* OncoGenex's stock falls about 54 pct in premarket trading

* Drug fails in late-stage trial as first-line treatment (Adds details about study, stock movement)

April 28 (Reuters) - Teva Pharmaceutical Industries Ltd and OncoGenex Pharmaceuticals Inc said their experimental prostate cancer treatment failed to show improvement over standard chemotherapy in a late-stage trial.

OncoGenex's stock plunged about 54 percent in premarket trading on Monday.

The study, which enrolled 1,022 patients, tested the efficacy of the drug in combination with standard chemotherapy, compared to chemotherapy alone.

The drug, custirsen, did not show statistically significant improvement in overall survival in patients with previously untreated metastatic castrate-resistant prostate cancer (mCRPC), the companies said.

Custirsen, OncoGenex's lead drug candidate, aims to inhibit the production of the protein clusterin, which may play a fundamental role in cancer cell survival and treatment resistance.

It is also undergoing development as a second-line treatment for mCRPC, and being evaluated for use in lung cancer.

Bothell, Washington-based OncoGenex's shares were at $4.50 before the bell after closing at $9.70 on the Nasdaq on Friday.

(Reporting by Natalie Grover in Bangalore; Editing by Don Sebastian and Maju Samuel)