Hyaluronan is a natural polysaccharide with alternating D-glucuronic acid and N-acetyl-d-glucosamine units. Hyaluronan and its metabolites are eliminated by the lymphatics via receptor-mediated endocytosis and lysosomal degradation.1–4 Hyaluronan is part of the extracellular matrix and is also found in synovial fluid, cartilage, dermis, and vitreous humor.3,5 It is involved in multiple processes such as cell adhesion, organization of the extracellular matrix, growth, migration, tumor formation, and metastasis.3,5,6 Because hyaluronan is nonimmunogenic, it is an ideal nanocarrier for various drugs such as cisplatin, paclitaxel, doxorubicin, and mitomycin.1,5,7
Cisplatin (cis-diamminedichloroplatinum) is a chemotherapeutic agent that damages DNA and inhibits protein and rRNA synthesis.8,9 The in vitro cytotoxic effects of cisplatin include platinum binding to DNA, creation of interstrand cross-links, and formation of intrastrand bidentate N-7 adducts at d(GpG) and d(ApG).10 Cisplatin is cell cycle phase nonspecific and is eliminated via renal excretion.9 In human patients, cisplatin is used to treat many solid tumors including squamous sarcomas in the head and neck areas, lymphomas, and small cell and non-small cell lung, testicular, ovarian, gastric, esophageal, and pancreatic cancers. In veterinary medicine, cisplatin is used to treat solid tumors, including osteosarcomas, carcinomas, and sarcomas in companion animals.9,11 Common side effects associated with cisplatin administration include nephrotoxicosis (renal tubular inflammation and necrosis), leukopenia, nausea, anemia, and chronic neurotoxicosis and ototoxicosis.2,11 The toxic effects following clinical administration of cisplatin are similar for human and veterinary patients, and its use in veterinary medicine has been limited.
As peak plasma cisplatin concentration increases, the risk for systemic toxic effects increases but the therapeutic effects against the targeted tumor remain relatively stable.11 Various strategies have been proposed for cisplatin administration, including metronomic chemotherapy and local injection of cisplatin into affected tissues that can be concurrently isolated from systemic blood circulation so as to minimize peak plasma cisplatin concentration and decrease the risk of toxicosis, specifically nephrotoxicosis.11 Various routes of cisplatin administration have been evaluated in dogs. For dogs with appendicular osteosarcomas and in which limb-sparing surgery was to be performed, cisplatin administered intra-arterially in combination with radiation prior to surgery resulted in a high percentage of tumor necrosis with minimal loss of host bone viability.12 Severe toxic effects are associated with SC administration of cisplatin.13 Similar toxic effects were not detected following intracavitary (intrathoracic or intra-abdominal) adminstration of cisplatin, and this route of adminstration provided palliative treatment for pleural or abdominal effusion in 5 of 6 dogs with malignant neoplasia.14 Sustained release of cisplatin from a d, l–OPLA implant has been evaluated in dogs with nasal tumors,15 STSs,16 and osteosarcomas17–19; however, clinical improvement following administration of cisplatin via OPLA implant was equivocal. Intratumoral injection of hyaluronan nanocarriers conjugated with cisplatin represents a new modality for the administration of cisplatin that may decrease peak cisplatin concentration in plasma yet maintain cisplatin's efficacy against the targeted tumor.11
In addition to being nonimmunogenic, hyaluronan is a ligand for CD44 receptors that are located on lymphocytes and some cancer cells.11,20 Once bound to CD44, hyaluronan is catabolized, brought into the cell via receptor-mediated endocytosis, degraded in lysosomes, and then introduced into the lymphatic microcirculation.11 When cisplatin is combined with hyaluronan in a nanoconjugate, it remains inactive until the nanoconjugate comes in contact with hyaluronidase. Hyaluronidase expression is a marker for malignant cancers,21 and lymph nodes effectively catabolize hyaluronan.22 After intratumoral injection, the hyaluronan-cisplatin nanoconjugate undergoes receptor-mediated endocytosis or becomes activated by hyaluronidase, which causes cisplatin to be released from the nanoconjugate and absorbed into the peritumoral microlymphatics.3 In rodents, SC injection of a hyaluronan-cisplatin nanoconjugate resulted in increased concentrations of cisplatin in the localized tissue and lymphatics, compared with those obtained after IV administration of cisplatin.11
Soft tissue sarcomas are mesenchymal tumors that originate from connective tissue and represent approximately 8% to 17% of skin and subcutaneous tumors in dogs.23,24 These tumors are locally invasive, and surgical excision of the tumor with wide margins is generally the preferred treatment. Recurrence rate of STSs following surgery ranges from 7% to 32%.23,25,26 Adjuvant chemotherapy with cisplatin, doxorubicin, mitoxantrone, or paclitaxel has been used to treat various sarcomas, but the use of adjuvant chemotherapy for the treatment of dogs with STSs has not been fully evaluated and its effectiveness is relatively unknown.26 The clinical outcome for dogs with high-grade STSs that received doxorubicin as adjuvant chemotherapy after tumor excision did not significantly differ from that for dogs with high-grade STSs that were treated with tumor excision only.27 A protocol that used doxorubicin resulted in an overall response rate of 22% (11/51) of dogs with either naïve or recurrent sarcomas, including 8 of 34 STSs.28 The objectives of the study reported here were to assess the safety of hyaluronan as a nanocarrier for cisplatin for intratumoral injection in STSs of dogs, determine whether the hyaluronan-cisplatin nanoconjugate had preferential local lymphatic penetration, and characterize the pharmacokinetics of cisplatin after injection of the hyaluronan-cisplatin nanoconjugate. Dogs with STSs were chosen for this pilot study because STSs can be easily measured, are amenable to intratumoral drug administration, and can generally be completely excised; also, the lymph nodes draining STSs can usually be easily identified and removed. We hypothesized that the STSs of dogs would absorb the intratumoral injection of hyaluronan-cisplatin, cisplatin would become concentrated within the tumor and its associated lymphatics, the concentration of cisplatin within the tumor would be higher than that in plasma, and there would be no evidence of systemic toxicity following intratumoral injection of the hyaluronan-cisplatin nanoconjugate.
Area under the curve
Open cell polylactic acid
Soft tissue sarcoma
SpectrAA spectrometer with GTA-110 graphite furnace, Varian Inc, Walnut Creek, Calif.
Millennium VG gamma camera, GE Healthcare, Pewaukee, Wis.
Neoprobe Corp, Dublin, Ohio.
AxioCam HRc camera, Carl Zeiss Industrial Metrology, Maple Grove, Minn.
Axioplan 2 microscope, Carl Zeiss Industrial Metrology, Maple Grove, Minn.
Axiovision analysis software, Carl Zeiss Industrial Metrology, Maple Grove, Minn.
DOLT-4, National Research Council Canada, Institute for National Measurement Standards, Ottawa, ON, Canada.
Elan DRC II, PerkinElmer, Waltham, Mass.
Excel 2010, Microsoft Corp, Redmond, Wash.
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