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Alexei F. Kisselev, Ph.D.

Contact Information:

Professional Interests:

Professional interests: mechanisms of protein degradation by the ubiquitin-proteasome pathway; role of proteasome’s different active sites in protein breakdown and as targets of anti-neoplastic drugs; mechanisms by which proteasome inhibitors selectively kill malignant cells; development of site-selective proteasome inhibitors and their use for research and therapeutic purposes.

Dr. Kisselev received his Masters degree in Chemistry (with Honors) from the Moscow State University in Russia in 1991. He received a Ph.D. his bioorganic chemistry in 1995 form the same University for research on HIV protease carried out at the Max-von-Pettenkofer Institute at the University of Munich in Germany. He did his postdoctoral work with Prof. Alfred Goldberg at Harvard Medical School where he received fellowship awards from the Medical Foundation and the Leukemia and Lymphoma Society.

Proteins in all living cells are constitutively degraded and replaced by new ones. The ubiquitin-proteasome pathway is responsible for the majority of protein degradation in mammalian cells. 26S proteasomes is a large (2.5MDa) ATP-dependent proteolytic complex that degrades damaged and misfolded proteins into small peptides. Some of these peptides are then used in the MHC class I antigen presentation. Proteasomes also carry out specific and timely destruction of numerous regulatory proteins such as tumor suppressors p53 and Rb, cyclins, cdk inhibitors p27 and p21, other cell cycle regulators, and IkB inhibitor of the pro-inflammatory transcription factor NF-kB. Through degradation of these proteins, proteasomes play an essential role in the regulation of cell division, tumorigenesis and inflammation. Peptide boronate inhibitor of proteasome Velcade (bortezomib) is being used for the treatment of multiple myeloma and is in clinical trials for the treatment of other cancers. Because proteasomes play a role in the regulation of normal function of every cell of the organism, Velcade was expected to cause severe toxicity. However, Velcade selectively kills malignant cells, and clinical toxicities in multiple myeloma patients proved manageable. The mechanisms of this selective toxicity are not clear, and are being actively investigated in our laboratory.

Our second line of inquiry concerns the role of proteasome different active sites as targets for anti-cancer drugs. Eukaryotic proteasomes has 3 different types of proteolytic sites (“chymotrypsin-like”, “caspase-like” and “trypsin-like” sites) that cut proteins into small peptides, and Velcade and other proteasome inhibitors block protein degradation by inhibiting these sites. Relative contribution of these sites to protein breakdown in mammalian cells has not been studied systematically. Recently, we found that one needs to inhibit at least two types of active sites to achieve 50% inhibition of protein breakdown (in contrast to the popular believe that inhibition of the chymotrypsin-like sites is sufficient to block this process). Using the in vitro system of purified proteins, we found that relative contribution of these active sites to protein degradation depends on substrate. In order to address contribution of these sites to protein breakdown in cells and probe their role as targets for anti-neoplastic drugs, we are developing cell-permeable, specific inhibitors of these sites, with an ultimate goal of using these agents as leads for the development of new anti-neoplastic drugs.

While pursuing these 2 lines of research, we made an accidental observation that led to a third major project in the laboratory. We discovered that most proteasomes in mammalian cells are incorporated in larger macromolecular complexes. We are currently purifying these complexes, and characterizing their componenets. These studies may lead to the discovery of new components of the ubiquitin-proteasome pathway, will deepen our understanding of proteasome mechanism, and may lead to the discovery of new drug targets.

Courses Taught:

PEMM101; Medical Pharmacology

Grant Information:

RO1 CA124634-01A1; NCI; Kisselev (PI); 07/20/07-05/31/12
Different active sites of the proteasome as drug targets in cancer

The goal of this project is to test the hypothesis that all three active sites are drug’s molecular targets in multiple myeloma, inhibition of at least two sites is required to achieve optimal cytotoxicity, the therapeutic window of proteasome inhibitors depends on which active sites they target, and the exact pathways by which proteasome inhibitors induce apoptosis in myeloma cells depends on which active sites they target