DEMETHOXYCURCUMIN AND BISDEMETHOXYCURCUMIN SURPASS CURCUMIN IN REDUCING VIABILITY AND ENGAGE DISTINCT APOPTOTIC ROUTES IN CUTANEOUS MELANOMA CELLS

Cutaneous melanoma (CM), which arises from the malignant transformation of melanocytes, is the most lethal skin cancer due to its high potential for early metastasis. Among the compounds with antiproliferative activity against cancer, the bioactive curcuminoids of Curcuma longa stand out: curcumin (CUR – 77%), demethoxycurcumin (DMC – 17%) and bisdemethoxycurcumin (BDMC – 3%). CUR is a lipophilic polyphenol with antioxidant, anti-inflammatory, and anticancer properties. DMC and BDMC are structural analogs with fewer methoxy groups, a feature linked to greater stability and pronounced antineoplastic and antioxidant activity in different tumor cell lines. This study compared the effects of CUR, DMC, and BDMC on metastatic melanoma cells. We cultured human melanoma A375 cells in DMEM supplemented with 10% fetal bovine serum at 37 °C under 5% CO₂. We treated cells with curcuminoid (15 µg/mL, dissolved in 0.4% DMSO) for 24 h, with culture medium alone as the negative control. We determined cell viability by MTT assay (570 nm). We assessed caspase-8 and BAX gene expression by RT-qPCR on a QuantStudio 7 Pro system, using GAPDH as the reference gene for normalization by the 2^−ΔΔCq method. All three compounds significantly reduced cell viability versus the control (p < 0.0001), with values of 45.98 ± 3.21% for CUR, 39.49 ± 3.76% for BDMC, and 30.31 ± 4.09% for DMC; DMC was significantly more effective than CUR or BDMC. All three derivatives upregulated Caspase-8: CUR (1.38 ± 0.14; p = 0.0004), DMC (1.32 ± 0.11; p = 0.0017) and BDMC (1.48 ± 0.11; p < 0.0001). For BAX, DMC (2.08 ± 0.15; p < 0.0001) and BDMC (2.42 ± 0.06; p < 0.0001) increased transcript levels. The concurrent upregulation of Caspase-8 and BAX is consistent with extrinsic initiation followed by mitochondrial amplification, in which caspase-8 cleaves Bid to tBid and tBid engages BAX at the outer mitochondrial membrane. CUR, in contrast, upregulated Caspase-8 while reducing BAX transcript levels (0.73 ± 0.09; p = 0.0031); as BAX is regulated largely post-translationally, through conformational activation and mitochondrial translocation rather than transcription, this does not exclude the intrinsic mediation previously reported for curcumin. Notably, BDMC induced the highest marker levels yet was less effective than DMC in reducing viability, suggesting that DMC may additionally engage non-apoptotic mechanisms. These inferences rest on transcript abundance and remain to be confirmed at the protein level. Taken together, the findings indicate that DMC and BDMC reduce A375 viability more effectively than CUR and act through distinct apoptotic routes in cutaneous melanoma. CAPES (Finance Code 001), CNPq, and FAPESC funded this study.