Status: U.S. and EU applications withdrawn; BLA refiled in late 2008

Organizations involved:

Protherics PLC - Manuf.; R&D; Tech.; World mark.

Centre for Applied Microbiology & Research (CAMR) - R&D; Manuf.; Tech.; Former

Enact Pharma PLC - R&D; Tech.; Former

IDIS World Medicines - World mark.

Porton International plc - Former

Ipsen S.A. - Former

Kymed GB Ltd. - Former

Novozymes Delta Ltd. - Tech.

Novozymes A/S - Parent

Delta Biotechnology Ltd. - Former

National Cancer Inst. - U.S. mark.

Description: Voraxaze is a formulation of recombinant carboxypeptidase G2 enzyme (EC 3.4.17.11; CPG2) derived from Pseudomonas sp. strain RS-16 (now reclassified as Variovorax paradoxus) expressed in transformed Escherichia coli (E. coli). Carboxypeptidase G2 (CPG2) cleaves folates and related compounds containing folic acid moieties/structures. This makes it useful to break down (hydrolyze) excess (toxic) levels of methotrexate and other folate antagonists used for cancer chemotherapy. Accumulation of toxic levels of methotrexate, particularly in treated patients with renal failure, is a rare but life-threatening complication. CPG2 cleaves methotrexate into the non-toxic metabolites 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA) and glutamate.

CPG2 is a zinc-dependent dimeric protein of 83,000-84, 000 Dalton (83-84 kDa), with the enzyme naturally forming a complex of two protein chains and two zinc ions. The natural form (and also, presumably, the recombinant version) of the enzyme is a dimeric protein complex composed of two identical subunits of 41,800 Da (41.8 kDa; 415 amino acids) and four zinc ion (Zn2+) per enzyme molecule, with the zinc ions required for full activity.

Biological: CPG2 is a zinc-dependent enzyme isolated from Pseudomonads, including strains of Pseudomonas, Flavobacterium and Acinetobacter species. The carboxypeptidase G class of enzymes hydrolyzes the C-terminal glutamate moiety from folic acid and analogs such as methotrexate (MTX), polyglutamate derivatives of folic acid, subfragments such as p-aminobenzoylglutamate, and specific small peptides with C-terminal glutamate residues. CPG2 has no significant amino acid sequence homology with proteins of known structure. CPG2 is located in or near the periplasmic space of Pseudomonas sp. strain RS-16. CPG2 from Pseudomonas sp. strain RS-16 differs from the form of the enzyme originally reported in the literature and from the closely related carboxypeptidase G1 in both physical and kinetic properties. The complete gene sequence the Pseudomonas gene coding for carboxypeptidase G2 was reported by CAMR researchers in 1984 (Gene, vol. 31, p. 31-38,1984), with a correction published in 1986 (Gene, vol. 42, p. 353)

 CPG2 has a relatively restricted specificity and hydrolyses the C-terminal glutamic acid residue of folic acid, poly-glutamyl derivatives of folic acid and folate analogs containing pteroyl-L-glutamate (folic acid), releasing C-terminal glutamate from a wide range of N-acyl groups, including peptidyl, aminoacyl, benzoyl, benzyloxycarbonyl, folyl, and pteroyl groups. The enzyme follows Michaelis-Menten kinetics with Km values of 4.0 µM for folate, 8.0 µM for methotrexate and 34.0 µM for 5-methyltetrahydrofolate, the predominant form of reduced folate found in plasma. CPG2 has high affinities (Km values of 10-5 to 10-6 M) for both 5-methyltetrahydrofolate, the predominant circulatory form of folate in mammals, and the folic acid antagonist methotrexate. Trimetrexate, a common chemotherapy drug, is resistant to CPG2 cleavage.

Methods for quantification are reported in "Purification and properties of Carboxypeptidase G2 from Pseudomonas sp. strain RS-16. Use of a novel triazine dye affinity method." Eur. J. Biochem., 148, p. 447-453, 1985.

CPG2's ability to catabolize reduced and non-reduced folates has led to its use as a folate-depleting agent, including as a rescue agent for methotrexate-induced nephrotoxicity. Enzymes with carboxypeptidase G activity typically act to combat toxicity caused by antifolate compounds, e.g., methotrexate, by rapidly lowering plasma levels of the drug, thereby reducing the duration of exposure of normal tissues to the drug and preventing longer-term uptake.

The crystal structure of carboxypeptidase G2 was reported in 1997 (Structure, 15;5(3), p. 337-47, March 1997). Each subunit of the molecular dimer was shown to consist of a larger catalytic domain containing two zinc ions at the active site, and a separate smaller domain that forms the dimer interface. The two active sites in the dimer are more than 60 Angstroms apart and are presumed to be independent. Each active site contains a symmetric distribution of carboxylate and histidine ligands around two zinc ions 3.3 Angstroms apart. This distance is bridged by two shared zinc ligands, an aspartic acid residue and a hydroxyl ion. The CPG2 catalytic domain has some structural homology with other zinc-dependent exopeptidases, both those with a single zinc ion and those with a pair of zinc ions in the active site. The mechanism of peptide cleavage likely involves the bridging hydroxyl ion ligand acting as a primary nucleophile.

Voraxaze is designed to rapidly reduce blood levels of methotrexate (MTX; 4-amino-10-methylfolic acid; 4-amino-N10-methylpteroylglutamic acid), a commonly used cancer drug, by rapidly breaking it down to nontoxic metabolites - 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA) and glutamate. DAMPA is eliminated more rapidly than MTX, by means other than renal elimination. The cytotoxic effects of both MTX and its active metabolites involve inhibition of dihydrofolate reductase (DHFR), leading to inhibition of DNA synthesis, repair and cellular replication. Tumor and other fast-growing cells are more susceptible than normal cells to the cytotoxic effects of methotrexate, which is why it is used against tumors. MTX therapy, particularly high doses administered intrathecally, can cause kidney damage, with high doses compounding toxicity by slowing the elimination of MTX from the body. Prolonged exposure to high concentrations of MTX often results in serious toxic effects, such as mucositis (painful mouth sores), reduced platelet and white blood counts (myelosuppression), and kidney failure potentially leading to death. A number of cancer patients die every year from MTX-induced toxicity, mainly due to sepsis (bacterial blood infection).

Although actively proliferating malignant tissues are most sensitive to MTX, the drug can still be toxic to healthy cells in a dose- and time-dependent manner through two principle mechanisms. The first is common to all antifolates, involving the inhibition of DNA synthesis and cellular metabolism, which is the underlying mechanism that is responsible for MTX's cytotoxic anti-cancer action. The risk of significant toxicity to healthy cells correlates with increasing doses of MTX and the time of exposure. MTX therapy is associated with a spectrum of toxicities, with myelosuppression, mucositis, acute hepatitis and nephrotoxicity being the most frequent and serious complications. Additional toxicities seen with high dose therapy are acute desquamative dermatitis, B-lymphocyte (B-cell) dysfunction, and neurological effects. Similar common toxicities are also caused by other antifolate drugs, although they are generally administered at lower doses than MTX. The second mechanism is MTX-induced renal tubular obstruction and consequent renal dysfunction (MTX nephrotoxicity). MTX is naturally metabolized by liver aldehyde oxidase to 7-hydroxy-MTX. The aqueous solubility of 7-hydroxy-MTX is 3-5 times lower than that of the parent compound and, under certain conditions precipitates in the renal tubules, which is thought to be a principal mechanism in the pathogenesis of the MTX nephrotoxicity. Normal kidney function accommodates removal of a particular load in a given time, after which accumulation and damage will ensue. If a patient receiving MTX develops nephrotoxicity leading to impaired elimination of MTX, a self-perpetuating cycle is initiated of reduced elimination, sustained high plasma MTX levels. and subsequent exacerbation of both non-renal toxicity and progression of renal tubular damage, leading to the death of the patient (although mortality can occur even in the absence of total renal failure).

Nomenclature: Voraxaze [TR]; glucarpidase [INN]; recombinant glutamate carboxypeptidase [CAS/systematic]; hydrolase, gamma-glutamyl [CAS/systematic]; 9074-87-7 [CAS RN]; EC 3.4.17.11 [EC]; 111070-04-3 [CAS RN, other]; 37279-02-0 [CAS RN, other]; 55326-32-4 [CAS RN, other]; 61584-57-4 [CAS RN, other]; carboxypeptidase G2 [CAS/systematic]; CPG2 [SY]; glutamate carboxypeptidase [SY]; conjugase [SY]; glutamyl carboxypeptidase [SY]; folate conjugase [SY]; acetylaspartyl-glutamate dipeptidase [SY]; poly(gamma-glutamic acid) endohydrolase [SY]; N-acetylated-alpha-linked acidic dipeptidase [SY]; folate hydrolase [SY]; N-pteroyl-L-glutamate hydrolase [SY]; pteroylmonoglutamic acid hydrolase G2 [SY]; NSC 641273 [NCI; most likely for non-recombinant enzyme]; NSC 732443 [NCI]; EINECS 232-978-1 [EINECS]

Companies: Protherics PLC manufactures and markets Voraxase containing recombinant carboxypeptidase G2. Protherics was formed in Sept. 1999 from the merger of Proteus International plc and Therapeutic Antibodies Inc. Protherics acquired Enact Pharma, the original developers of recombinant CPG2, in June 2003 for £8.3 million (including expenses; see below).

Nonrecombinant enzyme derived from culture of Pseudomonas was originally manufactured by the Centre for Applied Microbiology and Research (CAMR; Porton Down, U.K.), U.K. Public Health Laboratory Service (PHLS), now the Health Protection Agency. During the mid-late 1980s and early 1990s, enzyme manufactured by CAMR was marketed by Porton International plc, which held exclusive rights to market products from CAMR, and later by Ipsen S.A., which acquired the biopharmaceuticals business lines of Porton. Nonrecombinant enzyme was marketed and sold directly to the U.S. National Cancer Institute (NCI) and the therapeutics purchasing and/or cancer research divisions of other countries, and the enzyme was also available, in the U.S. and elsewhere for named-patient, compassionate or other IND-type, unapproved use with methotrexate toxicity. At the time, it was reported, "CPG2 is currently produced at 400-liter fermentation scale from Pseudomonas sp. strain RS-16, with yields between 200 and 300 U/liter, representing <0.1% soluble protein."

Recombinant CPG2 (Voraxase) was developed by Centre for Applied Microbiology and Research (CAMR), which became the Health Protection Agency (HPA). One of the inventors, Dr. Atkinson acquired the licensing rights to carboxypeptidase G2 from CAMR and formed Kymed GB Ltd. to commercially develop what is now Voraxase. Kymed merged with Enzacta in 2000 to form the Enact Pharma PLC, with its primary late-stage product being Voraxase (from Enzacta). Protherics acquired Enact in June 2003 and continued Voraxase development.

IDIS acts as international named patient sales distributor for Protherics, but Protherics assumes marketing where Voraxase receives full approvals (see the Status section).

Manufacture: Large-scale preparation and purification of enzyme (non-recombinant) from culture of Pseudomonas sp. strain RS-16 was reported by CAMR researchers in 1985 ("Purification and properties of carboxypeptidase G2 from Pseudomonas sp. strain RS-16. Use of a novel triazine dye affinity chromatography method," Eur. J. of Biochem., vol. 148, p. 447-53, May 1985). The investigators reported, "Homogeneous enzyme was obtained by a three-step procedure involving ion-exchange chromatography and a novel triazine dye (affinity) chromatography step which utilizes Zn2+ to promote adsorption of the enzyme. Enzyme was selectively eluted by the use of a chelating agent (EDTA) and a step change in pH." The chromatography matrix was Procion Red H-8BN coupled Sepharose 6B. Binding to the dye component is dependent on the Zinc II ions of the enzyme complex. In the presence of Zn II ions, the enzyme was quantitatively bound to the dye-Sepharose. For further discussion of the medium-bound dye affinity chromatography method used for purification of the recombinant enzyme, see the Tech. transfer section below.

Researchers from CAMR reported the cloning of the carboxypeptidase G2 (CPG2) from Pseudomonas sp. strain RS-16 into Escherichia coli (E. coli; and also Pseudomonas putida) strain RS-16 bacteria in 1983 (J. Bacteriology, Dec. 1983, p. 1222-27). Acquisition of a functional CPG2 gene enable E. coli to utilize folic acid as a carbon source. A total of 2,400 gene bank clones were screened for the ability to grow on minimal medium containing folate as the sole source of carbon (i.e., Fol+). To isolate the gene for CPG2, chromosomal DNA prepared from the Pseudomonas host was partially digested with Sau3A, and fragments of between 6-8 megadaltons (Md) were isolated from agarose gels by electroelution. The isolated CPG2 plasmid (pNM1) directed the synthesis of low levels of the enzyme (100-fold lower than the source Pseudomonas sp. strain), confirming other findings that Pseudomonas genes are poorly expressed in E. coli. Higher expression levels (up to 5% soluble protein) were obtained in E. coli by subcloning a 3.1-megadalton BgII fragment of pNM1 into the BamHI site of plasmid pAT153. Expression from the BglII subfragment of pNM1was 3,000 to 3,500 U/L of culture, which represented 4.7% soluble protein. Production of carboxypeptidase was shown to be induced (two-fold) by the presence of folic acid, and the mature protein was shown to be located in the periplasmic space of E. coli, indicating the DNA sequence of the gene encodes a signal peptide at the N-terminal region of the protein.

Aspects of the production of recombinant carboxypeptidase G2 were reported by CAMR researchers in "Production of cloned carboxypeptidase G2 by Escherichia coli: Genetic and environmental consideration" (Biotechnology Letters, 11(10), p. 699-704, Oct., 1989). They report that optimum production of cloned carboxypeptidase G2 from plasmid pNM21 by Escherichia coli was found to be strongly strain- and temperature-dependent. The superior host was E. coli strain RV308 and the preferred growth temperature 28¡C.

FDA class: Biologic BLA

CBER class: Antitoxins, Antivenins, Enzymes and Venoms

Indications: [for which Protherics reportedly applied for approvals]:

for treatment of patients with, or at risk of, kidney damage from the toxic effects of methotrexate, a widely used chemotherapeutic agent [for which FDA orphan designation has been granted]; treatment of patients at risk of methotrexate toxicity [for which European Union orphan designation has been granted]: and adjunctive treatment in patients at risk of methotrexate toxicity

Status: A MAA seeking European Union approval was submitted in June 2005. In Jan. 2007, Protherics reported that EMEA/EU had requested additional studies of the potential for Voraxaze to interact with leucovorin, which is currently administered in conjunction with high dose methotrexate therapy. Protherics now projects EU approval in second-half 2008.

On Sept. 15, 2006, Protherics filed an BLA for FDA approval of Voraxase.

On Nov. 7, 2006, Protherics reported withdrawal of the BLA for Voraxase. FDA had asked for further information regarding its manufacture and stability, and a 12-patient study to assess the interaction of Voraxaze (carboxypeptidase G2) with leucovorin, a standard supportive therapy given along with high-dose methotrexate. The company expects to resubmit the BLA and receive approval in 2nd-half 2008 (a year later than previously projected). The BLA has Fast Track Designation, allowing submittal of sections of the BLA as they are completed, and will receive Priority Review (6 months target action date). Later in Nov. 2006, Protherics agreed to provide additional requested manufacturing and stability data to FDA and to resubmitting its BLA as a rolling submission, starting in early 2008.

On May 22, 2007, Protherics reported withdrawal of its European Union MAA for Voraxase. EMEA/EU had requested further information on marketing as well as additional data about the potential interaction between Voraxaze (carboxypeptidase G2) and leucovorin. Protherics stated it could not meet these requests in the timeframe available, and so had to withdraw its application for the time being. The company hopes that the extra information it will submit to FDA will also be enough to satisfy EMEA's requests. If this is the case, it will likely resubmit Voraxase for approval in Europe.

Voraxaze has orphan drug status in U.S. and European Union (EU) for "adjunctive treatment of patients at risk of methotrexate toxicity due to delayed elimination or accidental overdose." EU orphan designation (no. EU/3/02/1280) was granted to Enact Pharma PLC on March 2, 2003.

Enact/Protherics' manufactured its first batch of Voraxaze manufactured to GMP standards in 2003, enabling the global distribution of Voraxaze on a named patient basis outside of the U.S. Named patient sales in Europe began about Dec. 2003.

Voraxaze has been and continues to be available on a compassionate use basis in the U.S., and is sold on a named patient basis in the rest of the world. Nonrecombinant enzyme and now recombinant enzyme (Voraxase) has been available on named patient basis in the European Union and other countries. In many countries, medical practitioners are able to request and purchase certain unlicensed therapeutics on a named patient basis where there is unmet clinical need (no safe and effective alternative). Product sales commenced in Jan 2004, with Voraxase replacing the nonrecombinant enzyme. In the U.S., the National Cancer Institute (NCI) has purchased the enzyme and distributes it for compassionate use (presumably, under an IND).

Protherics intends to conduct further clinical studies with Voraxaze, after initial approval(s), to expand use of the product into larger markets. In the meantime, with its filings stalled in the U.S., and EU, the company will continue supplying Voraxaze in Europe on a named-patient basis for intervention use in those at risk of severe or life-threatening methotrexate toxicity.

On Nov. 20, 2008, Protheric initiated a rolling BLA filing with FDA (he BLA has Fast Track designation) for the interventional use of Voraxaze for the rapid and sustained reduction of methotrexate (MTX) in patients who have toxic MTX levels due to impaired renal function. The initial filing contained precliniccal studies. The remaining two modules containing the CMC (chemistry, manufacturing and control) and clinical data were scheduled for submission within the next 12 months. Protherics intends to seek a Priority Review

Tech. transfer: Protherics and two then (or former) CAMR (later Enact Pharma) researchers, Drs. R. Melling and T. Atkinson, are the assignees for CPG2-related patents/applications including , "Use of Enzyme," WO2005084695, application published Sept. 9, 2005, broadly covering use of enzymes with carboxypeptidase G activity for treatment of toxicity caused by a variety of antifolate compounds, including methotrexate. Protherics has full, exclusive rights to this and related applications/patents. There does not appear to be patents/applications concerning the sequence or cloning of CPG2.

Delta Biotechnology Ltd. (Nottinghamshire, U.K.), now Novozymes Delta, Ltd., a subsidiary of Novozymes A/S, has received U.S. 5,905,143, "Purification of proteins," concerning use of protein-binding dyes immobilized on a chromatographic matrix for affinity purification of proteins, followed by use of an ion-exchange resin (e.g., Dowex-1) and a disrupting material (e.g., salt and a fatty acid such as sodium octanoate) to separate any dye that has eluted off the column and into the protein fraction. Procion Red H-8BN is cited as an example for purification of carboxypeptidase G2. It is unknown, currently, whether Protherics uses this technology, or has or will license this invention. Presuming that Procion Red H-8BN or similar ligand is used by Protherics for manufacture of recombinant enzyme, the company has likely licensed this and related patents/applications from Delta/Novozymes, or may face infringement suits.

Trials: Methotrexate (MTX), a synthetic folate analog, has been in clinical use since 1948 and is an important component of various chemotherapeutic regimens used for the treatment of patients with neoplastic diseases. Actively proliferating tissue, such as malignant cells, are in general more sensitive to this cellular interference and toxicity of MTX. In addition, MTX has immunomodulating effects and is often used in the treatment of a number of other diseases, such as rheumatoid arthritis (RA), multiple sclerosis (MS) and psoriasis. Application of high doses of MTX, usually administered as a prolonged infusion, is frequently used in patients with Non-Hodgkin's Lymphoma, acute lymphoblastic leukemia (ALL), soft tissue tumors such as osteosarcoma, and other cancers. Besides methotrexate, other folate cancer drugs include Tomudex (D1694, raltitrexed), approved in Europe for the treatment of colon cancer, and Pemetrexed (Alimta) approved in the U.S. for pleural mesothelioma

As a result of fatal outcomes from MTX toxicity, protection measures have been routinely included in MTX therapeutic regimes. These include leucovorin rescue using leucovorin calcium, the calcium salt of 5-formyl tetrahydrofolic acid (folinic acid/folinate), the DHFR metabolite of folic acid and an essential coenzyme for nucleic acid synthesis. Other approaches include lumbar puncture to drain the methotrexate from cerebrospinal fluid (CSF), ventriculolumbar CSF perfusion, and systemic corticosteroids and leucovorin. Leucovorin calcium is able to rescue MTX inhibited cells. However, at high MTX concentrations, leucovorin calcium may fail to prevent systemic toxicities. Reversal of MTX by leucovorin calcium is competitive, with relatively higher concentrations required as the MTX concentration increases. When concentrations of MTX reach 10 uM, even 10-fold higher leucovorin calcium concentrations (1, 000 uM) are unable to protect bone marrow cells from toxicity. Leucovorin rescue may lower systemic MTX toxicity, but it does not enhance MTX excretion. Another protective measure is hydration and alkalinization (raising blood pH) to enhance the solubility of MTX and prevent MTX nephrotoxicity. With these measures, the incidence of life-threatening MTX toxicity may be lowered to around 1.5%. However, despite these precautions, prolonged MTX accumulation due to drug-related renal insufficiency may develop and lead to severe and life-threatening systemic toxicities.

Within 7-50 minutes after CPG2 administration, serum MTX levels commonly fall to 1 mM or undetectable levels. CPG2 is a much more immediate antidote compared to all of the other approaches. In one clinical trial, intrathecal administration of 2,000 units of recombinant CPDG2 into the lumbar space 3-9 hours after accidental intrathecal methotrexate overdose led to a greater than 98% decline in CSF methotrexate concentrations. All patients receiving timely treatment with CPG2 for MTX toxicity can be expected to recover completely.

Trials: Various clinical trials have shown that the early use of Voraxaze to treat methotrexate toxicity can reduce deaths from kidney failure. Ongoing or recently concluded U.S. trials include A Trial of Carboxypeptidase-G2 (CPDG2) for the Management of Patients with Intrathecal Methotrexate Overdose, ClinTrials.gov no. NCT00001299, a Phase I trial nonrandomized interventional trial at the Clinical Center, National Institutes of Health (NIH), that started in March 1992, with eventual expected enrollment of 10 patients patients with an intrathecal methotrexate overdose. In clinical testing, Voraxaze has been well-tolerated, with only 8% of 329 patients reporting adverse events that were considered to be related to Voraxaze.

In Oct. 2004, interim results from the NCI trial were published (J. Natl. Cancer Inst.; vol. 96, no. 20, p. 1557-9). Voraxase containing recombinant CPDG2 (2,000 U) was administered intrathecally to 7 cancer patients 3-9 hours after they had received an accidental overdose of intrathecal methotrexate (median dose = 364 mg; range = 155-600 mg). Four of the seven patients had cerebrospinal fluid (CSF) exchange to remove methotrexate prior to CPDG2 administration. Before CPDG2 administration, the median concentrations of methotrexate in CSF were 264 µM (range = 97-510 µM) among patients who had CSF exchange and 8,050 µM (range = 2439-16,500 µM) among patients who had not. After intrathecal CPDG2 administration, methotrexate concentrations in CSF declined by more than 98%. All patients recovered completely from the intrathecal methotrexate overdose, except for two patients who had memory impairments. Antibodies to CPDG2 were not detected in plasma after treatment with intrathecal CPDG2. Intrathecal CPDG2 was well tolerated and efficacious for treating accidental intrathecal methotrexate overdoses.

In Feb. 2005, results from a European Phase II trial (May 1997-March 2002) were reported (Br. J. Cancer, vol. 92, no. 3, p. 480-7, Feb 14, 2005). CPDG2 was administered intravenously to 82 patients at a median dose of 50 U/kg (range 33-60 U/kg, with a typical 100 kg adult receiving an average of 5,000 Units. Eligible patients for this study had serum MTX concentrations of >10 µM at 36 hours or >5 µM at 42 hours after start of MTX infusion and documented renal failure (serum creatinine > or =1.5 times the upper limit of normal). The median MTX serum level before CPDG2 administration was 11.93 µM (range 0.52-901 µM). CPDG2 was given at a median of 52 hours (range 25-178 h) following the start of MTX infusion, and resulted in a rapid 97% (range 73-99%) reduction of the MTX serum level. Toxicity related to MTX was documented in about half the patients; and four patients died despite CPDG2 administration due to severe myelosuppression and septic complications. As with the NCI and other studies, it was concluded that administration of CPDG2 is a well-tolerated, safe and very effective for MTX elimination in delayed excretion due to renal failure. As with other trials, toxicity related to CPDG2 was not observed.

Disease: See the Medical and Biological sections above for discussion of methotrexate toxicity. Protherics estimates that about 11,300 patients/year in the European Union experience methotrexate toxicity and may be candidates for Voraxase therapy. Presumably, there is a roughly comparable number of candidate patients in the U.S.

Market.: Protherics is planning to launch Voraxaze in the US and EU through the company's own in-house sales and marketing operation together with local partners.

In its annual report for the year ending March 20, 2005, Protherics reported that named patient sales of Voraxaze increased to £0.5 million (~.873 million) from £0.1 million (~$175,000) in the previous year. Full potential of the product will not be realized until full marketing approval is achieved.

In Nov. 2008, Protherics estimated "that the global market potential for Voraxaze, for interventional use, is

approximately USD25-50m per annum." Protherics had previously reported, "The market potential for Voraxaze, when used as a rescue therapy in patients with impaired kidney function, is estimated to be $200 million. Presuming ²24,000 patients/year, the cost for Voraxase treatment would be on the order of $8,000/patient, a cost relatively reasonable (if not cheap) in comparison with some other life-saving biopharmaceuticals. U.S. and European Union product launches are planned using Protherics' own in-house sales and marketing staff." The company anticipates also market its CroFab and DigiFab products in the U.S. in 2010, about the time Voraxase is expected to entry the U.S. market.

In the future, a much bigger potential market looms for Voraxaze use in combination with methotrexate in all patients on high-dose methotrexate treatment to optimize therapy. Voraxaze may prove suitable for more routine adjunctive use with high-dose methotrexate to reduce the risk of toxicity and thereby allow optimization of methotrexate therapy. Protherics is preparing to initiate a number of planned use studies with a view to expanding the potential use of Voraxaze into this market.