Abstract 5938: Development of HH044, an orally bioavailable nNOS inhibitor, for the treatment of cutaneous melanoma
Authors: Patel Anika , Tong Shirley , Silverman Richard B. , Yang Sun 
Published: March 2024

Abstract
Background: Human cutaneous melanoma is one of the few cancers in which the incidence rate continues to increase, and despite recent advances in immune and targeted therapies, the 5-year survival rate of metastatic disease remains low. Neuronal nitric oxide synthase (nNOS) has been identified to contribute to melanoma development, stimulating disease progression, and facilitating escape of melanoma cells from the immune response. We developed a novel small molecule, HH044, which specifically inhibits nNOS activity and reduced nitric oxide production in melanoma cells. We aim to conduct a proof-of-concept study using our nNOS inhibitor administered orally for anti-melanoma treatment.
Methods: Human melanoma cell lines (A375, Sk-Mel-28, wm3211) were employed to analyze the anti-cancer activities of HH044 in vitro. An immune-competent syngeneic melanoma mouse model was used to determine the anti-tumor activity of HH044 when administered orally (50 mg/kg/day) or intraperitoneally (10 mg/kg/day) for 21 days. A pharmacokinetic study of drug levels in serum and tumor samples was conducted after a single dose given intraperitoneally or orally using LC-MS/MS analysis at different time points.
Results: HH044 has high selectivity of nNOS over iNOS (340-fold) and eNOS (540-fold). The IC50 of HH044 in melanoma cell lines was 5.27 ± 3.3 μM, while iNOS inhibitor 1200W did not exhibit any cytotoxicity up to 100 μM concentration. Of note, nNOS blockade by HH044 did not result in reactivation of iNOS, and expression levels of iNOS were not changed after HH044 treatment. In vivo studies demonstrated that HH044 treatment given intraperitoneally exhibited potent anti-tumor activity and reduced tumor weight to 45% of control. When administered orally, HH044 at 50 mg/kg significantly reduced tumor growth to 61% of control and extended mice median survival from 32 days to 53 days. Pharmacokinetic analysis showed that oral administration achieved sufficient drug levels in xenograft tumors, which were well above the Ki value (0.005 μM) despite a wide range of bioavailability. The drug level peaked at 2 hours after a single dose (2.27 ± 0.666 μM in the tumor and 23.68 ± 17.43 μM in the serum). Intraperitoneal injection achieved much higher levels in serum and tumor samples, which also declined slower compared to oral gavage administration. By 24 hours, the drug levels in serum and xenograft tumors remained at 1.55 ± 0.12 μM and 1.77 ± 0.24 μM concentration, respectively. No significant systemic toxicities were observed with HH044 treatments either given via i.p. injection or orally. Further in vivo studies combining nNOS inhibitors with immune checkpoint blockade are currently underway.
Conclusions: HH044, as the first-in-class nNOS inhibitor, exhibits potent anti-melanoma activity by oral administration. Developing selective nNOS inhibitors has shown to be a novel therapeutic strategy to improve melanoma treatment.
Citation Format: Anika Patel, Shirley Tong, Richard B. Silverman, Sun Yang. Development of HH044, an orally bioavailable nNOS inhibitor, for the treatment of cutaneous melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5938.