Mammary Tumor Agent Research Articles

The Viral Origin of Human Breast Cancer: From the Mouse Mammary Tumor Virus (MMTV) to the Human Betaretrovirus (HBRV).

A Human Betaretrovirus (HBRV) has been identified in humans, dating as far back as about 4500 years ago, with a high probability of it being acquired by our species around 10,000 years ago, following a species jump from mice to humans. HBRV is the human homolog of the MMTV (mouse mammary tumor virus), which is the etiological agent of murine mammary tumors. The hypothesis of a HMTV (human mammary tumor virus) was proposed about 50 years ago, and has acquired a solid scientific basis during the last 30 years, with the demonstration of a robust link with breast cancer and with PBC, primary biliary cholangitis. This article summarizes most of what is known about MMTV/HMTV/HBRV since the discovery of MMTV at the beginning of last century, to make evident both the quantity and the quality of the research supporting the existence of HBRV and its pathogenic role. Here, it is sufficient to mention that scientific evidence includes that viral sequences have been identified in breast-cancer samples in a worldwide distribution, that the complete proviral genome has been cloned from breast cancer and patients with PBC, and that saliva contains HBRV, as a possible route of inter-human infection. Controversies that have arisen concerning results obtained from human tissues, many of them outdated by new scientific evidence, are critically discussed and confuted.

A human MMTV-like betaretrovirus linked to breast cancer has been present in humans at least since the copper age.

The betaretrovirus Mouse Mammary Tumor Virus (MMTV) is the well characterized etiological agent of mammary tumors in mice. In contrast, the etiology of sporadic human breast cancer (BC) is unknown, but accumulating data indicate a possible viral origin also for these malignancies. The presence of MMTVenv-like sequences (MMTVels) in the human salivary glands and saliva supports the latter as possible route of inter-human dissemination. In the absence of the demonstration of a mouse-man transmission of MMTV, we considered the possibility that a cross-species transmission could have occurred in ancient times. Therefore, we investigated MMTVels in the ancient dental calculus, which originates from saliva and is an excellent material for paleovirology. The calculus was collected from 36 ancient human skulls, excluding any possible mouse contamination. MMTV-like sequences were identified in the calculus of 6 individuals dated from the Copper Age to the 17th century. The MMTV-like sequences were compared with known human endogenous betaretroviruses and with animal exogenous betaretroviruses, confirming their exogenous origin and relation to MMTV. These data reveal that a human exogenous betaretrovirus similar to MMTV has existed at least since 4,500 years ago and indirectly support the hypothesis that it could play a role in human breast cancer.

Pituitary Isograft Transplantation in Mice.

The mouse pituitary isograft is a technique developed to administer persistent hormone stimulation, thereby increasing cellular proliferation in the mammary tissue ( Christov et al., 1993 ). The pituitary isograft procedure was first described in 'Induction of Mammary Cancer in Mice without the Mammary Tumor Agent by Isografts of Hypophyses' by O. Mühlbock and L. M. Boot in 1959 (Muhlbock and Boot, 1959). Since then, the procedure has seen wide use. A pituitary gland is harvested posthumously from a donor mouse and implanted under the renal capsule of the recipient mouse through a small abdominal incision just below the last rib. Once the pituitary gland is implanted, it begins releasing hormones. These secretions increase serum levels of multiple hormones including prolactin, progesterone and 17β-estradiol ( Christov et al., 1993 ). Although the effects of these hormones on cancer cell proliferation, growth, differentiation, and longevity are not well characterized, and, in some cases, controversial, the net effect of a pituitary isograft is to increase the proliferation of murine breast tissue depending upon strain specific characteristics ( Lydon et al., 1999 ). Below is a protocol describing how to perform the pituitary isograft procedure. After many of the steps, a time reference is listed in parentheses. Each reference corresponds to a time point in the embedded video of the procedure. (Video 1) Video 1.Pituitary isograft transplantation in mice. Video portraying pituitary isograft transplantation procedure in donor and recipient mice.

A Novel Plant Sesquiterpene Lactone Derivative, DETD-35, Suppresses BRAFV600E Mutant Melanoma Growth and Overcomes Acquired Vemurafenib Resistance in Mice.

Acquired resistance to vemurafenib develops through reactivation of RAF/MEK/ERK signaling or bypass mechanisms. Recent combination therapies such as a MEK inhibitor combined with vemurafenib show improvement in major clinical end points, but the percentage of patients with adverse toxic events is higher than with vemurafenib monotherapy and most patients ultimately relapse. Therefore, there is an urgent need to develop new antimelanoma drugs and/or adjuvant agents for vemurafenib therapy. In this study, we created a novel semiorganically modified derivative, DETD-35, from deoxyelephantopin (DET), a plant sesquiterpene lactone demonstrated as an anti-inflammatory and anti-mammary tumor agent. Our results show that DETD-35 inhibited proliferation of a panel of melanoma cell lines, including acquired vemurafenib resistance A375 cells (A375-R) established in this study, with superior activities to DET and no cytotoxicity to normal melanocytes. DETD-35 suppressed tumor growth and reduced tumor mass as effectively as vemurafenib in A375 xenograft study. Furthermore, DETD-35 also reduced tumor growth in both acquired (A375-R) and intrinsic (A2058) vemurafenib resistance xenograft models, where vemurafenib showed no antitumor activity. Notably, the combination of DETD-35 and vemurafenib exhibited the most significant effects in both in vitro and in vivo xenograft studies due to synergism of the compound and the drug. Mechanistic studies suggested that DETD-35 overcame acquired vemurafenib resistance at least in part through deregulating MEK-ERK, Akt, and STAT3 signaling pathways and promoting apoptosis of cancer cells. Overall, our results suggest that DETD-35 may be useful as a therapeutic or adjuvant agent against BRAF(V600E) mutant and acquired vemurafenib resistance melanoma. Mol Cancer Ther; 15(6); 1163-76. ©2016 AACR.

No Evidence of Mammary Tumor Virus env Gene-Like Sequences among Iranian Women with Breast Cancer

Objective: The mouse mammary tumor virus (MMTV) is the well-established etiological agent of mammary tumors in mice. A series of studies have implicated that a human murine mammary tumor virus-like virus occurs in human breast cancer, but it is unclear whether it has any causal role. Methods: The aim of the present study was to investigate the presence of MMTV env gene-like sequences in a group of Iranian women with or without breast cancer. A total of 65 breast cancer and 65 noncancerous breast specimens from the Department of Pathology of Tabriz University in East Azerbaijan, Iran, were analyzed by nested PCR. Results: All breast cancer and benign breast samples were negative for MMTV env gene-like DNA. Conclusion: These results indicate that the MMTV env gene-like virus may not play a significant role in the etiology of breast cancer among Iranian women.

Human Mammary Tumor Virus (HMTV) in Endometrial Carcinoma

Human mammary tumor virus (HMTV) is 90% to 98% homologous to mouse mammary tumor virus, the etiological agent of mammary tumors in mice. Human mammary tumor virus sequences were found in 40% of the breast cancers studied in both American and Australian women. In addition, 10% of endometrial carcinomas studied in Australian women also contained HMTV sequences. We have explored the possibility that endometrial cancer of American women may also contain HMTV. Nested polymerase chain reactions, radioactive internal probing, and sequencing were used to establish the presence of unique nucleotide sequences of HMTV in human genomic DNA. The genomic DNAs were tested to guarantee that they were free of murine DNA. Immunohistochemistry with a monoclonal antibody specific for HMTV envelope protein demonstrated that HMTV sequences were translated. Thirteen (23.2%) of 56 of the endometrial cancers studied contained HMTV sequences and proteins. Human mammary tumor virus sequences and protein were not detected in the 33 normal endometria studied. Human mammary tumor virus, an agent with high homology to mouse mammary tumor virus, was found in 23.2% of the endometrial cancers studied, thus opening the possibility of a pathogenic role.

Variable Transcriptional Activity of Endogenous Retroviruses in Human Breast Cancer

Human endogenous retroviruses (HERVs) account for up to 9% of the human genome and include more than 800 elements related to betaretroviruses. While mouse mammary tumor virus (MMTV) is the accepted etiological agent of mammary tumors in mice, the role of retroviral elements in human breast cancer remains elusive. Here, we performed a comprehensive microarray-based analysis of overall retroviral transcriptional activities in 46 mammary gland tissue specimens representing pairs of nonmalignant and tumor samples from 23 patients. An analysis of nonmalignant tissue samples revealed a distinct, mammary gland-specific HERV expression profile that consists of 18 constitutively active HERV taxa. For corresponding tumor samples, a general trend toward lower levels of HERV transcription was observed, suggesting common regulatory mechanisms. In various subsets of patients, however, increased transcript levels of single class I HERV families (HERV-T, HERV-E, and HERV-F) and several class II families, including HML-6, were detected. An analysis of transcribed HML-6 sequences revealed either the activation of some or the increased activity of several proviral loci. No evidence for MMTV or human MMTV-like virus transcripts was found, indicating that transcriptionally active, MMTV analogous, exogenous viruses were not present in the breast cancer samples analyzed.

Possible Related Risks to Breastfeeding

Animal studies have identified a mouse mammary tumor agent transmitted through lactation that increases the incidence and reduces the age for tumor development in offspring. A similar viral particle has been detected with greater frequency in the milk of humans with a family history of breast carcinoma than in the milk of those with no history. Animal studies also indicate that a male offspring who has been breastfed, at low risk himself, could possibly transmit the agent through seminal fluid. The health team is encouraged to consider these factors when discussing infant feeding methods with women who have a positive family history of breast carcinoma.

Unique glycoprotein from mouse milk containing the mammary tumour agent.

MILK from mice containing the mammary tumour agent contains a unique chemical determinant which is antigenic in rabbits1–4. Agent-free mice can produce this antigen when they either suckle or receive by injection the milk containing the agent. We undertook the isolation and identification of this antigen to obtain insight into the mechanism of the malignant transformation—for its distribution and that of the tumorigenic potential in milk are similar4—and describe here our procedures.

The distribution of the mouse mammary tumor agent and its antigenicity in milk.

AbstractInbred mice with a propensity for mammary tumor development contain the mammary tumor agent and a specific soluble antigen in their milk. These were found in approximately equal proportions in both the supernatant and the pellet after ultracentrifugation. Over 90% of the agent and the highest antigen titer were located in a density range of 1.06–1.075 in ficoll density gradients. The low tumorigenic potential and the antigenicity of the B particle band (p = 1.12) remained with the particles after removal of proteinaceous contaminant by gel filtration. The immunogen from the upper portion (p = 1.06–1.075) of ficoll gradients appears to aggregate when concentrated and eluted from gel filtration columns. The tumorigenic material isolated from ECTEOLA and carboxymethylcellulose chromatographic columns does not show a high positive correlation with the distribution of the virus‐like B particles, which was consistent with the finding that the agent was concentrated in a narrow region with an average density of 1.28 in cesium chloride density gradients. The antigen associated with B particles and the lower molecular weight active component are immunologically identical.

Induction de tumeurs mammaires par injections d'extraits acellulaires de leucémies PS à des souriceaux d'autres souches

Cell free extracts from 10 leukaemias and 2 passages of leukaemic isografts PS were obtained following Gross's or Moloney's technique. Some of them were submitted to ultracentrifugation on preformed density gradients of potassium citrate. Cell free extracts and the zones collected after untralcentrifugation were injected into new-born and weanling mice of different strains: 101 BALB c , C3 H eB , Swiss and PS mice survived 9 months. The occurrence of mammary tumours was the prominent feature of this study: 62,5 per cent of the BALB c , 66% of the C3 H eB , 23% of the Swiss developed mammary tumours. In the PS strain, the mean age of mammary tumours' development fell from 10,3 months in the controls to 6,4 months in the inoculated mice. These results are discussed. So is the action of polyoma virus and the blood-borne activity of mammary tumour agent. These results are compared with those obtained with other strains of mice carrying both a mammary tumour agent and a leukaemia virus.

Propagation of the Mammary Tumor Agent (Bittner Virus) in the Absence of Mammary Glands in Mice

Propagation of the Mammary Tumor Agent (Bittner Virus) in the Absence of Mammary Glands in Mice

The mammary tumor virus (MTV).

During the early decades of this century, three factors were found to play major roles in the genesis of mammary tumors in mice: the genetic constitution of the mouse, hormonal stimulation, and the milk-transmitted mammary tumor agent or virus (Bittner, 1939b, 1939d, 1942c). The fact that mouse strains with a high incidence of mammary tumors as well as strains with a very low incidence could be developed by inbreeding and selection suggested the importance of the genotype of the mouse. The observation that tumors appeared only in females indicated the role of hormonal stimulation, which was established by experiments involving castration and exogenous hormone administration. Reciprocal crosses between strains revealed the presence of an extrachromosomal maternal influence, which was soon identified as a milk-transmitted virus.

Studies on hypophyseal isografts in mice. I. Biologic aspects

Experiments are reported on the induction of mammary carcinoma in intact, mammary tumor agent (MTA)-free female (♀ O20 x ♂ DBAf)F1 mice by single and multiple (4) prolactin-producing hypophyseal isografts in the kidney. Tumor incidences varying between 67 and 88% were recorded in the treated groups as against 2% in virgin controls. Identical treatment of intact and castrated males proved totally ineffective. In the female hosts all grafts became extremely enlarged—some weighing up to 2000 mg or even more—whereas in the male animals they seldom exceeded 10 mg. Evidence is put forward which suggests a difference in hypothalamic control over the ectopic hypophyses between female and male animals due to a basic difference in hypothalamic prolactin-inhibiting factor (PIF) potency, which is enhanced by the suppression of PIF by estrogens. The neoplastic transformation of the enlarged grafts is questioned.

Localization of an Inhibitor preventing Mammary Tumour Development in Mice

MANY research workers have found it difficult to get high incidences of tumours using a partially purified mammary tumour agent injected into test mice. It was found that the agent retains its high biological activity after centrifugation in caesium chloride density gradients1. This finding makes it unlikely that the usual procedures for purifying the agent, such as clarification with versene and ultracentrifugation, inactivate it.

Decreased susceptibility to the mammary tumour agent in mice with advancing age.

AbstractIn mice, susceptibility to the mammary tumour agent (Bittner virus) decreases with advancing age. With the newly developed technique of transplantation of the mammary gland and of complete extirpation of all mammary glands, the role of the host and of the mammary gland with regard to the decreased susceptibility towards the mammary tumour agent was investigated. The experiments were done with female hybrids (♀ O20 × ♂ DBAf) F1. The susceptibility to the mammary tumour agent was determined by the percentage of mammary tumours which appeared in the transplanted glands. Comparison was made between the tumour incidence in young mammary glands transplanted into both young and old hosts and in old mammary glands transplanted into young and old hosts. Both the age of the host and the age of the mammary gland are determining factors in the development of mammary tumours. With advancing age of the host and advancing age of the mammary gland, tumour incidence in the mammary gland decreases and the induction time is longer under otherwise equal conditions.

Tumour incidence in mammary glands transplanted from the strains C3H and O20 into their mammectomized F1-hybrids.

AbstractIt has been demonstrated that genetic factors play an important role in the genesis of mammary cancer in mice but it was not known if the genetic action is localized in the mammary gland tissues or if the genetic influence is effective through some systemic mechanism. In this investigation the mammary glands from the inbred strains C3Hf and O20, differing in the incidence of mammary tumours, were transplanted into a common host, the F1 hybrid, so that systemic influences would be equal. A difference in susceptibility to tumour development was found between the transplanted C3Hf and O20 mammary glands. In the group of animals free of the agent there is a difference in tumour frequency. In the animals carrying the mammary tumour agent this difference is expressed in the average tumour age at which the tumours develop. The genetic susceptibility in these two strains is, therefore, retained in the transplanted mammary glands.Transplantation per se has no influence on tumour development.Transplanted mammary glands react in the same manner as mammary glands in situ. All transplantations have been done into completely mammectomized hosts to avoid interference with tumours developing in the glands of the host. Investigations with partly mammectomized animals have shown that the mammary tumour frequency and the average tumour age are related to the amount of mammary gland tissue present. A reduction of the mammary gland tissue also reduces the tumour frequency or delays the appearance of mammary tumours.

Note on a new inbred mouse-strain GR/A

A new inbred mouse -strain GR has been developed. Breeding females have a high incidence of mammary tumors, which are highly hormone responsive. A mammary tumour agent is present in this strain, which can be transmitted by the milk but also by other pathways. In this respect this new strain is different from other known inbred strains.

Study of B Particles in Stomach Milk of Nursing Mice<xref ref-type="fn" rid="FN2">2</xref>

With procedures effective for isolation of B particles from breast milk, no particles were found in extracts of coagulated stomach milk from suckling mice nursing on mothers containing the mammary tumor agent. Treatment at 37° C for ½ hour of coagulated stomach milk slurries with stomach juices, trypsin, chymotrypsin, or pepsin yielded extracts from which B particles could be sedimented. Morphologically and in their buoyant densities in cesium chloride these B particles were indistinguishable from those obtained from breast milk. The activity of stomach milk was associated with the supernatant fraction after ultracentrifugation of buffered extracts of stomach milk. The washed sediments containing B particles were inactive. These results indicate the active principle in stomach milk is a molecule unsedimentable after 1 hour at 100,000 × g.

Development of a virus-resistant inbred mouse strain for the study of innate resistance to Arbo B viruses.

Through a system of backcross and brother-sister mating based essentially on a design devised bySnell (9), a C3HRV strain of mice congenic with the virus-susceptible C3H/He strain has been developed. This C3HRV strain is homozygous for the gene of resistance to Arbo B viruses and can be used for exchanging transplants of various organs and tissues. Susceptibility of the C3HRV strain to the mammary tumor agent seemed to be equal to the parent C3H/He strain. Availability of this strain makes it possible to investigate more fully the nature of natural resistance to virus infection.