While the peptide and protein therapeutic market has developed significantly in the past decades, delivery has limited their use. Although oral delivery is preferred, most are currently delivered intravenously or subcutaneously due to degradation and limited absorption in the gastrointestinal tract. Therefore, absorption enhancers, enzyme inhibitors, carrier systems and stability enhancers are being studied to facilitate oral peptide delivery. Additionally, transdermal peptide delivery avoids the issues of the gastrointestinal tract, but also faces absorption limitations. Due to proteases, opsonization and agglutination, free peptides are not systemically stable without modifications. This review discusses oral and transdermal peptide drug delivery, focusing on barriers and solutions to absorption and stability issues. Methods to increase systemic stability and site-specific delivery are also discussed.

The oncoprotein Bcr-Abl drives aberrant downstream activity through trans-autophosphorylation of homo-oligomers in chronic myelogenous leukemia (CML).1,2 The formation of Bcr-Abl oligomers is achieved through the coiled-coil domain at the N-terminus of Bcr.3, 4 We have previously reported a modified version of this coiled-coil domain, CCmut2, which exhibits disruption of Bcr-Abl oligomeric complexes and results in decreased proliferation of CML cells and induction of apoptosis.5 A major contributing factor to these enhanced capabilities is the destabilization of the CCmut2 homo-dimers, increasing the availability to interact with and inhibit Bcr-Abl. Here, we included an additional mutation (K39E) that could in turn further destabilize the mutant homo-dimer. Incorporation of this modification into CCmut2 (C38A, S41R, L45D, E48R, Q60E) generated what we termed CCmut3, and resulted in further improvements in the binding properties with the wild-type coiled-coil domain representative of Bcr-Abl. A separate construct containing one revert mutation, CCmut4, did not demonstrate improved oligomeric properties and indicated the importance of the L45D mutation. CCmut3 demonstrated improved oligomerization via a two-hybrid assay as well as through colocalization studies, in addition to showing similar biologic activity as CCmut2. The improved binding between CCmut3 and the Bcr-Abl coiled-coil may be used to redirect Bcr-Abl to alternative subcellular locations with interesting therapeutic implications.

In doping control laboratories, autologous blood transfusions are currently detected using an indirect method that monitors changes in an athlete's hemoglobin concentration [Hb] and reticulocyte percent (Ret%) over time. The method is limited by the need for a phlebotomist to collect venous blood and the limited blood stability which requires temperature-controlled shipment and analysis within 72 hours. These limitations significantly reduce the number of samples collected from each athlete and thus the utility of the method. We have recently developed a method to measure immature reticulocytes (IRC) and red blood cells (RBC) in dried blood spots, which could replace the current venous blood method. In the DBS method, cell-specific proteins are digested with trypsin and measured by mass spectrometry. Two proteins, CD71 and Band3, are measured to count IRC and RBC, respectively. The method was tested in an autologous transfusion study consisting of 15 subjects who received blood and 11 subjects who received saline. After transfusion, the average CD71/Band3 ratio in the blood group was statistically different from the saline group at days 5, 6, 13, and 20. The average CD71/Band3 ratio decreased to a minimum of 61 ± 8% of baseline, while Ret% decreased to 75 ± 5% of baseline. Based on experimentally defined criteria, the CD71/Band3 ratio could detect 7 out of 10 blood transfusion subjects, while Ret% could detect 3 out of 10. Thus, the DBS method could improve detection of autologous transfusion and allow increased sample collection.

In 2012, ponatinib (Iclusig®), an orally available pan-BCR-ABL tyrosine kinase inhibitor (TKI) developed by ARIAD Pharmaceuticals, Inc., was approved by the US Food and Drug Administration for use in resistant or intolerant chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL). Ponatinib is the only approved TKI capable of inhibiting BCR-ABL with the gatekeeper T315I kinase domain mutation, known to be the cause for 20% of resistant or relapsed CML cases. In 2013, ponatinib sales were temporarily suspended due to serious side effects seen in nearly 12% of the patient population. These side effects are thought to stem from the potent nature and pan-activity of this TKI. ARIAD Pharmaceuticals, Inc. has since been permitted to resume sales and marketing of ponatinib to a limited patient population with an expanded black box warning. In the following review, the use of ponatinib in CML and Ph+ALL will be discussed. Mechanisms of resistance in CML are discussed, which provide insight and background into the need for this third generation TKI, followed by the molecular design and pharmacology of ponatinib, which lead to its success as a therapeutic. Finally, the efficacy, safety, and tolerability of ponatinib will be highlighted, including summaries of the important clinical trials involving ponatinib as well as its current place in therapy.

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