Last fall, the American Cancer Society bestowed its highest award, the ACS Medal of Honor, on four Americans: a lawmaker (U.S. Sen. Edward Kennedy), a philanthropist (Jon M. Huntsman, founder and chair of the Huntsman Corporation), and two scientists. The scientists—Berkeley National Laboratory’s Mina Jahan Bissell and Albert Einstein College of Medicine’s Susan Band Horwitz—are both undergraduate alumnae of Bryn Mawr.
Horwitz, distinguished professor and co-chair of the department of molecular pharmacology at Albert Einstein College of Medicine of Yeshiva University, graduated from Bryn Mawr with a major in biology in 1958 and then became a member of the first class to earn a Ph.D. in biochemistry at Brandeis University. She won the ACS Medal of Honor for Clinical Research.
Bissell serves the life sciences division of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory in the capacity of distinguished scientist after stepping down after 16 years as its director. She spent two years at Bryn Mawr as a member of the Class of 1963 before transferring to Radcliffe, where she married a Harvard student and completed her bachelor’s degree in chemistry before enrolling in a Ph.D. program in microbiology at Harvard Medical School. Her award was the ACS Medal of Honor for Basic Research.
Throughout her career, Horwitz has made invaluable contributions to our scientific understanding of the biochemical processes underlying the tumor-inhibiting properties of certain natural products. Her most celebrated research identified the mechanism of action of Taxol (or Paclitaxel), which led to clinical trials of what has since become the world’s most-prescribed anticancer drug.
Taxol, a molecule that was first isolated from the bark of the Pacific yew tree, prevents cancerous cells from reproducing themselves through its action on microtubules, a part of the cellular “skeleton” that is critical for cell division. Unlike other antitumor drugs, it doesn’t break down the proteins in microtubules but instead effectively “freezes” them, preventing them from depolymerizing, which ultimately leads to the death of the cancerous cell.
Horwitz’ laboratory continues to research the Taxol molecule, focusing now on the mechanisms by which some tumors become resistant to the drug. Other research projects include compounds isolated from corals and sponges.
“These living organisms, which are unable to move, have developed very complex mechanisms to protect themselves from their environments,” Horwitz explains. “It has always been very interesting to me what the role of these small molecules could be in inhibiting the growth of human cancers.”
Bissell’s research, which has long stressed the importance of the cellular “microenvironment” on the behavior of cancer cells, is partly a product of her stubborn commitment to unconventional thinking. At a time when the Human Genome Project was all the rage and the word “genetic” seemed to be the “Open, Sesame” of cancer-research funding, Bissell was steadily advancing the then-unpopular idea that that the tissue around a cancer cell is as important as the genetic mutations inside the cell.
“Each cell in our body has the same DNA,” Bissell explains, “but cells in one organ behave very differently from cells in another organ. For a breast cell to remember to act like a normal breast cell, the tissue around it has to be just right. If you disrupt that extracellular matrix, you can cause cancer.”
Perhaps more exciting to clinical practitioners is the reverse proposition: that cancerous cells with genetic mutations can be made to behave normally when their microenvironments are restored. Bissell’s laboratory has reversed tumors this way both in vitro and in animal subjects, inspiring the hope that cancer may one day be treated as a chronic condition that can be arrested and controlled with drugs.
Both Horwitz and Bissell encourage young women not to be deterred from scientific careers by the hurdles that arise for young parents. Bissell astonished her professors and colleagues at Harvard in the early 1960s when she remained in the Ph.D. program after announcing her pregnancy.
“I worked until the week before my daughter was born,” she says. “I was lucky that I grew up in a family in Iran in which all the women worked and had children. They were very supportive.”
“But what’s important to remember is that we don’t all have to do it the same way,” Horwitz adds.
Horwitz, who gave birth to twins five days after defending her dissertation, worked part time until her children reached school age. “That kept me up to date and made it easy for me to move right back into full-time research,” she says. “There should be plenty of opportunities for women to stay in the profession while they are raising children,” she says. “It is very for a young scientist who wants to have a family to discuss this when she is choosing a mentor. You need one who is supportive.”
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