ABSTRACT
While current analytical methodologies can readily identify cannabis use, definitively establishing recent use within the impairment window has proven to be far more complex, requiring a new approach. Recent studies have shown no direct relationship between impairment and Δ9-tetra-hydrocannabinol (Δ9-THC) concentrations in blood or saliva, making legal "per se" Δ9-THC limits scientifically unjustified. Current methods that focus on Δ9-THC and/or metabolite concentrations in blood, saliva, urine, or exhaled breath can lead to false-positive results for recent use due to the persistence of Δ9-THC well outside of the typical 3-4 h window of potential impairment following cannabis inhalation. There is also the issue of impairment due to other intoxicating substances-just because a subject exhibits signs of impairment and cannabis use is detected does not rule out the involvement of other drugs. Compounding the matter is the increasing popularity of hemp-derived cannabidiol (CBD) products following passage of the 2018 Farm Bill, which legalized industrial hemp in the United States. Many of these products contain varying levels of Δ9-THC, which can lead to false-positive tests for cannabis use. Furthermore, hemp-derived CBD is used to synthesize Δ8-THC, which possesses psychoactive properties similar to Δ9-THC and is surrounded by legal controversy. For accuracy, analytical methods must be able to distinguish the various THC isomers, which have identical masses and exhibit immunological cross-reactivity. A new testing approach has been developed based on exhaled breath and blood sampling that incorporates kinetic changes and the presence of key cannabinoids to detect recent cannabis use within the impairment window without the false-positive results seen with other methods. The complexity of determining recent cannabis use that may lead to impairment demands such a comprehensive method so that irresponsible users can be accurately detected without falsely accusing responsible users who may unjustly suffer harsh, life-changing consequences.
Subject(s)
Cannabis , Dronabinol , Substance Abuse Detection , Humans , Dronabinol/analysis , Substance Abuse Detection/methods , Cannabis/chemistry , Saliva/chemistry , Cannabidiol/analysis , Marijuana Abuse , Breath Tests/methods , Marijuana UseABSTRACT
Legalization of cannabis for medicinal and/or recreational use is expanding globally. Although cannabis is being regulated country by country, an accurate recent use test with indisputable results correlated with impairment has yet to be discovered. In the present study, a new approach for determining recent cannabis use within the impairment window after smoking was developed by studying 74 subjects with a mean age of 25 years and average use history of 9 years. Horizontal gaze nystagmus was evaluated along with subject self-assessments of impairment, and blood and breath samples were collected before and after smoking cannabis. Breath and blood pharmacokinetic parameters and cannabinoid profiles determined recent use within the impairment window. No subjects were positive for recent use pre-smoking, although all subjects had detectable cannabinoids in breath samples. We describe an inhaled cannabis recent use test that correlates with impairment and helps protect against wrongful prosecution and workplace discrimination.
Subject(s)
Breath Tests/methods , Cannabinoids/analysis , Cannabis/chemistry , Substance Abuse Detection/methods , Administration, Inhalation , Adult , Cannabinoids/administration & dosage , Female , Humans , Male , Middle Aged , Young AdultABSTRACT
BACKGROUND: Cannabis legalization is expanding rapidly throughout the United States, but there is no reliable means of establishing recent use. OBJECTIVE: To develop and validate a bioanalytical method for determination of Δ9-tetrahydrocannabinol (Δ9-THC), cannabinol, 11-hydroxy-Δ9-THC, 11-nor-9-carboxy-Δ9-THC, and 8ß,11-dihydroxy-Δ9-THC in whole blood microsamples by liquid chromatography high-resolution mass spectrometry (LC-HRMS). METHODS: Cannabinoid extraction from whole blood was performed using a mixture of n-hexane/ethyl acetate (90:10, v/v). Chromatographic separation was performed with a C18 column using a binary mobile phase gradient of water and acetonitrile, each with 0.1% formic acid. Detection was performed by positive ion mode heated electrospray ionization with full scan MS on an Orbitrap mass spectrometer. A clinical study was performed in 30 subjects to identify recent cannabis use based on analysis of cannabinoids in blood samples up to 200 min post-smoking. RESULTS: Acceptable linearity of all calibration curves was observed (r2>0.99) for all analytes over a 1-100 ng/mL concentration range, with acceptable accuracy. Limit of detection (LOD) was 0.5 ng/mL. Accuracy and precision met acceptance criteria for all analytes. Repeatability (CV) was <5% at low (3 ng/mL) and high (90 ng/mL) concentrations. In the clinical study, the ratios between 11-nor-9-carboxy-Δ9-THC and Δ9-THC fell immediately after smoking and returned to near baseline levels by 200 min post-smoking, which is consistent with recent use. CONCLUSIONS AND HIGHLIGHTS: The developed LC-HRMS bioanalytical method is suitable for quantification of five key cannabinoids in whole capillary blood microsamples and can be used in conjunction with a test for determining recent cannabis use.
Subject(s)
Cannabinoids , Cannabis , Cannabinoids/analysis , Chromatography, Liquid , Dronabinol/analysis , Humans , Tandem Mass SpectrometryABSTRACT
OBJECTIVE: Ospemifene, an estrogen receptor agonist/antagonist approved for the treatment of dyspareunia and vaginal dryness in postmenopausal women, has potential new indications as an immune modulator. The overall objective of the present series of preclinical studies was to evaluate the immunomodulatory activity of ospemifene in combination with a peptide cancer vaccine. METHODS: Immune regulating effects, mechanism of action and structure activity relationships of ospemifene and related compounds were evaluated by examining expression of T-cell activating cytokines in vitro, and antigen-specific immune response and cytotoxic T-lymphocyte activity in vivo. The effects of ospemifene (OSP) on the immune response to a peptide cancer vaccine (PV) were evaluated after chronic [control (nâ=â22); OSP 50âmg/kg (nâ=â16); PV (nâ=â6); OSP+PV (nâ=â11)], intermittent [control (nâ=â10); OSP 10 and 50âmg/kg (nâ=â11); PV (nâ=â11); combination treatment (nâ=â11 each dose)] and pretreatment [control; OSP 100âmg/kg; PV 100âµg; combination treatment (nâ=â8 all groups)] ospemifene oral dosing schedules in a total of 317 mixed-sex tumor-bearing and nontumor-bearing mice. RESULTS: The results showed that ospemifene induced expression of the key TH1 cytokines interferon gamma and interleukin-2 in vitro, which may be mediated by stimulating T-cells through phosphoinositide 3-kinase and calmodulin signaling pathways. In combination with an antigen-specific peptide cancer vaccine, ospemifene increased antigen-specific immune response and increased cytotoxic T-lymphocyte activity in tumor-bearing and nontumor-bearing mice. The pretreatment, intermittent, and chronic dosing schedules of ospemifene activate naive T-cells, modulate antigen-induced tolerance and reduce tumor-associated, pro-inflammatory cytokines, respectively. CONCLUSIONS: Taken together, ospemifene's dose response and schedule-dependent immune modulating activity offers a method of tailoring and augmenting the efficacy of previously failed antigen-specific cancer vaccines for a wide range of malignancies.
Subject(s)
Breast Neoplasms/immunology , Cytokines/blood , Immunologic Factors/pharmacology , Lung Neoplasms/drug therapy , Lymphocyte Activation/drug effects , T-Lymphocytes, Cytotoxic/drug effects , Tamoxifen/analogs & derivatives , Animals , Antineoplastic Combined Chemotherapy Protocols/immunology , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Calmodulin/metabolism , Cancer Vaccines/administration & dosage , Cancer Vaccines/immunology , Carcinogenesis , Chromones/pharmacology , Drug Administration Schedule , Drug Repositioning , Female , Flavonoids/pharmacology , Gene Expression/drug effects , Humans , Immunologic Factors/administration & dosage , Immunologic Factors/chemistry , Immunologic Factors/immunology , Interferon-gamma/blood , Interferon-gamma/genetics , Interleukin-2/genetics , Jurkat Cells , Lung Neoplasms/blood , Lung Neoplasms/chemically induced , Membrane Glycoproteins/administration & dosage , Membrane Glycoproteins/immunology , Mice , Mice, Transgenic , Morpholines/pharmacology , Mucin-1/genetics , Phosphatidylinositol 3-Kinases/metabolism , RNA, Messenger/metabolism , Signal Transduction/drug effects , Structure-Activity Relationship , T-Lymphocytes, Regulatory/drug effects , Tamoxifen/administration & dosage , Tamoxifen/chemistry , Tamoxifen/immunology , Tamoxifen/pharmacology , Trifluoperazine/pharmacologyABSTRACT
The clinical success of monoclonal antibody immune checkpoint modulators such as ipilimumab, which targets cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), and the recently approved agents nivolumab and pembrolizumab, which target programmed cell death receptor 1 (PD-1), has stimulated renewed enthusiasm for anticancer immunotherapy, which was heralded by Science as 'Breakthrough of the Year' in 2013. As the potential of cancer immunotherapy has been recognized since the 1890s when William Coley showed that bacterial products could be beneficial in cancer patients, leveraging the immune system in the treatment of cancer is certainly not a new concept; however, earlier attempts to develop effective therapeutic vaccines and antibodies against solid tumors, for example, melanoma, frequently met with failure due in part to self-tolerance and the development of an immunosuppressive tumor microenvironment. Increased knowledge of the mechanisms through which cancer evades the immune system and the identification of tumor-associated antigens (TAAs) and negative immune checkpoint regulators have led to the development of vaccines and monoclonal antibodies targeting specific tumor antigens and immune checkpoints such as CTLA-4 and PD-1. This review first discusses the established targets of currently approved cancer immunotherapies and then focuses on investigational cancer antigens and their clinical potential. Because of the highly heterogeneous nature of tumors, effective anticancer immunotherapy-based treatment regimens will likely require a personalized combination of therapeutic vaccines, antibodies and chemotherapy that fit the specific biology of a patient's disease.
ABSTRACT
Concurrent and sequential cisplatin-based chemoradiotherapy regimens are standard therapeutic approaches in cancer treatment. Recent clinical data suggest that these different dosing schedules may adversely affect antigen-specific immunotherapy. The goal of the present preclinical study was to explore the effects of concurrent and sequential cisplatin/radiotherapy on immune status in a lung cancer mouse model. A total of 150 C57BL/6 mice were randomized into six treatment groups: control; 8 Gy thoracic radiotherapy (dose schedules 1 and 2); cisplatin 2.5 mg/kg i.p.; cisplatin + radiotherapy (concurrent); and cisplatin + radiotherapy (sequential; n = 25, all groups). At the end of the study (week 41), serum cytokines were assessed by multiplex immunoassay, surface markers of spleen-derived lymphocytes were assessed by immunostaining and flow cytometry, lung tumor expression of programmed death ligands 1 and 2 (PD-L1/2) was evaluated by immunohistochemistry, and miRNA profiling was performed in serum and lymphocytes by quantitative real-time PCR. Lung whole mounts were prepared to assess treatment effects on lung tumor foci formation. The results showed that sequential chemoradiotherapy (two cycles of cisplatin followed by 8 Gy radiotherapy) had equivalent antitumor activity as concurrent therapy. However, sequential cisplatin/radiotherapy resulted in significant differences in several immune response biomarkers, including regulatory T cells, miR-29c, expression of costimulatory molecule CD28, and serum IFNγ. PD-L1 and PD-L2 were strongly expressed in tumor foci, but no trend was seen between groups. These results suggest that monitoring immune status may be necessary when designing treatment regimens combining immunotherapy with chemoradiotherapy.
Subject(s)
Adenoma/radiotherapy , Cisplatin/administration & dosage , Cytokines/blood , Lung Neoplasms/radiotherapy , MicroRNAs/blood , Adenoma/drug therapy , Animals , Combined Modality Therapy , Humans , Lung Neoplasms/drug therapy , Mice , Mice, Inbred C57BL , Mice, Transgenic , Treatment Outcome , Tumor Microenvironment , Urethane/therapeutic use , Xenograft Model Antitumor AssaysABSTRACT
The identification of tumor-associated antigens (TAA) has made possible the development of antigen-specific cancer immunotherapies such as tecemotide. One of those is mucin 1 (MUC1), a cell membrane glycoprotein expressed on some epithelial tissues such as breast and lung. In cancer, MUC1 becomes overexpressed and aberrantly glycosylated, exposing the immunogenic tandem repeat units in the extracellular domain of MUC1. Designed to target tumor associated MUC1, tecemotide is being evaluated in Phase III clinical trials for treatment of unresectable stage IIIA/IIIB non-small cell lung cancer (NSCLC) as maintenance therapy following chemoradiotherapy. Additional Phase II studies in other indications are ongoing. This review discusses the preclinical and clinical development of tecemotide, ongoing preclinical studies of tecemotide in human MUC1 transgenic mouse models of breast and lung cancer, and the potential application of these models for optimizing the timing of chemoradiotherapy and tecemotide immunotherapy to achieve the best treatment outcome for patients.
Subject(s)
Antigens, Neoplasm/immunology , Cancer Vaccines/therapeutic use , Immunotherapy/methods , Membrane Glycoproteins/therapeutic use , Mucin-1/immunology , Animals , Breast Neoplasms/immunology , Breast Neoplasms/therapy , Carcinoma, Non-Small-Cell Lung/immunology , Carcinoma, Non-Small-Cell Lung/therapy , Chemoradiotherapy , Disease Models, Animal , Female , Humans , Lung Neoplasms/immunology , Lung Neoplasms/therapy , Mice , Mice, TransgenicABSTRACT
During the menopausal transition, women experience a number of symptoms due to declining estrogen levels, including vasomotor symptoms and vulvar and vaginal atrophy (VVA). Unlike vasomotor symptoms, vaginal dryness and dyspareunia, the main symptoms of VVA, typically worsen without treatment and can significantly impact the quality of life. Up to 60% of postmenopausal women may be affected by VVA, but many women unfortunately do not seek treatment due to embarrassment or other factors. After 20+ years in development, ospemifene (Osphena™) was approved by the US Food and Drug Administration in 2013 for treatment of moderate-to-severe dyspareunia associated with VVA due to menopause. As the first non-hormonal alternative to estrogen-based products for this indication, the approval of ospemifene represents a significant milestone in postmenopausal women's health. Ospemifene is a non-steroidal estrogen receptor agonist/antagonist, also known as a selective estrogen receptor modulator (SERM), from the same chemical class as the breast cancer drugs tamoxifen and toremifene. Unlike other selective estrogen receptor modulators, ospemifene exerts a strong, nearly full estrogen agonist effect in the vaginal epithelium, making it well suited for the treatment of dyspareunia in postmenopausal women. Results of Phase III clinical trials showed that ospemifene significantly improved the vaginal maturation index (decreased parabasal cells and increased superficial cells), decreased vaginal pH, and decreased severity of the self-identified most bothersome symptom (dyspareunia or vaginal dryness) compared to placebo. Long-term safety studies revealed that 60 mg ospemifene given daily for 52 weeks was well tolerated and was not associated with any endometrium or breast-related safety concerns. This review discusses the preclinical and clinical data supporting the use of ospemifene for the treatment of dyspareunia associated with VVA due to menopause and provides an overview of its clinical safety.
Subject(s)
Dyspareunia/drug therapy , Postmenopause , Tamoxifen/analogs & derivatives , Vagina , Vulva , Animals , Atrophy/complications , Dyspareunia/etiology , Dyspareunia/physiopathology , Female , Humans , Randomized Controlled Trials as Topic , Rats , Selective Estrogen Receptor Modulators/therapeutic use , Tamoxifen/adverse effects , Tamoxifen/therapeutic useABSTRACT
The goals of the present study were to define the effects of simultaneous cisplatin/tecemotide therapy on tumor development in a human mucin 1 (MUC1) transgenic lung cancer mouse model and to examine the effects of radiotherapy (RTX) on splenocytes, serum cytokines, and immune response to tecemotide. Two hundred twenty-six human MUC1 transgenic C57BL/6 mice were used in five studies designed to assess (i) serum cytokine and immune responses following four weekly 10-µg doses of tecemotide; (ii) the effects of simultaneous administration of cisplatin (2.5 mg/kg × 2 doses/cycle × 4 cycles) and tecemotide (2 cycles × 8 weekly 10-µg doses/cycle) therapy on tumor development, serum cytokines, and immune response; (iii) the dose-response effects of RTX on lymphocyte counts 16 hours following doses of 2 to 8 Gy; (iv) the time course of lymphocyte recovery from 16 hours to 20 days following 8-Gy RTX; and (v) the effects of simultaneous administration of RTX (8 Gy) and tecemotide on the immune response to tecemotide (four weekly 10-µg doses). Serum cytokines were analyzed by multiplex immunoassay, IFNγ immune responses by enzyme-linked immunosorbent spot (ELISpot), and lung tumor foci by lung whole mounts. Simultaneous cisplatin/tecemotide therapy resulted in significant and additive reduction in lung tumor foci compared with control mice, with significantly elevated serum IFNγ levels and specific IFNγ immune responses observed in both tecemotide and tecemotide + cisplatin-treated mice. Finally, neither cisplatin nor radiation interfered with the immune response to tecemotide.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Lung Neoplasms/therapy , Analysis of Variance , Animals , Cancer Vaccines/administration & dosage , Cisplatin/administration & dosage , Cytokines/drug effects , Cytokines/metabolism , Cytokines/radiation effects , Disease Models, Animal , Dose-Response Relationship, Radiation , Female , Immunity, Cellular/drug effects , Immunity, Cellular/radiation effects , Immunotherapy/methods , Lung Neoplasms/radiotherapy , Lymphocyte Count , Male , Membrane Glycoproteins/administration & dosage , Mice, Inbred C57BL , Mucin-1/genetics , T-Lymphocytes/drug effects , T-Lymphocytes/radiation effectsABSTRACT
A preclinical model of invasive bladder cancer was developed in human mucin 1 (MUC1) transgenic (MUC1.Tg) mice for the purpose of evaluating immunotherapy and/or cytotoxic chemotherapy. To induce bladder cancer, C57BL/6 mice (MUC1.Tg and wild type) were treated orally with the carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN) at 3.0 mg/day, 5 days/week for 12 weeks. To assess the effects of OH-BBN on serum cytokine profile during tumor development, whole blood was collected via submandibular bleeds prior to treatment and every four weeks. In addition, a MUC1-targeted peptide vaccine and placebo were administered to groups of mice weekly for eight weeks. Multiplex fluorometric microbead immunoanalyses of serum cytokines during tumor development and following vaccination were performed. At termination, interferon gamma (IFN-γ)/interleukin-4 (IL-4) ELISpot analysis for MUC1 specific T-cell immune response and histopathological evaluations of tumor type and grade were performed. The results showed that: (1) the incidence of bladder cancer in both MUC1.Tg and wild type mice was 67%; (2) transitional cell carcinomas (TCC) developed at a 2:1 ratio compared to squamous cell carcinomas (SCC); (3) inflammatory cytokines increased with time during tumor development; and (4) administration of the peptide vaccine induces a Th1-polarized serum cytokine profile and a MUC1 specific T-cell response. All tumors in MUC1.Tg mice were positive for MUC1 expression, and half of all tumors in MUC1.Tg and wild type mice were invasive. In conclusion, using a team approach through the coordination of the efforts of pharmacologists, immunologists, pathologists and molecular biologists, we have developed an immune intact transgenic mouse model of bladder cancer that expresses hMUC1.
Subject(s)
Carcinoma, Transitional Cell/immunology , Carcinoma, Transitional Cell/therapy , Mucin-1/immunology , Urinary Bladder Neoplasms/immunology , Urinary Bladder Neoplasms/therapy , Animals , Butylhydroxybutylnitrosamine , Cancer Vaccines/immunology , Cancer Vaccines/pharmacology , Carcinogens , Carcinoma, Transitional Cell/chemically induced , Carcinoma, Transitional Cell/genetics , Cytokines/blood , Cytokines/immunology , Disease Models, Animal , Female , Humans , Immunotherapy , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Mucin-1/genetics , T-Lymphocytes, Cytotoxic/immunology , Urinary Bladder Neoplasms/chemically induced , Urinary Bladder Neoplasms/geneticsABSTRACT
Ospemifene is a selective estrogen receptor modulator (SERM), or estrogen receptor agonist/antagonist, that was recently approved by the US Food and Drug Administration for the treatment of dyspareunia associated with vulvar and vaginal atrophy, a chronic condition that affects up to 60% of postmenopausal women. Ospemifene is the first and only nonestrogen compound approved for this indication. Compared with other approved SERMs, such as tamoxifen, toremifene, bazedoxifene, and raloxifene, the estrogen-like effects of ospemifene in the vaginal epithelium are unique. This review first discusses the rationale for developing ospemifene, including its mechanism of action, and then focuses on the clinical development of ospemifene for the treatment of dyspareunia associated with vulvar and vaginal atrophy. Included are discussions of the effects of ospemifene on the endometrium, serum lipids, coagulation markers, bone, and breast cancer. In conclusion, ospemifene is a SERM with a unique estrogen agonist/antagonist tissue profile that was recently approved in the US for the treatment of dyspareunia associated with vulvar and vaginal atrophy in postmenopausal women. Ospemifene warrants further clinical investigation for the treatment and prevention of osteoporosis and breast cancer.
ABSTRACT
BACKGROUND: L-BLP25 antigen-specific cancer immunotherapeutic agent is currently in phase III clinical trials for non-small cell lung cancer. Using a novel human MUC1 transgenic (hMUC1.Tg) lung cancer mouse model, we evaluated effects of L-BLP25 combined with low-dose cyclophosphamide (CPA) pretreatment on Th1/Th2 cytokine production and antitumor activity. METHODS: A chemically-induced lung tumor model was developed in hMUC1.Tg C57BL/6 mice by administering 10 weekly 0.75-mg/g doses of the chemical carcinogen urethane by intraperitoneal injection. Serum cytokines associated with Th1/Th2 polarization and inflammation were measured by multiplex cytokine assay during tumorigenesis. Antitumor activity of L-BLP25 (10 µg) with CPA (100 mg/kg) pretreatment was evaluated following either one or two eight-week cycles of treatment by preparing lung whole mounts and counting tumor foci, and assessing IFN-γ production by ELISpot assay. RESULTS: During the carcinogenesis phase, no detectable Th1- or Th2-associated cytokine responses were observed, but levels of pro-inflammatory cytokines were increased with distinctive kinetics. A single cycle of L-BLP25 consisting of eight weekly doses was ineffective, whereas adding a second cycle given during tumor progression showed a significant reduction in the incidence of tumor foci. Administering two cycles of L-BLP25 induced Th1 cytokines IL-12, IL-2 and IFNγ at 24 h after the last dose, while Th2 and inflammatory cytokines were elevated to a lesser extent. CONCLUSIONS: Urethane-induced lung tumors in hMUC1.Tg mice can be used as a model to assess the efficacy of the MUC1 antigen-specific cancer immunotherapeutic agent L-BLP25. The results indicate that the antitumor response to L-BLP25 requires at least two cycles and pre-treatment with CPA. In addition, monitoring pro-inflammatory serum cytokines may be useful as a biomarker of L-BLP25 response. Taken together, the preclinical lung tumor model can be utilized for determining effective combinations of L-BLP25 with chemotherapy and/or other immunotherapies.
Subject(s)
Adenoma/immunology , Adenoma/therapy , Antigens, Neoplasm/immunology , Cancer Vaccines/immunology , Immunotherapy , Lung Neoplasms/immunology , Lung Neoplasms/therapy , Membrane Glycoproteins/immunology , Mucin-1/immunology , Adenoma/drug therapy , Adenoma/pathology , Animals , Carcinogenesis/pathology , Cyclophosphamide/pharmacology , Cyclophosphamide/therapeutic use , Cytokines/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Humans , Immunity/drug effects , Inflammation Mediators/metabolism , Lung Neoplasms/drug therapy , Lung Neoplasms/pathology , Mice, Inbred C57BL , Mice, Transgenic , Th1 Cells/drug effects , Th1 Cells/immunology , Time Factors , UrethaneABSTRACT
The results of a recently completed Phase III clinical trial suggest that concurrent chemoradiotherapy followed by tecemotide provides superior benefits to Stage IIIa and IIIb non-small cell lung carcinoma patients as compared with sequential chemoradiotherapy followed by tecemotide. These clinical observations will be dissected in a transgenic model of lung cancer that we have recently established (hMUC1.Tg C57BL/6 mice).
ABSTRACT
Cw-ESR distance measurement method is extremely valuable for studying the dynamics-function relationship of biomolecules. However, extracting distance distributions from experiments has been a highly technique-demanding procedure. It has never been conclusively identified, to our knowledge, that the problems involved in the analysis are ill posed and are best solved using Tikhonov regularization. We treat the problems from a novel point of view. First of all, we identify the equations involved and uncover that they are actually two linear first-kind Fredholm integral equations. They can be combined into one single linear inverse problem and solved in a Tikhonov regularization procedure. The improvement with our new treatment is significant. Our approach is a direct and reliable mathematical method capable of providing an unambiguous solution to the ill-posed problem. It need not perform nonlinear least-squares fitting to infer a solution from noise-contaminated data and, accordingly, substantially reduces the computation time and the difficulty of analysis. Numerical tests and experimental data of polyproline II peptides with variant spin-labeled sites are provided to demonstrate our approach. The high resolution of the distance distributions obtainable with our new approach enables a detailed insight into the flexibility of dynamic structure and the identification of conformational species in solution state.