231P - The impact of calcitriol and tacalcitol on the Th17 lymphocytes in breast cancer

Background

Our research is focused on vitamin D₃ active form calcitriol and its analog tacalcitol, and their interactions on the immune system, including Th17 lymphocytes, which plays a significant role in the development and progression of breast cancer. The aim was to analyze the direct effect of vitamin D compounds on its nuclear receptors in Th17 cells and changes in IL-17 production. The interaction with osteopontin (OPN) was examined as the example of indirect influence on Th17 cells population in breast cancer. Taking into account the hormonal status during disease development and stimulation of the immune system, we used mice: 6-8 weeks old as a premenopausal and 35-40 weeks old, ovariectomized, as a postmenopausal model. Our research was mainly focused on CD4+ lymphocytes isolated from spleens, looking forward to Th17 helper lymphocytes differentiation after treatment.

Methods

Animals bearing EMT6 or E0771 murine mammary gland cancer tumours were administered with calcitriol or tacalcitol from day 7 after inoculation, every three days, in the dose of 0.5 μg/kg or 1 μg/kg body weight/day, respectively. Local Ethics Committee permission No 50/2020. CD4+ cells (splenocytes) were isolated, cultured and examined for subpopulation phenotype, differentiation into Th17, gene expression profile, OPN impact on Th17 differentiation, expression of OPN receptors.

Results

Both compounds inhibited E0771 tumor growth, but tacalcitol increased metastasis in aged mice. The growth of EMT-6 tumors was stimulated in young and inhibited in aged mice after tacalcitol treatment. Metastasis was inhibited independently of the age by tacalcitol. In the E0771 premenopausal and EMT6 postmenopausal groups, tacalcitol increased the number of gene transcripts for IL17. The same tendency was observed in the E0771 postmenopausal group for the Il17 and Rorc genes. Blocking of selected CD4+ surface receptors (CD44, CD51), related to OPN functions, resulted in an increase of iTh17 cells after tacalcitol treatment. Tacalcitol in iTh17 cells induced the mRNA level for VDR, OPN, IL-21 and IL17R coding genes.

Conclusions

The Th17 induction via the OPN plays an important role, especially after tacalcitol treatment. Both compounds affect Th17 lymphocytes depending on the tumor type and age of mice.

Legal entity responsible for the study

The authors.

Funding

The National Science Center, OPUS 18 grant No. 2019/35/B/NZ5/01250.

Disclosure

All authors have declared no conflicts of interest.