Neil P. Shah

Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia

Through sequencing analysis of blood or bone marrow samples from patients with chronic myeloid leukemia, we identified BCR-ABL kinase domain mutations in 29 of 32 patients whose disease relapsed after an initial response to the tyrosine kinase inhibitor imatinib. Fifteen different amino acid substitutions affecting 13 residues in the kinase domain were found. Mutations fell into two groups-those that alter amino acids that directly contact imatinib and those postulated to prevent BCR-ABL from achieving the inactive conformational state required for imatinib binding. Distinct mutations conferred varying degrees of imatinib resistance. Mutations detected in a subset of patients with stable chronic phase disease correlated with subsequent disease progression. Multiple independent mutant clones were detected in a subset of relapsed cases. Our data support a clonal selection model of preexisting BCR-ABL mutations that confer imatinib resistance.

Dasatinib versus Imatinib in Newly Diagnosed Chronic-Phase Chronic Myeloid Leukemia

BACKGROUND Treatment with dasatinib, a highly potent BCR-ABL kinase inhibitor, has resulted in high rates of complete cytogenetic response and progression-free survival among patients with chronic myeloid leukemia (CML) in the chronic phase, after failure of imatinib treatment. We assessed the efficacy and safety of dasatinib, as compared with imatinib, for the first-line treatment of chronic-phase CML. METHODS In a multinational study, 519 patients with newly diagnosed chronic-phase CML were randomly assigned to receive dasatinib at a dose of 100 mg once daily (259 patients) or imatinib at a dose of 400 mg once daily (260 patients). The primary end point was complete cytogenetic response by 12 months, confirmed on two consecutive assessments at least 28 days apart. Secondary end points, including major molecular response, were tested at a significance level of 0.0001 to adjust for multiple comparisons. RESULTS After a minimum follow-up of 12 months, the rate of confirmed complete cytogenetic response was higher with dasatinib than with imatinib (77% vs. 66%, P=0.007), as was the rate of complete cytogenetic response observed on at least one assessment (83% vs. 72%, P=0.001). The rate of major molecular response was higher with dasatinib than with imatinib (46% vs. 28%, P<0.0001), and responses were achieved in a shorter time with dasatinib (P<0.0001). Progression to the accelerated or blastic phase of CML occurred in 5 patients who were receiving dasatinib (1.9%) and in 9 patients who were receiving imatinib (3.5%). The safety profiles of the two treatments were similar. CONCLUSIONS Dasatinib, administered once daily, as compared with imatinib, administered once daily, induced significantly higher and faster rates of complete cytogenetic response and major molecular response. Since achieving complete cytogenetic response within 12 months has been associated with better long-term, progression-free survival, dasatinib may improve the long-term outcomes among patients with newly diagnosed chronic-phase CML. (ClinicalTrials.gov number, NCT00481247.)

Dynamics of chronic myeloid leukaemia

The clinical success of the ABL tyrosine kinase inhibitor imatinib in chronic myeloid leukaemia (CML) serves as a model for molecularly targeted therapy of cancer, but at least two critical questions remain. Can imatinib eradicate leukaemic stem cells? What are the dynamics of relapse due to imatinib resistance, which is caused by mutations in the ABL kinase domain? The precise understanding of how imatinib exerts its therapeutic effect in CML and the ability to measure disease burden by quantitative polymerase chain reaction provide an opportunity to develop a mathematical approach. We find that a four-compartment model, based on the known biology of haematopoietic differentiation, can explain the kinetics of the molecular response to imatinib in a 169-patient data set. Successful therapy leads to a biphasic exponential decline of leukaemic cells. The first slope of 0.05 per day represents the turnover rate of differentiated leukaemic cells, while the second slope of 0.008 per day represents the turnover rate of leukaemic progenitors. The model suggests that imatinib is a potent inhibitor of the production of differentiated leukaemic cells, but does not deplete leukaemic stem cells. We calculate the probability of developing imatinib resistance mutations and estimate the time until detection of resistance. Our model provides the first quantitative insights into the in vivo kinetics of a human cancer.

A Phase 2 Trial of Ponatinib in Philadelphia Chromosome–Positive Leukemias

BACKGROUND Ponatinib is a potent oral tyrosine kinase inhibitor of unmutated and mutated BCR-ABL, including BCR-ABL with the tyrosine kinase inhibitor-refractory threonine-to-isoleucine mutation at position 315 (T315I). We conducted a phase 2 trial of ponatinib in patients with chronic myeloid leukemia (CML) or Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-positive ALL). METHODS We enrolled 449 heavily pretreated patients who had CML or Ph-positive ALL with resistance to or unacceptable side effects from dasatinib or nilotinib or who had the BCR-ABL T315I mutation. Ponatinib was administered at an initial dose of 45 mg once daily. The median follow-up was 15 months. RESULTS Among 267 patients with chronic-phase CML, 56% had a major cytogenetic response (51% of patients with resistance to or unacceptable side effects from dasatinib or nilotinib and 70% of patients with the T315I mutation), 46% had a complete cytogenetic response (40% and 66% in the two subgroups, respectively), and 34% had a major molecular response (27% and 56% in the two subgroups, respectively). Responses were observed regardless of the baseline BCR-ABL kinase domain mutation status and were durable; the estimated rate of a sustained major cytogenetic response of at least 12 months was 91%. No single BCR-ABL mutation conferring resistance to ponatinib was detected. Among 83 patients with accelerated-phase CML, 55% had a major hematologic response and 39% had a major cytogenetic response. Among 62 patients with blast-phase CML, 31% had a major hematologic response and 23% had a major cytogenetic response. Among 32 patients with Ph-positive ALL, 41% had a major hematologic response and 47% had a major cytogenetic response. Common adverse events were thrombocytopenia (in 37% of patients), rash (in 34%), dry skin (in 32%), and abdominal pain (in 22%). Serious arterial thrombotic events were observed in 9% of patients; these events were considered to be treatment-related in 3%. A total of 12% of patients discontinued treatment because of an adverse event. CONCLUSIONS Ponatinib had significant antileukemic activity across categories of disease stage and mutation status. (Funded by Ariad Pharmaceuticals and others; PACE ClinicalTrials.gov number, NCT01207440 .).

Ponatinib in Refractory Philadelphia Chromosome–Positive Leukemias

BACKGROUND Resistance to tyrosine kinase inhibitors in patients with chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-positive ALL) is frequently caused by mutations in the BCR-ABL kinase domain. Ponatinib (AP24534) is a potent oral tyrosine kinase inhibitor that blocks native and mutated BCR-ABL, including the gatekeeper mutant T315I, which is uniformly resistant to tyrosine kinase inhibitors. METHODS In this phase 1 dose-escalation study, we enrolled 81 patients with resistant hematologic cancers, including 60 with CML and 5 with Ph-positive ALL. Ponatinib was administered once daily at doses ranging from 2 to 60 mg. Median follow-up was 56 weeks (range, 2 to 140). RESULTS Dose-limiting toxic effects included elevated lipase or amylase levels and pancreatitis. Common adverse events were rash, myelosuppression, and constitutional symptoms. Among Ph-positive patients, 91% had received two or more approved tyrosine kinase inhibitors, and 51% had received all three approved tyrosine kinase inhibitors. Of 43 patients with chronic-phase CML, 98% had a complete hematologic response, 72% had a major cytogenetic response, and 44% had a major molecular response. Of 12 patients who had chronic-phase CML with the T315I mutation, 100% had a complete hematologic response and 92% had a major cytogenetic response. Of 13 patients with chronic-phase CML without detectable mutations, 100% had a complete hematologic response and 62% had a major cytogenetic response. Responses among patients with chronic-phase CML were durable. Of 22 patients with accelerated-phase or blast-phase CML or Ph-positive ALL, 36% had a major hematologic response and 32% had a major cytogenetic response. CONCLUSIONS Ponatinib was highly active in heavily pretreated patients with Ph-positive leukemias with resistance to tyrosine kinase inhibitors, including patients with the BCR-ABL T315I mutation, other mutations, or no mutations. (Funded by Ariad Pharmaceuticals and others; ClinicalTrials.gov number, NCT00660920.).

Dasatinib or imatinib in newly diagnosed chronic-phase chronic myeloid leukemia: 2-year follow-up from a randomized phase 3 trial (DASISION)

Dasatinib is a highly potent BCR-ABL inhibitor with established efficacy and safety in imatinib-resistant/-intolerant patients with chronic myeloid leukemia (CML). In the phase 3 DASISION trial, patients with newly diagnosed chronic-phase (CP) CML were randomized to receive dasatinib 100 mg (n = 259) or imatinib 400 mg (n = 260) once daily. Primary data showed superior efficacy for dasatinib compared with imatinib after 12 months, including significantly higher rates of complete cytogenetic response (CCyR), confirmed CCyR (primary end point), and major molecular response (MMR). Here, 24-month data are presented. Cumulative response rates by 24 months in dasatinib and imatinib arms were: CCyR in 86% versus 82%, MMR in 64% versus 46%, and BCR-ABL reduction to ≤ 0.0032% (4.5-log reduction) in 17% versus 8%. Transformation to accelerated-/ blast-phase CML on study occurred in 2.3% with dasatinib versus 5.0% with imatinib. BCR-ABL mutations, assessed after discontinuation, were detected in 10 patients in each arm. In safety analyses, fluid retention, superficial edema, myalgia, vomiting, and rash were less frequent with dasatinib compared with imatinib, whereas pleural effusion and grade 3/4 thrombocytopenia were more frequent with dasatinib. Overall, dasatinib continues to show faster and deeper responses compared with imatinib, supporting first-line use of dasatinib in patients with newly diagnosed CML-CP. This study was registered at ClinicalTrials.gov: NCT00481247.

Intermittent Target Inhibition With Dasatinib 100 mg Once Daily Preserves Efficacy and Improves Tolerability in Imatinib-Resistant and -Intolerant Chronic-Phase Chronic Myeloid Leukemia

PURPOSE Dasatinib is a BCR-ABL inhibitor, 325-fold more potent than imatinib against unmutated BCR-ABL in vitro. Phase II studies have demonstrated efficacy and safety with dasatinib 70 mg twice daily in chronic-phase (CP) chronic myelogenous leukemia (CML) after imatinib treatment failure. In phase I, responses occurred with once-daily administration despite only intermittent BCR-ABL inhibition. Once-daily treatment resulted in less toxicity, suggesting that toxicity results from continuous inhibition of unintended targets. Here, a dose- and schedule-optimization study is reported. PATIENTS AND METHODS In this open-label phase III trial, 670 patients with imatinib-resistant or -intolerant CP-CML were randomly assigned 1:1:1:1 between four dasatinib treatment groups: 100 mg once daily, 50 mg twice daily, 140 mg once daily, or 70 mg twice daily. RESULTS With minimum follow-up of 6 months (median treatment duration, 8 months; range, < 1 to 15 months), marked and comparable hematologic (complete, 86% to 92%) and cytogenetic (major, 54% to 59%; complete, 41% to 45%) response rates were observed across the four groups. Time to and duration of cytogenetic response were similar, as was progression-free survival (8% to 11% of patients experienced disease progression or died). Compared with the approved 70-mg twice-daily regimen, dasatinib 100 mg once daily resulted in significantly lower rates of pleural effusion (all grades, 7% v 16%; P = .024) and grade 3 to 4 thrombocytopenia (22% v 37%; P = .004), and fewer patients required dose interruption (51% v 68%), reduction (30% v 55%), or discontinuation (16% v 23%). CONCLUSION Dasatinib 100 mg once daily retains the efficacy of 70 mg twice daily with less toxicity. Intermittent target inhibition with tyrosine kinase inhibitors may preserve efficacy and reduce adverse events.

Genetic Alterations Activating Kinase and Cytokine Receptor Signaling in High-Risk Acute Lymphoblastic Leukemia

Genomic profiling has identified a subtype of high-risk B-progenitor acute lymphoblastic leukemia (B-ALL) with alteration of IKZF1, a gene expression profile similar to BCR-ABL1-positive ALL and poor outcome (Ph-like ALL). The genetic alterations that activate kinase signaling in Ph-like ALL are poorly understood. We performed transcriptome and whole genome sequencing on 15 cases of Ph-like ALL and identified rearrangements involving ABL1, JAK2, PDGFRB, CRLF2, and EPOR, activating mutations of IL7R and FLT3, and deletion of SH2B3, which encodes the JAK2-negative regulator LNK. Importantly, several of these alterations induce transformation that is attenuated with tyrosine kinase inhibitors, suggesting the treatment outcome of these patients may be improved with targeted therapy.

Validation of ITD mutations in FLT3 as a therapeutic target in human acute myeloid leukaemia

Effective targeted cancer therapeutic development depends upon distinguishing disease-associated ‘driver’ mutations, which have causative roles in malignancy pathogenesis, from ‘passenger’ mutations, which are dispensable for cancer initiation and maintenance. Translational studies of clinically active targeted therapeutics can definitively discriminate driver from passenger lesions and provide valuable insights into human cancer biology. Activating internal tandem duplication (ITD) mutations in FLT3 (FLT3-ITD) are detected in approximately 20% of acute myeloid leukaemia (AML) patients and are associated with a poor prognosis. Abundant scientific and clinical evidence, including the lack of convincing clinical activity of early FLT3 inhibitors, suggests that FLT3-ITD probably represents a passenger lesion. Here we report point mutations at three residues within the kinase domain of FLT3-ITD that confer substantial in vitro resistance to AC220 (quizartinib), an active investigational inhibitor of FLT3, KIT, PDGFRA, PDGFRB and RET; evolution of AC220-resistant substitutions at two of these amino acid positions was observed in eight of eight FLT3-ITD-positive AML patients with acquired resistance to AC220. Our findings demonstrate that FLT3-ITD can represent a driver lesion and valid therapeutic target in human AML. AC220-resistant FLT3 kinase domain mutants represent high-value targets for future FLT3 inhibitor development efforts.

Sequential ABL kinase inhibitor therapy selects for compound drug-resistant BCR-ABL mutations with altered oncogenic potency

Molecularly targeted kinase inhibitor cancer therapies are currently administered sequentially rather than simultaneously. We addressed the potential long-term impact of this strategy in patients with chronic myelogenous leukemia (CML), which is driven by the fusion oncogene BCR-ABL. Analysis of BCR-ABL genotypes in CML patients who relapsed after sequential treatment with the ABL inhibitors imatinib and dasatinib revealed evolving resistant BCR-ABL kinase domain mutations in all cases. Twelve patients relapsed with the pan-resistant T315I mutation, whereas 6 patients developed novel BCR-ABL mutations predicted to retain sensitivity to imatinib based on in vitro studies. Three of these patients were retreated with imatinib (or the chemically related compound nilotinib) and responded; however, selection for compound mutants (2 or 3 BCR-ABL mutations in the same molecule) can substantially limit the potential effectiveness of retreating patients with inhibitors that have previously failed. Furthermore, drug-resistant mutations, when compounded, can increase oncogenic potency relative to the component mutants in transformation assays. The Aurora kinase inhibitor VX-680, currently under clinical evaluation based on its activity against the T315I mutation, is also effective against the other commonly detected dasatinib-resistant mutation in our analysis, V299L. Our findings demonstrate the potential hazards of sequential kinase inhibitor therapy and suggest a role for a combination of ABL kinase inhibitors, perhaps including VX-680, to prevent the outgrowth of cells harboring drug-resistant BCR-ABL mutations.