Frederick E. Durr

Molecular and biochemical pharmacology of mitoxantrone

Evidence has been presented which indicates that Nv: intercalates DNA and additionally causes inter- and intra-strand crosslinking possibly associated with its charged side arms; there is an apparent preference for G-C base pairs; induces single strand and double strand breaks in DNA; strongly inhibits DNA and RNA synthesis; causes nuclear aberrations and chromosomal scattering; induces a block in the G2 phase of the cell cycle with an increase in cellular RNA and polyploidy; is not cell cycle phase-specific with respect to cell kill; does not induce free-radical formation; does not induce lipid peroxidation or superoxide formation; rather it may inhibit ADR-stimulated lipid peroxidation and microsomal superoxide production; does not appear to have a strong potential for cardiotoxicity on the basis of currently postulated mechanisms of action; is capable of inducing cellular resistance in vitro; resistance is associated with an apparent alteration in the cell membrane impairing drug transport into the cell. Although the precise mechanism(s) of tumor cell killing has not been fully defined it is most likely associated with an interaction by Nv with chromosomes resulting in DNA damage, which if not efficiently repaired, will lead to inhibition of nucleic acid synthesis and eventual cell death.

Development of mitoxantrone

SummaryMitoxantrone (Novantrone®; dihydroxyanthracenedione) belongs to a new structural class of antineoplastic agents, the anthracenediones. It was the outcome of a program in synthetic chemistry, at the Medical Research Division of the American Cyanamid Company, which started from a molecule with structural features predicted to favor intercalation with double stranded DNA.The initial lead compound had immunomodulatory effects and was subsequently found also to possess significant activity against transplantable murine tumors. A large series of analogues was synthesized and mitoxantrone was selected for clinical trial on the basis of its potency and excellent antitumor activity in mice. It is a cytotoxic agent that will kill both proliferating and non-proliferating cells.A variety of experiments conducted with both intact cells and cell-free systems have revealed mitoxantrones ability to bind to single stranded and double stranded RNA and DNA. The drug inhibits cellular RNA and DNA synthesis to about the same extent and causes chromosomal aberrations. In vivo experiments using murine models have demonstrated good activity for mitoxantrone against a variety of transplantable tumors including both leukemias and solid types, in many cases giving putative cures. Surprisingly, it is effective when given up to 30 days before tumor implantation. Combination studies with standard anticancer agents gave evidence of therapeutic synergy in a number of cases.Preclinical studies in several animal models indicate that mitoxantrone does not have the cumulative cardiotoxic liability associated with anthracycline antibiotics such as doxorubicin.

Inhibition of the induction of alloreactivity with mitoxantrone

A clinically active anticancer agent, mitoxantrone (MX): 1, 4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9, 10-anthracenedione dihydrochloride, was studied for its potential inhibitory effect on alloreactivity induction. Addition of MX to mixed lymphocyte cultures (MLC) not only inhibited the proliferative response of lymphocytes to alloantigens but also prevented the generation of cytolytic T lymphocytes (CTL). MX showed a long-lasting effect in vitro and acted at the inductive rather than the effector phase of the CTL response as indicated by its failure to alter the activity of those CTL already generated in MLC. MX also inhibited CTL induction in mice. However, the precursors of CTL appeared to be spared in these animals as supported by limiting dilution analysis and also because CTL could be reactivated by exposure of splenocytes to the same or different alloantigens in MLC. The present findings demonstrate that MX is a potent immunosuppressive agent and as such might prove to be clinically useful in the treatment of autoimmune diseases or find utility in the organ transplantation field.

Low molecular weight immunopotentiators

It has long been recognized that modulation of the immune system by various agents may have potential for the management of certain infectious and neoplastic diseases. Both natural products as well as chemically synthesized compounds have been investigated for immunotherapeutic potential. Over the years, conflicting reports on the clinical efficacy of these agents have left the early promise of immunotherapy unfulfilled. However, the manipulation of the immune system to generate a desired effect is becoming feasible as the mechanisms which regulate the immune network are better understood. Much of the early work on immunotherapy concentrated on the development of immunopotentiators, agents which enhance the hosts own immune system against cancer cells or infectious pathogens. Furthermore, with the development of subunit and/or synthetic vaccines, which are often weakly immunogenic, the importance of developing agents capable of acting as adjuvants became apparent. As a result, the utility of immunopotentiators has now extended to the area of vaccines. There are a number of reviews available on immunomodulators [see Fenichel, R. L. and Chirigos, M. A. (eds) (1984), Immune Modulation Agents and Their Mechanisms, Marcel Dekker, New York]. The purpose of this article is to provide an update on low molecular weight agents capable of potentiating the immunological network. Attention will be given to those agents which have undergone significant clinical development in the areas of cancer, infectious diseases and vaccination over the past several years. These agents will be categorized as to whether they are naturally occurring or chemically synthesized.

Relationship of chemical structures of anthraquinones with their effects on the suppression of immune responses.

A series of 37 anthraquinones were evaluated for their ability to inhibit the induction of cytolytic T-lymphocytes in a mixed lymphocyte culture system, useful as a preliminary screen for immunosuppressive agents. These compounds were also tested for their ability to prevent the production of antibody in mice. It was demonstrated that 1,4-bis [(2-aminoethyl)amino]-5, 8-dihydroxy-9,10-anthracenedione dihydrochloride (AEAD, 2) derived from mitoxantrone (MX, 1) by removing hydroxyethyl groups from both side chains was extremely active in depressing immune responses in vitro and in vivo. Four additional anthraquinones related to AEAD were also identified to share similar suppressive activity. They include a Schiff base, 1,4-dihydroxy-5,8-bis[[2-[(3-pyridinylmethylene)amino]ethyl]amino] -9,10-anthracenedione; a dimer with N-terminals methylated, 1,1-[ethylenebis (iminoethyleneimino)]-bis [5,8-dihydroxy-4-[(2-methylamino-ethyl)amino] anthraquinone tetrahydrochloride; an oxazolidine, 1,4-dihydroxy-5,8-bis [[2-(2-propyl-3-oxazolidinyl)ethyl]amino] anthraquinone; and its polymeric oxazolidine, poly [5,8-dihydroxy-1,4-anthraquinonyleneiminoethylene-3,2-oxazolidine- diyltrimethylene-2,3-oxazolidinediylethyleneimino]. These compounds may warrant further consideration as candidates for the treatment of refractory autoimmune diseases and in organ transplantation.

Induction of alloreactive immunosuppression by 1,4-bis [(2-aminoethyl)amino]-5,8-dihydroxy-9,10-anthracenedione dihydrochloride (CL 232,468)

1,4-bis[2-aminoethyl)amino]-5,8-dihydroxy-9,10-anthracenedione (AEAD) has been investigated for its potential immunosuppressive effect on cell-mediated immune responses. Addition of the compound to mixed lymphocyte cultures (MLC) not only significantly inhibited these cells from responding to alloantigens but also prevented the induction of cytolytic T lymphocytes (CTL). A structurally related compound, mitoxantrone, was also found to be active in inhibiting CTL induction. AEAD had to be present during the first 3 days of a 5-day MLC in order to produce a significant effect and it had no effect on those CTL already generated, suggesting that it acted upon induction of CTL rather than the effector phase. Lymphocytes from mice treated with the compound were incapable of responding to alloantigens in vitro and the effect was dose- and time-dependent. Furthermore, lymphocytes from treated mice were found to inhibit CTL generation from normal mouse lymphocytes, indicating that a suppressor cell population might be induced in the spleens of animals treated with the compound. The present findings clearly demonstrate that AEAD is a compound with potent immunosuppressive activity on alloreactive immune responses.

Development of Resistance and Characteristics of a Human Colon Carcinoma Subline Resistant to Mitoxantrone in vitro

A subline of human colon carcinoma cells (WiDr/R) resistant to the cytotoxic effects of mitoxantrone in vitro, was developed by continuous exposure to increasing concentrations of drug. After 16 culture passages in the presence of mitoxantrone, a cell population emerged which was 30-40 times more resistant to the cytolytic effect of mitoxantrone than the mitoxantrone-sensitive parent (WiDr/S) line. Resistance to mitoxantrone was retained by WiDr/R cells propagated for more than 40 cell generations in mitoxantrone-free medium. Decreased drug sensitivity was strongly associated with reduced intracellular accumulation of mitoxantrone. Moderate differences in drug retention by sensitive and resistant cells were demonstrated. However, decreased uptake due to alterations at the cell membrane which impair transport of drug into the cell, reducing interaction with DNA, appears to be the principal basis of resistance in these cells.

Internalization and re-expression of antigens of human melanoma cells following exposure to monoclonal antibody

Modulation of the surface membrane of human Sk-Mel-28 melanoma cells by monoclonal antibody (MoAb) 96.5 recognizing p97 determinants was examined using direct radioimmunoassay and indirect fluorescent antibody-staining techniques. It was determined that the majority of 111In-labeled antibody that remained associated with cells after a 24-hr incubation at 37 degrees C had been internalized because MoAb 96.5 was no longer visible on the cell surface. A second treatment of these cells with the same antibody 24 hr later not only increased the cell-associated radioactivity, reflecting an increase of total antibody bound, but also rendered these cells membrane immunofluorescent again, indicating the re-expression of surface antigens. Autoradiographs of the electrophoretically analyzed membrane components of Sk-Mel-28 cells further demonstrated the appearance of newly synthesized 97-kDa proteins that were immunoprecipitable with MoAb 96.5. Taken together, the present findings suggest that p97 antigens undergo endocytosis in Sk-Mel-28 cells following exposure to MoAb 96.5. However, the same antigens were regenerated and expressed on the cell surface within a period of 24 hr. The re-expression of tumor cell surface antigen following initial internalization of the MoAb-antigen complex may have implications for diagnosis and therapy.

Arabinofuranosyl-5-azacytosine: activity against human tumors in athymic mice

SummaryArabinofuranosyl-5-azacytosine (Ara-AC), a new compound structurally related to arabinofuranosyl-cytosine (Ara-C) and 5-azacytidine (5-AC), has demonstrated significant therapeutic activity against a wide spectrum of murine tumors and three human tumor xenografts in the NCI tumor panel. Studies on the activity of Ara-AC in these and other human tumor xenograft models were undertaken to define its potential antihuman-tumor profile more completely. Ara-AC demonstrated marked antitumor activity against human tumor xenografts, including leukemias and solid tumors that do not respond to Ara-C or 5-AC. An important finding was the demonstration that Ara-AC was as effective by the oral route as when given intraperitoneally. Furthermore, the compound demonstrated synergism when combined with cisplatin in the treatment of refractory solid tumors and also induced monocyte-type differentiation of promyelocytic leukemia (HL-60) cells in vitro. Ara-AC is a promising new compound that may have utility in the treatment of human cancer beyond that anticipated for a cytotoxic nucleoside.

Modulation of the immune response to tumors by a novel synthetic compound, N-[4-[(4-fluorophenyl)sulfonyl]phenyl] acetamide (CL 259,763)

SummaryCL 259,763, N-[4-[(4-fluorophenyl)sulfonyl]phenyl] acetamide, is an orally active compound capable of modifying the reactivity of certain lymphoid cell populations affected by the growth of a tumor. The compound augmented the response of lymphocytes from tumor-primed animals to syngeneic tumor cells, resulting in a marked increase in tumor cell destruction. Likewise, it enhanced macrophage inhibitory effects on the growth of tumor cells in vitro. These “activated” macrophages were detectable in peritoneal exudates of treated mice 4 to 12 days after receiving a single oral dose of CL 259,763, with peak activity being demonstrable by day 7. The compound also restored the alloreactivity of lymphocytes from immunodepressed mice bearing the Lieberman plasma cell tumor, possibly by interferring with suppressor cells. Macrophages and lymphocytes from treated mice released significantly more IL-1 and IL-2-like factors in culture than did the control counterparts. Sera from treated mice also possessed more colony stimulating factor than those from normal mice. Immunoadjuvant effects were evident when the compound was administered with an inactivated L1210 leukemia vaccine and it enhanced the effectiveness of cytotoxic chemotherapy when given to mice challenged with P388 murine leukemia. These immunomodulating effects of CL 259,763 may hopefully be exploited in efforts to augment the immune response of the host to a progressively growing tumor.