Exploration of the Synergistic Effect of Chitosan Oligosaccharide and Dacarbazine (DTIC) in the Treatment of Melanoma

Introduction: Dacarbazine (DTIC)-based chemotherapy remains the first-line treat-ment for melanoma. However, its low response rate and evident side effects limit its clinical application. The combined use of chitosan oligosaccharide (COS) and other drugs has been shown to have good anti-tumor effects. Therefore, this study aimed to investigate whether COS can be combined with DTIC for the treatment of melanoma. Methods: By constructing a tumor-bearing model, statistical analysis of tumor size, TUNEL staining, and immunohistochemical detection of CD8, F4/80, and other indicators were con-ducted on tumor tissue to clarify the synergistic effect and molecular mechanism of the com-bination therapy. results: 3.1. COS-2 inhibited melanoma cell growth and induced apoptosis COS used in this study was prepared in our laboratory according to a previously described method (Lyu et al., 2014). Both TLC and HPLC showed that the synthesized COS, named COS-2, was mainly composed of 67% dimers and 33% trimers (Supplementary 1). COS has been shown to inhibit tumor progression in various cancers, including lung (Shen et al., 2009) and cervical (Huang et al., 2006) cancers; however, its therapeutic effects against melanoma remain unclear. Therefore, to examine the role of COS in the development of melanoma, we investigated the effects of COS-2 on the melanoma cell line B16 in vitro. MTT assay showed that COS-2 significantly inhibited the proliferation of B16 cells in a dose-dependent manner (Figure 1a). Transwell migration assay and wound healing assay showed that COS-2 suppressed the invasive and migratory abilities of B16 cells (Figures 1b, c). Consistent with the results of MTT assay, Ki67 staining showed that COS-2 inhibited the proliferation of B16 cells (Figure 1d). In addition, live/dead cell staining showed that COS-2 induced B16 cell necrosis. These results collectively indicated that COS-2 inhibited the proliferative, invasive, and metastatic abilities of B16 cells and promoted their death in vitro. COS has been reported to have similar inhibitory effects on the gastric cancer cell line SGC-7901(Luo et al., 2014). To assess whether COS-2 can enhance the anti-tumor effects of DTIC, the combination index (CI) of COS-2 and DTIC was calculated for B16 cells (CI values of