Published in Cancer Detection and Prevention 1993; 17(2):347.

In Vitro and In Vivo Studies to Assess the Effectiveness of Differentiating Agents (Retinoids and Carotenoids) in Cancer Chemoprevention

S. Toma, MD, PhD,a R. Palumbo, MD,b E. Albanese, MD,b G. Nicolo, MD,b S. Monteghirfo, MD,b P.E. Mangiante, MD,b S. Bonatti, MD,b G. Mergello, MD,b and R. Cancedda, PhDa

aIstituto di Oncologia Clinica e Sperimentale, Università di Genova; and bIstituto Nazionale per Ia Ricerca sul Cancro, Viale Benedetto XV, 10, 16043, Genova, Italy

I. INTRODUCTION: Toxicity and compliance are the most important problems in plans of chemoprevention therapy because of the need for long-term treatment and the risk/benefit ratio must be carefully evaluated in each patient. In our department, we set up in vitro and in vivo studies to evaluate the role of retinoids and carotenoids in the prevention of oral cancer, as effective agents on cell growth and differentiation. II. IN VITRO RESULTS: As support of clinical application, we devised an in vitro system to investigate the action of various differentiating agents on both primary and stabilized cultures. Human keratinocytes, obtained from biopsies of healthy and preneoplastic oral mucosa, and human cell lines from oral cavity tumors (KB; SCC-25) were treated with β-carotene (10 mM). The colony forming efficiency (CEE), the proliferation rate, and the frequency of micronucleated cells were measured. CEE was significantly reduced (p <0.05) by β-carotene treatment in cells from healthy mucosa and in KB cells and decreased in cells from pathological mucosa and in SCC-25 cells. Finally, the frequency of micronucleated cells was significantly decreased (p <0.05) in cultures from oral mucosa, both healthy and pathologic. Our results indicate that β-carotene is able to reduce the clonogenic activity (CFE), and it also displays a protective effect on genotoxic damage. III. IN VIVO RESULTS (a) Study: A phase II study on patients (pts) with oral leukoplakia and treated with 13-carotene (90 mg/day) for 6 months was started. Of the 23 pts entered (10 male and 13 female, aged between 17 and 85), 18 were evaluated. Eight objective responses (6 complete, 2 partial) were obtained (44.4%). Four CR and one PR appeared unexpectedly within 2 to 7 months after the end of therapy. No significant toxicity was detected in any of the pts. We want to stress the need to investigate both the use of higher doses of the drug and on the extension of the post-therapeutic follow-up; in fact, we do not know whether the responses obtained after treatment are due to therapy or to a spontaneous regression, which in the oral cavity is not unusual. IN VIVO RESULTS (B) Treatment: We treated 16 leukoplakia-affected pts using incremental doses of 13-cis-retinoic acid. The initial dose, given for 3 months, was 0.2 mg/kg/day, increased by a further 0.2 mg/kg/day in each one of the following 3-month cycles. The maximum dosage reached was 1.0 mg/kg/day. Ten pts completed the cycle of 0.8 mg/kg/day (12 months' treatment in total), but did not continue due to toxicity, which was cutaneous and hematologic. The toxicity was found to be reversible in all cases. Of the 14 evaluable pts, 4 were PR (3 obtained at 0.2 mg/kg/day and 1 at 0.6 mg/kg/day), and I was CR at 0.4 mg/kg/day. This study shows that 13-cis-retinoic acid at low dosages is effective, and that it is not feasible to treat these pts at doses above 0.8 mg/kg/day, due to the difficulties of compliance rather than to toxicity. IV. CONCLUSIONS: We believe that an experimental model, allowing growth and reproduction of the pathological epithelium of each patient, could be an effective system to assess the efficacy of several differentiating agents in single patients, to identify a specific treatment.

KEY WORDS: retinoids, beta-carotene, cell cultures, chemoprevention, oral leukoplakia .