Immunopotentiating activities of a low molecular weight lipopeptide, RP 56 142--studies in infectious models.

RP 56 142, N2-[N-(N-lauroyl-L-alanyl)-gamma-D glutamyl] L,L-2,6-diaminopimelamic acid belongs to a family of immunomodulating lipopeptides. Its structure is directly derived from that of lauroyltetrapeptide RP 40 639 which is a mixture of two stereoisomers, one of which (with D,D-2,6 diaminopimelamic acid) is totally devoid of in vivo activity. RP 56 142 displayed potent protective activities against bacterial infections such as K. pneumoniae, L. monocytogenes or S. typhimurium (at doses ranging between 0.03 and 100 mg/kg s.c., i.p., i.v.). In combined treatment protocols, suboptimal doses of RP 56 142 given preventively (day-1) or curatively (day 0 + 4h) significantly protected mice receiving antibiotics at doses which were ineffective when administered by themselves. Given s.c. 1 or 2 days before infectious challenge, RP 56 142 was able to normalize and even enhance significantly the resistance of mice previously immunocompromised by lomustine, 5-fluorouracile or hydrocortisone. These results correlated with the stimulation of the clearance of a virulent Salmonella typhimurium strain and with an important production of colony-stimulating factor in RP 56 142-treated mice.