K-Ras is one of the most important oncogenes in human oncogenesis. K-Ras transfection of normal rat fibroblasts induces phenotypic change from flat to round morphology. Then, we screened compounds inducing flat morphology in K-Ras transformed fibroblasts from microbial culture filtrates and plant extracts. As a result, the alkaloid conophylline was isolated from the leaves of Ervatamia microphylla collected in Thailand. Conophylline induced flat morphology and inhibited cellular invasion in K-Ras–transformed normal rat kidney (K-Ras-NRK) cells. It also inhibited the growth of the K-Ras-NRK tumor in mice. Cancer-associated fibroblasts are now considered to activate cancer growth. Conophylline was found to suppress secretions of various inflammatory cytokines by pancreatic cancer–associated fibro-blasts. Moreover, when combined with gemcitabine, it inhibited the growth of pancreatic cancer growth in mice. Cono-phylline is orally active. Thus, the plant-derived alkaloid conophylline inhibited cancer growth directly and indirectly, and it shows promise as a new anticancer agent. © 2021 by Begell House, Inc. www-begellhouse-com.webvpn.scut.edu.cn.