A Mount Sinai School of Medicine and Case Western Reserve University team has found a new use for the dopamine receptor antagonist trifluoperazine: restoring the sensitivity of tumors to epidermal growth factor receptor inhibitors.1 The key is trifluoperazine's off-target activity related to the export of the tumor suppressor forkhead box O1, which suggests other drugs in the class also could be repurposed to treat resistant cancers.

Although epidermal growth factor receptor (EGFR) inhibitors are a mainstay for treating lung cancers, the drugs are limited by primary or acquired drug resistance that can arise through multiple molecular mechanisms.2-4

To better understand the mediators of that resistance, the Sinai-Case Western group focused on two tumor suppressors: Kruppel-like factor 6 (KLF6; COPEB; ZF9) and forkhead box O1 (FOXO1). Prior studies showed that KLF6 levels are lower in lung adenocarcinomas than in matched normal lung tissue.

FOXO1 is the direct transcriptional activator of KLF6 and is inactivated in cancers. The inactivation occurs when FOXO1 is sequestered in the cytoplasm instead of the nucleus where it normally localizes.5,6

In mice with EGFR-activated lung adenocarcinoma, the EGFR inhibitor Tarceva erlotinib induced apoptosis and increased levels of KLF6 compared with those in control animals. Moreover, in human EGFR-activated lung adenocarcinoma cell lines that were sensitive to Tarceva, cells given the drug showed greater levels of KLF6, nuclear accumulation of FOXO1 and apoptosis than untreated cells.

By contrast, human EGFR-activated lung adenocarcinoma cell lines that were Tarceva resistant did not undergo apoptosis, had no KLF6 activation and had FOXO1 that remained in the cytoplasm.

In the Tarceva-sensitive cell lines, small interfering RNA targeting FOXO1 or KLF6 prevented drug-mediated apoptosis, suggesting FOXO1 and KLF6 are necessary for Tarceva-mediated apoptosis and sensitivity to anti-EGFR therapy.

The next step was to try to re-establish sensitivity to Tarceva by enhancing the nuclear accumulation of FOXO1 and the subsequent upregulation of KLF6.

To do so, the researchers turned to trifluoperazine, which is approved as an antipsychotic and antiemetic. The drug had been tried in cancer trials in combination with chemotherapy because trifluoperazine has off-target activity on the p-glycoprotein drug resistance pump, although none of the studies bore fruit.7-10

In 2003, a team at Harvard Medical School and the Dana-Farber Cancer Institute showed the molecule also was an effective nuclear export inhibitor of FOXO1.11

In Tarceva-resistant human adenocarcinoma cell lines, trifluoperazine increased nuclear accumulation of FOXO1 and levels of KLF6 compared with vehicle. In mice with human-derived Tarceva-resistant tumors, trifluoperazine plus Tarceva increased levels of KLF6 and apoptosis and decreased tumor volume compared with Tarceva alone.

The findings could help explain the biology underlying prior observations that both schizophrenic patients receiving dopamine receptor antagonists and dopaminergic-deficient Parkinson's disease patients have a lower incidence of some cancers than the general population.12,13

Results were published in The Journal of Clinical Investigation.

Tarceva is marketed by Astellas Pharma Inc., Chugai Pharmaceutical Co. Ltd. and Roche for non-small cell lung cancer (NSCLC) and pancreatic cancer.

Eye on the target

According to Goutham Narla, Mount Sinai and Case Western team leader and assistant professor of medicine and transformative molecular medicine at Case Western, "Our combination of trifluoperazine and erlotinib resulted in a successful therapeutic strategy because the combination provides a marked synergy due to a known mechanism of action-nuclear accumulation of FOXO1 and increased expression of KLF6."

Narla thinks it would be a good idea to "go back and screen other FDA-approved drugs of this class to see if they could be resurrected to treat anti-EGFR-resistant cancers."

Because dopamine receptors are a subclass of G protein-coupled receptors (GPCRs), Narla said the repurposing search could be far-reaching.

"Compounds that target dopamine receptors or GPCRs might also affect the nuclear accumulation of FOXO1 or other downstream mediators of EGFR signaling, which would have before been considered off-target activity considering their original purpose," he said.

He added, "Drugs that are just sitting on the shelf because they had shown a suboptimal profile as GPCR antagonists could be rescreened as anticancer therapeutics. We have been using cancer cell viability assays to reevaluate GPCR antagonists as anticancer agents" but want to take a step forward and incorporate a new assay being developed by Mick Bhatia (see Box 1, "Honing in on differentiation").

In addition to looking for repurposing opportunities, the group is synthesizing analogs of trifluoperazine. The molecule's "backbone is a rich scaffold that can be derivatized to provide us a compound with improved pharmacology, particularly with respect to CNS effects," noted Narla. "Michael Ohlmeyer will be leading the medicinal chemistry aspect of the project, and his team was a recipient of the 2012 NYCIF BioAccelerate prize for this work." The $250,000 award for one year is intended to fund biomedical research with commercial promise.

Ohlmeyer is an associate professor of structural and chemical biology at the Mount Sinai School of Medicine. He cofounded chemistry company Pharmacopeia Inc., now Accelrys Inc., and is an author on the JCI paper.

Other next steps include clinical trials and testing the combination of trifluoperazine with other EGFR-targeting therapies in other cancers.

Mount Sinai has filed a patent application covering the work, which is available for licensing.

Baas, T. SciBX 5(28); doi:10.1038/scibx.2012.719 Published online July 19, 2012

REFERENCES

1.   Sangodkar, J. et al. J. Clin. Invest.; published online June 1, 2012; doi:10.1172/JCI62058 Contact: Goutham Narla, Case Western Reserve University and University Hospitals, Cleveland, Ohio e-mail: goutham.narla@mssm.edu or goutham.narla@case.edu

2.   Kobayashi, S. et al. N. Engl. J. Med. 352, 786-792 (2005)

3.   Pao, W. et al. PLoS Med. 2, e73; published online Feb. 22, 2005; doi:10.1371/journal.pmed.0020073

4.   Shepherd, F.A. et al. N. Engl. J. Med. 353, 123-132 (2005)

5.   Maekawa, T. et al. Oncol. Rep. 22, 57-64 (2009)

6.   Brunet, A. et al. Cell 96, 857-868 (1999)

7.   Schroder, L.E. et al. Urol. Oncol. 3, 94-98 (1997)

8.   Budd, G.T. et al. Invest. New Drugs 11, 75-79 (1993)

9.   Murren, J.R. et al. Cancer Chemother. Pharmacol. 38, 65-70 (1996)

10. Hait, W.N. et al. Cancer Res. 50, 6636-6640 (1990)

11. Kau, T.R. et al. Cancer Cell 4, 463-476 (2003)

12. Dalton, S.O. et al. Schizophr. Res. 75, 315-324 (2005)

13. Driver, J.A. et al. Cancer Epidemiol. Biomarkers Prev. 16, 1260-1265 (2007)

14. Werbowetski-Ogilvie, T.E. et al. Nat. Biotechnol. 27, 91-97 (2009)

15. Sachlos, E. et al. Cell; published online May 24, 2012; doi: 10.1016/j.cell.2012.03.049 Contact: Mick Bhatia, McMaster University, Hamilton, Ontario, Canada e-mail: mbhatia@mcmaster.ca

COMPANIES AND INSTITUTIONS MENTIONED

      Accelrys Inc. (NASDAQ:ACCL), San Diego, Calif.

      Actium Research Inc., Toronto, Ontario, Canada

      Astellas Pharma Inc. (Tokyo:4503), Tokyo, Japan

      Case Western Reserve University, Cleveland, Ohio     

      Chugai Pharmaceutical Co. Ltd. (Tokyo:4519), Tokyo Japan

      Dana-Farber Cancer Institute, Boston, Mass.

      Harvard Medical School, Boston, Mass.

      McMaster University, Hamilton, Ontario, Canada

      Mount Sinai School of Medicine, New York, N.Y.

      Roche (SIX:ROG; OTCQX:RHHBY), Basel, Switzerland

      Teva Pharmaceutical Industries Ltd. (NYSE:TEVA), Petah Tikva, Israel