Brigitte Kircher

Modulation of the Biological Properties of Aspirin by Formation of a Bioorganometallic Derivative

Despite recent advances in modern tumor therapy the development of effective drugs remain a challenge for medicinal chemists. The demand for innovative agents triggers interest in novel chemical strategies and new concepts for modern drug design. The vast majority of drugs used to date are purely “organic” compounds. However, stimulated by the tremendous success of the inorganic compound cisplatin in modern tumor therapy, interest in the development of other metal complexes has been rapidly growing. Bioorganometallic chemistry is a novel emerging field in medicinal chemistry, which aims at probing the biological (and therapeutic) potential of organometallic compounds. As a result of their different coordination geometries, chemical properties, and reactivities, metal complexes offer a wide spectrum of functional groups more or less unexplored in modern drug design and development. The hexacarbonyldicobalt moiety Co2(CO)6 bound to an alkyne, is one such functional group, for which promising results on medical applications have been reported. For example, Co2(CO)6 derivatives of antiepileptic drugs (e.g. carbamazepine) were used as diagnostic tools in the so-called carbonyl metallo immuno assay (CMIA), and complexes with fructopyranose, nucleoside, and neuropeptide ligands displayed interesting bioactivities. We have recently reported on alkyne hexacarbonyldicobalt species with promising antiproliferative properties. Interestingly, the cell growth inhibitory activity of the complexes depended strongly on the chemical structure of the alkyne ligand. Weakly active and inactive derivatives showed that the cobalt cluster does not cause general (unspecific) cytotoxic effects. In further studies the Co2(CO)6 complex of the aspirin (o-acetylsalicylic acid, ASS) derivative prop-2-ynyl-2-acetoxybenzoate (Co-ASS) emerged as a lead compound for this class of antiproliferative agents.

Phenotype Frequencies of Autosomal Minor Histocompatibility Antigens Display Significant Differences among Populations

Minor histocompatibility (H) antigens are allogeneic target molecules having significant roles in alloimmune responses after human leukocyte antigen–matched solid organ and stem cell transplantation (SCT). Minor H antigens are instrumental in the processes of transplant rejection, graft-versus-host disease, and in the curative graft-versus-tumor effect of SCT. The latter characteristic enabled the current application of selected minor H antigens in clinical immunotherapeutic SCT protocols. No information exists on the global phenotypic distribution of the currently identified minor H antigens. Therefore, an estimation of their overall impact in human leukocyte antigen–matched solid organ and SCT in the major ethnic populations is still lacking. For the first time, a worldwide phenotype frequency analysis of ten autosomal minor H antigens was executed by 31 laboratories and comprised 2,685 randomly selected individuals from six major ethnic populations. Significant differences in minor H antigen frequencies were observed between the ethnic populations, some of which appeared to be geographically correlated.

Impact of natural killer cell dose and donor killer-cell immunoglobulin-like receptor (KIR) genotype on outcome following human leucocyte antigen-identical haematopoietic stem cell transplantation.

To define the role of quantitative graft composition and donor killer‐cell immunoglobulin‐like receptor (KIR) genotype in clinical outcome following unmanipulated peripheral blood stem cell transplantation (PBSCT) from human leucocyte antigen (HLA)‐identical siblings, 43 consecutive transplants for haematological malignancies were analysed retrospectively. Twenty‐four patients underwent myeloablative conditioning and 19 received busulphan/fludarabine‐based reduced intensity conditioning (RIC). In patients with acute myelogenous leukaemia or myelodysplastic syndrome (AML/MDS; n = 18), no relapse occurred following transplants meeting both a high (above median) natural killer (NK) cell count and missing HLA‐ligand(s) to donors KIR(s), compared to all other AML/MDS patients (0% versus 44%; P = 0·049). Missing HLA‐B and/or HLA‐C ligand combined with missing HLA‐A3/11 (KIR3DL2 unblocked) predicted for reduced relapse incidence regardless of diagnosis or conditioning type (P = 0·028). Moreover, in AML/MDS patients, this constellation predicted superior overall survival (OS) (P = 0·046). Transplants with more than two different activating donor KIRs were associated with an increased risk for non‐relapse mortality (NRM), both by univariate and multivariate analysis. Quantitative graft composition had a significant impact exclusively in RIC transplants. Here, a trend towards reduced relapse incidence was found in patients receiving high numbers of NK cells (16% versus 54%; P = 0·09). In patients receiving high versus low T cell numbers, OS was superior (83% versus 37%; P = 0·01), due mainly to reduced NRM (0% versus 33%; P = 0·046). By multivariate analysis, relapse risk was decreased significantly in patients receiving high NK cell numbers (P = 0·039). These data suggest that both the number of transplanted NK cells and the donor KIR genotype play a role in graft‐versus‐malignancy mechanisms in HLA‐identical PBSCT.

Synthesis and Biological Activities of Transition Metal Complexes Based on Acetylsalicylic Acid as Neo-Anticancer Agents

[(μ(4)-η(2))-(Prop-2-ynyl)-2-acetoxybenzoate]dicobalthexacarbonyl (Co-ASS), a derivative of aspirin (ASS), demonstrated high growth-inhibitory potential against various tumor cells with interference in the arachidonic acid cascade as probable mode of action. The significance of the kind of metal and cluster was verified in this structure-activity study: Co(2)(CO)(6) was respectively exchanged by a tetrameric cobalt-, trimeric ruthenium-, or trimeric ironcarbonyl cluster. Furthermore, the metal binding motif was changed from alkyne to 1,3-butadiene. Compounds were evaluated for growth inhibition, antiproliferative effects, and apoptosis induction in breast (MCF-7, MDA-MB 231) and colon cancer (HT-29) cell lines and for COX-1/2 inhibitory effects at isolated isoenzymes. Additionally, the major COX metabolite prostaglandin E2 (PGE(2)) was quantified in arachidonic acid-stimulated MDA-MB 231 breast tumor cells. It was demonstrated that the metal cluster was of minor importance for effects on cellular activity if an alkyne was used as ligand. Generally, no correlation existed between growth inhibition and COX activity. Cellular growth inhibition and antiproliferative activity at higher concentrations of the most active compounds Prop-ASS-Co(4) and Prop-ASS-Ru(3) correlated well with apoptosis induction.

Donor cytomegalovirus seropositivity and the risk of leukemic relapse after reduced-intensity transplants

Abstract:  Objectives: Despite effective preemptive and prophylactic therapeutic strategies, cytomegalovirus (CMV) seropositivity of either recipient and/or donor still remains an important parameter for outcome even after reduced‐intensity allogeneic stem cell transplantation (SCT). Whether CMV seropositivity of the donor might have an impact on leukemic relapse is unknown. Patients: Between June 1999 and February 2004 48 patients ineligible for conventional allotransplantation underwent reduced‐intensity transplants at our institution. Twenty‐seven (56%) patients had a CMV‐seropositive donor. Results: While donor CMV seropositivity had no effect on overall survival, having a CMV‐seropositive donor was associated with a significantly lower risk for relapse (20% vs. 52%, P = 0.02). The beneficial effect of a CMV‐seropositive donor, however, was offset by a higher transplant‐related mortality (42% vs. 19% in patients with a CMV‐seronegative donor, P = 0.2). Donor CMV serostatus had no effect on the incidence of CMV infection/disease, and acute or chronic graft‐vs.‐host disease. Overall, 27 patients died during the observation period. Causes of death in patients with a CMV‐seropositive donor were primarily transplant‐related (11 vs. 4 in patients with CMV‐seronegative donors), whereas leukemic relapse was the leading cause of death in patients with a CMV‐seronegative donor (8 vs. 4 in patients with a CMV‐seropositive donor, P = 0.038, chi‐squared test). Multivariate Cox regression analysis showed risk category by the underlying disease and donor CMV seropositivity to be significant predictors of leukemic relapse following reduced‐intensity transplants. Conclusions: These preliminary results suggest a possible role of donor CMV serostatus on the risk of relapse following reduced‐intensity allogeneic SCT.

Anti-leukemic activity of valproic acid and imatinib mesylate on human Ph+ ALL and CML cells in vitro

The armamentarium of anti‐leukemic drugs has increased substantially since anti‐leukemic activities were recently found for a variety of non‐classical cytostatic drugs, among them the histone deacetylase (HDAC) inhibitor valproic acid (VPA). This study investigated the effect of VPA on proliferation and apoptosis of human Philadelphia chromosome‐positive (Ph+) acute lymphatic (ALL) and chronic myeloid leukemia (CML) cells and on colony formation of human chronic‐phase CML progenitor cells. Strong anti‐proliferative and pro‐apoptotic effects of VPA were observed on human ALL and CML cell lines at concentrations achievable in vivo. These effects were most pronounced in ALL cell lines as well as in primary ALL cells. Notably, VPA revealed enhanced activity with imatinib mesylate, nilotinib, the farnesyl transferase inhibitor SCH66336, interferon‐alpha and cytosine arabinoside. VPA inhibited the growth of colony‐forming cells from 12 Ph+ chronic‐phase CML patients but also of those from normal healthy controls in a dose‐dependent fashion. HDAC‐inhibiting activity of VPA was confirmed on ALL and CML cells. In conclusion, VPA, whether alone or in combination with other non‐classical anti‐leukemic compounds, exerts significant anti‐leukemic effects on human ALL and CML cells.

Hematopoietic lineage-restricted minor histocompatibility antigen HA-1 in graft-versus-leukemia activity after donor lymphocyte infusion.

Immunocompetent alloreactive donor lymphocytes directed against minor histocompatibility antigens are supposed to be responsible for graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) activity after allogeneic stem cell transplantation. The authors describe the detection of HA-1-specific T cells by peptide-loaded dimers and flow cytometry in the peripheral blood of a patient in complete remission but without GvHD after donor lymphocyte infusion for chemotherapy-resistant Philadelphia chromosome-positive acute lymphoblastic leukemia. The HA-1-specific T cells were sorted and an alloreactive, polyclonal T-cell line with specific lytic activity against HA-1-positive target cells, including leukemic cells, was established. Although P190 bcr/abl peptide-specific CD8positive T cells were detected in the peripheral blood at the same time, these T cells could not be expanded. Furthermore, no P190 bcr/abl peptide-specific T-cell response could be induced in vitro, even when peptide-loaded dendritic cells were used as stimulator cells. The authors conclude that in the absence of GvHD, HA-1-specific rather than P190 bcr/abl-specific T cells are responsible for ongoing GvL activity.

Synthesis and in vitro pharmacological behavior of platinum(II) complexes containing 1,2-diamino-1-(4-fluorophenyl)-2-alkanol ligands.

In continuation of our effort to optimize the pharmacological profile of [1,2-diamino-1,2-bis(4-fluorophenyl)ethane]dichloridoplatinum(II) complexes, we synthesized [1,2-diamino-1-(4-fluorophenyl)alkanol]dichloridoplatinum(II) analogs. The aim of this study was to evaluate the influence of hydroxyl groups at the C2 moiety on aqueous solubility, lipophilicity, cellular platinum accumulation, and cytotoxicity against MDA-MB-231, U-937, RAJI, and SC-1 cells as well as against cisplatin-sensitive and cisplatin-resistant A2780 and A2780cisR ovarian carcinoma cells. As expected, the OH groups improved the water solubility and decreased the lipophilicity of the neutral ligands, resulting in complexes with favorable pharmacokinetic properties. The cellular uptake of the compounds in MDA-MB-231 and U-937 cells proved to depend on the configuration and showed only a slight correlation with lipophilicity. The most active complexes were R,R/S,S configured, which points to a carrier-mediated mode of action. [threo-1,2-Diamino-1-(4-fluorophenyl)propan]dichloridoplatinum(II) and [threo-2,3-diamino-3-(4-fluorophenyl)propan-1-ol]dichloridoplatinum(II) possessed only low cross-resistance to cisplatin and were up to 10-fold more active in lymphoma cell lines.

Alkyne hexacarbonyl dicobalt complexes in medicinal chemistry and drug development

Background: Organometallic alkyne complexes of the hexacarbonyl dicobalt type (hexacarbonyl[µ-h4-(alkyne)]dicobalt (Co – Co) complexes) are an interesting class of compounds used in modern synthetic chemistry and an increasing number of reports deal also with the use of these complexes in the field of medicinal chemistry. Methods: This review highlights the applications of alkyne hexacarbonyl dicobalt species in biomedical research with a focus on anticancer drug development. Medline, Pubmed, Scifinder and Espacenet internet databases were searched for available literature and patents. Results/conclusion: Preclinical studies on hexacarbonyl dicobalt complexes containing various alkyne (bio)ligands demonstrated a high potential for application (e.g., as antitumor drugs, hormonally active or diagnostic agents). The biological properties of the compounds were mainly determined by the nature of the ligands and the presence of the metal center.

Effects of Metal Salophene and Saldach Complexes on Lymphoma and Leukemia Cells

Schiff base transition metal complexes are an important class of compounds with great potential for therapeutic interventions. However, data on antileukemic and antilymphoma effects of these complexes are limited. The activity of N,N′‐bis(salicylidene)‐1,2‐phenylenediamine (salophene, 1), its iron(II/III) and manganese(II/III) complexes as well as rac‐trans‐N,N′‐bis(salicylidene)‐1,2‐cyclohexanediamine (saldach, 2) and its respective iron(II/III) complexes was evaluated against U‐937 non‐Hodgkins lymphoma and the HL‐60, SUP‐B15, and K‐562 leukemia cell lines. The free ligands induced in all cell lines, if at all, only marginal, concentration‐dependent growth inhibitory effects, and did not trigger Cu/Zn superoxide dismutase (Cu/Zn SOD) release or induce apoptosis. [FeII(salophene)] (3) and [FeIII(salophene)Cl] (4) blocked cellular growth, caused a strong release of Cu/Zn SOD and induced apoptosis. In contrast, the manganese analogs [MnII(salophene)] (5) and [MnIII(salophene)OAc] (6) inhibited cell growth, caused the programmed cell death only at higher concentrations and did not provoke release of Cu/Zn SOD in any of the four cell lines. Weaker cell death‐promoting effects were observed when the salophene moiety of 3 and 4 was replaced with saldach (complexes 7 and 8), indicating the influence exerted by the ligand structure. In conclusion, Schiff base transition metal complexes induce strong inhibitory effects on human lymphoma and leukemia cells.