Monoclonal antibody C219 immunohistochemistry against P-glycoprotein: sequential analysis and predictive ability in dogs with lymphoma

Review of Canine Lymphoma Treated with Chemotherapy-Outcomes and Prognostic Factors

While canine lymphoma is a relatively common and important disease seen by veterinarians, there are limited comprehensive reviews of the literature regarding the remission and survival times following chemotherapy, and the associated prognostic factors. This comprehensive thematic review covers the available veterinary literature covering treatment outcomes and identified prognostic factors. A lack of standardised approaches to evaluate and report the outcomes was identified, including factors that would alter the duration of responses by weeks, or occasionally months. After publication of the suggested reporting criteria, this has improved but is still not uniformly applied. The prognostic factors included for evaluation varied from as few as three to seventeen, with over 50 studies using only univariate analysis. Individual papers reported much longer outcomes than others, but assessing the outcomes overall, there has been minimal change over the last 40 years. This supports the belief that novel approaches for lymphoma therapy will be required to substantively improve outcomes.

Comparative Cancer Cell Signaling in Muscle-Invasive Urothelial Carcinoma of the Bladder in Dogs and Humans

Muscle-invasive urothelial carcinoma (MIUC) is the most common type of bladder malignancy in humans, but also in dogs that represent a naturally occurring model for this disease. Dogs are immunocompetent animals that share risk factors, pathophysiological features, clinical signs and response to chemotherapeutics with human cancer patients. This review summarizes the fundamental pathways for canine MIUC initiation, progression, and metastasis, emerging therapeutic targets and mechanisms of drug resistance, and proposes new opportunities for potential prognostic and diagnostic biomarkers and therapeutics. Identifying similarities and differences between cancer signaling in dogs and humans is of utmost importance for the efficient translation of in vitro research to successful clinical trials for both species.

Efficacy and adverse events of continuous l-asparaginase administration for canine large cell lymphoma of presumed gastrointestinal origin

We examined the efficacy and adverse events of continuous l-asparaginase administration in dogs with large cell lymphoma of presumedgastrointestinal (GI) origin. We retrospectively reviewed medical records of dogs with large cell lymphoma of presumed GI origin treated with continuous l-asparaginase administration from 2009 to 2018. We collected information on the signalment, lesion site, complete blood count, serum biochemical profile, diagnostic imaging findings, cytological and histopathological findings, immunophenotype, l-asparaginase administration frequency, treatment response, adverse events, rescue protocol, and patient outcomes. Clinical outcomes were assessed using medical records or by contacting the owner or referring veterinarian. Thirty-two dogs with large cell lymphoma of presumed GI origin received weekly l-asparaginase administration. The median number of l-asparaginase injections was seven (range: 1-30). Although two of the 32 dogs had GI toxicity of grade 3 or higher, none developed a hypersensitivity reaction. The response rate based on ultrasonographic findings was 18/32 (56%) and that based on clinical signs was 30/32 (94%). The median overall progression-free survival was 50 days (range: 2-214 days), and median overall survival was 147 days (range: 2-482 days). Adverse events associated with continuous l-asparaginase administration were rare. Clinical signs at diagnosis improved in most cases. Based on these results, continuous l-asparaginase administration appears to be a reasonable treatment option for dogs with large cell lymphoma of presumed GI origin.

Drug dose and drug choice: Optimizing medical therapy for veterinary cancer

Although novel agents hold great promise for the treatment of animal neoplasia, there may be room for significant improvement in the use of currently available agents. These improvements include altered dosing schemes, novel combinations, and patient-specific dosing or selection of agents. Previous studies have identified surrogates for "individualized dose intensity,", for example, patient size, development of adverse effects, and pharmacokinetic parameters, as potential indicators of treatment efficacy in canine lymphoma, and strategies for patient-specific dose escalation are discussed. Strategies for treatment selection in individual patients include conventional histopathology, protein-based target assessment (eg, flow cytometry, immunohistochemistry, and mass spectrometry), and gene-based target assessment (gene expression profiling and targeted or global sequencing strategies). Currently available data in animal cancer evaluating these strategies are reviewed, as well as ongoing studies and suggestions for future directions.

Evaluation of the Tolerability of Combination Chemotherapy with Mitoxantrone and Dacarbazine in Dogs with Lymphoma

Combination chemotherapy can be an effective option for treating resistant lymphoma in dogs. This retrospective study examined the tolerability and efficacy of the combination of 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (dacarbazine) (DTIC) in a population of dogs with lymphoma resistant to a doxorubicin-containing chemotherapy protocol. Mitoxantrone was administered at 5 mg/m² IV over 10 min followed by DTIC at 600 mg/m² IV over 5 hr, every 3 wk. All dogs were treated with prophylactic trimethoprim-sulfadiazine and metoclopramide. The frequency of grade 4 neutropenia was 18%, and 5% of dogs were hospitalized from sepsis. Gastrointestinal toxicity was uncommon. The overall response rate was 34% (15 of 44; 95% confidence interval 20-48%) for a median duration of 97 days (range 24-636 days, 95% confidence interval 44-150 days). Fourteen of 15 dogs who received mitoxantrone and DTIC as first rescue responded to treatment. Dogs who achieved complete remission to their initial L-asparaginase, cyclophosphamide, doxorubicin, vincristine, and prednisone chemotherapy protocol were more likely to respond to mitoxantrone and DTIC (23 versus 11%, P = .035). The combination of mitoxantrone and DTIC is a safe treatment option for resistant lymphoma in dogs.

Transcriptome analysis of ABCB1, ABCG2 and the BCL2/BAX ratio in refractory and relapsed canine lymphomas under treatment and rescue protocol

The main problems that cause unresponsiveness to an anti-neoplastic drug are the overexpression of drug resistant and anti-apoptotic proteins in tumor cells. In a rescue protocol we evaluated the ability of toceranib phosphate concurrent with lomustine (CCNU) or L-asparaginase and vincristine to decrease drug resistant and apoptotic proteins in relapsed and refractory canine lymphomas. The peripheral blood samples were collected before and after the rescue treatment from fourteen dogs that were refractory to cyclophosphamide-vincristine-prednisolone (COP) or COP-doxorubicin (CHOP) treatment and had recurrent multicentric lymphoma. The mRNA expression level of ABCB1, ABCG2, Bcl2 and Bax were determined by quantitative real-time PCR. The fold-change in ABCB1, ABCG2, Bcl2 and Bax mRNA levels were analyzed in correlation with the progression-free survival (PFS). After the rescue treatment, the ABCB1 and ABCG2 mRNA expression levels were 1.57- and 1.85-fold lower (p = 0.4 and p = 0.87), respectively, compared to pre-treatment. Bcl2/Bax ratio was numerically but not significantly decreased 1.02-fold (p = 0.74). The overall response rate of this protocol was 50% with a median PFS of 79 days (range 14-207 days). The low medians of relative expression levels of ABCB1, ABCG2 and Bcl2/Bax ratio group did not correlate with the clinical outcomes when compared to the high medians of relative expression levels, and likewise with the clinical stage, immunophenotype, histological grade and sub-stage. Therefore, the administration of a rescue drug with toceranib phosphate might be beneficial in refractory and relapsed canine lymphoma.

Evaluation of a multi-agent chemotherapy protocol combining lomustine, procarbazine and prednisolone (LPP) for the treatment of relapsed canine non-Hodgkin high-grade lymphomas

The standard of care treatment for canine lymphoma is multi-agent chemotherapy containing prednisolone, cyclophosphamide, vincristine and an anthracycline such as doxorubicin (CHOP) or epirubicin (CEOP). Lomustine, vincristine, procarbazine, and prednisone (LOPP) has been evaluated as a rescue, with encouraging results; however, resistance to vincristine is likely in patients relapsing on CHOP/CEOP, and this agent may enhance LOPP toxicity without improving efficacy. The aim of this study was to evaluate responses to a modified-LOPP protocol that does not include vincristine (LPP) and is administered on a 21-day cycle. Medical records of dogs with high-grade multicentric lymphoma from 2012 to 2017 were reviewed. Dogs with relapsed lymphoma that received LPP as a rescue protocol were enrolled. Response, time from initiation to discontinuation (TTD) and toxicity of LPP were assessed. Forty-one dogs were included. Twenty-five dogs (61%) responded to LPP including 12 complete responses (CR) and 13 partial responses (PR). Responders had a significantly longer TTD (P < .001) compared to non-responders with 84 days for CR and 58 days for PR. Neutropenia was documented in 20 dogs (57%): 12 grade I to II, 8 grade III to IV. Thrombocytopenia was infrequent (20%): 5 grade I to II, 2 grade III to IV. Twelve dogs developed gastrointestinal toxicity (30%): 10 grade I to II and 2 grade III. Nineteen dogs had elevated ALT (59%): 9 grade I to II, 10 grade III to IV. Treatment was discontinued due to toxicity in 8 dogs (19%). The LPP protocol shows acceptable efficacy and toxicity-profile and minimizes in-hospital procedures.

Clinical Response and Adverse Event Profile of Bleomycin Chemotherapy for Canine Multicentric Lymphoma

Although canine multicentric lymphoma is initially responsive to multidrug chemotherapy, resistance and relapse create a need for novel chemotherapeutics. Bleomycin is an antitumor antibiotic with a minimal adverse event profile; though commonly used for human non-Hodgkin's lymphoma, its use is poorly characterized in dogs. The purpose of this retrospective case series was to describe the clinical response and adverse event profile of systemic bleomycin for canine multicentric lymphoma (n = 10). A partial response was noted in one dog that died 24 days later due to unrelated disease. Adverse events were infrequent and limited to grade 1 gastrointestinal and grade 1 constitutional toxicity. Although clinical response was minimal, systemic bleomycin was well tolerated when administered at 0.5 U/kg. Additional studies are warranted to determine the influence of administration schedule and dose on the efficacy of bleomycin for veterinary neoplasia.

Immunohistochemical Expression of P-glycoprotein and Breast Cancer Resistance Protein in Canine Mammary Hyperplasia, Neoplasia and Supporting Stroma

The ability of a tumour to become simultaneously resistant to different drugs is known as multidrug resistance and is often due to the expression of ATP-dependent binding cassette transporters (ABC-transporters) such as P-glycoprotein (PGP) and breast cancer resistance protein (BCRP). In this study, the expression of PGP and BCRP was determined in the components of hyperplastic and neoplastic canine mammary glands, including the supporting stroma. The variation of expression of these molecules in carcinomas was evaluated between lesions of different histological stage and grade of malignancy. Samples included 47 hyperplastic tissues and 10 benign and 46 malignant neoplasms. Tumours were classified into histological subtype, histological stage and grade. Immunohistochemical evaluation of PGP and BCRP expression showed that both markers are potentially expressed by epithelial cells, myoepithelial cells in complex tumours and mesenchymal cells in mixed tumours, but expression of both proteins was significantly higher in malignant epithelial cells versus hyperplastic epithelium or the epithelium of benign tumours. BCRP showed significantly higher expression in epithelial cells of simple carcinomas versus those of complex and mixed carcinomas. Grade II and III carcinomas had higher epithelial PGP expression than grade I tumours. The positivity of stromal fibroblasts was higher in histological stage II versus I carcinomas, and in histological grade II versus I carcinomas. Malignant and invasive tumours were more likely to express PGP and/or BCRP in luminal and stromal components and evaluation of these markers could provide valuable information for the identification of tumours characterized by an aggressive and chemoresistant phenotype.

Cell cycle kinetics, apoptosis rates and gene expressions of MDR-1, TP53, BCL-2 and BAX in transmissible venereal tumour cells and their association with therapy response

Transmissible venereal tumour (TVT) generally presents different degrees of aggressiveness, which makes them unresponsive to conventional treatment protocols. This implies a progressive alteration of their biological profile. This study aimed to evaluate the cytotoxicity, cell survival, apoptosis and cell cycle alterations in TVT cell cultures subjected to treatment with vincristine. Similarly, it assessed possible implications of MDR-1, TP53, BCL-2, and BAX gene expressions in eight TVT primary cultures for both resistance to chemotherapy and biological behaviour. When comparing TVT cells receiving vincristine to those untreated, a statistical difference related to increased cytotoxicity and decreased survival rates, and alterations in G1 and S cell cycle phases were found but without detectable differences in apoptosis. Increased MDR-1 gene expression was observed after treatment. The groups did not differ statistically in relation to the TP53, BAX and BCL-2 genes. Although preliminary, the findings suggest that such augmented expression is related to tumour malignancy and chemotherapy resistance.

Mechanisms of Drug Resistance in Veterinary Oncology- A Review with an Emphasis on Canine Lymphoma

Drug resistance (DR) is the major limiting factor in the successful treatment of systemic neoplasia with cytotoxic chemotherapy. DR can be either intrinsic or acquired, and although the development and clinical implications are different, the underlying mechanisms are likely to be similar. Most causes for DR are pharmacodynamic in nature, result from adaptations within the tumor cell and include reduced drug uptake, increased drug efflux, changes in drug metabolism or drug target, increased capacity to repair drug-induced DNA damage or increased resistance to apoptosis. The role of active drug efflux transporters, and those of the ABC-transporter family in particular, have been studied extensively in human oncology and to a lesser extent in veterinary medicine. Methods reported to assess ABC-transporter status include detection of the actual protein (Western blot, immunohistochemistry), mRNA or ABC-transporter function. The three major ABC-transporters associated with DR in human oncology are ABCB1 or P-gp, ABCC1 or MRP1, and ABCG2 or BCRP, and have been demonstrated in canine cell lines, healthy dogs and dogs with cancer. Although this supports a causative role for these ABC-transporters in DR cytotoxic agents in the dog, the relative contribution to the clinical phenotype of DR in canine cancer remains an area of debate and requires further prospective studies.

Comparative Aspects of Molecular Mechanisms of Drug Resistance through ABC Transporters and Other Related Molecules in Canine Lymphoma

The most important causes of treatment failure in canine lymphoma include intrinsic or acquired drug resistance. Thus, elucidation of molecular mechanisms of drug resistance is essential for the establishment of better treatment alternatives for lymphoma patients. The overexpression of drug transporters is one of the most intensively studied mechanisms of drug resistance in many tumors. In canine lymphoma, it has also been shown that the overexpression of drug efflux pumps such as P-glycoprotein is associated with drug-resistant phenotypes. Canine lymphoma has many pathological similarities to human non-Hodgkin’s lymphoma, and they also share similar molecular mechanisms of drug resistance. We have previously demonstrated the association of the overexpression of drug transporters with drug resistance and indicated some molecular mechanisms of the regulation of these transporters’ expressions in canine and human lymphoid tumor cells. However, it has also been indicated that other known or novel drug resistance factors should be explored to overcome drug resistance in lymphoma. In this review, we summarize the recent findings on the molecular mechanisms of drug resistance and possible strategies to develop better treatment modalities for canine lymphoma from the comparative aspects with human lymphoid tumors.

Expression of P-glycoprotein, multidrug resistance-associated protein, glutathione-S-transferase pi and p53 in canine transmissible venereal tumor

The overexpression of proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP1), mutant p53, and the enzyme glutathione-S-transferase (GSTpi) are related to resistance to chemotherapy in neoplasms. This study evaluated the expression of these markers by immunohistochemistry in two groups of canine TVT, without history of prior chemotherapy (TVT1, n=9) and in TVTs presented unsatisfactory clinical response to vincristine sulfate (TVT2, n=5). The percentage of specimens positively stained for P-gp, MRP1, GSTpi and p53 were, respectively 88.8%, 0%, 44.5% and 22.2% in TVT1 and 80%, 0%, 80% and 0% in TVT2. In TVT1, one specimen presented positive expression for three markers and four specimens for two markers. In TVT2, three specimens expressed P-gp and GSTpi. In conclusion, the canine TVTs studied expressed the four markers evaluated, but just P-gp and GSTpi were significantly expressed, mainly at cytoplasm and cytoplasm and nuclei, respectively, either before chemotherapy as after vincristine sulfate exposure. Future studies are needed to demonstrate the function of these two markers in conferring multidrug resistance (MDR) or predict the response to chemotherapy in canine TVT.

The regulation of the expression of ABCG2 gene through mitogen-activated protein kinase pathways in canine lymphoid tumor cell lines

Treatments for canine lymphoma often fail, because tumor cells acquire multidrug resistance (MDR). MDR can develop through several mechanisms, among which the overexpression of drug transporters in tumor cells is a well-studied mechanism. ATP-binding cassette sub-family G member 2 (ABCG2) belongs to the ABC-transporters, that are representative drug efflux pumps associated with MDR in human tumor cells. However, the regulation of ABCG2 gene expression in canine tumors is not well understood. The purpose of the present study was to reveal the regulatory mechanism of ABCG2 gene expression in 4 canine lymphoid tumor cell lines, GL-1, CLBL-1, UL-1 and Ema. Treatment with phorbol 12-myristate 13-acetate (PMA), the protein kinase C (PKC) activator, stimulated MAPK/ERK pathway in GL-1, UL-1 and Ema cells and JNK pathway in UL-1 and Ema cells. When GL-1 and UL-1 cells were treated with PMA and the MAPK/ERK kinase inhibitor U0126, ABCG2 gene expression levels were elevated above those in untreated cells. Similarly, ABCG2 gene expression increased above control levels in UL-1 and Ema cells treated with PMA and the JNK inhibitor SP600125. However, ABCG2 gene expression was unaffected by U0126 exposure in CLBL-1 cells, in which activation of MAPK/ERK pathway was observed in non-treated cells. These results suggested that MAPK/ERK and JNK pathways downregulate ABCG2 gene expression, which is upregulated by unidentified but possibly PKC-dependent pathways, in several types of canine lymphoid tumor cells.

Mechlorethamine, vincristine, melphalan and prednisone (MOMP) for the treatment of relapsed lymphoma in dogs

Eighty-eight dogs with relapsed lymphoma were treated with the MOMP (mechlorethamine, vincristine, melphalan and prednisone) protocol on a 28-day treatment cycle. The overall response rate (ORR) to the MOMP protocol was 51.1% for a median of 56 days (range 7-858 days). Twelve percent of dogs experienced a complete response for a median of 81 days (range 42-274 days) and 38.6% experienced a partial response for a median of 49 days (range 7-858 days). Dogs with T-cell lymphoma had an ORR of 55% for a median of 60 days (range 49-858 days) while those with B-cell lymphoma had an ORR of 57% for a median of 81 days (range 7-274 days) (P = 0.783). The overall survival time for all dogs was 183 days (range 17-974 days). Fifty-four percent of dogs experienced toxicity with the majority classified as grade I. The MOMP protocol seems well-tolerated and is an option for dogs with relapsed lymphoma.

Determination of MDR1 gene expression for prediction of chemotherapy tolerance and treatment outcome in dogs with lymphoma

The multidrug resistance gene 1(MDR1) expression levels were analysed in 27 dogs with different types of malignant lymphomas receiving a standard chemotherapy protocol. Blood samples were used for MDR1 real-time PCR expression analysis. Treatment tolerance and outcome were evaluated on a regular basis by clinical examination and client questioning. Dogs developing severe adverse effects under treatment showed significantly lower basal MDR1 gene expression levels when compared with those who tolerated the drugs well. In the longitudinal MDR1 gene expression analysis during treatment, four dogs showed a greater than two-fold MDR1 up-regulation, compared to baseline expression. All four of these dogs, but none of the others, showed disease progression. In conclusion, basal and follow-up MDR1 gene expression levels could be of predictive value for the occurrence of severe adverse drug reactions and/or the development of MDR during chemotherapy for lymphoma in dogs.

Clinicopathologic Significance of Histologic Grade, Pgp, and P53 Expression in Canine Lymphoma

To characterize the expression of P-glycoprotein (Pgp) and p53 in different histologic grades of canine multicentric lymphosarcoma (LSA), 31 cases of LSA without prior treatment were studied. The expression levels of the Pgp and p53 proteins were evaluated for their clinicopathologic significance among standard histologic evaluation. Immunohistochemistry (IHC) was performed on formalin-fixed, paraffin-embedded archival samples of 31 previously untreated LSA cases to detect the expression of Pgp and p53. All dogs were subsequently treated with a combination chemotherapy protocol. Remission and survival durations were evaluated for correlation with histologic grade and presence of drug resistance markers. Of the 31 cases, 24 (80%) and 7 (22%) were positive for Pgp and p53, respectively. Overall, the median survival and duration of remission in the study was 246 days and 137 days, respectively. The National Cancer Institute working formulation histologic grade was not associated with either survival or duration of first remission (DOR). The Pgp protein expression and DOR and survival was not statistically significant. Expression of p53 was statistically correlated with survival.

High-mobility group B1 proteins in canine lymphoma: prognostic value of initial and sequential serum levels in treatment outcome following combination chemotherapy

Elevated high-mobility group box 1 (HMGB1) levels have been demonstrated in different human neoplasias. Information on serum HMGB1 before and during chemotherapy is lacking, as is data pertaining to its prognostic significance. The aim of this study was to characterize serum HMGB1 level in dogs with lymphoma and to assess its influence on the outcome following chemotherapy. Serum HMGB1 concentrations were measured in 16 dogs with lymphoma before treatment (W1) and on weeks 2 (W2), 6 (W6) and 12 (W12) of treatment with chemotherapy. Initial serum HMGB1 levels were significantly higher than HMGB1concentrations in control dogs and the levels in W2, W6 and W12. HMGB1-W1 concentrations were lower in dogs achieving complete remission than that in the single dog with partial remission. The ratio W12/W6 exhibited significant influence on remission duration. In these dogs with lymphoma, serum HMGB1 was elevated in comparison with that in controls. Initial serum HMGB1 level and its modulation during treatment may possess prognostic value.

Expression of the high mobility group A1 (HMGA1) and A2 (HMGA2) genes in canine lymphoma: analysis of 23 cases and comparison to control cases

Overexpression of high mobility group A (HMGA) genes was described as a prognostic marker in different human malignancies, but its role in canine haematopoietic malignancies was unknown so far. The objective of this study was to analyse HMGA1 and HMGA2 gene expression in lymph nodes of canine lymphoma patients. The expression of HMGA1 and HMGA2 was analysed in lymph node samples of 23 dogs with lymphoma and three control dogs using relative quantitative real-time RT-PCR. Relative quantity of HMGA1 was significantly higher in dogs with lymphoma compared with reference samples. HMGA2 expression did not differ between lymphoma and control dogs. With the exception of immunophenotype, comparison of disease parameters did not display any differences in HMGA1 and HMGA2 expression. The present findings indicate a role of HMGA genes in canine lymphoma. This study represents the basis for future veterinary and comparative studies dealing with their diagnostic, prognostic and therapeutic values.

Quantitative analysis of mRNA for 10 different drug resistance factors in dogs with lymphoma

Expression levels of ABCB1, ABCC1, Lung resistance-associated protein (LRP), ABCG2, p53, p21(waf1), Bcl-2, CD40L, glutathione S-transferase alpha (GSTα), and O⁶-methylguanine-DNA-methyltransferase (MGMT) genes, and mutation of p53 gene were examined in 23 dogs with multicentric high-grade lymphoma to explore their association with drug resistance of the tumor cells. Dogs were divided into chemotherapy-sensitive (n=13) and -resistant (n=10) groups according to the response to a 6-month modified version of the University of Wisconsin (UW)-Madison chemotherapy protocol (UW-25), and expression levels of these factors and frequency of p53 gene mutation were compared between groups. No significant differences were observed in expression levels of each factor between groups. However, 4 dogs in the chemotherapy-resistant group showed high expression of ABCB1. No significant difference was observed in the frequency of p53 mutation between groups. A possible association of ABCB1 with resistance to UW-25 was shown, but no uniform mechanism associated with drug resistance could be identified in dogs with lymphoma.

Expression of ABC-transport proteins in canine mammary cancer: consequences for chemotherapy

Intrinsic or acquired drug resistance is a major barrier for chemotherapy of cancer. Importantly, the presence of ATP-binding cassette, ABC-transport proteins in tumour cells circumvents an intracellular accumulation of chemotherapeutic drugs. In this study, 103 canine mammary tumour probes were investigated for mRNA expression of seven ABC-transporters by RT-PCR. All tumour samples expressed multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP). MRP7 was detected in 97.1% of tumour probes, MRP3 in 96.1%, Pgp in 92.2%, MRP5 in 85.4% and MRP6 in 64.1%. More of the half of tumour samples (56.1%) expressed all of the examined ABC-transport proteins. Approximately one-third of the tumour samples (32.7%) were lacking in one transporter and only 11.2% possessed from three to five transporters. The canine transporter cBCRP was functionally analysed in stable transfected Madin-Darby canine kidney-II cells using an MTT viability test. cBCRP transfected cells showed a 5.4-fold resistance to 10 microm doxorubicin. Cell survival in the presence of methotrexate was not affected by cBCRP. In conclusion, absence of efficiency of chemotherapy of canine mammary cancer can be caused by expression of seven various ABC-transport proteins. Because cBCRP is expressed in all examined tumour probes and induces resistance to doxorubicin, the application of doxorubicin for treatment of canine mammary is inappropriate.

Actinomycin D as rescue therapy in dogs with relapsed or resistant lymphoma: 49 cases (1999--2006)

OBJECTIVE

To evaluate response rate and disease-free interval in dogs with relapsed or resistant lymphoma treated with actinomycin D, determine hematologic toxicoses, and identify prognostic factors associated with response to treatment.

DESIGN

Retrospective case series.

ANIMALS

49 dogs with relapsed or resistant lymphoma.

PROCEDURES

Medical records were reviewed for information regarding signalment, physical examination findings, results of diagnostic testing, substage, previous chemotherapy, previous treatment with prednisone, actinomycin D dosage, number of doses administered, response, disease-free interval, and results of CBCs performed after treatment.

RESULTS

Actinomycin D was administered at a median dosage of 0.68 mg/m2 (range, 0.46 to 0.72 mg/m2), IV, every 3 weeks for 5 treatments or until disease progression. Twenty-six (53%) dogs received prednisone concurrently. Twenty (41%) dogs had a complete remission, and median disease-free interval in these dogs was 129 days. Thrombocytopenia was the most common hematologic toxicosis (n = 22 [45%]). Concurrent prednisone administration, a shorter duration of first remission, and an increased number of previous chemotherapy agents were significantly associated with a lower likelihood of responding to actinomycin D treatment. Concurrent prednisone administration and an increased number of previous chemotherapy agents were significantly associated with a shorter disease-free interval.

CONCLUSION AND CLINICAL RELEVANCE

Results suggested that administration of actinomycin D as a single agent was effective for rescue chemotherapy of dogs with relapsed or resistant lymphoma and that treatment was well tolerated, although mild thrombocytopenia developed commonly.

Immunophenotypic and cytomorphologic subclassification of T-cell lymphoma in the boxer breed

The boxer breed is at high risk for developing lymphoma and, in contrast to the general canine population, is predisposed to the T-cell variant of the disease. The purpose of this study was to more accurately classify lymphoma in this breed. Clinical, cytomorphologic and immunophenotypic data were examined in 43 boxers with lymphoma. Twenty-five cases were collected prospectively and a further 18 cases were obtained retrospectively. Lymphomas were classified as multicentric (n=29), mediastinal (n=6) and intestinal (n=8). Of the 40 immunophenotyped samples, 34 (85%) were T-cell, 5 (12.5%) were B-cell and 1 was a non-B-cell non-T-cell lymphoma. Immunophenotypic subtyping was done on prospectively collected T-cell lymphoma samples (n=22) to differentiate CD4 (helper) from CD8 (cytotoxic) T-cell origin as well as to determine the T-cell receptor (TCR) expression (TCRalphabeta vs. TCRdeltagamma). Phenotypic expression was CD4+ (n=12), double negative (DN) (n=6), double positive (DP) (n=1) and CD8+ (n=1), respectively, while two samples had no interpretable result. 20/22 samples were TCRalphabeta+ with only 1 sample being TCRdeltagamma+ and 1 with no interpretable result. Cytomorphologic analysis was done on the same 22 samples using the World Health Organization (WHO) classification scheme. According to this scheme, 17/22 samples were classified as lymphoblastic, 2/22 as large cell peripheral T-cell lymphoma-not otherwise specified (PTCL-NOS), 2/22 as large granular lymphoma (LGL) high-grade and 1/22 as small lymphocytic. The results of this study indicate that lymphoma in the boxer breed is a disease comprised predominantly of TCRalphabeta+, CD4+ (helper) T-cells with lymphoblastic (high-grade) morphology.

Expression of the MDR1 gene and P-glycoprotein in canine mast cell tumor cell lines

Cellular drug resistance to antineoplastic drugs is often due to the presence of a drug efflux pump that reduces intracellular drug accumulation and chemosensitivity. P-glycoprotein (P-gp), which is encoded by the MDR1 gene, is considered to function as an ATP-driven membrane drug efflux pump and appears to play an important role in tumor cell resistance. In the present report, we assessed the expression of MDR1 by RT-PCR in three canine mast cell tumor cell lines, TiMC, CoMS and LuMC, originating from a cutaneous tumor, an oral-mucosal tumor and a gastrointestinal tumor, respectively. P-gp expression was also examined by Western blot analysis, while the functional activity of P-gp was assessed by flowcytometric analysis of intracellular rhodamine-123 (Rhd-123) uptake. The results revealed that MDR1 gene and P-gp were both expressed in CoMS and LuMC cells, whereas neither was present in TiMC cells. In CoMS and LuMC cells, intracellular uptake of Rhd-123 increased in the presence of verapamil, a functional modulator of P-gp. In contrast, TiMC cells did not show any changes in the intracellular accumulation of Rhd-123 after the verapamil addition. These findings suggest that the expressions of MDR1 gene and P-gp probably contribute to cellular drug resistance in canine mast cell tumors.

Induction of chemoresistance in a cultured canine cell line by retroviral transduction of the canine multidrug resistance 1 gene

OBJECTIVE

To induce chemoresistance in a normal canine cell line through the transduction of the canine multidrug resistance 1 gene (mdr1).

SAMPLE POPULATION

Madin-Darby canine kidney (MDCK) epithelial cell line.

PROCEDURES

The full-length canine mdr1 cDNA clone isolated in our laboratory was inserted into a Moloney murine leukemia virus-based vector to construct the retroviral vector, pLNC-cMDR1. After retroviral transduction of pLNC-cMDR1 into MDCK cells, the expression and function of the P-glycoprotein, a product of mdr1, were assessed by immunoblotting, measurement of rhodamine123 (Rh123) retention, and drug sensitivity assays.

RESULTS

P-glycoprotein was strongly expressed in cells transduced with pLNC-cMDR1. This P-glycoprotein was fully functional, as demonstrated by the decreased Rh123 retention and the increased resistance to chemotherapeutic drugs. Measured as 50% inhibitory concentrations, resistance increased 59 times to vincristine and 25 times to doxorubicin in MDCK cells after transduction of pLNC-cMDR1.

CONCLUSIONS AND CLINICAL RELEVANCE

Transduction of canine mdr1 is an effective method for inducing chemoresistance in normal canine cells. This system may be applicable to the induction of drug resistance in hematopoietic cells.

P-glycoprotein Expression in Lamina Propria Lymphocytes of Duodenal Biopsy Samples in Dogs with Chronic Idiopathic Enteropathies

P-glycoprotein (p-gp) is a transmembrane protein functioning as a drug-efflux pump in the intestinal epithelium. Human patients with inflammatory bowel disease (IBD) who fail to respond to treatment with steroids express high levels of p-gp in lamina propria lymphocytes. The purpose of this study was to investigate p-gp expression in duodenal biopsy samples of dogs with chronic enteropathies and to evaluate the expression of p-gp after treatment with a known inducer of p-gp (prednisolone). Duodenal biopsy samples from 48 dogs were evaluated immunohistochemically with the mouse monoclonal antibody C219 for expression of p-gp in lamina propria lymphocytes. Biopsy samples were available from 15 dogs after treatment with prednisolone and 16 dogs after dietary therapy alone ("elimination diet"). Treatment with prednisolone resulted in an increase in p-gp expression (P=0.005). In contrast, dietary treatment alone produced no significant change in p-gp expression (P=0.59). A low p-gp score before initiation of steroid treatment was significantly associated with a positive response to treatment (P=0.01). These results indicate that lamina propria lymphocyte expression of p-gp is upregulated after prednisolone treatment in dogs with IBD, and that mucosal expression of p-gp may be of value in predicting the response to therapy.

Quantification of MDR-1 gene expression in canine tissues by real-time reverse transcription quantitative polymerase chain reaction

MDR-1 gene product mediated multidrug resistance is thought to play a major role in the outcome of chemotherapy in some canine tumors, especially malignant lymphoma. In the present study, MDR-1 RNA expression in normal lymph node and liver tissue as well as in tumor biopsies from 23 dogs with lymphomas and two dogs with liver tumors was measured by real-time RT-quantitative PCR. MDR-1 gene expression was detected in all samples analyzed. Comparably high MDR-1 RNA levels were measured in all normal liver tissues, one of the lymphomas and a cholangiocarcinoma. MDR-1 expression levels in canine lymphomas were found to vary over a wide range with most tumors expressing relative low levels. Interestingly, gastrointestinal lymphomas expressed higher MDR-1 RNA levels than multicentric lymphomas (p = 0.03). In conclusion, real-time RT-quantitative PCR appears to be a suitable method for sensitive and quantitative determination of MDR-1 gene expression in canine normal and neoplastic tissues.

Mechanisms of anticancer drug resistance

Chemotherapy agents are extremely important in the treatment of liquid malignancies, such as lymphoma, myeloma, and chronic lymphocytic leukemia. In addition, chemotherapy agents have proven effective in the adjuvant treatment of solid tumors, such as osteosarcoma, hemangiosarcoma, transitional cell carcinoma, and others. Unfortunately, chemotherapy resistance in these situations is the most significant cause of treatment failure. Therefore, the ability to predict, treat, or circumvent resistance is extremely likely to improve clinical outcomes. This article has reviewed the most widely investigated forms of chemotherapy resistance, such as reduced drug accumulation, increased DNA damage repair, decreased apoptosis, and others; however, new mechanisms are being found at an alarming pace. In addition, investigations to date have routinely centered on single-cell mechanisms of drug resistance, and cancer is truly a three dimensional disease. The elucidation of mechanisms surrounding (1) how tumors interact with their normal microenvironment, (2) how tumors interact in a three-dimensional environment, and (3) a better understanding of basic tumor physiology and biology may supersede in importance those previously elucidated single-cell mechanisms of chemoresistance.

Lymphoma updates

Canine and feline lymphoma is a common hematopoietic malignancy that generally responds well to systemic chemotherapy. In dogs, several recent investigations have underscored the beneficial effects of adjunctive radiation therapy for the treatment of multicentric lymphoma. With the emergence of effective immunotherapeutic agents against non-Hodgkin's lymphoma in people, some of these specific targeted immunotherapeutics may soon be a viable option for treating lymphoid malignancies in dogs. Although the effective and durable treatment of feline lymphoma remains disappointing, the identification of environmental etiologic factors may help to shape future recommendations for disease prevention. It is only reasonable to assume that as our fundamental understanding of lymphoid malignancies grows, better diagnostic tools, predictive markers, and therapeutic options will also emerge.