IHP-102 Reduces Hypoxia-Induced Pain Behaviors in Townes SCD Mice

Background: Sickle cell disease (SCD) is an inherited red cell disorder characterized by painful episodes known as vaso-occlusive events (VOEs). VOEs may be initiated by the adhesion of white blood cells (WBCs) to the endothelium via P-selectin. Red blood cells (RBC) then adhere to the WBCs, and oxygen dissociates. As a result, under this hypoxia, the abnormal sickle hemoglobin (HbS) polymerizes, causing the RBCs to become rigid, blocking the microvasculature and causing painful ischemic tissue damage, a VOE. These rigid RBCs also hemolyze, activating complement and exacerbating tissue damage, which also contributes to pain. SCD therapies able to modify the course of VOE once initiated are urgently needed. We propose to attenuate VOE by 1) preventing the inciting event of WBC adhesion via blockage of P-selectin binding to the endothelium and 2) reducing complement activation. IHP-102, a glycan-based therapeutic, targets multiple VOE-related mechanisms, including P-selectin and complement, and has been demonstrated to reduce pulmonary vessel occlusion in humanized SCD mice. Our objective is to evaluate the ability of IHP-102 to reduce acute hypoxia-induced pain behaviors in the Townes humanized SCD mouse model.

Methods: Male and female Townes SS (SCD) and AA (control) mice (between 8-12 weeks old) were used for these studies. Acute VOE-like pain behaviors were induced via hypoxia exposure (3 hr. at 8% O₂, followed by 1 hr. reoxygenation at 21% O₂). Baseline assessments for mechanical and thermal (hot & cold) hyperalgesia, as well as grip strength, were conducted 24-72 hours prior to drug administration and/or hypoxia exposure. In experiment 1 (hypoxia time-course), mice were given a subcutaneous (SC) injection of IHP-102 (0, 3, 10, 30 mg/kg) immediately prior to hypoxia exposure. Following hypoxia, mice were assessed for acute pain behaviors at 1-, 4-, 24-, and 72 hours post-exposure. In experiment 2 (mock hypoxia), a separate cohort of animals not exposed to hypoxia were evaluated similarly. Mice were given an acute SC injection of IHP-102, and behavioral pain assessments were conducted at 1-, 4-, 24-, 48-, and 72 hours post-injection. Data were analyzed by ANOVA (analysis of variance) and linear mixed models, reporting regression coefficients, standard errors, and 95% confidence intervals.

Results: Eight-week-old Townes HbSS mice exhibited no baseline pain behaviors compared to age-matched AA control mice. In Townes HbSS mice, hypoxia (8% O₂) exposure produced robust VOE-like pain behaviors, demonstrated by increased paw withdrawal frequency (PWF) to 1.0 gram von Frey filaments, reduced paw withdrawal latencies (PWL) to a 52° C hot plate, increased number of cold (4°C) plate responses (lifts, tremors, shivers, grooming) in 2 minutes, and diminished forepaw grip strength. These behaviors persisted for at least 72 hours after hypoxia exposure (p < 0.05 vs mock-hypoxia). IHP-102 (10 and 30 mg/kg) treatment reduced the number of cold responses in Townes SS mice at 1- and 4-hours post-hypoxia (p < 0.05 vs saline). IHP-102 treated animals exhibited a trend (p = 0.18 vs saline) toward lower PWF. Neither hypoxia nor IHP-102 treatment had any significant effect on behavior in HbAA control mice.

Discussion: IHP-102 acutely reduces hypoxia-induced cold hyperalgesia behaviors and had a trend toward reduction in mechanical hyperalgesia in Townes HbSS mice (ongoing studies). Of note, these analgesic effects of IHP-102 were diminished by 24 hours, suggesting repeated dosing will be required. In our current model, IHP-102 was administered immediately before the hypoxia trigger. In an analogous situation in an individual with SCD, this would require administration during a pain prodrome, or in situations in which a pain event is frequently triggered, such as menses-induced VOE. Future studies will determine if IHP-102 can reduce pain behaviors when given following hypoxia, analogous to the individual with SCD already experiencing pain. It is also likely that repeat administration may be needed, depending on VOE severity, potentially every 12 to 24 hours. With the successful completion of pre-clinical assessments and future clinical trials in individuals with SCD, IHP-102 has the potential to be a game-changing non-opioid, self-administrable VOE treatment option, allowing for at-home pain management by patients.