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imetelstat selectively attacks tumor cells that give rise to abnormal cells circulating in the blood.
Geron has now restructured its operations to focus on imetelstat. The company’s workforce, which numbered 175 before the stem cell program was halted, has been reduced to 64 employees.
Scarlett says Geron remains committed to move ahead with a tentative agreement to sell its stem cell assets to BioTime Acquisition Corporation (BAC), whose CEO, Thomas Okarma, is a former Geron chief executive. BAC is a subsidiary of the Alameda regenerative medicine company BioTime, whose CEO is Geron’s founder and former CEO, Dr. Michael West. The sale isn’t likely to produce cash to help fund Geron’s oncology program, however. Under a proposed agreement, Geron’s shareholders would receive shares of BAC, which was set up to acquire licenses and other stem cell assets.
Scarlett says Geron has the financial resources to regroup and explore imetelstat’s potential. He expects the company will end this year with a cash balance of $90 million. The burn rate of about $65 million in 2012 will be reduced to about $33 million in 2013, he says.
Geron’s fate now rests on the science of telomeres—those tail ends of chromosomes that control how many times a cell can divide before it dies. The telomeres are a bit like a commuter’s book of train tickets—they get smaller every time the cell divides. When the “tickets” are used up, most cells in the body stop dividing and die.
But in stem cells, like those that continuously give rise to new blood cells, there’s a way to add new tickets. An enzyme called telomerase tacks extensions onto the telomeres, so the stem cells can keep dividing indefinitely.
Unfortunately, some cancer cells can activate telomerase, which maintains their ability to divide, proliferate, and form tumors. Geron designed imetelstat to block telomerase from extending the telomeres—and the lives—of cancer cells.
Scarlett says imetelstat may work best in tumor cells that have short telomeres—perhaps because the enzyme telomerase can’t keep adding extensions fast enough to keep up with the rapid cell divisions of a fast-growing cancer. Most of the blood diseases called hematological malignancies have tumor cells with short telomeres, he says.
In 2013, Geron will probably begin a company-sponsored trial in one of those blood disorders, Scarlett says. The disease called myelofibrosis is a strong possibility, because a Mayo Clinic doctor has already begun an investigator-sponsored trial in that indication. Results from that study could guide the design of Geron’s trial, Scarlett says.
Geron hasn’t abandoned the idea of using imetelstat against solid tumors such as lung cancer. Although the Phase II trial of the drug in non-small cell lung cancer was disappointing when the effect on all trial subjects was considered, a subset of the participants did seem to benefit from the drug, according to Geron’s report on the study. Those subjects had tumor cells with short telomeres.
Scarlett says telomere lengths vary in lung tumors. The company is now refining a test for telomere length that could be used to select trial participants who would be likely to benefit from imetelstat.
Geron is studying its trial data and coordinating with regulators before deciding which trials to start in 2013, Scarlett says.
In a research note, JP Morgan analyst Cory Kasimov said Geron needs to show stronger evidence of imetelstat’s potential in cancer, beyond the positive signs in the company’s small early stage trial in essential thrombocythemia.
“Overall, we believe that GERN will need to replenish its pipeline and will likely stay off investors’ radars absent some compelling proof-of-concept,” Kasimov wrote.
Scarlett says Geron will look first to its own research platform for new pipeline candidates. Imetelstat was the first product of Geron’s proprietary process to create therapeutic oligonucleotides, compounds that can bind to cell molecules such as RNA that are involved in cell division and gene expression. The company has not yet announced the scope of that research platform or its disease targets, the CEO says.