2-O, 3-O desulfated heparin mitigates murine chemotherapy- and radiation-induced thrombocytopenia

Abstract

Thrombocytopenia is a significant complication of chemotherapy and radiation therapy. Platelet factor 4 (PF4; CXCL4) is a negative paracrine of megakaryopoiesis. We have shown that PF4 levels are inversely related to steady-state platelet counts, and to the duration and severity of chemotherapy- and radiation-induced thrombocytopenia (CIT and RIT, respectively). Murine studies suggest that blocking the effect of PF4 improves megakaryopoiesis, raising nadir platelet counts and shortening the time to platelet count recovery. We examined the ability of 2-O, 3-O desulfated heparin (ODSH), a heparin variant with little anticoagulant effects, to neutralize PF4's effects on megakaryopoiesis. Using megakaryocyte colony assays and liquid cultures, we show that ODSH restored megakaryocyte proliferation in PF4-treated Cxcl4^-/- murine and human CD34⁺-derived megakaryocyte cultures (17.4% megakaryocyte colonies, P < .01 compared with PF4). In murine CIT and RIT models, ODSH, started 24 hours after injury, was examined for the effect on hematopoietic recovery demonstrating higher platelet count nadirs (9% ± 5% treated vs 4% ± 4% control) and significantly improved survival in treated animals (73% treated vs 36% control survival). Treatment with ODSH was able to reduce intramedullary free PF4 concentrations by immunohistochemical analysis. In summary, ODSH mitigated CIT and RIT in mice by neutralizing the intramedullary negative paracrine PF4. ODSH, already in clinical trials in humans as an adjuvant to chemotherapy, may be an important, clinically relevant therapeutic for CIT and RIT.

Graphical abstract

Figure 1.

Chemical activity of ODSH. (A) Chemical structure of the ODSH polysaccharide showing replacement of 2 sulfhydryl groups with hydroxyl groups at the 2-O and 3-O positions. (B) ELISA performed with an LRP1-coated plate showing dose-dependent inhibition of PF4 binding with increasing ODSH concentrations. (C) Uptake of PF4 by cultured megakaryocytes. N = 3 experiments performed in duplicate. P < .001 for PF4 vs PF4+ODSH for WT murine megakaryocytes, and P = .002 for PF4 vs PF4+ODSH for Cxcl4^−/− murine megakaryocytes.

Figure 2.

In vitro anti-PF4 activity of heparin and ODSH. (A) Megakaryocyte colony assay showing the effect of PF4 (25 µg/mL) on colony formation and the effect of heparin (100 IU/mL). N = 4 experiments performed in duplicate. *P = .01 compared with PF4. **P = .01 compared with control. (B) Same as panel A except for ODSH (100 µg/mL). N = 4 experiments performed in duplicate. **P < .001 vs control; *P < .001 vs PF4. (C) Liquid megakaryocyte culture of human CD34⁺ cells in the presence of PF4 (25 µg/mL) ± ODSH (100 µg/mL). N = 6 experiments performed in duplicate. *P < .01 vs PF4; **P < .001 vs control.

Figure 3.

ODSH effect on blood counts in CIT. (A) Nadir platelet counts from mice shown in panel B demonstrating nadir platelet count was significantly higher in ODSH-treated mice vs control (P = .04) (N = 10 per arm). (B) Effect of ODSH SC injection starting 24 hours after administration of 5-FU in hPF4⁺/Cxcl4^−/− mice (red circles, ODSH; blue circles, vehicle control) compared with Cxcl4^−/− mice. Comparison of the curves showed the ODSH curve to be significantly different from the control curve; P < .04. Green circles represent WT animals examined simultaneously. Dashed line represents 100% baseline platelet count. N = 10 animals per arm.

Figure 4.

ODSH effect on blood counts in RIT in hPF4⁺/Cxcl4^−/−mice. (A) Nadir platelet counts of irradiated (6.5 Gy) hPF4⁺/Cxcl4^−/− animals as percentage of baseline platelet count, which occurred at day 10 for ODSH-treated animals vs control Cxcl4^−/− at day 12. P < .05. N = 20 animals per treatment arm. (B) Same as panel A but showing recovery of platelet count to baseline (dashed line demonstrates 100% baseline) after irradiation showing statistically different platelet counts starting at day 12 postirradiation (**P < .01 by Student t test after Bonferroni correction). N = 5 animals per arm. (C) Same as panel A, but showing survival of animals after irradiation, demonstrating improved survival in ODSH-treated animal (P < .04 by the Gehan-Breslow-Wilcoxon test). N = 20 animals per arm. (D) Same as panel A, but showing weight loss as percentage starting body weight for animals treated with ODSH or vehicle control. Dashed line is baseline body weight. N = 20 animals per arm. P < .001 for difference in curves.

Figure 5.

ODSH in RIT in WT animals. (A) Platelet counts of WT C57BL/6 animals as percentage of baseline platelet count after irradiation, showing statistically different platelet counts starting at day 8 postirradiation in animals treated with ODSH (25 mg/kg) starting 24 hours after irradiation and continuing for 3 doses every 12 hours. N = 15 animals per arm. P values by the Student t test after Bonferroni correction. (B) Same as panel A, but showing survival of irradiated animals. N = 15 animals per arm. P < .004 for survival difference by the Gehan-Breslow-Wilcoxon test.

Figure 6.

Effect of ODSH on intramedullary PF4 levels. (A) hPF4⁺/Cxcl4^−/− marrow 48 hours after irradiation stained with anti-hPF4 antibody. (B) Same as panel A, but for hPF4⁺/Cxcl4^−/− marrow treated with a total of 75 mg/kg ODSH. (C) As in panel A, but for WT animal without irradiation. (D) As in panel B, but for WT animal treated with ODSH without irradiation. (E) Same as panel C, but 48 hours after irradiation in a WT animal (treated with PBS). (F) Same as panel D, but 48 hours after irradiation in a WT animal treated with ODSH. For all panels, scale bar = 100 µm; immunohistochemical stain and counterstained with hematoxylin.