HU-444

HU-444, designated (-)-8,9-dihydrocannabidiol-7-oic acid diacetate, is a synthetic cannabidiol (CBD) derivative developed at the Hebrew University of Jerusalem by Haj, Sumariwalla, Hanus, Kogan, Yektin, Mechoulam, Feldmann, and Gallily and first reported in the Journal of Pharmacology and Experimental Therapeutics in 2015 [1]. The compound was designed through two critical structural modifications to the parent CBD scaffold: reduction of the 8,9-double bond (converting the isopropenyl to an isopropyl group) and oxidation of the C-7 methyl group to a carboxylic acid, followed by diacetylation of both phenolic hydroxyl groups. These modifications confer two essential properties that distinguish HU-444 from native CBD. First, the compound cannot undergo acid-catalyzed cyclization to a delta-9-tetrahydrocannabinol (THC)-like pyran ring, eliminating the principal chemical liability of CBD-based therapeutics. Second, HU-444 does not bind to either the CB1 or CB2 cannabinoid receptor (Ki values exceeding 10 micromolar for both), confirming the absence of psychotropic activity and placing the anti-inflammatory mechanism entirely outside the classical endocannabinoid receptor system.

In vitro pharmacology in RAW 264.7 murine macrophages and thioglycolate-elicited peritoneal macrophages demonstrated that HU-444 suppresses lipopolysaccharide-stimulated tumor necrosis factor alpha (TNF-alpha) production by up to 69 percent at 40 micrograms per milliliter, reduces zymosan-stimulated reactive oxygen intermediate (ROI) generation by 62 percent at 40 micrograms per milliliter, and inhibits lipopolysaccharide-stimulated nitric oxide (NO) production by 64 percent at 60 micrograms per milliliter [1]. In vivo, HU-444 at 10 mg/kg intraperitoneally suppressed serum TNF-alpha by 45 percent in a C57BL/6 mouse lipopolysaccharide challenge model. In the concanavalin A hepatitis model, HU-444 at 5 mg/kg reduced serum alanine aminotransferase (ALT) by 87 percent and aspartate aminotransferase (AST) by 85 percent, with histopathological scoring demonstrating near-complete hepatoprotection at this dose [1]. In murine collagen-induced arthritis, both intraperitoneal administration at 2.5 to 5 mg/kg and oral administration at 15 mg/kg produced significant reductions in clinical arthritis score and paw swelling, with joint histology confirming preservation of architecture and reduction of damaged joints by 36.7 percent (intraperitoneal) and 45.5 percent (oral) [1].

A notable pharmacological feature of HU-444 is its bell-shaped dose-response curve, with maximal anti-inflammatory efficacy at intermediate doses (5 mg/kg in the liver injury model, 2.5 to 5 mg/kg in arthritis) and diminished efficacy at higher doses (10 mg/kg), a pattern also observed with the parent compound CBD and attributed to the engagement of counterregulatory anti-inflammatory feedback at supratherapeutic concentrations [8]. The compound did not produce any delta-9-THC-like effects in the standard mouse tetrad assay (ring immobility, open field locomotor suppression, hypothermia, hot plate antinociception), confirming the absence of CB1 receptor-mediated psychoactivity.

HU-444 has not entered clinical development as of the most recent monograph revision. The compound is positioned as a research tool for the investigation of cannabinoid receptor-independent anti-inflammatory mechanisms and as a candidate scaffold for preclinical development in autoimmune and inflammatory disease. This monograph reviews the chemistry, synthesis, and structural rationale; the cannabinoid receptor-independent anti-inflammatory pharmacology; the preclinical evidence base across three murine disease models; the pharmacokinetic considerations extrapolated from the parent CBD scaffold; sourcing, reconstitution, and handling; stack-interaction considerations; the preclinical safety profile; and a comparative assessment of five nonpsychotropic cannabinoid anti-inflammatory candidates (cannabidiol, HU-320, lenabasum, HU-308, HU-446) against HU-444 on five competency standards. The compound is not approved by any regulatory authority for any indication. It is available as a research-grade preparation; investigators should obtain analytical confirmation of identity and purity on every lot.