Burkitt lymphoma (BL) is an aggressive mature B-cell non-Hodgkin's lymphoma, prevalent among children and immunocompromised individuals, and associated to high mortality. BL lacks more effective and less toxic treatment protocols. Studies indicate that, despite being a mature lymphoma, BL can express cancer stem cell (CSC) markers (such as ALDH1 and CD133). Recent studies suggest that cannabidiol (CBD), a non-psychotropic component of Cannabis sativa L., has inhibited cell proliferation and cancer-stem cell markers in some cancers; however, there are no studies evaluating such effects in BL to date.

To evaluate the potential anti-proliferation and anti-CSC effects of CBD in in vitro models of BL.

Cells from three commercial immortalized LB cell lines (Daudi, Raji, and Namalwa) were cultured and, upon reaching 80% confluence, were submitted to cytotoxicity assays (MTT). Each cell line was exposed to control treatment (no drugs) or to one of the following drugs, at concentrations of 10-4 to 100µg/mL: (1) daunorubicin (reference chemotherapy drug), (2) broad CBD nanoformulation (0%THC; Bisaliv® Power Broad, from Thronus), and (3) full CBD nanoformulation (0.3%THC; Bisaliv® Power Full, from Thronus). After 72h, the plates were subjected to the MTT protocol to assess cell viability (cytotoxicity). Absorbance was measured in a SpectraMax 340PC-384 plate reader (Molecular Devices, USA) at 570 nm. Three independent experiments were performed, with technical triplicates per group (n=9). In a second stage, BL lines were cultured in 6-well plates until semi-confluent (80%), treated for 24h with each drug at its respective IC50 concentration or without drugs (control), collected to obtain cell blocks and sent for immunocytochemical detection of cell proliferation (Ki67) and CSC markers (CD133 and ALDH1).

The concentration-response curves obtained with the MTT assays show that daunorubicin and both CBDs are cytotoxic to all cell lines, reducing cell viability in a concentration-dependent manner. Comparing the IC50 of each drug, we found that daunorubicin (IC50 = 0.008‒021 µg/mL) is significantly more cytotoxic than CBDs (IC50 = 0.55‒1.184 µg/mL) in 2 cell lines - Raji and Daudi (p<0.05, ANOVA + Tukey's post hoc test). Regarding cell proliferation, daunorubicin and broad CBD are associated with a significant reduction in Ki67 (up to 30%; p<0.05) in the Raji and Namalwa cell lines. Full CBD also reduces Ki67 (∼30%), but only in Namalwa cells (p<0.05). Results of CSC marker expression indicate that all pharmacological treatments significantly reduce the number of CD133+ cells in all cell lines (p<0.001). No treatment reduces ALDH1. In Daudi cells, daunorubicin significantly increases the number of ALDH1+ cells (p<0.01).

The in vitro cytotoxic, anti-proliferative and anti-CSC effects demonstrated in BL lines when exposed to nanoformulations of CBD suggest the potential of these compounds for in vivo antineoplastic actions (particularly, with the use of broad nano-CBD). However, given the general limitations of in vitro research, such anti-cancer potential must be thoroughly scrutinized by in vivo and clinical studies.