We designed high-affinity primers for the
mRNA sequence of human
tyrosinase to test the value of molecular detection of circulating
melanoma cells by reverse transcription-polymerase chain reaction (RT-PCR). The optimization process included in vitro settings and in vivo studies in a xenograft mouse model. We detected
tyrosinase expression with at least 40 pg and 1.5 pg of total
RNA extracted from cultured SKmel human
melanoma cells, using a first round of PCR amplification and nested PCR, respectively. Human
tyrosinase expression was found in the blood of nude mice bearing subcutaneous SKmel
tumors, and the expression bands were stronger after manipulation of the
tumor mass. We also examined the fate of circulating
melanoma cells in the present
melanoma model.
Tyrosinase expression declined in blood 6 h after a direct
intravenous injection of SKmel cells. A preliminary study in human blood samples demonstrated a baseline positive
tyrosinase determination in 64% (16/25) of advanced
melanoma patients using the RT-PCR nested assay. Baseline
tyrosinase expression was significantly associated with
disease progression after 12 months, and sequential determination during follow-up of the remaining disease-free patients showed a progressive increase of negative results.