Promising new developments in cancer chemotherapy.
The positive impact on survival of traditional chemotherapeutic agents has renewed interest in developing newer cytotoxic agents and orally active compounds with improved therapeutic indices. In addition, new insights into the pathways of human tumorigenesis have led to novel approaches aimed at specific mechanism-based targets. The taxane class, of which paclitaxel was the first member, has the unique ability to promote and stabilize microtubule function directly, thereby inhibiting mitotic progression and inducing apoptotic cell death. Paclitaxel provides treatment benefit in a broad range of solid tumors including breast, ovarian, and lung cancer. The success with paclitaxel stimulated interest in the microtubule as a new therapeutic target. Taxane analogues with improved preclinical efficacy have been identified and are entering clinical trials. The enthusiasm for oral anticancer agents and the therapeutic importance of platinum compounds has led to the development of JM216 (satraplatin), a novel platinum IV coordination complex with oral activity in cisplatin-resistant cell lines, which is now in phase III trials in prostate cancer. Another compound in late development is DPPE, a chemopotentiator that enhances the in vivo antitumor effects of cytotoxic agents such as doxorubicin, cyclophosphamide, and cisplatin. Agents that inhibit topoisomerase I and II have also been of interest. TAS-103 is a dual topoisomerase I and II inhibitor with preclinical efficacy in a broad spectrum of tumors and in multidrug-resistant tumor cell lines. Vaccination strategies represent a rational therapeutic approach in the minimal residual disease or high-risk adjuvant therapy setting. The GMK and MGV vaccines utilizing ganglioside antigens overexpressed on human tumors such as melanoma and small cell lung cancer appear to induce antibody production reliably at tolerable doses and are under further clinical investigation. Inhibition of matrix metalloproteinases (MMPs) is another attractive target for intervention in several aspects of tumor progression. Local production of MMPs with subsequent degradation of the extracellular matrix is implicated in supporting tumor growth, invasion, and angiogenesis. The development of orally active, nontoxic MMP inhibitors is critical since these compounds will likely require chronic administration in conjunction with other therapies. Oncogenes and tumor suppressor genes are appealing targets for therapy since they are thought to be responsible for a significant number of cancers. Mutations in the Ras oncogene occur with great frequency in a number of human cancers including lung, pancreas, and colon cancer. Clinical development of potent and selective inhibitors of farnesyltransferase, the Ras-processing enzyme, is ongoing. These compounds uncouple Ras activity, affect tumor growth, and have demonstrated significant antitumor activity against experimental models of human cancer. The exciting compounds and novel therapeutic approaches currently under investigation by Bristol-Myers Squibb Pharmaceutical Research Institute offer great potential as effective cancer chemotherapy agents for the near future.