Clinical investigators as critical determinants in pharmaceutical innovation

Photochemical and Photodynamical Properties of Sulfur-Substituted Nucleic Acid Bases

Sulfur-substituted nucleobases (a.k.a., thiobases) are among the world's leading prescriptions for chemotherapy and immunosuppression. Long-term treatment with azathioprine, 6-mercaptopurine and 6-thioguanine has been correlated with the photoinduced formation of carcinomas. Establishing an in-depth understanding of the photochemical properties of these prodrugs may provide a route to overcoming these carcinogenic side effects, or, alternatively, a basis for developing effective compounds for targeted phototherapy. In this review, a broad examination is undertaken, surveying the basic photochemical properties and excited-state dynamics of sulfur-substituted analogs of the canonical DNA and RNA nucleobases. A molecular-level understanding of how sulfur substitution so remarkably perturbs the photochemical properties of the nucleobases is presented by combining experimental results with quantum-chemical calculations. Structure-property relationships demonstrate the impact of site-specific sulfur substitution on the photochemical properties, particularly on the population of the reactive triplet state. The value of fundamental photochemical investigations for driving the development of ultraviolet-A chemotherapeutics is showcased. The most promising photodynamic agents identified thus far have been investigated in various carcinoma cell lines and shown to decrease cell proliferation upon exposure to ultraviolet-A radiation. Overarching principles have been elucidated for the impact that sulfur substitution of the carbonyl oxygen has on the photochemical properties of the nucleobases.

Excited-State Dynamics of the Thiopurine Prodrug 6-Thioguanine: Can N9-Glycosylation Affect Its Phototoxic Activity?

6-Thioguanine, an immunosuppressant and anticancer prodrug, has been shown to induce DNA damage and cell death following exposure to UVA radiation. Its metabolite, 6-thioguanosine, plays a major role in the prodrug's overall photoreactivity. However, 6-thioguanine itself has proven to be cytotoxic following UVA irradiation, warranting further investigation into its excited-state dynamics. In this contribution, the excited-state dynamics and photochemical properties of 6-thioguanine are studied in aqueous solution following UVA excitation at 345 nm in order to provide mechanistic insight regarding its photochemical reactivity and to scrutinize whether N9-glycosylation modulates its phototoxicity in solution. The experimental results are complemented with time-dependent density functional calculations that include solvent dielectric effects by means of a reaction-field solvation model. UVA excitation results in the initial population of the S₂(ππ*) state, which is followed by ultrafast internal conversion to the S₁(nπ*) state and then intersystem crossing to the triplet manifold within 560 ± 60 fs. A small fraction (ca. 25%) of the population that reaches the S₁(nπ*) state repopulates the ground state. The T₁(ππ*) state decays to the ground state in 1.4 ± 0.2 μs under N₂-purged conditions, using a 0.2 mM concentration of 6-thioguanine, or it can sensitize singlet oxygen in 0.21 ± 0.02 and 0.23 ± 0.02 yields in air- and O₂-saturated solution, respectively. This demonstrates the efficacy of 6-thioguanine to act as a Type II photosensitizer. N9-glycosylation increases the rate of intersystem crossing from the singlet to triplet manifold, as well as from the T₁(ππ*) state to the ground state, which lead to a ca. 40% decrease in the singlet oxygen yield under air-saturated conditions. Enhanced vibronic coupling between the singlet and triplet manifolds due to a higher density of vibrational states is proposed to be responsible for the observed increase in the rates of intersystem crossing in 6-thioguanine upon N9-glycosylation.

The Triplet State of 6-thio-2'-deoxyguanosine: Intrinsic Properties and Reactivity Toward Molecular Oxygen

Thiopurine prodrugs are currently among the leading treatment options for leukemia, immunosuppression, and arthritis. Patients undergoing long-term thiopurine treatment are at a higher risk of developing sunlight-induced skin cancers than the general population. This side effect originates from the cellular metabolization of thiopurine prodrugs to form 6-thio-2'-deoxyguanosine, which can absorb UVA radiation, populating its reactive triplet state and leading to oxidatively generated damage. However, the photo-oxidation mechanism is not fully understood. In this contribution, the oxidation potential and the adiabatic triplet energy of 6-thio-2'-deoxyguanosine are estimated computationally, whereas the intrinsic rate of triple-state decay and the rate constant for triplet quenching by molecular oxygen are determined using time-resolved spectroscopic techniques. A singlet oxygen quantum yield of 0.24 ± 0.02 is measured in aqueous solution (0.29 ± 0.02 in acetonitrile). Its magnitude correlates with the relatively low percentage of triplet-O₂ collision events that generate singlet oxygen (S_Δ = 37%). This behavior is rationalized as being due to the exergonic driving force for electron transfer between the triplet state of 6-thio-2'-deoxyguanosine and molecular oxygen (ΔG_ET = -69.7 kJ mol^-1 ), resulting in the formation of a charge-transfer complex that favors nonradiative decay to the ground state over triplet energy transfer.

Hartmann Stahelin (1925-2011) and the contested history of cyclosporin A

The aims of this study are twofold: (i) to pay tribute to Hartmann Stahelin for his scientific research on cyclosporin A; and (ii) to consider possible lessons for future pharmacological innovation by revisiting Stahelin's personal struggles to obtain fair recognition for his contribution to transplantation medicine.

Disparities in the early adoption of chemoimmunotherapy for diffuse large B-cell lymphoma in the United States

BACKGROUND

Since the 1970s, CHOP chemotherapy has been the standard treatment for patients with diffuse large B-cell lymphoma (DLBCL). In 2002, randomized trials changed this standard by showing that adding rituximab immunotherapy to CHOP improved survival. However, how these results influenced chemoimmunotherapy adoption in clinical practice remains unclear.

METHODS

Using the National Cancer Database to compare chemoimmunotherapy use with chemotherapy alone, we collected data on demographics, stage, health insurance, area-level socioeconomic status (SES), facility characteristics, and type of treatment for DLBCL patients diagnosed in the United States 2001-2004. Multivariable log binomial models examined associations between race, insurance, and treatment allocation, adjusting for covariates.

RESULTS

Among 38,002 patients with DLBCL, 27% received chemoimmunotherapy and 50% chemotherapy alone. Patients who had localized disease, were diagnosed in 2001 or who were black, uninsured/Medicaid insured, or lower SES were less likely to receive any form of chemotherapy (all P < 0.0001). Patients who were diagnosed in 2001 or who were black [relative risk (RR), 0.83; 95% confidence interval (CI), 0.78-0.89], >60 years (RR, 0.94; 95% CI, 0.90-0.98), or had localized disease (RR, 0.89; 95% CI, 0.86-0.92) were less likely to receive chemoimmunotherapy. Receiving treatment at high DLBCL volume teaching/research facilities was associated with the greatest likelihood of chemoimmunotherapy (RR, 1.69; 95% CI, 1.52-1.89).

CONCLUSIONS

Black DLBCL patients were less likely to receive chemotherapy or chemoimmunotherapy during this period.

IMPACT

This large national cohort study shows disparities in the diffusion of chemoimmunotherapy for DLBCL. Improving DLBCL outcomes will require efforts to extend access to proven advances in therapy to all segments of the population.

Analysis of the workforce and workplace for rheumatology and the research activities of rheumatologists early in their careers

OBJECTIVE

To assess the workforce and workplace in rheumatology, and the research work of early-career rheumatologists.

METHODS

Early-career rheumatologists were defined as practicing physicians who joined the American College of Rheumatology (ACR) in 1991-2005, were 49 years of age or younger when they joined, and reside in North America. This cohort participated in a Web-based survey distributed by the ACR. A total of 247 surveys (21.2% response) were used for this analysis. Survey questions were designed to obtain core insights about the workforce, workplace, research activities, funding, and the demographic profile of respondents.

RESULTS

Respondents from all workplaces-clinical, academic, federal, and industry-engaged in clinical care, teaching, administration, and research. The time devoted to these tasks was employer dependent, and workplaces shaped the scale and scope of research. Patient-oriented research was predominant across all workplaces. Disease, population, and translational research were intermediate, and few respondents pursued basic or prevention-oriented research in any type of workplace. Rheumatologists obtained extramural funds (21.3%) and intramural funds (78.7%) to pay portions of their salaries for time spent on research. Receiving a National Institutes of Health K08/K23 award was associated with receipt of a federal research project grant (P < 0.001). Respondents associated investigative work with reduced earnings, a perception validated by an estimated drop in pre-tax annual earnings of 2.3% for each half-day/week dedicated to research (P < 0.01).

CONCLUSION

The results of this study justify interventions for closing gaps embedded in investigational rheumatology. These include improved funding for clinical research, increasing the number of K08/K23 awards, and recruiting rheumatologists from underrepresented demographic groups.

Thiopurines in current medical practice: molecular mechanisms and contributions to therapy-related cancer

Thiopurines have diverse clinical applications and their long-term use as anti-rejection drugs in transplant patients has been associated with a significantly increased risk of various types of cancer. Although they are slowly being replaced by a new generation of non-thiopurine immunosuppressants, it is anticipated that their use in the management of inflammatory and autoimmune diseases will continue to increase. Therapy-related cancer will remain a potential consequence of prolonged treatment for these generally non-life-threatening conditions. Understanding how thiopurines contribute to the development of cancer will facilitate clinical decisions about the potential risks to patients of long-term treatment for chronic inflammatory disorders.

Patient-oriented research: principles and new approaches to training

Remarkable advances in modern biology have enhanced our understanding of disease, permitting us to define-and potentially to treat-illness at the cellular and molecular level. The challenge we now face as physicians and physician-scientists is ensuring that these advances find expression in clinical practice. Thus far, the distance from the bench to the bedside has been surprisingly difficult to span, reflecting the need to develop broader, more integrative approaches to understanding how component molecules and physiologic systems function in the context of the whole person. Although there appears to be a consensus about the need to pursue such integrative, patient-oriented research, a mechanism for training future investigators in this discipline is less well established. In this essay, we present and develop the rationale for a set of underlying principles for patient-oriented research that can be used to guide appropriate training in this field. We also describe briefly a recently established prototype program-the Harvard initiative in Patient-Associated Science: Training, Education, Understanding, and Research (PASTEUR)-that we hope will help cultivate patient-oriented investigators and catalyze the evolution of patient-oriented research into a fully realized academic discipline.