What Is Vorinostat (Zolinza)? FDA Approval, Licensing and Reimbursement in Türkiye

• FDA Approval: Yes (first approval date: October 6, 2006)
• Brand Name: Zolinza
• Active Ingredient: Vorinostat (Suberoylanilide Hydroxamic Acid - SAHA)
• Route of Administration: Oral capsules; an intravenous formulation has also been evaluated in clinical trials
• Class: Histone deacetylase (HDAC) inhibitor
• Category: Antineoplastic / epigenetic regulator
• Manufacturer: Merck & Co
• Distribution in Türkiye: Not licensed by the Turkish Medicines and Medical Devices Agency (TİTCK); access is possible through TEB (the Turkish Pharmacists' Association).
• Approved Cancers: Cutaneous T-cell lymphoma, particularly forms resistant to other systemic treatments or recurrent disease.

What Is Vorinostat and How Does It Work?

Vorinostat (suberoylanilide hydroxamic acid, SAHA) is an anticancer drug in the histone deacetylase (HDAC) inhibitor class. It is FDA-approved for advanced cutaneous T-cell lymphoma and is also being investigated as a potential option in various solid tumors and hematologic malignancies.

How Does It Work?

Vorinostat inhibits histone deacetylase (HDAC) enzymes. HDACs remove acetyl groups from histone proteins, tightening chromatin and suppressing gene expression. Inhibition causes histone hyperacetylation, allowing DNA to adopt a more open conformation and increasing gene transcription.

This epigenetic regulation:

• Increases tumor-suppressor gene expression
• Induces apoptosis (programmed cell death)
• Arrests the cell cycle, particularly in G1 and G2/M
• Reduces angiogenesis and metastatic potential

HDAC inhibition affects not only histones but also acetylation of nonhistone proteins such as p53, HSP90, and α-tubulin, allowing vorinostat to act through multiple intracellular pathways.

FDA (US Food and Drug Administration) Approval History

• March 16, 2004: The FDA granted vorinostat Orphan Drug designation, providing incentives for drugs treating rare diseases.
• June 7, 2006: The FDA granted vorinostat Priority Review, accelerating its evaluation.
• October 6, 2006: The FDA approved vorinostat for cutaneous T-cell lymphoma in patients who had not responded to at least two systemic therapies.

Licensing in Türkiye

• Vorinostat (brand name Zolinza) is not licensed by the Turkish Medicines and Medical Devices Agency (TİTCK) and therefore cannot be obtained directly from pharmacies or hospitals in Türkiye.
• Patients can access vorinostat only through TEB because it is not licensed in Türkiye. A physician must submit a detailed report and justification to TİTCK. With approval, the drug may be imported and supplied to the patient.

Reimbursement

Vorinostat is not on the Social Security Institution (SGK) reimbursement list in Türkiye. Its cost is therefore generally covered by the patient or family.

Mechanisms of Resistance

• HDAC Overexpression or Mutation: Tumor cells may overproduce targeted HDAC isoforms, making vorinostat inhibition insufficient. Rare HDAC mutations may also reduce drug-binding effectiveness.
• Drug Efflux: ATP-dependent efflux pumps, particularly ABCB1/MDR1 and ABCG2, may become overactive, expelling drugs such as vorinostat from cells and reducing intracellular concentrations and therapeutic efficacy.
• Disruption of Apoptotic Pathways: Vorinostat acts by inducing apoptosis. However, p53 mutations and overexpression of antiapoptotic proteins such as Bcl-2 or Bcl-xL may block apoptosis, allowing cell survival.
• Compensation for Nonhistone Protein Acetylation: Vorinostat acetylates nonhistone proteins such as p53 and tubulin as well as histones. Tumor cells may compensate for these effects, limiting drug activity.
• Increased DNA Damage Repair: Vorinostat may cause DNA damage in some cells. If repair proteins such as PARP or ATM/ATR are overactive, this damage is rapidly repaired, reducing treatment sensitivity.
• Epigenetic Reprogramming: Cells may develop alternative epigenetic pathways that bypass vorinostat, such as increased DNA methyltransferase activity, suppressing gene expression again.

Absorption

Vorinostat is rapidly absorbed orally, with increased bioavailability when fasting. Maximum plasma concentration (C_max) is generally reached within 2 hours. Absolute bioavailability is approximately 43%.

Distribution

Plasma protein binding is 71%. Vorinostat distributes widely into tissues and can penetrate tumor cells in particular. Data on central nervous system entry are limited, although preliminary studies suggest possible penetration.

Metabolism

Vorinostat inhibits class I and II HDAC enzymes, increasing histone acetylation, relaxing chromatin, and facilitating tumor-suppressor gene expression. This causes cell-cycle arrest, differentiation, and apoptosis. Acetylation of nonhistone proteins such as p53 and Hsp90 also contributes to antitumor activity.

Elimination

Vorinostat is mainly metabolized in the liver into inactive metabolites through glucuronidation and β-oxidation. Excretion is primarily urinary (approximately 92% within 24 hours), with very little unchanged drug (<1%). Elimination half-life is approximately 2 hours.

Dose Range

• Approved dose: 400 mg orally daily as a single dose, with or without food; fasting may provide higher bioavailability.
• Alternative Dose (if Not Tolerated): Lower doses such as 200 mg daily or 300 mg/day may be divided, for example 100–150 mg morning and evening. This is generally preferred after toxicity develops or in older, frail patients.
• Continued until disease progression or intolerable toxicity.
• Different regimens are being investigated in solid tumors or hematologic malignancies, such as 300 mg/day for 5 consecutive days followed by a 2-day break. These are not yet standard routine practice.

Drug Interactions

• Interactions with CYP Enzymes: Vorinostat is not a major CYP450 substrate; it is metabolized by hepatic UDP-glucuronosyltransferase (UGT) enzymes. CYP inducer/inhibitor interactions are therefore limited, but caution remains necessary. Inducers such as rifampin, phenytoin, or carbamazepine may theoretically lower vorinostat levels. Inhibitors such as ketoconazole, erythromycin, or verapamil may increase plasma concentrations; caution is needed despite limited definitive clinical evidence.
• Risk of QT Prolongation: Vorinostat may rarely prolong QT. Combining it with other QT-prolonging drugs, including amiodarone, sotalol, haloperidol, methadone, cisapride, some macrolides such as erythromycin, or fluoroquinolones such as levofloxacin, is therefore risky. Hypokalemia and hypomagnesemia increase the risk.
• Interactions with Anticoagulants: Caution is needed with vitamin K antagonists such as warfarin. INR monitoring is recommended because of potential pharmacokinetic and pharmacodynamic interactions. Bleeding risk may increase.
• Combination with Myelosuppressive Drugs: Vorinostat may cause thrombocytopenia and leukopenia. Myelosuppression risk can increase when combined with chemotherapy, lenalidomide, thalidomide, or azacitidine.
• Alcohol and CNS Depressants: Vorinostat can cause dizziness and fatigue. Alcohol or central nervous system depressants such as benzodiazepines or opioids may intensify these effects.

Points Requiring Attention

• Hematologic Toxicity: Thrombocytopenia, anemia, and neutropenia may develop. Monitor complete blood counts regularly at baseline and during treatment, particularly in combinations with myelosuppressive agents.
• Gastrointestinal Adverse Reactions: Nausea, vomiting, diarrhea, and anorexia are common. Severe diarrhea may disrupt fluid and electrolyte balance, requiring dose reduction or temporary interruption when necessary.
• Thromboembolic Events: Serious events such as deep vein thrombosis (DVT) and pulmonary embolism (PE) have been reported. Use caution in patients with a thrombosis history and assess risk factors.
• Risk of QT Prolongation: Vorinostat may rarely prolong QT. Caution is needed with other QT-prolonging drugs, electrolyte imbalances, or cardiac disease. ECG and electrolyte monitoring may be required.
• Hyperglycemia and Metabolic Disorders: Vorinostat may increase blood glucose, particularly causing hyperglycemia in patients with diabetes. Monitor fasting glucose and HbA1c.
• Hydration: Dehydration risk increases during treatment, especially with diarrhea or anorexia. Ensure sufficient fluid intake and monitor dehydrated patients closely.
• Liver Dysfunction: Because vorinostat undergoes hepatic metabolism, caution is required in liver impairment. Dose adjustment may be necessary.
• Pregnancy and Breastfeeding: Animal studies found embryotoxicity; human data are insufficient. Use in pregnancy is not recommended (Category D). Breastfeeding should be discontinued.
• Older Patients: Patients aged ≥65 may have a greater risk of adverse reactions, requiring lower starting doses or close monitoring.

Adverse Reactions

• Fatigue 58%
• Nausea 56%
• Diarrhea 52%
• Anorexia (reduced appetite) 44%
• Thrombocytopenia 43%
• Dysgeusia (altered taste) 41%
• Vomiting 33%
• Anemia 30%
• Dizziness 30%
• Weight loss 26%
• Neutropenia 24%
• Hyperglycemia 24%
• Hair loss (alopecia) 22%
• Constipation 22%
• Elevated liver enzymes (ALT/AST) 20–25%
• Pulmonary embolism (PE) 5%
• Deep vein thrombosis (DVT) 4%
• QT prolongation <1%