Ixekizumab treatment for psoriasis: integrated efficacy analysis of three double-blinded, controlled studies (UNCOVER-1, UNCOVER-2, UNCOVER-3).

BACKGROUND: Ixekizumab, a high-affinity monoclonal antibody that selectively targets interleukin (IL)-17A, is approved for the treatment of moderate-to-severe psoriasis. OBJECTIVES: This analysis represents an overview of the efficacy outcomes from three phase III psoriasis studies. METHODS: Data were integrated from the 12-week induction period of three studies in which patients received ixekizumab 80 mg every 2 weeks (IXE Q2W; n = 1169) or every 4 weeks (IXE Q4W; n = 1165) after an initial 160-mg dose for both; etanercept (50 mg biweekly; n = 740; two studies) or placebo (n = 792). The coprimary end points were the percentages of patients with response of static Physician's Global Assessment (sPGA; score 0 or 1) and ≥ 75% improvement in baseline Psoriasis Area and Severity Index (PASI 75) at week 12. Response rates were compared between treatments using the Cochran-Mantel-Haenszel test stratified by study. Treatment comparisons with placebo included data from three studies, whereas etanercept comparisons were based on two studies. RESULTS: Ixekizumab treatment was superior to placebo (P < 0·001) and etanercept (P < 0·001) on sPGA (0, 1) and PASI 75, with significant differences in PASI improvement at week 1. With IXE Q2W, at week 12, the frequencies of patients achieving PASI 75, 90 and 100 were nearly 90%, 70% and 40%, respectively. Ixekizumab-treated patients showed significantly greater improvement vs. placebo and etanercept in percentage body surface area involvement and fingernail psoriasis. IXE Q2W was superior to IXE Q4W on all treatment outcomes. CONCLUSIONS: Ixekizumab therapy at both dosing regimens demonstrated rapid onset and superior efficacy to placebo and etanercept, with IXE Q2W providing better outcomes than IXE Q4W during the first 12 weeks of treatment.

Improvement of scalp and nail lesions with ixekizumab in a phase 2 trial in patients with chronic plaque psoriasis.

BACKGROUND: Scalp and nail psoriasis have a major impact on quality of life and are traditionally resistant to therapy. Ixekizumab is a monoclonal antibody that targets IL-17A, a key cytokine in psoriasis pathogenesis. OBJECTIVE: Changes in nail and scalp psoriasis associated with ixekizumab treatment were evaluated in a post hoc analysis of a phase 2 study comprising a 20-week randomized, placebo-controlled (RCT) period and 48 weeks of an open-label extension (OLE) period. METHODS: There were 142 patients with moderate-to-severe plaque psoriasis at baseline of the RCT. Patients were randomized to receive placebo, 10, 25, 75 or 150 mg of ixekizumab injected subcutaneously at weeks 0, 2, 4, 8, 12 and 16. In the OLE, all patients received 120 mg ixekizumab every 4 weeks. Nail Psoriasis Severity Index (NAPSI) and Psoriasis Scalp Severity Index (PSSI) were used to evaluate nail and scalp psoriasis respectively. Fifty-eight (41.0%) patients had nail psoriasis (NAPSI > 0) and 105 (74.0%) had scalp psoriasis (PSSI > 0) at baseline; these cases were evaluated for the present analyses. RESULTS: At RCT week 20, patients with scalp psoriasis in the 25-, 75- and 150-mg groups had significant mean change and percent improvement from baseline PSSI of -16.3 (75.3%; P = 0.001), -11.6 (83.7%; P = 0.001) and -18.2 (82.2%; P < 0.001) respectively compared to -6.0 (18.8%) in placebo. Patients with nail psoriasis in the 75- and 150-mg groups had significant improvements from baseline NAPSI of -26.3 (63.8%; P = 0.003) and -23.1 (52.6%; P = 0.009) respectively compared to 0.4 (-1.7%) in placebo. By OLE week 48, 78.0% of patients with scalp psoriasis and 51.0% of patients with nail psoriasis experienced complete resolution of lesions (PSSI = 0 or NAPSI = 0). CONCLUSIONS: Ixekizumab monotherapy improved scalp psoriasis quickly with maintenance of clinical response and complete resolution of plaques in the majority of patients. Additionally, over 50.0% of patients with nail psoriasis experienced complete resolution of nail lesions by OLE week 48.

Early clinical response as a predictor of subsequent response to ixekizumab treatment: results from a phase II study of patients with moderate-to-severe plaque psoriasis.

BACKGROUND: Early identification of responsiveness to biologic treatments in psoriasis has significant clinical and economic implications. OBJECTIVES: To evaluate whether early clinical improvements in Psoriasis Area and Severity Index (PASI) scores could predict subsequent clinical responses in patients treated with ixekizumab, an anti-interleukin-17 monoclonal antibody. METHODS: This post hoc analysis was derived from a phase II study in patients with moderate-to-severe plaque psoriasis (n = 114) who received multiple doses of ixekizumab 10, 25, 75 or 150 mg subcutaneously over 20 weeks. PASI score improvements from baseline to weeks 2, 4 and 6 were evaluated to determine the optimal threshold for predicting subsequent PASI responses at week 12. RESULTS: Early clinical improvement in disease symptoms at weeks 4 and 6 was predictive of ≥ 75% improvement in PASI score (PASI 75) at week 12 with ≥ 90% predictability. A 40-50% improvement in PASI (PASI 40 to PASI 50) from baseline to weeks 4 and 6 was the optimum range for predicting PASI 75 response at week 12. For all doses combined, achieving PASI 40 at week 4 or week 6 was associated with high negative predictive values (NPVs) (80% and 95%, respectively) and positive predictive values (PPVs) (89% and 84%, respectively). For all doses combined, achieving PASI 50 at week 4 or week 6 was associated with NPVs of 71% and 89% and PPVs of 94% and 89%, respectively. Sensitivity analysis with the high-dose group (75 and 150 mg) results confirmed these findings. CONCLUSIONS: Early clinical responses (and nonresponse) may help predict later clinical responses in patients treated with ixekizumab.

Oxidized low-density lipoprotein and autoimmune antibodies in patients with antiphospholipid syndrome with a history of thrombosis.

The prevalence and clinical significance of plasma oxidized low-density lipoprotein (oxLDL) and antibodies against oxLDL (anti-oxLDL) were evaluated in patients with antiphospholipid syndrome (APS). OxLDL and IgG anti-oxLDL were determined by enzyme-linked immunosorbent assay in plasma samples from 80 patients with APS. Positive values (mean + 3 SD) for oxLDL and anti-oxLDL were found in 21 (26%) and 19 (24%) of 80 patients with APS, respectively These values were significantly higher than those in healthy subjects. Levels of oxLDL and anti-oxLDL antibodies in subgroupings of patients with APS who had experienced thrombotic events were compared. There were significant differences among the groups for the levels of both oxLDL and anti-oxLDL antibodies. Pairwise comparisons between the groups yielded similar but not identical results. There was a significant, positive correlation between levels of plasma oxLDL and anti-oxLDL. These results suggest that elevated levels of plasma oxLDL and anti-oxLDL may be risk factors and potential markers for thrombosis, especially for arterial thrombotic events, in patients with APS.

Histologic features of actinic keratoses in solid organ transplant recipients and healthy controls.

BACKGROUND: Squamoproliferative lesions are common in patients who are immunosuppressed, particularly in recipients of solid organ transplants. Histologic features in such biopsy specimens may differ from those of otherwise healthy patients. Actinic keratoses (AKs) in transplant recipients may possess pathologic characteristics that suggest that they arose in an immunosuppressed host. OBJECTIVE: We evaluated 30 randomly selected AKs from 25 recipients of solid organ transplants and compared their histologic features to those of 50 AKs from 45 patients who were not immunosuppressed. METHODS: Tissue samples were categorized by sex, patient age, and site of biopsy. Sixteen separate histologic criteria were evaluated in a blinded fashion in each specimen. Statistical analysis was performed between the two groups with and without controlling for the age of the patient. RESULTS: The transplant group was significantly younger (54.8 years) than the nontransplant group (70.0) and contained more men (88%) than women (51%). AKs from transplant recipients were statistically more likely to demonstrate bacterial colonization, confluent parakeratosis, hyperkeratosis, increased mitotic activity, and verrucous changes. After controlling for age only, hyperkeratosis failed to be more prevalent in the transplant group. CONCLUSION: Certain histopathologic features are more common in AKs of immunosuppressed transplant recipients and may be used to distinguish between those removed from otherwise healthy persons.

Elevated anti-annexin V antibody levels in antiphospholipid syndrome and their involvement in antiphospholipid antibody specificities.

To clarify the involvement of annexin V (ANX) in antiphospholipid antibody (APA) specificities, we studied antiANX antibodies (aANX) using 2 kinds of enzyme-linked immunosorbent assay plates (plain and gamma-irradiated) and anti-beta 2-glycoprotein I antibodies (a-beta 2GPI) in 53 patients with antiphospholipid syndrome (APS). The incidence of aANX IgG-positive results in the autoimmune APS group was significantly higher than that of healthy control subjects. However, we could not demonstrate a significantly higher incidence in the infection- or drug-induced group. Nor could we find an increased incidence of IgM isotype. When the 2 plates were compared, the discrepancies of positivity were demonstrated in both isotypes. We speculated that these discrepancies between the plate surfaces were attributed to the altered antigenicity of ANX. Although positivity of a-beta 2GPI was associated significantly with clinical manifestations, no significant associations were demonstrated between the incidence of aANX-positive results and clinical manifestations. We inferred that the involvement of aANX in the pathogenic mechanism of APS is unlikely.

Cigarette smoking-associated elastotic changes in the skin.

BACKGROUND: Clinical features of the skin in persons who smoke include increased wrinkling, gauntness, and discoloration that has been termed smoker's face. The histologic changes in the sun-exposed skin of these patients have not been previously elucidated. OBJECTIVE: The purpose of this study was to assess the amount of elastosis in the sun-exposed skin of smokers and nonsmokers. METHODS: We evaluated the skin from the forehead and cheeks of 17 smokers and 14 nonsmokers for the presence of elastosis. With the use of a computer-generated analysis of tissue sections at 4 different levels, the amount of elastotic material was expressed as an average percent of the field staining for elastic tissue. Patients were also evaluated for the presence of other malignancies, arsenic and radiation exposure, and previous skin cancers. RESULTS: There was a significantly greater amount of elastosis (P < .05) in the skin of patients who smoked compared with those patients who did not. No significant differences were found between the 2 groups with regard to the other parameters evaluated. CONCLUSION: Cigarette smoking is associated with an increase in elastosis, which may contribute to the clinical features of "smoker's face."

Antioxidant nutrients protect against UVB-induced oxidative damage to DNA of mouse keratinocytes in culture.

Ultraviolet B radiation (UVB) induces oxidative damage in DNA, resulting in the formation of the adduct 8-hydroxydeoxyguanosine. Previous studies from this laboratory have demonstrated a decrease in antioxidant enzyme defenses after UVB radiation in Skh: HR-1 hairless mice, implicating antioxidant status in protection against oxidative damage. The present study was undertaken to examine mechanisms of UVB damage to DNA and modulation by vitamin C, selenite, or Trolox, a water-soluble vitamin E analog. BALB/c MK-2 mouse keratinocytes were exposed to a dose range of UVB from 4 to 750 mJ/cm2. DNA damage in the form of 80 HdG was measured using high-pressure liquid chromatography coupled with electrochemical and UV absorbance detection. Preincubation of the cells for 2 days with 0.4 or 0.8 microgram/ml ascorbic acid, 10 or 20 micrograms/ml Trolox, and 5 or 12.5 microM selenite resulted in a significant decrease in the number of 8-hydroxydeoxyguanosine adducts per 10(5) deoxyguanines induced by 500 mJ/cm2 UVB. The results indicate a potential role for antioxidant nutrients in protection against UVB damage to skin cells.

The effects of chronic sunscreen use on the histologic changes of dermatoheliosis.

BACKGROUND: Sunscreen application to the skin of hairless mice is effective in reversing the histologic changes associated with photoaging (solar elastosis, epidermal thickening, collagen depletion, glycosaminoglycan deposition). These reparative processes have not been studied in human beings. OBJECTIVE: The aim of this study was to evaluate histologically the effects of daily application of a UVA/UVB sunscreen versus placebo. METHODS: We examined 46 patients who were given either sunscreen or vehicle and asked to apply it daily for 24 months. Punch biopsy specimens were obtained from preauricular skin at 0, 12, and 24 months. Each specimen was examined for epidermal thickening and organization and dermal inflammatory infiltrate by light microscopy. Computer-generated analysis of tissue sections was used to evaluate solar elastosis. RESULTS: A significant difference in solar elastosis was found between the treatment groups; however, the other features remained largely unchanged. CONCLUSION: The dermal changes of photoaging may be affected differently than epidermal changes when UV radiation exposure is diminished. UVA and UVB may contribute diversely to these cutaneous changes. Computer-generated evaluation of dermatoheliosis may be more accurate than visual inspection.

High sun protection factor sunscreens in the suppression of actinic neoplasia.

BACKGROUND AND DESIGN: A controlled trial was undertaken from December 1987 to December 1990 to test the hypothesis that a strong sunscreen can reduce the number of cancerous and precancerous skin lesions. Candidates were selected from a high-risk population attending either a university- or Veterans Affairs-based dermatology practice in Lubbock, Tex, for a prospective, double-blind, controlled trial of daily application of sunscreen vs placebo over a 2-year period. Participants were asked to volunteer if they had demonstrated premalignant changes (actinic keratoses) or nonmelanoma skin cancer (basal cell carcinoma or squamous cell carcinoma), had continuing sun exposure, and were not using sunscreen on a regular basis. Fifty-three volunteers were initially enrolled in the study, and 37 came for the final 24-month visit. RESULTS: The rate of appearance of new precancerous skin lesions was less for the treatment group than for control subjects. People with darker skin had fewer actinic keratoses, women had fewer lesions than men, and people with fewer lesions at enrollment had fewer lesions during the study. The numbers of new nonmelanoma skin cancers appearing during the study period were too small for statistical analysis. CONCLUSIONS: The regular use of sunscreens can significantly reduce cutaneous neoplasia, as indicated by its suppression of precancerous lesions. A longer and/or larger study would be necessary to demonstrate an effect on malignant lesions.

Identification and activity of cytosol creatine phosphokinase enzymes in normal and diseased skin.

Phosphocreatine molecules (PCR) in skin regenerate adenosine triphosphate and help cutaneous tissue survive ischemia associated with skin flaps, grafts, and hair transplantation procedures. In addition, PCR concentration in psoriasis is elevated many times above normal, indicating either overproduction of PCR by mitochondrial creatine phosphokinase (CPK) enzymes or a defect in cytosol CPK enzymatic activity. Skin CPK isoenzymes, before this study, have not been identified. Herein, for the first time, cytosol CPK enzymatic activity was measured in normal and psoriatic, involved and uninvolved skin, skin tumors, and mouse skin and keratinocyte cell cultures. Creatine phosphokinase MM is the major isoenzyme in normal, uninvolved psoriatic and mouse skin. Total CPK enzymatic activity was increased in psoriasis and skin tumors. These data clearly indicate that increased PCR concentration in a psoriatic skin is not a result of decreased cytosol CPK enzymatic activity.

Late anastomotic ulceration after ileocolic resection in childhood [corrected].

Anastomotic ulcers are a rare late complication of ileocolic resection in children. The authors describe the cases of two patients who presented 10 and 8 years, respectively, after ileocolic resection. Both had suffered from iron-deficiency anemia caused by an anastomotic ulcer. In one patient the anemia improved after resection of the ulcer; in the second patient cholestyramine and a lactose-free diet resolved the problems of anemia and diarrhea. Anastomotic ulceration should be suspected in any child who has undergone an ileocolic anastomosis and subsequently presents with persistent iron-deficiency anemia and occult blood in the stool.

Measurement of phosphocreatine in cutaneous tissue by high pressure liquid chromatography.

A high pressure liquid chromatography technique for measuring phosphocreatine and adenine nucleotides in human cutaneous tissue is described. The presence of phosphocreatine in human skin was confirmed by this analytic method. Molar concentration of phosphocreatine and adenine nucleotides were determined in normal skin and in benign and malignant skin lesions. The preliminary results suggest that absolute amounts of phosphocreatine and adenine nucleotides and phosphocreatine/adenosine triphosphate ratios in malignant skin neoplasms and benign cutaneous lesions are different from those measured in normal nonischemic human skin.

Effects of multiple applications of tumor promoters and ultraviolet radiation on epidermal proliferation and antioxidant status.

The dorsal skin of hairless mice (Skh:HR-1) was treated with multiple applications of acetone, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or ethyl phenylpropionate (EPP) two times per week, or exposed to ultraviolet radiation (UVR) three times per week for treatment periods up to 16 weeks. Epidermal hyperplasia, as measured by epidermal thickness, was increased in all three treatment groups after a single (0.5 weeks) TPA, EPP, or UVR treatment. TPA- and EPP-induced hyperplasia had begun to subside by 16 weeks, whereas UVR-induced hyperplasia was still increasing at that point. Epidermal homogenates were examined for ornithine decarboxylase (ODC) activity 6 h after the final treatment at 0.5, 2, 8, and 16 weeks of treatment. ODC activity was elevated in all treatment groups (TPA greater than EPP greater than UVR), with UVR induction returning to near control (acetone) levels by 16 weeks even though the UVR-induced hyperplasia continued to increase at the 16-week point. Homogenates examined for superoxide dismutase (SOD), catalase (CAT), and xanthine oxidase (XO) activity 48 h after the final treatment at 0.5, 2, 4, 8, 12, and 16 weeks had decreased activities of both SOD and CAT. TPA and EPP elevated XO, but UVR had little or no effect. Our data indicate that promoter-induced hyperplasia persists for extended periods of time and that diminution of antioxidant defenses observed following prolonged tumor-promoter treatment persists through the time period when tumors would be expected to begin. This antioxidant diminution may be one of a cascade of events that leads to epidermal proliferation and tumor promotion in mouse skin.

Tumour promoter-induced release and metabolism of arachidonic acid: Comparison between mouse and human epidermal cells.

Arachidonic acid (AA) release and metabolism to prostaglandins (PG) in response to the complete mouse skin tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and the first-stage promoter A23187 were compared in keratinocytes from normal adult human and two different strains of mouse with different sensitivities to TPA as a tumour promoter. The rate, extent and distribution of incorporated [(14)C]AA among the classes of phospholipids were similar in cultures of either CD-1, SSIN or human keratinocytes. Using prelabelled cultures, the amount of radiolabel released in control cultures was nearly identical for human and both strains of mice. Distinct species differences were observed, however, after TPA treatment. Cultures of human epidermal keratinocytes (HEK) released only half as much label by 6 hr compared with either strain of mouse. In addition, whereas the mouse epidermal keratinocytes (MEK) metabolized AA readily to PGE(2), very little PGE(2) could be detected in the human cultures. The extent of variability between individual human samples (n = 11) in response to 0.1 mug TPA/ml ranged from a 20% increase to a 200% increase in release of label, with a mean increase of 50%, whereas murine cells produced a mean increase of 400%. When MEK and HEK were stimulated with 10(-6) and 10(-5)m-A23187, an increase in the release of arachidonate by 200 and 400%, respectively, was observed for both species. Under these conditions of equal release, equivalent amounts of PGE(2) were produced. To compare further the ability of mouse and human cells to metabolize exogenous AA to PGE(2), freshly isolated, as well as cultured, cells from each species were incubated with [(14)C]arachidonate. Under both conditions, HEK have approximately the same ability as MEK to metabolize AA to PGE(2) (approx. 2% of the arachidonate for both species). The reduced ability of HEK, compared with MEK, to produce PGE(2) is specific to TPA and is due primarily to insufficient substrate, that is, low levels of arachidonic acid release.

Tumor-promoting activity of ethyl phenylpropiolate.

The ability of the hyperplasiogenic irritant ethyl phenylpropiolate (EPP) to act as a tumor promoter in two-stage carcinogenesis and to stimulate cellular events commonly cited as markers of tumor promoter action was evaluated. Treatment of adult, inbred SENCAR (SSIN) mice, initiated with 7,12-dimethylbenz(a)anthracene, with 5 mg of EPP twice weekly resulted in 100% of the mice developing tumors (4.8 tumors/mouse) after 40 weeks of promotion. Treatment with 3 mg EPP (twice weekly) resulted in 52% of the mice developing tumors (0.9 tumor/mouse). This treatment regimen with EPP produces a sustained epidermal hyperplasia without being overtly toxic. In addition, a 5-mg dose of EPP induced ornithine decarboxylase activity to a level comparable to that induced by the tumor promoter phorbol 12-myristate 13-acetate (PMA): 2.3 nmol CO2/mg protein/h for EPP versus 4.5 nmol CO2/mg protein/h for PMA versus 0.04 nmol CO2/mg protein/h for acetone control. Likewise, the time course of ornithine decarboxylase induction by EPP was the same as that seen with PMA (maximum induction at approximately 6 h). Vascular permeability of the dorsal skin increased significantly in response to EPP (8 times that seen in acetone controls) and exhibited the same kinetics as that seen after exposure to PMA. Activity of protein kinase C (PKC), the cellular receptor for PMA, decreased by 75 to 95% 48 h after treatment with PMA. In contrast, EPP treatment resulted in less than a 20% decrease in PKC activity 48 h after treatment. This slight decrease in PKC activity is thought to be an indirect effect caused by the hyperproliferative and inflammatory reactions, because EPP was found to be inactive as an in vitro activator of PKC. These results indicate not only that EPP is a good tumor promoter that causes morphological and biochemical responses similar to those induced by PMA, but also that the action of EPP is apparently mediated via a mechanism that does not involve direct interaction with PKC.

A prospective evaluation of the Button gastrostomy in children.

The Button gastrostomy has become popular for patients requiring long-term enteral feeding, because it is considered less irritating, more stable and more esthetically acceptable than the traditional tube gastrostomy. By a standardized questionnaire and personal interview, the authors evaluated prospectively the efficacy and complication rate in 19 children who had a Button gastrostomy inserted during a 6-month period. In 15 children the Button replaced a standard tube gastrostomy, and in 4 the Button was inserted surgically initially. Thirteen children had severe neurologic disabilities, and 6 required supplemental enteral feeding as part of the nutritional management of another chronic disease. In all 19 children, the Button was esthetically more acceptable and produced less skin irritation than the standard tube gastrostomy. All but one caregiver thought that the Button gastrostomy was preferable to a tube gastrostomy. This was especially apparent in the six neurologically normal children who were able to be more active and had an improved self-image. Cost analysis showed that, despite the higher initial cost of the Button, elimination of the need for frequent tube changes and hospital visits made it ultimately more cost effective than the standard tube gastrostomy. The authors conclude that the Button gastrostomy is a useful alternative to the standard tube gastrostomy in selected patients. Close long-term follow-up is extremely important to ensure a good result.

4 Beta- and 4 alpha-12-O-tetradecanoylphorbol-13-acetate elicit arachidonate release from epidermal cells through different mechanisms.

There is substantial evidence that the tumor promoter 4 beta-12-O-tetradecanoylphorbol-13-acetate (TPA) elicits enhanced arachidonic acid release and its metabolism to prostaglandins and lipoxygenase products in many cell types. The goal of this study was to determine whether 4 alpha-12-O-tetradecanoylphorbol-13-acetate (4 alpha TPA), a stereoisomer of TPA, can induce arachidonic acid release and whether it is by the same mechanism as release induced by TPA. The finding that 10 micrograms/ml 4 alpha TPA produces a response comparable with 1 microgram/ml TPA and with similar kinetics was unexpected. The mechanism mediating the TPA response appears to be the activation of protein kinase C (PKC), which subsequently results in phospholipase A2 activation. This is suggested by the observation that TPA-induced arachidonate release is inhibited 65% by 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), an inhibitor of PKC and that TPA completely down-regulates PKC. In addition, down-regulation or depletion of PKC by prior treatment with TPA results in a 75% loss of response to a second TPA treatment. In vitro activation of partially purified PKC could be demonstrated for TPA but not 4 alpha TPA. 4 alpha TPA thus appears to induce the release of arachidonate by a different but unknown mechanism. The 4 alpha TPA effect is not significantly reduced by the PKC inhibitor H-7, and no evidence of PKC activation or down-regulation was observed. Additionally, 4 alpha TPA is unable to "down-regulate" arachidonate release when the two-treatment protocol is used and the down-regulation of PKC by TPA has little effect on 4 alpha TPA-induced arachidonate release. Cycloheximide inhibited TPA-induced arachidonate release by 80% and 4 alpha TPA-induced release by 50%, indicating a partial requirement for protein synthesis for both phorbol esters. Actinomycin D, on the other hand, inhibited the TPA response by 70%, but enhanced the 4 alpha TPA response by 169%. When used at 10- or 100-micrograms doses, 4 alpha TPA was found to lack activity with respect to ornithine decarboxylase induction, oxidant production, hyperplasia, inflammation, and tumor promotion, suggesting that arachidonate release is not sufficient to induce these events. This may be related to the observation that with TPA the extent of arachidonate metabolism to prostaglandin E2 is four- to fivefold greater than occurred with 4 alpha TPA, even under conditions of equivalent arachidonate release.