Solid cancers are often nutrient-starved due to poor blood circulation and show remarkable tolerance to nutrient deprivation, so antitumor substances targeting this resistance may have selective activity against solid cancer cells. In a screening for selective cytotoxic compounds under nutrient-deprived conditions, actinomycete strain RAI364 (identified as Streptomyces sp. via 16S rRNA sequence with high identity to Streptomyces cuspidosporus and Streptomyces ribosidificus) was found to produce active substances. From its culture broth, curromycin A (1) and a new cyclic dipeptide (2, cyclo(dehydroalanyl-N,O-dimethylthreonyl)) were isolated. Their structures were determined using 1H/13C NMR, HMQC, HMBC, NOESY, high-resolution FAB-MS, and other physicochemical methods. Curromycin A showed potent cytotoxicity against MKN45 human gastric cancer cells in nutrient-deprived medium (IC50 15 ng ml−1) with selectivity over normal medium, and dose-dependently inhibited GRP78 gene expression (IC50 4.3 ng ml−1 in the presence of 10 mM 2-deoxyglucose) in HT1080 G-L cells (GRP78 is involved in nutrient-deprivation resistance). Compound 2 exhibited no cytotoxic activity at <10 μg ml−1. Thus, curromycin A is a GRP78 downregulator, and compound 2 is a new cyclic dipeptide from Streptomyces sp. RAI364.