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IB-367, a Protegrin Peptide with In Vitro and In Vivo Activities against the Microflora Associated with Oral Mucositis

ABSTRACT Although the microflora associated with oral mucositis initiated by cytotoxic therapy is not well characterized, several studies suggest that reduction of the microbial load in the oral cavity has some clinical benefit. The MICs of IB-367, a synthetic protegrin analog, ranged from 0.13 to 64 μg/ml for gram-positive bacteria (Streptococcus mitis, Streptococcus sanguis,Streptococcus salivarius, and Staphylococcus aureus) and from 0.06 to 8 μg/ml for gram-negative species (Klebsiella, Escherichia, andPseudomonas). IB-367 exhibited rapid, microbicidal activity against both log- and stationary-phase cultures of methicillin-resistant Staphylococcus aureus (MRSA) andPseudomonas aeruginosa. At concentrations near the MICs for these two organisms (4 and 2 μg/ml, respectively), IB-367 reduced viability by more than 3 logs in less than 16 min. Similarly, IB-367 effected a 4-log reduction of the endogenous microflora in pooled human saliva within 2 min at 250 μg/ml, a concentration readily attained by local delivery. After nine serial transfers at 0.5× the MIC, the MIC of IB-367 for MRSA and P. aeruginosa increased only two to four times. In a phase I clinical study with healthy volunteers, IB-367 was well tolerated, with no detectable systemic absorption. One hour after treatment with 9 mg of IB-367, the prevalence of gram-negative bacteria and yeast was reduced, and the density of the predominant gram-positive oral flora was decreased 1,000 times. IB-367's properties (speed of killing, breadth of spectrum, and lack of resistance) make the compound a strong candidate for the prophylaxis of oral mucositis. Phase II clinical trials with IB-367 are under way for this indication in immunocompromised subjects.