COX-2, a key enzyme that catalyzed the rate-limiting steps in the conversion of arachidonic acid to prostaglandins, played a pivotal role in the inflammatory process. Different from other family members, COX-2 was barely detectable in normal physiological conditions and highly inducible during the acute inflammatory response of human bodies to injuries or infections. Therefore, the therapeutic utilization of selective COX-2 inhibitors has already been considered as an effective approach for the treatment of inflammation with diminished side effects. Currently, both traditional and newer NSAIDs are the commonly prescribed medications that treat inflammatory diseases by targeting COX-2. However, due to the cardiovascular side-effects of the NSAIDs, finding reasonable alternatives for these frequently prescribed medicines are a hot spot in medicinal chemistry research. Naturallyoccurring compounds have been reported to inhibit COX-2, thereby possessing beneficial effects against inflammation and certain cell injury. The review mainly concentrated on recently identified natural products and derivatives as COX-2 inhibitors, the characteristics of their structural core scaffolds, their anti-inflammatory effects, molecular mechanisms for enzymatic inhibition, and related structure-activity relationships. According to the structural features, the natural COX-2 inhibitors were mainly divided into the following categories: natural phenols, flavonoids, stilbenes, terpenoids, quinones, and alkaloids. Apart from the anti-inflammatory activities, a few dietary COX-2 inhibitors from nature origin also exhibited chemopreventive effects by targeting COX-2-mediated carcinogenesis. The utilization of these natural remedies in future cancer prevention was also discussed. In all, the survey on the characterized COX-2 inhibitors from natural sources paves the way for the further development of more potent and selective COX-2 inhibitors in the future.

Shikonin, alkannin and their derivatives, the main ingredient of Lithospermum erythrorhizon and Arnebia euchroma (Royle) Johnst native to Inner Mongolian and Northwest of China respectively, hold promising potentials for antitumor effects via multiple-target mechanisms. This review will emphasize the importance of their antitumor activity in apoptosis, necroptosis and immunogenic cell death, and expound the relationship of their antitumor activity and naphthoquinone scaffold that could generate ROS and alkylating agent. Meanwhile, the antitumor mechanisms of naturally-occurring shikonin, alkannin and their derivatives, which were divided into the direct interaction involved in alkylating agent, covalently binding the DNA and protein, as well as the indirect interaction mediated by ROS, nonspecifically influencing the mitochondria or multiple signal pathways, will be systematically summarized and discussed.

Since Human CYP1 enzymes catalyze the metabolic activation of procarcinogens and deactivation of certain anticancer drugs, the inhibition of these enzymes has been considered as an effective approach for chemoprevention and treatment of CYP1-mediated drug resistance. Recent knowledge relating to the enhanced expression of CYP1B1 in tumors also provided certain advantages in cancer therapy by the activation of prodrugs only in tumor cells. This review concentrates on the characterized CYP1 inhibitors and CYP1-activatied anticancer prodrugs. The mechanism for enzyme inhibition and activation of prodrugs, the cancer preventive/therapeutic potential of these chemicals and their related SARs are highlighted. According to their structural features, CYP1 inhibitors are divided into the following categories: flavonoids, trans-stilbenes, coumarins, terpenoids, alkaloids, quinones, isothiocyanates and synthetic aromatics. In the same way, CYP1-activatied prodrugs are categorized into four groups: benzothiazoles, flavonoids, stilbenes and alkylating agents. Almost all of these inhibitors and prodrugs are planar molecules with one aromatic ring and some have similarity with identified CYP1 substrates. CYP1 inhibitors could effectively block the procarcinogen-induced tumor initiation in animal models and benefit us with chemoprevention. The advent of Phortress and aminoflavone as clinical candidates shows promising perspectives in developing CYP1-mediated prodrugs as chemotherapeutic drugs that are specifically activated in tumors. All of these preclinical and clinical studies indicate that inhibitors and prodrugs target CYP1 are promising anticancer strategies.