Rabacfosadine for relapsed canine B-cell lymphoma: Efficacy and adverse event profiles of 2 different doses.

Rabacfosadine (RAB), a novel double prodrug of the acyclic nucleotide phosphonate PMEG, preferentially targets neoplastic lymphocytes with reduced off target toxicity. Historical studies have suggested that every 21-day dosing is effective with acceptable toxicity. The purpose of this study was to evaluate RAB's safety and efficacy at 2 different doses every 21 days in dogs with relapsed B-cell lymphoma. Dogs that had failed 1 doxorubicin-based chemotherapy protocol were eligible for inclusion in this prospective trial. Once enrolled, dogs were randomized to receive RAB at either 0.82 mg/kg or 1.0 mg/kg as a 30-minute IV infusion every 21 days for up to 5 treatments. Response assessment and adverse event (AE) evaluation were performed every 21 days via VCOG criteria. Fifty dogs were enrolled, with 16 treated at 0.82 mg/kg and 34 treated at 1.0 mg/kg. The overall response rate was 74%, with 45% of dogs experiencing a complete response (CR). The median progression free intervals (PFIs) were 108 days, 172 days and 203 days for all dogs, all responders, and all CRs, respectively. Response rates and PFIs were similar in both treatment groups. The incidence of AEs, dose delays, dose reductions and withdrawals were not statistically different between the 2 groups. The AEs observed were similar to those previously reported and included hematologic, gastrointestinal, dermatologic and pulmonary AEs. One dog had grade 5 pulmonary fibrosis; otherwise, AEs resolved with supportive treatment. Rabacfosadine is a generally well tolerated, effective chemotherapy option for dogs with relapsed B-cell lymphoma.

Preliminary investigation of blood concentrations of insulin-like growth factor, insulin, lactate and ß-hydroxybutyrate in dogs with lymphoma as compared with matched controls.

It is well established that tumour cells have metabolic differences when compared with normal cells. This is particularly true for energy metabolism in which dogs with cancer have been reported to have higher blood insulin and lactate concentrations than control dogs. Moreover, some human and animal studies suggest that the insulin-like growth factor 1 (IGF-1) signalling pathway may play a role in tumorigenesis and tumour progression. At present, IGF-1 has not been evaluated in dogs with multicentric lymphoma. In this prospective, cross-sectional study, blood levels of IGF-1, as well as other markers of energy metabolism-insulin, glucose, lactate, and ß-hydroxybutyrate-were measured in 16 dogs with histologically or cytologically confirmed treatment-naïve lymphoma. These results were compared with 16 age-, sex- and weight-matched healthy controls. Dietary histories were collected, and protein, fat and carbohydrate intake were compared between groups. Results demonstrated that IGF-1, insulin, glucose and insulin:glucose ratio were not different between groups. However, lactate and ß-hydroxybutyrate were higher in the dogs with lymphoma than that in the control dogs (1.74 ± 0.83 mmoL/L vs 1.08 ± 0.27 and 2.59 ± 0.59 mmol/L vs 0.77 ± 0.38 mmol/L, respectively). Median dietary protein, fat and carbohydrates did not differ between the groups. This preliminary study suggests that higher insulin and IGF-1 levels relative to controls may not be a consistent finding in dogs with lymphoma. The significance of increased ß-hydroxybutyrate in dogs with lymphoma warrants further investigation in a larger prospective study.

MetaNetter 2: A Cytoscape plugin for ab initio network analysis and metabolite feature classification.

Metabolomics frequently relies on the use of high resolution mass spectrometry data. Classification and filtering of this data remain a challenging task due to the plethora of complex mass spectral artefacts, chemical noise, adducts and fragmentation that occur during ionisation and analysis. Additionally, the relationships between detected compounds can provide a wealth of information about the nature of the samples and the biochemistry that gave rise to them. We present a biochemical networking tool: MetaNetter 2 that is based on the original MetaNetter, a Cytoscape plugin that creates ab initio networks. The new version supports two major improvements: the generation of adduct networks and the creation of tables that map adduct or transformation patterns across multiple samples, providing a readout of compound relationships. We have applied this tool to the analysis of adduct patterns in the same sample separated under two different chromatographies, allowing inferences to be made about the effect of different buffer conditions on adduct detection, and the application of the chemical transformation analysis to both a single fragmentation analysis and an all-ions fragmentation dataset. Finally, we present an analysis of a dataset derived from anaerobic and aerobic growth of the organism Staphylococcus aureus demonstrating the utility of the tool for biological analysis.

Treatment of advanced canine anal sac adenocarcinoma with hypofractionated radiation therapy: 77 cases (1999-2013).

Currently no standard of care exists for advanced, inoperable or metastatic anal sac adenocarcinoma (ASAC). The objective of this retrospective study was to assess the role of hypofractionated radiation therapy (RT) in 77 dogs with measurable ASAC. A total of 38% of dogs experienced a partial response to RT. For dogs presenting with clinical signs related to the tumour, improvement or resolution of signs was noted in 63%. For dogs presenting with hypercalcemia of malignancy, resolution was noted in 31% with RT alone and an additional 46% with radiation, prednisone, and/or bisphosphonates. Median overall survival was 329 days (range: 252-448 days). Median progression free survival was 289 days (range: 224-469). There was no difference in survival based on radiation protocol, use of chemotherapy, previous surgery or advanced stage. Radiation toxicities were mild and infrequent. Hypofractionated RT is well tolerated and is applicable in the treatment of advanced primary, locoregional or metastatic ASAC.

A retrospective evaluation of lomustine (CeeNU) in 32 treatment naïve cats with intermediate to large cell gastrointestinal lymphoma (2006-2013).

Multi-drug chemotherapy protocols for feline lymphoma have demonstrated variable efficacy and tolerability. In phase I trials, lomustine has demonstrated efficacy for cats with lymphoma though its use for treatment naïve feline intermediate/large cell gastrointestinal (GI) lymphoma remains unknown. This study evaluated the efficacy and tolerability of lomustine for the treatment of feline GI lymphoma. Thirty-two cats with histologically or cytologically confirmed intermediate/large cell GI lymphoma were evaluated retrospectively. Factors assessed included clinical signs, hematologic/biochemical parameters and use of l-asparaginase at induction. A response rate of 50% (16/32), with median duration of response of 302 days (range 64-1450 days), was found. Median progression-free interval was 132 days (range 31-1450 days), with overall median survival time of 108 days (range 4-1488 days). History of hyporexia, presence of anaemia and dose of lomustine were significantly associated with progression-free survival. Overall, lomustine is a well-tolerated and effective treatment for feline GI lymphoma.

Utility of Computed Tomography versus Abdominal Ultrasound Examination to Identify Iliosacral Lymphadenomegaly in Dogs with Apocrine Gland Adenocarcinoma of the Anal Sac.

BACKGROUND: Apocrine gland adenocarcinoma of the anal sac (AGAAS) is associated with high rates of iliosacral lymph node metastasis, which may influence treatment and prognosis. Magnetic resonance imaging (MRI) recently has been shown to be more sensitive than abdominal ultrasound examination (AUS) in affected patients. OBJECTIVE: To compare the rate of detection of iliosacral lymphadenomegaly between AUS and computed tomography (CT) in dogs with AGAAS. ANIMALS: Cohort A: A total of 30 presumed normal dogs. Cohort B: A total of 20 dogs with AGAAS that underwent AUS and CT. METHODS: Using cohort A, mean normalized lymph node : aorta (LN : AO) ratios were established for medial iliac, internal iliac, and sacral lymph nodes. The CT images in cohort B then were reviewed retrospectively and considered enlarged if their LN : AO ratio measured 2 standard deviations above the mean normalized ratio for that particular node in cohort A. Classification and visibility of lymph nodes identified on AUS were compared to corresponding measurements obtained on CT. RESULTS: Computed tomography identified lymphadenomegaly in 13 of 20 AGAAS dogs. Of these 13 dogs, AUS correctly identified and detected all enlarged nodes in only 30.8%, and either misidentified or failed to detect additional enlarged nodes in the remaining dogs. Despite limitations in identifying enlargement in all affected lymph nodes, AUS identified at least 1 enlarged node in 100% of affected dogs. CONCLUSION AND CLINICAL IMPORTANCE: Abdominal ultrasound examination is an effective screening test for lymphadenomegaly in dogs with AGAAS, but CT should be considered in any patient in which an additional metastatic site would impact therapeutic planning.

Histologic and immunohistochemical characterization of thymic epithelial tumours in the dog.

Thymic epithelial tumour (TET) histologic subclassification has not been well described in the veterinary literature as it has in humans. The objective of this study was to identify and describe TET subtypes in dogs and to determine the utility of immunohistochemistry (IHC) in differentiating these subtypes. Samples were reviewed and classified according to a modified World Health Organization (WHO) criteria for human tumours of thymic origin. Signallment, presenting signs, treatment and survival data was collected from medical records. Histologic review confirmed the same subtypes as described in humans. Presence of high stage disease, pleomorphism, mitotic figures and capsular invasion was more common in atypical thymomas and thymic carcinomas than in thymomas. IHC was performed for GLUT-1, CD5, CD117 and CK8/18; however, this was not useful in classifying the tumours.

Doxorubicin chemotherapy for presumptive cardiac hemangiosarcoma in dogs†.

Sixty-four dogs were treated with single-agent doxorubicin (DOX) for presumptive cardiac hemangiosarcoma (cHSA). The objective response rate (CR + PR) was 41%, and the biologic response rate (CR + PR + SD), or clinical benefit, was 68%. The median progression-free survival (PFS) for treated dogs was 66 days. The median survival time (MST) for this group was 116 days and was significantly improved compared to a MST of 12 days for untreated control dogs (P = 0.0001). Biologic response was significantly associated with improved PFS (P < 0.0001) and OS (P < 0.0001). Univariate analysis identified larger tumour size as a variable negatively associated with PFS. The high rate of clinical benefit and improved MST suggest that DOX has activity in canine cHSA.

Phase II evaluation of VDC-1101 in canine cutaneous T-cell lymphoma.

BACKGROUND: Canine cutaneous T-cell lymphoma (CTCL) is an uncommon disease for which efficacious therapies are lacking. The novel anticancer nucleotide prodrug VDC-1101 (formerly known as GS-9219) has shown efficacy in dogs with multicentric lymphoma. One of the observed adverse effects with this drug was a skin change characterized by hair loss, erythema, and pruritus, implying delivery of VDC-1101 to the skin. HYPOTHESIS/OBJECTIVES: The primary study objective was to identify the objective response rate (ORR) to VDC-1101 in canine CTCL; secondary objectives included characterization of progression-free survival (PFS) and adverse events (AEs). ANIMALS: Twelve dogs with chemotherapy-naïve or relapsed, histologically and immunohistochemically confirmed CTCL. METHODS: Dogs received VDC-1101 as a 30-minute IV infusion once every 21 days. Prednisone (1 mg/kg PO q48h) was administered concurrently. RESULTS: In 11 evaluable patients, responses included 1 complete response (CR), 4 partial responses (PR), 2 stable disease (SD), and 4 progressive disease for an ORR of 45% and biologic response rate (CR/PR/SD) of 64%. The median PFS was 37.5 days (26 to >399 days), which includes 1 durable and ongoing CR (>1 year). Gastrointestinal and hematologic AEs were mild; no dogs developed grade 3 or 4 AEs. Three dogs developed dermatopathies and 1 of these dogs was removed from the study as a result of this AE. CONCLUSIONS AND CLINICAL IMPORTANCE: VDC-1101 has activity against canine CTCL and could provide another treatment option in a disease process with a poor prognosis.

Molecular profiling reveals prognostically significant subtypes of canine lymphoma.

We performed genomewide gene expression analysis of 35 samples representing 6 common histologic subtypes of canine lymphoma and bioinformatics analyses to define their molecular characteristics. Three major groups were defined on the basis of gene expression profiles: (1) low-grade T-cell lymphoma, composed entirely by T-zone lymphoma; (2) high-grade T-cell lymphoma, consisting of lymphoblastic T-cell lymphoma and peripheral T-cell lymphoma not otherwise specified; and (3) B-cell lymphoma, consisting of marginal B-cell lymphoma, diffuse large B-cell lymphoma, and Burkitt lymphoma. Interspecies comparative analyses of gene expression profiles also showed that marginal B-cell lymphoma and diffuse large B-cell lymphoma in dogs and humans might represent a continuum of disease with similar drivers. The classification of these diverse tumors into 3 subgroups was prognostically significant, as the groups were directly correlated with event-free survival. Finally, we developed a benchtop diagnostic test based on expression of 4 genes that can robustly classify canine lymphomas into one of these 3 subgroups, enabling a direct clinical application for our results.

Do Fitflops increase lower limb muscle activity?

BACKGROUND: Fitness toning shoes are becoming increasingly popular, they aim to increase muscle activity, raise energy expenditure and improve overall health while wearing them. Yet there is a lack of consensus in the literature regarding their effectiveness. One such shoe on the market is the Fitflop designed to activate leg muscles through density shifts in the shoe's sole. The purpose of this study was to investigate the effect of wearing Fitflops on the muscle activity of the lower limb. METHODS: Twenty three females (age 20.8 (1.3)years, mass 62.9 (11.9)kg, height 165.4 (5.6)cm) participated in the study. Muscle activity of the medial gastrocnemius, biceps femoris, rectus femoris and gluteus maximus of the participants' right limb were recorded using surface electromyography during participation in three different tasks to simulate daily living activities. These were a) treadmill walking b) stair climbing and c) zigzag walking around cones. The participants completed the tasks barefoot, while wearing Fitflops and while wearing regular flip flops so that comparisons between muscle activity in the different shoe conditions could be made. FINDINGS: The results show that there was no significant difference in the activity of the medial gastrocnemius, biceps femoris, rectus femoris and gluteus maximus muscles across all shoe conditions and simulated daily activities (P>0.05). INTERPRETATION: Based on these results, the use of Fitflops is not recommended as a means of increasing muscle activity of the medial gastrocnemius, biceps femoris, rectus femoris and gluteus maximus during activities of daily living in a healthy recreationally active female population.

Angiofibroma of the nasal cavity in 13 dogs.

This case series describes a rare entity, nasal angiofibroma, in 13 dogs that were presented to the University of Wisconsin, School of Veterinary Medicine from 1988 to 2000. All dogs in this case series presented with clinical signs and radiographic changes that were strongly suggestive of a locally invasive neoplasm. However, histopathology completed on transnostral core biopsy samples revealed benign appearing vascular proliferation with secondary lymphosuppurative inflammation was established despite cytologic criteria of malignancy present in five dogs. On the basis of the outcomes in this case series, nasal angiofibroma should be considered a differential for dogs presenting with clinical signs consistent with a malignant nasal tumour.

A tumor-related lymphoid progenitor population supports hierarchical tumor organization in canine B-cell lymphoma.

BACKGROUND: Tumors have heterogeneous properties, which could be explained by the existence of hierarchically and biologically distinct tumor cells such as tumor-initiating cells (TICs). This model is clinically important, as TICs are promising targets for cancer therapies. However, TICs in spontaneous B-cell lymphoma have not been conclusively identified. HYPOTHESIS/OBJECTIVES: Tumor cells with a progenitor phenotype exist in B-cell lymphoma, reflecting a hierarchical organization. ANIMALS: Twenty-eight client-owned dogs with previously untreated B-cell lymphoma and 6 healthy dogs. METHODS: This was a prospective study. Flow cytometry was used to identify lymphoid progenitor cells (LPCs) that coexpressed hematopoietic progenitor antigens CD34, CD117, and CD133, with lymphoid differentiation markers CD21 and/or CD22 in B-cell lymphoma. The polymerase chain reaction for antigen receptor rearrangements was used to analyze clonality and relatedness of tumor populations. A xenograft model with NOD/SCID/IL-2Rγ(-/-) mice was adapted to expand and serially transplant primary canine B-cell lymphoma. RESULTS: LPCs were expanded in lymph nodes from 28 dogs with B-cell lymphoma compared with 6 healthy dogs (P= .0022). LPCs contained a clonal antigen receptor gene rearrangement identical to that of the bulk of tumor cells. Canine B-cell lymphoma xenografts in recipient mice that maintained LPCs in the tumors were recurrently observed. CONCLUSIONS AND CLINICAL IMPORTANCE: These results suggest the presence of a hierarchy of tumor cells in B-cell lymphoma as has been demonstrated in other cancers. These findings have the potential to impact not only the understanding of lymphoma pathogenesis but also the development of lymphoma therapies by providing novel targets for therapy.

Serum relaxin levels affect the in vivo properties of some but not all tendons in normally menstruating young women.

Relaxin (hRLX) is a hormone reported to affect collagen synthesis. Its effects are also thought to be modulated by other sex hormones, including oestrogen, which has previously been found to be associated with alterations of in vivo tendon properties. There is thus a potential for hRLX to impact on collagen, which could result in tendon structural and mechanical properties being modified. The present study therefore aimed to determine any interaction between hRLX and tendon stiffness, in normally menstruating women (n = 12). Tendon properties were determined using a combination of dynamometry and B-mode ultrasound, whilst serum hRLX levels were established by ELISA. Serum hRLX level was seen to be negatively associated with patellar tendon stiffness (r = -0.56; P < 0.001), explaining 31% of the variance in this parameter. There was no association between hRLX and gastrocnemius tendon stiffness (P > 0.05), or with the cross-sectional area of either of the two tendons (P > 0.05). In young, normally menstruating women, hRLX appears to have a significant effect on the patellar but not the gastrocnemius tendon stiffness. Where it has an effect, this appears to be on the intrinsic properties rather than on the dimensions of said tendon. Future work to elucidate the physiological cause of this selectivity in the impact of relaxin will be key to mapping the impact of the endocrine system on the phenotype of tendinous tissue.

Efficacy of maropitant in the prevention of delayed vomiting associated with administration of doxorubicin to dogs.

BACKGROUND: Vomiting, nausea, inappetence, and diarrhea are common delayed adverse effects of doxorubicin. Maropitant, a neurokinin-1 receptor antagonist, is known to prevent acute vomiting in dogs receiving cisplatin. OBJECTIVE: To evaluate the efficacy of maropitant in preventing delayed vomiting after administration of doxorubicin to dogs. ANIMALS: Fifty-nine dogs with cancer. METHODS: This randomized, double-blind, placebo-controlled study used a cross-over design. Dogs were randomized into 1 of 2 treatment groups. Group A received maropitant after the 1st doxorubicin, and placebo after the 2nd. Group B received placebo first, and maropitant second. Maropitant (2 mg/kg) or placebo tablets were administered PO for 5 days after doxorubicin treatment. Owners completed visual analog scales based on Veterinary Cooperative Oncology Group-Common Terminology Criteria for Adverse Events to grade their pet's clinical signs during the week after administration of doxorubicin. Statistical differences in gastrointestinal toxicosis and myelosuppression between maropitant and placebo treatments were evaluated. RESULTS: Significantly fewer dogs had vomiting (P=.001) or diarrhea (P=.041), and the severity of vomiting (P<.001) and diarrhea (P=.024) was less the week after doxorubicin when receiving maropitant compared with placebo. No differences were found between maropitant and placebo for other gastrointestinal and bone marrow toxicoses. CONCLUSIONS AND CLINICAL IMPORTANCE: Maropitant is effective in preventing delayed vomiting induced by doxorubicin. Its prophylactic use might improve quality of life and decrease the need for dose reductions in certain dogs.

Menstrual cycle variations in oestradiol and progesterone have no impact on in vivo medial gastrocnemius tendon mechanical properties.

BACKGROUND: Tendon tissue contains oestrogen receptors and is therefore likely to be responsive to female sex hormones. Here we examine any effect of levels of female sex hormones associated with the menstrual cycle phase on corresponding tendon mechanical properties. METHODS: Fifteen healthy females aged 23 (SEM 1.0 years) underwent three assessments of medial gastrocnemius tendon mechanical properties. Assessments were carried out once during days 1-4, 12-14 and 20-23 (with day 1 being the first day of menstruation). Venous blood samples were taken on the same days as tendon properties assessments to quantify serum levels of oestradiol and progesterone. FINDINGS: There was no significant difference in the stiffness of the medial gastrocnemius tendon over the course of the menstrual cycle (days 1-4, 65.08 (SEM 5.16 Nm m(-1)), days 12-14, 62.73 (SEM 5.82 Nm m(-1)), days 20-23, 66.74 (SEM 7.14 Nm m(-1))). There were also no significant differences in tendon length and cross-sectional area which led to no significant differences in Young's modulus values. No correlations were found between serum levels of oestradiol and/or progesterone and tendon stiffness and/or Young's modulus. INTERPRETATION: Acute fluctuations in female sex hormones have no significant effect on medial gastrocnemius tendon mechanical properties. In a context where studies are often limited to selecting only oral contraceptive-users as participants in order to minimise potential noise related to the anticipated effects of menstrual cycle hormones on physical performance, our findings provide the basis for enabling the pooling of female tendon data, regardless of the phase of the menstrual cycle of individual participant.

Tendon structural and mechanical properties do not differ between genders in a healthy community-dwelling elderly population.

Elderly women are reportedly at higher risk of falling than their male counterparts. Postural balance is highly associated with fall risk and is also correlated with tendon structural and mechanical properties. Gender differences in tendon properties could partly explain the discrepancy in fall risk. Thus the purpose of this study was to investigate the possible gender difference in tendon properties in the elderly. The properties of the patellar tendon of 55 elderly (men n = 27, aged 72 +/- 1 years, women n = 28, aged 70 +/- 1 years) participants were tested. Tendon stiffness (K), length (L), and cross-sectional area (CSA) were measured using B-mode ultrasonography, dynamometry, and electromyography during ramped isometric knee extensions. There were no significant differences (p > 0.05) between men and women in tendon stiffness (elderly men 550.9 +/- 29.2 vs. women 502.9 +/- 44.9 Nmm(-1)) or in Young's modulus (elderly men 0.32 +/- 0.02 vs. women 0.36 +/- 0.04 GPa). This elderly group had similar tendon structural and mechanical properties. The comparable characteristics in gender-specific tendon properties in an elderly population exhibiting similar lifestyle characteristics to the current sample may not explain the reports in the literature regarding increased fall risk in elderly women relative to that seen in men of a similar age.

Response of canine cutaneous epitheliotropic lymphoma to lomustine (CCNU): a retrospective study of 46 cases (1999-2004).

BACKGROUND: Epitheliotropic lymphoma (ELSA) is an uncommon cutaneous canine malignancy of T lymphocytes. A consensus regarding the therapeutic standard of care is lacking, warranting evaluation of chemotherapeutic agents traditionally employed against canine nodal lymphoma in the treatment of ELSA. HYPOTHESIS: The purpose of this retrospective, multi-institutional study was to evaluate the efficacy of 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea (CCNU) in the treatment of ELSA. ANIMALS: Forty-six dogs with adequate follow-up and treatment response information. METHODS: All cases were diagnosed histopathologically. Immunohistochemisty (CD3, CD79a) was performed on 42/46 samples. RESULTS: Presenting skin lesions included generalized scales (25/46), plaques or nodules (22/46), mucocutaneous lesions (14/ 46), and corneal involvement (1/46). Lymph node involvement and Sézary syndrome were documented in 7 and 2 dogs, respectively. The median number of CCNU treatments was 4 (range, 1-11), with a median starting dose of 60 mg/m(2) (range, 30-95). Of the 46 dogs, 15 achieved complete remission, 23 achieved partial remission, 5 had stable disease, and 3 had progressive disease, for an overall response rate of 83%. The median number of treatments to achieve a response was 1 (range, 1-6). The overall median duration of response was 94 days (range, 22-282). Sixteen dose reductions were required because of neutropenia (10/46), thrombocytopenia (1/46), anemia (1/46), increased liver enzyme activity (3/46), or unspecified reasons (1/46). CONCLUSIONS AND CLINICAL IMPLICATIONS: Given the high response rate and well tolerated protocol, prospective studies are warranted to investigate the utility of CCNU alone or in multi-agent protocols for the treatment of ELSA.

Efficacy and toxicity of paclitaxel (Taxol) for the treatment of canine malignant tumors.

Paclitaxel (Taxol) was administered to 25 dogs with histologically confirmed malignant tumors at a dosage of 165 mg/m2 i.v. over 3-6 hours every 3 weeks. Dogs received premedication with antihistimines and corticosteroids to reduce hypersensitivity reactions. However, 64% of the dogs still experienced allergic reactions. Six dogs (24%) had grade 3 or 4 neutropenia, 6 dogs (24%) required hospitalization and 3 dogs (12%) died of sepsis. Five dogs (20%) had a partial response (osteosarcoma [2 dogs] mammary carcinoma [2 dogs] and malignant histiocytosis [1 dog]) for a median duration of 53 days. The overall toxicity was unacceptable at the 165 mg/m2 dose. Therefore, subsequent evaluations of paclitaxel in tumor-bearing dogs should a starting dose of 132 mg/m2 i.v. every 3 weeks.

CD5 acts as a tyrosine kinase substrate within a receptor complex comprising T-cell receptor zeta chain/CD3 and protein-tyrosine kinases p56lck and p59fyn.

T-cell antigens including CD2, CD4, CD6, CD8, and CD28 serve as coreceptors with the T-cell receptor (TCR)/CD3 complex in control of T-cell growth. The molecular basis by which these antigens fulfill this role has remained a major issue. An initial clue to this question came with our finding that the sensitivity of in vitro kinase labeling (specifically using protein-tyrosine kinase p56lck) allowed detection of a physical association between CD4-p56lck and the TCR/CD3 complexes. Another T-cell antigen, CD5, is structurally related to the macrophage scavenger receptor family and, as such, can directly stimulate and/or potentiate T-cell proliferation. In this study, we reveal that in Brij 96-based cell lysates, anti-CD5 antibodies coprecipitated TCR zeta chain (TCR zeta)/CD3 subunits as well as the protein-tyrosine kinases p56lck and p59fyn. Conversely, anti-CD3 antibody coprecipitated CD5, p56lck, and p59fyn. Indeed, anti-CD5 and anti-CD3 gel patterns were virtually identical, except for a difference in relative intensity of polypeptides. Anti-CD4 coprecipitated p56lck, p32, and CD3/TCR zeta subunits but precipitated less CD5, suggesting the existence of CD4-TCR zeta/CD3 complexes distinct from the CD5-TCR zeta/CD3 complexes. Consistent with the formation of a multimeric CD5-TCR zeta/CD3 complex, anti-CD5 crosslinking induced tyrosine phosphorylation of numerous T-cell substrates, similar to those phosphorylated by TCR zeta/CD3 ligation. Significantly, as for TCR zeta, CD5 was found to act as a tyrosine kinase substrate induced by TCR/CD3 ligation. The kinetics of phosphorylation of CD5 (t1/2 = 20 sec) was among the earliest of activation events, more rapid than seen for TCR zeta (t1/2 = 1 min). CD5 represents a likely TCR/CD3-associated substrate for protein-tyrosine kinases (p56lck or p59fyn) and an alternative signaling pathway within a multimeric TCR complex.