The IDO-Inhibitor Race Is On to Improve Cancer Treatment

By Todd

NewLink Genetics (NASDAQ: NLNK) and Incyte Corporation (NASDAQ: INCY) are racing a new class of drugs through clinical trials, and if these trials are successful, these new drugs may change how doctors treat cancer, including melanoma.

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Indoleamine 2,3-dioxygenase (IDO) is a protein that suppresses the immune system that cancer cells sometimes hijack. By inhibiting IDO, NewLink Genetics and Incyte hope torestore immune system responses so that cancer cells can be more easily identified and destroyed.


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At NewLink Genetics, researchers are working on two IDO-inhibitors: indoximod, which it's developing on its own, and GDC-0919, which it's developing withRoche Holdings(NASDAQOTH: RHHBY).

Last week, NewLink Genetics unveiled updated results from a 60-person phase 2 study evaluating indoximod alongside Merck & Co.'s (NYSE: MRK) Keytruda in advanced melanoma. In this trial, 52% of patients responded to this two-drug therapy, and 73% had either a complete response, partial response, or stable disease.

The response rates are intriguing in part because the FDA approved Keytruda monotherapy in advanced melanoma after 33% of Keytruda patients responded to the drug in trials.

Incyte is also putting up impressive results in trials evaluating its IDO-inhibitor, epacadostat. In December, Incyte reported a 58% overall response rate inadvanced melanoma patients who were given epacadostat and Keytruda. Overall, 74% of patients saw a complete response, partial response, or stable disease in this trial.

Which one's better?

NewLink Genetics data failed to impress investors who were hoping for a better than Incyte result, and because of that, NewLink Genetics shares have fallen.

NLNK data by YCharts.

However, investors might not want to draw too many conclusions between the two drugs and their efficacy. After all, these drugs are not being studied in head-to-head trials, so it's bad science to compare these trials with one another, especially since Incyte's trial included only 19 patients, while NewLink Genetics trial included 60 patients.Also, while both of thesedrugs target IDO, they do so differently. Epacadostat targets the IDO enzyme directly, while indoximod inhibits the effects of IDO via cell-signaling.

Because of differences in trial size and mechanism of action, investors are probably best served considering the results from both of these trials as evidence that targeting IDO puts both of these companies on the right track.

What's next

NewLink Genetics and Incyte are also evaluating IDO-inhibitors in solid tumors.

NewLink Genetics and Roche Holdings' GDC-0919 works in a manner that's more similar to epacadostat than indoximod, and results from a phase 1b study evaluating its use alongside Roche's Tecentriq (a drug that's similar to Keytruda) in solid tumors should be available later this year. Meanwhile, Incyte's epacadostat studies include seven trials that could support FDA filings for approval, if they're successes.

Of course, it's anyone's guess if these trials pan out, but if they do, then IDO-inhibitors may not only transform how we treat advanced melanoma, but also how we treatnon-small lung cancer, triple negative breast cancer, and bladder cancer, too. And, that's potentially very big news for both of these companies.

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Todd Campbell has no position in any stocks mentioned.His clients may have positions in the companies mentioned.The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.