Tumor targeting by covalent conjugation of a natural fatty acid to paclitaxel.

Certain natural fatty acids are taken up avidly by tumors for use as biochemical precursors and energy sources. We tested in mice the hypothesis that the conjugation of docosahexaenoic acid (DHA), a natural fatty acid, and an anticancer drug would create a new chemical entity that would target tumors and reduce toxicity to normal tissues. We synthesized DHA-paclitaxel, a 2'-O-acyl conjugate of the natural fatty acid DHA and paclitaxel. The data show that the conjugate possesses increased antitumor activity in mice when compared with paclitaxel. For example, paclitaxel at its optimum dose (20 mg/kg) caused neither complete nor partial regressions in any of 10 mice in a Madison 109 (M109) s.c. lung tumor model, whereas DHA-paclitaxel caused complete regressions that were sustained for 60 days in 4 of 10 mice at 60 mg/kg, 9 of 10 mice at 90 mg/kg, and 10 of 10 mice at the optimum dose of 120 mg/kg. The drug seems to be inactive as a cytotoxic agent until metabolized by cells to an active form. The conjugate is less toxic than paclitaxel, so that 4.4-fold higher molar doses can be delivered to mice. DHA-paclitaxel in rats has a 74-fold lower volume of distribution and a 94-fold lower clearance rate than paclitaxel, suggesting that the drug is primarily confined to the plasma compartment. DHA-paclitaxel is stable in plasma, and high concentrations are maintained in mouse plasma for long times. Tumor targeting of the conjugate was demonstrated by pharmacokinetic studies in M109 tumor-bearing mice, indicating an area under the drug concentration-time curve of DHA-paclitaxel in tumors that is 8-fold higher than paclitaxel at equimolar doses and 57-fold higher at equitoxic doses. At equimolar doses, the tumor area under the drug concentration-time curve of paclitaxel derived from i.v. DHA-paclitaxel is 6-fold higher than for paclitaxel derived from i.v. paclitaxel. Even at 2 weeks after treatment, 700 nM paclitaxel remains in the tumors after DHA-paclitaxel treatment. Low concentrations of DHA-paclitaxel or paclitaxel derived from DHA-paclitaxel accumulate in gastrocnemius muscle; which may be related to the finding that paclitaxel at 20 mg/kg caused hind limb paralysis in nude mice, whereas DHA-paclitaxel caused none, even at doses of 90 or 120 mg/kg. The dose-limiting toxicity in rats is myelosuppression, and, as in the mouse, little DHA-paclitaxel is converted to paclitaxel in plasma. Because DHA-paclitaxel remains in tumors for long times at high concentrations and is slowly converted to cytotoxic paclitaxel, DHA-paclitaxel may kill those slowly cycling or residual tumor cells that eventually come into cycle.

Tumor targeting by conjugation of DHA to paclitaxel.

Targeting an anti-cancer drug to tumors should increase the Area Under the drug concentration-time Curve (AUC) in tumors while decreasing the AUC in normal cells and should therefore increase the therapeutic index of that drug. Anti-tumor drugs typically have half-lives far shorter than the cell cycle transit times of most tumor cells. Tumor targeting, with concomitant long tumor exposure times, will increase the proportion of cells that move into cycle when the drug concentration is high, which should result in more tumor cell killing. In an effort to test that hypothesis, we conjugated a natural fatty acid, docosahexaenoic acid (DHA), through an ester bond to the paclitaxel 2'-oxygen. The resulting paclitaxel fatty acid conjugate (DHA-paclitaxel) does not assemble microtubules and is non-toxic. In the M109 mouse tumor model, DHA-paclitaxel is less toxic than paclitaxel and cures 10/10 tumored animals, whereas paclitaxel cures 0/10. One explanation for the conjugate's greater therapeutic index is that the fatty acid alters the pharmacokinetics of the drug to increase its AUC in tumors and decrease its AUC in normal cells. To test that possibility, we compared the pharmacokinetics of DHA-paclitaxel with paclitaxel in CD2F1 mice bearing approximately 125 mg sc M109 tumors. The mice were injected at zero time with a bolus of either DHA-paclitaxel or paclitaxel formulated in 10% cremophor/10% ethanol/80% saline. Animals were sacrificed as a function of time out to 14 days. Tumors and plasma were frozen and stored. The concentrations of paclitaxel and DHA-paclitaxel were analyzed by LC/MS/MS. The results show that DHA targets paclitaxel to tumors: tumor AUCs are 61-fold higher for DHA-paclitaxel than for paclitaxel at equitoxic doses and eight-fold higher at equimolar doses. Likewise, at equi-toxic doses, the tumor AUCs of paclitaxel derived from i.v. DHA-paclitaxel are 6.1-fold higher than for paclitaxel derived from i.v. paclitaxel. The tumor concentration of paclitaxel derived from i.v. paclitaxel drops rapidly, so that by 16 h it has fallen to the same concentration (2.8 microM) as after an equi-toxic concentration of DHA-paclitaxel. In plasma, paclitaxel AUC after an MTD dose of DHA-paclitaxel is approximately 0.5% of DHA-paclitaxel AUC. Thus, the increase in tumor AUC and the limited plasma AUC of paclitaxel following DHA-paclitaxel administration are consistent with the increase in therapeutic index of DHA-paclitaxel relative to paclitaxel in the M109 mouse tumor model. A phase I clinical study has been completed at The Johns Hopkins Hospital to evaluate the safety of DHA-paclitaxel in patients with a variety of solid tumors. Twenty-one patients have been treated to date. The recommended phase II dose is 1100 mg/m(2), which is equivalent to 4.6 times the maximum approved paclitaxel dose on a molar basis. No alopecia or significant peripheral neuropathy, nausea, or vomiting have been observed. Asymptomatic, transient neutropenia has been the primary side effect. Eleven of 22 evaluable phase I patients transitioned from progressive to stable disease, as assessed by follow-up CT. Significant quality of life improvements have been observed. Thus, DHA-paclitaxel is well tolerated in patients and cures tumors in mice by targeting drug to tumors.

Fatty acid derivatives of clozapine: prolonged antidopaminergic activity of docosahexaenoylclozapine in the rat.

Stable amides of clozapine derived from fatty acids prominent in cerebral tissue might enhance the central activity of clozapine and reduce its exposure to peripheral tissues. Such derivatives might enhance the safety of this unique drug, which is the only agent with securely established superior antipsychotic effectiveness, but with a risk of potentially lethal systemic toxicity. Amide derivatives of clozapine were prepared from structurally varied fatty acid chlorides and evaluated for ability to inhibit behavioral arousal in rat induced by dopamine agonist apomorphine and to induce catalepsy. Their duration-of-action and potency were compared to free clozapine, and concentrations of clozapine were assayed in brain and blood. Selected agents were also evaluated for affinity at dopamine receptors and other potential drug-target sites. Clozapine-N-amides of linoleic, myristic, oleic, and palmitic acids had moderate initial central depressant activity but by 6 h, failed to inhibit arousal induced by apomorphine. However, the docosahexaenoic acid (DHA) derivative was orally bioavailable, 10-times more potent (ED(50) 5.0 micromol/kg) than clozapine itself, and very long-acting (>/= 24 h) against apomorphine, and did not induce catalepsy. DHA itself was inactive behaviorally. Clozapine showed expected dopamine receptor affinities, but DHA-clozapine was inactive at these and other potential target sites. After systemic administration of DHA-clozapine, serum levels of free clozapine were very low, and brain concentrations somewhat lower than after administering clozapine. DHA-clozapine is a long-acting central depressant with powerful and prolonged antidopaminergic activity after oral administration or injection without inducing catalepsy, and it markedly reduced peripheral exposure to free clozapine. It lacked the receptor-affinities shown by clozapine, suggesting that DHA-clozapine may be a precursor of free, pharmacologically active clozapine. Such agents may represent potential antipsychotic drugs with improved central/peripheral distribution, and possibly enhanced safety.

Molecular and genetic analysis of liver oncogenesis in transforming growth factor alpha transgenic mice.

Overexpression of a transforming growth factor alpha (TGF-alpha) transgene induced the development of liver tumors in 69 of 93 (74%) adult male mice. To identify factors associated with oncogenesis, liver tumors from transgenic animals were characterized at the molecular level. TGF-alpha RNA transcripts were elevated in 17 of 25 (68%) liver tumors, relative to adjacent nontumorous tissue. Expression of the endogenous c-myc and insulin-like growth factor II genes was enhanced in 7 of 19 (37%) and 12 of 16 (75%) tumors, respectively. In contrast, epidermal growth factor receptor RNA levels were unchanged or reduced in all liver tumors, and mutations were not detected in either the Ha-ras or Ki-ras genes. The occurrence of liver tumors in castrated TGF-alpha transgenic mice was reduced about 7-fold, while in ovariectomized transgenic animals the incidence was increased about 6-fold. The progeny of a cross between CD1-derived TGF-alpha transgenic (MT42) and C57BL/6 mice exhibited no reduction in tumor burden (83%); however, the incidence of tumor formation in MT42 x FVB/N offspring was substantially lower (19%). We conclude that in these transgenic mice TGF-alpha promotes tumor formation and appears to play a major role in tumor progression. Moreover, other factors that may collaborate in TGF-alpha-induced hepatocarcinogenesis include c-myc, insulin-like growth factor II, sex hormones, and the genetic background upon which the transgene operates.

Reversal of transformed phenotypes by antisense fos.

The therapeutic use of antisense DNA has started a revolution in pharmacology. As a model system for demonstrating the therapeutic power of the antisense concept, we sought to interrupt signal transduction in H-ras transformed cells to attempt to down-regulate their oncogenic phenotype. We hypothesized that down-regulation of c-fos translation by antisense-fos expression would decrease oncogenic signal transduction through the fos pathway and thus reverse the tumorigenic phenotype of these cells. To test this hypothesis, we transfected H-ras cells with a plasmid containing an 84-base sequence antisense to the 5' end of the mouse c-fos gene. The antisense-fos was under the transcriptional control of the MMTV promoter and inducible by dexamethasone. Two of the antisense-fos clones grew in a density-dependent manner, exhibiting both a flat morphology and a quiescence in low serum medium unlike the sense-fos controls. Antisense-fos also inhibited soft agar growth to 1% of control values and dramatically reduced tumor growth in nude mice. Antisense-fos had no effect on ras expression but greatly reduced c-fos protein levels as assayed by immunofluorescence. These findings suggest that down-regulation of signal transduction pathways by antisense therapeutic compounds might have major therapeutic benefits against malignant cells transformed by ras or other oncogenes.

Activation of the Ha-, Ki-, and N-ras genes in chemically induced liver tumors from CD-1 mice.

We compared the profile of ras gene mutations in spontaneous CD-1 mouse liver tumors with that found in liver tumors that were induced by a single i.p. injection of either 7,12-dimethylbenz(a)anthracene (DMBA), 4-aminoazobenzene, N-hydroxy-2-acetylaminofluorene, or N-nitrosodiethylamine. By direct sequencing of polymerase chain reaction-amplified tumor DNA, the carcinogen-induced tumors were found to have much higher frequencies of ras gene activation than spontaneous tumors. Furthermore, each carcinogen caused specific types of ras mutations not detected in spontaneous tumors, including several novel mutations not previously associated with either the carcinogen or mouse hepatocarcinogenesis. For example, the model compound DMBA is known to cause predominantly A to T transversions in Ha-ras codon 61 in mouse skin and mammary tumors, consistent with the ability of DMBA to form bulky adducts with adenosine. Our results demonstrate that the predominant mutation caused by DMBA in mouse liver tumors is a G to C transversion in Ki-ras codon 13 (DMBA is also known to form guanosine adducts), illustrating the influence of both chemical- and tissue-specific factors in determining the type of ras gene mutations in a tumor. 4-Aminoazobenzene and N-hydroxy-2-acetylaminofluorene also caused the Ki-ras codon 13 mutation. In addition, we found that N-nitrosodiethylamine, 4-aminoazobenzene, and N-hydroxy-2-acetylaminofluorene all caused G to T transversions in the N-ras gene (codons 12 or 13). This is the first demonstration of N-ras mutations in mouse liver tumors, establishing a role for the N-ras gene in mouse liver carcinogenesis. Finally, comparison of the ras mutations detected in the direct tumor analysis with those detected after NIH3T3 cell transfection indicates that spontaneous ras mutations (in Ha-ras codon 61) are often present in only a small fraction of the tumor cells, raising the possibility that they may sometimes occur as a late event in CD-1 mouse hepatocarcinogenesis.

Polymerase chain reaction/sequencing analysis of ras mutations in paraffin-embedded tissues as compared with 3T3 transfection and polymerase chain reaction/sequencing of frozen tumor deoxyribonucleic acids.

The efficiency of detection of H- and K-ras mutations in 27 CD-1 mouse liver tumors by direct sequencing of polymerase chain reaction (PCR)-amplified DNA isolated from formalin-fixed and paraffin-embedded tissues was compared with that after assay by both NIH 3T3 transfection (followed by sequencing of amplified transformant DNA) and direct sequencing of PCR-amplified DNA isolated from frozen tumors. Some tumor samples were chosen for comparison because they contained ras mutations that were detected by either NIH 3T3 transfection or sequencing of PCR-amplified DNA derived from frozen tumors, but were not detected by both techniques. The efficiency of detecting K-ras mutations was similar for sequencing of amplified fragments derived from both paraffin-embedded tissues and from frozen tumors. However, these two techniques differed in their efficacy for detection of H-ras codon 61 mutations. Furthermore, this difference appeared to be mutation-specific: the sequencing of amplified products from paraffin-embedded tumor tissues allowed increased detection of CAA to AAA mutations but decreased detection of CAA to CTA mutations relative to sequencing of amplified fragments derived from frozen tumor DNA. Direct sequencing of PCR products from paraffin-embedded sections was more sensitive than NIH 3T3 transfection for detection of activated K-ras genes containing codon 13 mutations but less sensitive for detection of activated H-ras genes containing codon 61 mutations. In summary, direct sequencing of amplified DNA from either frozen tumors or formalin-fixed, paraffin-embedded tissues can be more sensitive than NIH 3T3 transfection for detection of codon 13-activated K-ras genes. However, it appears to be less sensitive than NIH 3T3 transfection for detection of certain activating H-ras mutations. Depending upon the questions being asked of the data, each of the methods can provide useful information about ras gene mutations in tumor samples. The apparent differences in sensitivities between the methods is not yet understood, but such differences should be considered in the analysis of data obtained when only one method is used.

Influence of chromatin structure on the induction of DNA double strand breaks by ionizing radiation.

Pulsed field gel electrophoresis was used to examine the influence of chromatin structure on the induction of DNA double strand breaks by gamma-irradiation in CHO-WBL cells, nuclei, and a series of protein-depleted chromatin substrates. We developed a method to isolate intact nuclei in agarose plugs that avoids DNA shearing and nucleolytic degradation during sample preparation, and facilitates nuclear protein extraction. Agarose plug-isolated nuclei are extracted with increasing concentrations of NaCl to selectively strip off: (a) nonhistone chromosomal proteins (NHP); (b) NHP and histone H1; (c) NHP, H1, and histone H2A-H2B dimers; or (d) NHP, H1, and H2A-H2B dimers and histone H3-H4 tetramers. Following treatment with up to 40 Gy of gamma-radiation, DNA from each sample is purified and the relative induction of DNA double strand breaks is assayed by asymmetric field inversion gel electrophoresis. At a dose of 20 Gy, removal of nonhistone proteins from nuclei results in a 3-fold increase in DNA double strand breaks, compared to intact CHO cells. Additional stripping of histone H1 results in an incremental increase in double strand break induction, whereas further removal of H2A-H2B dimers yields a greater than 10-fold increase in DNA double strand breaks compared to intact CHO cells. The dose-response profile for this latter sample is similar to that observed for purified DNA. These data indicate that distinct classes of chromosomal proteins afford the DNA with different levels of protection against gamma-ray-induced DNA double strand breaks. Thus, chromatin domains that differ in tertiary structure and protein composition may also differ in their susceptibility to DNA double strand breaks induced by ionizing radiation and, perhaps, other clastogens.

Murine p53 intron sequences 5-8 and their use in polymerase chain reaction/direct sequencing analysis of p53 mutations in CD-1 mouse liver and lung tumors.

Inactivating point mutations and small deletions in the p53 tumor suppressor gene have been found in human liver and lung tumor--derived cell lines and tumors. However, little evidence has been reported concerning inactivation or mutation of the p53 gene in mouse primary tumors. To examine CD-1 mouse liver and lung tumors for mutations in the p53 gene, we first sequenced p53 introns 5-8 so that polymerase chain reaction amplification and sequencing primers located within the introns could be prepared. Use of these primers prevented amplification of the mouse p53 pseudogene and allowed sequencing of exons 5-8 in their entirety as well as their intron-exon junctions. DNA isolated from CD-1 mouse tumors was amplified and directly sequenced using nested primers. Nine spontaneous hepatocellular carcinomas (HCCs) and 34 chemically induced HCCs (induced by single intraperitoneal injections of N-nitrosodiethylamine [DEN] [8 HCCs], 7,12-dimethylbenz[a]anthracene [DMBA] [8 HCCs], 4-aminoazobenzene [8 HCCs], and N-OH-2-acetylaminofluorene [10 HCCs]) were examined for mutations in exons 5-8 of the p53 gene. In addition, 12 spontaneous, 10 DMBA-induced, and 13 DEN-induced lung adenocarcinomas or adenomas were analyzed for mutations. No mutations were found in any of the tumors examined. However, a mutation was demonstrated at codon 135 in the positive-control plasmid LTRp53cG(val). The results of this study suggest that inactivation of p53 is unlikely to play a major role in murine lung or liver carcinogenesis. However, inactivation of p53 may occur at a very low frequency, or it may occur as a late event and therefore be present in only a very small number of the tumor cells, rendering it undetectable by this method. Lastly, although few p53-inactivating mutations are found outside of exons 5-8 in human tumors, it is possible that these murine tumors contained mutations outside of this region and were therefore missed by our approach.

Activation of the Ki-ras gene in spontaneous and chemically induced lung tumors in CD-1 mice.

As part of an evaluation of the effectiveness of using ras mutation analysis for distinguishing carcinogen-induced from spontaneous tumors, we examined the profile of ras gene point mutations in spontaneous, 7,12-dimethylbenz[a]anthracene (DMBA)-induced, and N-nitrosodiethylamine (DEN)-induced lung tumors from Crl:CD-1(ICR)BR (CD-1) mice. Although all of the lung tumors were assayed for mutations in the Ha-ras, Ki-ras, and N-ras genes (codons 12, 13, and 61), only Ki-ras mutations were found, which is consistent with other studies that have noted a strong preference for Ki-ras gene activation in mouse, rat, and human lung tumors. We found that spontaneous CD-1 mouse lung tumors had a very high frequency of Ki-ras gene activation (17 of 20 tumors; 85%), distributed among codons 12 (5 of 20), 13 (1 of 20), and 61 (11 of 20). DMBA-induced lung tumors had a slightly higher frequency of Ki-ras gene mutations (16 of 16; 100%), again distributed among codons 12 (5 of 16), 13 (2 of 16), and 61 (9 of 16). However, seven of the DMBA tumors had mutations qualitatively different from those found in spontaneous tumors. In contrast to DMBA-induced tumors, DEN-induced tumors had a lower frequency of Ki-ras mutations (36%) when compared with spontaneous lung tumors, suggesting that DEN primarily induces lung carcinogenesis by a mechanism other than ras gene activation. Thus, although spontaneous and induced CD-1 mouse lung tumors have a strong tissue-specific preference for carrying an activated Ki-ras gene, the nature of the initiating carcinogen can influence the frequency or profile of Ki-ras mutations.

Gender differences in age-related decline in DNA double-strand break damage and repair in lymphocytes.

DNA repair capacity has been suggested to be a genetic mechanism which influences the rate of ageing and length of life. We recently reported an age-related decline in DNA double-strand break (DSB) repair in unstimulated human lymphocytes (Mayer, Lange, Bradley, and Nichols 1989, 1990). In that work peripheral lymphocytes isolated from whole blood donated by 20 normal, healthy subjects aged 23-78 years, were X-irradiated (30 Gy) on ice and incubated at 37 degrees C for repair times of 15, 30, and 120 min, and neutral filter elution was used to assay DSB induction and completeness of DSB rejoining. Further analysis reveals that the decrease in DSB rejoining appears to be more pronounced in older women than in older men (and may begin after age 65 years). Moreover the reported age-related decline in DSB induction occurs more rapidly (by a factor of ca. 2) in women than in men. We had previously demonstrated that, independently of in vivo age, cells with lower radiosensitivity (i.e. lesser DSB induction) appear to be less repair-proficient (Mayer et al. 1990). The present analysis reveals a gender-specific pattern in this correlation between extent of DSBs induced and percentage of DSBs rejoined: at comparable levels of DSB induction, cells from men rejoin a higher percentage of DSBs than do cells from women. This preliminary study suggests the following hypothesis: age-related DSB effects (i.e. induction and rejoining) are due to changes in chromatin structure and males are less sensitive than females to the influence which age-related alterations in chromatin exert on DSB effects.

The effect of deuterium labeling on the genotoxicity of N-nitrosodimethylamine, epichlorohydrin and dimethyl sulfate.

Deuterated and non-deuterated N-nitrosodimethylamine, epichlorohydrin and dimethyl sulfate were evaluated for the ability to induce DNA single-strand breaks in rat hepatocytes as measured by alkaline elution. Non-deuterated nitrosodimethylamine induced twice the amount of DNA-strand breaks as the deuterated form. No evidence of a deuterium isotope effect was seen for the direct-acting alkylating agents epichlorohydrin and dimethyl sulfate.

Selection of low frequency tumor cells from cell culture by growth in nude mice.

Tissue cultures of tumor cells are frequently utilized to characterize chromosomal changes when direct cytogenetic preparations on tumors fail. The present study demonstrates that chromosomal markers found in direct tumor preparations can become undetectable in cell culture at variable rates presumably because of overgrowth of normal cell components in the culture. Injection of cultured tumor cells into nude mice followed by direct chromosomal preparations on the resulting nude mouse tumors can be used to select cells with the original tumor karyotype. This is true even when the tumor cell frequency in the culture is so low that they are not found in routine chromosomal preparations of the cultured cells. This technique can thus complement tissue culture findings and provide additional useful information about the original karyotype in cases where direct chromosomal preparations from tumors have failed.

Investigation of the neutral filter elution technique I. Effects of pore density and pore diameter on elution rate at pH 9.6.

To understand better the biophysical mechanism of neutral filter elution (pH 9.6), we eluted genomes of known size and shape: coliphage T4c (Mr 1.15 x 10(8), E. coli (Mr 2.7 x 10(9)), and Chinese hamster lung fibroblasts (V79, Mr 2-4 x 10(10)). DNA eluted through 15% sucrose atop the filter in a biphasic pattern. The elution rate of the initial component correlated (r greater than 0.97) exponentially with 1/Mr for monodisperse samples of DNA eluted through pore sizes 0.1-3.0 microns. Using this relationship between elution rate and Mr, we estimated Mn of polydisperse, X-irradiated (253 Gy) samples of DNA from E. coli or V79 cells to be 3.15 +/- 1.46 and 1.42 +/- 0.33, respectively, compared to expected values of 2.93 and 3.52 (10(8) Da). The best predictor of elution rate for DNA from T4c and intact and X-irradiated V79 cells was pore density, and pore diameter for DNA from X-irradiated E. coli. The rate of elution of DNA from unirradiated E. coli was unrelated to pore density or diameter. While the mechanism of neutral filter elution remains unknown, its use for linear DNAs with Mn ca. 10(8) Da appears to be valid quantitatively.

Significance and measurement of DNA double strand breaks in mammalian cells.

Techniques for measuring DNA double strand breaks in mammalian cells are being used increasingly by researchers studying both physiological processes, such as recombination, replication, and apoptosis, as well as pathological processes, such as clastogenesis induced by ionizing radiation, chemotherapeutic drugs, and chemical toxicants. In this review we evaluate commonly used assays for measuring DNA double strand breaks, focusing on neutral filter elution and pulsed field gel electrophoresis, and explore the advantages and limitations of applying these techniques to problems of current interest in carcinogenesis and genetic toxicology.

DNA fingerprinting of 7,12-dimethylbenz[a]anthracene-induced and spontaneous CD-1 mouse liver tumors.

Determining to what degree chemicals and environmental agents contribute to the development of cancer would be materially enhanced by the ability to distinguish chemically induced tumors from those that arise spontaneously. Using DNA fingerprinting as an assay, we investigated whether somatic DNA rearrangements are more frequent in chemically induced mouse liver tumors than they are in spontaneous mouse liver tumors. Tumors were induced by a single i.p. injection of 12-day old male Crl:CD-1(ICR)BR (CD-1) mice with 20 nmol/g 7,12-dimethylbenz[a]-anthracene and were harvested 9 to 12 months after injection. Spontaneous tumors were obtained from 94- to 98-week old male CD-1 mice. We detected 8 rearrangements in 14 7,12-dimethylbenz[a]anthracene-induced tumors, which corresponds to a high rearrangement frequency of about 2% (of the minisatellite bands examined). Furthermore, 6 of these rearrangements included complete band losses which must have occurred early in tumor development. However, only 2 band changes were observed in 15 spontaneous tumors, and both changes were intensity shifts which may represent rearrangements that occurred later during tumor progression. Histological examination showed that the higher frequency of rearrangements in 7,12-dimethylbenz[a]anthracene-induced tumors versus spontaneous tumors was not related to differences in the degree of tumor progression or malignancy. Our results suggest that DNA fingerprinting may be a valuable assay for differentiating certain chemically induced tumors from spontaneous tumors.

Preparation of synthetic tandem-repetitive probes for DNA fingerprinting.

DNA fingerprints are generated using probes that hybridize to hypervariable minisatellites, also known as variable number tandem repeat loci. Cloned minisatellites have served as the predominant source of DNA fingerprinting probes. A short segment within the repeat units of minisatellites, called the "core" sequence, is highly conserved within a family of related minisatellites, thereby allowing a single-cloned minisatellite to cross-hybridize to 20 to 40 other minisatellites. In this article, we describe a method for the synthetic preparation of polymeric core sequence probes for DNA fingerprinting. Unlike "monomeric" oligonucleotide probes, the polymeric probes mimic the tandem-repetitive structure of minisatellites, and thus each probe molecule can potentially form many sites of hybridization with a target minisatellite. The synthetic probes are cloned into plasmid DNA to provide a perpetual source of probe material.

Antisense-fos RNA causes partial reversion of the transformed phenotypes induced by the c-Ha-ras oncogene.

Several lines of evidence have suggested that c-fos may act downstream from c-Ha-ras in a growth-regulatory signal transduction pathway. We used antisense RNA to inhibit c-fos gene expression and investigated the effects of diminished c-fos expression on the phenotypes induced by the EJ c-Ha-ras oncogene in NIH 3T3 cells. Immunofluorescent staining demonstrated that the antisense RNA caused a marked reduction in the amount of c-fos protein expressed following serum stimulation. EJ cells containing antisense-fos RNA continued to overexpress ras and remained capable of proliferating in vitro. However, the antisense-fos RNA caused a partial reversion of the major transformed phenotypes of EJ cells, including a restoration of both density-dependent growth arrest and the ability to be rendered quiescent by serum deprivation, a reversion to a flat morphology, inhibition of anchorage-independent growth, and inhibition of tumorigenicity in nude mice. Our results indicate that inhibition of c-fos expression, to a level still supporting in vitro proliferation, prevents the transforming effects of the ras oncogene; they thus provide additional evidence for the participation of c-fos in ras-regulated signal transduction pathways.