ackground: Tamoxifen is the first line of treatment in hormone receptor-positive breast cancer. Letrozole
is developed for postmenopausal patients and metastatic breast cancer. Patients with concomitant chronic
toxoplasmosis are at risk of reactivation of tissue cysts. It is still unknown whether these drugs will cause
protection against reactivated toxoplasmosis or exacerbated symptoms.
Objective: This study aimed to investigate the possible effect of Tamoxifen and Letrozole on T. gondii freed
bradyzoites in case of rupture tissue cyst with their subsequent reactivation to tachyzoites.
Material and Methods: The study was conducted using in vitro cultured T. gondii tachyzoites in a cultured
Vero cell line. Different concentrations of Tamoxifen and Letrozole were used (0.24-125 ug/ml). Antiproliferative
effect was determined by methyl thiazolyl tetrazolium (MTT) cytotoxicity assay estimated as
cell line viability% reflecting the inhibition of tachyzoites proliferation after 24 and 48 h treatment. Antiinvasive
effect was determined by counting Giemsa-stained intracellular tachyzoites inside infected Vero
cells using light microscopy. Induced cytotoxic morphological changes in the tachyzoites was determined
by transmission electron microscopy (TEM).
Results: By MTT, cytotoxicity of both drugs to the infected cultured Vero cells indirectly assayed the
decreased tachyzoites proliferation compared to the control drug-free parasites (P<0.01). Letrozole
proved to be more cytotoxic than Tamoxifen after 48 h treatment (P<0.05). Both drugs decreased the
ability of tachyzoites' invasion compared to drug-free tachyzoites (P<0.05) with no statistical difference
between the used drugs. Additionally, TEM demonstrated tachyzoites damage caused by both drugs.
Conclusion: Tamoxifen and Letrozole demonstrated anti-toxoplasmic activity, indicating that administering
these drugs in cancer patients may also prevent the possibility of reactivated toxoplasmosis. In vivo studies
are recommended to evaluate their efficacy.