Table 1.

Suppression of MT dynamic instability in MCF7 cells incubated with maytansine, S-methyl DM1, B38.1-SMCC-DM1, and B38.1-SPP-DM1

A. Suppression of MT dynamic instability in MCF7 cells by maytansine and S-methyl DM1 after 5-h incubation with cell cycle 1 × IC50 concentrations
MT dynamic instability parametersControlS-methyl DM1 (340 pmol/L)% changeMaytansine (310 pmol/L)% Change
Growth rate, μm/min12.9 ± 1.09.9 ± 1.2**−226.9 ± 0.5**−45
Shortening rate, μm/min20.0 ± 2.314.3 ± 1.6**−2812.5 ± 1.3**−37
% Time spent growing5127−4730−41
% Time spent shortening2614−4511−58
% Time spent attenuated235915759158
Catastrophe frequency, no./MT/min2.5 ± 0.31.6 ± 0.2 *−361.0 ± 0.1**−61
Rescue frequency, no./MT/min6.6 ± 0.511.0 ± 0.7**687.8 ± 0.619
Growth distance, no./MT/μm0.36 ± 0.060.77 ± 0.201130.49 ± 0.0735
Shortening distance, no./MT/μm0.35 ± 0.041.11 ± 0.11**2130.83 ± 0.10**136
Dynamicity12.0 ± 0.65.0 ± 0.6**−584.3 ± 0.3**−65
Nondynamic MT5%45%48%
B. Time dependence for suppression of MT dynamic instability in MCF7 cells by 10 nmol/L B38.1-SMCC-DM1
MT dynamic instability parametersControl5 h% Change10 h% Change24 h% Change
Growth rate, μm/min12.9 ± 1.011.4 ± 1.2−1011.7 ± 1.6−86.95 ± 0.5**−45
Shortening rate, μm/min20.0 ± 2.313.6 ± 1.2**−3113.7 ± 2.4**−3111.0 ± 1.0**−45
% Time spent growing5143−1639−2417−67
% Time spent shortening2615−419−657−74
% Time spent attenuated2342835213076235
Catastrophe frequency, no./MT/min2.5 ± 0.31.3 ± 0.1**−481.1 ± 0.2**−551.2 ± 0.1**−50
Rescue frequency, no./MT/min6.6 ± 0.58.1 ± 0.52310.4 ± 1.0**5810.6 ± 0.9**62
Growth distance, no./MT/μm0.36 ± 0.060.40 ± 0.06110.39 ± 0.0871.00 ± 0.14**173
Shortening distance, no./MT/μm0.35 ± 0.040.69 ± 0.06**951.03 ± 0.2**1921.17 ± 0.14**232
Dynamicity12.0 ± 0.67.5 ± 0.6**−375.9 ± 0.9**−513.0 ± 0.3**−75
Nondynamic MT5%6%17%44%
C. Time dependence for suppression of MT dynamic instability in MCF7 cells by 10 nmol/L B38.1-SPP-DM1
MT dynamic instability parametersControl5 h% Change10 h% Change24 h% Change
Growth rate, μm/min12.9 ± 1.010.5 ± 0.7**−179.9 ± 0.8**−226.4 ± 0.6**−50
Shortening rate, μm/min20.0 ± 2.314.4 ± 1.3**−2812.3 ± 1.4**−387.8 ± 1.0**−61
% Time spent growing5131−3926−5024−52
% Time spent shortening2621−2111−565−82
% Time spent attenuated23481116317671211
Catastrophe frequency, no./MT/min2.5 ± 0.31.9 ± 0.1*−251.2 ± 0.1**−510.6 ± 0.1**−75
Rescue frequency, no./MT/min6.6 ± 0.57.1 ± 0.599.6 ± 0.7**4610.9 ± 1.2*67
Growth distance, no./MT/μm0.36 ± 0.060.66 ± 0.09*790.75 ± 0.10**1040.95 ± 0.35160
Shortening distance, no./MT/μm0.35 ± 0.040.63 ± 0.06**791.08 ± 0.10**2071.70 ± 0.26**382
Dynamicity12.0 ± 0.66.49 ± 0.5**−464.2 ± 0.4**−652.1 ± 0.3**−83
Nondynamic MT5%20%42%38%

NOTE: For A, cells were incubated for 5 h with maytansine or S-methyl DM1 at G2-M arrest 1 × IC50 concentrations (310 and 340 pmol/L, respectively) before time-lapse microscopy. For B38.1-SMCC-DM1 (B) and B38.1-SPP-DM1 (C), cells were incubated with 10 nmol/L of AMC for the indicated periods of time before time-lapse microscopy. Results presented are average values ± SEM as well as the corresponding percentage of change from control. Values with ** are significantly different from control at ≥99% confidence interval, and values with * are significantly different from control at ≥95% confidence interval by Student's t test. Values for percentage of time spent in growth, shortening, and attenuation were calculated for the entire population of microtubules and, thus, the confidence intervals for these parameters cannot be computed.

Abbreviation: MT, microtubule.