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In the present study, we screened newly synthesized antiviral aminopyrazoloquinoline derivatives for cytotoxic potential in human normal and breast cancer cell lines using apoptosis as biomarker. These derivatives and the well known antiviral drug, acyclovir, were incubated with the normal (MCF-10A, MCF-12A) and cancer (MCF-7, MDA-MB-231) cell lines at 10, 50 and 100 μM for 72 h at 37°C. Both the parent compounds and their sugar derivatives were found to be differentially cytotoxic in various cell lines. MCF-7 cells were more or less completely resistant to all these compounds while MDA-MB-231 cells were significantly killed by apoptosis. The methoxy derivative of aminopyrazoloquinoline (compound 3) was found to be the most cytotoxic in the normal breast epithelial cell lines (MCF-10A and MCF-12A) and MDA-MB-231 cell lines at 100 μM killing over 90% of the cells with up to 80% apoptosis. Interestingly MCF-7 cells showed only up to 50% killing at 100 μM dose with less than 20% apoptosis. Acyclovir did not cause any cytotoxicity, apoptosis or cell cycle arrest in any of the cells lines at the doses tested. Our results suggest that the newly synthesized antiviral compounds have an associated risk of being cytotoxic compared to the acyclovir.

Newly synthesized phthalazine derivatives including copper and platinum complexes were evaluated for cytotoxicity in human breast cancer cell lines. The cells were incubated with the compounds (100 microM) for 72 h and cytotoxicity, apoptosis and DNA content were measured by flow cytometery. Our results suggest that the parent (H1-2), copper (C1-2)- and platinum (P1-2)-derivatized compounds were relatively more active in inducing apoptosis and cell killing in both human breast cancer cell lines, MDA-MB-231 cells being the more sensitive. Other compounds showed weak or no response towards these parameters except H-5 causing 40% apoptosis in MDA-MB-231 cells. Addition of copper or platinum in the structures generally reduced the apoptotic potential. Possible roles for structure activity relationships are discussed.

This study was conducted to examine the sensitivity of primary skin fibroblasts from Saudi thyroid cancer (TC) patients to ultraviolet (UV) irradiation. Cell survival was studied by a colony forming assay and DNA repair defects with a host cell reactivation (HCR) assay using UV-irradiated Herpes Simplex Virus (HSV). In addition, p53 gene expression was examined in the same TC cells exhibiting enhanced radiosensitivity. Skin fibroblasts from TC patients (n=4) showed significantly enhanced sensitivity to UV radiation. The average UV dose to reduce survival to 37% of the initial survival (D(37)) value (in Jm(-2)) for fibroblasts from TC patients was 4.6 (3.7-5.6) compared to 7.3 (6.3-8.3) for healthy individuals (n=3). UV-sensitive xeroderma pigmentosum (XP) cells, which were used as positive control, were found to be extremely sensitive with a D(37) value of 0.6 Jm(-2). In a host cell reactivation assay, UV-irradiated HSV was tested for its plaque-forming ability (PFA), by plating infected fibroblasts from TC patients (used as host cells) on African Green Monkey (Vero) kidney cells to form plaques. A significant reduction in the PFA of the UV-irradiated virus (about three fold) on TC cells compared to fibroblasts from the healthy subjects was seen, suggesting a DNA-repair deficiency in the primary fibroblasts of the TC patients. Furthermore, no significant accumulation in radiation-induced p53 expression was observed in cells from the TC patients. Our results, based on a relatively small group of subjects, indicate that Saudi TC patients primary fibroblasts (non-cancerous in nature) may be carriers of cancer-susceptible gene(s) arising from defective DNA repair/processing. These results warrant a larger study to investigate the role of UV-induced bulky DNA damage in thyroid cancer susceptibility.

Ataxia-telangiectasia (A-T), is an autosomal recessive disease characterized by neurological and immunological symptoms, radiosensitivity and cancer predisposition. A-T cells exhibit a greatly decreased survival and a reduction in DNA synthesis inhibition as well as p53 induction in response to ionizing radiation. Occasionally, some strains of A-T cells have been reported to manifest a slightly enhanced sensitivity with no consistent observations of a deficiency in either cell cycle control or the repair of DNA damage after treatment with ultraviolet (UV) light. In the present study it is shown that skin fibroblasts from four A-T patients, compared with the control, display enhanced sensitivity to the killing effect of UV-light, moderate radioresistant DNA synthesis, and a reduction in viral recovery in the host cell reactivation (HCR) assay. PCR based analysis indicated that three of these UV-sensitive A-T cell strains bear a large deletion in the ATM gene, and no ATM polypeptide was detected in their cell free extracts. Moreover, it is shown that, in non-replicative conditions, these A-T cells are less efficient than normal cells in repairing the T4 endonuclease V sensitive sites. These results constitute the first clear evidence showing the deficiency of A-T cells in the repair of UV-induced DNA damage, and provide further information on the relationship between cell cycle control and DNA repair in human cells.

Genotoxic agents, including gamma-rays and UV light, induce transient arrest at different phases of the cell cycle. These arrests are required for efficient repair of DNA lesions, and employ several factors, including the product of the tumor suppressor gene p53 that plays a central role in the cellular response to DNA damage. p53 protein has a major function in the gamma-ray-induced cell cycle delay in G(1) phase. However, it remains uncertain as to whether p53 is also involved in the UV-mediated G(1) delay. This report provides evidence that p53 is not involved in UV-induced cellular growth arrest in late G(1) phase. This has been demonstrated in HeLa cells synchronized at the G(1)/S border by aphidicolin, followed by UV exposure. Interestingly, the length of this p53-independent G(1) arrest has been shown to be UV dose-dependent. Similar results were also obtained with other p53-deficient cell lines, including human promyelocytic leukemia HL-60 and mouse p53 knock-out cells. As expected, all of these cell lines were defective in gamma-ray-induced cell growth arrest at late G(1). Moreover, it is shown that in addition to cell cycle arrest, HL-60 cells undergo apoptosis in G(1) phase in response to UV light but not to gamma-rays. Together, these findings indicate that p53- compromised cells have a differential response following exposure to ionizing radiation or UV light.