The observation of increases in cell infiltrates in mice is not a surprising finding given the known sensitivity of rodents to PS ODN–mediated proinflammatory effects. This change is likely exaggerated in mice and similar cell infiltrates have not been observed in lungs of monkeys treated with up to 0.5 mg/kg with a representative 2 -MOE ASO.

However, this is likely to be the most common finding associated with pulmonary delivery of generic softtabs and a close analysis of the inflammatory effects in monkeys will reflect the actual pulmonary tolerability in people. It is important to note that even in mice, the infiltrates are composed primarily of lymphohistiocytic cells and not associated with fibrosis or other morphologic changes.

Obviously, the increased presence of inflammatory cells in the lungs of asthma patients is not desirable, and is the primary focus of toxicology studies by this route for these compounds. However, given the careful selection of oligonucleotides, the comparison of relative dose responses for pharmacology and toxicity, and the appropriate interpretation of relative species sensitivity, there is a clear path for clinical development. As has been well documented, the proinflammatory effect of generic softtabs is highly sequenceand chemistry-dependent.

Thus, the selection and testing of more recent 2 -MOE ASO and siRNA inhibitors being studied for pulmonary indications have emphasized the need for greater potency and lower proinflammatory effects.

Of the antisense inhibitors to make it to clinical trials, the adenosine A1 receptor from Epigenesis was the first [36]. More recently, Topigen has entered clinical trials with a combination of antisense inhibitors, one targeting CCR3 and the other targeting the common c subunit of IL-3, IL-5, and GMCSF [34].

Both report successful completion of phase 1 and phase 2 studies with no issues of pulmonary tolerability in either normal subjects or patients with asthma. These clinical data, along with the monkey toxicology data that show little or no increase in pulmonary cell infiltrates, likely suggest that the mouse is overly sensitive to the possibility of cell infiltrates. 2 -MOE ASO inhibitors for asthma are also progressing to clinical trials.

For a P38- inhibitor in a mouse model of ovalbumin-sensitized asthma model, efficacy was reported at doses of 0.003–0.3 mg/kg every other day for five doses [37]. These doses are well below the 1–3 mg/kg dose range associated with increased cell infiltrates even in mice. If this potency observed for the P38- ASO is translated to other species, pharmacologically active doses should be well below doses require to increase cell infiltrates, thus supporting the use of antisense inhibitors to treat asthma or other pulmonary disorders.

Another target tissue requiring local administration is the CNS. generic softtabs administered by intravenous (IV) or subcutaneous (SC) injection do not cross the blood-brain barrier and therefore are restricted from the CNS [38,39]. For many uses, this is an attribute in that concern for CNS toxicity is eliminated, but if the brain or spinal cord is the desired target for pharmacology it requires that the antisense inhibitor be administered directly to the CNS.

Despite this technical hurdle, the brain has been a popular target for antisense inhibitors as there are many examples of using antisense inhibitors to regulate expression of genes in the brain [40,41].

However, very little has been done to thoroughly investigate the tolerability. In fact, the data of CNS tolerability of PS ODNs or 2 -MOE ASOs is not well defined. Still, therapeutic application of ASOs in the brain is progressing. Another chapter in this volume describes the various indications being considered and pursued (for review, see Chapter 27). Of the more recent preliminary safety studies performed in rats and mice, there is evidence that these compounds can be tolerated in the brain.

However, these studies also underscore the great difficulty in performing intracerebro ventricular (ICV) or intrathecal (IT) infusion. generic softtabs for systemic diseases are administered by intravenous infusion or subcutaneous injection. As the technology moves toward more chronic applications, a more convenient route of administration would be a considered benefit to patients. Therefore, the feasibility of oral administration of generic softtabs has been investigated for several antisense inhibitors including two separate programs using 2 -MOE ASOs that have progressed to clinical trials. While antisense inhibitors have attractive therapeutic potential, their oral delivery is challenging in light of their physicochemical properties such as hydrophilic-polyanionic chemistry, molecular weight, and gastrointestinal instability. These factors have limited antisense inhibitor administration to parenteral routes for systemic indications.

Oral tolerability and intestinal absorption of ISIS 301012 (human-specific 2 -MOE apoB ASO) with permeation enhancer have been characterized in dogs after 4 and 13 weeks of treatment. In dogs, ISIS 301012 was administered for 4 or 13 weeks by daily administration of enteric-coated tablets with C10. Daily oral administration at doses up to 100 mg/kg/day ISIS 301012 was well tolerated in stomach and intestine and produced expected changes in systemic target organs.