Promising New Inhibitors of Tyrosyl-DNA Phosphodiesterase I (Tdp 1) Combining 4-Arylcoumarin and Monoterpenoid Moieties as Components of Complex Antitumor Therapy

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is an important DNA repair enzyme in humans, and a current and promising inhibition target for the development of new chemosensitizing agents due to its ability to remove DNA damage caused by topoisomerase 1 (Top1) poisons such as topotecan and irinotecan. Herein, we report our work on the synthesis and characterization of new Tdp1 inhibitors that combine the arylcoumarin (neoflavonoid) and monoterpenoid moieties. Our results showed that they are potent Tdp1 inhibitors with IC₅₀ values in the submicromolar range. In vivo experiments with mice revealed that compound 3ba (IC₅₀ 0.62 µM) induced a significant increase in the antitumor effect of topotecan on the Krebs-2 ascites tumor model. Our results further strengthen the argument that Tdp1 is a druggable target with the potential to be developed into a clinically-potent adjunct therapy in conjunction with Top1 poisons.

Gene expression profiling of tumor-initiating stem cells from mouse Krebs-2 carcinoma using a novel marker of poorly differentiated cells

Using the ability of poorly differentiated cells to natively internalize fragments of extracellular double-stranded DNA as a marker, we isolated a tumorigenic subpopulation present in Krebs-2 ascites that demonstrated the features of tumor-inducing cancer stem cells. Having combined TAMRA-labeled DNA probe and the power of RNA-seq technology, we identified a set of 168 genes specifically expressed in TAMRA-positive cells (tumor-initiating stem cells), these genes remaining silent in TAMRA-negative cancer cells. TAMRA+ cells displayed gene expression signatures characteristic of both stem cells and cancer cells. The observed expression differences between TAMRA+ and TAMRA- cells were validated by Real Time PCR. The results obtained corroborated the biological data that TAMRA+ murine Krebs-2 tumor cells are tumor-initiating stem cells. The approach developed can be applied to profile any poorly differentiated cell types that are capable of immanent internalization of double-stranded DNA.

Switching between control and phytohaemagglutinin-containing diets affects growth of Krebs II ascites cells and produces differences in the levels of putrescine, spermidine and spermine

Almost twice as many ascites tumour cells were recovered from mice pre-fed for 3 days on a lactalbumin (La)-based control diet, injected with Krebs II ascites cells and then maintained on the same diet for a further 8 days, when compared with mice fed on a phytohaemagglutinin-containing (PHA) diet for the whole period. A dietary switch on the day of injection of tumour cells produced an intermediate effect; mice switched to the La diet after pre-feeding on PHA for 3 days developed somewhat more tumour cells than when the opposite dietary switch was performed. The polyamine content in the tumour cells was lowest in the mice fed on La, and highest in mice fed PHA for the duration of the experiment, respectively. Since large amounts of extraneous polyamines are required in order to sustain tumour growth, and the hyperplastic growth of the gut which occurs in response to injesting the lectin is a polyamine-dependent process, it is evident that the two growth signals compete with one another for important nutrients/growth factors, including polyamines.

A diet containing the lectin phytohaemagglutinin (PHA) slows down the proliferation of Krebs II cell tumours in mice

Mice injected intraperitoneally with Krebs II cells and then fed on a diet containing the lectin phytohaemagglutinin (PHA) developed ascites tumours more slowly than mice fed on a control diet. After an 8-day period following injection the number of cells recovered from mice maintained on the PHA diet was half that from those fed the control diet. A switch of diet from control to PHA on day 4 after injection resulted in a large decrease in number of tumour cells recovered. Mice injected s.c. also developed tumours at later times when fed on the PHA diet. A quantitative of ribosomes in polysome-containing fractions showed no major differences in protein synthesis in control mice and those fed the PHA diet.

Treatment of mice bearing a Krebs ascitic tumor by means of a protocol based on radioactive copper (64Cu). III. Efficiency of the anticancer treatment according to the stage of tumor development

The treatment described previously (Anticancer Res 9:947-954,1989) was efficient when applied on day 1 or 6 after the injection of 5 x 10(5) Krebs ascitic cells in mice. Under our experimental conditions, all the untreated mice died within 12 to 25 days. The experiments described show that the treatment developed, is efficient when applied on day 11 but not on day 16. To understand the difference in the treatment efficiency between these two days, we tested the 64Cu incorporation inside the ascitic cells. It was observed that 64Cu incorporation exists on day 11 but no longer on day 16. On day 16, the inefficiency of the treatment must be correlated with the non-incorporation of 64Cu inside the ascitic cells. As the tumor growth is also arrested on day 16, an irreversible stage is reached. A model was developed to explain the results obtained. In this model, cancer develops in 3 successive stages. In the first stage, the cellular functioning is under the control of the malignant tumor cells and the number of cells with the "cancer functioning" is increasing with time, but decreasing after removal of the malignant tumor; in the second stage, tumor and cancer both develop independently, meaning that the number of cells with the "cancer functioning" will continue to increase after the removal of the malignant tumor; in the third stage, each cell of the organism has the "cancer functioning" and the characteristics of malignancy will by retroaction.

[Antiproliferative action of swine leukocyte interferon and of an inhibitor of interferon action]

The results of the study of the antiproliferative effect of swine leukocyte interferon and of an inhibitor of interferon effect in experimental mice with transplanted Krebs-2 ascitic carcinoma cells are presented. The interferon inhibitor exerted antiproliferative effect similar to that of native swine interferon. Combined use of swine interferon and interferon inhibitor did not lead to summation of the antiproliferative effect of these preparations.

Effects of growth rate and methotrexate on folate polyglutamates and folylpolyglutamate hydrolase activity in Krebs ascites cells

The activity of folylpolyglutamate hydrolase was measured throughout intraperitoneal growth of Krebs ascites cells in mice and after exposure to methotrexate. Hydrolase activity was lowest during the log phase of growth. Methotrexate administered intraperitoneally during log growth caused a dose- and time-dependent increase in hydrolase activity. Modest changes were observed in endogenous folate polyglutamate chain length distributions throughout growth and upon exposure to methotrexate, but these changes could not be correlated with hydrolase activity.

Ascites tumor invasion of mouse peritoneum studied by high-voltage electron microscope stereoscopy

Interaction of Krebs-2 and Ehrlich tetraploid cells with NYLR/Nya mouse peritoneum mesothelium and penetration of basal lamina and elastic reticulum were studied. Invasion of abdominal viscera was rare. Invading cells had a shrunken nucleus and cytoplasm like the "dark cells" of hyperplastic epithelia. High-voltage electron microscope stereoscopy showed that invasive cells pass through small holes in the elastic reticulum by adherence to the reticulum and by constriction of the cells. High voltage electron microscopy stereoscopy of collagen fibers near tumor cells indicated that fragmentation and loss of collagen is minimal. Rapid progression by ascites transfer appears to produce anchorage-independent cells adapted to ascites fluid growth, but new selection steps must be adopted to concentrate strongly invasive subpopulations.

Comparison of the rate of aminoacylation of tRNA isolated from NMRI mouse liver with tRNA isolated from Krebs II ascites or mouse plasmacytoma cells

A comparison of the initial rates of aminoacylation of tRNAs isolated from different sources for 17 amino acids was performed. tRNA was isolated from NMRI mouse liver (tRNA L) and from Krebs II ascites tumors (tRNA Asc), and aminoacyl-tRNA synthetases were prepared from the latter cells. The aminoacylation of tRNA Asc was 31-88% slower than the charging of tRNA L. In similar studies, tRNA from a mouse plasmacytoma tumor (tRNA Mt) and from suspension cultured cells of the same cell line (tRNA M) were compared to tRNA L in the aminoacylation reaction catalysed by synthetases isolated from tumor or suspension cultured cells. About half of the tRNAs (Mt or M) for the 17 amino acids tested differed in charging rate when compared to tRNA L, but the differences were not as great as those observed in the experiments where tRNA Asc and tRNA L were compared.

Comparison of phosphorylation of ribosomal proteins from HeLa and Krebs II ascites-tumour cells by cyclic AMP-dependent and cyclic GMP-dependent protein kinases

Phosphorylation of eukaryotic ribosomal proteins in vitro by essentially homogeneous preparations of cyclic AMP-dependent protein kinase catalytic subunit and cyclic GMP-dependent protein kinase was compared. Each protein kinase was added at a concentration of 30nM. Ribosomal proteins were identified by two-dimensional gel electrophoresis. Almost identical results were obtained when ribosomal subunits from HeLa or ascites-tumour cells were used. About 50-60% of the total radioactive phosphate incorporated into small-subunit ribosomal proteins by either kinase was associated with protein S6. In 90 min between 0.7 and 1.0 mol of phosphate/mol of protein S6 was incorporated by the catalytic subunit of cyclic AMP-dependent protein kinase. Of the other proteins, S3 and S7 from the small subunit and proteins L6, L18, L19 and L35 from the large subunit were predominantly phosphorylated by the cyclic AMP-dependent enzyme. Between 0.1 and 0.2 mol of phosphate was incorporated/mol of these phosphorylated proteins. With the exception of protein S7, the same proteins were also major substrates for the cyclic GMP-dependent protein kinase. Time courses of the phosphorylation of individual proteins from the small and large ribosomal subunits in the presence of either protein kinase suggested four types of phosphorylation reactions: (1) proteins S2, S10 and L5 were preferably phosphorylated by the cyclic GMP-dependent protein kinase; (2) proteins S3 and L6 were phosphorylated at very similar rates by either kinase; (3) proteins S7 and L29 were almost exclusively phosphorylated by the cyclic AMP-dependent protein kinase; (4) protein S6 and most of the other proteins were phosphorylated about two or three times faster by the cyclic AMP-dependent than by the cyclic GMP-dependent enzyme.

Inhibiting effect of vitamins C and B12 on the mitotic activity of ascites tumors

The mitotic activity of the transplantable mouse tumors, Sarcoma 37, Krebs-2, and Ehrlich carcinomas, in the ascites form, were inhibited after treatment with a mixture of vitamins C and B12 with no apparent toxic side effects. These vitamins when administered alone, at the same dosage, did not seem to have any apparent effect on mitosis or the morphology of the cells studied. Microscopic examination of the stained ascites fluid taken from the mice treated with the vitamin mixture showed few tumor cells, and these in various stages of disintegration. Also, an increase in lymphocytes, monocytes and neutrophils were noticed; however, later in the experiment, no tumor cells could be found and monocytes and macrophages were abundant.

Inhibition and stimulation of the growth of Krebs-2 carcinoma by BCG vaccine

The effect of BCG vaccine on the growth of imtransplants of Krebs-2 carcinoma in mice was studied. The simultaneous injection of BCG and tumor cells either inhibited tumor growth (BCG given in admixture with tumor cells) or stimulated it (BCG injected contralateral to the tumor transplantation site). The BCG dose was directly related to the effect. Tumor growth was also stimulated by the ip injection of starch or liquid paraffin. In these experiments, the BCG effect was attributed to the redistribution of cells involved in nonspecific and specific tumor resistance. Shortly after BCG prevaccination, particularly when BCG doses were high and mice were susceptible to vaccine infection, BCG was either without effect or stimulated tumor growth; later, however, tumor growth was inhibited regardless of the BCG dose and the injection site of the BCG. The effect of BCG prevaccination was suggested to be due to: 1)the distraction of macrophages and T-lymphocytes to defend the host against the multiplying mycobacteria, and 2)the activation of the pool of these cells that become capable to participate in antitumor resistance after mycobacteria elimination.

[Stimulation of the inhibiting effect of interferon on the growth of ascitic carcinoma in relation to host responsiveness and cells]

When Krebs-2 ascitic carcinoma is transplanted to mice, administration of interferon may produce either a stimulating or an inhibiting effect on replication of carcinoma cells in the peritoneal cavity depending on the responsiveness of mice (intact or vaccinated with Newcastle disease virus) and the state of the transplanted cells ("common" or "tolerant"). Parallelism was observed in changes of the intensity of cell multiplications and indices of their enzymatic activity under the influence of exogenic interferon.

[Change in cellular surface structures and volume under the action of colchicine]

Effect of colchicine upon the surface structures and volume of embryonic pig kidney cells and mouse ascite carcinoma Krebs II cells involved an increase of the cells volume. This was confirmed by the scanning electron microscopy data. The surface of colchicine-treated pig cells has less microvilli due, probably, to their enlarged volume. Swelling of mitochondrial matrix as well as some other ultrastructural changes in cytoplasm of the drug-treated cells suggest that the increase in the volume is a result of cell hydration. Disturbance of the osmotic equilibrium following the depolymerization of microtubles in the mitotic spindle and cytoplasm, is discussed.