Considering the importance of 'Communities of Practice' and Health Promotion Constructs for Upstream Suicide Prevention

Background

Suicide is a serious and growing health inequity for Alaska Native (AN) youth (ages 15-24), who experience suicide rates significantly higher than the general U.S. youth population. In low-resourced, remote communities, building on the local and cultural resources found in remote AN communities to increase uptake of prevention behaviors like lethal means reduction, interpersonal support, and postvention can be more effective at preventing suicide than a risk-referral process. This study expands the variables we hypothesize as important for reducing suicide risk and supporting wellbeing. These variables are: 1) perceived suicide prevention self-efficacy, 2) perceived wellness self-efficacy, and 3) developing a 'community of practice' (CoP) for prevention/wellness work.

Method

With a convenience sample (N = 398) of participants (ages 15+) in five remote Alaska Native communities, this study characterizes respondents' social roles: institutional role if they have a job that includes suicide prevention (e.g. teachers, community health workers) and community role if their primary role is based on family or community positioning (e.g. Elder, parent). The cross-sectional analysis then explores the relationship between respondents' wellness and prevention self-efficacy and CoP as predictors of their self-reported suicide prevention and wellness promotion behaviors: (1) working together with others (e.g. community initiatives), (2) offering interpersonal support to someone, (3) reducing access to lethal means, and (4) reducing suicide risk for others after a suicide death in the community.

Results

Community and institutional roles are vital, and analyses detected distinct patterns linking our dependent variables to different preventative behaviors. Findings associated wellness self-efficacy and CoP (but not prevention self-efficacy) with 'working together' behaviors, wellness and prevention self-efficacy (but not CoP) with interpersonal supportive behaviors; both prevention self-efficacy and CoP with higher postvention behaviors. Only prevention self-efficacy was associated with lethal means reduction.

Conclusions

The study widens the scope of suicide prevention. Promising approaches to suicide prevention in rural low-resourced communities include: (1) engaging people in community and institutional roles, (2) developing communities of practice for suicide prevention among different sectors of a community, and (3) broadening the scope of suicide prevention to include wellness promotion as well as suicide prevention.

What Kinds of Support are Alaska Native Youth and Young Adults Reporting? An Examination of Types, Quantities, Sources, and Frequencies of Support

American Indian and Alaska Native (AI/AN) youth, particularly males, experience disproportionately high rates of suicide compared to other young people in the United States. Therefore, enacting suicide prevention efforts for AI/AN youth is especially important. Since research shows that strengthening social, cultural, and emotional support can reduce suicide risk, many recent prevention efforts focus on these strategies. Yet, to reinforce and to extend the positive impact of these strategies for suicide risk reduction, we argue it is useful to identify baseline levels and other features of already-existing support. Toward this end, we describe the types (i.e., category), quantities (i.e., distribution and average number), sources (i.e., from whom), and frequencies (i.e., how often) of social support that AN young people report receiving, and we examine if these "support profiles" differ by age and sex. We use survey data from 165 ANs under age 30, collected as part of a participatory intervention study focused on Promoting Community Conversations About Research to End Suicide (PC CARES). We find that: 1) most ANs reported receiving nearly all supports, 2) compared with females, males reported receiving fewer supports on average, 3) family was the most selected support source, followed by close friends and service providers, and 4) family (e.g., parents, siblings, and grandparents) provided support regularly (i.e., monthly or more). Though our findings may suggest fruitful avenues for interventions targeted toward AN males, we discuss these findings in relation to the gendered nature of suicide prevention and assessment.

Implementation beyond the clinic: Community-driven utilization of research evidence from PC CARES, a suicide prevention program

While implementation and dissemination of research is a rapidly growing area, critical questions remain about how, why, and under what conditions everyday people integrate and utilize research evidence. This mixed-methods study investigates how participants of Promoting Community Conversations About Research to End Suicide (PC CARES) make sense of and use research evidence about suicide prevention in their own lives. PC CARES is a health intervention addressing the need for culturally responsive suicide prevention practices in rural Alaska through a series of community Learning Circles. We analyzed PC CARES transcripts and surveys for 376 participants aged 15+ across 10 Northwest Alaska Native villages. Quantitative analysis showed significant correlations between five utilization of research evidence (URE) factors and participants' intent to use research evidence from PC CARES Learning Circles. Key qualitative themes from Learning Circle transcripts expanded upon these URE constructs and included navigating discordant information, centering relationships, and Indigenous worldviews as key to interpreting research evidence. We integrate and organize our findings to inform two domains from the Consolidated Framework for Research Implementation: (1) intervention characteristics and (2) characteristics of individuals, with emphasis on findings most relevant for community settings where self-determined, evidence-informed action is especially important for addressing health inequities.

Adapting PC CARES to Continue Suicide Prevention in Rural Alaska During the COVID-19 Pandemic: Narrative Overview of an In-Person Community-Based Suicide Prevention Program Moving Online

This paper presents how a community mobilization program to prevent suicide was adapted to an online format to accommodate the impossibility of in-person delivery in Alaska Native communities during the COVID-19 pandemic. The intervention, Promoting Community Conversations About Research to End Suicide (PC CARES), was created collaboratively by researchers and Alaska Native communities with the goal of bringing community members together to create research-informed and community-led suicide prevention activities in their communities. To continue our work during the COVID-19 pandemic and restrictions, we adapted the PC CARES model to a synchronous remote delivery format. This shift included moving from predominantly Alaska Native participants to one of a mainly non-Native school staff audience. This required a pivot from Alaska Native self-determination toward cultural humility and community collaboration for school-based staff, with multilevel youth suicide prevention remaining the primary aim. This reorientation can offer important insight into how to build more responsive programs for those who are not from the communities they serve. Here, we provide a narrative overview of our collaborative adaptation process, illustrated by data collected during synchronous remote facilitation of the program, and reflect on how the shift in format and audience impacted program delivery and content. The adaptation process strove to maintain the core animating features of self-determination for Alaska Native communities and people as well as the translation of scientific knowledge to practice for greater impact.

Letsemot, “Togetherness”: Exploring How Connection to Land, Water, and Territory Influences Health and Wellness with First Nations Knowledge Keepers and Youth in the Fraser Salish Region of British Columbia

Connection to land has been identified as a central determinant of the health and well-being of First Nations in Canada. The wholistic, interconnected, spiritual, and sacred relationship that many Indigenous Peoples have with the land is an integral part of strengthening physical, spiritual, mental, and emotional health and well-being. However, there has been little empirical evidence on how to assess, measure, and report on connection to land for First Nations Peoples. Using a Two- Eyed Seeing approach, this study explores what connection to land, water, and territory means for health and wellness for First Nations in the Fraser Salish region in the province of British Columbia (BC), Canada. Data were collected through a sharing circle with five First Nations Knowledge Keepers and five youth from Stó:lō communities as part of a land-based gathering in Stó:lō territory. Three themes were identified: (a) “the spirits of the land, water, and territory are within us”: the intersection of cultural identity, spirituality, ancestral knowledge, and health and well-being; (b) letsemot, “togetherness”: relationality; and (c) disruptions and new ways of living. For Stó:lō Peoples, connection to the land is an integral component of health and well-being. Connection to land was found to strongly influence physical, spiritual, mental, and emotional aspects of health while also intersecting with Stó:lō cultural identity, spirituality, ancestral knowledge, and ways of living. The findings can be used to inform the development of an indicator for connection to land, water, and territory as a measurement of ecological wellness for the First Nations Population Health and Wellness Agenda in BC.

The Development of a Measure of Alaska Native Community Resilience Factors through Knowledge Co-production

BACKGROUND

The Alaska Native Community Resilience Study (ANCRS) is the central research project of the Alaska Native Collaborative Hub for Research on Resilience (ANCHRR), one of three American Indian and Alaska Native (AIAN) suicide prevention hubs funded by the National Institute of Mental Health.

OBJECTIVE

This paper describes the development of a structured interview to identify and measure community-level protective factors that may reduce suicide risk among youth in rural Alaska Native communities.

METHODS

Multilevel, iterative collaborative processes resulted in: a) expanded and refined constructs of community-level protection, b) clearer and broadly relevant item wording, c) respectful data collection procedures, and d) Alaska Native people from rural Alaska as primary knowledge-gathering interviewers.

LESSONS LEARNED

Moving beyond engagement to knowledge co-production in Alaska Native research requires flexibility, shared decision-making and commitment to diverse knowledge systems; this can result in culturally attuned methods, greater tool validity, new ways to understand complex issues and innovations that support community health.

PGR - 3 Adapting Neuropsychological Evaluation for a Complex Pediatric Patient with Challenging Behaviors

Objective

The detrimental impact of in utero substance use on developing fetuses manifests well into adolescence (Wu, Ju, & Lu, 2011; Minnes, Lang, & Singer, 2011). Likewise, the effects of early childhood neglect during critical developmental periods may be long lasting (de Bellis, et al., 2009; Hildyard & Wolfe, 2002). Factors such as these may require creative adaptation of assessment. This case illustrates the process of evaluating a child presenting with an unusual developmental history and extremely challenging behaviors and describes efforts to maintain engagement while eliciting valid data. Successful and unsuccessful interventions will be reviewed.

Method

Patient is a 12-year-old Caucasian male admitted to a state psychiatric hospital with a complex presentation of emotional, behavioral, and cognitive difficulties. Aggravating factors consist of likely in utero drug and alcohol exposure, early trauma, chronic neglect, and unusually small physical stature. Neuropsychological evaluation was completed over the course of five days. Testing sessions were brief, on a unit where no one was present, and were structured using both intermittent and scheduled reinforcement to maintain effort and engagement.

Results

Testing indicated significant and consistent weaknesses in executive functioning, learning, memory, and attention. Despite the use of stimulant medication, difficulty with vigilance, sustained attention, and impulsivity persisted. Diagnoses were Neurodevelopmental Disorder associated with prenatal substance exposure, Generalized Anxiety Disorder, Attention Deficit/Hyperactivity Disorder, Combined presentation, and Oppositional Defiant Disorder, Moderate.

Conclusions

Unconventional history warrants unconventional approach to assessment. Recommendations included not only approaches to improving his attention, but just as important, strategies to elicit his best performance in various settings.

Decoloniality as a Framework for Indigenous Youth Suicide Prevention Pedagogy: Promoting Community Conversations About Research to End Suicide

Indigenous youth suicide remains a substantial health disparity in circumpolar communities, despite prevention efforts through primary health care, public health campaigns, school systems, and social services. Innovations in prevention practice move away from expert-driven approaches to emphasize local control through processes that utilize research evidence, but privilege self- determined action based on local and personal contexts, meanings, and frameworks for action. "Promoting Community Conversations About Research to End Suicide" is a community health intervention that draws on networks of Indigenous health educators in rural Alaska, who host learning circles in which research evidence is used to spark conversations and empower community members to consider individual and collective action to support vulnerable people and create health-promoting conditions that reduce suicide risk. The first of nine learning circles focuses on narratives of local people who link the contemporary youth suicide epidemic to 20th century American colonialism, and situates prevention within this context. We describe the theoretical framework and feasibility and acceptability outcomes for this learning circle, and elucidate how the educational model engages community members in decolonial approaches to suicide prevention education and practice, thus serving as a bridge between Western and Indigenous traditions to generate collective knowledge and catalyze community healing.

Promoting Community Conversations About Research to End Suicide: learning and behavioural outcomes of a training-of-trainers model to facilitate grassroots community health education to address Indigenous youth suicide prevention

Alaska Native (AN) youth suicide remains a substantial and recalcitrant health disparity, especially in rural/remote communities. Promoting Community Conversations About Research to End Suicide (PC CARES) is a community health intervention that responds to the need for culturally responsive and evidence-supported prevention practice, using a grassroots approach to spark multilevel and community-based efforts for suicide prevention. This paper describes theoretical and practical considerations of the approach, and assesses the feasibility and preliminary learning and behavioural outcomes of the training-of-trainers model. It details the training of a first cohort of intervention facilitators in Northwest Alaska (NWA). Thirty-two people from 11 NWA village communities completed the PC CARES facilitator training, preparing them to implement the intervention in their home communities. Facilitator pre-post surveys focused on readiness to facilitate, a group quiz assessed participants' understanding of relevant research evidence, and practice facilitation exercises demonstrated competency. Curriculum fidelity and accuracy scores were calculated using audio recordings from learning circles conducted by facilitators in their home communities. Facilitator reflections describe the successes of the model and identify several areas for improvement. As of March 2017, 20 of the 32 trained facilitators in 10 of the 11 participating villages have hosted 54 LCs, with a total of 309 unique community members. Coding of these LCs by 2 independent raters indicate acceptable levels of fidelity and accurate dissemination of research evidence by facilitators. Facilitator reflections were positive overall, suggesting PC CARES is feasible, acceptable and potentially impactful as a way to translate research to practice in under-resourced, rural AN communities. PC CARES represents a practical community education and mobilisation approach to Indigenous youth suicide prevention that displays preliminary success in learning and behavioural outcomes of local facilitators.

Creating a Community of Practice to Prevent Suicide Through Multiple Channels: Describing the Theoretical Foundations and Structured Learning of PC CARES

It is critical to develop practical, effective, ecological, and decolonizing approaches to indigenous suicide prevention and health promotion for the North American communities. The youth suicide rates in predominantly indigenous small, rural, and remote Northern communities are unacceptably high. This health disparity, however, is fairly recent, occurring over the last 50 to 100 years as communities experienced forced social, economic, and political change and intergenerational trauma. These conditions increase suicide risk and can reduce people's access to shared protective factors and processes. In this context, it is imperative that suicide prevention includes--at its heart--decolonization, while also utilizing the "best practices" from research to effectively address the issue from multiple levels. This article describes such an approach: Promoting Community Conversations About Research to End Suicide (PC CARES). PC CARES uses popular education strategies to build a "community of practice" among local and regional service providers, friends, and families that fosters personal and collective learning about suicide prevention in order to spur practical action on multiple levels to prevent suicide and promote health. This article will discuss the theoretical underpinnings of the community intervention and describe the form that PC CARES takes to structure ongoing dialogue, learning, solidarity, and multilevel mobilization for suicide prevention.

EXPERIMENTAL HYPERTHYROIDISM AND ITS EFFECT UPON THE MYOCARDIUM IN GUINEA PIGS AND RABBITS

A study has been made of the pathological changes in the hearts and other tissues of animals rendered hyperthyroid with thyroxine. Forty-four rabbits and seventeen guinea pigs were given intramuscular injections of thyroxine every other day and sacrificed at varying intervals. Tissues from a series of normal animals (twenty guinea pigs and forty-three rabbits) were examined as a control. The changes in the heart and other tissues of hyperthyroid animals were insignificant and varied but little from changes seen in normal control animals. Of eight thyrotoxic guinea pigs that developed coincidental infection (bronchisepticus) all showed myocardial lesions. Of nine thyrotoxic guinea pigs, free of infection, only one gave evidence of myocardial change. It is pointed out that hyperthyroidism, per se, cannot be held responsible for these lesions, which would appear to have been associated with the infection. It was noted that rigor mortis of the skeletal muscles occurred much sooner in the bodies of hyperthyroid animals than in normal animals.

Effect of (-)-gossypol (AT-101) on transcriptional regulation of Noxa and Puma and on Mcl-1-mediated cancer cell resistance to apoptosis

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Background: AT-101 is being evaluated in Phase II clinical trials for the treatment of human cancers and demonstrates anticancer activity as a single agent and in combination with docetaxel. Despite extensive investigations, the mechanism of action for its antitumor activity is not completely understood. In this study, we have performed detailed investigations using a panel of human cancer cell lines on the mechanism of action for AT-101. Methods: A series of human breast and prostate cancer cell lines were utilized to evaluate the antitumor activity of AT-101. Cell growth inhibition, cell viability and apoptosis were determined by WST assay, trypan blue assay and flow cytometry, respectively. Gene specific siRNAs were used to knockdown target gene expression. Quantitative RT- PCR was performed to detect the mRNA levels of Puma and Noxa. Co-immunoprecipitation was carried out to detect the association between Mcl-1 and Noxa or Puma. Results: AT-101 induced apoptosis in both Bax/Bak-dependent and -independent manners in a variety of human cancer cell lines concomitant with increased expression of Noxa and Puma in a p53-independent manner. The up-regulation of Noxa was not observed in normal primary breast epithelial cells or normal-like human breast epithelial MCF-12F cells. Transcription inhibitor actinomycin D blocked AT-101-induced up-regulation of Puma and Noxa. Knockdown of Noxa or Puma attenuated AT-101-induced apoptosis. Furthermore, AT-101 effectively overcame Mcl-1-mediated cancer cell resistance to apoptosis. Co-immunoprecipitation studies demonstrated that Mcl-1 specifically associated with Noxa but not Puma. Conclusions: Our findings suggest that transcriptional up-regulation of pro-apoptotic Noxa and Puma contributes to the antitumor activity of AT-101, which plays a dominant role in antagonizing Mcl-1 and overcoming Mcl-1-mediated resistance to apoptosis of cancer cells. AT-101 functions as an antagonist of Bcl-2, Bcl-xL and Mcl-1 through direct binding to these proteins, as well as through upregulation of Noxa and Puma.

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Gesture-speech combinations as a transition to multiword utterances

This study was designed to determine if certain types of gesture-speech combinations act as transitional phenomena preceding production of 2-word utterances. Ten normally developing children with a mean age of 15 months at the beginning of the study participated in this research. The children were sampled longitudinally at monthly intervals as they approached the onset of early multiword utterances. Temporally synchronized gesture-speech combinations were analyzed over a 6-month period to describe whether they encoded 1 semantic element (pointing to a car and saying "car") or 2 semantic elements (pointing to a car and saying "big"). These gesture-speech combinations were examined in terms of their onset in relation to early multiword combinations. It was found that there was a significant increase in gesture-speech combinations encoding 2 semantic elements during the 6-month period and that the onset of these combinations preceded or co-occurred with the 1st productions of multiword utterances. This finding, coupled with prior studies on smaller numbers of participants, suggests that gesture-speech combinations encoding 2 elements may be a transitional element between single-word communication and the onset of multiword combinations.

Comparison of tumor growth between hsp25- and hsp27-transfected murine L929 cells in nude mice

We have developed a novel system for examining the possible contribution of small heat shock proteins (hsp) to tumor growth. L929 fibrosarcoma cells, which do not express significant levels of endogenous hsp25, were stably transfected with either murine hsp25 or human hsp27. Both transfected genes were over-expressed and the respective proteins were phosphorylated in L929 cells. L929 cells transfected with hsp25 exhibited enhanced tumor growth compared to control transfected L929 cells upon s.c. injection into nude mice. In contrast, cells transfected with hsp27 exhibited delayed tumor progression in comparison to controls. Although these 2 heat shock genes and respective proteins are structurally very similar, they apparently exhibit distinct effects on tumor growth in this system.

Sensitivity of human cells to mild hyperthermia

The cytotoxic effects of short duration, high temperature, and long duration, low temperature hyperthermia were determined in human cells growing in culture. The human tumor cell lines A549 (lung carcinoma), WiDr (colon carcinoma), and U87MG (glioblastoma) were used. In addition, a normal human lung fibroblast cell type 18Lu was used. Sensitivity to direct cell killing was measured at 41, 43, and 45 degrees C. Heat induced perturbations of cell cycle and proliferation were also analyzed. The results obtained on sensitivity of the above human cell lines at 43 and 45 degrees C are similar to those of the previous work of others in that the human cell lines were observed to be relatively resistant to thermal killing at 43 or 45 degrees C, when compared to heat sensitive rodent cell lines. The comparison is important because most prior hyperthermic research has been performed with rodent cells and clinical protocols have been designed with the use of rodent data. In contrast to the 43 degrees C response, most of the human cells we tested were killed by 41 degrees C heating to an extent greater than that observed for rodent cells. The heat sensitivities of the four different human cell lines varied widely. This appeared to be due to differences in both intrinsic heat sensitivity and tolerance development. During 41 degrees C heating, human cells did not proliferate and cell cycle perturbations developed but did not correlate with sensitivity to killing. Our heat sensitivity measurements point out the shortcomings of using data derived from rodent systems to predict clinical outcome of hyperthermia therapy.

Sequential alteration of peanut agglutinin binding-glycoprotein expression during progression of murine mammary neoplasia

A sequential, quantitative loss of Peanut agglutinin (PNA) binding with progression of mouse mammary cells from normal to preneoplastic to neoplastic phenotypes was observed. Normal mammary epithelium, preneoplastic mammary lesions designated D2HAN (D2-type hyperplastic alveolar nodules) and a series of nine spontaneous tumours (D2ST1, D2ST2, D2ST3, D2ST4, D2A1, D2F2, D2.0R, D2.1, EMT6R08) derived from mice bearing D2HAN were grown in culture and analysed by flow cytometry with respect to PNA binding intensity to the cell surface. Primary cultures of normal mammary epithelium strongly bound PNA. A stepwise decrease in PNA binding by preneoplastic D2HAN cells and subsequent tumours arising from those hyperplastic lesions was observed. Three cloned tumour subpopulations derived from such tumours exhibited dramatic differences in PNA binding ranging from high (D2.0R) to low (D2.1) to very low (D2A1 cells). Their growth rate in vitro was similar. However, an inverse correlation between PNA binding and malignant characteristics, such as the incidence and latency of subcutaneous tumours and the efficiency of the tumour cells to form lung colonies after i.v. injection, existed. Cells subsequently derived from tumours resulting from injection of the D2.0R clone (high PNA binding, low tumorigenicity) were found to have diminished PNA binding properties and to be more tumorigenic when reimplanted into syngeneic mice. The difference in PNA binding (up to 50-fold) between normal mammary cells and other mouse mammary tumour cells, i.e., unrelated to D2HAN lesions, was also seen. These include six sister subpopulations derived from a single BALB/cfC3H mouse mammary tumour (lines: 67, 66c14, 168FARN, 4TO7, 68H, 64pT) as well as SP1 spontaneous CBA/J mouse mammary carcinoma. The difference was greatly reduced by neuraminidase treatment suggesting a masking of PNA binding sites by sialic acid. Separation of cell lysates by SDS-PAGE revealed a high molecular weight PNA binding glycoprotein (greater than 250 kd) expressed by normal mammary epithelium and preneoplastic D2HAN cells, but not by tumour cells regardless of neuraminidase treatment. A PNA reactive glycoprotein of approximately 90 kd was uniquely expressed in normal mammary epithelial lysates, although neuraminidase treatment exposed a similar band in a few tumour lines. Normal mammary epithelium, preneoplastic D2HAN cells, and the poorly tumorigenic clone D2.0R expressed a PNA binding glycoprotein of approximately 150 kd. This band appeared to be specifically sialylated during transition from the high PNA binding, low tumorigenic phenotype of D2.0R cells to the low PNA binding, highly tumorigenic phenotype of cells isolated from tumours resulting from s.c. implantation of D2.0R cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of lung colonization at two different steps in the metastatic sequence

Two immunomodulatory protocols were evaluated for their ability to inhibit lung colonization by mouse mammary tumor line 4T07. Preimmunization with tumor cells or pretreatment with poly I:C were equally effective at inhibiting lung colonization but a clonogenic tumor cell assay demonstrated that the treatments reduced tumor cell burden at different steps during the metastatic process. Poly I:C pretreatment accelerated tumor cell clearance based on the recovery of clonogenic tumor cells from lungs dispersed within 6 h post-arrest. Preimmunization inhibited the subsequent replication of tumor cells which survived and established in the lung, as indicated by the expansion of clonogenic cell numbers between 1 day and 7 days post-arrest. Histologic examination of serial sections of lungs demonstrated that very few (6%) of the tumor cells were extravascular 6 h post-tumor cell injection. By 24 h and 168 h the percentages of tumor cells which were extravascular had increased to 62% and 86%, respectively. Thus, poly I:C pretreatment appears to enhance killing of tumor cells prior to extravasation, whereas preimmunization appears to inhibit tumor cells after extravasation.

Efficiency of communication between tumour cells in collagen gel cultures

Mixtures of drug-resistant and drug-sensitive tumour cells growing in 3-dimensional boluses in collagen gel matrix are shown to be effectively coupled so that the response of the mixture is significantly influenced by a subpopulation making up only 1% of the total cells.

Growth regulation of mouse mammary tumor cells in collagen gel cultures by diffusible factors produced by normal mammary gland epithelium and stromal fibroblasts

We have reported previously that both normal mammary epithelium and stroma stimulate the growth of mouse mammary tumors in vivo. We have devised a method to investigate the role of diffusible factors in these growth interactions in vitro. Because an appropriate matrix, a particular cell shape, or multicellular organization may be required for the production of factors and/or for the response to such factors, the method assesses the expansion of boluses of cells in collagen gel matrix. Under these culture conditions, paracrine effects were detected which were not observed when cells were growing in monolayer on plastic. The growth of mammary tumor lines 66, 410.4, and D2A1 was stimulated by both mammary epithelial cells and fibroblasts prepared from midpregnant mouse mammary glands. In contrast, these mammary tumor lines were inhibited by coculturing with normal mammary cells in monolayer on plastic. Stimulation in collagen and inhibition in monolayer cultures were both dose dependent; increasing numbers of regulator mammary cells increased the effects on tumor growth. Additional tumor cells did not stimulate growth of target tumor cell boluses in collagen gel cultures. This attempt to model the in situ situation may be a more appropriate model for the detection and characterization of relevant diffusible growth regulatory factors than monolayers on plastic and/or colonies growing in agar.

Production of a more aggressive tumor cell variant by spontaneous fusion of two mouse tumor subpopulations

A hybrid cell formed by the spontaneous fusion of two sister subpopulations was isolated and was found to combine clinically aggressive features of both parental cells. Subpopulation 168FAR is highly tumorigenic but does not metastasize spontaneously from a s.c. site. Subpopulation 44FTO is a variant selected for resistance to 6-thioguanine and to ouabain. It is poorly tumorigenic but spontaneously metastasizes to the lungs and livers of mice in which primary tumors do form. The two parental subpopulations are differentially sensitive to chemotherapeutic drugs; 168FAR is relatively more resistant to methotrexate, whereas 44FTO is more resistant to 5-fluorouracil. Both are about equally sensitive to melphalan. The hybrid 168FAR x 44FTO clone was isolated by growth in hypoxanthine-aminopterin-thymidine medium which also contained 3 mM ouabain; neither 168FAR nor 44FTO survive in this medium. The hybrid nature of the isolated clone was confirmed by cytogenetic analysis and determination of DNA content. The hybrid clone was highly tumorigenic, spontaneously metastasized from the subcutis, was nearly as resistant to 5-fluorouracil as the most resistant parental line, and was more resistant to both melphalan and methotrexate than either parental subpopulation. These results illustrate the role that cell fusion could play in progression by allowing the rapid assimilation of aggressive phenotypes from distinct coexisting subpopulations.

Epilepsy

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