Factors affecting human percutaneous penetration of methotrexate and its analogues in vitro

Nano Methotrexate versus Methotrexate in Targeting Rheumatoid Arthritis

Nanomedicine has emerged as an important approach for targeting RA medication. Rheumatoid arthritis (RA) is a widespread autoimmune disorder marked by multiple inflamed joints. Gold nanoparticles (GNPs) have been demonstrated as efficacious nanocarriers due to their unique characteristics and the relative simplicity of their synthesis in varied sizes; moreover, they have the capability to alleviate several inflammatory markers. The current objective was to combine methotrexate (MTX) with GNPs to overcome MTX restrictions. GNPs were fabricated by a chemical reduction technique, utilizing sodium citrate and tween 20. The MTX-GNPs formulations were characterized in vitro by % entrapment efficiency (%EE), particle size, polydispersity index (PDI) zeta potential, and % release. The MTX-GNPs formulation was administrated as an intra-articular solution, and additionally, incorporated into a Carbopol gel to investigate its anti-arthritic effectiveness and bioavailability in vivo. The results indicated that a %EE of 87.53 ± 1.10%, and a particle size of 60.62 ± 2.41 nm with a PDI of 0.31 ± 0.03, and a zeta potential of −27.80 ± 0.36 mV were optimal. The in vitro release of MTX from the MTX-GNPs formulation demonstrated that the MTX-GNPs formulation’s release was 34.91 ± 1.96% and considerably (p < 0.05) lower than that of free MTX, showing a significant difference in dissolution patterns (p < 0.05). In vivo, MTX-GNPs formulations inhibited IL-6 by 36.52%, ACCP (63.25 %), COMP (28.16%), and RANKL (63.67%), as well as elevated IL-10 by 190.18%. Transdermal MTX-GNPs decreased IL-6 by 22.52%, ACCP (56.63%), COMP (52.64%), and RANKL (79.5%), as well as increased IL-10 by 168.37%. Histological investigation supported these recent findings. Conclusions: Marked improvements in MTX anti-arthritic effects are seen when it is conjugated to GNPs.

Iontophoretic delivery of methotrexate in the treatment of palmar psoriasis: A randomised controlled study

BACKGROUND/OBJECTIVES

Palmoplantar psoriasis is a localised variant of psoriasis. Topical therapy is the preferred treatment modality, but in severe and recalcitrant cases, systemic drugs like methotrexate are prescribed, with potential for significant adverse effects. Iontophoresis is gaining popularity in enhancing the transdermal delivery of drugs in ionic state. This study was undertaken to evaluate and compare the efficacy of topical methotrexate by iontophoresis technique with clobetasol propionate 0.05% ointment in the treatment of palmar psoriasis.

METHODS

This was a prospective randomised controlled study conducted on patients with palmar psoriasis. Group 1 patients (n = 31) were treated with once weekly iontophoretic delivery of methotrexate over 6 sittings, and group 2 patients (n = 31) were treated with clobetasol propionate 0.05% ointment, twice daily for 6 weeks. Severity of palmar psoriasis was assessed by modified Palmoplantar Pustular Psoriasis Area and Severity Index (m-PPPASI), and treatment was considered as satisfactory when there was >50% improvement.

RESULTS

Sixty two patients were recruited, of which 50 completed the study. Eight out of 25 (32%) patients in group 1 and 12 out of 25 (48%) patients in group 2 showed satisfactory improvement at the end of 6 weeks. However, this difference was statistically not significant (P = 0.25). Burn injury was noted in 12 (48%) group 1 patients with no adverse effects in group 2.

CONCLUSION

Iontophoretic delivery of methotrexate is a promising therapeutic modality, the efficacy of which is comparable to that of clobetasol propionate ointment in the treatment of palmar psoriasis.

Confocal laser scanning microscopy to estimate nanoparticles' human skin penetration in vitro

Objective

With rapid development of nanotechnology, there is increasing interest in nanoparticle (NP) application and its safety and efficacy on human skin. In this study, we utilized confocal laser scanning microscopy to estimate NP skin penetration.

Methods

Three different-sized polystyrene NPs marked with red fluorescence were applied to human skin, and Calcium Green 5N was used as a counterstain. Dimethyl sulfoxide (DMSO) and ethanol were used as alternative vehicles for NPs. Tape stripping was utilized as a barrier-damaged skin model. Skin biopsies dosed with NPs were incubated at 4°C or 37°C for 24 hours and imaged using confocal laser scanning microscopy.

Results

NPs were localized in the stratum corneum (SC) and hair follicles without penetrating the epidermis/dermis. Barrier alteration with tape stripping and change in incubation temperature did not induce deeper penetration. DMSO enhanced NP SC penetration but ethanol did not.

Conclusion

Except with DMSO vehicle, these hydrolyzed polystyrene NPs did not penetrate intact or barrier-damaged human “viable” epidermis. For further clinical relevance, in vivo human skin studies and more sensitive analytic chemical methodology are suggested.

Topically applied methotrexate is rapidly delivered into skin by fractional laser ablation

OBJECTIVES

Methotrexate (MTX) is a chemotherapeutic and anti-inflammatory drug that may cause systemic adverse effects. This study investigated kinetics and biodistribution of MTX delivered topically by ablative fractional laser (AFXL).

METHODS

In vitro passive diffusion of 10 mg/ml MTX (1 w/v%) was measured from 0.25 to 24 h through AFXL-processed and intact porcine skin in Franz Cells (n = 46). A 2,940 nm fractional Erbium Yttrium Aluminium Garnet laser generated mid-dermal microchannels at 2.4% density, and 256 mJ/microchannel. HPLC quantified MTX-concentrations in extracts from mid-dermal skin sections, donor and receiver compartments. Fluorescence microscopy of UVC-activated MTX-fluorescence and desorption electro-spray ionization mass spectrometry imaging (DESI-MSI) evaluated MTX biodistribution.

RESULTS

AFXL-processed skin facilitated rapid MTX delivery through cone-shaped microchannels of 690 µm ablation depth, lined by the 47 µm thermal coagulation zone (CZ). Quantitatively, MTX was detectable by HPLC in mid-dermis after 15 min, significantly exceeded deposition in intact skin after 1.5 h, and saturated skin after 7 h at a 10-fold increased MTX-deposition versus intact skin (3.08 vs 0.30 mg/cm(3), p = 0.002). Transdermal permeation was < 1.5% of applied MTX before skin saturation, and increased up to 8.0% after 24 h. Qualitatively, MTX distributed into CZ within 15 min (p = 0.015) and further into surrounding dermal tissue after 1.5 h (p = 0.004). After skin saturation at 7 h, MTX fluorescence intensities in CZ and tissue were similar and DESI-MSI confirmed MTX biodistribution throughout the mid-dermal skin section.

CONCLUSIONS

MTX absorbs rapidly into mid-dermis of AFXL-processed skin with minimal transdermal permeation until skin saturation, suggesting a possible alternative to systemic MTX for some skin disorders.

Progress in Psoriasis Therapy via Novel Drug Delivery Systems

Psoriasis is a lifelong condition which is caused by the negative signals produced by immune system, which leads to hyper proliferation and other inflammatory reactions on the skin. In this case, keratinocytes which are the outermost layer of skin possess shortened life cycle and results in the alteration of desquamation process where the cytokines will come out through lesions of affected patients and as a result, scaling marks appears on the skin. These conditions may negatively affect the patient’s quality of life and lead to psychosocial stress. Psoriasis can be categorized as mild, moderate and severe conditions. Mild psoriasis leads to the formation of rashes, and when it becomes moderate, the skin turns into scaly. In severe conditions, red patches may be present on skin surface and becomes itchy. Topical therapy continues to be one of the pillars for psoriasis management. Drug molecules with target effect on the skin tissues and other inflammations should be selected for the treatment of psoriasis. Most of the existing drugs lead to systemic intoxication and dryness when applied in higher dose. Different scientific approaches for topical delivery are being explored by researches including emollient, modified gelling system, transdermal delivery, spray, nanogels, hydrogels, micro/nano emulsion, liposomes, nano capsules etc. These topical dosage forms are evaluated for various physico chemical properties such as drug content, viscosity, pH, extrudability, spreadability, toxicity, irritancy, permeability and drug release mechanism. This review paper focus attention to the impact of these formulation approaches on various anti-psoriasis drugs for their successful treatment.

Pilot study of topical delivery of methotrexate by electroporation

BACKGROUND

The topical administration of methotrexate (MTX) for the treatment of psoriasis and neoplastic diseases is restricted by the poor diffusion of MTX across the stratum corneum.

OBJECTIVES

We applied electroporation to increase the transdermal transport of MTX.

METHODS

Electrodes were placed either side-by-side on the surface of excised full thickness pig skin, or on a piece of skin clamped between compartments of a vertical diffusion chamber. Sixty rectangular electric pulses at 120 V, 1 ms and 1 Hz were applied across the skin. MTX was left on the skin surface for an additional 10 min to take advantage of diffusion through electropores. Cumulative drug transport was measured by radioactive tracing, using [3H]-methotrexate, from punch biopsy samples taken from under the cathode. The integrity of the radioisotope was verified by high-performance liquid chromatography.

RESULTS

Using side-by-side electrodes, treatment with the pulses alone resulted in a 2.5-fold increase; adding anionic lipid enhancers to the pulses resulted in a 4.4-fold enhancement compared with passive diffusion. Concurrent iontophoresis for the 11-min time period made a nonsignificant contribution. To reduce tissue resistance we used 40 degrees C hyperthermia in a vertical diffusion chamber; transport was increased 11-fold to 53 microg cm(-2) (flux = 290 microg cm(-2) h(-1)). MTX penetration profiles indicated that more than half of the MTX was confined to the epidermis and papillary dermis. The tissue concentration in this superficial reactive unit was 1.7 mmol L(-1).

CONCLUSIONS

Electroporation of MTX with an anion lipid enhancer under a mild hyperthermic environment provided a significant transdermal delivery within a short application time. The method may be an effective means of drug delivery for treating psoriasis or other MTX-sensitive disorders and avoids the potential systemic toxicity.

Effect of vehicles and penetration enhancers on the in vitro and in vivo percutaneous absorption of methotrexate and edatrexate through hairless mouse skin

PURPOSE

Low-dose methotrexate (MTX) is approved for the treatment of recalcitrant rheumatoid arthritis (RA). The objective of this study was to determine the effect of vehicles and penetration enhancers on the percutaneous absorption of MTX and its analog edatrexate (EDAM), and develop transdermal (TD) delivery systems of the drugs for the treatment of RA.

METHODS

From previously published pharmacokinetic parameters with low-dose MTX therapy, and considering a 50 cm2 diffusional area, the target steady state in vitro TD flux for MTX was calculated to be 35 micrograms/cm2/hr. Modified Franz diffusion chambers and hairless mouse skin were used for in vitro skin permeation studies. Hairless mice were used for in vivo studies. Delivered amounts of MTX and EDAM were determined by assaying the receiver phase fluid (or blood) with validated reversed phase HPLC methods.

RESULTS

Intrinsic partition coefficient of MTX was low (log P = -1.2). Target MTX fluxes of > or = 35 micrograms/cm2/hr were achievable only with 1-15% (v/v) Azone in propylene glycol (PG). Flux of EDAM (85 micrograms/cm2/hr) was higher than MTX from an isopropyl alcohol (IPA)-5% (v/v) Azone system. Clinically significant steady state in vivo blood concentration of MTX and EDAM was achieved using delivery systems containing > or = 2.5% Azone in PG. Area under the drug concentration-time curves (AUC0-24 hr) for MTX were 2379 and 3534 ng*hr/ml from PG-2.5% Azone and PG-7.5% Azone systems respectively. AUC0-24 hr of EDAM was 6893 ng*hr/ml using a PG-2.5% Azone system.

CONCLUSIONS

Results of this study show the feasibility of using a transdermal delivery system of MTX and EDAM for the treatment of rheumatoid arthritis.

Influence of counter ions on the skin permeation of methotrexate from water--oil microemulsions

The influence on the permeation of methotrexate across intact hairless mouse skin of different counter ions added to water--oil (w/o) microemulsions containing lecithin, as surfactant, and water--propylene glycol at different pH values, as internal phase, was studied. As counter ions, monooctyl phosphate, monodecyl phosphate, monodecyl glycerophosphate, taurodeoxycholate, dodecyl sulfate and dioctyl sulfosuccinate were used. At pH 4.0, the transport of methotrexate was enhanced by the counter ions and a marked increase in the flux of the drug was measured when dodecyl sulfate and dioctyl sulfosuccinate were used. At pH 5.0 only a slight increase of the flux was observed. The increased permeation was attributed to the lipophilization of methotrexate as a consequence of ion pair formation.

Elevated numbers of proliferating mononuclear cells in the peripheral blood of psoriatic patients correlate with disease severity

Although psoriasis is characterized by the accumulation of activated proliferating lymphoid cells in the psoriatic skin lesion, it is not known whether these cells are activated and proliferating before entry into the psoriatic plaque. The current study evaluates the number and phenotype of proliferating lymphoid cells in the blood of psoriatic patients. Proliferation of peripheral blood mononuclear cells was evaluated on cytospun preparations of these cells using autoradiographic techniques after pulsing the mononuclear cells with 3H-methyl thymidine for 2 h. The phenotypes of the labeled peripheral blood mononuclear cells were determined combining autoradiography and immunohistochemistry with monoclonal antibodies directed at CD3, CD4, CD8, CD11c, CD22, and human leukocyte antigen-DR. The data demonstrated elevated numbers of proliferating lymphoid cells in the blood of psoriatic patients compared with normal nonpsoriatic volunteers (p < 0.01). Furthermore, the number of circulating proliferating mononuclear cells increased significantly with increasing psoriasis skin disease severity (correlation coefficient 0.95; p < 0.0001). When the phenotype of the proliferating cells in the blood was examined, the numbers of T cells (CD3+, CD4+, CD8+ cells), B cells (CD22+ cells), monocytes (CD11c+ cells), and human leukocyte antigen-DR+ cells were significantly elevated compared with nonpsoriatic skin (p < 0.01) and increased with increasing disease activity (correlation coefficient range 0.48-0.74; p < 0.05). The data suggest a generalized systemic activation of T, B, and monocytic cells that results in labeling of up to 0.16% of the circulating mononuclear cells with 3H-methyl thymidine (i.e., proliferating and presumably activated) when assayed in vitro.

Methotrexate therapy of psoriasis: differential sensitivity of proliferating lymphoid and epithelial cells to the cytotoxic and growth-inhibitory effects of methotrexate

Although methotrexate (MTX) is one of the most clinically effective therapies employed to treat psoriasis, the mechanism by which low-dose MTX acts to modulate the hyperplasia of psoriasis, leading to the restoration of clinically normal skin, is only partially understood. MTX has been considered a cytotoxic agent that mediates its effect primarily on proliferating or cycling epidermal cells. Recently, proliferating lymphoid cells have been identified in psoriatic lesions, raising the possibility that proliferating lymphoid cells could be another target cell that is killed by MTX. In this study, we examined the growth-inhibitory and cytotoxic effects of MTX on proliferating lymphoid cells [THP-1 (macrophage), and MOLT-4 (T cell)], epithelial cells (HeLa, and HaCat), and normal human keratinocytes (NHK) in vitro. The proliferating cells were exposed to MTX for 24 h, and placed in fresh media to mimic the transient MTX blood levels that result from once-weekly therapy. THP-1 and MOLT-4 were found to be 10-100 times more sensitive to the cytotoxic effects of MTX than were HeLa and HaCat, and more than 1000 times more sensitive than primary human keratinocytes. At MTX concentrations that would be expected to occur in vivo during once-weekly therapy, a large percentage (> 95%) of proliferating lymphoid targets would be killed, and only a small percentage (< 10%) of proliferating epidermal cells would be affected. This in vitro data suggests that in psoriasis proliferating lymphoid cells are more likely than epithelial cells to be a major cellular target of MTX in vivo.

Some general influences of n-decylmethyl sulfoxide on the permeation of drugs across hairless mouse skin

The influences of n-decylmethyl sulfoxide (NDMS) on the permeation of phenyl propanolamine, propranolol, acyclovir, and hydrocortisone through hairless mouse skin were investigated. Permeation of these compounds increased systematically with increasing NDMS concentration up to a limiting value for the permeability coefficient of about 0.1 cm/h. Permeability coefficients obtained with stripped skin indicated that, where NDMS has its maximal effect, the compounds diffuse through the skin as if there were no stratum corneum. Diffusion lag times of the test compounds through skin sections exposed to NDMS were far shorter than lag times in control experiments. The kinetics of NDMS action were assessed by pretreating skin sections for various periods of time with the enhancer and then assessing permeability. When applied as a 10 mM aqueous solution, the full effect of NDMS was obtained in 3 h of exposure and the effect lasted for at least 24 h. Treating the skin with ethanol/water (2:1) to elute NDMS after the pretreatment did not diminish its effect. Propranolol and phenyl propanolamine solubilized NDMS, presumably through the formation of mixed micelles, which had a profound effect on the permeation rates of both drug and enhancer.

Differences in the biochemical activity in hairless mouse skin and other organs after systemic and topical methotrexate treatment

DNA synthesis in epidermis, spleen, small intestine, and muscle of the hairless mouse was measured after systemic and topical methotrexate dosing. Mice intraperitoneally injected with methotrexate (5 mg/Kg) incorporated 3H-UdR in epidermis at 90% of baseline at 3 hrs, and the incorporation was not suppressed at 24 hrs. Muscle DNA synthesis was not suppressed. In the spleen and small intestine, incorporation was greatly suppressed to 10% at 3 hrs. On the other hand, after topically applied methotrexate (25 mg/Kg) treatment, epidermis and muscle were 60-90% of baseline at 3-24 hrs and spleen and small intestine were 5-10% at 3-6 hrs. In a prolonged time schedule study (4 days), epidermal incorporation after intraperitoneally applied methotrexate (5 mg/Kg) showed no suppression, but was instead stimulated to 180% at 2 days. 5-Fluorouracil, a thymidine kinase inhibitor in antitumor agents, was topically applied (25 mg/Kg) and compared for DNA synthesis. The incorporation of 3H-UdR was drastically suppressed at 3 hrs. The results suggest that methotrexate is percutaneously absorbed, but does not extensively suppress epidermal DNA synthesis in hairless mice, although it does suppress spleen and intestinal DNA synthesis.

Biological effects of acetamide, formamide, and their monomethyl and dimethyl derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

Development of a topical hematoporphyrin derivative formulation: characterization of photosensitizing effects in vivo

Photochemotherapy offers a unique approach for the selective therapy of skin diseases. Hematoporphyrin derivative (HPD) in combination with visible light exhibits cytocidal activity in vitro and systemically has demonstrated applicability to the treatment of experimental and human tumors. This study was undertaken to investigate the phototoxic effects in guinea pig skin of systemic HPD in comparison with locally (intradermal) and topically administered HPD. Maximum erythema was obtained by irradiation with red light or UVA 6 h postsystemic HPD (10 mg/kg). Erythema response was dependent upon the dose of irradiation. Systemic HPD produced complete inhibition of epidermal DNA, RNA, and protein synthesis 6-12 h postirradiation with red light, with a lesser degree of inhibition in the deeper hair roots. Local (intradermal) HPD (5-500 micrograms) in combination with red light or UVA produced a dose-dependent erythema and inhibition of epidermal DNA synthesis. Effective in vitro percutaneous penetration of HPD was demonstrated in vehicles containing Azone and N-methylpyrrolidone. Topical application of these HPD formulations in vivo in combination with red light or UVA produced significant erythema and inhibition of epidermal DNA synthesis. These results suggest that HPD can cause photosensitization of the skin. It may therefore be reasonable to explore topical applications as an alternative approach for the photochemotherapy of psoriasis and other cutaneous diseases.

Pharmacologic studies on the dibutyl and gamma-monobutyl esters of methotrexate in the rhesus monkey

The pharmacokinetics and metabolism of dibutyl methotrexate (DBMTX) and gamma-monobutyl methotrexate (gamma-MBMTX) were studied in Rhesus monkeys. When a bolus IV dose of either [3H]DBMTX or [3H] gamma-MBMTX was given, the principal species in serum for up to 1 h was the monoester, with MTX accounting for less than 10% of the total radioactivity. Products other than gamma-MBMTX and MTX were formed in substantial amounts with DBMTX, but not with gamma-MBMTX. Total radioactivity recovered in the bile 5 h after [3H]DBMTX injection accounted for 32% of the administered dose, indicating high hepatic extraction for this lipophilic compound. Serum and CSF levels of unchanged gamma-MBMTX, as well as of MTX arising via esterase cleavage, were measured by HPLC after IV infusion of gamma-MBMTX (10 g/m2). Efflux of monoester from CSF was slower than disappearance from serum. However, gamma-MBMTX levels in CSF were no higher than could be attained by infusing MTX itself at the same dose rate. While CSF/serum ratios were ca. 10-fold higher for gamma-MBMTX than for MTX, this difference could be explained on the basis of the very different affinities of the two compounds for serum proteins. HPLC analysis of serum processed by methanol precipitation as opposed to ultrafiltration of the proteins showed gamma-MBMTX to be greater than 99% bound, whereas for MTX this value was 50% or less. When gamma-MBMTX and MTX levels measured after ultrafiltration were corrected for this difference in serum protein binding the total amount of the two drugs in serum became almost equivalent.

Percutaneous absorption of methotrexate: effect on epidermal DNA synthesis in hairless mice

One of the presumed reasons for the lack of clinical activity of topical methotrexate in psoriasis is insufficient percutaneous penetration necessary to inhibit epidermal DNA synthesis. The present study was undertaken to select a vehicle to optimize penetration of methotrexate in vitro and to determine the effects of this topical formulation on epidermal DNA synthesis in vivo in hairless mouse skin. Increased penetration of methotrexate was obtained in human skin in vitro with Vehicle N compared to water and n-decylmethylsulfoxide vehicles. Repeated topical application of this methotrexate/Vehicle N preparation produced marked epidermal atrophy in treated sites in both normal and hyperproliferative essential fatty acid deficient hairless mouse skin without similar effects at a distant skin site. Local inhibition of epidermal DNA synthesis was also obtained without systemic effects at a distant site. These studies demonstrate that methotrexate in Vehicle N may produce a direct effect on epidermis which may be useful for the topical therapy of psoriasis.

In vitro screening of biochemical activity of folic acid antagonists in skin

Dihydrofolate reductase (DHFR) inhibitors, which differ from the classical folate antagonists in physicochemical and pharmacologic parameters such as lipid solubility and mechanisms of cellular transport, were screened for DHFR inhibitory activity and biologic activity in newborn rat skin. The most effective drugs from this screen were tested for their effects on de novo DNA synthesis in psoriatic epidermis in vitro. Of the 24 compounds studied, methotrexate (MTX) was the most potent inhibitor of rat skin DHFR (I50=8.6 X 10(-9) M). Methotrexate-dimethylester, methasquin-diethylester, DDEP (2,4-diamino-5-(3',4'-dichlorophenyl)-6-ethylprimidine), and Baker's triazine antifolate (NSC 139105), while less effective than MTX as DHFR inhibitors, were more effective than MTX as inhibitors of de novo DNA synthesis in rat skin in vitro. Baker's antifolate was the only compound tested which was considerably more effective than MTX as an inhibitor of de novo DNA synthesis in psoriatic epidermis in vitro.

Cytokinetics and chemotherapy of psoriasis

The successful treatment of psoriasis with folic acid antagonists during the past 25 years has led to extensive research in the areas of cytokinetics and chemotherapy. In this paper we shall review selected aspects of these topics relevant to the treatment of psoriasis. The effectiveness of methotrexate treatment of psoriasis can be related to both the hyperproliferative cytokinetics of psoriasis and an increased biochemical sensitivity of psoriatic epidermal cells to this drug. Future research goals in chemotherapy of psoriasis include (a) optimizing drug schedules for available drugs; (b) identifying other susceptible biochemical points of selective drug attack; (c) identifying secondary advantages in order to facilitate selective drug action in psoriasis, such as ultraviolet light therapy in combination with a systemic drug; and (d) developing topically effective chemotherapeutic agents. Approaches to research on topical therapy are reviewed with specific reference to animal testing models for psoriasis and percutaneous penetration of topically applied agents.