Optimising treatment outcomes: a review of current management strategies in first-line chemotherapy of metastatic breast cancer

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.

Progress Toward the Development of Noscapine and Derivatives as Anticancer Agents

Many nitrogen-moiety containing alkaloids derived from plant origins are bioactive and play a significant role in human health and emerging medicine. Noscapine, a phthalideisoquinoline alkaloid derived from Papaver somniferum, has been used as a cough suppressant since the mid 1950s, illustrating a good safety profile. Noscapine has since been discovered to arrest cells at mitosis, albeit with moderately weak activity. Immunofluorescence staining of microtubules after 24 h of noscapine exposure at 20 μM elucidated chromosomal abnormalities and the inability of chromosomes to complete congression to the equatorial plane for proper mitotic separation ( Proc. Natl. Acad. Sci. U. S. A. 1998 , 95 , 1601 - 1606 ). A number of noscapine analogues possessing various modifications have been described within the literature and have shown significantly improved antiprolific profiles for a large variety of cancer cell lines. Several semisynthetic antimitotic alkaloids are emerging as possible candidates as novel anticancer therapies. This perspective discusses the advancing understanding of noscapine and related analogues in the fight against malignant disease.

Vinflunine: review of a new vinca alkaloid and its potential role in oncology

Objective: To review the pharmacology, pharmacokinetics, in vitro and in vivo efficacy, and safety profile of vinflunine in the treatment of various solid tumors.

Data sources: A literature search was conducted using keywords included vinflunine, vinca alkaloid, Javlor, and solid tumor in PubMed/MEDLINE (1950—January 2009) and International Pharmaceutical Abstracts (1950—January 2009). Study selection and data extraction: Published studies, posters, and meeting abstracts evaluating the in vitro and in vivo efficacy of vinflunine were reviewed.

Data synthesis: Vinflunine is the newest member of the vinca alkaloid family. It has the weakest affinity to tubulins, but is shown to have unique receptor-independent antiangiogenesis, and antimetastasis properties. After administration, it is distributed extensively into tissues, metabolized via the CYP3A4 system, and eventually excreted in urine and feces. Phase II/III trials reported activities of vinflunine in advanced stage nonsmall-cell lung cancer, metastatic breast cancer, metastatic renal cell carcinoma, transitional cell carcinomas of the urothelium, small-cell lung cancer, and malignant pleural mesothelioma as monotherapy and in combination with other chemotherapy agents. More ongoing trials are evaluating its use in other solid tumors and in combination regimens. The most common adverse events in these trials were hematological (anemia and neutropenia), constipation, fatigue, abdominal pain, and myalgia.

Conclusions: Vinflunine is a new vinca alkaloid for the treatment of advanced staged solid tumors. Available data showed promising activities in various malignancies. Further studies are needed to further define vinflunine’s role in oncology.

Pharmacokinetics, tissue distribution and excretion of vinflunine

The plasma pharmacokinetics, tissue distribution, excretion and binding to plasma proteins of vinflunine, were investigated after intravenous (iv) administration. We obtained plasma profiles after iv administration of vinflunine at the doses of 3.5, 7 and 14 mg/kg in rats. The t1/2 values for vinflunine were estimated to be 18.38+/-1.20, 17.05+/-0.77, 18.35+/-1.57 h, and the mean AUC0-t values were 3.48+/-0.38, 6.54+/-0.68, 12.79+/-2.93 microg x h/ml, respectively. Of the various tissues tested, vinflunine was widely distributed into tissues, with the highest concentrations of vinflunine being found in well perfused organs. Maximal concentration of vinflunine was reached at 0.5 h postdose in the majority of tissues. In tumor-bearing mice, the similar pattern of tissue distribution was observable, except that vinflunine can be distributed into tumor. The binding of vinflunine in human and rat plasma proteins were 39.6% and 58.4% respectively. Within 96 h after administration, 9.58%, 15.36% and 0.71% of the given dose was excreted in urine, feces and bile, respectively. In conclusion, Vinflunine had a longer terminal half-life, a wide tissue distribution and less than 25% of the given dose was excreted as unchanged drug, suggesting metabolism as a major style of elimination.

Enhanced proliferation of functionally competent bone marrow cells in different strains of mice treated with swainsonine

The immunomodulatory alkaloid swainsonine (8alphabeta-indolizidine-1alpha,2alpha,8beta-triol) has potential for overcoming the bone marrow suppressive effects of cancer chemotherapy and radiotherapy. An earlier study showed that multiple doses of swainsonine enhanced bone marrow cellularity in four different strains (C57BL/6; C3H-HEN; Balb/C and DBA-2 mice) of inbred mice which were not exposed to any chemotherapeutic agents or radiation. In vitro assessment of total colony formation capacity of bone marrow cells (BM CFUs) showed a 2- to 8-fold increase in swainsonine-treated mice compared to control mice that were given sham injections of physiological saline. In the current study, we have evaluated the functional competence of the bone marrow cells produced in response to swainsonine treatment of normal healthy mice. In particular, colony forming units-granulocyte-macrophage (CFU-GM), erythroid-burst forming units (BFUe) and CFU-Mix (or CFU-granulocyte-erythrocyte-monocyte-megakaryocyte (CFU-GEMM)) levels, were determined using in vitro assays. The time course of the changes in CFU-GM, BFUe and CFU-Mix (CFU-GEMM) were also followed. Our results demonstrate that swainsonine bolsters the CFU capacity of BM cells without loss of function to levels which are several folds higher than in sham-treated control mice. Swainsonine treatment caused an increase in all lineages of marrow cells without loss of function. This effect was reproduced in all four strains of inbred mice in this investigation. Examination of the peripheral blood did not reveal increase in white blood cells or changes in the hematocrit levels. The long-term effects of swainsonine treatment are not known at present. Nonetheless, swainsonine-induced increase in CFU capacity of bone marrow cells and related cells along the different differentiation paths should find clinical application in cancer treatment with chemotherapeutic agents and/or radiation.

Mechanism of mitotic block and inhibition of cell proliferation by the semisynthetic Vinca alkaloids vinorelbine and its newer derivative vinflunine

The two second-generation Vinca alkaloids, vinorelbine and vinflunine, affect microtubule dynamics very differently from vinblastine, a first generation Vinca alkaloid. For example, vinblastine strongly suppresses the rate and extent of microtubule shortening in vitro, whereas vinorelbine and vinflunine suppress the rate and extent of microtubule growing events. We asked whether these differences result in differences in mitotic spindle organization that might be responsible for the superior antitumor activities of the two second-generation Vinca alkaloids. IC(50) values for inhibition of HeLa cell proliferation for vinflunine, vinorelbine, and vinblastine were 18, 1.25, and 0.45 nM, respectively, similar to the concentrations that induced mitotic block at the metaphase/anaphase transition (38, 3.8, and 1.1 nM, respectively), indicating that mitotic block is a major contributor to antiproliferative action for all three drugs. Mitotically blocked cells exhibited aberrant spindles, consistent with induction of block by suppression of microtubule dynamics. Despite differences in their actions on individual dynamic instability parameters, morphologically detectable differences in spindle effects among the three drugs were minimal, indicating that overall suppression of dynamics may be more important in blocking mitosis than specific effects on growth or shortening. We also found that the peak intracellular drug concentration at the mitotic IC(50) value was highest for vinflunine (4.2 +/- 0.2 microM), intermediate for vinorelbine (1.3 +/- 0.1 microM), and more than 10-fold lower for vinblastine (130 +/- 7 nM), suggesting that intracellular binding reservoir(s) may be partially responsible for vinflunine's high efficacy and minimal side effects.

Role of specific apoptotic pathways in the restoration of paclitaxel-induced apoptosis by valspodar in doxorubicin-resistant MCF-7 breast cancer cells

Paclitaxel (Taxol) kills tumor cells by inducing both cellular necrosis and apoptosis. A major impediment to paclitaxel cytotoxicity is the establishment of multidrug resistance whereby exposure to one chemotherapeutic agent results in cross-resistance to a wide variety of other drugs. For example, selection of MCF-7 breast cancer cells for resistance to doxorubicin (MCF-7ADR cells) results in cross-resistance to paclitaxel. This appears to involve the overexpression of the drug transporter P-glycoprotein which can efflux both drugs from tumor cells. However, MCF-7ADR cells possess a deletion mutation in p53 and have considerably reduced levels of the Fas receptor, Fas ligand, caspase-2, caspase-6, and caspase-8, suggesting that paclitaxel resistance may also stem from a bona fide block in paclitaxel-induced apoptosis in these cells. To address this issue, we examined the ability of the P-glycoprotein inhibitor valspodar to restore paclitaxel accumulation, paclitaxel cytotoxicity, and paclitaxel-induced apoptosis. Compared to drug sensitive MCF-7 cells, MCF-7ADR cells accumulated >6-fold less paclitaxel, were approximately 100-fold more resistant to killing by the drug, and were highly resistant to paclitaxel-induced apoptosis. In contrast, MCF-7ADR cells pretreated with valspodar were indistinguishable from drug-sensitive cells in their ability to accumulate paclitaxel, in their chemosensitivity to the drug, and in their ability to undergo paclitaxel-induced apoptosis. Valspodar, by itself, did not affect these parameters. This suggests that the enhancement of paclitaxel toxicity in MCF-7ADR cells involves a restoration of apoptosis and not solely through enhanced drug-induced necrosis. Morever, it appears that changes in the levels/activity of p53, the Fas receptor, Fas ligand, caspase-2, caspase-6, or caspase-8 activity have little effect on paclitaxel-induced cytotoxicity and apoptosis in human breast cancer cells.