$$216m^4n^4 \cdot (-\frac{1}{6} m^2n)^3 = 216m^4n^4 \cdot (-\frac{1}{6})^3 (m^2)^3 n^3 = 216m^4n^4 \cdot (-\frac{1}{216}) m^6 n^3 = -\frac{216}{216} m^{4+6} n^{4+3} = -m^{10}n^7$$
Ответ: $$-m^{10}n^7$$