Tamoxifen for the treatment of myeloproliferative neoplasms: A Phase II clinical trial and exploratory analysis

Current therapies for myeloproliferative neoplasms (MPNs) improve symptoms but have limited effect on tumor size. In preclinical studies, tamoxifen restored normal apoptosis in mutated hematopoietic stem/progenitor cells (HSPCs). TAMARIN Phase-II, multicenter, single-arm clinical trial assessed tamoxifen's safety and activity in patients with stable MPNs, no prior thrombotic events and mutated JAK2V617F, CALRins5 or CALRdel52 peripheral blood allele burden ≥20% (EudraCT 2015-005497-38). 38 patients were recruited over 112w and 32 completed 24w-treatment. The study's A'herns success criteria were met as the primary outcome ( ≥ 50% reduction in mutant allele burden at 24w) was observed in 3/38 patients. Secondary outcomes included ≥25% reduction at 24w (5/38), ≥50% reduction at 12w (0/38), thrombotic events (2/38), toxicities, hematological response, proportion of patients in each IWG-MRT response category and ELN response criteria. As exploratory outcomes, baseline analysis of HSPC transcriptome segregates responders and non-responders, suggesting a predictive signature. In responder HSPCs, longitudinal analysis shows high baseline expression of JAK-STAT signaling and oxidative phosphorylation genes, which are downregulated by tamoxifen. We further demonstrate in preclinical studies that in JAK2V617F+ cells, 4-hydroxytamoxifen inhibits mitochondrial complex-I, activates integrated stress response and decreases pathogenic JAK2-signaling. These results warrant further investigation of tamoxifen in MPN, with careful consideration of thrombotic risk.

Longitudinal trends of peripheral blood counts in polycythaemia vera and essential thrombocythemia patients in the UK

There is sparse evidence of how well haematological targets are met in practice for essential thrombocythemia (ET) and polycythaemia vera (PV) patients. Patient data was collected between 2008 and 2020 from two UK NHS Trusts for ET and PV patients. Longitudinal changes in peripheral blood counts, including the proportion of patients meeting peripheral blood count remission, was modelled. Relative risk of cardiovascular‐related events for patients achieving remission within 3‐months was estimated. A total of 620 ET and 429 PV patients were analysed. For high‐risk patients, haematological parameters decreased in the first months of observation then stabilised within normal reference ranges until year 5. Total time spent in peripheral blood count remission was 39.2% for ET and 29.1% for PV. A lower proportion of ET patients reached target platelet counts (48.3%) compared to WBC (79.1%), whilst PV patients were less likely to reach target haematocrit levels (56.9%) compared to platelets (77.3%) or WBC (74.6%). There was no statistically significant association between reaching target blood counts within 3‐months and cardiovascular risk. Complete haematological remission remains a challenging target in managing PV and ET, however this study was unable to show statistically‐significant evidence that this was associated with increased risk of cardiovascular events.

Safety and efficacy of avapritinib in advanced systemic mastocytosis: the phase 1 EXPLORER trial

Advanced systemic mastocytosis (AdvSM) is a rare hematologic neoplasm driven by the KIT D816V mutation and associated with poor survival. This phase 1 study (NCT02561988) evaluated avapritinib (BLU-285), a selective KIT D816V inhibitor, in patients with AdvSM. The primary endpoints were the maximum tolerated dose, recommended phase 2 dose and safety of avapritinib. Secondary endpoints included overall response rate and changes in measures of mast cell burden. Avapritinib was evaluated at doses of 30–400 mg once daily in 86 patients, 69 with centrally confirmed AdvSM. Maximum tolerated dose was not reached, and 200 mg and 300 mg daily were studied in dose-expansion cohorts. The most frequent adverse events observed were periorbital edema (69%), anemia (55%), diarrhea (45%), thrombocytopenia (44%) and nausea (44%). Intracranial bleeding occurred in 13% overall, but in only 1% of patients without severe thrombocytopenia (platelets <50 × 10⁹/l). In 53 response-evaluable patients, the overall response rate was 75%. The complete remission rate was 36%. Avapritinib elicited ≥50% reductions in marrow mast cells and serum tryptase in 92% and 99% of patients, respectively. Avapritinib induced deep and durable responses, including molecular remission of KIT D816V in patients with AdvSM, and was well tolerated at the recommended phase 2 dose of 200 mg daily.

In a phase 1 trial of patients with advanced systemic mastocytosis, avapritinib, a selective KIT inhibitor, was generally well tolerated, elicited durable clinical responses and led to reductions in mast cell disease burden.

Murine double minute 2 inhibition alone or with cytarabine in acute myeloid leukemia: Results from an idasanutlin phase 1/1b study⋆

The prognosis remains poor for patients with relapsed or refractory (r/r) acute myeloid leukemia; thus, novel therapies are needed. We evaluated idasanutlin-a new, potent murine double minute 2 antagonist-alone or with cytarabine in patients with r/r acute myeloid leukemia, de novo untreated acute myeloid leukemia unsuitable for standard treatment or with adverse features, or secondary acute myeloid leukemia in a multicenter, open-label, phase 1/1b trial. Primary objectives were to determine the maximum tolerated dose (MTD) and recommended dose for expansion (RDE) and characterize the safety profile of idasanutlin monotherapy and combination therapy. Clinical activity and pharmacokinetics were secondary objectives. Two idasanutlin formulations were investigated: a microprecipitate bulk powder (MBP) and optimized spray-dried powder (SDP). Following dose escalation, patients (N = 122) received idasanutlin at the RDE in the extension cohorts. No formal MTD was identified. Idasanutlin was tolerable alone and in combination with cytarabine. The RDE was determined as 600 mg twice a day for the MBP formulation and 300 mg twice a day for the SDP formulation. Adverse events were mostly grade 1/2 (76.2 %). The most common any-grade adverse events were gastrointestinal (including diarrhea [90.2 %]). The early death rate across all patients was 14.8 %. Plasma idasanutlin exposure was dose related. In TP53 wild-type patients, composite complete remission rates were 18.9 % with monotherapy and 35.6 % with combination therapy. Based on these results, idasanutlin development continued with further investigation in the treatment of acute myeloid leukemia. ClinicalTrials.gov: NCT01773408.

Developments in chemotherapy for the treatment of acute myeloid leukemia

Mark Drummond obtained his medical degree from the University of Glasgow (UK) and since then has trained as a hematologist in the West of Scotland and the Canterbury District Health Board (Christchurch, New Zealand) and back at Glasgow University, where he also gained a PhD in chronic myeloid leukemia. He is currently a consultant hematologist and honorary senior lecturer at the Beatson Cancer Centre (Glasgow, UK) as well as an investigator on multiple UK and international clinical trials.

Here he talks to Commissioning Editor Jennifer Straiton, commenting on the recent announcement from the Scottish Medicines Consortium, regarding their acceptance of the use of the combination chemotherapy treatment Vyxeos^® (daunorubicin and cytarabine) for the treatment of high-risk acute myeloid leukemia in adults. He then discusses the ongoing and future clinical trials in this disease area and then turns to more personalized treatments.

Results of the Phase I Trial of RG7112, a Small-Molecule MDM2 Antagonist in Leukemia

PURPOSE

RG7112 is a small-molecule MDM2 antagonist. MDM2 is a negative regulator of the tumor suppressor p53 and frequently overexpressed in leukemias. Thus, a phase I study of RG7112 in patients with hematologic malignancies was conducted.

EXPERIMENTAL DESIGN

Primary study objectives included determination of the dose and safety profile of RG7112. Secondary objectives included evaluation of pharmacokinetics; pharmacodynamics, such as TP53-mutation status and MDM2 expression; and preliminary clinical activity. Patients were divided into two cohorts: Stratum A [relapsed/refractory acute myeloid leukemia (AML; except acute promyelocytic leukemia), acute lymphoblastic leukemia, and chronic myelogenous leukemia] and Stratum B (relapsed/refractory chronic lymphocytic leukemia/small cell lymphocytic leukemia; CLL/sCLL). Some Stratum A patients were treated at the MTD to assess clinical activity.

RESULTS

RG7112 was administered to 116 patients (96 patients in Stratum A and 20 patients in Stratum B). All patients experienced at least 1 adverse event, and 3 dose-limiting toxicities were reported. Pharmacokinetic analysis indicated that twice-daily dosing enhanced daily exposure. Antileukemia activity was observed in the 30 patients with AML assessed at the MTD, including 5 patients who met International Working Group (IWG) criteria for response. Exploratory analysis revealed TP53 mutations in 14% of Stratum A patients and in 40% of Stratum B patients. Two patients with TP53 mutations exhibited clinical activity. p53 target genes were induced only in TP53 wild-type leukemic cells. Baseline expression levels of MDM2 correlated positively with clinical response.

CONCLUSIONS

RG7112 demonstrated clinical activity against relapsed/refractory AML and CLL/sCLL. MDM2 inhibition resulted in p53 stabilization and transcriptional activation of p53-target genes. We provide proof-of-concept that MDM2 inhibition restores p53 function and generates clinical responses in hematologic malignancies.

Primary lymphedema and acute leukemia--is there a link?

The lymphedema service in Glasgow has been treating patients with lymphedema of all causes since 1991. In the past five years 3 patients with primary lymphedema have been diagnosed with myelodysplasia (leading to acute leukemia) or acute leukemia. These are relatively unusual malignancies given the ages of the patients and all three of these patients died within an average of 12 months of diagnosis. A connection between the presence of primary lymphedema and the subsequent development of the hematological disorder is postulated. Standard marrow cytogenetics failed to identify a common abnormality but the authors feel that further study is warranted.

Early prediction of success or failure of treatment with second-generation tyrosine kinase inhibitors in patients with chronic myeloid leukemia

BACKGROUND

Second-generation tyrosine kinase inhibitors induce cytogenetic responses in approximately 50% of patients with chronic myeloid leukemia in chronic phase in whom imatinib treatment has failed. However, it has not yet been established which of the patients in whom imatinib treatment fails are likely to benefit from therapy with second-generation tyrosine kinase inhibitors.

DESIGN AND METHODS

We analyzed a cohort of 80 patients with chronic myeloid leukemia who were resistant to imatinib and who were treated with dasatinib or nilotinib while still in first chronic phase. We devised a scoring system to predict the probability of these patients achieving complete cytogenetic response when treated with second-generation tyrosine kinase inhibitors.

RESULTS

The system was based on three factors: cytogenetic response to imatinib, Sokal score and recurrent neutropenia during imatinib treatment. We validated the score in an independent group of 28 Scottish patients. We also studied the relationship between cytogenetic responses at 3, 6 and 12 months and subsequent outcome. We classified the 80 patients into three categories, those with good risk (n=24), intermediate risk (n=27) and poor risk (n=29) with 2.5-year cumulative incidences of complete cytogenetic response of 100%, 52.2% and 13.8%, respectively (P<0.0001). Moreover, patients who had less than 95% Philadelphia chromosome-positive metaphases at 3 months, those with 35% or less Philadelphia chromosome-positive metaphases at 6 months and patients in complete cytogenetic response at 12 months all had significantly better outcomes than patients with lesser degrees of cytogenetic response.

CONCLUSIONS

Factors measurable before starting treatment can accurately predict response to second-generation tyrosine kinase inhibitors. Cytogenetic responses at 3, 6 and 12 months may influence the decision to continue treatment with second-generation tyrosine kinase inhibitors.

Concise review: Telomere biology in normal and leukemic hematopoietic stem cells

The measurement of telomere length can give an insight into the replicative history of the cells in question. Much of the observed telomere loss occurs at the stem and progenitor cell level, even though these populations express the enzyme telomerase. Telomerase-transfected hematopoietic stem cells (HSC), although able to maintain telomere length, are still limited in terms of ability to undergo sequential transplantation, and other factors require to be addressed to achieve optimal levels of stem cell expansion. Unchecked telomere loss by HSC, meanwhile, would appear to play a significant role in the pathogenesis of bone marrow failure, as observed in the condition dyskeratosis congenita. This heterogeneous inherited condition appears to exhibit telomerase dysfunction as a common final pathogenic mechanism. Although less well-established for acquired marrow failure syndromes, mutations in key telomerase components have been described. The identification of the leukemic stem cell (LSC), along with the desire to target this population with anti-leukemia therapy, demands that telomerase biology be fully understood in this cell compartment. Future studies using primary selected LSC-rich samples are required. A better understanding of telomerase regulation in this population may allow effective targeting of the telomerase enzyme complex using small molecule inhibitors or additional novel approaches. Disclosure of potential conflicts of interest is found at the end of this article.

Dysregulated expression of the major telomerase components in leukaemic stem cells

Telomere loss is rapid during the progression of chronic myeloid leukaemia (CML) and correlates with prognosis. We therefore sought to measure expression of the major telomerase components (hTR and hTERT) in CD34+ cells from CML patients and normal controls, to determine if their altered expression may contribute to telomere attrition in vivo. High-purity (median 94.1%) BCR-ABL+ CD34+ cells from CML (n=16) and non-CML (n=14) patients were used. CML samples had a small increase in telomerase activity (TA) compared to normal samples (approximately 1.5-fold, P=0.004), which was inversely correlated with the percentage of G0 cells (P=0.02) suggesting TA may not be elevated on a cell-to-cell basis in CML. Consistent with this, hTERT mRNA expression was not significantly elevated; however, altered mRNA splicing appeared to play a significant role in determining overall full length, functional hTERT levels. Interestingly, Q-RT-PCR for hTR demonstrated a mean five-fold reduction in levels in the chronic phase (CP) CML samples (P=0.002), raising the possibility that telomere homeostasis is disrupted in CML. In summary, the molecular events regulating telomerase gene expression and telomere maintenance during the CP of CML may influence the disease progression observed in these patients.

Mobilization of Ph chromosome-negative peripheral blood stem cells in chronic myeloid leukaemia patients with imatinib mesylate-induced complete cytogenetic remission

Imatinib mesylate (IM, STI 571, Glivec) can induce a high rate of complete cytogenetic response (CCR) in chronic myeloid leukaemia (CML) patients, although to date the majority of patients continue to have detectable disease by sensitive reverse transcription polymerase chain reaction (RT-PCR). It is therefore possible that these patients may ultimately relapse and require treatment such as autologous peripheral blood stem cell transplant (APBSCT). We attempted mobilization of haemopoietic progenitor cells from 58 patients in CCR using recombinant human granulocyte colony-stimulating factor [rHu-G-CSF; 10 micro g/kg/d subcutaneously (s.c.) for at least 4 d] alone, while continuing IM treatment. The median d 5 (peak) CD34+ count was 11.5/ microl (range 0-108/ microl), and 43/58 (74%) patients underwent a median of two (range 1-3) apheresis procedures. A median dose of 2.1 x 10(6)/kg CD34+ cells (range 0.1-6.5 x 10(6)/kg) was collected. Some 84% of 31 collections analysed were negative for the Philadelphia (Ph) chromosome or breakpoint cluster region and Abelson murine leukaemia viral oncogene homologue (BCR-ABL) translocation by cytogenetics or fluorescent in situ hybridization respectively. No toxicity was reported with the regimen. Overall, the target CD34+ dose (2 x 10(6)/kg CD34+) was attained in 23/58 (40%) patients who entered the study. In summary, we have demonstrated that successful mobilization of Ph- CD34+ cells from IM-treated patients in CCR is possible using rHu-G-CSF alone.

Elucidating critical mechanisms of deregulated stem cell turnover in the chronic phase of chronic myeloid leukemia

Chronic myeloid leukemia (CML) has been studied intensively for many years; yet its treatment remains problematic and its biology remains elusive. In chronic phase, the leukemic clone appears to be maintained by a small number of BCR-ABL-positive hematopoietic stem cells that differentiate normally and amplify slowly. In contrast, as these cells enter the intermediate stages of lineage restriction, their progeny are selectively expanded and generate an enlarged pool of neoplastic progenitors. Recent analyses of purified subsets of primitive CML cells have provided a coherent explanation for this dichotomous behavior of BCR-ABL-positive stem and progenitor cells based on the discovery of an unusual autocrine IL-3/G-CSF mechanism activated in them. This only partially counteracts in vivosignals that maintain normal stem cells in a quiescent state but, when active in CML stem cells, promotes their differentiation in favor of their self-renewal. In more differentiated CML progenitors, the same mechanism has a more potent mitogenic effect which is then extinguished when the cells enter the terminal stages of differentiation. Thus, further expansion of the clone is limited until inevitably additional mutations are acquired that further distort or override the regulatory mechanisms still operative in the chronic phase.

Tyrosine kinase inhibitors in the treatment of chronic myeloid leukaemia: so far so good?

Chronic myeloid leukaemia (CML) is characterized by marked expansion of the myeloid series, and is thought to arise as a direct result of the bcr-abl fusion-gene. The BCR-ABL oncoprotein is a constitutively active protein tyrosine kinase (PTK), which results in altered cell signalling and is responsible for the changes that characterize the malignant cells of CML. It has been shown that the increased tyrosine kinase activity of BCR-ABL is a requirement for transformation and is, therefore, a legitimate target for pharmacological inhibition. Several compounds have now been identified as relatively selective inhibitors of BCR-ABL, including members of the tyrphostin family, herbimycin A and most importantly the 2-phenylaminopyrimidine ST1571. Having established the efficacy of this agent in vitro, phase I trials using an oral formulation were commenced in the USA in mid 1998. Early data from an interferon-alpha (IFN) resistant/refractory or intolerant cohort demonstrated good patient tolerance and effective haematological control at doses above 300 mg. More promising was its ability to induce cytogenetic responses in this pretreated group of patients. Phase II data, albeit far from complete, appear to confirm its efficacy even in the context of advanced disease and phase III clinical trials are currently underway in many countries. Recent laboratory evidence, however, suggests that the development of drug resistance is a possibility (via amplification of the bcr-abl fusion gene, overexpression of P-glycoprotein or binding of ST1571 to alpha1 acid glycoprotein) and that combination therapy including ST1571 should be considered.

Successful treatment with lamivudine for fulminant reactivated hepatitis B infection following intensive therapy for high-grade non-Hodgkin's lymphoma

Chronic carriers of Hepatitis B virus (HBV) infection, who are treated for malignant lymphoma, are at high risk of mortality from reactivated HBV infection. We report a case of a 29-year-old male chronic HBV carrier who developed fulminant reactivated HBV infection following intensive chemotherapy for stage IVB large cell B-cell non-Hodgkin's lymphoma associated with extensive central nervous system and bone marrow involvement. Prior to chemotherapy the patient had normal liver function tests and was negative for HBV DNA by semiquantitative PCR assay. Fulminant HBV reactivation was confirmed following clinical deterioration, massive rises in hepatic transaminases (peak alanine aminotransferase = 2,850 U/l), liver biopsy and rising levels of serum HBV DNA. Following treatment with lamivudine 150 mg bd for 18 weeks dramatic and sustained recovery ensued. Symptoms and liver function tests improved within days and HBV DNA became negative within 12 weeks. Our patient later died from relapsed lymphoma but without evidence of reactivated HBV infection. We advise that lamivudine should be considered during intensive chemotherapy treatment of chronic carriers of HBV.