Cell cycle regulation and cell growth are interesting targets in the search for new antitumor agents as these processes are highly disturbed in malignant cells. E7070 is a novel synthetic sulfon-amide that targets the G1 phase of the cell cycle and is currently in clinical development for the treatment of solid tumors. The potential antitumor activity of the compound was discovered through optimization of the structure-activity relationships of a series of sulfonamide structures. E7070 causes a blockade in the G1/S transition through inhibition of the activation of both cyclin-dependent kinase 2 and cyclin E. Preclinical studies with E7070 showed activity in multiple tumor types, most prominently in colon and lung cancer. A phase I clinical program was conducted with E7070 evaluating different treatment regimens. Dose-limiting toxicities were hematological, including neutropenia and thrombocytopenia. Preliminary results of phase II studies demonstrated limited antitumor activity following treatment with E7070 as single agent in heavily pretreated patients with non-small cell lung and colon cancer. Studies evaluating the activity of E7070 in combination with other chemotherapeutic agents are being conducted.