On April 20, 2016 Medivation, Inc. (NASDAQ: MDVN) reported that data from an investigator-sponsored Phase II study of enzalutamide, an androgen receptor inhibitor, was presented at the American Association for Cancer Research (AACR) (Free AACR Whitepaper) Annual Meeting 2016 in New Orleans (Press release, Medivation, APR 20, 2016, View Source [SID:1234511146]). Preliminary data from a 12-patient subset demonstrated that treatment with enzalutamide alone resulted in potential immune-activating properties in patients with non-metastatic castration sensitive prostate cancer. The primary objective of the study was to evaluate the effect of a short-course of enzalutamide (three months) alone or in combination with a therapeutic cancer vaccine (PROSTVAC) on prostate specific antigen kinetics four months after completing enzalutamide. Data from 12 patients treated with enzalutamide alone was presented by the study’s lead investigator Ravi Madan, M.D., Principal Investigator of the Study and Clinical Director, Genitourinary Malignancies Branch at the National Cancer Institute.

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"Existing literature already suggests that inhibition of androgen receptor signaling can potentiate the function of the thymus and improve the profile of the immune system. These new data suggest that in prostate cancer patients, enzalutamide may also enhance immune cell killing of prostate cancer cells throughout the body," said David Hung M.D., Founder, President and Chief Executive Officer of Medivation. "We are very encouraged by these new data and believe that the potential immune-activating properties of enzalutamide warrant further investigation, particularly in combination with other immunotherapy agents."

The effect of enzalutamide on peripheral immune cells was measured in 12 patients who were receiving enzalutamide alone (160 mg daily for 84 days, without androgen deprivation therapy). Measurements of CD4+ and CD8+ T cells, T-regulatory cells (Treg), B cells, conventional and plasmacytoid dendritic cells (cDC, pDC), natural killer cells (NK), natural killer T cells (NKT), and myeloid derived suppressor cells (MDSC), as well as 114 subsets related to immune cell maturation and function, were evaluated. Peripheral blood mononuclear cells were also assessed for T cell receptor excision circles (TREC) to identity recent thymic emigrants and to determine changes in global gene expression.

Results showed that treatment with enzalutamide induced several notable alterations in immune cells consistent with general immune activation. These changes occurred early following treatment, and included an increase in NK cells, decreased frequencies of MDSCs with a suppressive phenotype and decreased frequencies of both CD4+ and CD8+ T-lymphocytes expressing the immune inhibitory checkpoint molecule CTLA4. Additionally, treatment with enzalutamide increased TREC levels by more than 75% in 7 of 12 patients compared with pre-therapy levels (p=0.012). Gene expression analysis of PBMCs corroborated these findings, showing that enzalutamide increased activation of interferon-gamma signaling and related immune-activating pathways. These immune-activating activities for enzalutamide support evaluating the drug in combination with a number of immune-stimulating treatments including checkpoint inhibitors and vaccines.

Enzalutamide is being developed through a collaboration between Medivation and Astellas. Enzalutamide, which is known by the brand name XTANDI, is currently approved by the U.S. Food and Drug Administration for the treatment of patients with metastatic castration-resistant prostate cancer (CRPC).

About XTANDI
XTANDI (enzalutamide) capsules is an androgen receptor inhibitor that blocks multiple steps in the androgen receptor signaling pathway within the tumor cell. In preclinical studies, enzalutamide has been shown to competitively inhibit androgen binding to androgen receptors, and inhibit androgen receptor nuclear translocation and interaction with DNA. The clinical significance of this MOA is unknown.

XTANDI is approved by the U.S. Food and Drug Administration for the treatment of patients with metastatic castration-resistant prostate cancer (CRPC).

Important Safety Information
Contraindications XTANDI is not indicated for women and is contraindicated in women who are or may become pregnant. XTANDI can cause fetal harm when administered to a pregnant woman.

Warnings and Precautions
Seizure In Study 1, conducted in patients with metastatic castration-resistant prostate cancer (CRPC) who previously received docetaxel, seizure occurred in 0.9% of XTANDI patients and 0% of placebo patients. In Study 2, conducted in patients with chemotherapy-naive metastatic CRPC, seizure occurred in 0.1% of XTANDI patients and 0.1% of placebo patients. There is no clinical trial experience re-administering XTANDI to patients who experienced a seizure, and limited safety data are available in patients with predisposing factors for seizure. Study 1 excluded the use of concomitant medications that may lower threshold; Study 2 permitted the use of these medications. Because of the risk of seizure associated with XTANDI use, patients should be advised of the risk of engaging in any activity during which sudden loss of consciousness could cause serious harm to themselves or others. Permanently discontinue XTANDI in patients who develop a seizure during treatment.

Posterior Reversible Encephalopathy Syndrome (PRES) In post approval use, there have been reports of PRES in patients receiving XTANDI. PRES is a neurological disorder which can present with rapidly evolving symptoms including seizure, headache, lethargy, confusion, blindness, and other visual and neurological disturbances, with or without associated hypertension. A diagnosis of PRES requires confirmation by brain imaging, preferably MRI. Discontinue XTANDI in patients who develop PRES.

Adverse Reactions
The most common adverse reactions ( ≥ 10%) reported from two combined clinical studies that occurred more commonly ( ≥ 2% over placebo) in XTANDI patients were asthenia/fatigue, back pain, decreased appetite, constipation, arthralgia, diarrhea, hot flush, upper respiratory tract infection, peripheral edema, dyspnea, musculoskeletal pain, weight decreased, headache, hypertension, and dizziness/vertigo.

In Study 1, Grade 3 and higher adverse reactions were reported among 47% of XTANDI patients and 53% of placebo patients. Discontinuations due to adverse events were reported for 16% of XTANDI patients and 18% of placebo patients. In Study 2, Grade 3-4 adverse reactions were reported in 44% of XTANDI patients and 37% of placebo patients. Discontinuations due to adverse events were reported for 6% of both study groups.

Lab Abnormalities: Grade 1-4 neutropenia occurred in 15% of XTANDI patients (1% Grade 3-4) and 6% of placebo patients (0.5% Grade 3-4). Grade 1-4 thrombocytopenia occurred in 6% of XTANDI patients (0.3% Grade 3-4) and 5% of placebo patients (0.5% Grade 3-4). Grade 1-4 elevations in ALT occurred in 10% of XTANDI patients (0.2% Grade 3-4) and 16% of placebo patients (0.2% Grade 3-4). Grade 1-4 elevations in bilirubin occurred in 3% of XTANDI patients (0.1% Grade 3-4) and 2% of placebo patients (no Grade 3-4).
Infections: In Study 1, 1% of XTANDI patients compared to 0.3% of placebo patients died from infections or sepsis. In Study 2, 1 patient in each treatment group (0.1%) had an infection resulting in death.

Falls (including fall-related injuries), occurred in 9% of XTANDI patients and 4% of placebo patients. Falls were not associated with loss of consciousness or seizure. Fall-related injuries were more severe in XTANDI patients, and included non-pathologic fractures, joint injuries, and hematomas.

Hypertension occurred in 11% of XTANDI patients and 4% of placebo patients. No patients experienced hypertensive crisis. Medical history of hypertension was balanced between arms. Hypertension led to study discontinuation in < 1% of all patients.
Drug Interactions

Effect of Other Drugs on XTANDI Avoid strong CYP2C8 inhibitors, as they can increase the plasma exposure to XTANDI. If co-administration is necessary, reduce the dose of XTANDI.

Avoid strong CYP3A4 inducers as they can decrease the plasma exposure to XTANDI. If co-administration is necessary, increase the dose of XTANDI.

Effect of XTANDI on Other Drugs Avoid CYP3A4, CYP2C9, and CYP2C19 substrates with a narrow therapeutic index, as XTANDI may decrease the plasma exposures of these drugs. If XTANDI is co-administered with warfarin (CYP2C9 substrate), conduct additional INR monitoring.

For Full Prescribing Information for XTANDI (enzalutamide) capsules, please visit View Source

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