Analysis of Radiation Therapy Quality Assurance in NRG Oncology RTOG 0848

PURPOSE

NRG/Radiation Therapy Oncology Group 0848 is a 2-step randomized trial to evaluate the benefit of the addition of concurrent fluoropyrimidine and radiation therapy (RT) after adjuvant chemotherapy (second step) for patients with resected pancreatic head adenocarcinoma. Real-time quality assurance (QA) was performed on each patient who underwent RT. This analysis aims to evaluate adherence to protocol-specified contouring and treatment planning and to report the types and frequencies of deviations requiring revisions.

METHODS AND MATERIALS

In addition to a web-based contouring atlas, the protocol outlined step-by-step instructions for generating the clinical treatment volume through the creation of specific regions of interest. The planning target volume was a uniform 0.5 cm clinical treatment volume expansion. One of 2 radiation oncology study chairs independently reviewed each plan. Plans with unacceptable deviations were returned for revision and resubmitted until approved. Treatment started after final approval of the RT plan.

RESULTS

From 2014 to 2018, 354 patients were enrolled in the second randomization. Of these, 160 patients received RT and were included in the QA analysis. Resubmissions were more common for patients planned with 3-dimensional conformal RT (43%) than with intensity modulated RT (31%). In total, at least 1 resubmission of the treatment plan was required for 33% of patients. Among patients requiring resubmission, most only needed 1 resubmission (87%). The most common reasons for resubmission were unacceptable deviations with respect to the preoperative gross target volume (60.7%) and the pancreaticojejunostomy (47.5%).

CONCLUSION

One-third of patients required resubmission to meet protocol compliance criteria, demonstrating the continued need for expending resources on real-time, pretreatment QA in trials evaluating the use of RT, particularly for pancreas cancer. Rigorous QA is critically important for clinical trials involving RT to ensure that the true effect of RT is assessed. Moreover, RT QA serves as an educational process through providing feedback from specialists to practicing radiation oncologists on best practices.

Curietherapy User eXperience Pilot Study: A Novel Augmented Reality Educational Tool during Radiation Oncology Consultation for Patients with Breast Cancer

PURPOSE/OBJECTIVE(S)

Improved communication and knowledge delivery by clinicians at initial consultation may reduce anxiety and psychological burdens associated with cancer treatment. Based on our pilot qualitative study which involved semi-structured interviews of breast cancer patients, we developed Curietherapy User eXperience (CurieUx), an educational tool integrating augmented reality display technology into radiation oncology consultations.

MATERIALS/METHODS

We developed an interactive 3-dimensional hologram using a frictionless, augmented reality desktop display. Animated modules on patient-specific anatomy (breast, regional lymph nodes, organs-at-risk), linear accelerator, and positioning (prone and breath holding techniques) were created. Patients with newly diagnosed localized breast cancer undergoing radiation oncology treatment were prospectively enrolled in this IRB approved study to evaluate the impact of integrating augmented reality educational tools during radiation therapy consultation (n = 40). Likert scale surveys on anxiety (NIH PROMIS), radiation knowledge, and augmented reality experience (modified IBM technology usability survey) were administered to patients before and after radiation consultation.

RESULTS

A total of 40 newly diagnosed breast cancer patients were enrolled in this study with a median age of 67 years. Majority were diagnosed with T1-T2N0 (75.0%), followed by Tis (17.5%) and N1+ (7.5%). Of the 36 patients who proceeded with radiation, prone technique was utilized in 83.3% and deep inspiratory breath holding technique in 16.7%. Patients reported decreases in multiple components of anxiety after consultation with the CurieUx platform, including in fearfulness (2.13 vs 1.78, p = 0.003), uneasiness (2.28 vs. 1.82, p = 0.008), nervousness (2.41 vs 2.06, p = 0.005), and tenseness (2.28 vs 1.87, p = 0.004). Patients reported significant increases in radiation knowledge across multiple domains, including treatment machine (2.35 vs 4.7, p<0.001), radiation (2.7 vs 4.58, p<0.001), positioning (2.49 vs 4.68, p<0.001), and confidence (2.4 vs 4.3, p<0.001). An overwhelming majority of patients had positive experiences (4 or 5 on Likert scale) with using the CurieUx hologram display as part of consultation, including its ease of understanding (97%), clarity (93%), comfort (100%), value (97%), and satisfaction (97%).

CONCLUSION

Curietherapy User eXperience is a valuable educational tool that reduces patient anxiety and promotes radiation knowledge. CurieUx is easily incorporated into the existing radiation oncology consultation practice with the vast majority of patients believing it to be a valuable addition to the consultation process.

Understanding Treatment Anxiety and Utility of Mixed Media Educational Tools in Radiation Oncology Consultation: A Qualitative Study

PURPOSE/OBJECTIVE(S)

Anxiety and adjustment disorders are prevalent in cancer patients, especially at the initiation of treatment, which may be alleviated by improved communication at initial consultation. The purpose of this study is to explore patients' needs in how radiation consultation may improve treatment-related anxiety and the role of multimedia visual tools.

MATERIALS/METHODS

Eight patients previously treated with partial or whole breast irradiation at our institution were interviewed in a semi-structured manner at a median of 1.54 months (range 0.13 - 12.42) after they completed radiation. Interview questions included expectations prior to consultation, experience of consultation and treatment, and the role of augmented reality or multimedia tools. Two independent reviewers performed an inductive, thematic analysis to generate themes and subthemes (inter-rater reliability = 0.79).

RESULTS

Four main themes were identified in thematic analysis: information expectations, anxiety, personalized education, and visual aids. Patients described preconceptions of radiation, desire for greater volume of information, importance of repetition from providers, benefit of seeing treatment set-up during simulation, and frustrations with the breath-holding process. Anxiety was related to fear of the unknown, difficulty remembering information when anxious, difficulty asking questions, and ambiguity of information worth worrying about. Patients expressed a desire for personalized education, including accounting for prior health conditions, varying health literacy, preference for individualized presentations, and minimizing extraneous input from those not on the healthcare team. Patients desired visuals during consultation, favored 3D technology over 2D mediums, acknowledged differences in learning style, and preferred an interactive component of patient education done in conjunction with visual tools.

CONCLUSION

While verbal consultation process provides valuable education regarding radiation treatment, patients continue to experience anxiety attributed to fear of the unknown. Augmenting the standard initial consultation with interactive visual aids, particularly in the form of a 3D medium, may enhance the patient experience at time of consultation. The results of this study will inform the development of a patient educational tool and clinical study named Curie therapy User eXperience (CurieUx) to be used during radiation oncology consultations.

Racial Disparities in the Utilization of Stereotactic Body Radiation Therapy (SBRT) in Patients with Hepatocellular Carcinoma

PURPOSE/OBJECTIVE(S)

SBRT has now been demonstrated to improve OS, PFS and TTP in patient with hepatocellular carcinoma (HCC) when compared to systemic therapy alone. Disparities in the availability and utilization of SBRT for minority racial patients may affect oncologic outcomes. This study examines racial and sociodemographic disparities in the utilization of SBRT for HCC patients.

MATERIALS/METHODS

In this registry-based cohort study, data from the American College of Surgeons National Cancer Database (NCDB) from 2004 - 2017 was analyzed. Adults with a new diagnosis of localized, non-metastatic, HCC were included in this analysis. Patients were sub-grouped by race and whether they were treated with liver SBRT. In this analysis, SBRT was defined as radiation delivered in 3-5 fractions and in the 30-60Gy range. The primary outcome of this study was the utilization rate of liver SBRT in HCC, depending on race. Survival was also examined in these patients. Statistical analysis was performed using SPSS v28 for univariate and multivariate logistical regression and Kaplan-Meier analysis.

RESULTS

From 2004 - 2017, 95132 cases of localized HCC were identified in patients who were white, non-Spanish, non-Hispanic (WNH) and 40964 cases who were black or Hispanic/Spanish (BH). Of all these patients, only 1963 patients, or 1.4%, were treated with liver SBRT. Comparing WNH patients to BH patients, 1423 (1.5%) WNH patients were treated with SBRT and 334 (0.8%) BH patients were treated with SBRT (p<0.001). Looking at the number of patients treated with SBRT each year, there has been a yearly increase in the use of liver SBRT, from 48 patients in 2007 to 340 patients in 2017. The utilization of SBRT in WNH patients has increased at a higher rate than for BH patients over this time period. The median survival for patients with localized HCC was similar for both WNH and BH patients with a median survival of 17 months (p = 0.36). However, patients who were treated with liver SBRT had an improved median survival of 25 months for WNH patients and 34 months for BH patients (p<0.001).

CONCLUSION

Overall, liver SBRT is severely underutilized for patients with localized HCC in the patient population represented in this database, and fewer BH patients are treated with liver SBRT compared with WNH patients. Liver SBRT is associated with improved survival of HCC patients in this study. With the findings of the RTOG 1112 trial, demonstrating improved OS and PFS with the use of SBRT for HCC, it is essential to adopt liver SBRT more broadly and to develop strategies to reduce the racial disparities in utilization.

[Mid-term efficacy of sacral nerve stimulation for the treatment of chronic constipation]

Objective: To investigate the mid-term efficacy of sacral nerve stimulation (SNS) for chronic constipation. Methods: A descriptive case series study was conducted. Patients with chronic constipation were treated in Xijing Hospital of Digestive Disease from February 2013 to December 2018 were retrospectively enrolled. The types of constipation were confirmed based on colon slow transit test, anorectal manometry and defecography in Xi'an Mayinglong Coloproctological Hospital. This study has been registered in China clinical trial registry (Registration No.: ChiCTR-ROC-16008945). Case inclusion criteria: (1) constipation was diagnosed according to Rome III criteria; (2) traditional treatment, including education, diet adjustment, laxative, biofeedback treatment, failed for at least 1 year; (3) there were no constipation-related organic diseases. After excluding neurogenic diseases, including spinal cord injury and multiple sclerosis, 21 patients were included in this study. There were 10 males and 11 females, with an average age of 50.9 (14-76) years. After the relevant examination and evaluation of patients, they underwent percutaneous nerve evaluation (PNE). If patient experienced a good response to PNE after 2 or 3 weeks (≥50%), permanent SNS implantation was performed. The improvement of clinical symptoms and quality of life between the baseline, PNE, and latest follow-up time points were compared. Improvement of clinical symptoms, including autonomic stool frequency per week, autonomic stool days per week, defecation time, visual analogue scale (VAS, lower score indicates more serious symptoms) score and Cleveland clinic constipation score (CCCS, higher score indacates more serious symptoms) criteria. The change of quality of life was scored by SF-36 questionnaires (the higher score indicates better quality of life). Results: Of 21 patients, 18 (85.7%) experienced significant improvement in symptoms with PNE, and 2 patients discontinued treatment due to their dissatisfaction. Sixteen patients (76.2%) received permanent SNS implantation, two of whom underwent bilateral PNE implantation. These patients were followed-up for mean 56 (34-72) months. The treatment was continuously effective in 13 patients (61.9%), including 3 of ODS, 1 of STC and 9 of mixed constipation. Compared with baseline, the score of constipation patients receiving permanent SNS implantation at latest follow-up was shown. The median autonomic stool frequency per week increased from 1.0 (0-7) to 7.5 (0-10) (P<0.001), the median autonomic stool days per week increased from 1.0 (0-7) d to 4.5 (0-7) d (P<0.001), the median defecation time decreased from 19.0 (8-40) minutes to 4.0 (3-31) minutes (P<0.001), the median CCCS decreased from 20.0 (13-30) to 9.0 (6-30) (P<0.001), and the median VAS score increased from 9.0 (7-40) to 80.0 (15-90) (P<0.001). The values of the 8 parts of the SF-36 questionnaire increased (all P<0.05). Conclusion: SNS implantation is safe and has obvious effects on severe constipation with stable mid-term efficacy.

Interprofessional Image Verification Workshop for Physician and Physics Residents: A Multi-Institutional Experience

PURPOSE

Verification of patient position through pretreatment setup imaging is crucial in modern radiation therapy. As treatment complexity increases and technology evolves, physicist-physician collaboration becomes imperative for safe and successful radiation delivery. Despite the importance of both, residency programs lack formal interprofessional education (IPE) activities or structured training for image verification. Here we show the impact of an interprofessional image verification workshop for residents in a multi-institutional setting.

METHODS

The workshop included a lecture by the attending physicist and physician, and hands-on image registration practice by learners (medical physics residents, MP; and radiation oncology residents, RO). All participants filled out pre- and postactivity surveys and rated their comfort from 1 to 10 in (A) selecting what type of imaging to order for a given case and (B) independently assessing the setup quality based on imaging. A paired 1-tailed t test (α = 0.05) was used to evaluate significance; Spearman rank correlation coefficient was used to assess correlation of ratings and RO postgraduate year (PGY). Surveys had free-response questions about IPE and image verification activities in residency.

RESULTS

A total of 71 residents from 7 institutions participated between 2018 and 2020. Pre- and postsurveys were completed by 50 residents (38RO, 12MP) and showed an increase in (A) from 5.5 ± 2.2 to 7.1 ± 1.6 (P < .001) and in (B) from 5.1 ± 2.3 to 6.8 ± 1.5 (P < .001), with significant increases per subgroup (A_{Δ, RO} = 1.8 ± 1.7, P < .001; B_{Δ, RO} = 1.9 ± 1.8, P <. 001; A_{Δ, MP} = 1.1 ± 1.4, P = .012; B_{Δ, MP} = 1.2 ± 1.6, P = .016). RO confidence scores moderately correlated with PGY. Survey responses indicated that image verification training is mostly unstructured, with extent of exposure varying by program and attending; most with little-to-no training. Time constraints were identified as the main barrier. IPE was noted as a useful way to incorporate different perspectives into the process.

CONCLUSIONS

Formal image verification training increases resident comfort with setup imaging review and provides opportunities for interprofessional collaboration in radiation oncology residency programs.

Breaking Tradition to Bridge Bench and Bedside: Accelerating the MD-PhD-Residency Pathway

PROBLEM

Physician-scientists are individuals trained in both clinical practice and scientific research. Often, the goal of physician-scientist training is to address pressing questions in biomedical research. The established pathways to formally train such individuals are mainly MD-PhD programs and physician-scientist track residencies. Although graduates of these pathways are well equipped to be physician-scientists, numerous factors, including funding and length of training, discourage application to such programs and impede success rates.

APPROACH

To address some of the pressing challenges in training and retaining burgeoning physician-scientists, New York University Grossman School of Medicine formed the Accelerated MD-PhD-Residency Pathway in 2016. This pathway builds on the previously established accelerated 3-year MD pathway to residency at the same institution. The Accelerated MD-PhD-Residency Pathway conditionally accepts MD-PhD trainees to a residency position at the same institution through the National Resident Matching Program.

OUTCOMES

Since its inception, 2 students have joined the Accelerated MD-PhD-Residency Pathway, which provides protected research time in their chosen residency. The pathway reduces the time to earn an MD and PhD by 1 year and reduces the MD training phase to 3 years, reducing the cost and lowering socioeconomic barriers. Remaining at the same institution for residency allows for the growth of strong research collaborations and mentoring opportunities, which foster success.

NEXT STEPS

The authors and institutional leaders plan to increase the number of trainees who are accepted into the Accelerated MD-PhD-Residency Pathway and track the success of these students through residency and into practice to determine if the pathway is meeting its goal of increasing the number of practicing physician-scientists. The authors hope this model can serve as an example to leaders at other institutions who may wish to adopt this pathway for the training of their MD-PhD students.

Predictors of Complete Response and Disease Recurrence Following Chemoradiation for Rectal Cancer

OBJECTIVE

Approximately 10-40% of rectal patients have a complete response (CR) to neoadjuvant chemoradiation (CRT), and these patients have improved survival. Thus, non-operative management ("watch-and-wait" approach) may be an option for select patients. We aimed to identify clinical predictors of CR following CRT.

METHODS

Patients treated with definitive CRT for T3-T4, locally unresectable T1-T2, low-lying T2, and/or node-positive rectal cancer from August 2004 to February 2015 were retrospectively reviewed. Most patients were treated with 50.4 Gy radiation and concurrent 5-fluoruracil or capecitabine. Patients were considered to have a CR if surgical pathology revealed ypT0N0M0 (operative management), or if they had no evidence of residual disease on clinical and radiographic assessment (non-operative management). Statistical analysis was carried out to determine predictors of CR and long-term outcomes.

RESULTS

Complete records were available on 138 patients. The median follow-up was 24.5 months. Thirty-six patients (26.3%) achieved a CR; 30/123 operatively managed patients (24.5%) and 6/15 (40%) non-operatively managed patients. None of the 10 patients with mucinous adenocarcinoma achieved a CR. Carcinoembryonic antigen (CEA) ≥5 μg/L at diagnosis (OR 0.190, 95% CI 0.037-0.971, p = 0.046), tumor size ≥3 cm (OR 0.123, 95% CI 0.020-0.745, p = 0.023), distance of tumor from the anal verge ≥3 cm (OR 0.091, 95% CI 0.013-0.613, p = 0.014), clinically node-positive disease at diagnosis (OR 0.201, 95% CI 0.045-0.895, p = 0.035), and interval from CRT to surgery ≥8 weeks (OR 5.267, 95% CI 1.068-25.961, p = 0.041) were independent predictors of CR. The CR group had longer 3-year distant metastasis-free survival (DMFS) (93.7 vs. 63.7%, p = 0.016) and 3-year disease-free survival (DFS) (91.1 vs. 67.8%, p = 0.038). Three-year locoregional control (LRC) (96.6 vs. 81.3%, p = 0.103) and overall survival (97.2 vs. 87.5%, p = 0.125) were higher in the CR group but this did not achieve statistical significance. CR was not an independent predictor of LRC, DMFS, or DFS.

CONCLUSION

CEA at diagnosis, tumor size, tumor distance from the anal verge, node positivity at diagnosis, and interval from CRT to surgery were predictors of CR. These clinical variables may offer insight into patient selection and timing of treatment response evaluation in the watch-and-wait approach.

Comparison of anal cancer outcomes in public and private hospital patients treated at a single radiation oncology center

OBJECTIVE

To compare clinical and treatment characteristics and outcomes in locally advanced anal cancer, a potentially curable disease, in patients referred from a public or private hospital.

METHODS

We retrospectively reviewed 112 anal cancer patients from a public and a private hospital who received definitive chemoradiotherapy at the same cancer center between 2004 and 2013. Tumor stage, radiotherapy delay, radiotherapy duration, and unplanned treatment breaks ≥10 days were compared using t-test and χ(2) test. Overall survival (OS), disease free survival (DFS), and colostomy free survival (CFS) were examined using the Kaplan-Meier method and compared with the log-rank test. Cox proportional hazard models for OS and DFS were developed.

RESULTS

The follow-up was 14.9 months (range, 0.7-94.8 months). Public hospital patients presented with significantly higher clinical T stage (P<0.05) and clinical stage group (P<0.05), had significantly longer radiotherapy delays (P<0.05) and radiotherapy duration (P<0.05), and had more frequent radiation therapy (RT) breaks ≥10 days (P<0.05). Three-year OS showed a marked trend in favor of private hospital patients for 3-year OS (72.8% vs. 48.9%; P=0.171), 3-year DFS (66.3% vs. 42.7%, P=0.352), and 3-year CFS (86.4% vs. 68.9%, P=0.299). Referral hospital was not predictive of OS or DFS on multivariate analysis.

CONCLUSIONS

Public hospital patients presented at later stage and experienced more delays in initiating and completing radiotherapy, which may contribute to the trend in poorer DFS and OS. These findings emphasize the need for identifying clinical and treatment factors that contribute to decreased survival in low socioeconomic status (SES) populations.

Radiation therapy improves survival in rectal small cell cancer - Analysis of Surveillance Epidemiology and End Results (SEER) data

Background

Small cell carcinoma of the rectum is a rare neoplasm with scant literature to guide treatment. We used the Surveillance Epidemiology and End Results (SEER) database to investigate the role of radiation therapy in the treatment of this cancer.

Methods

The SEER database (National Cancer Institute) was queried for locoregional cases of small cell rectal cancer. Years of diagnosis were limited to 1988–2010 (most recent available) to reduce variability in staging criteria or longitudinal changes in surgery and radiation techniques. Two month conditional survival was applied to minimize bias by excluding patients who did not survive long enough to receive cancer-directed therapy. Patient demographics between the RT and No_RT groups were compared using Pearson Chi-Square tests. Overall survival was compared between patients who received radiotherapy (RT, n = 43) and those who did not (No_RT, n = 28) using the Kaplan-Meier method. Multivariate Cox proportional hazards model was used to evaluate important covariates.

Results

Median survival was significantly longer for patients who received radiation compared to those who were not treated with radiation; 26 mo vs. 8 mo, respectively (log-rank P = 0.009). We also noted a higher 1-year overall survival rate for those who received radiation (71.1% vs. 37.8%). Unadjusted hazard ratio for death (HR) was 0.495 with the use of radiation (95% CI 0.286-0.858). Among surgery, radiotherapy, sex and age at diagnosis, radiation therapy was the only significant factor for overall survival with a multivariate HR for death of 0.393 (95% CI 0.206-0.750, P = 0.005).

Conclusions

Using SEER data, we have identified a significant survival advantage with the use of radiation therapy in the setting of rectal small cell carcinoma. Limitations of the SEER data apply to this study, particularly the lack of information on chemotherapy usage. Our findings strongly support the use of radiation therapy for patients with locoregional small cell rectal cancer.

Chemoradiation therapy versus chemotherapy alone for gastric cancer after R0 surgical resection: a meta-analysis of randomized trials

OBJECTIVE

Current national guidelines include category 1 recommendations for perioperative chemotherapy or adjuvant chemoradiation with surgical resection for patients with stage IB-IIIB gastric cancer. We conducted a meta-analysis of randomized trials in which chemotherapy was prospectively tested against chemoradiation with surgical resection.

METHODS

We electronically searched PubMed and EMBASE for randomized, controlled clinical trials involving patients with gastric adenocarcinoma, status post-R0 resection. The interventions compared were adjuvant chemotherapy versus chemoradiation, with any chemotherapy regimen. The primary outcomes of interest were disease-free survival and overall survival. The Mantel-Haenszel random-effects model was used to calculate effect sizes.

RESULTS

Six trials that included 1,171 patients were evaluated; 599 were randomized to adjuvant chemoradiation and 572 to chemotherapy alone. Chemoradiation was associated with a significant increase in disease-free survival (odds ratio 1.48, 95% confidence interval 1.08-2.03) when compared to chemotherapy alone. However, there was no significant difference in overall survival (odds ratio 1.27, 95% confidence interval 0.95-1.71). Five trials found no statistically significant differences in toxicities between the two groups.

CONCLUSION

In patients with gastric cancer status post-R0 resection, adjuvant chemoradiation was associated with higher disease-free survival when compared to chemotherapy alone. It remains appropriate to design trials testing new systemic agents with radiotherapy.

Preliminary results of interstitial motexafin lutetium-mediated PDT for prostate cancer

BACKGROUND AND OBJECTIVES

Interstitial photodynamic therapy (PDT) is an emerging modality for the treatment of solid organ disease. Our group at the University of Pennsylvania has performed extensive studies that demonstrate the feasibility of interstitial PDT for prostate cancer. Our preclinical and clinical experience is herein detailed.

STUDY DESIGN/MATERIALS AND METHODS

We have treated 16 canines in preclinical studies, and 16 human subjects in a Phase I study, using motexafin lutetium-mediated PDT for recurrent prostate adenocarcinoma. Dosimetry of light fluence, drug level and oxygen distribution for these patients were performed.

RESULTS

We demonstrate the safe and comprehensive treatment of the prostate using PDT. However, there is significant variability in the dose distribution and the subsequent tissue necrosis throughout the prostate.

CONCLUSIONS

PDT is an attractive option for the treatment of prostate adenocarcinoma. However, the observed variation in PDT dose distribution translates into uncertain therapeutic reproducibility. Our future focus will be on the development of an integrated system that is able to both detect and compensate for dose variations in real-time, in order to deliver a consistent overall PDT dose distribution.

Megakaryoblastic Leukemia Factor-1 Transduces Cytoskeletal Signals and Induces Smooth Muscle Cell Differentiation from Undifferentiated Embryonic Stem Cells

The SAP domain transcription factor myocardin plays a critical role in the transcriptional program regulating smooth muscle cell differentiation. In this report, we describe the capacity of myocardin to physically associate with megakaryoblastic leukemia factor-1 (MKL1) and characterize the function of MKL1 in smooth muscle cells (SMCs). The MKL1 gene is expressed in most human tissues and myocardin and MKL are co-expressed in SMCs. MKL1 and myocardin physically associate via conserved leucine zipper domains. Overexpression of MKL1 transactivates serum response factor (SRF)-dependent SMC-restricted transcriptional regulatory elements including the SM22alpha promoter, smooth muscle myosin heavy chain promoter/enhancer, and SM-alpha-actin promoter/enhancer in non-SMCs. Moreover, forced expression of MKL1 and SRF in undifferentiated SRF(-/-) embryonic stem cells activates multiple endogenous SMC-restricted genes at levels equivalent to, or exceeding, myocardin. Forced expression of a dominant-negative MKL1 mutant reduces myocardin-induced activation of the SMC-specific SM22alpha promoter. In NIH3T3 fibroblasts MKL1 localizes to the cytoplasm and translocates to the nucleus in response to serum stimulation, actin treadmilling, and RhoA signaling. In contrast, in SMCs MKL1 is observed exclusively in the nucleus regardless of serum conditions or RhoA signaling. However, when actin polymerization is disrupted MKL1 translocates from the nucleus to the cytoplasm in SMCs. Together, these data were consistent with a model wherein MKL1 transduces signals from the cytoskeleton to the nucleus in SMCs and regulates SRF-dependent SMC differentiation autonomously or in concert with myocardin.

Myocardin is a critical serum response factor cofactor in the transcriptional program regulating smooth muscle cell differentiation

The SAP family transcription factor myocardin functionally synergizes with serum response factor (SRF) and plays an important role in cardiac development. To determine the function of myocardin in the smooth muscle cell (SMC) lineage, we mapped the pattern of myocardin gene expression and examined the molecular mechanisms underlying transcriptional activity of myocardin in SMCs and embryonic stem (ES) cells. The human and murine myocardin genes were expressed in vascular and visceral SMCs at levels equivalent to or exceeding those observed in the heart. During embryonic development, the myocardin gene was expressed abundantly in a precise, developmentally regulated pattern in SMCs. Forced expression of myocardin transactivated multiple SMC-specific transcriptional regulatory elements in non-SMCs. By contrast, myocardin-induced transactivation was not observed in SRF(-/-) ES cells but could be rescued by forced expression of SRF or the SRF DNA-binding domain. Furthermore, expression of a dominant-negative myocardin mutant protein or small-interfering-RNA-induced myocardin knockdown significantly reduced SM22 alpha promoter activity in SMCs. Most importantly, forced expression of myocardin activated expression of the SM22 alpha, smooth muscle alpha-actin, and calponin-h1 genes in undifferentiated mouse ES cells. Taken together, these data demonstrate that myocardin plays an important role in the SRF-dependent transcriptional program that regulates SMC development and differentiation.

Binding of serum response factor to CArG box sequences is necessary but not sufficient to restrict gene expression to arterial smooth muscle cells

Serum response factor (SRF) plays an important role in regulating smooth muscle cell (SMC) development and differentiation. To understand the molecular mechanisms underlying the activity of SRF in SMCs, the two CArG box-containing elements in the arterial SMC-specific SM22alpha promoter, SME-1 and SME-4, were functionally and biochemically characterized. Mutations that abolish binding of SRF to the SM22alpha promoter totally abolish promoter activity in transgenic mice. Moreover, a multimerized copy of either SME-1 or SME-4 subcloned 5' of the minimal SM22alpha promoter (base pairs -90 to +41) is necessary and sufficient to restrict transgene expression to arterial SMCs in transgenic mice. In contrast, a multimerized copy of the c-fos SRE is totally inactive in arterial SMCs and substitution of the c-fos SRE for the CArG motifs within the SM22alpha promoter inactivates the 441-base pair SM22alpha promoter in transgenic mice. Deletion analysis revealed that the SME-4 CArG box alone is insufficient to activate transcription in SMCs and additional 5'-flanking nucleotides are required. Nuclear protein binding assays revealed that SME-4 binds SRF, YY1, and four additional SMC nuclear proteins. Taken together, these data demonstrate that binding of SRF to specific CArG boxes is necessary, but not sufficient, to restrict transgene expression to SMCs in vivo.

Analysis of SM22alpha-deficient mice reveals unanticipated insights into smooth muscle cell differentiation and function

SM22alpha is a 22-kDa smooth muscle cell (SMC) lineage-restricted protein that physically associates with cytoskeletal actin filament bundles in contractile SMCs. To examine the function of SM22alpha, gene targeting was used to generate SM22alpha-deficient (SM22(-/-LacZ)) mice. The gene targeting strategy employed resulted in insertion of the bacterial lacZ reporter gene at the SM22alpha initiation codon, permitting precise analysis of the temporal and spatial pattern of SM22alpha transcriptional activation in the developing mouse. Northern and Western blot analyses confirmed that the gene targeting strategy resulted in a null mutation. Histological analysis of SM22(+/-LacZ) embryos revealed detectable beta-galactosidase activity in the unturned embryonic day 8.0 embryo in the layer of cells surrounding the paired dorsal aortae concomitant with its expression in the primitive heart tube, cephalic mesenchyme, and yolk sac vasculature. Subsequently, during postnatal development, beta-galactosidase activity was observed exclusively in arterial, venous, and visceral SMCs. SM22alpha-deficient mice are viable and fertile. Their blood pressure and heart rate do not differ significantly from their control SM22alpha(+/-) and SM22alpha(+/+) littermates. The vasculature and SMC-containing tissues of SM22alpha-deficient mice develop normally and appear to be histologically and ultrastructurally similar to those of their control littermates. Taken together, these data demonstrate that SM22alpha is not required for basal homeostatic functions mediated by vascular and visceral SMCs in the developing mouse. These data also suggest that signaling pathways that regulate SMC specification and differentiation from local mesenchyme are activated earlier in the angiogenic program than previously recognized.