Differential antitumor effects of vitamin D analogues on colorectal carcinoma in culture.

Colorectal cancer (CRC) is an emerging global problem with the rapid increase in its incidence being associated with an unhealthy lifestyle. Epidemiological studies have shown that decreased levels of vitamin D3 significantly increases the risk of CRC. Furthermore, negative effects of vitamin D3 deficiency can be compensated by appropriate supplementation. Vitamin D3 was shown to inhibit growth and induce differentiation of cancer cells, however, excessive vitamin D3 intake leads to hypercalcemia. Thus, development of efficient vitamin D3 analogues with limited impact on calcium homeostasis is an important scientific and clinically relevant task. The aims of the present study were to compare the antiproliferative potential of classic vitamin D3 metabolites (1α,25(OH)2D3 and 25(OH)D3) with selected low calcemic analogues (calcipotriol and 20(OH)D3) on CRC cell lines and to investigate the expression of vitamin D-related genes in CRC cell lines and clinical samples. Vitamin D3 analogues exerted anti-proliferative effects on all CRC cell lines tested. Calcipotriol proved to be as potent as 1α,25(OH)2D3 and had more efficacy than 20-hydroxyvitamin D3. In addition, the analogs tested effectively inhibited the formation of colonies in Matrigel. The expression of genes involved in 1α,25(OH)2D3 signaling and metabolism varied in cell lines analysed, which explains in part their different sensitivities to the various analogues. In CRC biopsies, there was decreased VDR expression in tumor samples in comparison to the surgical margin and healthy colon samples (p<0.01). The present study indicates that vitamin D3 analogues which have low calcemic activity, such as calcipotriol or 20(OH)D3, are very promising candidates for CRC therapy. Moreover, expression profiling of vitamin D-related genes is likely to be a powerful tool in the planning of anticancer therapy. Decreased levels of VDR and increased CYP24A1 expression in clinical samples underline the importance of deregulation of vitamin D pathways in the development of CRC.

Ecto-5'-nucleotidase (eN, CD73) is coexpressed with metastasis promoting antigens in human melanoma cells.

Upregulated expression of eN has been found in the highly invasive human melanoma cell lines but neither in melanocytes nor in primary tumor cells. Membrane proteins associated with cell adhesion and metastasis: alpha5-, beta1-, beta3-integrins, and CD44 were elevated gradually in accordance with increasing metastatic potential. alphav-integrin was seen mostly in aggressive melanomas. The expression of eN correlated with a number of metastasis-related markers and thus may have a function in the process. eN activity went parallel with its amount in all cells. Concanavalin A strongly inhibited the enzyme in a noncompetitive way. Clustering of eN protein in overexpressing cells by ConA-treatment increased the enzyme association with the heavy cytoskeletal complexes. A similar shift towards cytoskeletal fractions took also place with other membrane proteins coexpressed with eN. This ConA-induced association may reflect a putative interaction of eN with physiological ligand, that upon interaction, aggregates protein components of lipid rafts and triggers signaling pathway that may be intrinsically involved in cell-stroma adhesion.