CDK4 and CDK6 Inhibitor Abemaciclib. Credit: Lilly OncologyNew results from a Phase 1 clinical trial that tested Eli Lilly’s investigational CDK4/6 inhibitor abemaciclib confirms the treatment showed clinical activity against several cancer types, including breast cancer, melanoma, and non-small cell lung cancer (NSCLC) — indicating that abemaciclib is in line to become an FDA-approved CDK4/6 inhibitor.

CDK4/6 inhibitors are designed to treat cancers by preventing overproliferation of cancer cells. The first of its kind, Pfizer’s palbociclib (Ibrance), was FDA approved in February 2015 for use in postmenopausal women with estrogen receptor-positive, HER2-negative advanced breast cancer. Novartis is also working on a pivotal study for CDK4/6 inhibitor, ribociclib.

While Pfizer’s and Novartis’s CDK4/6 inhibitors are typically dosed three weeks on and one week off, Eli Lilly’s abemaciclib’s can be continually dosed.

The treatments’ response rates also differ: “For the other two agents (palbociclib and ribociclib), the (single agent) response rates are low with these drugs,” Dana Farber Investigator Geoffrey Shapiro, who’s worked on all three CDK4/6 inhibitors, said in a FierceBiotech article.

Researchers tested abemaciclib as a single agent in 225 patients with various types of late-stage cancers (47 patients with breast cancer, 68 with NSCLC, 17 with glioblastoma, 26 with melanoma, and 15 with colorectal cancer.

Among the 36 patients with hormone receptor-positive breast cancer, 11 had a partial response and an additional 18 patients had stable disease. Among 68 patients with NSCLC, two had a partial response and 31 had stable disease. Among the 26 patients with melanoma, one had a partial response and six had stable disease. Three of the 17 patients with glioblastoma had stable disease, with two of them continuing to receive treatment without disease progression.

The most common treatment-related adverse events among these patients were fatigue, diarrhea, nausea, vomiting, anorexia, weight loss, kidney function, and decreased red and white blood cell counts.

“These data show that abemaciclib is an oral drug that can be taken on a continuous schedule and achieve durable clinical activity against multiple tumors including breast and lung cancers,” said Shapiro.

That said, the study results are still preliminary. The researchers question if continual inhibition of CDK4/6 might encourage resistance to the drug. Clinical trials in specific patient populations are still needed to confirm abemaciclib’s results.

Full data results will be published in Cancer Research.