In vivo circumvention of P-glycoprotein-mediated multidrug resistance of tumor cells with SDZ PSC 833.

The new nonimmunosuppressive cyclosporin analogue, SDZ PSC 833, is a very potent multidrug-resistance modifier. In vitro, it was shown to be at least 10-fold more active than cyclosporin A (Sandimmune), itself more active than verapamil, on most P-glycoprotein-expressing multidrug-resistant (MDR) tumor cell lines. In vivo, SDZ PSC 833 was tested in a few protocols of combined therapy with either Vinca alkaloids or doxorubicin as anticancer drugs, using the homologous tumor-host system (P388 cells of DBA/2 origin grafted into DBA/2 or B6D2F1 mice). Although these MDR-P388 tumor cells belong to a highly resistant variant that in vitro required about 150-fold more anticancer drug for 50% cell growth inhibition than the parental P388 cells, significant prolongation of survival times of the MDR-P388 tumor-bearing mice was obtained when treated with a combination of SDZ PSC 833 p.o. were otherwise ineffective doses of anticancer drugs given i.p. This chemosensitizing effect of SDZ PSC 833 was dose-dependent and was most effective in a protocol combining administration of SDZ PSC 833 p.o. 4 h before a doxorubicin i.p. injection: in comparison with the survival of MDR-P388 tumor-bearing mice treated with the anticancer drug alone, the pretreatment with SDZ PSC 833 at 25 and 50 mg/kg gave 2- to 3-fold increases of survival times. Since the MDR-P388 tumor cells used in our studies belong to a highly resistant variant, with a much higher degree of drug resistance than the one known to occur in cancer patients, SDZ PSC 833 appears to be a very promising chemosensitizer.

Expression of P-glycoprotein on normal lymphocytes: enhancement of the doxorubicin-sensitivity of concanavalin A-responding mouse spleen cells by P-glycoprotein blockers.

The in vitro proliferative response of mouse spleen cells (SC) to the T-cell mitogen, concanavalin A (ConA), displays a doxorubicin (DOX)-resistant component. This T-cell proliferative response displays a much higher DOX sensitivity in the presence of novel potent inhibitors of P-glycoprotein (Pgp)-mediated multidrug resistance (MDR), the cyclosporin (Cs) derivative, SDZ PSC 833, and the semi-synthetic cyclopeptolide, SDZ 280-446. Another resistance modulator, verapamil, might share this property, but its detection was impaired by the intrinsic toxicity of this calcium channel blocker for T-cell proliferation. A CD8+ cell-depleted SC suspension displayed a higher sensitivity to DOX alone, as well as a different sensitivity profile to SDZ 280-446. The CD8+ cells that are sensitized to DOX by the resistance modulating agents (RMA) might correspond to a formerly described T-cell subpopulation with the MDR phenotype, which seems to be essentially constituted of CD8+ (cytotoxic) T cells. Our results may open the way to a novel form of immunomodulation combining classical antineoplastic agents with Pgp-blocking Cs analogs (even non-immunosuppressive ones), which may be particularly useful when treating acute graft rejection.

Lymphotoxicity and myelotoxicity of doxorubicin and SDZ PSC 833 combined chemotherapies for normal mice.

In the mouse, the P-glycoprotein-directed chemosensitizer SDZ PSC 833 could both restore a therapeutic window for doxorubicin against multidrug-resistant tumors, by inhibiting P-glycoprotein function, and increase the anti-cancer drug efficacy against drug-sensitive tumors, by increasing doxorubicin bioavailability. Since the success of such combined chemotherapy treatments might have been limited by the myelotoxicity of doxorubicin and the P-glycoprotein expression on some blood cells, their lymphotoxicity and myelotoxicity was studied on normal B6D2F1 mice, and whenever possible, the persistence of blood cell alterations was also searched for in scid recipients of lymphohaematopoietic grafts from the donor mice. Analyzed parameters were blood, lymphoid and myeloid cell numbers, proliferative responses to T- and B-cell mitogens, and serum immunoglobulin levels. Cell alterations caused by doxorubicin alone were potentiated by SDZ PSC 833, but did not persist in scid recipients. Chemotherapy regimens combining SDZ PSC 833 and doxorubicin, and known for their therapeutic benefit for multidrug-resistant tumor-bearing mice, only caused a rather mild toxicity for the lympho-myeloid system of normal mice.

[Experimental angiogenesis : strategy for the functional study of the transcription factors of the Ets family during morphogenesis of the vascular tree]. / Angiogenèse expérimentale : stratégies pour l'étude fonctionnelle des facteurs de transcription de la famille Ets dans la morphogenèse du réseau vasculaire.

During morphogenesis of the vascular tree, the massive outgrowth of primitive capillaries is followed by the development and the maturation of some capillary branches whereas others regress. The direct observation and the manipulation of in vivo models, including a series of recent knock-out experiments, allow to delineate the mechanisms controlling this process, and to identify factors involved in the formation of a mature capillary, surrounded with a basal lamina and pericytes. The expression of several members of the Ets family of transcription factors, Ets1, Erg and Fli, correlates with the occurrence of invasive processes, such as angiogenesis during normal and pathological development. The description of the phenotype of cultured endothelial cells expressing the DNA binding domain of Ets1 suggests that members of the Ets family take part in the morphogenesis of the -vascular tree. Although transient transfection experiments allowed the identification of putative targets genes for Ets1 during angiogenesis, deciphering the Ets1 regulation networks remains a major goal for the future.

Mannose-binding lectin polymorphisms in a Canary Islands (Spain) population.

We have compared the structural and promoter variants of the mannose-binding lectin (MBL) gene in a population from Gran Canaria with that from other populations previously reported. The observed frequencies of the seven alleles of the MBL gene in our population were: HYPA, 0.24; LYQA, 0.22; LYPA, 0.08; LXPA, 0.19; LYPB, 0.17; LYQC, 0.03 and HYPD, 0.07. The frequency of non-producer alleles and of MBL-deficient individuals in our population is higher than in other European and Asian population.

Restoration of daunomycin retention in multidrug-resistant P388 cells by submicromolar concentrations of SDZ PSC 833, a nonimmunosuppressive cyclosporin derivative.

Overexpression of P-glycoprotein may cause increased efflux of a variety of anticancer drugs (ACD) leading to multidrug resistance (MDR) of tumor cells. Two sublines of murine monocytic leukemia P388 cells were used, one parental (Par-P388) and one multidrug resistant (MDR-P388). In cell growth inhibition assays in vitro, the Par-P388 cells showed a normal sensitivity to daunomycin (DAU) while the MDR-P388 cells were 200-fold resistant. In cellular fluorescence assays, DAU retention in MDR-P388 cells reached only 5% of the level achieved in Par-P388 cells. This cell line pair was used to compare the nonimmunosuppressive cyclosporin analog PSC 833 with several resistance-modifying agents (RMAs) for their in vitro chemosensitizing activity and for their restoration of DAU retention. PSC 833 sensitized the MDR-P388 cells 60- and 140-fold when used at 0.1 and 0.3 micrograms/ml (0.08 and 0.25 microM), respectively, a complete restoration of sensitivity being obtained at 1.0 micrograms/ml PSC 833. Similarly as little as 0.1 micrograms/ml (0.08 microM) PSC 833 was sufficient to restore intracellular DAU retention to 60% of the level found in Par-P388 cells, a 3-fold higher concentration restoring virtually the whole DAU retention. For both these activities, PSC 833 was at least one order of magnitude more active than CsA, which was itself an order of magnitude stronger than verapamil, another RMA already used in clinic. Since PSC 833 had no effect on the PAR-P388 cells, neither on chemosensitization nor on drug retention, it is assumed that it acts on the P-glycoprotein, which is highly expressed on the membrane of the MDR-P388 cells, by inhibiting the function of the P-glycoprotein pump and thus restoring a normal ACD-sensitivity of the MDR-P388 cells.

FK-506 (fujimycin) reverses the multidrug resistance of tumor cells in vitro.

Cyclosporin A (CsA) and FK-506 have similar immunosuppressive activity profiles and cyclophilin-like intracellular targets. Since CsA can reverse the multidrug resistance of tumor cells showing P-glycoprotein-mediated drug efflux, the possible resistance-modulating activity of FK-506 was evaluated in vitro with multidrug-resistant P388 cells and their sensitive parental controls. Higher concentrations of FK-506 than CsA were needed to achieve a similar degree of chemosensitization, suggesting that FK-506 might interact less efficiently than CsA with the P-glycoprotein expressed in multidrug-resistant tumor cells. However, FK-506 was active on a broader range of concentrations than CsA, particularly because of direct cytostatic effects of CsA which appeared at concentrations only slightly higher than those required to show a significant resistance-modulating activity.

SDZ PSC 833 and SDZ 280-446 are the most active of various resistance-modifying agents in restoring rhodamine-123 retention within multidrug resistant P388 cells.

Multidrug resistance (MDR) of tumor cells may result from overexpression of P-glycoprotein (Pgp) but may be down-modulated by resistance-modifying agents (RMAs). The cyclosporin SDZ PSC 833 and the cyclopeptolide SDZ 280-446 were found to be the strongest RMAs known to date for restoring the sensitivity of MDR cells to anticancer drugs, as well as for restoring their retention of daunomycin, a fluorescent anthracycline. Using rhodamine-123 (Rhod-123), another fluorescent probe of Pgp function which also differentiates sensitive and MDR cells, several RMAs were compared for their capacity to inhibit Pgp function. At variance with the data obtained with the daunomycin probe, a series of RMAs did not detectably restore Rhod-123 retention by the MDR cells. With the remaining RMAs, achieving the same levels of Rhod-123 retention required 3 times lower RMA concentrations when the RMA was added to the MDR cells for both the initial uptake and the efflux of Rhod-123 rather than for its uptake only. Nevertheless, the data emphasized the large superiority of SDZ PSC 833 and SDZ 280-446 over all other RMAs.

SDZ 280-446, a novel semi-synthetic cyclopeptolide: in vitro and in vivo circumvention of the P-glycoprotein-mediated tumour cell multidrug resistance.

SDZ 280-446 is a semi-synthetic derivative of a natural cyclic peptolide. Its ability to sensitise in vitro tumour cells whose resistance is due to P-glycoprotein-mediated anticancer-drug efflux was shown using four different pairs of parental drug-sensitive (Par-) and multidrug-resistant (MDR-) cell lines, from three different species (mouse, human, Chinese hamster) representing four different cell lineages (monocytic leukaemia, nasopharyngeal epithelial carcinoma, colon epithelial carcinoma, ovary fibroblastoid carcinoma), and using four different drug classes (colchicine, vincristine, daunomycin/doxorubicin and etoposide). By measuring its capacity to restore normal drug sensitivity of MDR-cells in culture in vitro, it appeared that SDZ 280-446 belongs to the same class of very potent chemosensitisers as the cyclosporin derivative SDZ PSC 833: both are about one order of magnitude more active than cyclosporin A (CsA), which is itself about one order of magnitude more active than other known chemosensitisers (including verapamil, quinidine and amiodarone which have already entered clinical trials in MDR reversal). Low concentrations of SDZ 280-446 could also restore cellular daunomycin retention in MDR-P388 cells to the levels found in the Par-P388 cells. SDZ 280-446 was also effective as a chemosensitiser when given orally in vivo. In a syngeneic mouse model, combined therapy with vinca alkaloids given i.p. and SDZ 280-446 given per os for 5 consecutive days significantly prolonged the survival of MDR-P388 tumour-bearing mice, when compared with mice receiving vinca alkaloids alone. Another protocol, using three cycles of i.p. doxorubicin at 4 day intervals, could also not increase MDR-P388 tumour-bearing mouse survival unless the mice received SDZ 280-446 orally 4 h before each doxorubicin injection. Though only very few combined therapy treatment protocols have been tested so far, clear increases in survival time of MDR-tumour-bearing mice were regularly obtained, leaving hope for major improvement of the therapy using other dosing schedules.

Multidrug resistance protein-mediated transport of chlorambucil and melphalan conjugated to glutathione.

The human multidrug resistance protein (MRP1) confers resistance of cells to a number of different cytostatic drugs and functions as an export pump for glutathione S-conjugates, glucuronides and other amphiphilic anions. The present study details for the first time MRP1-mediated ATP-dependent transport of various glutathione S-conjugates of the bifunctional alkylating agents chlorambucil and melphalan. In membrane vesicles prepared from cells expressing recombinant MRP1, the conjugates were transported at rates in the following order: monoglutathionyl chlorambucil > bisglutathionyl chlorambucil > monohydroxy monoglutathionyl chlorambucil and monoglutathionyl melphalan > monohydroxy monoglutathionyl melphalan. In addition, we show that membranes from chlorambucil-resistant GST-alpha-overexpressing CHO cells as well as from their parental cells express the hamster homologue of MRP1. With both CHO cell membrane preparations, we observed ATP-dependent transport of monoglutathionyl chlorambucil and of leukotriene C4, a glutathione S-conjugate and high-affinity substrate of MRP1. The transport rates measured in the resistant cells were only two- to three-fold higher than those measured in the control cells. These results together with cytotoxicity assays comparing MRP1-overexpressing cell pairs with the CHO cell pair indicate that, although MRP1-mediated transport is active, it may not be the rate-limiting step in chlorambucil resistance in these cell lines.