A number of publications show that mice bearing progressive syngeneic tumors can acquire suppressor T cells, as measured by a variety of assays (reviewed in 1). In support of this evidence, a series of studies in this laboratory (2, 3) has shown that the acquisition of suppressor T cells by a tumor-bearing host is responsible for the failure of passively transferred, tumor-sensitized T cells to cause the regression of its tumor. First, it was shown with two different immunogenic tumors (2, 3) that in order for passively transferred sensitized T cells from immunized donors to cause the complete regression of an established tumor, the tumor-bearing recipient needs to have been made T cell deficient by thymectomy and lethal irradiation, and then restored with bone marrow (TXB mice) ~ or immunodepressed by treatment with cyclophosphamide (4) or exposure to sublethal irradiation (5). It was revealed next that tumor regression in TXB test recipients caused by the passive transfer of immune T cells can be inhibited by the transfer of T cells from immunocompetent tumor-bearing donors. It was hypothesized, on the basis of this and other evidence (6), that progressive growth of an immunogenic tumor eventually evokes the generation of a mechanism of T cell-mediated immunosuppression.However, the demonstration that tumor-bearing mice acquire suppressor T cells does not in itself provide a satisfactory explanation of how tumors with transplantation rejection antigens escape destruction by the immune system. What is needed in addition is evidence that suppressor T cells either can prevent an antitumor immune response from developing or can down-regulate an immune response that already is in progress. In support of the latter possibility are numerous descriptions in the literature of the acquisition and subsequent loss by a host with a progressive tumor of a paradoxical state of concomitant immunity that enables the host to prevent the growth of an implant of cells of that tumor (reviewed in 7). It seems reasonable to suggest, therefore, that the function of suppressor T cells would be to down-regulate a concomitant antitumor immune

The new cytotoxic agents rakicidins A and B were isolated from cultured broth of a Micromonospora sp. Spectroscopic and amino acid analysis has shown that rakicidin A is a new cyclic lipopeptide, consisting of 4-amino-penta-2,4-dienoic acid, 3-hydroxy-2,4,16-trimethylheptadecanoic acid, sarcosine, and 3-hydroxyasparagine. Rakicidin B differs by one methylene group in the lipid side chain. These compounds exhibited cytotoxicity against the Ml09 cell line. In our continuing search for newantitumor agents from microorganisms, an isolate of Micromonospora was selected for further evaluation. This research led to the discovery of two newcytotoxic lipopeptides, rakicidins A and B (Fig. 1). This paper describes the fermentation, biological evaluation, purification, physico-chemical characterization, and structure elucidation of these compounds. Fermentation Microorganism The producing organism was isolated from a soil sample collected at Andhra Pradesh, India and was identified as a Micromonospora sp., strain No. R385-2. Media and Culture Conditions Micromonospora strain No. R385-2 was grown on slants of modified Bennett's mediumwhich contained the following: 0.5% Japanese potato starch (Generichem DEC. 1995 Corp. Acadama Dextrin No. 3), 0.5% glucose, 0.1% fish meat extract (Mikuni Chem. Industry), 0.1% yeast extract (Difco), 0.2% N-Z Case (Sheffield Products), 0.2% NaCl, 0.1% CaCO3, 1.5% agar. The medium was sterilized at 121°C for 20 minutes. The culture was transferred from the slant into 100ml of GERmedium in a 500ml flask. The medium contained the following: 2.4% Japanese potato starch, 0.1% dextrose, 0.3% beef extract (BBL), 0.5% tryptone (Difco), 0.5% yeast extract (BBL), 0.2% CaCO3 and was adjusted to pH 7.6 before autoclaving. The mediumwas sterilized at 121°C for 20

High throughput screening identified 2-acetamido-thiazolylthio acetic ester 1 as an inhibitor of cyclin-dependent kinase 2 (CDK2). Because this compound is inactive in cells and unstable in plasma, we have stabilized it to metabolic hydrolysis by replacing the ester moiety with a 5-ethyl-substituted oxazole as in compound 14. Combinatorial and parallel synthesis provided a rapid analysis of the structure-activity relationship (SAR) for these inhibitors of CDK2, and over 100 analogues with IC(50) values in the 1-10 nM range were rapidly prepared. The X-ray crystallographic data of the inhibitors bound to the active site of CDK2 protein provided insight into the binding modes of these inhibitors, and the SAR of this series of analogues was rationalized. Many of these analogues displayed potent and broad spectrum antiproliferative activity across a panel of tumor cell lines in vitro. In addition, A2780 ovarian carcinoma cells undergo rapid apoptosis following exposure to CDK2 inhibitors of this class. Mechanism of action studies have confirmed that the phosphorylation of CDK2 substrates such as RB, histone H1, and DNA polymerase alpha (p70 subunit) is reduced in the presence of compound 14. Further optimization led to compounds such as water soluble 45, which possesses a favorable pharmacokinetic profile in mice and demonstrates significant antitumor activity in vivo in several murine and human models, including an engineered murine mammary tumor that overexpresses cyclin E, the coactivator of CDK2.

It was shown in the preceding companion paper (1) that early progressive growth of an immunogenic fibrosarcoma results in the acquisition by its syngeneic host of concomitant immunity to growth of a challenge implant, and of tumorsensitized Ly-l-2 + T cells that are capable of adoptively immunizing against an established tumor in y-irradiated recipients. It was shown, in addition, that after the tumor reaches a certain size, concomitant immunity and tumor-sensitized T cells are progressively lost, and that this is associated with the generation of Ly-1 +2-suppressor T cells capable, on passive transfer, of inhibiting the expression of adoptive immunity against an established tumor in T cell-deficient (TXB) 1 recipients. The evidence was interpreted as showing that progressive tumor growth evokes a mechanism of T cell-mediated concomitant immunity that is down-regulated by suppressor T cells before it develops sufficiently in magnitude to destroy the tumor. This knowledge that progressive tumor growth evokes a concomitant immune response that subsequently decays under the influence of suppressor T cells must surely be taken into account in assessing the results of the most commonly used test for tumor immunogenicity (2-4): determining whether surgical removal of a tumor results in immunity to growth of a subsequent implant of cells of that tumor. It might be expected, in this regard, that the immunological consequences of excising an immunogenic tumor would be determined by whether excision is performed during the generation of concomitant immunity or after it has decayed under the influence of suppressor T cells. It is apparent from the literature (5) that little is known about the relationship between the ability to demonstrate postexcision antitumor immunity and the state of concomitant immunity of the host at the time of excision. This paper will show that excising the meth A fibrosarcoma during the time that concomitant immunity is being generated results in the preservation of this immunity for a long period of time. In contrast, excising the tumor after T ceilmediated suppression of concomitant immunity does not result in the reemergence of immunity. Instead, the host remains unresponsive to the meth A tumor

A novel triterpenoid saponin, pittoviridoside (1), which possesses an unusual 2,3,4-trisubstituted glycosidic linkage, has been isolated from Pittosporum viridiflorum using the engineered yeast strains 1138, 1140, 1353, and Sc-7 for bioactivity-guided fractionation. The structure of this compound was determined to be 3-O-[beta-D-glucopyranosyl(1-->2)]-[alpha-D-arabinopyranosyl(1-->3)],[alpha-l-arabinofuranosyl(1-->4)-beta-D-glucuronopyranosyl-21-angeloyl-22-senecioylolean-12-en-3beta,15alpha,16alpha,21beta,22alpha,28-hexol by spectral, chemical, and GC analyses. This compound showed weak cytotoxicity against the A2780 human ovarian cancer cell line.