Immunotherapy is well-practiced as one of the main adjuvant
therapies for
melanoma patients. Until now, many immunotherapeutic investigations have focused on improving the effector side of the antitumor response, but only a few studies have been concerned with preventing the loss of
tumor-associated
antigen (TAA) expression. Loss of TAA should be an important problem for the recognition of
tumor cells by cytotoxic T lymphocytes. If any agents that augment the expression of
melanoma antigens were found, they could improve the efficacy of
immunotherapy by increasing the
antigens. To detect effective chemicals, we made a fluorescent cellular reporter system for screening promising candidate chemicals. In this system, the fusion gene of the
Melan-A/MART-1 promoter sequence followed by the
green fluorescent protein (GFP) coding region was stably transfected into MUX human
melanoma cells which are known to express little or no
Melan-A/MART-1.
Melan-A/MART-1 is a well-known
melanoma antigen recognized by autologous cytotoxic T cells, and is a
glycoprotein associated with the melanosome, the organelle in which
melanin synthesis proceeds. By using this screening system,
daunorubicin,
doxorubicin and
cytochalasin D, which enhanced the green fluorescent, were selected and then were confirmed to actually increase the expression of
Melan-A/MART-1
mRNA and
protein in human
melanoma cells of MU89, MM96L(+) and SK-MEL-28, but also in low-antigen presenting cells such as MM96L(-), MUX, and A375. In conclusion, we have successfully established a well-functioning screening system, which will allow us to find candidate chemicals that up-regulate or maintain the
melanoma antigen expression.