We have used an in vivo tumor model to evaluate the consequences of p53 tumor suppressor protein deficiency in a tissue-specific context. By breeding MMTV-ras transgenic mice, which are highly susceptible to the development of mammary and salivary tumors, with p53 ؊/؊ mice, we generated three classes of animals which contained the MMTV-ras transgene but differed in their p53 functional status (ras/p53؊/؊ ). ras/p53 ؊/؊ mice developed tumors more rapidly than animals of the other two genotypes; however, the distribution of tumors was unexpectedly altered. Whereas the most frequently observed tumors in ras/p53 ؉/؉ and ras/p53 ؉/؊ mice were of mammary origin, ras/p53 ؊/؊ mice developed primarily salivary tumors. In addition, the mammary and salivary tumors from ras/p53 ؊/؊ mice consistently exhibited a number of unfavorable characteristics, including higher histologic grades, increased growth rates, and extensive genomic instability and heterogeneity, relative to tumors from ras/p53 ؉/؉ mice. Interestingly, the increased growth rates of ras/p53 ؊/؊ tumors appear to be due to impaired cell cycle regulation rather than decreased apoptosis, suggesting that p53-mediated tumor suppression can occur independent of its role in apoptosis.

The farnesyltransferase inhibitor L-744,832 selectively blocks the transformed phenotype of cultured cells expressing a mutated H-ras gene and induces dramatic regression of mammary and salivary carcinomas in mouse mammary tumor virus (MMTV)-v-Ha-ras transgenic mice. To better understand how the farnesyltransferase inhibitors might be used in the treatment of human tumors, we have further explored the mechanisms by which L-744,832 induces tumor regression in a variety of transgenic mouse tumor models. We assessed whether L-744,832 induces apoptosis or alterations in cell cycle distribution and found that the tumor regression in MMTV-v-Ha-ras mice could be attributed entirely to elevation of apoptosis levels. In contrast, treatment with doxorubicin, which induces apoptosis in many tumor types, had a minimal effect on apoptosis in these tumors and resulted in a less dramatic tumor response. To determine whether functional p53 is required for L-744,832-induced apoptosis and the resultant tumor regression, MMTV-v-Ha-ras mice were interbred with p53 ؊/؊ mice. Tumors in ras/p53 ؊/؊ mice treated with L-744,832 regressed as efficiently as MMTV-v-Haras tumors, although this response was found to be mediated by both the induction of apoptosis and an increase in G 1 with a corresponding decrease in the S-phase fraction. MMTV-v-Ha-ras mice were also interbred with MMTV-c-myc mice to determine whether ras/myc tumors, which possess high levels of spontaneous apoptosis, have the potential to regress through a further increase in apoptosis levels. The ras/myc tumors were found to respond nearly as efficiently to L-744,832 treatment as the MMTV-v-Ha-ras tumors, although no induction of apoptosis was observed. Rather, the tumor regression in the ras/myc mice was found to be mediated by a large reduction in the S-phase fraction. In contrast, treatment of transgenic mice harboring an activated MMTVc-neu gene did not result in tumor regression. These results demonstrate that a farnesyltransferase inhibitor can induce regression of v-Ha-ras-bearing tumors by multiple mechanisms, including the activation of a suppressed apoptotic pathway, which is largely p53 independent, or by cell cycle alterations, depending upon the presence of various other oncogenic genetic alterations.

Background. The authors evaluated the effects of taxol, a microtubular inhibitor, as a possible radiation sensitizer on the human leukemic cell line (HL‐60). Taxol acts as a mitotic inhibitor, blocking cells in the G2M‐phase of the cell cycle. The differential radiation sensitivity of cells in various phases of the cell cycle has been well recognized. This study was focused on the possible interaction between radiation and a microtubular inhibitor, taxol, in regard to its ability to synchronize cells at the G2M‐phase of cell cycle and, thereby, enhance the radiation sensitivity of the cells. Methods. HL‐60 cells were exposed to 3 × 10−8 M concentrations of taxol for 1 hour at 37°CCfollowed by reculturing for 24 hours in drug‐free medium. The cells were then seeded into 60‐mm diameter plastic dishes at appropriate cell concentrations to estimate their colonyforming efficiency. The radiation dose ranged from 0–400 cGy and was delivered in a single fraction. The cellular survival after treatment with the drug and/or radiation was determined using a soft agar clonogenic assay. Results. When HL‐60 cells were treated with taxol, up to 70% of the cells were blocked in G2M‐phase, as determined by flow cytometric analysis. At the low cytotoxic dose of 3 × 10−8 M, the sensitizing enhancement ratio was 1.48. Conclusions. It appears that taxol has a radiation‐sensitizing effect on HL‐60 cells and deserves further investigation with other cell lines.

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Stable aqueous dispersions consisting of CdS nanoparticles having modal diameters, ranging between 2 and 8 nm, were prepared with amino-derivatized polysaccharides (aminodextrans, hence abbreviated as Amdex) as the stabilizing agents. The size, stability, and luminescence intensity of such dispersions were shown to be dependent on the types of the cadmium salts and aminodextrans used, as well as on the reactant concentrations. Specifically, it was demonstrated that the degree of substitution of amino groups in the aminodextran molecules greatly affected the properties of the dispersions; i.e., with higher degree of substitution, smaller CdS particles and higher luminescence intensity were achieved. It was also shown that the Amdex-CdS nanoparticle complexes could be activated and conjugated with antibody by conventional means. Molecular weight ranges of the Amdex and their complexes with CdS nanoparticles and the purity of antibody-Amdex-CdS nanoparticle conjugates were determined by polyacrylamide gel electrophoresis combined with Coomassie blue staining of resultant gel bands. The purified conjugate of the aminodextran-CdS nanoparticle complex with anti-CD4 monoclonal antibody was mixed with a whole blood control, followed by indirect sheep antimouse antibody-phycoerythrin (SAM-PE) labeling of washed cells incubated with T4-5X-Amdex-CdS. Red blood cells were then lysed and quenched, and the resulting mixture, which was run on a flow cytometer with 488.0 nm argon ion laser excitation, suggested that the T4 antibody from the conjugate was present specifically on lymphocytes.