Long-Term Therapy with GBT021601 and Moderate Chronic Transfusion Therapy Prevent the Development of Hyperalgesia

Background: Sickle cell disease (SCD) is an inherited multisystem blood disorder that produces sickle-shaped erythrocytes that obstruct blood flow, leading to severe clinical complications, including painful vaso-occlusive events (VOE). Acute pain is the single most common cause of hospitalization, but by adulthood, 55% develop chronic pain. Repeated VOEs can compromise bone integrity and lead to development of chronic pain syndromes. The sickle mouse bone is characterized by hypoxia-induced angiogenesis, which is hyperinflammatory and linked to chronic pain, and can be reversed with chronic transfusion therapy (CTT)¹. In the Stroke Prevention Trial (STOP), CTT used for primary stroke prevention showed reduction in pain events². However, significant risks of alloimmunization, iron overload, and cost associated with CTT led others to liberate hemoglobin S (HbS) goals to <50%³. We have shown previously that GBT021601 (601), a potent anti-sickling oral agent, can increase hemoglobin (Hb) and reverse pathologic angiogenesis in the sickle mouse bone. Here we assess the ability of 601 or moderate CTT (HbS <50%) to modify pain phenotypes in the sickle mouse model.

Methods: 7-to-9-week-old Townes HbSS mice were fed with chow containing 0.4% of 601, control chow, or received CTT. After 1, 4, or 12 weeks of 601 chow, complete blood count was measured from peripheral blood using an Element HT5 (HESKA) hematology analyzer and pain phenotypes were assessed in the von Frey, hot plate, cold plate (number of responses over 2 minutes and latency), and grip strength tests. In the transfusion arm, HbSS mice were transfused retro-orbitally with washed, packed red blood cells (RBC) collected from HbAA mice at a total volume of 200ul. Transfusions occurred 1-2x a week to achieve a HbS goal of 20-50% for 8 weeks and measured by HPLC (BioRad D-10). Control mice received 200ul of PBS. Pain phenotypes were assessed at the end of CTT. All statistical analysis was performed using the Mann-Whitney test.

Results: 601 increased hemoglobin (Hb) by 4 and 12 weeks of therapy (16.2 g/dL and 16.5 g/dL) compared to control mice (9.9g/dL, p<0.001). At week 1 of chow, von Frey, cold and hot plate tests, and grip strength measurements were similar between HbSS mice on control (n=8) compared to HbSS mice on 601 chow (n=8). With 4 weeks of treatment, untreated HbSS mice showed an increase in paw withdrawal frequency (PWF) in the von Frey test (6.25 vs 4, p=0.02) and number of responses to cold stimuli compared to 601-treated mice (26 vs 8, p=0.003). Only PWF was significantly increased in untreated HbSS mice (n=5) compared to those treated with 12 weeks of 601 (n=5) (7 vs 3.5, p=0.02). In the CTT arm, average HbS% after initiation of CTT was 41.2% (range 19.5%-71.3%) with an average Hb of 9.9 g/dL (range 5.4g/dL-14.1g/dL) by 8 weeks. At completion of CTT (n=8) or PBS (n=6), PWF was significantly lower in the CTT arm (6 vs 3.5, p=0.01) with improved latency response time to cold stimuli compared to controls (53s vs 15s, p=0.02). Comparison of von Frey testing between groups receiving CTT and 4 or 12 weeks of 601 chow was not significantly different.

Conclusions: We show for the first time the impact of CTT for 8 weeks with a moderate HbS% goal of <50% can modify pain behaviors in the sickle mouse, most significantly measured by the von Frey method. The von Frey method is a validated method to assess both allodynia and hyperalgesia, suggesting CTT may reduce chronic pain behaviors. Limitation of the CTT arm includes pain testing at one time point. More importantly, an oral agent 601 equally reduces development of chronic pain as early as 4 weeks of therapy in the sickle mouse model. Pain phenotypes should be further investigated with 601 in the prevention of chronic pain in clinical studies.

References:

1. Park et al. (2020). Blood 135(23): 2071-2084

2. Miller et al. (2001). The Journal of Pediatrics 139(6): 785-789

3. Choi et al. (2023). Journal of Clinical Apheresis 38(6): 677-684