**4. (2**′**-5**′**)oligoadenylates containing** *epoxy-***groups rather than 2**′**,3**′**-cis-diol group**

The use of 2-5A analogs in kidney transplant surgeries in monkeys was demonstrated in [49]. Based on the results, 2-5A analogs were selected from a variety of synthesized compounds in which 2′(3′)-terminal adenosine moiety of the molecule was substituted with 9-(2,3-anhydro-β-D-ribofuranosyl)adenine [(2′,5′)A2ARA] or 9-(2,3-anhydro-β-D-lyxofuranosyl)adenine [(2′,5′)A2 ALA] (**Figure 4**).

These compounds (*i*) were more resistant to snake venom phosphodiesterase compared to the parent trimer, (2′,5′)A3, (t1/2 hydrolysis 16 h, 10.5 h, and 27 min, respectively), *(ii)* exhibited no toxicity in mice at a concentration of 1 mg per kg of body weight and *(iii)* showed peculiar characteristics of lymphocytes in blastogenic response in the presence of mitogens during the *in vitro* experiments (**Tables 3** and **4**). The effects produced by these isomeric analogs were much more pronounced and they differed from 2′-5′A3 in their response to concanavalin A (Con A)- and lipopolysaccharide (LPS)-induced lymphocyte blastogenic response (**Table 3**). Con A primarily stimulates T-lymphocyte division whereas LPS acts on β-lymphocytes.

Biochemical test results convincingly demonstrated the potential of two analogs (2′,5′)A3, (2′,5′)A2ARA, and (2′,5′)A2ALA for the treatment of various conditions including those associated with T-cell immunodeficiency diseases, autoimmune diseases, viral infections, lymphocytic malignant transformations, graft failure prevention following the bone marrow transplantation and perhaps, complications associated with the recipient's transplant rejection.

#### **Figure 4.**

*2-5A dephosphorylated analogs containing epoxy-groups rather than 2*′*,3*′*-cis-diol group in A3 moiety in ribo- [(2*′*,5*′*)A2ARA] and lyxo-(2*′*,5*′*)A2ALA] configurations.*


#### **Table 3.**

*Comparative analysis of in vitro mammalian lymphocyte blastogenic response.*


#### **Table 4.**

*Concentration dependence of in vitro lymphocyte blastogenic response as affected by (2*′*,5*′*)A2ARA vs. (2*′*,5*′*)A3.*

The potential use of (2′,5′)A2ARA and (2′,5′)A2ALA analogs for kidney transplantation in rabbits and monkeys has been thoroughly studied [49]. Daily intravenous injection of (2′,5′) A2ARA to rabbits at a dose of 5 μg/kg of body weight ensures the normal functioning of the transplanted kidney in 4 out of 10 animals within 3 months. The lymphocyte blastogenic response in positive rabbits was suppressed by about 10 times by concanavalin (Con A) stimulation within 2 weeks after surgery.

Immunotropic activity of (2′,5′)A2ARA and (2′,5′)A2ALA analogs vs. (2′,5′)A3 was assessed in a group of monkeys aged 4. The parent trimer (2′,5′)A3 showed no immunosuppressive activity at a concentration of 0.5 mg/kg (data not shown). Moreover, a single intravenous injection resulted in a ~ 50% increase in T-helpers and T-killers responsible for the transplant rejection.

The results of the (2′,5′)A2ARA study are summarized in **Table 5**. It should be emphasized that the analog inhibits interleukin-2 (IL-2) and T-lymphocyte subpopulation and concurrently stimulates αIFN and γIFN in blood lymphocytes for 2–3 weeks with a single injection at a concentration of 50 μg/kg (**Table 5**) and 25 μg/ kg (data not shown).

After cross-allotransplantation of the kidney in two groups of monkeys, they were followed up for 3 months. Of note, normal functioning of the transplanted kidney occurred within 10 hours after the operation.

The data shown in **Table 5** suggest selective suppression of T-lymphocyte subpopulation immediately after surgery, subsequent recovery to preoperative levels followed by mild reduction of T-helper and T-killer populations, and slight increase in T-suppressor count. This trend persisted throughout the postoperative follow-up period.

Experiments in monkeys have shown that intravenous (2′-5′)A2ARA given every 48 hours at a concentration of 50 μg/kg provides immunosuppression, protects the *Modified (2*′*,5*′*)Oligonucleotides: The Influence of Structural and Steriochemical Factors… DOI: http://dx.doi.org/10.5772/intechopen.108630*


#### **Table 5.**

*Effect of a single intravenous injection of trimer (2*′*,5*′*)A2ARA at a dose of 50 μg/kg on the immune system of macaque Rh monkeys.*


#### **Table 6.**

*Effect of intravenous administrations of (2*′*-5*′*)A2ARA (50 μg/kg) on the immune system of macaque Rh. Monkeys after kidney transplantation. Intravenous administration (50 μg/kg) on day 2, 6, and 12 after surgery and every sixth day thereafter.*

graft from rejection, and resumes normal functioning of the kidney transplant. T-helper and T-killer counts during the first two most critical postoperative weeks were reduced by 2–3 times remaining at 30% of a normal value (**Table 6**).
