Modulation of proliferation kinetics in human squamous cell carcinomas of the head and neck

Cell, tissue and organ culture as in vitro models to study the biology of squamous cell carcinomas of the head and neck

In vitro models are currently being used to study head and neck squamous cell carcinoma (HNSCC). Several hundred HNSCC cell lines have been established by various investigators and used to study a broad spectrum of questions related to head and neck cancer. The head and neck model with respect to multistage carcinogenesis is now complete. Several techniques exist for the culture of normal epithelial cells from the upper aerodigestive tract (UADT). The biology of these UADT cells (oral cavity, oropharynx, hypopharynx and larynx) is being studied. Successful culture of premalignant lesions (dysplastic mucosa, leukoplakia, erythroplakia) has resulted in establishment of a limited number of premalignant cell lines and cell cultures. HPV infection of normal oral epithelial cells for immortalization (approximately premalignant cells) coupled with transformation with carcinogens (malignant cells) has established an experimental model for progression. Two in vivo models for oral carcinogenesis, the 7,12 dimethylbenz(a)anthracene-induced hamster cheek pouch model and the 4-nitroquinoline-N-oxide rat oral model, have been established in culture. Thus, multistage carcinogenesis models have been established from both human tissues and animal models and include cultures of normal, premalignant and malignant cells. Culture techniques for growing dissociated primary tumor cells for short term experimental analysis are being used. The culture of normal or tumor tissue as organ/explant cultures allows for the maintenance of normal cell-cell and cell-matrix interaction, but limits experimentation since these cultures cannot be propagated. Several three dimensional model systems are being used to obtain this histological complexity but allow for experimentation. The ability to culture normal, premalignant and malignant cells coupled with the use of a variety of culture techniques, should allow for the continued growth and experimentation in head and neck cancer research.

DNA ploidy in nonmelanoma skin cancer

BACKGROUND

Patients with head and neck squamous cell carcinoma die of locoregional recurrence and those with basal cell carcinoma suffer cosmetic and functional changes from its treatment. Prognostic factors are based upon tumor characteristics and host factors. Flow cytometry can assist with prognostic characterization of nonmelanoma skin cancer.

METHODS

Specimens from 40 sequential patients with head and neck nonmelanoma skin cancers were prospectively obtained at the time of surgery. The patients were followed for four years for local recurrence and metastasis to regional lymph nodes. Samples were prepared from frozen specimens using a modification of the Vindelov procedure.

RESULTS

DNA aneuploidy or tetraploidy and histology of well differentiated squamous cell carcinoma were significantly associated with metastasis to regional lymph nodes. Direct extension of tumor below the adipose tissue was associated with an S-phase greater than 4.1 and a proliferative fraction greater than 5.5. No tumors recurred at the site of surgical resection.

CONCLUSIONS

The measurement of DNA ploidy of well differentiated squamous cell carcinoma, and proliferative capacity or S-phase of both basal cell and squamous cell carcinomas assists in predicting the biologic proclivity for locoregional invasion or metastasis of nonmelanoma skin cancer. Identification of aggressive tumors at the time of surgery may offer the opportunity for prevention of lethal metastasis by using adjunctive therapy.

Slowing proliferation in head and neck tumors: in vitro growth inhibitory effects of the polyamine analog BE-4-4-4-4 in human squamous cell carcinomas

PURPOSE

These preclinical studies were carried out to examine the potential of the antiproliferative polyamine analog 1,19-bis-(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) to serve as a therapy adjuvant to radiation for patients with rapidly dividing tumors of the head and neck (H&N).

METHODS AND MATERIALS

Cytostatic and cytotoxic effects of this polyamine analog were investigated in three squamous cell carcinoma (SCC) cell lines derived from human H&N tumors.

RESULTS

Growth inhibition was achieved in all cell lines within 3-4 days of continuous 10 microM drug exposure, and inhibition of cell cycle proliferation kinetics was confirmed via flow cytometry. Cytotoxicity was pronounced (3-4 log cell kill) in the SCC-38 and SCC-4Y cell lines with continuous 10 microM analog exposure over 5 days, and was minimal in the SCC-13Y cell line. No demonstrable effect of BE-4-4-4-4 on single dose radiation survival was identified in any SCC cell line. Ornithine decarboxylase (ODC) activity was rapidly inhibited (1-2 h) following 10 microM BE-4-4-4-4 exposure in all SCC cell lines (approximately 90%), whereas identical exposure to 10 microM difluoromethylornithine (DFMO) induced animal ODC inhibition (approximately 10%). Dose-dependent depletion of endogenous polyamines (putrescine, spermidine, spermine) was achieved in all SCC cell lines following 1 microM and 10 microM BE-4-4-4-4 exposures. Difluoromethylornithine was significantly less potent than BE-4-4-4-4 in its capacity to deplete endogenous polyamines, with no measureable depletion of spermine pools even with 5 mM x 48 h DFMO exposures.

CONCLUSIONS

These data evaluate cytostatic and cytotoxic properties of the polyamine analog BE-4-4-4-4 in human SCCs, and suggest a role for investigation of such agents as an adjuvant to radiation in the therapeutic approach to rapidly dividing human tumors such as those that occur in the H&N.

Combining polyamine depletion with radiation therapy for rapidly dividing head and neck tumors: strategies for improved locoregional control

PURPOSE

Locoregional control is adversely affected as clonogens from rapidly proliferating tumors repopulate during a course of radiation therapy. The cytostatic agent alpha-difluoromethylornithine (DFMO) was investigated for its capacity to slow proliferation kinetics in human squamous cell carcinomas (SCC) of the head and neck (H&N), with the ultimate objective of improving locoregional control in rapidly dividing tumors treated with radiation therapy.

METHODS AND MATERIALS

Three human SCC cell lines established from primary H&N tumors were evaluated in vitro (cell culture) and in vivo (SCC tumor xenografts in athymic mice) for the capacity of DFMO to induce growth inhibition. Flow cytometry analysis of SCC tumor growth kinetics and quantitative assessment of polyamine biosynthesis inhibition was performed to verify DFMO activity. DFMO effects on in vitro SCC radiosensitivity using clonogenic survival were also studied.

RESULTS

A noncytotoxic exposure to DFMO (5mM x 72 hours) induced pronounced growth inhibition in all three SCC cell lines (70-90% at 7 days), and induced a 2-3 fold delay in volume doubling time for SCC tumor xenografts when administered orally in the drinking water (1.5%) to athymic mice. Kinetic analysis via flow cytometry confirmed that DFMO produced a lengthening of SCC cell cycle times, but did not alter in vitro radiosensitivity. Inhibition of ornithine decarboxylase (ODC) activity and depletion of endogenous polyamines (putrescine and spermidine), were confirmed in normal tissue (mouse skin) and in human SCC tumor xenografts of athymic mice receiving continuous oral DFMO.

CONCLUSION

These data indicate that antiproliferative agents, such as DFMO, are capable of altering human SCC growth kinetics without altering intrinsic radiosensitivity. Such kinetic modulation may therefore provide a strategy to reduce the adverse impact of tumor cell proliferation during a radiotherapy treatment course for rapidly dividing tumors such as those in the H&N.

New approaches to cell kinetics in human tumors

Both clinical and laboratory evidence indicate that local control rates for many experimental and clinical human tumors decrease with protraction of the overall duration of radiation therapy. A likely basis for this is tumor cell repopulation during treatment. Such observations have stimulated interest in tumor kinetics, and a number of techniques have evolved to increase the potential for meaningful clinical study of the proliferative behavior of tumors. This review discusses the clinical and experimental evidence for proliferation during treatment, describes two potential approaches--accelerated fractionation and inhibition of proliferation--that could be employed in attempting to overcome such intratreatment proliferation, explores both past and newer, evolving methods available for measuring tumor cytokinetics, and discusses how such kinetic information could be used in the future to tailor therapy to a tumor's individual characteristics.