The peroxisome proliferator-activated receptors (PPARs) include three receptor subtypes encoded by separate genes: PPAR␣, PPAR␦, and PPAR␥. PPAR␥ has been implicated as a mediator of adipocyte differentiation and the mechanism by which thiazolidinedione drugs exert in vivo insulin sensitization. Here we characterized novel, non-thiazolidinedione agonists for PPAR␥ and PPAR␦ that were identified by radioligand binding assays. In transient transactivation assays these ligands were agonists of the receptors to which they bind. Protease protection studies showed that ligand binding produced specific alterations in receptor conformation. Both PPAR␥ and PPAR␦ directly interacted with a nuclear receptor co-activator (CREB-binding protein) in an agonist-dependent manner. Only the PPAR␥ agonists were able to promote differentiation of 3T3-L1 preadipocytes. In diabetic db/db mice all PPAR␥ agonists were orally active insulin-sensitizing agents producing reductions of elevated plasma glucose and triglyceride concentrations. In contrast, selective in vivo activation of PPAR␦ did not significantly affect these parameters. In vivo PPAR␣ activation with WY-14653 resulted in reductions in elevated triglyceride levels with minimal effect on hyperglycemia. We conclude that: 1) synthetic non-thiazolidinediones can serve as ligands of PPAR␥ and PPAR␦; 2) ligand-dependent activation of PPAR␦ involves an apparent conformational change and association of the receptor ligand binding domain with CREB-binding protein; 3) PPAR␥ activation (but not PPAR␦ or PPAR␣ activation) is sufficient to potentiate preadipocyte differentiation; 4) non-thiazolidinedione PPAR␥ agonists improve hyperglycemia and hypertriglyceridemia in vivo; 5) although PPAR␣ activation is sufficient to affect triglyceride metabolism, PPAR␦ activation does not appear to modulate glucose or triglyceride levels.

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The thiazolidinediones are novel insulin sensitizers that serve as orally active antidiabetic agents, in rodents, nonhuman primates, and man. We have examined the effects of 4-week oral administration of three thiazolidinediones (AD-5075, BRL 49653, and CS-045) on plasma glucose and triglyceride concentrations in obese hyperglycemic db/db mice. All three agents lower plasma glucose and triglyceride concentrations. Normal levels of glucose are achieved after treatment with AD-5075 (> 1.7 mg/kg) or BRL 49653 (> or = 30 mg/kg), whereas CS-045 (100 or 300 mg/kg) produces only modest reductions in either parameter. Although the thiazolidinediones have demonstrated insulin-sensitizing activities both in vivo and in vitro, their primary molecular target has been unclear. We have compared the in vivo antidiabetic actions described above with the in vitro activities on peroxisomal proliferator-activated receptor-gamma (PPAR gamma). Hamster PPAR gamma 1 was transiently expressed in COS-1 cells to study the binding of [3H]AD-5075. The concentrations of compounds needed to displace radiolabeled AD-5075 from PPAR gamma correlate with their in vivo potency; the Ki values for displacement by cold AD-5075, BRL 49653, and CS-045 are 22, 68, and 1600 nM, respectively. To examine activation of the receptor, it was transiently cotransfected into COS-1 cells with a reporter plasmid containing two copies of a peroxisome proliferator response element. The EC50 values for activation are 2, 6, and 140 nM for AD-5075, BRL 49653, and CS-045, respectively. We have also analyzed limited proteolytic digests of in vitro translated hamster PPAR gamma. The thiazolidinediones produce a conformational change in PPAR gamma analogous to those produced by agonists of other nuclear hormone receptors. In the presence of saturating concentrations of either AD-5075 or BRL 49653, a receptor fragment of 27 kDa is protected from proteolysis by trypsin. These data support the conclusion that the antidiabetic actions of the thiazolidinediones are directly mediated through binding to PPAR gamma and the resulting active conformation of the receptor. Therefore, binding and transactivation assays using PPAR gamma should serve to identify other novel therapeutic agents with potential antidiabetic activities.

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PURPOSE To report the results of a phase II clinical trial of de-intensified chemoradiotherapy for patients with human papillomavirus–associated oropharyngeal squamous cell carcinoma. MATERIALS AND METHODS Major inclusion criteria were (1) having American Joint Committee on Cancer (AJCC) 7th edition T0-T3, N0-N2c, M0 (AJCC 8th edition T0-T3, N0-N2, M0), (2) being p16 positive, and (3) reporting minimal or remote smoking history. Treatment was limited to 60 Gy intensity-modulated radiotherapy with concurrent intravenous cisplatin 30 mg/m2 once per week. Patients with T0-T2 N0-1 (AJCC 7th edition) did not receive chemotherapy. All patients had a 10- to 12-week post-treatment positron emission tomography/computed tomography to assess for neck dissection. The primary end point was 2-year progression-free survival. Secondary end points included 2-year local-regional control, distant metastasis-free survival and overall survival, and patient-reported outcomes (European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire and the patient-reported outcomes version of the Common Terminology Criteria for Adverse Events). RESULTS One hundred fourteen patients were enrolled (median follow-up of 31.8 months), with 81% having a minimum follow-up of 2 years. Eighty percent of patients had 10 or fewer tobacco pack-years. Two-year local-regional control, distant metastasis-free survival, progression-free survival, and overall survival were as follows: 95%, 91%, 86%, and 95%, respectively. Mean pre- and 2-year post-treatment European Organisation for Research and Treatment of Cancer quality of life scores were as follows: global, 79/84 (lower worse); swallowing, 8/9 (higher worse); and dry mouth, 14/45 (higher worse). Mean pre- and 2-year post-treatment patient-reported outcomes version of the Common Terminology Criteria for Adverse Events scores (0 to 4 scale, higher worse) were as follows: swallowing, 0.5/0.7, and dry mouth, 0.4/1.3. Thirty-four percent of patients required a feeding tube (median, 10.5 weeks; none permanent). There were no grade 3 or higher late adverse events. CONCLUSION Clinical outcomes with a de-intensified chemoradiotherapy regimen of 60 Gy intensity-modulated radiotherapy with concurrent low-dose cisplatin are favorable in patients with human papillomavirus–associated oropharyngeal squamous cell carcinoma. Neither neoadjuvant chemotherapy nor routine surgery is needed to obtain favorable results with de-escalation.