutated gene was TP53 and most commonly altered gene category was epigenetic regulators. Younger patients with de novo MDS represented a unique subset with high-risk disease features (adverse cytogenetics, higher R-IPSS) frequently observed along with alterations in TP53 and genes related to epigenetic and transcription pathways.
•Younger patients with de novo MDS frequently exhibit high-risk disease features.•Most such patients are treated with allogeneic hematopoietic cell transplantation.•Epigenetic regulators and transcription/DNA repair genes were commonly mutated.
Xenotransplantation of primary AML samples into immunodeficient mice (PDX models) represents a unique opportunity for pre-clinical testing on a group of primary human samples that possess defined ...genomic lesions. However, given recent recognition that multiple genomically distinct sub-clones can exist in AML, there is a risk that there may be selection for sub-clones from the transplanted sample that might not fully represent the patient’s disease.
We transplanted 160 (70 T-ALL 56 AML, 32 B-ALL, 2 MLL) patient samples of which 120 engrafted into at least 1 irradiated NSG mouse. 45 AML samples engrafted with a median latency 107+/-41 days. Transplantation of 6 PDX AML samples resulted in immunophenotypically identical disease within 87+/-35 days. 2 MLL samples engrafted in 100% of mice with a median latency of 103+/-13 days. 25 B-ALL samples engrafted with a median latency of 95+/-44 days. Secondary transplantation of 3 PDX B-ALL samples resulted in engraftment of leukemia cells with an identical immunophenotype in 100% of transplanted mice within 52+/-3 days. 48 T-ALL samples engrafted in at least one mouse within 50 days. Secondary transplantation of a single T-ALL PDX sample resulted in 100% engraftment within 31+/-10 days.
Genomic DNA and total RNA were isolated from 150 (AML: 16Pt+33PDX; MLL 2Pt+6PDX; B-ALL 17Pt+38PDX; T-ALL 19Pt+19PDX) samples. Adaptor ligated sequencing libraries were captured by solution hybridization using baitsets for 405 cancer-related genes and selected introns for 31 genes frequently rearranged for DNA-seq, and 405 cancer-related and 265 genes frequently rearranged for RNA-seq. All libraries were sequenced averaging >500x for DNA and >6M total pairs for RNA (HiSeq). We detected on average 23+/-12 including a mean 5+/-4 known pathogenic variants such as CDKN2A/B deletion (20/13); FLT3 (SNV & -ITD) and NOTCH (11 ea); WT1 and TP53 (10 ea); NRAS (9); PTPN11 (7); NPM1c, PTEN, and KRAS (6) DNMT3A, IDH1/2, and ASXL1 (5 ea); FBXW7, CEBPA, and TET2 (4 ea); PHF6 and NF1 (3 ea); IKZF1, ATM, and JAK2 (2 ea). Analyses of fusion RNA molecules detected known fusions: MLL-AF4 (4); MLL-AF9 (2), CRLF2-P2RY8, ETV6-RUNX1 or TEL-AML1, PBX1-TCF3 (2 ea); MLL-AF10, MLL-ELL, MLL-EP300, MLL-PTD, BCR-ABL, BCL2-IGK, MYH11-CBFB, along with novel fusions: TCF3-OAZ1, RB1-RCBTB2, PAX5-FLI1, and PAX5-MSI2.
The mutations found in the 54 patient samples were consistently identified in the 96 PDX, however some cases showing variation in allele frequency between diagnostic and engrafted samples. Collectively, all 1420 and 288 disease relevant variant allele frequency (VAF) correlated significantly between patient and PDX samples (R2=0.55, R2=0.43), respectively. We then assessed VAF changes from diagnostic to PDX sample as a measure of clonal concordance. Diagnostic and PDX sample were considered discordant if at least one disease relevant VAF demonstrated significant variation between these samples, accounted for small variability of infrequent variances considering SD of sequencing detection. 31 samples were scored as concordant and 23 as discordant which were similarly distributed between disease lineages and did not correlate with diseases status, future relapse or overall survival.
Using the same rules we further accessed concordance only between PDX samples in 23 cases when patient samples were transplanted into multiple mice. All 10 groups of PDX samples that were concordant with patient samples were also concordant within the groups. 5 groups of PDX samples that were discordant with patient samples were concordant within groups. 8 groups of PDX samples that were discordant with patient samples were also discordant within their groups. Overall 15 samples produced concordant engraftment in mice and 8 samples produced discordant engraftment. We hypothesized that specific genomic lesions in the 8 groups might underline this discordance. Mutations of FLT3, RAS, TP53, PTPN11 and NOTCH1 correlated with clonal discordance.
These findings show that the leukemias that are engrafted in mice mirror the genomic diversity of primary leukemia samples, and that the majority of PDX samples have a genotype similar to that observed in the clinical isolate. More importantly, our data demonstrate the feasibility of developing a large, genetically annotated bank of PDX leukemia models that can be used to test and credential novel therapeutics that target driver mutations in different leukemia subsets.
Stein:Seattle Genetics, Inc.: Research Funding; Janssen Pharmaceuticals: Consultancy. Wang:Foundation Medicine Inc: Employment. Miller:Foundation Medicine: Employment. Armstrong:Epizyme: Consultancy.
Xenotransplantation of primary AML samples into immunodeficient mice (PDX models) represents a unique opportunity for pre-clinical testing on a group of primary human samples that possess defined ...genetic lesions. However, given our recent recognition that multiple genetically distinct subclones can exist in AML, there is a risk that there may be selection for sub-clones from the xenotransplanted sample that might not fully represent the patient's disease.
We sought to establish a collection of genetically defined AML samples capable of engraftment in immunodeficient mice. We transplanted 30 AML patient samples; within 150 days (median 91 days) post transplantation 12 samples produced human CD45+ CD33+ CD19- CD3- engraftment in one or multiple NSG mice. Median patient sample amplification in 25 mice was 21 fold.
Genomic DNA and total RNA was isolated from 7 AML patient samples (3 diagnostic samples from patients who remain in remission; 2 diagnostic samples from patients who later relapsed, 2 diagnostic samples from patients with refractory disease) and 14 matched xenotransplanted samples (2 mice per patient sample). Adaptor ligated sequencing libraries were captured by solution hybridization using two custom baitsets targeting 374 cancer-related genes and 24 genes frequently rearranged for DNA-seq, and 272 genes frequently rearranged for RNA-seq. All captured libraries were sequenced to high depth (Illumina HiSeq), averaging >499x for DNA and >20,000,000 total pairs for RNA, to enable the sensitive and specific detection of genomic alterations. The mutations found in the 7 diagnostic samples were consistently identified in the 14 engrafted AML samples, but with some cases showing variation in allele frequency between diagnostic and engrafted samples. This finding shows that the human disease that engrafted in mice mimics the genetic makeup of the disease found in patients.
We then assessed for allele frequency (AF) changes from diagnostic to xenografted sample as a measure of clonal progression. Clonal progression was defined as emergence of a clone carrying a novel genetic variant in the xenografted sample as compared to the diagnostic patient sample. Five patient samples (from 10 mice) did not show emergence of novel genetic lesions. In this group 2 patients had refractory disease and 3 patients remain in remission. Two patient samples (from 4 mice) demonstrated apparent emergence of novel genetic lesions not detected in diagnostic patient samples. Both of these patients have relapsed since the diagnostic samples were acquired. In the first case, both xenotransplanted mice engrafted with disease carrying NRAS N12S mutation (AF 0.05 and 0.09), which subsequent evaluation revealed to be present below the limit-of-detection (AF 0.004) in the clinical isolate obtained from patient presentation. We are currently conducting the same analysis on the relapsed sample from this patient. In the second case, both mice engrafted with disease carrying PTPN11 E76V (AF 0.03 and 0.0016) while the patient diagnostic sample did not contain any evidence of the alteration at 718x unique sequence coverage.
Of note, one xenografted sample had an IDH1 R132C and another had IDH2 R140Q mutation, both of which have previously been shown to play a role in AML pathogenesis. Available AML cell lines do not carry IDH1/2 mutations, making it challenging to test IDH1/2 inhibitors in pre-clinical settings. These xenografted samples offer an opportunity to test such inhibitors.
Overall we conclude that the xenotransplanted samples possess the diversity of genetic abnormalities found in diagnostic AML samples and thus can be used to assess efficacy of novel targeted therapies. We would like to further investigate a model in which the absence of clonal progression in xenografted samples would predict a better patient outcome, while emergence of novel clones might indicate an increased potential for relapse. We are currently expanding the study to include more diagnostic, xenotransplanted and relapsed samples to assess the associations between the ability of a sample to engraft in mice with clinical outcome and genetic/epigenetic lesions.
Armstrong:Epizyme Inc.: Has consulted for Epizyme Inc. Other.
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