Fraser L. Baker

CELLULAR RADIOSENSITIVITY OF PRIMARY HEAD AND NECK SQUAMOUS CELL CARCINOMAS AND LOCAL TUMOR CONTROL

The low dose survival parameters of human tumor cell lines have been shown to correlate with the perceived clinical radiosensitivity of different tumor histologic types. This conclusion has been generated from the analysis of a large number of cell lines and has, therefore, served as the basis for attempts to develop predictive assays of tumor radiocurability. In this study, the tumors from 72 patients with head and neck squamous cell carcinoma have been grown in an adhesive tumor cell assay system and their sensitivity to radiation has been measured. All patients in this study were treated with post-operative radiotherapy, the surgical margins were negative, and any patient that had received chemotherapy was excluded. The average S2 (survival at 2.0 Gy) value of the 72 cultures was 0.33, with the values ranging from 0.11 to 0.91. All patients were evaluated for local tumor control. They have been followed for about 1 year and continued follow-up is still in progress. The average survival at 2.0 Gy of cultures derived from the 12 patients that have had recurrences so far is slightly higher (0.40) than that from those who appear so far to have local tumor control (0.30). Although the general trend is that recurrent tumors yield primary cultures that are slightly more resistant, the difference is not statistically significant.

Radiosensitivity of human head and neck squamous cell carcinomas in primary culture and its potential as a predictive assay of tumor radiocurability

The intrinsic radiosensitivity of human tumor cell cultures correlates with the clinical radiosensitivity of several different tumor histologies, as evidenced by analyses of low dose parameters of radiation survival curves generated from a large number of cell lines. Such radiosensitivity has therefore served as a basis of attempts to develop predictive assays of tumor radiocurability. In this study, the tumors from 72 patients with head and neck squamous carcinoma have been grown in an adhesive tumor-cell assay system and radiosensitivity (S2: survival at 2.0 Gy) values have been measured. The characteristics of these cultures, such as growth rate, clonogenicity and growth enhancement by epidermal growth factor, do not correlate with S2. The average S2 value of the 72 cultures is 0.33, which is lower than for cultures derived from melanomas and lung adenocarcinomas. Twenty-six patients followed up for at least 15 months have been evaluated for local tumor control. The average S2 value of the seven patients with recurrences in this group is slightly higher (0.43) than that from the other patients (0.30). There is considerable overlap of S2 values in the two groups, and more patients must be evaluated before the groups can be compared statistically.

Comparison between clinical response and in vitro drug sensitivity of primary human tumors in the adhesive tumor cell culture system.

The newly described adhesive tumor cell culture system (ATCCS) offers a distinct advantage over other assays in that it has a high plating efficiency requiring low cell inoculum, it affords workable assays in approximately 70% of specimens from the heterogenous tumor types, and it has the ability to assay up to nine drugs at four different concentrations. Clinical correlations based on the ATCCS were obtained in 65 patients undergoing 71 clinical trials. Patients with melanoma, lung cancer, and sarcoma dominated the group. The most active in vitro drug was correlated per clinical trial. Thirteen of 17 (76%) sensitive in vitro predictions and 51 of 54 (94%) resistant in vitro predictions were accurate. The assay in this study had a sensitivity of 81% and specificity of 93%. These preliminary results are encouraging and warrant prospective trials to establish the true value of this assay to patients.

Comparison of antitumor activity of standard and investigational drugs at equivalent granulocyte-macrophage colony-forming cell inhibitory concentrations in the adhesive tumor cell culture system: An in vitro method of screening new drugs☆

We compared the in vitro growth inhibition of primary human tumor cells in the adhesive tumor cell culture system (ATCCS), exposed to the investigational agents caracemide, spirogermanium and taxol and to standard chemotherapy agents at equitoxic concentrations for granulocyte-macrophage colony-forming cells (GM-CFC) in vitro. Clinically active standard agents tested at up to GM-CFC 90% inhibitory concentrations (IC90) resulted in in vitro activity (greater than or equal to 50% tumor growth inhibition) in at least 30% of tumors tested. In vitro responses for taxol, caracemide and spirogermanium were 78%, 9% and 7%, respectively. This paper proposes a model that incorporates two hypotheses: (1) myelotoxic drugs which inhibit tumor growth at concentrations equal to or less than equitoxic GM-CFC ICs will demonstrate clinical activity; and (2) both myelotoxic and particular nonmyelotoxic drugs inactive in vitro at these doses will not be active clinically. If this drug screening concept is valid, taxol may be clinically more active than caracemide and spirogermanium.

In vitro activity of amonafide against primary human tumors compared with the activity of standard agents

Amonafide, one of a series of benz[de]-isoquinoline-1,3-dione compounds, is now entering phase II clinical trials in this country. We tested amonafide, exposed continuously for 5 days, at four different concentrations against 56 primary human tumors in vitro. The drug concentration range used was based on amonafides inhibitory activity against human bone marrow cells. The antitumor activity of 5-fluorouracil, mitomycin C, cisplatin, and etoposide against tumors from this panel of 56 was compared with that of amonafide at in vitro concentrations equitoxic against human bone marrow cells. Amonafide was active against only 12% of tumors compared with standard agents, which were active against more than 40% of tumors in the human bone marrow inhibitory range. Our data suggested that amonafide is less likely to be clinically active against human solid tumors than the standard agents.

Activity of 2-fluoro-Ara AMP against gynecologic tumors in the soft agar assay.

SummaryTo characterize in vitro activity of 2-fluoro-Ara AMP and its relation to the activities of cisplatin and doxorubicin, 28 specimens from patients with gynecologic tumors (predominantly ovarian) were tested in a soft agar assay. Twenty-six of 28 (93%) grew when the medium was supplemented with four hormones (epidermal growth factor, hydrocortisone, estradiol-17, and insulin). Normal bone marrow cells were utilized as a biologic control to define in vitro concentrations of the three drugs. Tumors were exposed continuously to three different concentrations of each drug. 2-fluoro-Ara AMP was tested against 26 tumors, cisplatin against 24, and doxorubicin against 14. In vitro sensitivity was defined as ≥ 50% colony inhibition at a drug concentration within the bone marrow inhibitory range. Seven of 26 (27%) tumor specimens were sensitive to 2-fluoro-Ara AMP. Among these, four tumors were derived from previously treated patients. However, in the 2-fluoro-Ara AMP concentration range (0.26 μg/ml to 0.78 μg/ml) tested, five of eight (62.5%) tumors from untreated patients achieved IC50 compared to only seven of 18 (39%) tumors from treated patients. Five of six (83%) specimens demonstrated cross-sensitivity between cisplatin and 2-fluoro-Ara AMP. Seventeen of 18 (94%) specimens demonstrated cross-resistance between cisplatin and 2-fluoro-Ara AMP, and 13 of 13 (100%) specimens demonstrated cross-resistance between 2-fluoro-Ara AMP and doxorubicin. A higher proportion of tumors from previously untreated patients achieved ≥ 50% colony inhibition when exposed to 2-fluoro-Ara-AMP or cisplatin than did those from previously treated patients. Our data suggest that 2-fluoro-Ara AMP has in vitro activity against gynecologic tumors (predominantly ovarian). Tumors from untreated patients were more sensitive than tumors from treated patients. At all concentrations of 2-fluoro-Ara AMP tested, bone marrow cells were more sensitive than the tumor cells suggesting a concerning notion that the clinical efficacy of this agent could be compromised by the myelosuppressive properties of this agent.