Gemcitabine in hematologic malignancies

Obinutuzumab-Based Drug-Free Macromolecular Therapeutics Synergizes with Topoisomerase Inhibitors

Drug-free macromolecular therapeutics (DFMT) utilizes modified monoclonal antibodies (or antibody fragments) to generate antigen-crosslinking-induced apoptosis in target cells. DFMT is a two-component system containing a morpholino oligonucleotide (MORF1) modified antibody (Ab-MORF1) and human serum albumin conjugated with multiple copies of complementary morpholino oligonucleotide (MORF2), (HSA-(MORF2)x ). The two components recognize each other via the Watson-Crick base pairing complementation of their respective MORFs. One HSA-(MORF2)x molecule can hybridize with multiple Ab-MORF1 molecules on the cell surface, thus serving as the therapeutic crosslink-inducing mechanism of action. Herein, various anti-neoplastic agents in combination with the anti-CD20 Obinutuzumab (OBN)-based DFMT system are examined. Three different classes of chemotherapies are examined: DNA alkylating agents; proliferation pathway inhibitors; and DNA replication inhibitors. Chou-Talalay combination index mathematics is utilized to determine which drugs engaged synergistically with OBN-based DFMT. It is determined that OBN-based DFMT synergizes with topoisomerase inhibitors and DNA nucleotide analogs but is antagonistic with proliferation pathway inhibitors. Cell mechanism experiments are performed to analyze points of synergism or antagonism by investigating Ca2+ influx, mitochondrial health, lysosomal stability, and cell cycle arrest. Finally, the synergistic drug combinatorial effects of OBN-based DFMT with etoposide in vivo are demonstrated using a human xenograft non-Hodgkin's lymphoma mouse model.

Improving Osteosarcoma Treatment: Comparative Oncology in Action

Osteosarcoma (OSA) is the most common pediatric malignant bone tumor. Although surgery together with neoadjuvant/adjuvant chemotherapy has improved survival for localized OSA, most patients develop recurrent/metastatic disease with a dismally poor outcome. Therapeutic options have not improved for these OSA patients in recent decades. As OSA is a rare and "orphan" tumor, with no distinct targetable driver antigens, the development of new efficient therapies is still an unmet and challenging clinical need. Appropriate animal models are therefore critical for advancement in the field. Despite the undoubted relevance of pre-clinical mouse models in cancer research, they present some intrinsic limitations that may be responsible for the low translational success of novel therapies from the pre-clinical setting to the clinic. From this context emerges the concept of comparative oncology, which has spurred the study of pet dogs as a uniquely valuable model of spontaneous OSA that develops in an immune-competent system with high biological and clinical similarities to corresponding human tumors, including in its metastatic behavior and resistance to conventional therapies. For these reasons, the translational power of studies conducted on OSA-bearing dogs has seen increasing recognition. The most recent and relevant veterinary investigations of novel combinatorial approaches, with a focus on immune-based strategies, that can most likely benefit both canine and human OSA patients have been summarized in this commentary.

The Antiproliferative Activity of Oxypeucedanin via Induction of G2/M Phase Cell Cycle Arrest and p53-Dependent MDM2/p21 Expression in Human Hepatoma Cells

Oxypeucedanin (OPD), a furocoumarin compound from Angelica dahurica (Umbelliferae), exhibits potential antiproliferative activities in human cancer cells. However, the underlying molecular mechanisms of OPD as an anticancer agent in human hepatocellular cancer cells have not been fully elucidated. Therefore, the present study investigated the antiproliferative effect of OPD in SK-Hep-1 human hepatoma cells. OPD effectively inhibited the growth of SK-Hep-1 cells. Flow cytometric analysis revealed that OPD was able to induce G₂/M phase cell cycle arrest in cells. The G₂/M phase cell cycle arrest by OPD was associated with the downregulation of the checkpoint proteins cyclin B1, cyclin E, cdc2, and cdc25c, and the up-regulation of p-chk1 (Ser345) expression. The growth-inhibitory activity of OPD against hepatoma cells was found to be p53-dependent. The p53-expressing cells (SK-Hep-1 and HepG2) were sensitive, but p53-null cells (Hep3B) were insensitive to the antiproliferative activity of OPD. OPD also activated the expression of p53, and thus leading to the induction of MDM2 and p21, which indicates that the antiproliferative activity of OPD is in part correlated with the modulation of p53 in cancer cells. In addition, the combination of OPD with gemcitabine showed synergistic growth-inhibitory activity in SK-Hep-1 cells. These findings suggest that the anti-proliferative activity of OPD may be highly associated with the induction of G₂/M phase cell cycle arrest and upregulation of the p53/MDM2/p21 axis in SK-HEP-1 hepatoma cells.

The potential of radiolabeled chemotherapeutics in tumor diagnosis: Preliminary investigations with 68 Ga-gemcitabine

Preclinical Research & Development Gemcitabine, a nucleoside analog, is a well-known chemotherapeutic drug that is used either alone or with other agents to treat a wide variety of cancers. The aim of the present work was to evaluate the potential of ⁶⁸ Ga-labeled gemcitabine for its application in positron emission tomography (PET) imaging of tumorous lesions. Gemcitabine was coupled with p-NCS-benzyl-DOTA in order to facilitate radiolabeling with ⁶⁸ Ga. The gemcitabine-p-NCS-benzyl-DOTA was radiolabeled with ⁶⁸ Ga, obtained from a ⁶⁸ Ge/⁶⁸ Ga radionuclide generator. The radiolabeled product was characterized by high performance liquid chromatography (HPLC) and its tumor specificity was evaluated by biodistribution studies in Swiss mice bearing fibrosarcoma tumors. Preliminary bioevaluation study showed good tumor uptake within 1 hr post-administration [2.5% Injected Activity (IA) per g of tumor] with rapid renal clearance (>90% IA) and a high tumor to muscle ratio. ⁶⁸ Ga-gemcitabine may have potential as a PET agent for tumor imaging.

Biweekly dose-dense gemcitabine-oxaliplatin and dexamethasone for relapsed/refractory aggressive non-Hodgkin lymphoma: A multicenter, single-arm, phase II trial

AIM

We performed a phase II study to evaluate the efficacy of combination chemotherapy consisting of gemcitabine, dexamethasone and oxaliplatin (GemDOx) as a biweekly regimen and salvage therapy in patients with relapsed or refractory aggressive non-Hodgkin lymphoma (NHL).

METHODS

Gemcitabine (1000 mg/m(2) ) and oxaliplatin (85 mg/m(2) ) were administered intravenously on days 1 and 15, and dexamethasone (40 mg) was administered orally on days 1-4.

RESULTS

Twenty-nine patients were enrolled, and most patients had diffuse large B-cell lymphoma (n = 18). The median age of the patients and median prior number of chemotherapy cycles were 53 (range, 26-74) years and 1 (range, 1-4) cycle, respectively. Only 17 (58.6%) and 9 (31.0%) patients completed two or more and four or more cycles, respectively, and the median number of received cycles was two (range, 1-8). Overall response rates were 27.6% (complete response in 13.8%) among intent-to-treat patients and 47.1% (complete response in 23.5%) among patients who had received at least two GemDOx cycles. Median progression-free survival and median overall survival were 3.9 and 20.5 months, respectively. The most-frequent grade 3 or 4 toxicity was neutropenia (22.9%), and no grade 3 or 4 peripheral neurotoxicity was noted.

CONCLUSION

GemDOx chemotherapy, therefore, showed modest activity against relapsed or refractory aggressive NHL, although toxicities were acceptable.

Gemcitabine and Chlorotoxin Conjugated Iron Oxide Nanoparticles for Glioblastoma Therapy

Many small-molecule anti-cancer drugs have short blood half-lives and toxicity issues due to non-specificity. Nanotechnology has shown great promise in addressing these issues. Here, we report the development of an anti-cancer drug gemcitabine-conjugated iron oxide nanoparticle for glioblastoma therapy. A glioblastoma targeting peptide, chlorotoxin, was attached after drug conjugation. The nanoparticle has a small size (~32 nm) and uniform size distribution (PDI ≈ 0.1), and is stable in biological medium. The nanoparticle effectively enter cancer cells without losing potency compared to free drug. Significantly, the nanoparticle showed a prolonged blood half-life and the ability to cross the blood-brain barrier in wild type mice.

Cutaneous T-cell lymphomas: a review of new discoveries and treatments

Treatment regimens of patients with CTCL vary widely based on clinician preference and patient tolerance. Skin directed therapies are recommended for patients with early stage IA and IB MF, with combinations used in refractory cases. While no regimen has been proven to prolong survival in advanced stages, immunomodulatory regimens should be used initially to reduce the need for cytotoxic therapies. In more advanced stages of disease, treatment efforts should strive for palliation and improvement of quality of life. With many new therapies and strategies on the horizon, the future looks promising for CTCL patients. Unfortunately, other than allogeneic HCT, there are no potential curative therapies for CTCL. Clinical trials are currently underway to identify new therapies to improve quality of life for patients, and researchers are hard at work to identify novel pathways and genes for prognostication and as targets for therapies. Importantly, collaborative clinical trials to enhance rates of accrual need to be conducted, and improved interpretation of data via standardizing end points and response criteria should be an emphasis. Recently, the International Society for Cutaneous Lymphomas (ISCL), the United States Cutaneous Lymphoma Consortium (USCLC), and the Cutaneous Lymphoma Task Force of the European Organisation for Research and Treatment of Cancer (EORTC) met to develop consensus guidelines to facilitate collaboration on clinical trials. These proposed guidelines consist of: recommendations for standardizing general protocol design; a scoring system for assessing tumor burden in skin, lymph nodes, blood, and viscera; definition of response in skin, nodes, blood, and viscera; a composite global response score; and a definition of end points. Although these guidelines were generated by consensus panels, they have not been prospectively or retrospectively validated through analysis of large patient cohorts.

Exploiting the nucleotide substrate specificity of repair DNA polymerases to develop novel anticancer agents

The genome is constantly exposed to mutations that can originate during replication or as a result of the action of both endogenous and/or exogenous damaging agents [such as reactive oxygen species (ROS), UV light, genotoxic environmental compounds, etc.]. Cells have developed a set of specialized mechanisms to counteract this mutational burden. Many cancer cells have defects in one or more DNA repair pathways, hence they rely on a narrower set of specialized DNA repair mechanisms than normal cells. Inhibiting one of these pathways in the context of an already DNA repair-deficient genetic background, will be more toxic to cancer cells than to normal cells, a concept recently exploited in cancer chemotherapy by the synthetic lethality approach. Essential to all DNA repair pathways are the DNA pols. Thus, these enzymes are being regarded as attractive targets for the development of specific inhibitors of DNA repair in cancer cells. In this review we examine the current state-of-the-art in the development of nucleotide analogs as inhibitors of repair DNA polymerases.

Incorporation of gemcitabine and cytarabine into DNA by DNA polymerase beta and ligase III/XRCC1

1-Beta-D-arabinofuranosylcytosine (cytarabine, araC) and 2',2'-difluoro-2'-deoxycytidine (gemcitabine, dFdC), are effective cancer chemotherapeutic agents due to their ability to become incorporated into DNA and then subsequently inhibit DNA synthesis by replicative DNA polymerases. However, the impact of these 3'-modified nucleotides on the activity of specialized DNA polymerases has not been investigated. The role of polymerase beta and base excision repair may be of particular importance due to the increased oxidative stress in tumors, increased oxidative stress caused by chemotherapy treatment, and the variable amounts of polymerase beta in tumors. Here we directly investigate the incorporation of the 5'-triphosphorylated form of araC, dFdC, 2'-fluoro-2'-deoxycytidine (FdC), and cytidine into two nicked DNA substrates and the subsequent ligation. Opposite template dG, the relative k(pol)/K(d) for incorporation was dCTP > araCTP, dFdCTP >> rCTP. The relative k(pol)/K(d) for FdCTP depended on sequence. The effect on k(pol)/K(d) was due largely to changes in k(pol) with no differences in the affinity of the nucleoside triphosphates to the polymerase. Ligation efficiency by T4 ligase and ligase III/XRCC1 was largely unaffected by the nucleotide analogues. Our results show that BER is capable of incorporating araC and dFdC into the genome.

Cell cycle arrest and apoptosis in TP53 subtypes of bladder carcinoma cell lines treated with cisplatin and gemcitabine

Currently, the combination of cisplatin and gemcitabine is considered a standard chemotherapeutic protocol for bladder cancer. However, the mechanism by which these drugs act on tumor cells is not completely understood. The aim of the present study was to investigate the effects of these two antineoplastic drugs on the apoptotic index and cell cycle kinetics of urinary bladder transitional carcinoma cell lines with wild-type or mutant TP53 (RT4: wild type for TP53; 5637 and T24: mutated TP53). Cytotoxicity, cell survival assays, clonogenic survival assays and flow cytometric analyses for cell cycle kinetics and apoptosis detection were performed with three cell lines treated with different concentrations of cisplatin and gemcitabine. G1 cell cycle arrest was observed in the three cell lines after treatment with gemcitabine and gemcitabine plus cisplatin. A significant increase in cell death was also detected in all cell lines treated with cisplatin or gemcitabine. Lower survival rates occurred with the combined drug protocol independent of TP53 status. TP53-wild type cells (RT4) were more sensitive to apoptosis than were mutated TP53 cells when treated with cisplatin or gemcitabine. Concurrent treatment with cisplatin and gemcitabine was more effective on transitional carcinoma cell lines than either drug alone; the drug combination led to a decreased cell survival that was independent of TP53 status. Therefore, the synergy between low concentrations of cisplatin and gemcitabine may have clinical relevance, as high concentrations of each individual drug are toxic to whole organisms.

Inactivation of Lactobacillus leichmannii ribonucleotide reductase by 2',2'-difluoro-2'-deoxycytidine 5'-triphosphate: covalent modification

Ribonucleotide reductase (RNR) from Lactobacillus leichmannii, a 76 kDa monomer using adenosylcobalamin (AdoCbl) as a cofactor, catalyzes the conversion of nucleoside triphosphates to deoxynucleotides and is rapidly (<30 s) inactivated by 1 equiv of 2',2'-difluoro-2'-deoxycytidine 5'-triphosphate (F(2)CTP). [1'-(3)H]- and [5-(3)H]F(2)CTP were synthesized and used independently to inactivate RNR. Sephadex G-50 chromatography of the inactivation mixture revealed that 0.47 equiv of a sugar was covalently bound to RNR and that 0.71 equiv of cytosine was released. Alternatively, analysis of the inactivated RNR by SDS-PAGE without boiling resulted in 33% of RNR migrating as a 110 kDa protein. Inactivation of RNR with a mixture of [1'-(3)H]F(2)CTP and [1'-(2)H]F(2)CTP followed by reduction with NaBH(4), alkylation with iodoacetamide, trypsin digestion, and HPLC separation of the resulting peptides allowed isolation and identification by MALDI-TOF mass spectrometry (MS) of a (3)H/(2)H-labeled peptide containing C(731) and C(736) from the C-terminus of RNR accounting for 10% of the labeled protein. The MS analysis also revealed that the two cysteines were cross-linked to a furanone species derived from the sugar of F(2)CTP. Incubation of [1'-(3)H]F(2)CTP with C119S-RNR resulted in 0.3 equiv of sugar being covalently bound to the protein, and incubation with NaBH(4) subsequent to inactivation resulted in trapping of 2'-fluoro-2'-deoxycytidine. These studies and the ones in the preceding paper (DOI: 10.1021/bi9021318 ) allow proposal of a mechanism of inactivation of RNR by F(2)CTP involving multiple reaction pathways. The proposed mechanisms share many common features with F(2)CDP inactivation of the class I RNRs.

Targeting glucose consumption and autophagy in myeloma with the novel nucleoside analogue 8-aminoadenosine

Multiple myeloma, an incurable plasma cell malignancy, is characterized by altered cellular metabolism and resistance to apoptosis. Recent connections between glucose metabolism and resistance to apoptosis provide a compelling rationale for targeting metabolic changes in cancer. In this study, we have examined the ability of the purine analogue 8-aminoadenosine to acutely reduce glucose consumption by regulating localization and expression of key glucose transporters. Myeloma cells counteracted the metabolic stress by activating autophagy. Co-treatment with inhibitors of autophagy results in marked enhancement of cell death. Glucose consumption by drug-resistant myeloma cells was unaffected by 8-aminoadenosine, and accordingly, no activation of autophagy was observed. However, these cells can be sensitized to 8-aminoadenosine under glucose-limiting conditions. The prosurvival autophagic response of myeloma to nutrient deprivation or to nucleoside analogue treatment has not been described previously. This study establishes the potential of metabolic targeting as a broader means to kill and sensitize myeloma and identifies a compound that can achieve this goal.

Phase I clinical trial of intrathecal gemcitabine in patients with neoplastic meningitis

PURPOSE

A phase I study of intrathecal (IT) gemcitabine was performed to define a safe dose and characterize the toxicity profile and CSF pharmacokinetics of gemcitabine and its major metabolite 2',2'-difluoro-deoxyuridine (dFdU) in patients 3 years of age and older with neoplastic meningitis.

EXPERIMENTAL DESIGN

Gemcitabine was administered via Ommaya reservoir or lumbar puncture at three dose levels: 5 mg weekly, 5 mg twice-weekly, and 10 mg twice-weekly using a standard phase I dose escalation design. Serial CSF samples were obtained for pharmacokinetic studies in seven patients with Ommaya reservoirs. Serial blood samples for pharmacokinetic studies were also obtained from three patients.

RESULTS

Ten patients were enrolled in this study. Significant neurological toxicities occurred in two patients including myelitis in a patient at the 5 mg twice-weekly dose level and somnolence in a patient at the 10 mg twice-weekly dose level. No complete responses were seen; however, three patients had stable disease. Gemcitabine was rapidly eliminated from the CSF with a terminal half-life of 61 +/- 50 min. No gemcitabine or dFdU was detected in plasma.

CONCLUSIONS

IT gemcitabine was associated with significant neurotoxicity; therefore, its further development for IT use is not recommended.

Cytotoxic activity of gemcitabine and correlation with expression profile of drug-related genes in human lymphoid cells

Gemcitabine is an inhibitor of ribonucleotide reductase (RR) and DNA polymerization with promising activity in hematologic malignancies. Gemcitabine enters the cell mostly via the human equilibrative nucleoside transporter-1 (hENT1), while drug metabolism occurs by phosphorylation by deoxycytidine kinase (dCK), 5'-nucleotidase (cN-II) and cytidine deaminase (CDA) are the main inactivating enzymes. The aim of this study was to investigate the role of these determinants in gemcitabine cytotoxicity and analyze their expression in lymphoid cells. Cytotoxicity was assessed by MTT, and modulated by simultaneous addition of 2'-deoxycytidine (dCK natural substrate), tetrahydrouridine (CDA competitive inhibitor) and diethylpyrocarbonate (cN-II non-competitive inhibitor), while the expression of hENT1, dCK, cN-II, CDA and RR in WIL2-S, Jurkat and CCRF-CEM cells as well as in lymphoid cells from 25 chronic lymphocytic B-leukemia (B-CLL) patients was studied with quantitative-PCR. Cell cycle modulation and induction of apoptosis were analyzed by cytofluorimetry and bisbenzimide staining. Gemcitabine was highly cytotoxic, increased the cells in S-phase and significantly enhanced apoptosis. The crucial role of metabolism in gemcitabine activity was confirmed by the significant modulation of cytotoxicity by inhibitors of dCK, CDA and cN-II. Furthermore, PCR demonstrated a correlation between gemcitabine sensitivity and expression of its determinants, and that their values were within those observed in patients. These data indicate that gemcitabine is cytotoxic against lymphoid cells, affecting cell cycle and apoptosis. Furthermore, chemosensitivity may be predicted on the basis of gene expression profile of critical determinants involved in gemcitabine mechanism of action, suggesting the use of pharmacogenetic profiling for treatment optimization.

Pharmacokinetics, Metabolism, and Oral Bioavailability of the DNA Methyltransferase Inhibitor 5-Fluoro-2′-Deoxycytidine in Mice

PURPOSE

In vivo, 5-fluoro-2'-deoxycytidine (FdCyd) is rapidly and sequentially converted to 5-fluoro-2'-deoxyuridine, 5-fluorouracil, and 5-fluorouridine. The i.v. combination of FdCyd and 3,4,5,6-tetrahydrouridine (THU), a cytidine deaminase (CD) inhibitor that blocks the first metabolic step in FdCyd catabolism, is being investigated clinically for its ability to inhibit DNA methyltransferase. However, the full effects of THU on FdCyd metabolism and pharmacokinetics are unknown. We aimed to characterize the pharmacokinetics, metabolism, and bioavailability of FdCyd with and without THU in mice.

EXPERIMENTAL DESIGN

We developed a sensitive high-performance liquid chromatography tandem mass spectrometry assay to quantitate FdCyd and metabolites in mouse plasma. Mice were dosed i.v. or p.o. with 25 mg/kg FdCyd with or without coadministration of 100 mg/kg THU p.o. or i.v.

RESULTS

The oral bioavailability of FdCyd alone was approximately 4%. Coadministration with THU increased exposure to FdCyd and decreased exposure to its metabolites; i.v. and p.o. coadministration of THU increased exposure to p.o. FdCyd by 87- and 58-fold, respectively. FdCyd exposure after p.o. FdCyd with p.o. THU was as much as 54% that of i.v. FdCyd with i.v. THU.

CONCLUSIONS

FdCyd is well absorbed but undergoes substantial first-pass catabolism by CD to potentially toxic metabolites that do not inhibit DNA methyltransferase. THU is sufficiently bioavailable to reduce the first-pass effect of CD on FdCyd. Oral coadministration of THU and FdCyd is a promising approach that warrants clinical testing because it may allow maintaining effective FdCyd concentrations on a chronic basis, which would be an advantage over other DNA methyltransferase inhibitors that are currently approved or in development.

Phase II Evaluation of Gemcitabine Monotherapy for Cutaneous T-Cell Lymphoma

PURPOSE

The purpose of this study was to investigate safety and efficacy of gemcitabine monotherapy for cutaneous T-cell lymphoma (CTCL).

PATIENTS AND METHODS

Twenty-five patients with CTCL on a phase II open-label trial and 8 patients off study received intravenous gemcitabine (1000 mg/m2) on day 1, 8, and 15 for > or = 6 cycles. Physicians' global assessment was based on body surface area involvement in skin, measurement of lymph nodes, and blood by flow cytometry.

RESULTS

Two patients with CD30+ anaplastic large T-cell lymphoma and 31 with mycosis fungoides (stage IB [T2, n = 2], stage IIA [T2, n = 1], stage IIB [T3, n = 13], stage IVA [T3 N3, n = 3; T4b2, n = 2; T4b2 N3, n = 2], and stage IVB [T4b2 N1, n = 6; T4 N3b2 M1, n = 1; T3 N3 M1, n = 1]) had received a median of 5 previous therapies (range, 1-13 therapies). Responses were seen in 17 of 25 (68%) study patients (2 complete responses [8%]) and 4 of 8 patients (1 complete response) off protocol. Seven of 13 patients with mycosis fungoides (T3) responded, 10 had tumor burden reductions, and 8 of 11 patients with Sezary syndrome responded. Gemcitabine was well tolerated. Myelosuppression (n = 14; grade 3, n = 8), hemolytic uremic syndrome (in 2 elderly patients with Sezary syndrome), pulmonary embolism (n = 2), and 1 episode each of congestive heart failure, acute myocardial infarction, and stable angina were observed. Increased hepatic transaminases (n = 4), mucositis (n = 3), lethargy (n = 7), fever (n = 8), cutaneous hyperpigmentation (n = 6), infusion-related maculopapular rash (n = 1), and radiation recall (n = 1) were also seen.

CONCLUSION

Gemcitabine is an effective monotherapy with a 68% overall response rate in patients with advanced, heavily pretreated CTCL.

Pharmacokinetics of gemcitabine and its primary metabolite in dogs after intravenous infusion

Gemcitabine is a relatively new chemotherapeutic compound used to treat a variety of cancers in dogs. Previous work presented in a companion paper explored the plasma kinetics of gemcitabine and its inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU), in dogs after an intravenous bolus gemcitabine dose and demonstrated the saturation of intracellular dFdCTP (2',2'-difluorodeoxycytidine 5'-triphosphate) occurs in vitro with increasing extracellular gemcitabine exposure in canine melanoma cells. In this study, the plasma pharmacokinetics (PKs) of gemcitabine and dFdU are further explored after gemcitabine doses of 10, 30, and 60 mg/kg administered by intravenous infusion with a loading dose. Gemcitabine displayed linear PKs, while the kinetics of dFdU were not dose proportional. The overall clearance, volume of distribution at steady-state, and terminal elimination half-life (t(1/2)) for gemcitabine were 0.421 L/h.kg, 0.822 L/kg, and 1.49 h, respectively. Plasma concentrations of dFdU peaked at approximately 2 h postdosing and had a t(1/2) of 14.9 h.

Pharmacokinetics of gemcitabine and its primary metabolite in dogs after intravenous bolus dosing and its in vitro pharmacodynamics

Gemcitabine is a chemotherapeutic agent used to treat a variety of cancers in humans and dogs. In this study, the plasma pharmacokinetics of gemcitabine and its inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU), were investigated in dogs after intravenous bolus gemcitabine doses of 3, 10, and 30 mg/kg. Furthermore, the intracellular accumulation of the active metabolite gemcitabine triphosphate, as a surrogate pharmacodynamic endpoint, was also determined in vitro in canine melanoma cells. Gemcitabine was characterized by linear kinetics, while dFdU dose proportionality remains unknown. The average gemcitabine clearance was 0.560 L/h.kg and volume of distribution at steady-state of 1.27 L/kg. The average terminal elimination half-life, depending on dose, ranged from 1.75 to 3.23 h. Plasma concentrations of dFdU peaked at approximately 2 h post-dosing. In vitro intracellular gemcitabine triphosphate accumulation was saturated with increasing extracellular gemcitabine concentrations. These data can be used to rationally design gemcitabine dosage regimes for canine oncology patients and as a basis for future investigations on the in vivo intracellular accumulation of gemcitabine triphosphate in dogs.

Gemcitabine-induced activation of checkpoint signaling pathways that affect tumor cell survival

Two signaling pathways are activated by antineoplastic therapies that damage DNA and stall replication. In one pathway, double-strand breaks activate ataxia-telangiectasia mutated kinase (ATM) and checkpoint kinase 2 (Chk2), two protein kinases that regulate apoptosis, cell-cycle arrest, and DNA repair. In the second pathway, other types of DNA lesions and replication stress activate the Rad9-Hus1-Rad1 complex and the protein kinases ataxia-telangiectasia mutated and Rad3-related kinase (ATR) and checkpoint kinase 1 (Chk1), leading to changes that block cell-cycle progression, stabilize stalled replication forks, and influence DNA repair. Gemcitabine and cytarabine are two highly active chemotherapeutic agents that disrupt DNA replication. Here, we examine the roles these pathways play in tumor cell survival after treatment with these agents. Cells lacking Rad9, Chk1, or ATR were more sensitive to gemcitabine and cytarabine, consistent with the fact that these agents stall replication forks, and this sensitization was independent of p53 status. Interestingly, ATM depletion sensitized cells to gemcitabine and ionizing radiation but not cytarabine. Together, these results demonstrate that 1) gemcitabine triggers both checkpoint signaling pathways, 2) both pathways contribute to cell survival after gemcitabine-induced replication stress, and 3) although gemcitabine and cytarabine both stall replication forks, ATM plays differential roles in cell survival after treatment with these agents.

Gemcitabine, vinorelbine and prednisone for refractory or relapsed aggressive lymphoma,results of a phase II single center study

The optimum therapy for patients with relapsed or refractory aggressive non-Hodgkin's lymphomas (NHL) not qualifying for platinum-based and/or high-dose chemotherapy is not known. We conducted a prospective phase II study evaluating a regimen consisting of gemcitabine (1 g/m2, days 1 and 8), vinorelbine (30 mg/m2, days 1 and 8) and prednisone (100 mg/day, days 1-8) (GVP) given every 21 days. Fifteen patients with a median age of 68 years and a median of three previous therapies were enrolled. Diagnoses included B lymphoblastic (n=1), diffuse large B cell (n=10), anaplastic large T cell (n=2) and peripheral T-cell NHL (n=2). The median international prognostic index score was 3 (six patients with a score of 4 or 5). Five patients achieved a complete remission and three patients a partial remission. The median overall survival was 13.8 months, and the median time to next treatment was 4.4 months. Haematological toxicities of World Health Organisation grades 3/4 were leucopenia in 58%, thrombocytopenia in 33% and anaemia in 17% of all courses. Three patients had grade 3 infections. There was no treatment-related mortality. GVP shows substantial activity in poor prognosis relapsed or refractory aggressive lymphomas and is generally well tolerated, but haematological toxicity is dose limiting.

Enhanced efficacy of gemcitabine in combination with anti-CD20 monoclonal antibody against CD20+ non-Hodgkin's lymphoma cell lines in vitro and in scid mice

Background

Despite exciting new targeted therapeutics against non-Hodgkin's lymphoma (NHL), chemotherapy remains a cornerstone of therapy. While purine nucleoside analogs have significant activity in low grade NHL, the pyrimidine nucleoside analog gemcitabine has been less extensively studied, but has important activity. Use of the anti-CD20 monoclonal antibody rituximab in combination with chemotherapy for B-NHL is becoming prevalent in clinical practice, but has not been extensively studied in pre-clinical models.

Methods

We have tested the activity of gemcitabine ± rituximab in vitro and in scid/human NHL xenograft models. We used two t(14;18)+, CD20+ follicular B cell NHL cell lines, DoHH2 a transformed NHL line and WSU-FSCCL isolated from pleural fluid of a patient with indolent NHL.

Results

Gemcitabine is cytotoxic to DoHH2 and WSU-FSCCL cells in vitro, and the IC₅₀ is 2–3 fold lower in the presence of rituximab. Apoptosis is also enhanced in the presence of rituximab. Clearance of NHL cells from ascites in scid mice is prolonged by the combination, as compared with either agent alone. Most importantly, survival of scid mice bearing human NHL cells is significantly prolonged by the combination of gemcitabine + rituximab.

Conclusion

Based on our pre-clinical data showing prolonged survival of mice bearing human lymphoma cell line xenografts after treatment with gemcitabine + anti-CD20 antibody, this combination, expected to have non-overlapping toxicity profiles, should be explored in clinical trials.

Therapeutic effects of gemcitabine on cutaneous manifestations in an Adamantiades-Behçet's disease-like mouse model

The aim of this work was to study the effects and side effects of gemcitabine (2',2'-difluorodeoxycytidine, dFdC), a pyrimidine synthesis inhibitor, on skin lesions of a herpes simplex virus (HSV)-induced Adamantiades-Behçet's disease (ABD)-like mouse model. For the dose-escalation study, ICR mice were treated intraperitoneally with dFdC over 5 days. For the efficacy study, ICR mice were inoculated with HSV and classified as having ABD according to a revised Japanese classification, and then 18 ABD mice were randomly assigned to placebo, 0.06 or 0.12 microg of dFdC/day over 5 days. Serum levels of interleukin-4 (IL-4), IL-6, IL-10, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) were determined using enzyme-linked immunosorbent assay. After application of 3 microg of dFdC over 5 days, alanine aminotransferase increased (P = 0.032), but all other kidney and liver parameters were unchanged. In ABD mice, 5 days of dFdC treatment with 0.06 or 0.12 microg of dFdC/day resulted in a dose-dependent improvement of cutaneous manifestations by more than 60% (P = 0.017). There was no significant change in cytokine levels, and none of the cytokine levels correlated with response to treatment. Moreover, dFdC shows promising effects to improve cutaneous lesions in the HSV-induced ABD-like mouse model. In this animal model, effects of dFdC on the cytokine profile remained inconclusive.

Analysis of human equilibrative nucleoside transporter 1 (hENT1) protein in non-Hodgkin's lymphoma by immunohistochemistry

The human equilibrative nucleoside transporter 1 (hENT1) is a member of the equilibrative nucleoside transporter family that mediates cellular entry of gemcitabine, cytarabine, and fludarabine. Deficiency in hENT1 confers resistance to toxicity of these drugs in a variety of model systems. Since some nucleoside analogs have a role in treating patients with non-Hodgkin's lymphoma (NHL), this study was undertaken to assess hENT1 abundance in NHL. A total of 115 cases of NHL of various subtypes and 15 reactive lymph nodes were evaluated for the presence of hENT1 protein using immunohistochemistry applied to frozen tissues. Samples were considered positive when >or=50% of neoplastic cells showed immunostaining. In reactive lymph nodes, hENT1 was confined to the germinal centers, whereas mantle zone B-cells and interfollicular T-cells were negative. In NHL, a relatively high frequency of hENT1 positivity was found in Burkitt lymphoma/leukemia (63%), diffuse large B-cell lymphoma (DLCL; 45%), and follicular lymphoma (40%). In DLCL, 26% of cases were positive for CD10, and CD10-positive DLCL cases were more likely to be hENT1 positive than CD10-negative cases (P=0.025). A lower frequency of hENT1 positivity was found in mantle cell lymphoma (13%) and peripheral T-cell lymphomas (37%). All marginal zone lymphomas (n=5), chronic lymphocytic leukemia small lymphocytic lymphomas (n=10), plasmacytoma (n=3), acute lymphoblastic lymphoma/leukemia, and anaplastic large-cell lymphomas (n=5) were negative. In conclusion, hENT1 was most frequently found in benign and malignant follicular center cells. Prospective studies to assess the value of hENT1 immunostaining in predicting resistance to nucleoside chemotherapy for NHL are warranted.

Extracellular signal-regulated kinase activation and Bcl-2 downregulation mediate apoptosis after gemcitabine treatment partly via a p53-independent pathway

Gemcitabine is a promising compound for the treatment of human lung cancer. Although apoptosis has been shown to play a role in certain cell types with gemcitabine, the steps leading to cell death after the drug-target interaction are not well understood. We studied the molecular mechanisms of gemcitabine-induced apoptosis and determined the role of p53 function on the cytotoxic effects of gemcitabine in human nonsmall cell lung cancer (NSCLC) H1299 and H1299/p53 cells. Here, we found that gemcitabine induced an apoptotic cell death via a Bcl-2-dependent caspase-9 activation pathway. Moreover, phosphorylated activation of extracellular signal-regulated kinase (ERK) was observed upon gemcitabine treatment. Genetical or pharmacological inhibition of ERK activation markedly blocked gemcitabine-induced cell death. Furthermore, inactivation of Akt was also involved in this event. Taken together, our observations indicate that ERK activation and Akt inactivation mediated gemcitabine-induced apoptosis independently of p53 in human NSCLC H1299 cells.

In vitro cytotoxicity of aplidin and crossresistance with other cytotoxic drugs in childhood leukemic and normal bone marrow and blood samples: a rational basis for clinical development

To determine the potential of aplidin as a cytotoxic agent in pediatric leukemia, we tested bone marrow (BM) and peripheral blood (PB) samples (n=72) of children with different types of leukemia and healthy children in the methyl-thiazol-tetrazolium assay. Also, we compared these results with other cytotoxic drugs. Aplidin was cytotoxic in vitro at nanomolar concentrations, in a dose-dependent fashion. L-carnitine, that is applied in clinical studies to prevent myotoxicity caused by aplidin, had no effect on aplidin cytotoxicity in vitro. Aplidin cytotoxicity in vitro was not different when initial and relapsed acute lymphoblastic leukemia (ALL) or initial ALL and initial acute myeloid leukemia were compared. However, normal BM (n=19) and PB (n=13) cells were more resistant to aplidin than leukemic cells (median two- to seven-fold, P=0.001 and median four- to 11-fold, P&<0.0001, respectively). In leukemia samples, no significant crossresistance between aplidin and other cytotoxic drugs was found, except for a trend for correlation with 2',2'-difluorodeoxycytidine (rho=0.71, P=0.02). In normal BM samples, significant crossresistance with the epipodophyllotoxins was found, which is not readily explained by the currently known mechanisms of action of aplidin. In conclusion, we show that aplidin has selective cytotoxicity in vitro towards childhood leukemia cells and generally lacks crossresistance with other known cytotoxic drugs, which warrants clinical studies.

New chemotherapy agents in veterinary medicine

Several anticancer drugs have been added to the therapeutic armamentarium in recent years. Some of these agents are traditional drugs with a long history of use in human oncology. Increased sophistication in clinical trial design in veterinary oncology has allowed the incorporation of agents previously viewed as excessively toxic. Other agents have been developed more recently. This article summarizes the veterinary experience with two older alkylating agents, lomustine and streptozocin, and newer compounds ifosfamide and gemcitabine. The published literature regarding veterinary use of these agents is limited, and the reader is advised to contact a veterinary oncologist for current guidelines when contemplating use of these agents.

Rituximab-mediated sensitization of B-non-Hodgkin's lymphoma (NHL) to cytotoxicity induced by paclitaxel, gemcitabine, and vinorelbine

Non-Hodgkin's lymphoma (NHL) responds initially to chemotherapy, however, the disease often relapses and acquires a chemoresistant phenotype. Third line treatment options such as paclitaxel, gemcitabine, and vinorelbine have been tried in patients with refractory or relapsed NHL with antilymphoma activity. Currently, rituximab (anti-CD20) has been approved for treatment of indolent NHL, with significant activity in a wide spectrum of B-cell malignancies, though a percentage of patients do not respond to rituximab treatment. Previous findings from our laboratory have demonstrated that rituximab can sensitize drug-resistant NHL B-lymphoma in vitro to some chemotherapeutic drugs. Hence, in this study, we examined the effect of combination treatment of rituximab and the drugs paclitaxel, gemcitabine, and vinorelbine on various NHL cell lines. Our findings indicate that pretreatment of NHL tumor cells with rituximab sensitizes drug-resistant NHL tumor cells to drug-mediated cytotoxicity. These findings suggest the potential clinical application of combination treatments of rituximab and paclitaxel, gemcitabine or vinorelbine in the treatment of drug/rituximab refractory non-Hodgkin's lymphoma.