Cannabinoid receptor 2 knockdown in breast cancer cells: an impossible feat?

Breast cancer, which often leads to metastasis to bone, is the most frequent malignant tumor in women in North America and the second deadliest form of cancer in women in the U.S. Cannabinoids have been well established as mediators of tumor cell proliferation in several cancer models including breast cancer. Due to a marked upregulation of cannabinoid receptor 2 (CB2) in numerous tumor cell lines the activity of CB2 agonists have been extensively studied over the last decade, though their mechanisms of action have yet to be defined in the context of altering tumor proliferation. Elimination of a functional CB2 pathway is a crucial component in defining the underlying molecular mechanisms of CB2. We have attempted several pharmacological and genomic approaches in blocking CB2 activity and show here that CB2 agonist effects on breast cancer proliferation are not blocked by pretreatment with pertussis toxin, the CB2 antagonist SR144528 , the cannabinoid receptor 1 (CB1) antagonist SR141716 , or the TRPV1 antagonist capsazepine. Further, CB2 knockdown with lentiviral particles or siRNA yield a perplexing response: tumor cells either undergo apoptosis or respond with an even greater upregulation in CB2 expression. Studies are ongoing to generate a breast cancer cell line with reduced CB2 expression via transfection with an shRNA DNA plasmid in order to evaluate cellular response.