At follow up in the hematological out patient

At follow-up in the hematological out-patient clinic the patient had a normal HCT and the platelet count was slightly elevated at 515×109/L. However, no further cytoreductive treatment was initiated. At the beginning of 2011 (31 months after the PV-diagnosis) osteoporosis was diagnosed. Consequently, treatment with alendronate 70mg/week was initiated and continued for 18 months, until the patient changed treatment to Teriparatide – a PTH analog – for two years. Afterwards alendronate was reintroduced. During these 56 months, after initiation of alendronate, the patient was largely in complete hematological remission (the platelet count was temporarily above 400×109/L on some occasions) without need for further phlebotomies, and the JAK2-V617F mutation status 44 months after PV-diagnosis revealed a marked decrease in the allele burden from 64.0% to 21.4% (Fig. 1). The patient had no need of phlebotomies or cytoreductive treatment to reduce elevated cell counts, and no thrombohemorrhagic events occurred. Subsequent serial measurements of the JAK2-V617F allele burden have shown sustained values below 20% and even below 10% on some occasions. Two follow-up bone marrow biopsies at 33 and 53 months after institution of statin and bisphosphonate combination therapy (64 and 84 months after PV-diagnosis) displayed stable disease with remaining features of PV. Despite this, the vascular dilatation found in the initial bone marrow biopsy had disappeared in the two following biopsies (Fig. 2).
Discussion This case report demonstrates for the first time a remarkable hematological and molecular response with a marked sustained decrease in the JAK2-V617F allele burden during statin and bisphosphonate combination therapy of a patient with PV. Both agents potently inhibit the mevalonate pathway, which has been suggested as a therapeutic target in multiple cancer types [1] and also in the treatment of MPNs [2]. An association between chronic CUDC-907 weight and the development and progression of MPNs has been proposed [3], and both statins and bisphosphonates possess potent anti-inflammatory, anti-neoplastic, anti-thrombotic and anti-angiogenic properties unrelated to the cholesterol lowering effects of statins [1,2,4]. These effects are probably mediated by inhibiting the synthesis of the important isoprenoid intermediates such as farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGP). These intermediates are important in the posttranslational modification of a variety of proteins. When activated these pathways induce increased cellular growth, proliferation, migration and oxidative stress. Accordingly, their inhibition might theoretically dampen inflammation and ultimately tumor development [1,4]. Importantly, simvastatin (and other statins) induce apoptosis and inhibit JAK2-V617F-dependent cell growth in MPN cell lines. Furthermore, the MPN-associated JAK2-V617F kinase localization to lipid rafts and its signaling is inhibited by statins [5]. Also, the pro-inflammatory cytokines TNF-alpha and IL-6 are decreased during statin treatment in a wide variety of inflammatory conditions [6], TNF-alpha being able to facilitate clonal expansion of JAK2-V617F-positive cells in MPNs [7]. Both statins and bisphosphonates inhibit the release of VEGF. VEGF mediated neo-angiogenesis may in part be responsible for the bone marrow fibrosis observed in myelofibrosis [1,2]. This effect may be observed in the bone marrow of this patient, where the CD34 staining revealed vascular dilatation in 2008 but not in the following two biopsies. Release of VEGF from the tumor cells may be responsible for the vascular dilatation observed [8]. Regarding the reduction in JAK2-V617F allele burden, the patient only received treatment with HU for 18 days during the initial disease course. Thus, it is reasonable to conclude, that the ensuing marked decrease in the JAK2-V617F allele burden over the first 44 months after the PV diagnosis was not related to HU-treatment. Although HU has been shown to reduce the JAK2-V617F allele burden in some studies, other studies have failed to reproduce this effect [9]. Importantly, the effect of HU on peripheral blood cell counts and the JAK2-V617F allele burden is but temporary with rising cell counts within a few days after HU being discontinued. We believe that the response is a result of the treatment with simvastatin and from month 31 the addition of alendronate. However, since 44 months elapsed between the first two JAK2-V617F analyses, we are unable to relate the decrease in the JAK2-V617F allele burden directly to the initiation of alendronate treatment. Interestingly, during the two years of teriparatide treatment, when alendronate was paused, the JAK2-V617F allele burden was relatively stable. The following stabilization of the disease parameters might suggest that a long-term bisphosphonate treatment is redundant, and instead a short-term treatment plan with bisphosphonate followed by continuous statin treatment might be a better strategy. During this period the patient was treated with the platelet inhibitors ASA and dipyramidole. Dipyramidole is a phosphodiesterase inhibitor similar to anagrelide which is used in the treatment of essential thrombocytosis to reduce platelet count, but not in the standard treatment of PV [10]. Dipyramidole has been shown to inhibit the proliferation of peripheral blood mononuclear cells from patients with CML and AML in-vitro [11], and could have influenced the hematological response in this patient. On the other hand dipyramidole can also stimulate hematopoietic reconstitution in irradiated mice [12]. No studies have shown an effect on human blood cell counts in-vivo. Thus, we do not believe that dipyramidole is responsible for the remarkable response. Likewise, there is no evidence to suggest that ASA could have caused the response.