Three over-the-counter antihistamines, clemastine, desloratadine, and loratadine, preferentially induce cell death through lysosomal membrane permeabilization in chronic lymphocytic leukemia cells, compared with normal lymphocytes, according to the results of an in vitro study published in Leukemia Research.
In addition, the antihistamines showed a synergistic effect in killing off chronic lymphocytic leukemia (CLL) cells when combined with the tyrosine kinase inhibitor, ibrutinib, but not with chemotherapy, according to Aaron Chanas-Larue of CancerCare Manitoba, Winnipeg, Man., and colleagues.
Blood from CLL patients and age-matched healthy donors was collected, treated, and compared with two malignant B-cell lines. Cells were treated with the three different antihistamines at various concentrations alone and in the presence of ibrutinib. Cell death was determined by flow cytometry using fluorescent staining and EC50 (half-maximal effective concentration) values were calculated.
Of the three drugs, clemastine demonstrated the greatest degree of cytotoxicity, with a mean EC50 value of 12.3 mcmol in CLL cells. Desloratadine and loratadine also had a greater effect on leukemic cells, with mean EC50 values of 27.2 mcmol and 17.2 mcmol, respectively, according to the researchers.
Clemastine also showed the greatest tumor sensitivity, with an EC50 nearly three times lower for CLL cells (EC50, 12.3 mcmol) than for normal peripheral blood mononuclear cells (EC50, 32 mcmol). In addition, clemastine induced cell death over a 72-hour time course in CLL cells, and was equally effective against CLL cells with del17p, unmutated immunoglobulin heavy chain gene, or high Zeta-chain–associated protein kinase 70 expression.
Effective synergy
The researchers found that clemastine enhanced cell death when combined with targeted CLL therapies ibrutinib, idelalisib, or venetoclax, but did not enhance the activities of the chemotherapeutics fludarabine, chlorambucil, or bendamustine.
Ibrutinib increased cell death to the greatest degree when combined with antihistamines. The effect was demonstrated to be synergistic, showing “a unique interaction between the activities of the antihistamines and this inhibitor of the B-cell pathway, suggesting a clinical potential for this combination,” the authors stated.
“Repurposing well-characterized drugs such as antihistamines with defined mechanisms and toxicities allows for repositioning of these drugs to use in CLL treatment in the near future in the context of targeted therapies,” they concluded.
The study was supported by grants from the Cancer Research Society and the CancerCare Manitoba Foundation. The authors reported that they had no conflicts.
SOURCE: Chanas-Larue A et al. Leuk Res. 2020 Jul 17. doi: 10.1016/j.leukres.2020.106423.