Aureobasidins: structure-activity relationships for the inhibition of the human MDR1 P-glycoprotein ABC-transporter.

Cyclic depsipeptide cyclo-[D-Hmp(1)-L-MeVal(2)-L-Phe(3)-L-MePhe(4)-L-Pro(5)-L-aIle+ ++(6)-L-MeVal(7)-L-Leu(8)-L-betaHOMeVal(9)], the antifungal antibiotic aureobasidin A (AbA), was reported to interfere with ATP-binding cassette (ABC) transporters in yeast and mammalian cells, particularly the MDR1 P-glycoprotein (Pgp), a transmembrane phospholipid flippase or "hydrophobic vacuum cleaner" that mediates multidrug resistance (MDR) of cancer cells. In a standardized assay that measures Pgp function by the Pgp-mediated efflux of the calcein-AM Pgp substrate and uses human lymphoblastoid MDR-CEM (VBL(100)) cells as highly resistant Pgp-expressing cells and the cyclic undecapeptide cyclosporin A (CsA) as a reference MDR-reversing agent (IC(50) of 3.4 microM), AbA was found to be a more active Pgp inhibitor (IC(50) of 2.3 microM). Out of seven natural analogues and 18 chemical derivatives of AbA, several were shown to display even more potent Pgp-inhibitory activity. The Pgp-inhibitory activity was increased about 2-fold by some minor modifications such as those found in the naturally occurring aureobasidins AbB ([D-Hiv(1)]-AbA), AbC ([Val(6)]-AbA), and AbD [gammaHOMeVal(9)]-AbA). The replacement of the [Phe(3)-MePhe(4)-Pro(5)] tripeptide by an 8-aminocaprylic acid or the N(7)()-desmethylation of MeVal(7) led to only a 3.3-fold decreased capacity to inhibit Pgp function, suggesting that the Pgp inhibitory potential of aureobasidins, though favored by the establishment of an antiparallel beta-sheet between the [D-Hmp(1)-L-MeVal(2)-L-Phe(3)] and [L-aIle(6)-L-MeVal(7)-L-Leu(8)-] tripeptides, does not critically depend on the occurrence of the [L-Phe(3)-L-MePhe(4)-L-Pro(5)-L-aIle(6)] type II' beta-turn secondary structure. In contrast, the most potent Pgp inhibitors were found among AbA analogues with [betaHO-MeVal(9)] residue alterations, with some data suggesting a negative impact of the [L-Leu(8)-L-betaHOMeVal(9)-D-Hmp(1)] gamma-turn secondary structure on Pgp inhibitory potential. The [2,3-dehydro-MeVal(9)]-AbA was the most potent Pgp inhibitory aureobasidin, being 13-fold more potent than AbA and 19-fold more potent (on a molar basis) than CsA. Finally, there was no correlation between the SAR for the human MDR1 Pgp inhibition and the SAR for Saccharomyces cerevisiae antifungal activity, which is mediated by an inositol phosphoceramide synthase activity.

The potent immunosuppressive cyclosporin FR901459 inhibits the human P-glycoprotein and formyl peptide receptor functions.

By sequestering cytosolic calcineurin into a molecular complex with cyclophilin and its consequent T-cell dysfunction, some cyclosporins, such as CsA and FR901459 ([Thr2-Leu5-Leu10]-CsA), display potent immunosuppressive activity. Independently on this property, cyclosporins may display one or more other biological activities mediated by interaction with cell surface glycoproteins. Several cyclosporins inhibit the function of human MDRI-encoded P-glycoprotein (Pgp), a flippase known to cause cancer multidrug resistance, but also expressed by some normal immunocompetent cells and by normal epithelial cells which control drug bioavailability in vivo. CsA is known to be a potent Pgp inhibitor with a 3.2 microM IC50 in an assay where the most potent derivative SDZ PSC 833 gives a 0.49 microM IC50. FR901459 is now shown to be a good Pgp inhibitor, being 2-fold weaker only (IC50 of 6 microM) than CsA. Some cyclosporins may also inhibit the function of the human FPR1-encoded formyl peptide receptor (FPR), a chemotactic receptor whose absence is known to impair antibacterial immunity. Yet this inhibition is very weak for all, but one of them, CsH, whose 0.15 micro/M IC50 makes it a much more potent FPR inhibitor than CsA (IC50 >10 microM in the same assay). FR901459 is now shown to be a very potent inhibitor of FPR function (IC50 of 0.6 microM). Since CsH shows little Pgp-inhibitory activity and has no known immunosuppressive activity, FR901459 displays a unique pharmacological profile: like CsA, it inhibits T-cell function; less than CsA, it can inhibit Pgp function on selected leukocyte subsets and on epithelial barriers known to control drug bioavailability; however, much more efficiently than CsA, it can inhibit the FPR function, a receptor involved in some leukocytic inflammatory responses to chemotactic peptides.

The MultiScreen filtration system to measure chemoattractant-induced release of leukocyte granule enzymes by differentiated HL-60 cells or normal human monocytes.

A variety of chemoattractants initiate chemotaxis by selective binding to chemoattractant receptors (CARs), a subfamily of seven transmembranous G-protein coupled receptors (7TM-GPCRs) expressed in the leukocyte plasma membrane. Whatever the chemoattractant, signaling leading to chemotaxis involves several common biological steps which occur within seconds to minutes of CAR ligand binding. Though each step can be used to study the progress of the chemotaxis activation process. only certain biological events are suitable for monitoring chemotaxis signaling on large sample numbers as required for drug screening. An example of such is the release of granule enzymes by leukocytes in response to a CAR ligand. In this study, promyelocytic HL-60 cells were employed to set up a 96-well microplate methodology using filtration instead of centrifugation to collect the extracellular fluid together with the cell-released enzymes. Undifferentiated HL-60 cells were found not to respond to any of the CAR ligands. With various types of HL-60 cells which had differentiated along the neutrophilic or monocytic pathways, a large enzyme release was dose-dependently triggered by fMLF or C5a, but none of the tested CC or CXC chemokines. The highest responsiveness was found for neutrophilic HL-60 cells differentiated with dibutyryl cyclic AMP. With normal human monocytes (prepared from the blood of healthy donors by leukapheresis and elutriation), the granule enzyme release response was large to fMLF or C5a, substantial to MCP-1, low to RANTES or MIP-1alpha, but insignificant to Eotaxin, IL-8 and GROalpha. The method readily measures N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase and elastase activities, and requires approximately five times fewer cells than classical methods, a very important feature when normal human cells are to be used in screening assays. The method was also adapted to large scale screening of antagonists such as cyclosporins A and H for fMLF-mediated signaling using HL-60 cells and monocytes, and truncated (9-76) MCP-1 for MCP-1-mediated signaling using monocytes.

Valspodar: current status and perspectives.

Valspodar (Amdray, SDZ PSC 833) is derived from cyclosporin, but lacks the immunosuppressive and most of the collateral activities of cyclosporin A (CsA, Sandimmune, Neoral); it exhibits an enhanced capacity to chemosensitise tumour cells showing the classical type multiple drug-resistance (MDR) associated with MDR1 P-glycoprotein (Pgp) overexpression. This valspodar-mediated chemosensitisation of MDR tumour cells is reviewed with regard to its mechanism of inhibition on Pgp flippase function, and its potential inhibition of anticancer drug (ACD) metabolisation by CYP3A enzymes is discussed. Potent inhibition of the membranous and cytoplasmic detoxification mechanisms expressed by cells at the absorption and clearance borders in the body by valspodar results in the many pharmacokinetic interactions with other drugs that are substrates of either, or both, Pgp and CYP classes of detoxifying enzyme. In view of the present ability to restrict oral bioavailability of valspodar within a narrow range, and to adapt adequately the chemotherapeutic dosages to achieve their equivalent exposure in the presence or absence of valspodar, current clinical data on its efficacy and safety permit optimism for ongoing Phase III trials. The potential of valspodar to increase exposure or to modulate the biodistribution of other chemotherapeutics, such as HIV protease inhibitors to the brain, is further evoked, as this might become another application of the new drug. This evaluation of valspodar compared to CsA attempts to interpret its mechanisms of action, rather than to serve as a complete and comparative repertoire of all published preclinical and clinical data.

The abamectin derivative ivermectin is a potent P-glycoprotein inhibitor.

Among the compounds endowed with the capacity to reverse the P-glycoprotein (Pgp)-mediated multidrug resistance of cancer cells, a powerful agent was found to be the cyclosporin D derivative SDZ PSC 833. After in vivo treatment with SDZ PSC 833, mice showed a decreased tolerability to cyclosporin A (CsA), but also to ivermectin, a widely used polycyclic lactone pesticide of Streptomyces avermitilis origin. The sequels were suggestive of CsA- or ivermectin-induced central nervous system dysfunction; they were interpreted as caused by the neutralization of the Pgp at the blood-brain barrier level, implying that CsA and ivermectin were Pgp substrates. CsA was already known to display both Pgp substrate and Pgp inhibitor properties. It now appears that ivermectin may also inhibit Pgp function. When compared in short-term assays for Pgp function inhibition, which measure the restoration of the retention of two Pgp probes in multidrug-resistant (MDR) cells to their parental (Par) cell levels, ivermectin appeared only a few fold weaker that SDZ PSC 833 in the case of murine monocytic leukemia MDR-P388 cells and nearly as active as SDZ PSC 833 in the case of human lymphocytic leukemia MDR-CEM cells. Therefore, like CsA or FK-506, ivermectin may also be a substrate and an inhibitor of Pgp.

Ranking of P-glycoprotein substrates and inhibitors by a calcein-AM fluorometry screening assay.

In order to compare the capacities of a variety of compounds to interfere with P-glycoprotein (Pgp) function, a novel assay was set up to work on a large screening scale. The model assay measures the capacity of parental sensitive (Par) and multidrug-resistant (MDR) cells to efflux a small fixed amount of acetoxymethyl calcein (calcein-AM) after their pretreatment with concentration ranges of known Pgp modulators. This microplate cytometry-based assay was performed with two different pairs of cell lines, the human lymphocytic leukemia CEM cells and the murine monocytic leukemia P388 cells. For a given Pgp-expressing MDR cell line, a Pgp modulator EC50 was defined as the concentration required to restore half of the calcein retention shown by similarly treated Par cells. With both MDR-P388 and MDR-CEM cells, EC50 comparisons ranked five reference Pgp modulators as follows: SDZ 280-446 > SDZ PSC 833 > cyclosporin A > verapamil > vinblastine. Further use of the MDR-CEM cells could rank 15 Pgp modulators for their capacity to interfere with calcein-AM efflux as follows: SDZ 280-446 1.9 x > SDZ PSC 833 8.3 x > cyclosporin A 3.8 x > amiodarone 1.1 x > quinacrine 1.6 x > verapamil 1.4 x > quinidine 1.1 x > vinblastine 11 x > vincristine 2 x > chloroquine > beta-lumicolchicine > or = gamma-lumicolchicine > or = colchicine > etoposide > or = doxorubicin. This calcein-AM assay should open the way for ranking large numbers of novel structures for their potential Pgp modulator properties, particularly for an efficient screening of Pgp function antagonists, but it does not allow defining whether their inhibition may be competitive or not.

Detection of P-glycoprotein expression by tumoral cells with NBDL-CsA, a fluorescent derivative of cyclosporin A.

The P-glycoprotein (P-gp) molecules which are expressed on multidrug-resistant (MDR) tumor cells efflux a variety of anti-cancer drugs, such as doxorubicin. Though first described as an inhibitor of P-gp function, cyclosporin A (CsA) was more recently shown to behave as a substrate of the P-gp pump. The retention of [3H]CsA was reduced in MDR cells of the human leukemic CEM cell subline, in comparison with the drug-sensitive parental (Par) subline. MDR-CEM cell treatment by the P-gp blockers restored the [3H]CsA retention to the control Par-CEM cell levels. Using a novel fluorescent CsA derivative, [N-epsilon-(4-nitrobenzofurazan-7-yL)-D-Lys8] cyclosporin (NBDL-CsA), we now show that MDR cells can be distinguished from Par cells both at the cell population level (in microculture) and at the single cell level (by use of flow cytometry).

Decreased biotolerability for ivermectin and cyclosporin A in mice exposed to potent P-glycoprotein inhibitors.

SDZ PSC 833 or SDZ 280-446 are strong blockers of the function of class I mdr gene-encoded P-glycoprotein molecules, which were developed for the reversal of multi-drug-resistance of tumor cells. When treated with such drugs, normal mice may display hypersensitivity to cyclosporin A and ivermectin. The recorded signs of acute toxicity are compatible with alterations of the murine central nervous system functions and with earlier data suggesting that P-glycoprotein expressed at the murine blood-brain barrier might be involved in the exclusion of cyclosporin A or ivermectin from brain tissue.

Decreased uptake of cyclosporin A by P-glycoprotein (Pgp) expressing CEM leukemic cells and restoration of normal retention by Pgp blockers.

The P-glycoprotein (Pgp) molecules which are expressed on multidrug resistant (MDR) tumor cells can efflux a variety of cytostatics. In both normal and tumoral epitheliums, Pgp molecules are selectively expressed on the apical surface of the epithelial cells. Such a distribution seems to be responsible for the transcellular transport of Pgp substrates, including cyclosporin A (CsA), from the basal to the apical side. Some normal lymphoid cells also express small amounts of Pgp molecules, for as yet unknown functions. Nevertheless, the sensitivity of their mitogen-induced proliferation to cytostatics, including doxorubicin and CsA, could be increased by the Pgp blockers. Using isotopically-labeled CsA and tumoral lymphoid cell lines, we now show a higher CsA retention in Pgp-lacking parental ('Par') cells than in Pgp-expressing MDR cells. The Pgp blockers can restore the CsA retention in the MDR cells to its level in the Par cells.

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.

Development of grafted gld cells in athymic and euthymic recipients.

Mice homozygous for the gld (generalized lymphoproliferative disease) and lpr (lymphoproliferation) mutations display similar autoimmune and lymphoproliferative diseases. Both result from defective apoptosis, the targets of the lpr and gld mutations being the genes for, respectively, an apoptosis-signalling receptor [the Fas antigen receptor (FasR)] and its counter-receptor [the Fas ligand (FasL)]. Though this definitely causes the development and accumulation of large numbers of unusual Thy-1+ B220+ cells in peripheral lymphoid organs, details on how this actually occurs are still lacking. Whether differentiation of gld T cells into Thy-1+ B220+ cells might depend on the environment was analysed by phenotyping the cells which expanded in four different immunodeficient environments (nubg, nulpr, scid and scidbg). Though all four types of congenic chimeras developed hyperglobulinaemia, autoimmunity and a lymphoproliferative disease, substantial differences were found for the athymic and euthymic chimeras. In the athymic gld chimeras, the lymphoproliferation concerned all cell subsets, whereas in the euthymic gld chimeras it was, as in gld mice, due to the accumulation of cells of the Thy-1+ B220+ subset. Thus, the gld T cells could proliferate without differentiating into the Thy-1+ B220+ subset, but this depended on the nature of the environment. Furthermore, emergence of a gld syndrome in these four environments would suggest that B cells and stromal cells do not express FasL, at least in levels sufficient to compensate for the deficiency of the grafted gld cells.

Serological abnormalities induced by engraftment of viable motheaten hematopoietic cells in nude beige recipients.

C57BL/6J (B6) mice homozygous for the viable motheaten (mev) mutation are short-lived and display severe immunodeficiency, autoimmunity and inflammatory disease. B6 mice doubly homozygous for the nude (nu) and beige (bg) mutations (nubg mice) are also short-lived and immunodeficient. Nevertheless, grafts of mev lympho-hematopoietic cells increased life expectancy of nubg recipients. Such [mev --> nubg] chimeras did not develop any mev-like inflammatory pathology but showed autoimmunity features, particularly hyperglobulinemia which, unlike the mev one, was due to IgG rather than IgM. Serological studies of [mev IgHb --> nubg Igha] chimeras surprisingly revealed the exclusive host B-cell origin of the IgG2a overproduced by these chimeras. Yet, about half of such chimera serum IgM being IgMb, mev B cells had actually engrafted the nubg hosts. Together with the lack of transfer of the inflammatory pathology, this suggests that a non-mev environment might succeed acting as a regulator of some mev-induced dysfunctions.

Interactions of B6 wild and B6 gld cells engrafted within athymic nude beige recipients.

The murine gld mutation is targetted to the gene coding for the ligand of the Fas receptor for apoptosis. Gld mice display a lymphoproliferative and autoimmune syndrome that can be transferred in both irradiated euthymic wild and athymic beige (nubg) recipients. In order to test whether a supply of normal wild cells could correct the development of the gld syndrome, nubg mice were grafted with mixtures of gld and wild spleen cells from congenic donors which differed for the allotypes of the T-cell Thy1 membrane glycoprotein and/or of the B-cell Ig heavy chain. In the nubg chimeras, the wild spleen cells could down-regulate the hyperactivation of the B cells and the proliferation of the gld T cells, but this was not due to total eradication of the gld T-cell subset. Since this occurred in an athymic recipient, the correction of the gld syndrome did not require wild stem cell differentiation within a thymic environment, but should only depend on a sufficient Fas ligand supply by normal wild cells. Since the gld cells could proliferate in the nubg environment, the nubg environment could not provide sufficient Fas ligand to regulate the gld cell proliferation. Thus, the nubg B cells might lack Fas ligand expression, or express it but to a lower extent that T cells.

Influence of the lpr environment on the lymph node cell phenotypes in C57BL/6 nubg and nulpr chimeras.

Mice homozygous for the lpr gene show a marked lymphoproliferative syndrome. Most T cells which accumulate in their lymphoid organs belong to a fairly unusual subpopulation. Although being CD44+ T cells expressing neither CD4 nor CD8, they are CD3 T-cell receptor (TCR) alpha beta positive and express both Thy-1 and B220, the B-cell form of the CD45 marker. To support engraftment and development of transferred lpr lymphomyeloid cells, athymic recipients must be genetically lpr. While nude/beige (nubg) recipients do not allow the development of any lymphoproliferative syndrome, this is variable in nude/lpr (nulpr) recipients, and the genotypic origin of the proliferating lymphocytes in nulpr recipients is unclear. In this study, the surface phenotype of lymph node cells from nulpr recipients of lpr grafts ([lpr-->nulpr] chimeras) was analysed by flow cytometry, and compared with various chimeras and parental (donor and recipient) strains as controls. Abnormal cells of the lpr type were not detectable either in [lpr-->nubg] chimeras or in [wild-->nubg] controls. Absence of lpr cells was also seen in neonatal lpr thymus-grafted nubg mice engrafted previously with lpr haematopoietic cells. In contrast, a substantial emergence of double-positive B220+ Thy-1+ cells occurred in [lpr-->nulpr] chimeras, together with high levels of CD4+ cells, a substantial fraction of which might express B220. Finally, in thymus-grafted nulpr mice, the levels of B220+ Thy-1+ cells were as high as in lpr mice and there was again an expansion of CD4+ (potentially B220+) cells. Abnormality of the nulpr haemopoietic environment was also shown by the low percentages of T cells, particularly CD8+ cells, in short-lived [wild-->nulpr] chimeras. Taken together, our results underline the differences between the nubg and nulpr environments.

Modulation of human P-glycoprotein epitope expression by temperature and/or resistance-modulating agents.

Three monoclonal antibodies (mAb), MRK16, MM4.17 and MC57, directed against distinct epitopes on the external domain of human P-glycoprotein (Pgp), were used to follow its expression on multidrug resistant (MDR)-cells. The linear MM4.17 epitope and conformational MRK16 epitope showed a 4-fold higher expression at 37 degrees C than at 4 degrees C, while the detection of the conformational MC57 epitope did not change. Inhibition of Pgp function, by a short pretreatment of the MDR-cells with resistance-modulating agents (RMA), such as SDZ PSC 833 and SDZ 280-446, could not be related to depletion of Pgp from the cell surface, since their expression of the MM4.17 and MRK16 epitopes was found unchanged. However, a substantially higher expression of MC57 epitopes was found on RMA-treated cells than on untreated ones. Since this effect correlated to the strength of different RMA in reversing the MDR phenotype, MC57 epitopes might be more efficiently expressed on inactivate(d) forms of the Pgp molecules, suggesting that RMA might inhibit Pgp function by disturbing the conformation of individual Pgp molecules, their topographical distribution or polymerization status in the membrane.

The Yaa gene-dependent B-cell deficiency worsens the generalized lymphadenopathy and autoimmunity of C57BL/6-gld male mice.

The BXSB mice are unique among murine models for systemic lupus erythematosus in that males are much more severely affected than females. The BXSB male disease is associated with a Y-chromosome-linked gene, which is an autoimmunity accelerator gene (Yaa). The Yaa mutation affects the B-cell subset, which becomes hyper-responsive to T-cell signals. The Yaa mutation was combined to the generalized lymphadenopathy disease (gld) gene in order to know whether an additional intrinsic B-cell defect might enhance gld disease in the male mice. The B6-gld-Yaa male mice were shown to display earlier and exacerbated lymphoproliferative and autoimmune features. It appeared that the milder gld syndrome observed in B6-gld male mice with a normal Y-chromosome was dependent on the mechanisms of B-cell activation and that the B cells could also accelerate the lymphoproliferation and the differentiation of T cells into Thy-1+ B220+ cells.

Myeloid and lymphoid cell alterations in normal mice exposed to chemotherapy with doxorubicin and/or the multidrug-resistance reversing agent SDZ PSC 833.

The cyclosporin SDZ PSC 833 (PSC) is a potent in vivo chemosensitizer for tumor cells with P-glycoprotein(Pgp)-dependent multidrug resistance (MDR). However, Pgp expression also occurs in CD8+ T cells, NK cells, macrophages and stem cells. In order to find whether PSC might display specific myelotoxicity or potentiate the toxicity of anti-cancer drugs, healthy mice were exposed to single doxorubicin (DOX) and combined (DOX + PSC) chemotherapy protocols known to be near or above the borderline of toxicity for tumor-bearing mice. Mice treated with DOX alone or with (DOX + PSC) showed transient spleen hypoplasia, with a general decrease of all leucocyte lineages and a persistent fall in the numbers of B cells in the bone marrow. In (DOX + PSC)-treated mice, PSC only potentiated the DOX effects without inducing specific depletions of the Pgp-expressing leukocytes (CD8+ and Mac-I+ cells). Hematopoietic cell grafts from normal mice to (DOX +/- PSC)-treated mice did not correct their B-cell lineage deficiency. When lethally irradiated mice were rehabilitated with hematopoietic cells from (DOX +/- PSC)-treated mice (including those with very reduced survival), all chimeras survived for at least 8 months after the cell graft, at which time their leucocyte population profiles were similar to those of control chimeras.

The Yaa mutation induces the development of autoimmunity in mice heterozygous for the gld (generalized lymphadenopathy disease) mutation.

Mice homozygous for either the generalized lymphoproliferative disease (gld) or the lymphoproliferation (lpr) nonallelic mutations develop similar syndromes combining systemic autoimmunity and lymphoproliferative disease. Though essentially recessive, the lpr and gld mutations may be expressed in the heterozygous state: [lpr/+] mice displayed a mild "lpr-like" autoimmunity, and the [lprcg/+ gld/+] mice developed a "gld-like" disorder, showing interactions of the gld gene product with the nonallelic lprcg product. The Y-chromosome-linked autoimmune accelerator (Yaa) mutation being an autoimmunity accelerator, its association with an heterozygous gld gene might also bring a gld-like syndrome. The [gld/+ Yaa] mice were shown here to develop autoimmunity and splenomegaly like [gld/gld] mice, but without their typical lymphadenopathy. Furthermore, the [gld/+ Yaa] splenomegaly was not due to the expansion of the unusual Thy1+ B220+ T-cell subset typical of the gld syndrome, but rather to a polyclonal expansion of the major lymphoid cell subsets. Thus, the syndrome shown by [gld/+ Yaa] mice was not a gld-like syndrome. This suggests that the interactions of the gld gene product with the Yaa product and with the lprcg product must be different.

SDZ 280-125: a cyclopeptolide endowed with an in vitro cyclosporin A-like profile of activity for the reversion of the P-glycoprotein-mediated multidrug resistance of tumor cells.

Tumor cells whose multidrug resistance is caused by the P-glycoprotein (Pgp) mediated anti-cancer drug (ACD) efflux can be chemosensitized by cyclosporins, whose derivatives were found to display a whole range of resistance-modulating activities. Similarly, derivatives of the non-immunosuppressive natural fungus cyclic peptolide SDZ 90-215 were recently shown to display a broad range of chemosensitizing activities. With highly resistant cells expressing high levels of Pgp, one such compound (SDZ 280-125) was shown here to restore both a normal sensitivity to the growth-inhibitory effects of ACD and a normal retention of an anthracycline antibiotic. With both read-outs, SDZ 280-125 activity was about 3-fold that of cyclosporin A (CsA). SDZ 280-125 also displayed the same profile of chemosensitization as CsA for different ACD classes.

Derivatives of a novel cyclopeptolide. 2. Synthesis, activity against multidrug resistance in CHO and KB cells in vitro, and structure-activity relationships.

A series of derivatives of the novel cyclopeptolide 1 was prepared, and their ability to chemosensitize multi drug resistant CHO and KB cells in vitro was evaluated. In contrast to the parent compound, several of the derivatives were found to be highly active. In particular, conversion of the R-lactic acid residue of 1 into its S-isomer via lactone ring cleavage and recyclization with inversion resulted in a marked enhancement of activity. Some of these derivatives (e.g., 15a, SDZ 280.446) belong to the most potent resistance modulating compounds known so far.