Exth-05. toward 100% clinical efficacy for tumor-treating fields

Abstract In vitro and in animal models of various tumor cell types, empirical data suggest tumor-treating fields (TTFields) can attain 100% efficacy, with two pre-conditions: 1) Delivering sufficient electric field strength to the target tumor cells, and 2) Changing the direction of the imposed electric field such that intra-cellular structures at any angle with respect to the field see the required efficacious field strength. Requirement #2 reflects empirical findings as well as prevailing theories of TTFields’ mechanism of action, which center on mitosis disruption via energy imparted to polarizable intracellular structures aligned with the field. We tried various trial curve-fits to TTFields empirical dose-response curves. Quadratic formulae yield a close fit, resembling well-known radiotherapy linear-quadratic (LQ) curves and suggesting a connection between the mechanisms of the two treatment modalities: F98 (rat glioma): -16.3271x2 - 0.664019x+100 (R2=0.9995); MDA-MB-231 (human breast cancer): -9.64922x2 + 2.96348x + 100 (R2=0.9999); H1299 (human non-small cell lung carcinoma): -12.0515x2 - 1.58272x + 100 (R2=0.9993); B16 (mouse melanoma): -83.8066x2 + 47.4537x + 100 (R2=0.9954). We extrapolate these fits to predict the approximate required field strength seen at the target cells for 100% efficacy: F98: 2.45 V/cm; MDA-MB-231: 3.4 V/cm; H1299: 2.8 V/cm; B16: 1.4 V/cm. Alternatively, the LQ fits may not reflect the extrapolated high amplitude range for which data is lacking. Under two assumptions, 1) intracellular structures are randomly oriented in vivo, and 2) only two changes of TTFields direction are used, as is the current clinical practice, then extrapolating the dose-response curves predicts that infinite field strength is required for 100% efficacy, since some intracellular structures must be oriented at 90 degrees to the imposed field and the cosine of 90 degrees is zero. Adding a third TTFields direction, not necessarily orthogonal to the plane of the other two directions, can solve this problem.