The U.S. pharmaceutical company Bristol-Myers Squibb has halted development of tanespimycin, a new drug that had been in late-stage clinical trials as a potential treatment for multiple myeloma.

In a statement to The Myeloma Beacon, a Bristol representative explained that “After careful assessment and consideration, Bristol-Myers Squibb made the decision to terminate our development program for tanespimycin, which was in Phase 3 trials for the potential treatment of multiple myeloma.” 

The Bristol-Myers statement was issued after the Beacon inquired about the status of the tanespimycin development program. 

In a subsequent clarification to the Beacon, Bristol noted that its decision is a general decision, affecting all development work on tanespimycin – not just work related to myeloma.

The company also emphasized that its decision about tanespimycin does not reflect any change in plans for elotuzumab, another potential myeloma treatment Bristol has been developing.  In the company's statement to the Beacon about tanespimycin, it said “We remain committed to finding new treatments for patients with myeloma,” and then provided information about the company's ongoing elotuzumab research program.

Tanespimycin, also known as 17-AAG and KOS-953, belongs to a class of drugs called heat shock protein 90 (Hsp90) inhibitors.  Researchers have long believed that drugs in this class could be potent anti-cancer agents.  However, no Hsp90 inhibitor has yet made it through clinical trials and been approved by the Food and Drug Administration as a cancer treatment.

Tanespimycin itself was tested in a number of different types of cancer.  In myeloma, it was tested primarily in combination with Velcade (bortezomib).  The results of those tests were described by Dr. Paul Richardson of Harvard Medical School as “very encouraging.”  In an email to the Beacon, Dr. Richardson went on to say that tanespimycin showed “durable activity as well as responses in [Velcade]-resistant disease and favorable toxicity, especially in reducing peripheral neuropathy.” 

Dr. Richardson was an investigator in several of the tanespimycin myeloma trials.  He told the Beacon that further development of the drug most likely was halted because tanespimycin is difficult to produce and there is only limited time remaining before the drug’s patent expires.  Combined, these factors would make further investment in the drug difficult to justify financially.

There are, however, other Hsp90 inhibitors being tested as potential myeloma treatments.  The Japanese pharmaceutical company Kyowa Hakko Kirin is testing the Hsp90 inhibitor KW-2478 in combination with Velcade in a Phase 1/2 myeloma trial.  Similarly, the Swiss pharmaceutical company Novartis is testing its Hsp90 inhibitor, AUY922, alone and in combination with Velcade and dexamethasone, in a Phase 1-1b/2 myeloma trial.

In addition, Infinity Pharmaceuticals is developing retaspimycin (IPI-504), a very close chemical relative to tanespimycin.  Although Infinity is not currently sponsoring any trials of its drug in myeloma, it could reconsider this decision given the positive trial results for tanespimycin in myeloma.

Tanespimycin entered Bristol-Myers Squibb’s portfolio of potential new drugs in 2008 when the company acquired California-based Kosan Biosciences.  Bristol-Myers was criticized at the time for the acquisition, in part because it paid Kosan’s investors more than three times the stock market value of the company prior to Bristol's acquisition bid.

The Bristol-Myers decision to halt further development of tanespimycin is likely to reignite criticism of the Kosan acquisition, since tanespimycin and its sales potential were an important justification for the acquisition.