Phuong Dang

Safety and efficacy of imatinib cessation for CML patients with stable undetectable minimal residual disease: results from the TWISTER study

Most patients with chronic myeloid leukemia (CML) treated with imatinib will relapse if treatment is withdrawn. We conducted a prospective clinical trial of imatinib withdrawal in 40 chronic-phase CML patients who had sustained undetectable minimal residual disease (UMRD) by conventional quantitative polymerase chain reaction (PCR) on imatinib for at least 2 years. Patients stopped imatinib and were monitored frequently for molecular relapse. At 24 months, the actuarial estimate of stable treatment-free remission was 47.1%. Most relapses occurred within 4 months of stopping imatinib, and no relapses beyond 27 months were seen. In the 21 patients treated with interferon before imatinib, a shorter duration of interferon treatment before imatinib was significantly associated with relapse risk, as was slower achievement of UMRD after switching to imatinib. Highly sensitive patient-specific BCR-ABL DNA PCR showed persistence of the original CML clone in all patients with stable UMRD, even several years after imatinib withdrawal. No patients with molecular relapse after discontinuation have progressed or developed BCR-ABL mutations (median follow-up, 42 months). All patients who relapsed remained sensitive to imatinib re-treatment. These results confirm the safety and efficacy of a trial of imatinib withdrawal in stable UMRD with frequent, sensitive molecular monitoring and early rescue of molecular relapse.

Dasatinib Cellular Uptake and Efflux in Chronic Myeloid Leukemia Cells: Therapeutic Implications

Purpose: The organic cation transporter OCT-1 mediates active transport of imatinib. We recently showed that low OCT-1 activity is a major contributor to suboptimal response in chronic myeloid leukemia (CML) patients treated with imatinib. The relevance of OCT-1 activity and efflux pumps in determining intracellular uptake and retention (IUR) of dasatinib was assessed. Experimental Design: The effect of OCT inhibitors on [14C]dasatinib and [14C]imatinib IUR was compared using peripheral blood mononuclear cells from newly diagnosed CML patients. The role of efflux transporters was studied using ABCB1- and ABCG2-overexpressing cell lines and relevant inhibitors. Results: Unlike imatinib, there was no significant difference in the dasatinib IUR at 37°C and 4°C (P = 0.8), and OCT-1 inhibitors including prazosin did not reduce dasatinib IUR significantly. In CML mononuclear cells, prazosin inhibitable IUR was significantly higher for imatinib than dasatinib (6.38 versus 1.48 ng/200,000 cells; P = 0.002; n = 11). Patients with high OCT-1 activity based on their imatinib uptake had IC50dasatinib values equivalent to patients with low OCT-1 activity. Dasatinib IUR was significantly lower in ABCB1-overexpressing cell lines compared with parental cell lines (P < 0.05). PSC833 (ABCB1 inhibitor) significantly increased the dasatinib IUR (P < 0.05) and reduced IC50dasatinib (from 100 to 8 nmol/L) in K562-DOX cell line. The ABCG2 inhibitor Ko143 significantly increased dasatinib IUR in ABCG2-overexpressing cell lines and reduced IC50dasatinib. Conclusion: Unlike imatinib, dasatinib cellular uptake is not significantly affected by OCT-1 activity, so that expression and function of OCT-1 is unlikely to affect response to dasatinib. Dasatinib is a substrate of both efflux proteins, ABCB1 and ABCG2.

Functional Activity of the OCT-1 Protein Is Predictive of Long-Term Outcome in Patients With Chronic-Phase Chronic Myeloid Leukemia Treated With Imatinib

PURPOSE Organic cation transporter-1 (OCT-1) activity (OA), a measure of the OCT-1-mediated influx of imatinib into CML mononuclear cells (MNCs), is predictive of major molecular response (MMR) at 12 and 24 months in patients with untreated CML. We now report the impact of OA on loss of response, disease transformation, and survival after 5 years of imatinib. PATIENTS AND METHODS OA is defined as the difference in intracellular concentration of carbon-14-imatinib with and without OCT-1 inhibition. OA was measured in blood from 56 patients with untreated chronic-phase CML. RESULTS More patients who had high OA (ie, > median OA value) achieved MMR by 60 months compared with patients who had low OA (89% v 55%; P = .007). A low OA was associated with a significantly lower overall survival (87% v 96%; P = .028) and event-free survival (EFS; 48% v 74%; P = .03) as well as a higher kinase domain mutation rate (21% v 4%; P = .047). These differences were highly significant in patients who averaged less than 600 mg/d of imatinib in the first 12 months but were not significant in patients averaging >/= 600 mg/d. Patients with very low OA (ie, quartile 1) were the only group who developed leukemic transformation (21% in quartile 1 v 0% in all other quartiles; P = .002). CONCLUSION Measurement of OA pretherapy is a predictor for the long-term risk of resistance and transformation in patients with imatinib-treated CML. Early dose-intensity may reduce the negative prognostic impact of low OA. We propose that OA could be used to individualize dosage strategies for patients with CML to maximize molecular response and optimize long-term outcome.

Chronic phase chronic myeloid leukemia patients with low OCT-1 activity randomized to high-dose imatinib achieve better responses and have lower failure rates than those randomized to standard-dose imatinib

Background The functional activity of the organic cation transporter 1 (OCT-1) protein (OCT-1 activity) is an excellent predictor of molecular response and progression-free survival in patients with newly diagnosed chronic phase chronic myeloid leukemia treated with imatinib as front-line therapy. Design and Methods In this study the predictive value of OCT-1 activity in patients treated with imatinib 400 mg/day or 800 mg/day was evaluated in relation to trough imatinib plasma levels assessed in 100 patients enrolled in the Tyrosine Kinase Inhibitor Optimization and Selectivity (TOPS) trial. Results The rate of major molecular responses by 24 months in patients on imatinib 400 mg/day was significantly higher in those with high OCT-1 activity than in those with low OCT-1 activity (low OCT-1 activity, 57% of patients; high OCT-1 activity, 100%; P<0.001); the corresponding difference in patients treated with imatinib 800 mg/day did not reach statistical significance (low OCT-1 activity, 68%; high OCT-1 activity, 95%; P=0.073). In addition, the combination of low trough imatinib levels (<1200 ng/mL) and low OCT-1 activity defined a group of patients who had the lowest rates of major molecular response (47%) by 24 months compared to all other patients (81%, P=0.009). These patients were also at the highest risk of failed imatinib therapy when compared to all other patients (P<0.001). Conclusions High-dose imatinib leads to superior molecular responses in patients with low OCT-1 activity. In this group trough imatinib levels may define a group with inferior outcomes. Among patients with high OCT-1 activity, neither higher imatinib dose nor monitoring imatinib trough levels was found to be of significant clinical value. Hence OCT-1 activity determined prior to the start of therapy in newly diagnosed CML patients provides a valuable prognostic tool to determine the optimal up-front dose of imatinib in patients with newly diagnosed chronic phase chronic myeloid leukemia.

OCT-1 activity measurement provides a superior imatinib response predictor than screening for single-nucleotide polymorphisms of OCT-1

OCT-1 activity measurement provides a superior imatinib response predictor than screening for single-nucleotide polymorphisms of OCT-1

The clinical significance of ABCB1 overexpression in predicting outcome of CML patients undergoing first-line imatinib treatment

Tyrosine kinase inhibitor (TKI) therapy results in excellent responses in the majority of patients with chronic myeloid leukaemia. First-line imatinib treatment, with selective switching to nilotinib when patients fail to meet specific molecular targets or for imatinib intolerance, results in excellent overall molecular responses and survival. However, this strategy is less effective in cases of primary imatinib resistance; moreover, 25% of patients develop secondary resistance such that 20–35% of patients initially treated with imatinib will eventually experience treatment failure. Early identification of these patients is of high clinical relevance. Since the drug efflux transporter ABCB1 has previously been implicated in TKI resistance, we determined if early increases in ABCB1 mRNA expression (fold change from diagnosis to day 22 of imatinib therapy) predict for patient response. Indeed, patients exhibiting a high fold rise (⩾2.2, n=79) were significantly less likely to achieve early molecular response (BCR-ABL1IS ⩽10% at 3 months; P=0.001), major molecular response (P<0.0001) and MR4.5 (P<0.0001). Additionally, patients demonstrated increased levels of ABCB1 mRNA before the development of mutations and/or progression to blast crisis. Patients with high fold rise in ABCB1 mRNA were also less likely to achieve major molecular response when switched to nilotinib therapy (49% vs 82% of patients with low fold rise). We conclude that early evaluation of the fold change in ABCB1 mRNA expression may identify patients likely to be resistant to first- and second-generation TKIs and who may be candidates for alternative therapy.

Relapse of BCR-ABL1-like ALL mediated by the ABL1 kinase domain mutation T315I following initial response to dasatinib treatment.

Relapse of BCR-ABL1- like ALL mediated by the ABL1 kinase domain mutation T315I following initial response to dasatinib treatment

High prevalence of relapse in children with Philadelphia-like acute lymphoblastic leukemia despite risk-adapted treatment

Acute lymphoblastic leukemia (ALL) remains a leading cause of cancer-related death in children and young adults. Since the 1960s, improvements in the treatment of children with ALL have led to 10-year survival rates now exceeding 85%.[1][1] Philadelphia-like (Ph-like) ALL is characterized by a gene

Xenograft-directed personalized therapy for a patient with post-transplant relapse of ALL

The outcome for ALL relapsing after BM transplantation (BMT) remains poor. International Bone Marrow Transplant Register data suggest that about 30% of patients can be cured with a second BMT and that younger age (o20 years), longer interval between transplants (46 months) and deeper molecular remission contribute to greater likelihood of success. The selection of chemotherapy to achieve deep remission before second BMT is often complicated by the patient’s previous exposures to agents with cumulative toxicities such as anthracyclines and/or slow minimal residual disease (MRD) responses to previous induction therapy. The use of novel therapies targeted to specific ALL biology is attractive and has been pioneered for tyrosine kinase inhibitors in Ph-like ALL. Although integrated genomic analysis may identify novel treatment options for relapsed ALL, it is important to establish if targeted therapy will be more effective than conventional remission induction which works in 60–70% of cases. Xenograft models accurately reproduce ALL in preclinical studies and patient-derived xenografts (PDX) could be used to assess this and to prioritize therapy for individual ALL relapse cases. We demonstrate that biologic, genetic and expression analyses combined with the treatment of a patient’s ALL in PDX mice were able to provide relevant information in time to guide therapy selection for a patient with a post-transplant relapse resulting in a complete molecular remission and enabling a second BMT. A 3-year-old girl diagnosed with pre-B-ALL was treated as a high standard-risk patient following the Children’s Oncology Group protocol (ALL0331) due to a slow early marrow response with high minimal residual disease (MRD410 ; Supplementary Table S1). She completed therapy but had an isolated BM relapse 35 months after diagnosis. The patient was enrolled in the UKALL-R3 trial in the intermediate risk group and had high MRD (1 × 10 ) at end of induction. As per trial recommendation, she received a matched-sibling-donor BMT. She had low level MRD (positive o5 × 10 ) pre-BMT and a second isolated BM relapse occurred 15 months after the first transplant. The family wished to pursue curative therapy, with the plan to induce a third remission followed by a second BMT. Treatment with fludarabine, cytarabine and mitoxantrone (FLAG-M) was commenced 5 days after the second relapse (Figure 1, Table 1). A multi-disciplinary panel was convened to determine whether alternate treatment(s) could be identified and validated in real-time in the event of failure of FLAG-M to achieve a third remission. The panel reviewed diagnostic information, results from the literature and the Pediatric Preclinical Testing Program (PPTP) and chose targeted genetic analyses to be performed to facilitate rapid analysis and enable PDX validation. In particular we tested for a BCR-ABL1-like expression signature including specific targetable fusions, performed phospho-flow cytometry for targetable kinase activity; low-density genomic analysis by multiplex ligation-dependent PCR (MLPA); and screened for activating RAS or JAK mutations. Twenty non-irradiated, immune-deficient, NOD/SCID/IL-2 receptor gamma /− (NOD.Cg-Prkdc Il2rg/SzJ, NSG) mice were inoculated by tail vein injection 8 days after the 2nd relapse with 2 × 10 BM cells (from the 2nd relapse) to establish the PDX.

BCR-ABL1 genomic DNA PCR response kinetics during first-line imatinib treatment of chronic myeloid leukemia.

Accurate quantification of minimal residual disease (MRD) during treatment of chronic myeloid leukemia (CML) guides clinical decisions. The conventional MRD method, RQ-PCR for BCR-ABL1 mRNA, reflects a composite of the number of circulating leukemic cells and the BCR-ABL1 transcripts per cell. BCR-ABL1 genomic DNA only reflects leukemic cell number. We used both methods in parallel to determine the relative contribution of the leukemic cell number to molecular response. BCR-ABL1 DNA PCR and RQ-PCR were monitored up to 24 months in 516 paired samples from 59 newly-diagnosed patients treated with first-line imatinib in the TIDEL-II study. In the first three months of treatment, BCR-ABL1 mRNA values declined more rapidly than DNA. By six months, the two measures aligned closely. The expression of BCR-ABL1 mRNA was normalized to cell number to generate an expression ratio. The expression of e13a2 BCR-ABL1 was lower than that of e14a2 transcripts at multiple time points during treatment. BCR-ABL1 DNA was quantifiable in 48% of samples with undetectable BCR-ABL1 mRNA, resulting in MRD being quantifiable for an additional 5-18 months (median 12 months). These parallel studies show for the first time that the rapid decline in BCR-ABL1 mRNA over the first three months of treatment is due to a reduction in both cell number and transcript level per cell, whereas beyond three months, falling levels of BCR-ABL1 mRNA are proportional to the depletion of leukemic cells.