Synthesis of Novel Cannabinoid Ligands and Their Use as Anti-Glioma and Anti-Inflammatory Agents

Following the discovery of the cannabinoid receptors, research in the field of cannabinoids has grown exponentially over the last two decades. Cannabinoids have been shown to have tremendous therapeutic potential in the treatment of several pathological conditions ranging from inflammation to asthma, multiple sclerosis, Parkinson’s disease, epilepsy, glaucoma, septic shock, hemorrhagic shock, and cancer. Our research has focused on two major conditions for which cannabinoids hold great promise for drug development, namely, cancer and inflammation. Our focus in the field of cancer has been on the devastatingly lethal brain tumor glioblastoma multiforme. Due to the high expression of the CB2 receptor in human gliomas, we chose to focus on two CB2 selective lead compounds for these studies: KM-233 (CB2 antagonist) and HB-I-172 (CB2 inverse agonist). Both compounds showed in vitro efficacy against four human glioma cell lines (EC50s = 2.27 ± 0.18µM to 6.34 ± 4.10µM) while HB-I-172 also showed efficacy against prostate, lung, and colorectal tumor lines (2.38 ± 0.75µM to 5.22 ± 1.2µM). Significant reductions in tumor load were also observed in vivo in both side flank and intracranial models of glioblastoma. The anti-glioma efficacies of the two lead compounds were not altered by pharmacologic blockade of the CB1 and CB2 receptors which points to a non-CB1/CB2 mediated signaling pathway. This pathway was examined in the human glioma line U-87 MG and determined to involve reductions in pMEK1/2, pERK1/2, pAkt, and p-p70S6K with increases in pGSK3B, p53, and cleaved caspases 3 and 9, and PARP. Immunohistochemical studies revealed loss of mitochondrial membrane polarization with release of cytochrome-C, DNA fragmentation and condensation, and alterations in cytoskeletal structure. The current focus in the field of cannabinoids as anti-inflammatory agents is on CB2 selective compounds which are devoid of the CNS side-effects which could limit their therapeutic usefulness. We screened a variety of novel cannabinoids and the CB2 inverse agonist HB-I-172 emerged as a lead. In vitrotreatment with HB-I-172 caused a significant reduction in a number of proinflammatory cytokines and chemokines in both neoplastic lung epithelial cell and macrophage models and in primary human lung epithelial and endothelial cells, macrophages, and microglia. We believe that HB-I-172 and other CB2 selective cannabinoids are promising treatments for a variety of inflammatory conditions from neuro-inflammatory disorders such as multiple sclerosis and Huntington’s disease to systemic conditions such as atherosclerosis and inflammatory pain. Finally, three new series of heterocyclic cannabinoid ligands were synthesized and screened. The hexahydro pyrimidine classical, pyrimidine nonclassical, and furanopyrimidine cannabinoids were designed with CB2 selectivity in mind. After many failed synthetic routes were abandoned, the three new classes were successfully generated. Many of these compounds showed good CB2 selectivity (77-fold) and showed efficacy in both anti-glioblastoma and anti-inflammatory studies