Actin depolymerization is associated with meiotic acceleration in cycloheximide-treated ovine oocytes.

Oocytes treated with the protein synthesis inhibitor cycloheximide (CHX) arrest at the germinal vesicle (GV) stage and undergo accelerated GV breakdown (GVBD) after CHX is removed. However, little is known about the underlying mechanism of accelerated meiotic maturation. Here, we investigated this mechanism and found that oocytes released from CHX arrest have higher amounts of cyclin B1 (CCNB1) and phosphorylated mitogen-activated protein kinase (pMAPK) proteins. Increased levels of these factors were not associated with mRNA polyadenylation or increased transcription rates of CCNB1 and MOS (Moloney murine sarcoma viral oncogene homolog) during CHX arrest. We found that treatment of CHX-arrested oocytes with the actin filament-stabilizing agent Jasplakinolide (Jasp) delayed GVBD following release from CHX arrest and that this was correlated with reduced maturation-promoting factor (MPF) activity. These results suggest that CCNB1 mRNAs released from actin filaments during CHX arrest increase CCNB1 transcripts available for translation after release from CHX arrest, leading to the precocious activation of MPF and accelerated meiotic progression.

Significant differences in integration sites of Moloney murine leukemia virus/Moloney murine sarcoma virus retroviral vector carrying recombinant coagulation factor IX in two human cell lines.

Ligation-mediated-PCR was performed followed by the mapping of 177 and 150 integration sites from HepG2 and Hek293 transduced with chimera vector carrying recombinant human Factor IX (rhFIX) cDNA, respectively. The sequences were analyzed for chromosome preference, CpG, transcription start site (TSS), repetitive elements, fragile sites and target genes. In HepG2, rhFIX was had an increased preference for chromosomes 6 and 17; the median distance to the nearest CpG islands was 15,240 base pairs and 37 % of the integrations occurred in RefSeq genes. In Hek293, rhFIX had an increased preference for chromosome 5; the median distance to the nearest CpG islands was 209,100 base pairs and 74 % of the integrations occurred in RefSeq genes. The integrations in both cell lines were distant from the TSS. The integration patterns associated with this vector are different in each cell line.

Design, synthesis, and biological evaluation of unconventional aminopyrimidine, aminopurine, and amino-1,3,5-triazine methyloxynucleosides.

Herein we describe a class of unconventional nucleosides (methyloxynucleosides) that combine unconventional nucleobases such as substituted aminopyrimidines, aminopurines, or aminotriazines with unusual sugars in their structures. The allitollyl or altritollyl derivatives were pursued as ribonucleoside mimics, whereas the tetrahydrofuran analogues were pursued as their dideoxynucleoside analogues. The compounds showed poor, if any, activity against a broad range of RNA and DNA viruses, including human immunodeficiency virus (HIV). This inactivity may be due to lack of an efficient metabolic conversion into their corresponding 5'-triphosphates and poor affinity for their target enzymes (DNA/RNA polymerases). Several compounds showed cytostatic activity against proliferating human CD4(+) T-lymphocyte CEM cells and against several other tumor cell lines, including murine leukemia L1210 and human prostate PC3, kidney CAKI-1, and cervical carcinoma HeLa cells. A few compounds were inhibitory to Moloney murine sarcoma virus (MSV) in C3H/3T3 cell cultures, with the 2,6-diaminotri-O-benzyl-D-allitolyl- and -D-altritolyl pyrimidine analogues being the most potent among them. This series of unconventional nucleosides may represent a novel family of potential antiproliferative agents.

Detection and identification of cancerous murine fibroblasts, transformed by murine sarcoma virus in culture, using Raman spectroscopy and advanced statistical methods.

BACKGROUND: Cancer is one of the leading worldwide causes of death. It may be induced by a variety of factors, including carcinogens, radiation, genetic factors, or DNA and RNA viruses. The early detection of cancer is critical for its successful therapy, which can result in complete recovery from some types of cancer. METHODS: Raman spectroscopy has been widely used in medicine and biology. It is a noninvasive, nondestructive, and water-insensitive technique that can detect changes in cells and tissues that are caused by different disorders, such as cancer. In this study, Raman spectroscopy was used for the identification and characterization of murine fibroblast cell lines (NIH/3T3) and malignant fibroblast cells transformed by murine sarcoma virus (NIH-MuSV) cells. RESULTS: Using principal component analysis and LDA it was possible to differentiate between the NIH/3T3 and NIH-MuSV cells with an 80-85% success rate based on their Raman shift spectra. CONCLUSIONS: The best results for differentiation were achieved from spectra that were obtained from the rich membrane sites. GENERAL SIGNIFICANCE: Because of its homogeneity and complete control of most factors affecting its growth, cell culture is a preferred model for the detection and identification of specific biomarkers related to cancer transformation or other cellular modifications.

Synthesis and antiviral activity of N9-[3-fluoro-2-(phosphonomethoxy)propyl] analogues derived from N6-substituted adenines and 2,6-diaminopurines.

An efficient method for the synthesis of N(9)-[3-fluoro-2-(phosphonomethoxy)propyl] (FPMP) derivatives of purine bases has been developed. Both (R)- and (S)-enantiomers of the N(6)-substituted FPMP derivatives of adenine and 2,6-diaminopurine were prepared and their anti-human immunodeficiency virus (HIV) and anti-Moloney murine sarcoma virus (MSV) activity was evaluated. Whereas none of the 6-substituted FPMPA derivatives showed any antiviral activity, several FPMPDAP derivatives had a moderate antiretroviral activity. Moreover, the data obtained from the study of the substrate activity of the active derivatives towards N(6)-methyl-AMP aminohydrolase support the notion that the studied N(6)-substituted FPMPDAP derivatives act as prodrugs of the antiretroviral FPMPG analogues.

Effects of time of initial exposure to MSV sarcoma on bone induction by dentine matrix implants and on orthotopic femora.

HCl-demineralized murine lower incisors were implanted intramuscularly into syngeneic BALB/c mice to induce heterotopic osteogenesis. Implants were exposed at the early, preosteogenic stage (4), or at the later, osteogenic stage (12) to the Moloney sarcoma virus (MSV), which within 3-4 days results in a sarcoma. The yield of bone induction was determined by weight of dry bone mass following NaOH hydrolysis of soft tissues. To verify the effect of this sarcoma on orthotopic local femoral bone, the dry mass of the tumor-exposed femora was measured and compared with the weight of MSV-unexposed contralateral controls. MSV-sarcoma or cells involved with their spontaneous rejection have a stimulatory effect on the periosteal membrane of the tumor-adjacent femoral bones, increasing their dry mass on average by 18%. No stimulatory effect on heterotopic bone induction was observed when the MSV sarcoma grew during the early, preosteogenic stage (4 onward), but when the tooth matrix had been exposed to such tumor at the already bone-forming stage, (12 onward), the yield of bone induction was enhanced. Thus, it is postulated that lesions induced by MSV during the early, preosteogenic stage inhibit recruitment of osteoprogenitor cells or degrade Bone Morphogenetic Proteins (BMPs) released by matrix resorbing inflammatory cells, whereas when acting on already existing bone they have a stimulatory effect.

Peripheral blood and lymphatic organs in BALB/c mice during the progressive and regressive phases of Moloney sarcoma development.

Blood cell counts, differential blood cell counts and weights of the spleen and peripheral lymph nodes draining the area of lesions induced by Moloney sarcoma virus inoculation into the quadriceps shank muscles of inbred BALB/c mice were examined at various stages of tumor development and regression. The blood cell count remained constant through the observation period up to 27 days post tumor development and regression. Differential counts revealed some changes in the cellular composition of the peripheral blood. The most pronounced was an increase of neutrophiles at the stage of tumor development, and their decline with tumour regression. The enlargement of the spleen and of the popliteal lymph nodes draining the tumour site, at the peak of tumor development on day 13 post MSV inoculation, involved at least a doubling of splenic weight, and a much greater weight increase for lymph nodes. This was a long-lasting, although declining event, extending beyond tumor regression.

Evidence for a potential tumor suppressor role for the Na,K-ATPase beta1-subunit.

The Na,K-ATPase, consisting of two essential subunits (alpha, beta), plays a critical role in the regulation of ion homeostasis in mammalian cells. Recent studies indicate that reduced expression of the beta1 isoform (NaK-beta1) is commonly observed in carcinoma and is associated with events involved in cancer progression. In this study, we present evidence that repletion of NaK-beta1 in Moloney sarcoma virus-transformed Madin-Darby canine kidney cells (MSV-MDCK), a highly tumorigenic cell line, inhibits anchorage independent growth and suppresses tumor formation in immunocompromised mice. Additionally, using an in vitro cell-cell aggregation assay, we showed that cell aggregates of NaK-beta1 subunit expressing MSV-MDCK cells have reduced extracellular regulated kinase (ERK) 1/2 activity compared with parental MSV-MDCK cells. Finally, using immunohistochemistry and fully quantitative image analysis approaches, we showed that the levels of phosphorylated ERK 1/2 are inversely correlated to the NaK-beta1 levels in the tumors. These findings reveal for the first time that NaK-beta1 has a potential tumor-suppressor function in epithelial cells.

Overexpression/enhanced kinase activity of BCR/ABL and altered expression of Notch1 induced acute leukemia in p210BCR/ABL transgenic mice.

Chronic myelogenous leukemia (CML) is a hematopoietic disorder, which begins as indolent chronic phase but inevitably progresses to fatal blast crisis. p210BCR/ABL, a constitutively active tyrosine kinase, is responsible for disease initiation but molecular mechanism(s) underlying disease evolution remains largely unknown. To explore this process, we employed retroviral insertional mutagenesis to CML-exhibiting p210BCR/ABL transgenic mice (Tg). Virus infection induced acute lymphoblastic leukemia (ALL) in p210BCR/ABL Tg with a higher frequency and in a shorter latency than wild-type littermates, and inverse PCR detected two retrovirus common integration sites (CISs) in p210BCR/ABL Tg tumors. Interestingly, one CIS was the transgene itself, where retrovirus integrations induced upregulation of p210BCR/ABL and production of truncated BCR/ABL with an enhanced kinase activity. Another CIS was Notch1 gene, where retrovirus integrations resulted in overexpression of Notch1 and generation of Notch1 lacking the C-terminal region (Notch1DeltaC) associated with stable expression of its activated product, C-terminal-truncated Notch intracellular domain (NICD Delta C). In addition, generation of Tg for both p210BCR/ABL and Notch1DeltaC developed ALL in a shortened period with Stat5 activation, demonstrating the cooperative oncogenicity of Notch1DeltaC/NICD Delta C with p210BCR/ABL involving Stat5-mediated pathway. These results demonstrated that overexpression/enhanced kinase activity of BCR/ABL and altered expression of Notch1 induces acute leukemia in a transgenic model for CML.

Tumor induced by Moloney sarcoma virus causes periosteal osteogenesis engaging osteopontin, fibronectin, stromelysin-1 and tenascin.

Excessive bone formation occurring in such conditions as paravertebral ligamentous ossification, hallux osteophytes or some neoplastic tumors, presents a significant problem, both epidemiological and clinical. Since pathogenesis of this disorder is still unclear, we studied its mechanism in experimental model utilizing inducible orthotopic osteogenesis. Periosteal bone apposition stimulated by Moloney sarcoma is characterized by unusually high volume of new bone tissue appearing subperiosteally in the bone adjacent to the tumor. Genes engaged in this growth have not been characterized so far. Here we show the results of mRNA Representation Difference Analysis in Moloney sarcoma, which reveal high expression of four genes coding extracellular matrix proteins: osteopontin, fibronectin, stromelysin-1 and tenascin. These findings suggest that the uncommon dynamics of the Moloney sarcoma-induced osteogenesis depends on high expression of these extracellular matrix proteins.

Pronounced in vitro and in vivo antiretroviral activity of 5-substituted 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy] pyrimidines.

OBJECTIVES: To discover new potent and selective anti-human immunodeficiency virus (HIV) acyclic nucleoside phosphonate (ANP) drugs with in vivo antiretroviral activity. METHODS: New acyclic pyrimidine nucleoside phosphonate derivatives that mimic the structure of the anti-HIV purine nucleoside phosphonates 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir) and (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA, tenofovir) were designed by linking the acyclic side chain of the ANPs through an ether bond to the C-6 position instead of the N-1 position of the pyrimidine ring. The compounds were evaluated against HIV and Moloney murine sarcoma virus (MSV) in cell culture, including a broad variety of HIV-1 clade clinical isolates and relevant mutant (drug-resistant) HIV-1 isolates. Their antiviral activities were correlated and investigated in an in vivo model consisting of MSV-infected newborn mice. MSV-induced tumour formation and associated death were recorded in drug-treated animals. RESULTS: Several 5-substituted 6-[2-(phosphonomethoxy)ethoxy]-2,4-diaminopyrimidine (PMEO-DAPy) analogues were found to inhibit a broad variety of HIV-1 clinical isolates. They showed a more favourable cross-resistance profile to mutant virus isolates than adefovir and tenofovir. There was a close correlation between inhibition of MSV in C3H/3T3 cells and inhibition of HIV-1 in CEM cells. The PMEO-DAPy derivatives potently inhibited MSV-induced tumour cell formation in newborn mice. The 5-methyl analogue PMEO-5-Me-DAPy proved markedly more inhibitory to MSV-induced tumour cell formation and associated animal death than its unsubstituted parent PMEO-DAPy derivative. When compared with adefovir, PMEO-5-Me-DAPy was less toxic and more antivirally active in MSV-infected mice. CONCLUSIONS: PMEO-5-Me-DAPy deserves further (pre)clinical investigations as a candidate anti-HIV drug.

Architecture of a gamma retroviral genomic RNA dimer.

Retroviral genomes contain two sense-strand RNAs that are noncovalently linked at their 5' ends, forming a dimer. Establishing a structure for this dimer is an obligatory first step toward understanding the fundamental role of the dimeric RNA in retroviral biology. We developed a secondary structure model for the minimal dimerization active sequence (MiDAS) for the Moloney murine sarcoma virus in the final dimer state using selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE). In this model, two self-complementary, or palindromic, sequences (PAL1 and PAL2) form extended intermolecular duplexes of 10 and 16 base pairs, respectively. The monomeric starting state was shown previously to contain a flexible domain in which nucleotides do not form stable interactions with other parts of the RNA. In the final dimer state, portions of this initial flexible domain form stable base pairs, while previously base-paired elements lie in a new flexible domain. Thus, partially overlapping and structurally well-defined flexible domains are prominent features of both monomer and dimer states. We then used hydroxyl radical cleavage experiments to characterize the global architecture of the dimer state. Extensive regions, including portions of both PAL1 and PAL2, are occluded from solvent-based cleavage indicating that the MiDAS domain does not function simply as a collection of autonomous secondary structure elements. Instead, the retroviral dimerization domain adopts a compact architecture characterized by close packing of its constituent helices.

The SL1-SL2 (stem-loop) domain is the primary determinant for stability of the gamma retroviral genomic RNA dimer.

Retroviral genomes are assembled from two sense-strand RNAs by noncovalent interactions at their 5' ends, forming a dimer. The RNA dimerization domain is a potential target for antiretroviral therapy and represents a compelling RNA folding problem. The fundamental dimerization unit for the Moloney murine sarcoma gamma retrovirus spans a 170-nucleotide minimal dimerization active sequence. In the dimer, two self-complementary sequences, PAL1 and PAL2, form intermolecular duplexes, and an SL1-SL2 (stem-loop) domain forms loop-loop base pairs, mediated by GACG tetraloops, and extensive tertiary interactions. To develop a framework for assembly of the retroviral RNA dimer, we quantified the stability of and established nucleotide resolution secondary structure models for sequence variants in which each motif was compromised. Base pairing and tertiary interactions between SL1-SL2 domains contribute a large free energy increment of -10 kcal/mol. In contrast, even though the PAL1 and PAL2 intermolecular duplexes span 10 and 16 bp in the dimer, respectively, they contribute only -2.5 kcal/mol to stability, roughly equal to a single new base pair. First, these results emphasize that the energetic costs for disrupting interactions in the monomer state nearly balance the PAL1 and PAL2 base pairing interactions that form in the dimer. Second, intermolecular duplex formation plays a biological role distinct from simply stabilizing the structure of the retroviral genomic RNA dimer.

The scaffold protein Cybr is required for cytokine-modulated trafficking of leukocytes in vivo.

Trafficking and cell adhesion are key properties of cells of the immune system. However, the molecular pathways that control these cellular behaviors are still poorly understood. Cybr is a scaffold protein highly expressed in the hematopoietic/immune system whose physiological role is still unknown. In vitro studies have shown it regulates LFA-1, a crucial molecule in lymphocyte attachment and migration. Cybr also binds cytohesin-1, a guanine nucleotide exchange factor for the ARF GTPases, which affects actin cytoskeleton remodeling during cell migration. Here we show that expression of Cybr in vivo is differentially modulated by type 1 cytokines during lymphocyte maturation. In mice, Cybr deficiency negatively affects leukocytes circulating in blood and lymphocytes present in the lymph nodes. Moreover, in a Th1-polarized mouse model, lymphocyte trafficking is impaired by loss of Cybr, and Cybr-deficient mice with aseptic peritonitis have fewer cells than controls present in the peritoneal cavity, as well as fewer leukocytes leaving the bloodstream. Mutant mice injected with Moloney murine sarcoma/leukemia virus develop significantly larger tumors than wild-type mice and have reduced lymph node enlargement, suggesting reduced cytotoxic T-lymphocyte migration. Taken together, these data support a role for Cybr in leukocyte trafficking, especially in response to proinflammatory cytokines in stress conditions.

Fluvastatin does not elevate periosteal osteogenesis induce by Moloney sarcoma virus (MSV) in mice.

Several studies have demonstrated the pleiotropic effects of statins. Since Wang and associates reported that in rabbits lovastatin reduced steroid-induced bone loss, numerous authors have confirmed these data, however, others have reported conflicting results. In this study, the effects of fluvastatin on bone formation were investigated in early and late phase of osteogenesis. In the first set of experiments (early phase of osteogenesis) CFW/Ll mice were randomly divided into three groups. Two groups were injected with Moloney-murine sarcoma virus (Mo-MSV) into right thighs to induce orthotopic bone formation. Mice in the experimental group received fluvastatin for 11 consecutive days. Thirty days after Mo-MSV inoculation, total serum cholesterol, triglycerides, high- and low-density lipoprotein cholesterol, alkaline phosphatase (AP) were measured and bone mineral increase was calculated. In the second set of experiments (late phase of osteogenesis), fluvastatin was administered from day 11 after Mo-MSV inoculation for 20 consecutive days. Fluvastatin administration in the early phase of osteogenesis made no significant difference in average bone increase compared with mice receiving placebo. Lipid profile and AP were not significantly affected. During late phase of osteogenesis, the average increase in femural dry mass was significantly lower in the group of mice receiving fluvastatin than in the control group. Also, Mo-MSV-initiated tumors disappeared earlier in mice treated with fluvastatin. This may be attributed to the antioncogenic potential of fluvastatin. These results also point out that orthotopic bone formation at the sites of Mo-MSV inoculation in mice seems to be a useful model to examine the pleiotropic effects of statins.

Visualization of a primary anti-tumor immune response by positron emission tomography.

Current methodologies that monitor immune responses rely on invasive techniques that sample tissues at a given point in time. New technologies are needed to elucidate the temporal patterns of immune responses and the spatial distribution of immune cells on a whole-body scale. We describe a noninvasive, quantitative, and tomographic approach to visualize a primary anti-tumor immune response by using positron emission tomography (PET). Bone marrow chimeric mice were generated by engraftment of hematopoietic stem and progenitor cells transduced with a trifusion reporter gene encoding synthetic Renilla luciferase (hRluc), EGFP, and Herpes virus thymidine kinase (sr39TK). Mice were challenged with the Moloney murine sarcoma and leukemia virus complex (M-MSV/M-MuLV), and the induced immune response was monitored by using PET. Hematopoietic cells were visualized by using 9-[4-[(18)F]fluoro-3-(hydroxymethyl)butyl]guanine ([(18)F]FHBG), a radioactive substrate specific for the sr39TK PET reporter protein. Immune cell localization and expansion were seen at the tumor and draining lymph nodes (DLNs). 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG), which is sequestered in metabolically active cells, was used to follow tumor growth and regression. Elevated glucose metabolism was also seen in activated lymphocytes in the DLNs by using the [(18)F]FDG probe. When M-MSV/M-MuLV-challenged mice were treated with the immunosuppressive drug dexamethasone, activation and expansion of immune cell populations in the DLNs could no longer be detected with PET imaging. The method we describe can be used to kinetically measure the induction and therapeutic modulations of cell-mediated immune responses.

Antiviral potential of a new generation of acyclic nucleoside phosphonates, the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines.

Three acyclic nucleoside phosphonates (ANPs) have been formally approved for clinical use in the treatment of 1) cytomegalovirus retinitis in AIDS patients (cidofovir, by the intravenous route), 2) chronic hepatitis B virus (HBV) infections (adefovir dipivoxil, by the oral route), and 3) human immunodeficiency virus (HIV) infections (tenofovir disoproxil fumarate, by the oral route). The activity spectrum of cidofovir {(S)- 1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine [(S)-HPMPC)]}, like that of (S)-HPMPA [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine) and (S)-HPMPDAP [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-2, 6-diaminopurine), encompasses a broad spectrum of DNA viruses, including polyoma-, papilloma-, adeno-, herpes-, and poxviruses. Adefovir {9-[2-(phosphonomethoxy)ethyl]adenine (PMEA)} and tenofovir [(R)-9-[2-(phosphonomethoxy) propyl]adenine [(R)-PMPA)]} are particularly active against retroviruses (ie., HIV) and hepadnaviruses (ie., HBV); additionally, PMEA also shows activity against herpes- and poxviruses. We have recently identified a new class of ANPs, namely 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines, named, in analogy with their alkylpurine counterparts, HPMPO-DAPy, PMEO-DAPy, and (R)-PMPO-DAPy. These compounds exhibit an antiviral activity spectrum and potency that is similar to that of (S)-HPMPDAP, PMEA, and (R)-PMPA, respectively. Thus, PMEO-DAPy and (R)-PMPO-DAPy, akin to PMEA and (R)-PMPA, proved particularly active against HIV- 1, HIV-2, and the murine retrovirus Moloney sarcoma virus (MSV). PMEO-DAPy and (R)-PMPO-DAPy also showed potent activity against both wild-type and lamivudine-resistant strains of HBV. HPMPO-DAPy was found to inhibit different poxviruses (ie., vaccinia, cowpox, and orf) at a similar potency as cidofovir. HPMPO-DAPy also proved active against adenoviruses. In vivo, HPMPO-DAPy proved equipotent to cidofovir in suppressing vaccinia virus infection (tail lesion formation) in immunocompetent mice and promoting healing of disseminated vaccinia lesions in athymic-nude mice. The 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines offer substantial potential for the treatment of a broad range of retro-, hepadna-, herpes-, adeno-, and poxvirus infections.

Cytotoxic, antiviral (in-vitro and in-vivo), immunomodulatory activity and influence on mitotic divisions of three taxol derivatives: 10-deacetyl-baccatin III, methyl (N-benzoyl-(2'R,3'S)-3'-phenylisoserinate) and N-benzoyl-(2'R,3'S)-3'-phenylisoserine.

The aim of this study was to evaluate cytotoxic, antiviral (in-vitro and in-vivo) and immunomodulatory activity, as well as the influence on mitotic division, of three taxol derivatives representing modified parts of its molecule: 10-deacetyl-baccatin III, methyl (N-benzoyl-(2'R,3'S)-3'-phenylisoserinate) and N-benzoyl(2'R,3'S)-3'-phenylisoserine. The cytotoxicity of the compounds, assessed by the formazane method, was relatively low, with a 50% cytotoxic concentration (CC50)>500 microg mL-1. Moreover, all tested compounds inhibited Herpes simplex type 1 virus (HSV-1) replication in non-cytotoxic concentrations in-vitro. Selectivity indices were in the range 9.5-46.7. Anti-HSV-1 activity of the compounds may be associated with their influence on mitotic division. All of the compounds decreased the number of cell divisions. Mitotic indices ranged from 40/1000 (4.0%) to 62/1000 (6.2%). One compound, 10-deacetyl-baccatin III, influenced the growth of tumours induced in mice by infection with Moloney murine sarcoma virus. The effect of the tested compounds on T lymphocyte proliferation was evaluated by measurement of the activity of tritiated thymidine incorporated into DNA of dividing cells. One compound, methyl (N-benzoyl-(2'R,3'S)-3'-phenylisoserinate), inhibited T lymphocyte proliferation. This paper demonstrates that modified parts of the taxol molecule possess various types of biological activity in-vitro and in-vivo. Further experiments, focused on revealing their mechanisms of action, are necessary.