Background/Objectives: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) greatly complicates the treatment of skin and soft tissue infections (SSTI). It was previously found that subcutaneous (SQ) treatment with the mononuclear phagocyte (MP)-selective activator complement peptide-derived immunostimulant-02 (CPDI-02; formerly EP67) increases prophylaxis of outbred CD-1 mice against SQ infection with CA-MRSA. Here, we determined if treatment with CPDI-02 also increases curative protection. Methods: Female CD-1 mice were challenged SQ with CA-MRSA USA300 LAC, then CPDI-02 or inactive scCPDI-02 was administered by a topical, SQ, IM, or IV route at 6 or 24 h post-challenge. Abscess sizes were compared over 10 days and CA-MRSA burden, neutrophils, MP, and pro-inflammatory cytokines were compared in subcutaneous abscesses. CPDI-02 PK and distribution in female CD-1 mice were compared after IM or IV dosing and CPDI-02 toxicity in male and female CD-1 mice was determined by IM dose escalation and repeat IM dosing. Results: Repeat IM treatment starting at 6 h post-challenge decreased maximum abscess surface area, CA-MRSA burden, and time to resolution, whereas repeat treatment by a topical, SQ, or IV route had no effect. Repeat treatment starting at 24 h post-challenge was ineffective by the current routes. Single IM treatment starting at 6 h post-challenge was as effective as repeat IM treatment, increased systemic exposure to CPDI-02, and, in subcutaneous abscesses, initially decreased IL-1β and increased MP. CPDI-02 was tolerated between 130 and 170 mg/kg after IM dose escalation and between 65 and 130 mg/kg after repeat IM dosing with males being more tolerant. Conclusions: Single early-stage IM treatment with CPDI-02 may increase curative protection against SSTI caused by CA-MRSA and/or other pathogens controlled by activated MP.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) greatly complicates treatment of skin and soft tissue infections (SSTI). It was previously found that subcutaneous (SQ) treatment with the mononuclear phagocyte (MP)-selective activator, complement peptide-derived immunostimulant-02 (CPDI-02; formerly EP67), increases prophylaxis of outbred CD-1 mice against SQ infection with CA-MRSA. Here, we determined if treatment with CPDI-02 also increases curative protection. Methods: Female CD-1 mice were challenged SQ with CA-MRSA USA300 LAC then CPDI-02 or inactive scCPDI-02 was administered by a topical, SQ, IM, or IV route at 6- or 24-hrs post-challenge. Dermal abscess sizes were compared over 10 days and CA-MRSA burden, neutrophils, MP, and pro-inflammatory cytokines were compared in dermal abscesses. CPDI-02 PK and distribution in female CD-1 mice were compared after IM or IV dosing and CPDI-02 toxicity in male and female CD-1 mice was determined by IM dose escalation and repeat IM dosing. Results: Repeat IM treatment starting at 6-hrs post-challenge decreased maximum abscess surface area, CA-MRSA burden, and time to resolution, whereas repeat treatment by a topical, SQ, or IV route had no effect. Repeat treatment starting at 24-hrs post-challenge was ineffective by the current routes. Single IM treatment starting at 6-hrs post-challenge was as effective as repeat IM treatment, increased systemic exposure to CPDI-02, and, in dermal abscesses, initially decreased IL-1β and increased MP. CPDI-02 was tolerated to between 130-170 mg/kg after IM dose escalation and between 65-130 mg/kg after repeat IM dosing with males being more tolerant. Conclusions: Single early-stage IM treatment with CPDI-02 may increase curative protection against SSTI caused by CA-MRSA and/or other pathogens controlled by activated MP.

Encapsulating protein subunit vaccines in biodegradable microparticles (MP) can increase induction of long-term protective mucosal and systemic antibodies after respiratory administration but requires incorporation of a mucosal immunostimulant. We previously found that incorporating complement peptide-derived immunostimulant-02 (CPDI-02) with MP-encapsulated LPS-free OVA through surface modification of the same ~1 µm PLGA 50:50 MP greatly increases mucosal and systemic OVA-specific antibodies in young, naïve female C57BL/6 mice at 14 and 90 days post-intranasal administration. Here, we directly compared effects of incorporating CPDI-02 or inactive scCPDI-02 with MP-encapsulated LPS-free OVA by separate encapsulation (SE), co-encapsulation (CE), or surface modification (SM) on induction of OVA-specific IgA, IgM, and IgG antibody secreting cells (ASCs) in the lungs and spleen, IgA antibodies in nasal lavage fluid, IgA and IgG antibodies in bronchoalveolar lavage fluid, and IgG subclasses in the serum at 14 days post-intranasal administration. We found that SE incorporation induced greater or similar levels of mucosal and systemic OVA-specific ASCs and mucosal IgA and IgG titers but greater titers of systemic IgG subclasses than CE or SM incorporation versus inactive scCPDI-02. Thus, given that surface modification with CPDI-02 induces high titers of OVA-specific systemic and mucosal antibodies at 14 and 90 days post-intranasal immunization under the same experimental conditions, separate encapsulation of CPDI-02 is expected to more broadly induce long-term mucosal and systemic antibodies against MP-encapsulated protein vaccines than co-encapsulation and surface modification after intranasal and possibly other routes of mucosal immunization.