Evaluation of plitidepsin in patients with primary myelofibrosis and post polycythemia vera/essential thrombocythemia myelofibrosis: results of preclinical studies and a phase II clinical trial.

Previous data established that plitidepsin, a cyclic depsipeptide, exerted activity in a mouse model of myelofibrosis (MF). New preclinical experiments reported herein found that low nanomolar plitidepsin concentrations potently inhibited the proliferation of JAK2V617F-mutated cell lines and reduced colony formation by CD34+ cells of individuals with MF, at least in part through modulation of p27 levels. Cells of MF patients had significantly reduced p27 content, that were modestly increased upon plitidepsin exposure. On these premise, an exploratory phase II trial evaluated plitidepsin 5 mg/m(2) 3-h intravenous infusion administered on days 1 and 15 every 4 weeks (q4wk). Response rate (RR) according to the International Working Group for Myelofibrosis Research and Treatment consensus criteria was 9.1% (95% CI, 0.2-41.3%) in 11 evaluable patients during the first trial stage. The single responder achieved a red cell transfusion independence and stable disease was reported in nine additional patients (81.8%). Eight patients underwent a short-lasting improvement of splenomegaly. In conclusion, plitidepsin 5 mg/m(2) 3-h infusion q4wk was well tolerated but had a modest activity in patients with primary, post-polycythaemia vera or post-essential thrombocythaemia MF. Therefore, this trial was prematurely terminated and we concluded that further clinical trials with plitidepsin as single agent in MF are not warranted.

Targeted cancer exome sequencing reveals recurrent mutations in myeloproliferative neoplasms.

With the intent of dissecting the molecular complexity of Philadelphia-negative myeloproliferative neoplasms (MPN), we designed a target enrichment panel to explore, using next-generation sequencing (NGS), the mutational status of an extensive list of 2000 cancer-associated genes and microRNAs. The genomic DNA of granulocytes and in vitro-expanded CD3+T-lymphocytes, as a germline control, was target-enriched and sequenced in a learning cohort of 20 MPN patients using Roche 454 technology. We identified 141 genuine somatic mutations, most of which were not previously described. To test the frequency of the identified variants, a larger validation cohort of 189 MPN patients was additionally screened for these mutations using Ion Torrent AmpliSeq NGS. Excluding the genes already described in MPN, for 8 genes (SCRIB, MIR662, BARD1, TCF12, FAT4, DAP3, POLG and NRAS), we demonstrated a mutation frequency between 3 and 8%. We also found that mutations at codon 12 of NRAS (NRASG12V and NRASG12D) were significantly associated, for primary myelofibrosis (PMF), with highest dynamic international prognostic scoring system (DIPSS)-plus score categories. This association was then confirmed in 66 additional PMF patients composing a final dataset of 168 PMF showing a NRAS mutation frequency of 4.7%, which was associated with a worse outcome, as defined by the DIPSS plus score.

Prospective identification of high-risk polycythemia vera patients based on JAK2(V617F) allele burden.

The aim of this study was to determine whether the burden of JAK2(V617F) allele correlated with major clinical outcomes in patients with polycythemia vera (PV). To this end, we determined JAK2 mutant allele levels in granulocytes of 173 PV patients at diagnosis. The mean (+/-s.d.) mutant allele burden was 52% (+/-29); 32 patients (18%) had greater than 75% mutant allele. The burden of JAK2(V617F) allele correlated with measurements of stimulated erythropoiesis (higher hematocrit, lower mean cell volume, serum ferritin and erythropoietin levels) and myelopoiesis (higher white cell count, neutrophil count and serum lactate dehydrogenase) and with markers of neutrophil activation (elevated leukocyte alkaline phosphatase and PRV-1 expression). As compared to those with less than 25% mutant allele, patients harboring greater than 75% JAK2(V617F) allele were at higher relative risk (RR) of presenting larger spleen (RR 4.7; P<0.001) or suffering from pruritus (RR 3.1; P<0.001). In these patients, the risk of requiring chemotherapy (RR 1.8; P=0.001) or developing major cardiovascular events (RR 7.1; P=0.003) during follow up were significantly increased. We conclude that a burden of JAK2(V617F) allele greater than 75% at diagnosis points to PV patients with high-risk disease.

A quantitative assay for JAK2(V617F) mutation in myeloproliferative disorders by ARMS-PCR and capillary electrophoresis.

A point mutation in the Janus tyrosine kinase 2 (JAK2) gene has been described in patients with chronic myeloproliferative disorders (MPD), but the clinical significance of JAK2(V617F), which may be harbored in either the heterozygote or homozyote status, is still largely undefined. There are indirect suggestions that clinical phenotype and also some biological characteristics are dependent on the mutated allele levels. We have designed and validated in 179 MPD patients an amplification-refractory mutation sequencing PCR assay that allows the relative quantitation of mutated and normal JAK2 mRNAs using dye-labelled mutation-specific primers and capillary electrophoresis. Direct sequencing confirmed the specificity of the assay, which has a detection limit congruent with1% and allowed to identify 9% more JAK2-mutated patients as compared to conventional allele-specific PCR. The mutated mRNA ratio ranged from 5 to 51% in the JAK2(V617F) heterozygote and from 45 to 100% in the homozygote patients. Expression levels of both PRV-1 and NF-E2 gene, previously found to be overexpressed in MPD patients, were significantly correlated to the amount of mutated JAK2 mRNA. We propose that this method might complement current technologies based on genomic DNA analysis, and lead prospectively to a better clinically oriented assessment of the impact of JAK2(V617F) mutation in MPD.