Rapid evaluation in whole blood culture of regimens for XDR-TB containing PNU-100480 (sutezolid), TMC207, PA-824, SQ109, and pyrazinamide

Abstract

There presently is no rapid method to assess the bactericidal activity of new regimens for tuberculosis. This study examined PNU-100480, TMC207, PA-824, SQ109, and pyrazinamide, singly and in various combinations, against intracellular M. tuberculosis, using whole blood culture (WBA). The addition of 1,25-dihydroxy vitamin D facilitated detection of the activity of TMC207 in the 3-day cultures. Pyrazinamide failed to show significant activity against a PZA-resistant strain (M. bovis BCG), and was not further considered. Low, mid, and high therapeutic concentrations of each remaining drug were tested individually and in a paired checkerboard fashion. Observed bactericidal activity was compared to that predicted by the sum of the effects of individual drugs. Combinations of PNU-100480, TMC207, and SQ109 were fully additive, whereas those including PA-824 were less than additive or antagonistic. The cumulative activities of 2, 3, and 4 drug combinations were predicted based on the observed concentration-activity relationship, published pharmacokinetic data, and, for PNU-100480, published WBA data after oral dosing. The most active regimens, including PNU-100480, TMC207, and SQ109, were predicted to have cumulative activity comparable to standard TB therapy. Further testing of regimens including these compounds is warranted. Measurement of whole blood bactericidal activity can accelerate the development of novel TB regimens.

Figure 1. Effects of substituting regression analysis for point-to-point interpolation in calculating Δ log CFU from time to positivity (TTP) in mycobacterial growth indicator tubes (MGIT).

The left panel indicates the accuracy of curve fitting (the relationship between observed and predicted values). The right panel compares the results of the two methods (regression vs. interpolation).

Figure 2. Bactericidal activities of 2 and 3-drug combinations against intracellular M. tuberculosis in whole blood culture.

Negative values in these blocks indicate killing. A color gradient has been applied to indicate green as bacterial growth, and red as death. The difference from sum was determined by subtracting the activity predicted as the sum of both compounds tested individually from that observed when tested in combination. Positive values here indicate combinations less active than predicted. TMC207 and SQ109 showed additive activity when combined with PNU-100480. Combinations of PA-824 with either PNU-100480 or TMC207, or as a 3-drug combination, were less than additive.

Figure 3. Process for calculating cumulative whole blood bactericidal activity (WBA) of drug combinations.

Figure 4. Predicted whole blood bactericidal activity of TMC207 (J, bedaquiline) 400 mg QD and 200 mg TIW, and PNU-100480 (U, sutezolid) 600 mg BID, singly and together.