Preclinical and clinical studies conducted in the mid-1990s reported strong association and causality between the T-cell helper (T(H)) 1 inductor cytokine interleukin (IL)-12 and numerous immune-mediated disorders, which spurred the development of therapeutic agents targeting IL-12 function. One of the first to enter the clinic, ustekinumab, is a human monoclonal antibody (mAb) that binds to the p40 subunit of IL-12. Subsequent to the generation of ustekinumab, it was discovered that IL-23 also contains the p40 subunit. Thus, although ustekinumab was designed to target IL-12, it also modulates IL-23, a cytokine important to the development and/or maintenance of T(H)17 cells. Clinical observations established that IL-12/23p40 is integral to the pathologies of psoriasis, psoriatic arthritis and Crohn's disease. The molecular and cellular evaluations conducted in ustekinumab clinical programs have provided numerous insights into the pathologic processes of these disorders, illustrating how a novel molecular entity can contribute to our understanding of disease. The individual contributions of these cytokines to specific pathologies require investigation and clinical evaluation of the role of IL-12- and IL-23-specific inhibitors.

Exposure of macaque fetuses and infants to ustekinumab had no adverse effects on pre- and postnatal development.

Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32 P-labeled MCF-7 WT and MCF-7 DOX R cells inhibited phosphorylation of the myristoylated alaninerich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOX R cells did safingol treatment increase accumulation of [ 3 H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOX R cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P-glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOX R cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOX R cell membranes with safingol did not inhibit [ 3 H]vinblastine binding or [ 3 H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOX R cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOX R cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.Exposure of cancer cells to a single natural product antineoplastic drug can give rise to cells that also exhibit crossresistance to other unrelated natural cytotoxins. This phenotype is known as multidrug resistance and is characterized by the reduced intracellular accumulation of these drugs, due to drug efflux by P-glycoprotein (P-gp), 1 a 150 -180-kDa plasma membrane transport ATPase encoded by the human mdr1 gene (reviewed in Refs. 1 and 2)). A number of agents have been shown to inhibit multidrug resistance (3). Most modulators of multidrug resistance inhibit specific binding of drugs to P-gp in membranes derived from MDR cells (4 -7) and photoaffinity labeling of P-gp by photoactive drug analogs (4,8,9). These results suggest that competitive inhibition of P-gp drug binding is a mechanism by which P-gp function and multidrug resistance may be inhibited.P-gp is subject to phosphorylation (10, 11) and changes in P-gp phosphorylation have been associated with inhibition of P-gp drug transport by modulators of the MDR phenotype (12, 13). Although other kinases have been shown to phosphorylate P-gp in vitro (11,14), there is considerable experimental evidence that suggests that phosphorylation of P-gp by protein kinase C (PKC) may play a role in regulating multidrug resistance.PKC is a family of serine/threonine kinases, composed of calcium-dependent and calcium-independent isotypes, which are dependent upon phospholipid for activation (15). In vitro, P-gp is phosphorylated by PKC (13, 16) at serine residues (13, 17) primarily in the linker region of P-gp (18,19). ...

Abstract. The multidrug resistant (MDR) phenotype is a well-studied subject that has been recognized as a determinant underlying specific types of drug resistance in human cancer. Although it is clear that the P-glycoprotein plays a major role in MDR, it is not clear whether post-translational modifications such as phosphorylation have any major impact on its modulation.The laboratory of Dr. Bruce Chabner was one of the first to describe increased expression and activity of protein kinase C (PKC) associated with the MDR phenotype. Since that time, a similar correlation has been observed in many other MDR cell lines. Most of these studies have been performed with doxorubicin-selected cells that have acquired MDR and have shown increased PKC activity, mainly for PKC-α isoenzyme. Intrinsic MDR in human renal cell carcinoma lines has been shown to correlate directly with PKC activity, but further studies with intrinsic MDR cell lines are needed before any conclusions can be drawn.More recent evidence suggests that there is a complex biochemical process by which PKC isoenzymes differentially phosphorylate specific serine residues in the linker region of P-glycoprotein which may lead to alterations in P-glycoprotein ATPase and drug-binding functions. To further complicate matters, PKC plays an important role in anti-apoptotic pathways, which can confound the dissection and elucidation of drug-resistance mechanisms. However, these areas are still under active investigation and not fully answered. Further studies are needed to specifically answer the question of whether PKC directly modulates basal and/or drug-stimulated P-glycoprotein function.This manuscript reviews the majority of the literature on PKC and MDR, as well as offers caveats for interpretation of these studies to answer the above questions.