Arginine deiminase (ADI)-based arginine depletion is a novel strategy under clinical trials for the treatment of malignant melanoma with promising results. The sensitivity of melanoma to ADI treatment is based on its auxotrophy for arginine due to a lack of argininosuccinate synthetase (AS) expression, the rate-limiting enzyme for the de novo biosynthesis of arginine. We show here that AS expression can be transcriptionally induced by ADI in melanoma cell lines A2058 and SK-MEL-2 but not in A375 cells, and this inducibility was correlated with resistance to ADI treatment. The proximal region of the AS promoter contains an E-box that is recognized by c-Myc and HIF-1α and a GC-box by Sp4. Through ChIP assays, we showed that under noninduced conditions, the E-box was bound by HIF-1α in all the three melanoma cell lines. Under arginine depletion conditions, HIF-1α was replaced by c-Myc in A2058 and SK-MEL-2 cells but not in A375 cells. Sp4 was constitutively bound to the GC-box regardless of arginine availability in all three cell lines. Overexpressing c-Myc by transfection upregulated AS expression in A2058 and SK-MEL-2 cells, whereas cotransfection with HIF-1α suppressed c-Myc-induced AS expression. These results suggest that regulation of AS expression involves interplay among positive transcriptional regulators c-Myc and Sp4, and negative regulator HIF-1α that confers resistance to ADI treatment in A2058 and SK-MEL-2 cells. Inability of AS induction in A375 cells under arginine depletion conditions was correlated by the failure of c-Myc to interact with the AS promoter.

No abstract

The clinical impact of postoperative deep infection on survival remains controversial in osteosarcoma patients. The authors identified 31 osteosarcoma patients that developed a deep infection within 1 year of operation between 1990 and 2003, and compared clinicopathologic characteristics of 31 patients that developed an infection with those of 316 patients that did not. For survival analysis, 62 noninfected patients matched for prognostic factors such as histologic response, tumor size, and location were also selected. In infected patients, although it was not significant due to the small patient numbers, good response to preoperative chemotherapy and a proximal tibial location were frequently observed. No local recurrence developed in infected patients. Five-year overall and metastasis-free survival rates for the 31 infected patients were as high as 89% and 73%, respectively. However, after matching for clinical factors, no survival difference was noted between infected and noninfected patients. Deep infection has a multifaceted effect on patients. However, the present study suggests that the reported positive effect on survival is likely to be related to the clinical characteristics of infected patients rather than an antitumor effect due to the infection. Further investigations are needed to clarify the precise effects of infection.