Primary myelofibrosis (PMF) is a clonal myeloproliferative disorder caused by abnormal hematopoietic stem cells (HSC), and is a BCR-ABL negative myeloproliferative neoplasm (MPN) along with true erythroblastosis (PV) and primary thrombocytosis (ET). PMF is characterized by proliferation of bone marrow fibrous tissue and extramedullary hematopoiesis, with progressive anemia, splenomegaly, peripheral blood naïve cells, tear drop erythrocytes and bone marrow dry aspiration, accompanied by systemic symptoms such as fever, malaise, night sweats and wasting. PMF has the worst prognosis among MPN, with a median survival of about 5 years, and will eventually progress to bone marrow failure or convert to acute leukemia.
Table 1 DIPSS-plus risk groups
Risk grouping Integral value Median survival (years)
Low risk 0 15.4
Intermediate-risk-1 1 6.5
Intermediate-risk-2 2-3 2.9
High risk ≥4 1.3
In 2009, the International Collaborative Group (IWG-MRT) promulgated the International Prognostic Score System (IPSS) for PMF, but only for patients with initial untreated disease. 2010 saw the proposal of the International Dynamic Prognostic Scoring System (DIPSS) for patients at any point of disease. Recently, an enhanced version of the International Dynamic Prognostic Scoring System (DIPSS-plus) was proposed, which combines prognostic information on karyotype, platelet count, and transfusion status (Table 1). Poor prognostic factors included age >65 years, systemic symptoms (weight loss >10% 1 year prior to diagnosis, unexplained fever, severe night sweats for more than 1 month), HGB <100 g/L, PLT <100×109 wbc="">25×109/L, peripheral blood primitive cells ≥0.010, transfusion dependence, poor karyotype [complex karyotype, +8, -7/7q- i(17q), inv(3), -5/5q-, 12p-, or 11q23] [1].
Treatment options for PMF include hematopoietic stem cell transplantation, conventional drugs, surgical splenectomy, radiotherapy, and clinical trial drug therapy. Treatment strategies are selected according to prognostic subgroups, and it has been suggested that treatment options are selected based on the DIPSS-plus prognostic score (Figure 1) [2].
Figure 1 Treatment options for patients with primary myelofibrosis
I. Allogeneic hematopoietic stem cell transplantation (allo-HSCT)
Allo-HSCT is the only possible cure for PMF and is indicated for patients with poor prognosis and a suitable donor. allo-HSCT was performed in 51 patients with PMF selected by Stewart et al [3] for clear and non-clear pretreatment with allo-HSCT, with 3-year overall survival rates of 44% and 31%, relapse rates of 15% and 46%, non-relapse mortality rates of 41% and 32%, respectively. and 32%, and the incidence of chronic graft-versus-host disease (GVHD) was 30% and 35%, respectively. The efficacy of clear-marrow and non-clear-marrow allo-HSCT is comparable, with the former being suitable for younger patients and the latter for older patients or those who cannot tolerate clear-marrow transplantation due to complications. For patients who have relapsed after transplantation, infusion of donor lymphocytes has been suggested to exert graft-versus-myelofibrosis (GVM) effects.
Poor prognostic factors for allo-HSCT include IPSS intermediate-risk-II/high-risk, transfusion dependency, poor karyotype, unrelated donor or sibling donor HLA nonallogeneity, older age, significant splenomegaly, and myelosclerosis [4]. The results of a multicenter study showed that the 1- and 3-year overall survival rates of patients with high- or intermediate-risk PMF with indications for transplantation without transplantation ranged from 70.5% to 90.5% and 55.0% to 77.2% [5]. Therefore, the decision to transplant or not to transplant needs to be made by considering the prognostic subgroup of patients and the expected quality of survival.
II. Conventional drug therapy and progress
1. Improvement of anemia: treatment is started when HGB <100 g/L. Conventional drugs include glucocorticoids (0.5~1.0mg・kg-1・d -1), androgens (Danazol 200mg, 3 times daily or Stanozolol 2mg, 3 times daily), erythropoietin (EPO) (30~50,000U/week, subcutaneous injection) and immunomodulators, and the response rate of monotherapy for PMF anemia is 30%~40%. Primary patients can be treated with a combination of androgens and corticosteroids for at least 3 months, and if efficacious, androgens are continued and corticosteroids are tapered [6]. EPO is indicated for patients with serum EPO <100 U/L, is less effective in transfusion-dependent patients, and may aggravate splenomegaly when used in patients with moderate or greater splenomegaly. All of the above drugs have shortcomings. Choose the appropriate drug according to the patient's age and tolerance, etc.
Immunomodulators have anti-angiogenesis, down-regulation of TNF-α and IL-6, up-regulation of IL-2 and IFN-α and enhancement of T cell and NK cell proliferation and activity. Thalidomide improves anemia, thrombocytopenia and splenomegaly in PMF patients with an individual dosage of 100-400 mg/d, starting with a small dose (50-100 mg/d), with an overall efficiency of about 60%. Major adverse effects include neurotoxicity, constipation, thrombocytosis, drowsiness, headache, dry mouth, and rash, which are not tolerated by some patients.
Mesa et al [7] used low-dose thalidomide (50 mg/d) combined with prednisone (starting dose 0.5 mg・kg-1・d -1) to treat 21 patients with PNF, and prednisone was tapered after 3 months, 20 of them completed 3 months of treatment with an overall effective rate of 62%; 6 of 8 patients with PLT <100×109/L (75%) after treatment Weinkove et al [8] also used thalidomide (5 mg/d) in combination with prednisone ( 0.5 mg・kg-1・d -1) in 21 patients with MF (15 with PMF and 6 with MF after PV/ET). Among them, 5 cases got most response, 1 case got partial response, 5 cases got minor response, and 4 cases were ineffective (EUMNET criteria). The median efficacy maintenance time was 16 weeks, and the adverse effects were mild, mostly 1~2 degrees. The response rate of thalidomide for PMF anemia is 20%-30%, but it is especially suitable for patients with del(5q) chromosomal abnormalities, which need to be closely monitored for myelosuppressive toxicity.
2. Reduction of splenomegaly.
(1) Chemotherapy: Hydroxyurea (20-30 mg/kg, 2-3 times a week or 1.5 g/d) is preferred, and the efficiency of spleen reduction is about 40%. 2009 American Blood Annual Meeting Siragusa et al. presented a study on hydroxyurea treatment of splenomegaly in patients with PMF. The results showed an overall response rate of 35%, with response rates of 10%, 67% and 33% in patients with negative JAK2 V617F mutation, allelic load <50% and allelic load >50%, respectively. Therefore, the response rate to hydroxyurea was significantly higher in JAK2 V617F mutation-negative patients than in those who were negative. The major adverse effects of hydroxyurea include leukopenia, anemia or abnormal red blood cell morphology, thrombocytopenia, gastrointestinal symptoms, skin or mucosal ulcers, and neurological symptoms. Patients who are not responding to hydroxyurea may choose other chemotherapy drugs. Drugs recommended by the European Leukemia Network include cladribine (5 mg・m-2・d -1, infusion for 2 h for 5 d, 1 course per month, repeated for 4-6 courses), mafran (2.5 mg, 3 times a week), and leucovorin (2-6 mg/d) [9]. 6-Thioguanine (6-TG) and other alkylating agents have also been used in the treatment of PMF. close monitoring of the patient’s routine blood parameters and leukocytes is required during the application of chemotherapeutic drugs Fontana et al [10] reported that Danazol (200-800 mg/d) combined with intermittent chemotherapeutic agents (leucovorin 2-4 mg/d or 6-TG 50-100 mg/d or combined with cytarabine 100-200 mg/m capsule) was more effective and well tolerated in the treatment of elderly patients with myelofibrosis. It is well tolerated and can be used as an alternative treatment for elderly patients.
(2) Radiation therapy: Patients with severe splenic pain, significant splenomegaly with contraindication to splenectomy, peritoneal fluid due to peritoneal myeloid metaplasia, spinal cord compression symptoms or extramedullary fibrous hematopoietic tumors may choose radiation therapy. The effect of spleen reduction is significant, but the effect is not long-lasting (3 to 6 months). Radiation therapy is most suitable for patients with non-hepatosplenic extramedullary hematopoiesis. Low-dose irradiation (100~500 cGy in 5~10 fractions) provides significant results, but treatment-related death and persistent hematocrit may occur.
(3) Splenectomy: For patients with symptomatic splenomegaly, refractory anemia dependent on red blood cell transfusion, refractory thrombocytopenia, and symptomatic portal hypertension who have failed conservative treatment. Contraindications to surgery.
①Active hepatitis;
②Severe pulmonary and cardiovascular disease;
③Patients with high platelet count. Splenectomy can relieve local compression symptoms (50%), improve anemia (50%), improve thrombocytopenia (30%) and relieve portal hypertension (40%), with efficacy lasting about 1 year, median survival of about 2 years, and perioperative mortality of 5%-10%. extreme thrombocytosis and leukocytosis with primitive cellular excess [11]. Risk of thrombocytosis and thrombosis. Severe thrombocytopenia is a sign of impending leukemic transformation, and spleen excision does not have a favorable effect on the overall prognosis of such patients. Splenomegaly is a poor prognostic factor for patients proposed for hematopoietic hepatocyte transplantation, so it has been suggested that patients with significantly enlarged spleens should be splenectomized prior to transplantation.
3. Improvement of systemic symptoms: It is currently believed that systemic symptoms are related to the release of pro-inflammatory cytokines (IL-6). Treatment with spleen reduction effect can generally relieve systemic symptoms.
III. Experimental drug therapy and progress
The current drugs are mostly palliative treatment, which cannot change the course of PMF, much less cure PMF, so various new drugs are actively put into clinical trials.
1, JAK2 inhibitors: JAK2 V617F mutation occurs in about half of PMF patients. after JAK2 V617F mutation, even if no growth signal exists, JH2 pseudokinase domain inhibition of the JH1 kinase domain disappears, so that the JH1 region has a constituent row tyrosine kinase activity, and continues to phosphorylate downstream signaling molecules. The commonly used JAK2 inhibitors are divided into specific (class I) and non-specific (class II), with class I primarily targeting JAK family molecules and class II simultaneously targeting other molecules such as FLT3 and PKC.
INCB018424 (ruxolitinib) is a highly efficient, orally bioavailable selective JAK1/2 inhibitor, and is the closest targeted therapeutic agent to clinical application. The phase II clinical trial [12] selected 153 patients with MF (PMF and post-PV/ET MF patients), including those who were ineffective, intolerant or relapsed to their original treatment. The results confirmed the clinical efficacy of INCB018424 in patients with MF. The maximum tolerated dose was 25 mg twice daily or 100 mg once daily for a median duration of 14.7 months. The best efficacy and highest safety profile was achieved at the starting dose of 15 mg twice daily, with 17 of 33 patients (52%) showing rapid improvement in systemic symptoms and >50% reduction in spleen size for more than 12 months. INCB018424 was also effective in patients without the JAK2 V617F mutation. INCB01824 also reduced the levels of inflammatory cytokines such as IL-6 and TNF-α in peripheral blood. 3 of 153 patients converted to acute leukemia (AL) within 15 months, suggesting that INCBO18424 may have reduced the risk of conversion in patients with MF. INCB018424 was well tolerated, with a non-hematologic adverse effect rate of less than 10%, mostly of degree 1 to 2, and abrupt discontinuation of the drug could cause a “cytokine rebound”, leading to a relapse of symptoms. Hematologic adverse effects are mainly dose-related myelosuppression, and reversible thrombocytopenia is the most common. Two cases (1.3%) of systemic inflammatory response syndrome (SIRS) were recently reported after discontinuation of the drug.
The efficacy and safety of TG101348, an oral JAK2 inhibitor with high selectivity for JAK2, was investigated in a phase I/II multicenter clinical trial [13] in 59 patients with MF (44 with PMF and 15 with MF after PV/ET). The maximum tolerated dose was determined to be 680 mg/d for 28 d for 1 course, and 73% of the patients completed 6 courses of treatment, by which time 39% of the patients had significant spleen reduction, 57% of the patients with high leukocyte counts and 90% of the patients with high platelets had normalized their cell counts. 47% of the patients had spleen reduction, and 56% of the patients had normalized their leukocytes and platelets after 12 courses of treatment. TG101348 also reduced the level of pro-inflammatory cytokines in the blood, and more than half of the patients showed rapid improvement in night sweats, fatigue, itchy skin and cough. In addition, TG101348 significantly reduced the gene load of the JAK2 V617F mutation. Adverse reactions were reversible elevation of serum amylase and greater gastrointestinal reactions, with the incidence of nausea, vomiting, diarrhea, anemia and thrombocytopenia (degree 3-4) of 3%, 3%, 10%, 35% and 24%, respectively, and the adverse reactions were not dose-related.
CEP-701 (lestaurtinib) is an oral AK2 and FLT3 inhibitor that inhibits both mutant and wild-type JAK2. 22 patients with JAK2 V617F-positive MF (PMF and post-PV/ET MF), including relapsed, refractory, and newly diagnosed symptomatic intermediate- or high-risk patients, were selected for the phase II clinical trial [14] at a dose of 80 mg twice daily. Six of these patients (27%) achieved clinical improvement (IWG-MRT criteria), three had 50% or more spleen reduction, two were off transfusion, and one had 50% or more spleen reduction and a 100% or more increase in absolute platelet and neutrophil values. CEP-701 did not significantly reduce cytokine levels in the patients, and no reduction in JAK2 V617F gene load was observed.
Eight patients (36%) experienced grade 3 or 4 adverse reactions, mainly including myelosuppression (anemia in 14% and thrombocytopenia in 23%) and gastrointestinal reactions (diarrhea in 72%, nausea in 50%, and vomiting in 27%). Preliminary results of the multicenter phase I/II study of CEP-701, hosted by the Myeloproliferative Disease Research Consortium in the United States, using different drug doses and dosage forms, including CEP-701 oral solution (80-100 mg twice daily) and capsules (100-160 mg twice daily), showed that it was effective in reducing spleen, lowering leukocytes, improving transfusion-dependent status, and reducing JAK2 V617F load with average effect, high incidence of gastrointestinal reactions and better tolerability of capsules than oral solution.
The efficacy of JAK2 inhibition in PMF patients is clear, but the mutated genes of PMF also include MPL, CBL, LNK, etc. Therefore, the efficacy of JAK2 inhibitors is limited. JAK2 inhibitors not only act on JAK2, but also on other molecules such as FLT3, which produce different degrees of adverse effects.
2, histone deacetylase (HDAC) inhibitors: HDAC family includes 18 genes. Quantitative analysis of the expression and activity of class I-III HDAC mRNA in CD34+ cells from PMF patients showed increased expression of HDAC1, 2, 6, 8, 10 and SIRT1, 2, 3, 5, 7, while HDAC4, 5, 11, and SIRT4 expression was downregulated [15]. The HDAC inhibitors identified so far are classified by structure into the following types: short-chain fatty acids, oxoacids, cyclic tetrapeptides, ammonium phenylphenate, electrophilic ketones and unclassified types.
ITF2357 (givinostat) is a synthetic class I and II HDAC inhibitor. phase IIA trial [16] selected 12 patients with PV, 1 patient with ET and 16 patients with MF (PMF and post-PV/ET MF), all carrying the JAK2 V617F mutation as study subjects. The starting dose was 50 mg twice daily, and the mean duration of administration was 20 weeks. The results showed that ITF2357 reduced the pruritus symptoms and the efficiency of spleen reduction was 38% in MF patients. 7 MF patients completed the 24-week course, of which 2 reached clinical improvement and 5 reached disease stabilization (IWG-MRT criteria). ITF357 also reduced the gene load of JAK2 V617F mutation. Adverse effects were mostly of degree 1 to 2, mainly including diarrhea (62%), nausea (10%), gastroparesis (7%), anemia (21%), thrombocytopenia (10%), and fatigue (17%), and were well tolerated. In vitro assays showed that ITF2357 was more inhibitory to JAK2 V617F-positive cells, and the concentration required to inhibit the growth of JAK2 V617F-negative cell lines was 100-250 times higher than that required to inhibit positive cell lines [17].
HDAC inhibitory LBH589 synergistically induces apoptosis of MPN cells with the JAK2 inhibitor TG101209 [18].Preliminary results of a phase IA/II trial of LBH589 presented at the 2009 American Society of Hematology Annual Meeting showed that in 10 patients with PMF and 3 patients with MF after PV, 9 patients showed spleen shrinkage and reduction in systemic symptoms with efficacy lasting 39 months.
The phase II clinical trial [19] of 5-azacytidine, a DNA methylation enzyme inhibitor, selected 34 patients with MF (PMF and post-PV/ET MF) at a dose of 75 mg/m2 subcutaneously for 7 d for 4 weeks. 8 patients (24%) had an effect after 5 months, of whom 1 (3%) had a partial remission lasting The duration was greater than 22 months; 7 patients (21%) had bed improvement (IWG-MRT criteria), which was maintained for a mean of 4 months. Adverse effects were mainly myelosuppression, with 10 cases (29%) showing 3-4 degree neutropenia.
4. farnesylase transfer inhibitor: Mesa et al [20] hosted a phase II clinical trial of R11577 (tipifarnib). The study was conducted in 34 patients with MF (PMF and post-PV/ET MF) at a dose of 300 mg administered twice daily for 3 weeks, with 4 weeks as a course of treatment. The mean duration of administration was 4.6 months, and the effective rates for the treatment of hepatosplenomegaly and anemia were 33% and 38%. However, there were no significant changes in the degree of myelofibrosis, angiogenesis or cytogenetic status of the patients. Adverse effects mainly included myelosuppression, neurotoxicity, weakness, rash and hyponatremia.
5. pomalidomide: The phase II multicenter double-blind clinical trial of the third-generation immunomodulator pomalidomide [21] randomized patients with MF (PMF and post-PV/ET MF) into four treatment groups: pomalidomide (2 mg/d) combined with placebo, pomalidomide (2 mg/d) combined with prednisone The efficacy of pomalidomide in the treatment of anemia was 38%, 23%, 40%, and 25% after 3 courses of treatment, respectively. The main adverse effects of pomalidomide include neutropenia and thrombosis, which are significantly less neurotoxic than thalidomide and significantly less myelosuppressive than ralidomide. Increasing the dose of pomalidomide (>2 mg/d) increases the myelosuppressive effect, but does not improve the efficacy [22]. A recent phase II clinical trial conducted by Begna et al [23] showed that small doses (0.5 mg/d) of pomalidomide were significantly more effective in JAK2 V617F-positive patients than in negative ones.
6. recombinant interferon alpha: interferon alpha has extremely limited efficacy in PMF patients with severe anemia or splenomegaly, and its application is limited by more adverse effects. silver et al [24] selected 17 PMF patients with low-risk intermediate-risk-1 (IPSS) and gave recombinant interferon alpha-2a 50 ~ 3 million U 3 times a week or pegylated interferon alpha-2a 45 μ or 90 μ once a week, of which 2 cases had complete remission, 7 cases had partial remission, 1 case had clinical improvement, 4 cases had stable disease, and 3 cases had disease progression (IWG-MRT criteria), with an overall response rate of over 80% and small adverse effects, all of which were tolerable.
IV. Summary and outlook
The molecular mechanism of PMF is complex, including multiple genes and chromosomal alterations, and single drugs may not be sufficient to change the process of its occurrence and progression, perhaps the combination of drugs can reverse the process of PMF and restore the hematopoietic function of bone marrow. The molecular mechanism of PMF development needs to be elaborated in more detail, so that targeted therapies can be performed against multiple signaling molecules to inhibit the occurrence and development of PMF from multiple signaling pathways. More specific drugs need to be discovered to increase the therapeutic effect and reduce the adverse effects of treatment. In addition, further laboratory and clinical trials are needed to verify whether the drugs and doses suitable for patients in Western countries are also suitable for patients in China.