Metabolic adaptation to tyrosine kinase inhibition in leukemia stem cells.

Tyrosine kinase inhibitors (TKIs) are very effective in treating chronic myelogenous leukemia (CML), but primitive, quiescent leukemia stem cells persist as a barrier to the cure. We performed a comprehensive evaluation of metabolic adaptation to TKI treatment and its role in CML hematopoietic stem and progenitor cell persistence. Using a CML mouse model, we found that glycolysis, glutaminolysis, the tricarboxylic acid cycle, and oxidative phosphorylation (OXPHOS) were initially inhibited by TKI treatment in CML-committed progenitors but were restored with continued treatment, reflecting both selection and metabolic reprogramming of specific subpopulations. TKI treatment selectively enriched primitive CML stem cells with reduced metabolic gene expression. Persistent CML stem cells also showed metabolic adaptation to TKI treatment through altered substrate use and mitochondrial respiration maintenance. Evaluation of transcription factors underlying these changes helped detect increased HIF-1 protein levels and activity in TKI-treated stem cells. Treatment with an HIF-1 inhibitor in combination with TKI treatment depleted murine and human CML stem cells. HIF-1 inhibition increased mitochondrial activity and reactive oxygen species (ROS) levels, reduced quiescence, increased cycling, and reduced the self-renewal and regenerating potential of dormant CML stem cells. We, therefore, identified the HIF-1-mediated inhibition of OXPHOS and ROS and maintenance of CML stem cell dormancy and repopulating potential as a key mechanism of CML stem cell adaptation to TKI treatment. Our results identify a key metabolic dependency in CML stem cells persisting after TKI treatment that can be targeted to enhance their elimination.

Increased Grades of Rectal Intussusception: Role of Decline in Pelvic Floor Integrity and Association With Dyssynergic Defecation.

INTRODUCTION: The natural history of rectal intussusception (RI) is poorly understood. We hypothesized that decline in pelvic floor integrity and function leads to increasing RI grades. METHODS: Retrospective analysis of a registry of patients with defecatory disorders with high-resolution anorectal manometry and magnetic resonance defecography was performed. Association of risk factors on increasing RI grades was assessed using logistic regression. RESULTS: Analysis included a total of 238 women: 90 had no RI, 43 Oxford 1-2, 49 Oxford 3, and 56 Oxford 4-5. Age ( P = 0.017), vaginal delivery ( P = 0.008), and prior pelvic surgery ( P = 0.032) were associated with increased Oxford grades. Obstructive defecation symptoms and dyssynergic defecation were observed at relatively high rates across groups. Increased RI grades were associated with less anal relaxation at simulated defecation yet, higher rates of normal balloon expulsion ( P < 0.05), linked to diminished anal sphincter. Indeed, increased RI grades were associated with worsening fecal incontinence severity, attributed to higher rates of anal hypotension. Levator ani laxity, defined by increased levator hiatus length and its excessive descent at straining, was associated with increasing RI grades, independent of age, history of vaginal delivery, and pelvic surgeries and could independently predict increased RI grades. Concurrent anterior and posterior compartments, and visceral prolapse were associated with higher Oxford grades. DISCUSSION: Our data suggest that decline in pelvic floor integrity with abnormal levator ani laxity is associated with increased RI grades, a process that is independent of age, history of vaginal deliveries, and/or pelvic surgeries, and perhaps related to dyssynergic defecation.

MR-guided focused ultrasound therapy of extra-abdominal desmoid tumors: a multicenter retrospective study of 105 patients.

OBJECTIVE: To assess the safety and efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) for the treatment extra-abdominal desmoids. METHODS: A total of 105 patients with desmoid fibromatosis (79 females, 26 males; 35 ± 14 years) were treated with MRgFUS between 2011 and 2021 in three centers. Total and viable tumors were evaluated per patient at last follow-up after treatment. Response and progression-free survival (PFS) were assessed with (modified) response evaluation criteria in solid tumors (RECIST v.1.1 and mRECIST). Change in Numerical Rating Scale (NRS) pain and 36-item Short Form Health Survey (SF-36) scores were compared. Treatment-related adverse events were recorded. RESULTS: The median initial tumor volume was 114 mL (IQR 314 mL). After MRgFUS, median total and viable tumor volume decreased to 51 mL (95% CI: 30-71 mL, n = 101, p < 0.0001) and 29 mL (95% CI: 17-57 mL, n = 88, p < 0.0001), respectively, at last follow-up (median: 15 months, 95% CI: 11-20 months). Based on total tumor measurements (RECIST), 86% (95% CI: 75-93%) had at least stable disease or better at last follow-up, but 50% (95% CI: 38-62%) of remaining viable nodules (mRECIST) progressed within the tumor. Median PFS was reached at 17 and 13 months for total and viable tumors, respectively. NRS decreased from 6 (IQR 3) to 3 (IQR 4) (p < 0.001). SF-36 scores improved (physical health (41 (IQR 15) to 46 (IQR 12); p = 0.05, and mental health (49 (IQR 17) to 53 (IQR 9); p = 0.02)). Complications occurred in 36%, most commonly 1st/2nd degree skin burns. CONCLUSION: MRgFUS reduced tumor volume, reduced pain, and improved quality of life in this series of 105 patients with extra-abdominal desmoid fibromatosis. CLINICAL RELEVANCE STATEMENT: Imaging-guided ablation is being increasingly used as an alternative to surgery, radiation, and medical therapy for the treatment of desmoid fibromatosis. MR-guided high-intensity focused ultrasound is an incisionless ablation technique that can be used to reduce tumor burden effectively and safely. KEY POINTS: • Desmoid fibromatosis was treated with MR-guided high-intensity focused ultrasound in 105 patients. • MR-guided focused ultrasound ablation reduced tumor volume and pain and improved quality of life. • MR-guided focused ultrasound is a treatment option for patients with extra-abdominal desmoid tumors.

Anorectal manometry for the diagnosis of pelvic floor disorders in patients with hypermobility spectrum disorders and hypermobile Ehlers-Danlos syndrome.

INTRODUCTION: Functional gastrointestinal disorders (FGID) including impaired rectal evacuation are common in patients with Hypermobility Spectrum Disorder (HSD) or Hypermobile Ehlers-Danlos Syndrome (hEDS). The effect of connective tissue pathologies on pelvic floor function in HSD/hEDS remains unclear. We aimed to compare clinical characteristics and anorectal pressure profile in patients with HSD/hEDS to those of age and sex matched controls. METHODS: We conducted a retrospective review of all FGID patients who underwent high resolution anorectal manometry (HR-ARM) and balloon expulsion test (BET) for evaluation of impaired rectal evacuation. Patients with HSD/hEDS were age and sex matched to a randomly selected cohort of control patients without HSD/hEDS. An abnormal BET was defined as the inability to expel a rectal balloon within 2 minutes. Wilcoxon rank sum test and Fisher's exact test were used to make comparisons and logistic regression model for predictive factors for abnormal evacuation. RESULTS: A total of 144 patients (72 with HSD/hEDS and 72 controls) were analyzed. HSD/hEDS patients were more likely to be Caucasian (p < 0.001) and nulliparous. Concurrent psychiatric disorders; depression, and anxiety (p < 0.05), and somatic syndromes; fibromyalgia, migraine and sleep disorders (p < 0.001) were more common in these patients. Rate of abnormal BET were comparable among the groups. HDS/hEDS patients had significantly less anal relaxation and higher residual anal pressures during simulated defecation, resulting in significantly more negative rectoanal pressure gradient. The remaining anorectal pressure profile and sensory levels were comparable between the groups. While diminished rectoanal pressure gradient was the determinant of abnormal balloon evacuation in non HSD/hEDS patients, increased anal resting tone and maximum volume tolerated were independent factors associated with an abnormal BET in HSD/hEDS patients. Review of defecography data from a subset of patients showed no significant differences in structural pathologies between HSD/hEDS and non HSD/hEDS patients. CONCLUSIONS: These results suggest anorectal pressure profile is not compromised by connective tissue pathologies in HSD patients. Whether concurrent psychosomatic disorders or musculoskeletal involvement impact the pelvic floor function in these patients needs further investigation.

Consensus Definitions and Interpretation Templates for Magnetic Resonance Imaging of Defecatory Pelvic Floor Disorders: Proceedings of the Consensus Meeting of the Pelvic Floor Disorders Consortium of the American Society of Colon and Rectal Surgeons, the Society of Abdominal Radiology, the International Continence Society, the American Urogynecologic Society, the International Urogynecological Association, and the Society of Gynecologic Surgeons.

The Pelvic Floor Disorders Consortium (PFDC) is a multidisciplinary organization of colorectal surgeons, urogynecologists, urologists, gynecologists, gastroenterologists, radiologists, physiotherapists, and other advanced care practitioners. Specialists from these fields are all dedicated to the diagnosis and management of patients with pelvic floor conditions, but they approach, evaluate, and treat such patients with their own unique perspectives given the differences in their respective training. The PFDC was formed to bridge gaps and enable collaboration between these specialties. The goal of the PFDC is to develop and evaluate educational programs, create clinical guidelines and algorithms, and promote high quality of care in this unique patient population. The recommendations included in this article represent the work of the PFDC Working Group on Magnetic Resonance Imaging of Pelvic Floor Disorders (members listed alphabetically in Table 1). The objective was to generate inclusive, rather than prescriptive, guidance for all practitioners, irrespective of discipline, involved in the evaluation and treatment of patients with pelvic floor disorders.

Reduced-Intensity versus Myeloablative Conditioning in Cord Blood Transplantation for Acute Myeloid Leukemia (40-60 years) across Highly Mismatched HLA Barriers-On Behalf of Eurocord and the Cellular Therapy & Immunobiology Working Party (CTIWP) of EBMT.

The use of myeloablative conditioning (MAC) in umbilical cord blood transplantation (UCBT) has been associated with high nonrelapse mortality (NRM) in patients aged >40 years, especially those having a high HLA disparity, thus limiting wider applications. We hypothesized that the NRM advantage of reduced-intensity conditioning (RIC) and higher graft-versus-leukemia effect associated with greater HLA disparities would expand its use for patients (aged 40 to 60 years) without compromising efficacy and compared outcomes between RIC and MAC regimens. In total, 288 patients aged 40 to 60 years, with de novo acute myeloid leukemia, receiving UCBT with at least 2 HLA mismatches with RIC (n = 166) or MAC (n = 122) regimens were included. As compared to RIC, the MAC cohort included relatively younger patients, having received more single UCBT, with lower total nucleated cell counts and more in vivo T cell depletion. Median time to neutrophil engraftment, infections (bacterial, viral, and fungal), and grade II to IV acute and chronic graft-versus-host disease were similar in both groups. In the multivariate analysis, overall survival (hazard ratio [HR], 0.98; P = .9), NRM (HR, 0.68; P = .2), and relapse (HR, 1.24; P = .5) were not different between RIC and MAC. Refractory disease was associated with worse survival. Outcomes of UBCT for patients aged 40 to 60 years having ≥2 HLA mismatches are comparable after the RIC or MAC regimen.

Near-silent distortionless DWI using magnetization-prepared RUFIS.

PURPOSE: To develop a near-silent and distortionless DWI (sd-DWI) sequence using magnetization-prepared rotating ultrafast imaging sequence. METHODS: A rotating ultrafast imaging sequence was modified with driven-equilibrium diffusion preparation, including eddy-current compensation methods. To compensate for the T1 recovery during readout, a phase-cycling method was used. Both compensation methods were validated in phantoms. The optimized sequence was compared with an EPI diffusion sequence for image distortion, contrast, ADC, and acoustic noise level in phantoms. The sequence was evaluated in 1 brain volunteer, 5 prostate volunteers, and 10 pediatric patients with joint diseases. RESULTS: Combination of several eddy-current compensation methods reduced the artifact to an acceptable level. Phase cycling reduced T1 recovery contamination during readout. In phantom scans, the optimized sequence generated similar image contrast to the EPI diffusion sequence, and ADC maps between the sequences were comparable; sd-DWI had significantly lower acoustic noise (P < .05). In vivo brain scan showed reduced image distortion in sd-DWI compared with the EPI diffusion, although residual motion artifact remains due to brain pulsation. The prostate scans showed that sd-DWI can provide similar ADC compared with EPI diffusion, with no image distortion. Patient scans showed that the sequence can clearly depict joint lesions. CONCLUSION: An sd-DWI sequence was developed and optimized. Compared with conventional EPI diffusion, sd-DWI provided similar diffusion contrast, accurate ADC measurement, improved image quality, and minimal ambient scanning noise. The sequence showed the ability to obtain in vivo diffusion contrast in relatively motion-free body regions, such as prostate and joint.

Data-driven self-calibration and reconstruction for non-cartesian wave-encoded single-shot fast spin echo using deep learning.

BACKGROUND: Current self-calibration and reconstruction methods for wave-encoded single-shot fast spin echo imaging (SSFSE) requires long computational time, especially when high accuracy is needed. PURPOSE: To develop and investigate the clinical feasibility of data-driven self-calibration and reconstruction of wave-encoded SSFSE imaging for computation time reduction and quality improvement. STUDY TYPE: Prospective controlled clinical trial. SUBJECTS: With Institutional Review Board approval, the proposed method was assessed on 29 consecutive adult patients (18 males, 11 females, range, 24-77 years). FIELD STRENGTH/SEQUENCE: A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable 3.5× acceleration with full-Fourier acquisitions. Data-driven calibration of wave-encoding point-spread function (PSF) was developed using a trained deep neural network. Data-driven reconstruction was developed with another set of neural networks based on the calibrated wave-encoding PSF. Training of the calibration and reconstruction networks was performed on 15,783 2D wave-encoded SSFSE abdominal images. ASSESSMENT: Image quality of the proposed data-driven approach was compared independently and blindly with a conventional approach using iterative self-calibration and reconstruction with parallel imaging and compressed sensing by three radiologists on a scale from -2 to 2 for noise, contrast, sharpness, artifacts, and confidence. Computation time of these two approaches was also compared. STATISTICAL TESTS: Wilcoxon signed-rank tests were used to compare image quality and two-tailed t-tests were used to compare computation time with P values of under 0.05 considered statistically significant. RESULTS: An average 2.1-fold speedup in computation was achieved using the proposed method. The proposed data-driven self-calibration and reconstruction approach significantly reduced the perceived noise level (mean scores 0.82, P < 0.0001). DATA CONCLUSION: The proposed data-driven calibration and reconstruction achieved twice faster computation with reduced perceived noise, providing a fast and robust self-calibration and reconstruction for clinical abdominal SSFSE imaging. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:841-853.

Multimodal imaging assessment and histologic correlation of the female rat pelvic floor muscles' anatomy.

Pelvic floor disorders negatively impact millions of women worldwide. Although there is a strong epidemiological association with childbirth, the mechanisms leading to the dysfunction of the integral constituents of the female pelvic floor, including pelvic floor skeletal muscles, are not well understood. This is in part due to the constraints associated with directly probing these muscles, which are located deep in the pelvis. Thus, experimental models and non-invasive techniques are essential for advancing knowledge of various phenotypes of pelvic floor muscle injury and pathogenesis of muscle dysfunction, as well as developing minimally invasive approaches for the delivery of novel therapeutics. The most widely used animal model for pelvic floor disorders is the rat. However, the radiological anatomy of rat pelvic floor muscles has not been described. To remedy this gap, the current study provides the first detailed description of the female rat pelvic floor muscles' radiological appearance on MR and ultrasound images, validated by correlation with gross anatomy and histology. We also demonstrate that ultrasound guidance can be used to target rat pelvic floor muscles for possible interventional therapies.

Fludarabine-based reduced toxicity yet myeloablative conditioning is effective and safe particularly in patients with high-risk thalassemia undergoing allogeneic transplantation.

INTRODUCTION: Thalassemia major (TM) is an inherited disorder caused by ineffective erythropoiesis. At the present time, allogeneic stem cell transplantation (allo-SCT) is a curative option. Conventional busulfan and cyclophosphamide based myeloablative conditioning regimens are limited by increased toxicity, especially in high-risk patients. Replacement of cyclophosphamide with fludarabine has reduced toxicity and nonrelapse mortality (NRM), thus improving outcomes. We analyzed long-term data of our fludarabine-based myeloablative, reduced toxicity protocol, specifically in high-risk patients. METHODS: We retrospectively analyzed a cohort of 47 consecutive patients with TM undergoing allo-SCT from matched donors, using the fludarabine-based regimen (reduced toxicity regimen). The median age of the cohort was 10 years. Thirty-eight patients (80%) were in the high-risk and nine patients (20%) were in the low-risk category. The primary aim of this analysis was thalassemia-free survival (TFS). RESULTS: The rejection rate was 11% within high-risk patients with NRM of 2%. With a median follow-up period of 7 years (1-15 years), the 10-year TFS in the entire cohort was 87%, and the overall survival (OS) was 97%. The 10-year TFS and OS among the low-risk and high-risk groups were 90% versus 84%, respectively (P = 0.45) and 100% versus 96%, respectively (P = 0.5), and both subsets of patients did equally well. CONCLUSION: In conclusion, replacement of high-dose cyclophosphamide with fludarabine is well tolerated with minimal regimen-related toxicity and acceptable rejection rates, especially in high-risk patients.

Magnetic resonance imaging of myelin using ultrashort Echo time (UTE) pulse sequences: Phantom, specimen, volunteer and multiple sclerosis patient studies.

Clinical magnetic resonance imaging of multiple sclerosis (MS) has focused on indirect imaging of myelin in white matter by detecting signal from protons in the water associated with myelin. Here we show that protons in myelin can be directly imaged using ultrashort echo time (UTE) free induction decay (FID) and imaging sequences on a clinical 3T MR scanner. An adiabatic inversion recovery UTE (IR-UTE) sequence was used to detect signal from myelin and simultaneously suppress signal from water protons. Validation studies were performed on myelin lipid and myelin basic protein (MBP) phantoms in the forms of lyophilized powders as well as suspensions in D2O and H2O. IR-UTE sequences were then used to image MS brain specimens, healthy volunteers, and patients. The T2* of myelin was measured using a UTE FID sequence, as well as UTE and IR-UTE sequences at different TEs. T2* values of ~110-330µs were measured with UTE FID, as well as with UTE and IR-UTE sequences for myelin powders, myelin-D2O and myelin-H2O phantoms, consistent with selective imaging of myelin protons with IR-UTE sequences. Our studies showed myelin selective imaging of white matter in the brains in vitro and in vivo. Complete or partial signal loss was observed in specimens in areas of the brain with histopathologic evidence of myelin loss, and in the brain of patients with MS.

Use of gemcitabine-platinum in Indian patients with advanced gall bladder cancer.

BACKGROUND: Gemcitabine-platinum (Gem-P) is the current standard for patients with advanced gall bladder cancer. MATERIALS & METHODS: This is retrospective analysis of a prospectively maintained database of 210 patients with advanced gall bladder cancer treated with Gem-P between January 2012 and September 2013. RESULTS: Median age was 53 years, 65.2% females. In total,158 patients had metastatic and 52 had locoregional disease. Median number of cycles was 5 (1-12). At a median follow-up of 10 months, median overall survival/progression-free survival was 10/5 months, respectively. On multivariate analysis, patients who underwent prior surgery for primary and locoregional disease had a significantly better progression-free survival and those with locoregional disease had a significantly better overall survival. A total of 45.7% received second-line chemotherapy. CONCLUSION: Use of Gem-P in Indian patients leads to slightly worse outcomes suggesting an aggressive biology.

Detection of in vivo enzyme activity with CatalyCEST MRI.

PURPOSE: CatalyCEST MRI compares the detection of an enzyme-responsive chemical exchange saturation transfer (CEST) agent with the detection of an unresponsive "control" CEST agent that accounts for other conditions that influence CEST. The purpose of this study was to investigate the feasibility of in vivo catalyCEST MRI. METHODS: CEST agents that were responsive and unresponsive to the activity of urokinase plasminogen activator were shown to have negligible interaction with each other. A CEST-fast imaging with steady state precession (FISP) MRI protocol was used to acquire MR CEST spectroscopic images with a Capan-2 pancreatic tumor model after intravenous injection of the CEST agents. A function of (super)-Lorentzian line shapes was fit to CEST spectra of a region-of-interest that represented the tumor. RESULTS: The CEST effects from each agent showed the same initial uptake into tumor tissues, indicating that both agents had the same pharmacokinetic transport rates. Starting 5 min after injection, CEST from the enzyme-responsive agent disappeared more quickly than CEST from the unresponsive agent, indicating that the enzyme responsive agent was being catalyzed by urokinase plasminogen activator, while both agents also experienced net pharmacokinetic washout from the tumor. CONCLUSION: CatalyCEST MRI demonstrates that dynamic tracking of enzyme-responsive and unresponsive CEST agents during the same in vivo MRI study is feasible.

Nonoperative Management for Rectal Cancer.

ABSTRACT: The treatment paradigm for rectal cancer has been shifting toward de-escalated approaches to preserve patient quality of life. Historically, the standard treatment in the United States for locally advanced rectal cancer has standardly comprised preoperative chemoradiotherapy coupled with total mesorectal excision. Recent data challenge this "one-size-fits-all" strategy, supporting the possibility of omitting surgery for certain patients who achieve a clinical complete response to neoadjuvant therapy. Consequently, patients and their physicians must navigate diverse neoadjuvant options, often in the context of pursuing organ preservation. Total neoadjuvant therapy, involving the administration of all chemotherapy and radiation before total mesorectal excision, is associated with the highest rates of clinical complete response. However, questions persist regarding the optimal sequencing of radiation and chemotherapy and the choice between short-course and long-course radiation. Additionally, meticulous response assessment and surveillance are critical for selecting patients for nonoperative management without compromising the excellent cure rates associated with trimodality therapy. As nonoperative management becomes increasingly recognized as a standard-of-care treatment option for patients with rectal cancer, ongoing research in patient selection and monitoring as well as patient-reported outcomes is critical to guide personalized rectal cancer management within a patient-centered framework.

Use of a footstool improves rectal balloon expulsion in some patients with defecatory disorders.

BACKGROUND: Whether patients with defecatory disorders (DDs) with favorable response to a footstool have distinctive anorectal pressure characteristics is unknown. We aimed to identify the clinical phenotype and anorectal pressure profile of patients with DDs who benefit from a footstool. METHODS: This is a retrospective review of patients with high resolution anorectal manometry (HR-ARM) and balloon expulsion test (BET) from a tertiary referral center. BET was repeated with a 7-inch-high footstool in those who failed it after 120 s. Data were compared among groups with respect to BET results. KEY RESULTS: Of the 667 patients with DDs, a total of 251 (38%) had failed BET. A footstool corrected BET in 41 (16%) of those with failed BET. Gender-specific differences were noted in anorectal pressures, among patients with and without normal BET, revealing gender-based nuances in pathophysiology of DDs. Comparing patients who passed BET with footstool with those who did not, the presence of optimal stool consistency, with reduced instances of loose stools and decreased reliance on laxatives were significant. Additionally, in women who benefited from a footstool, lower anal pressures at rest and simulated defecation were observed. Independent factors associated with a successful BET with a footstool in women included age <50, Bristol 3 or 4 stool consistency, lower anal resting pressure and higher rectoanal pressure gradient. CONCLUSION & INFERENCES: Identification of distinctive clinical and anorectal phenotype of patients who benefited from a footstool could provide insight into the factors influencing the efficacy of footstool utilization and allow for an individualized treatment approach in patients with DDs.

Application of PET/MRI in Gynecologic Malignancies.

The diagnosis, treatment, and management of gynecologic malignancies benefit from both positron emission tomography/computed tomography (PET/CT) and MRI. PET/CT provides important information on the local extent of disease as well as diffuse metastatic involvement. MRI offers soft tissue delineation and loco-regional disease involvement. The combination of these two technologies is key in diagnosis, treatment planning, and evaluating treatment response in gynecological malignancies. This review aims to assess the performance of PET/MRI in gynecologic cancer patients and outlines the technical challenges and clinical advantages of PET/MR systems when specifically applied to gynecologic malignancies.

Microenvironmental CXCL12 deletion enhances Flt3-ITD acute myeloid leukemia stem cell response to therapy by reducing p38 MAPK signaling.

Fms-like tyrosine kinase 3 (Flt3) tyrosine kinase inhibitors (Flt3-TKI) have improved outcomes for patients with Flt3-mutated acute myeloid leukemia (AML) but are limited by resistance and relapse, indicating persistence of leukemia stem cells (LSC). Here utilizing a Flt3-internal tandem duplication (Flt3-ITD) and Tet2-deleted AML genetic mouse model we determined that FLT3-ITD AML LSC were enriched within the primitive ST-HSC population. FLT3-ITD LSC showed increased expression of the CXCL12 receptor CXCR4. CXCL12-abundant reticular (CAR) cells were increased in Flt3-ITD AML marrow. CXCL12 deletion from the microenvironment enhanced targeting of AML cells by Flt3-TKI plus chemotherapy treatment, including enhanced LSC targeting. Both treatment and CXCL12 deletion partially reduced p38 mitogen-activated protein kinase (p38) signaling in AML cells and further reduction was seen after treatment in CXCL12 deleted mice. p38 inhibition reduced CXCL12-dependent and -independent maintenance of both murine and human Flt3-ITD AML LSC by MSC and enhanced their sensitivity to treatment. p38 inhibition in combination with chemotherapy plus TKI treatment leads to greater depletion of Flt3-ITD AML LSC compared with CXCL12 deletion. Our studies support roles for CXCL12 and p38 signaling in microenvironmental protection of AML LSC and provide a rationale for inhibiting p38 signaling to enhance Flt3-ITD AML targeting.