Asparaginase (L-Asparaginase)
L-asparaginase is an enzyme antineoplastic used in selected veterinary lymphoma and other lymphoid-malignancy protocols. Unlike drugs that must enter a cell to damage DNA directly, it alters the extracellular supply of an amino acid on which some malignant cells depend. It is commonly considered for induction or rescue treatment rather than as a universal component of every cancer protocol.
Sensitivity depends on the tumor’s capacity to synthesize asparagine and on development of resistance. Historical reports in other tumors do not establish comparable effectiveness across all neoplasms.
Group
Antineoplastic enzyme
Mechanism of Action
L-asparaginase hydrolyzes circulating L-asparagine to aspartate and ammonia, reducing the extracellular asparagine available to cells. Some malignant lymphoid cells have insufficient asparagine-synthetase activity to replace this supply and therefore become unable to sustain normal protein synthesis.
Protein depletion disrupts growth and downstream nucleic-acid synthesis and can lead to cell death. Normal cells that synthesize adequate asparagine are relatively less affected, providing a degree of selectivity, although some normal tissues can still be injured. Activity is greatest in susceptible proliferating populations, particularly around the G1 phase.
This nutrient-depletion mechanism differs from most other cytotoxic drugs and supports combination use. Tumor adaptation can reduce sensitivity, while antibodies to the foreign enzyme can alter exposure or cause hypersensitivity; failure of response is not necessarily explained by insufficient dose alone.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lymphoma chemotherapy | 400 IU/kg | SC, IM | Every 168 h | Maximum 10000 IU/dose; Do not use in: Asparaginase hypersensitivity, Pancreatitis or previous pancreatitis |
| Lymphoma chemotherapy – surface-area alternative | Reference only | SC, IM | Maximum 10000 IU/dose; Up to 21 days; Do not use in: Asparaginase hypersensitivity, Pancreatitis or previous pancreatitis; 10,000 IU/m² weekly for 3 weeks; body-surface-area dosing is unsupported. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lymphoma chemotherapy | 400 IU/kg | SC, IM | Every 168 h | Maximum 10000 IU/dose; Do not use in: Asparaginase hypersensitivity, Pancreatitis or previous pancreatitis |
| Lymphoma – doxorubicin combination | 400 IU/kg | SC | Once | Maximum 10000 IU/dose; Do not use in: Asparaginase hypersensitivity, Pancreatitis or previous pancreatitis; Day 1 of the described doxorubicin combination protocol. |
Indications
- Treatment of selected canine and feline lymphomas within induction or rescue chemotherapy protocols.
- Selected other lymphoid malignancies, including reported treatment of acute lymphoid leukemia.
- Reported treatment of melanoma and mast-cell tumors; evidence is less established than for susceptible lymphoid malignancies.
Contraindications
- Known hypersensitivity to asparaginase.
- Do not use in food-producing animals.
- Current pancreatitis or a history of pancreatitis.
- Use cautiously with hepatic, renal, hematologic, gastrointestinal or CNS dysfunction.
Interactions
- Used in combination chemotherapy; addition to CHOP has not shown a clear benefit in the described evidence.
- May reduce methotrexate effectiveness until asparagine recovers.
- Prednisone may increase hyperglycemia risk.
- Concurrent vincristine can increase neurological or marrow toxicity; protocol spacing varies.
Adverse effects
- Hypersensitivity, especially after repeated injections.
- Hepatotoxicity, pancreatitis and hyperglycemia.
- Rare hyperammonemia and encephalopathy.
- Coagulation abnormalities and hemorrhagic pancreatitis; marrow suppression is uncommon but leukopenia occurs.
Toxicity
Repeated exposure can trigger serious hypersensitivity; monitor for acute reactions.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| L-asparaginase reconstituted IM 5000 IU/mL Specific 10,000 IU vial reconstituted with 2 mL saline; do not transfer to a different enzyme formulation. | Injection | 5000 IU / mL | IM |
Monitoring and Administration
Monitor CBC during chemotherapy and assess for hypersensitivity and metabolic complications. IM treatment was more effective than SC treatment in the described canine lymphoma experience.
A feline combination course used 400 IU/kg SC on day 1 with doxorubicin. Do not infer a doxorubicin dose.
Assess liver, renal, pancreatic/metabolic and hematopoietic function before and during treatment. Hypersensitivity risk rises with repeat exposure and IV administration. A described premedication is diphenhydramine 2 mg/kg SC in dogs or 1 mg/kg SC in cats, 30 minutes beforehand; this does not eliminate anaphylaxis risk.
For the specific 10,000 IU lyophilized vial, 2 mL saline produces an IM preparation of 5000 IU/mL; 5 mL saline or sterile water produces a 2000 IU/mL stock for IV use. Mix gently without vigorous shaking, refrigerate and use within the manufacturer-described 8-hour period; longer experimental storage periods are not adopted. Discard turbid solution. A 0.2-micron filter may reduce potency; a 5-micron filter is described for occasional gelatinous fibers.
Enzymatic ammonia generation may raise measured ammonia and BUN. Changes in thyroxine-binding globulin can affect thyroid-test interpretation. Treat overdose supportively and monitor for hypersensitivity and protein-synthesis-related toxicity.