July 2001

Shaping Science Policy — International, National and Regional

Symposium on Women in Science

Discovering How Taxol Works

The Mind of a Child

Changing Course to a Career in Medicine

Working at the Nexus of Law and Science

New Factors in the Chemistry Equation

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Al Dorof, Editor

© 2003


Bryn Mawr College
A quarterly newsletter on research, teaching, management, policy making and leadership in Science and Technology

Discovering How Taxol Works
By Karen Young Kreeger

Susan Band Horwitz ’58

Susan Band Horwitz ’58 recalls a story about L. Joe Berry, one of her former biology professors at Bryn Mawr. About four years after she graduated, Horwitz and her husband dropped in at Bryn Mawr on their way back to the Boston area from a camping trip in the Appalachians. "As we were walking down the corridor talking, Dr. Berry yelled out from his office, 'Gee, that sounds like Susan Band.' My husband was shocked. He had been at Harvard where there were big classes and no one would ever do that."

To Horwitz, this encounter exemplifies the kind of close relationships she cultivated during her undergraduate studies at Bryn Mawr. Over four decades later, Horwitz is now the Falkenstein Professor of Cancer Research at Albert Einstein College of Medicine in New York and co-chair of its department of molecular pharmacology.

Researching Anti-Tumor Drugs

One of Horwitz's most outstanding scientific achievements was determining how the anti-cancer drug Taxol slows tumor growth. This effort encouraged the National Cancer Institute to pursue Taxol as an antitumor drug and eventually led to the approval by the Food and Drug Administration of Taxol in the treatment of ovarian, breast and lung cancers.

Horwitz started her research on Taxol in 1976, about the same time she became interested in small molecules, particularly those of natural origin, and their use in treating disease. Taxol had been isolated from the bark of the yew tree and its structure determined. The fact that it had lengthened the lifespans of mice with some experimental cancers encouraged the NCI to look at Taxol as a potential anticancer agent. In 1976, NCI wrote to Horwitz, asking if she would look at Taxol's mechanism of action.

"The chemical structure of Taxol is unique and it looked extremely interesting to me, so I said yes, please send me 10 milligrams," she recalls. "Within a month we knew that we had a very interesting molecule that was doing something to cells, which no one else had seen occur with a small molecule. It was very exciting."

Specifically what Horwitz and colleagues found was that Taxol binds to microtubules, which are part of the cytoskeleton of all cells. Microtubules are important to cell division, and when Taxol binds to these structures, it paralyzes them, slowing dramatically the ability of the cell to divide.

A Bit of Serendipity

Horwitz’s work with Taxol unexpectedly renewed her ties to Bryn Mawr. She has collaborated on the drug's synthesis with a faculty member, Charles Swindell, a former chair of the Chemistry Department. "I happened to be glancing through the Bryn Mawr Alumnae Bulletin and I stopped at the word Taxol, seeing that Swindell received a grant to work on the synthesis of Taxol," she says. "I gave him a call and of course he didn't know that I had graduated from Bryn Mawr, but after a bit of introduction we became very good friends." They published many papers together, some co-authored with Nancy Krauss '91, a doctoral student who was studying with Swindell.

For the past three decades Horwitz’s lab — which by her count currently numbers more than 10 people, from Ph.D. students to postdocs and visiting scientists — has been researching not only Taxol and other potentially important anticancer drugs but also how tumors become resistant to drugs. "We're looking for new drugs that would demonstrate efficacy in different tumors from those treated by Taxol that would also be active in Taxol-resistant tumors."

Horwitz is also very active in the Albert Einstein Cancer Center, where she is the associate director for therapeutics. In addition, she was just elected president of the American Association for Cancer Research, a large nonprofit professional organization with 17,000 members. "This is a new activity for me and I'm looking forward to it," she says.

Balancing Professional and Family Life

After graduating from Bryn Mawr, Horwitz went on to Brandeis University, where she was in the first class of the newly formed graduate department of biochemistry. She received her Ph.D. there in 1963 for work on dehydrogenases, enzymes that modify sugar alcohols in microorganisms.

Of her graduate-school years, she says, "Lots of things happened to me besides getting my Ph.D." She married, and she delivered twin boys five days after defending her dissertation. From there she took a number of part-time postdoc positions before her children entered grade school — at Tufts University Medical School, Emory University and the Albert Einstein College of Medicine, where she has been since the late 1960s.

"After I worked part-time for a couple of years, I realized that I had to make a decision because my children were going into the first grade," she remembers. "Working part-time, I was paid miserably and it was clearly not going to get me anywhere. So I said to myself, ‘it's now or never — either come back full-time or be part-time forever.’" She immediately accepted a full-time position and hasn't regretted her decision one bit.

Horwitz is refreshingly open about how she melded her career in science with raising a family: "There's no single way to do it. Each of us has to find whatever way we're comfortable with, and follow the track that makes us happy and productive." She attributes part of this attitude and confidence to her days at Bryn Mawr: "I think the feeling that women can be productive and be successful is imbued in you at Bryn Mawr."

About the Author

Karen Young Kreeger is a science journalist who writes on biomedical and women’s health topics, as well as careers in science. Her most recent work has appeared in Bioscience, Genome Technology, Muse and The Scientist

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