This study was funded by Cidara Therapeutics.

PK/PD Target Characterization of the Novel Echinocandin CD101 Against Candida spp. in a Neutropenic Mouse Model of Disseminated CandidiasisA. J. Lepak,1 M. Zhao,1 B. VanScoy,2 T. Sandison,3* P. G. Ambrose,2 D. R. Andes1

1University of Wisconsin School of Medicine and Public Health, Madison, WI, 2Institute for Clinical Pharmacodynamics, Schenectady, NY, 3Cidara Therapeutics, San Diego, CA*Contact information: Taylor Sandison, MD | Phone: 858-249-7429 | Email: tsandison@cidara.com

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• CD101 is a novel echinocandin with extended half-life that supports once-weekly dosing in humans. CD101 has in vitro antifungal activity similar to other echinocandins against Candida spp.

• Objectives: to characterize the in vivo efficacy of CD101 against Candida albicans and Candida glabrata using a neutropenic murine disseminated candidiasis model.– Specifically, pharmacokinetic (PK)/pharmacodynamic (PD) targets were examined

to provide framework for further development of clinical dosing regimens, optimize therapy, and assist in establishment of preliminary susceptibility breakpoints.

METHODS

BACKGROUND

Strains and susceptibility testing: All isolates were tested in accordance with CLSI methodology. MICs (mg/L) were performed on 3 separate occasions in duplicate.

PK studies and analysis: Single-dose plasma PK analysis was performed by the sponsor following CD101 at 1, 4, 16, and 64 mg/kg IP. Plasma samples were collected (3 mice/time point); drug concentration measurements were performed by LC-MS/MS. A non-compartmental model was used for PK analysis. Mouse protein binding determined for a range of concentrations (7-60 mg/L) was 99.2%.

Murine disseminated candidiasis model: 6-week–old, specific pathogen–free, female ICR/Swiss mice weighing 23-27 g were used. Mice were rendered neutropenic by cyclophosphamide injection on days -4, -1, +2 and +4 to ensure neutropenia throughout the 7-d (168-h) experiment. Organisms were sub-cultured on sabouraud dextrose agar 24 h prior to infection. Disseminated infection was produced by injection of the inoculum (6.28 � 0.12 log10 CFU/ml) via the lateral tail vein 2 h prior to the start of therapy. At the end of the study, mice were euthanized and organism burden was determined by CFU counts of aseptically harvested kidneys (expressed as the mean � SD log10 CFU/kidneys).

Treatment efficacy – PD target determination: In vivo treatment studies were performed with all isolates. Four-fold increasing dosing regimens (range 0.25 to 64 mg/kg) of CD101 were administered IP (3 neutropenic infected mice/dose level). Due to enhanced effect against a single isolate, additional studies at 0.0156 and 0.0625 mg/kg were examined for C. glabrata 5592. Drug was administered once and mice monitored for 7 d before euthanization to determine fungal burden. The correlation between efficacy and the PK/PD parameter AUC/MIC was determined by nonlinear least-squares multivariate regression. AUC/MIC was chosen based on previous studies demonstrating this index to be predictive for echinocandins. The mathematical model used was derived from the Hill equation. The coefficient of determination (R2) was used to estimate the variance that might be due to regression with AUC/MIC. The dose required to produce net static effect (static dose) and 1 log10 kill (1 log kill dose) compared to the start of therapy was calculated for each drug/organism combination. The associated 24-h total and free drug AUC/MIC targets were calculated.

RESULTS

CONCLUSIONS• CD101 showed in vitro potency and in vivo efficacy against a diverse group of

C. albicans and C. glabrata over 7 days in neutropenic murine disseminated candidiasis.

• AUC/MIC was a robust predictor of treatment outcome, as for other echinocandins.• CD101 exposure-response curves were steep with C. albicans. Stasis 24-h free

drug AUC/MIC target for C. albicans was 2 – 5.3; whereas 1 log kill range was <2-fold higher (3.1 – 6.9). These are similar to other echinocandins in this model.

• CD101 demonstrated marked efficacy against C. glabrata, including an echinocandin-resistant strain, 10956 (Fks2 HS1 F659V). Stasis 24-h free drug AUC/MIC target for C. glabrata was 0.05 – 0.5; whereas 1 log kill range was 0.4 – 1.2. These values are significantly lower, by ≥10-fold, versus other echinocandins in this model.

• CD101 is a promising addition to the antifungal armory, warranting further clinical development for use in patients with candidemia and invasive candidiasis.

Fig 2. Each point = mean fungal burden (3 mice); dashed line = fungal burden at start oftherapy; above line = net growth; below line = net cidal activity. Emax, ED50, slope (N), andR2 are shown in figures at the bottom.

C. albicans C. glabrata

Net stasis (static dose) 1 log killDose,mg/kg

Total drug AUC0-168h /MIC

Free drug AUC0-168h /MIC

24-h avgfree drug AUC/MIC

Dose, mg/kg

Total drug AUC0-168h /MIC

Free drug AUC0-168h /MIC

24-h avgfree drug AUC/MIC

C. albicansK-1 2.52 3197.16 25.58 3.65 5.26 6005.95 48.05 6.86580 1.20 1769.30 14.15 2.02 2.03 2667.21 21.34 3.0598-17 1.34 1918.43 15.35 2.19 2.73 3433.40 27.47 3.9298-210 1.06 3241.65 25.93 3.70 2.28 5875.95 47.01 6.72Mean 1.53 2531.64 20.25 2.89 3.08 4495.63 35.97 5.14Median 1.27 2557.79 20.46 2.92 2.51 4654.68 37.24 5.32St Dev 0.67 796.71 6.37 0.91 1.49 1698.80 13.59 1.94

C. glabrata10956 6.29 418.68 3.35 0.48 17.25 1052.22 8.42 1.205592 0.06 43.16 0.35 0.05 0.43 317.50 2.54 0.3635315 0.34 62.50 0.50 0.07 2.39 367.06 2.94 0.42Mean 2.23 174.78 1.40 0.20 6.69 578.93 4.63 0.66Median 0.34 62.50 0.50 0.07 2.39 367.06 2.94 0.42St Dev 3.52 211.44 1.69 0.24 9.20 410.63 3.29 0.47

RESULTS (cont'd)

C. albicans CD101 MIC Growth in controlsa

K-1 0.06 3.30580 0.06 3.1098-17 0.06 2.9698-210 0.03 3.63

C. glabrata CD101 MIC Growth in controlsa

10956 1 2.185592 0.125 2.0735315 0.5 2.62

ain untreated controls (log10 CFU)

Table 1. Select strains used in study and in vitro susceptibility results (MIC, mg/L).

Fig 1. Plasma PK and select PK parameters, including AUC0-∞, Cmax, and elimination half-life (T1/2) are shown. AUC0-∞ was linear across the dose range (R2=0.999).

Dose-Response Curves

Total and free drug AUC0-168 h/MIC

24-h Average free drug AUC/MIC

Table 2. AUC/MIC targets for entire treatment period (168 h) and 24-h average AUC.