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BACKGROUND: Hypoxic cells in solid tumors are resistant to radiotherapy. Omniox has developed a novel class of oxygen carrier proteins termed H-NOX, engineered to deliver oxygen selectively into hypoxic tissues. Previous studies have shown that one of our H-NOX candidates, OMX-4.80, penetrates intracranial glioblastoma (GB) tumors in mice, and in a dose dependent manner decreases tumor hypoxia and extends survival when combined with radiotherapy. However, we discovered that the circulation half-life of OMX-4.80 is ∼1h in dogs, which may limit clinical utility. To improve the circulation half-life, we developed a PEGylated version of OMX-4.80 (OMX-4.80P). The aim of this study was to characterize the pharmacokinetic and safety profile of OMX-4.80P and examine its effect on tumor hypoxia. METHODS: After intravenous administration of OMX-4.80P to mice and rats bearing GB tumors, we collected tumors, blood and plasma, and analyzed OMX-4.80P pharmacokinetics, immunogenicity and its effects on blood cell counts and chemistries. We evaluated OMX-4.80P bio-distribution by immunohistochemistry and its effect on tumor hypoxia by ELISA of endogenous (HIF-1a) and exogenous (pimonidazole) hypoxia markers. RESULTS: Compared to OMX-4.80, OMX-4.80P has an increased stability and circulation half-life (30h vs. 1h), significantly longer tumor accumulation (48h vs. 4h), and is not immunogenic. Furthermore, OMX-4.80P crosses the blood tumor barrier in several different intracranial rodent GB models and reduces HIF-1a and pimonidazole accumulation by ∼50%. Pharmacokinetic and toxicology studies in rodents and dogs showed that OMX-4.80P is well tolerated, and has a circulation half-life of ∼52h in dogs. The resulting exposure is expected to be sufficient for OMX-4.80P to accumulate in human GB tumors and reduce hypoxia. CONCLUSIONS: In summary, the increased retention of OMX-4.80P in circulation, the longer exposure achieved in solid tumors and efficiency in delivering oxygen into hypoxic tissues suggest OMX-4.80P is a promising IND candidate for radiation therapy enhancement in GB.

BACKGROUND: Hypoxia in solid tumors blunts the tumor cytotoxicity of radiotherapy (RT) and is a major independent predictor of poor patient outcomes in glioblastoma (GB). To increase tumor oxygenation, Omniox has engineered a novel oxygen delivery protein, OMX-4.80P (OMX), tuned to release oxygen specifically in hypoxic tumor tissue. When given with radiotherapy, OMX significantly enhances RT efficacy in rodent tumor models. Since spontaneous canine brain cancers, including GB, share similarities with human brain cancers in terms of morphology, disease progression, and response to approved therapies, a Phase 0 clinical trial was conducted in patient dogs to assess OMX safety, PK/PD and signs of efficacy to inform human clinical strategy. METHODS: Dogs with presumed brain cancers (MRI) underwent either resection surgery with radiotherapy (Sx + RT) or stereotactic radiosurgery (SRS). In the Sx + RT group, OMX was administered once before surgery (4–48 hours pre-Sx) and twice weekly in conjunction with RT (20x2.5Gy). In the SRS group, OMX was dosed on 2 consecutive days in combination with SRS (3x8Gy). PK, CBC, blood chemistry, coagulation, and immune responses were assessed. Additionally, resected tumors were analyzed for OMX accumulation and hypoxia levels (ELISA, IHC). RESULTS: To date, 14 dogs have completed the trial (10 Sx, 5 Sx + RT, 4 SRS): Five dogs show no signs of tumor regrowth at 3 months and 2 dogs had no visible tumors at 6 months. OMX induced no dose-limiting adverse events and median T1/2 is 35h. Resected tumors show a strong correlation between OMX concentration in tumor tissue and reduced hypoxia with OMX penetrating deep into tumor tissue. CONCLUSIONS: When given in conjunction with RT regimens equivalent to human standard of care, OMX is safe and well-tolerated. Tumor tissue analysis suggests that OMX-4.80P decreases tumor hypoxia, thus supporting its further clinical development for the enhancement of radiotherapy efficacy in GB patients.

BACKGROUND: Omniox has engineered OMX-4.80P, a PEGylated H-NOX oxygen carrier, as a long-acting therapeutic candidate to enhance radiotherapy (RT) in the treatment of glioblastoma (GB) and other solid tumors. We have previously described the un-PEGylated OMX-4.80 variant, which can penetrate intracranial mouse GB tumors, release oxygen exclusively into hypoxic tumor tissue, and enhance tumor growth delay and survival when combined with RT. However, OMX-4.80 has a short circulation half-life that limits its clinical potential. Here, we describe the pre-clinical profile of PEGylated OMX-4.80 (OMX-4.80P), demonstrating it is well tolerated, long-lasting in circulation and tumors, and is significantly more efficacious than OMX-4.80. METHODS: We PEGylated OMX-4.80 to increase its circulation half-life while retaining its ability to preferentially accumulate in tumors and selectively release oxygen to hypoxic microenvironments. We characterized the efficacy of OMX-4.80P in large, hypoxic, radioresistant tumors, and its activity in intracranial GB models in nude mice and immunocompetent rats. We also conducted toxicology and pharmacokinetic studies in multiple animal models including naïve dogs. RESULTS: In xenograft studies of large, hypoxic, radioresistant tumors, single doses of OMX-4.80P in combination with RT result in apparent tumor cures in ∼30-50% of tumors compared to 0% cures in RT-only groups. Interestingly, the larger molecular size of OMX-4.80P (∼120kDa) did not prevent its passing the blood-tumor barrier in mouse and rat intracranial tumors and resulted in hypoxia reduction. Pharmacokinetic and toxicology studies using single or multiple supratherapeutic and therapeutic doses of OMX-4.80P in rodents and dogs demonstrated that it has a circulation half-life of ∼24h in rats and ∼52h in dogs, compared to 1-2h for OMX-4.80, and that it is well tolerated. Finally, OMX-4.80P has no detectable immunogenic response. CONCLUSIONS: The preclinical efficacy data, and promising pharmacokinetic and toxicology profile, of OMX-4.80P support its clinical development for the enhancement of radiotherapy in GB patients.