PHARMACODYNAMICS OF TAXOL IN HUMAN HEAD AND NECK TUMORS

The pharmacodynamics of taxol in human head and neck squamous cell car cinoma mere studied using histocultures of surgical specimens from pat ients (n = 22). Tumors were treated with taxol for 24 h, The inhibitio n of DNA synthesis was determined by 48 h cumulative bromodeoxyuridine (BrdUrd) incorporation. The induction of apoptosis was measured by mo rphological changes, in situ DNA end labeling, post-exonuclease III-Br dUrd labeling, and DNA fragmentation. Inhibition of the BrdUrd labelin g index (LI) by taxol was incomplete, with 11 tumors showing a maximal inhibition (E(max)) of 30-50% and the remaining 11 tumors showing an E(max) of 50-80%. For both groups, the inhibition approached maximum v alues at 1 mu M taxol concentration; an additional 10-fold increase in drug concentrations did not significantly enhance the inhibition, The taxol concentrations required for a 30% inhibition (IC30) were 4.2 an d 0.3 mu M for the first and second groups, respectively. The IC30 cor related with the E(max) (r(2) = 0.39; P < 0.001). Taxol induced apopto sis in all tumors; 11 tumors shelved a maximal fraction of apoptotic t umor cells between 3 and 10% and 11 tumors between 13 and 28%, whereas untreated controls showed a maximal apoptotic index of <1%. For indiv idual tumors, the maximal apoptotic index occurred between 0.1 and 3 m u M, and correlated with the BrdUrd LI for the untreated control (r(2) = 0.37; P < 0.01). It is interesting that >95% of apoptotic cells wer e BrdUrd labeled, whereas not all BrdUrd-labeled cells were apoptotic, To investigate the basis of the variable tumor response to taxol, we determined the expression of multidrug resistance P-glycoprotein (Pgp) , p53, and bcl-2 proteins, using immunohistochemical staining and West ern blot analysis. Eleven (50%), 10 (45%), and 7 (32%) tumors expresse d Pgp, p53, and bcl-2, respectively. Patients with Pgp-positive tumors showed a higher number of affected lymph nodes than those with Pgp-ne gative tumors (P < 0.05). Compared with moderately and well differenti ated tumors, the poorly differentiated tumors expressed p53 and Pgp mo re frequently and showed a lower maximum inhibition of DNA synthesis a nd a higher apoptotic fraction after taxol treatment (P < 0.05 in both cases), Pgp expression correlated differently with taxol-induced inhi bition of DNA synthesis than with apoptosis; Pgp-positive tumors showe d a significantly higher E(max) (63%) and IC30 (4.2 mu M) but also a h igher apoptotic index (17%) than Pgp-negative tumors (E(max), 36%; IC3 0, 0.3 mu M; and apoptotic index, 6%; P < 0.05 for all cases), p53 and bcl-2 expression did not correlate with taxol-induced inhibition of D NA synthesis or apoptosis. The data indicate that taxol acts through a poptosis and inhibition of proliferation in human head and neck cancer . Pgp overexpression appears to protect cells from the antiproliferati ve effect of taxol but correlates with a higher apoptosis.