Platinum drugs are among the most effective anticancer agents, but their mode of action is still not fully understood. We therefore carried out a systematic investigation on the cellular activities of cisplatin, carboplatin and oxaliplatin in A498 kidney cancer cells. Cytotoxicity was higher for cisplatin and oxaliplatin compared to carboplatin, with induction of apoptosis as the preferred mode of cell death. Gene expression profiling displayed modulation of genes related to DNA damage response/repair, cell cycle regulation and apoptosis which was more pronounced upon oxaliplatin treatment. Furthermore, repression of specific DNA repair genes was restricted to oxaliplatin. Transcriptional level observations were further analyzed on the functional level. Uptake studies revealed low intracellular platinum accumulation and DNA platination upon carboplatin treatment. Removal of overall DNA platination was comparable for the three drugs. However, no processing of oxaliplatin-induced interstrand crosslinks was observed. Cisplatin and carboplatin influenced cell cycle distribution comparably, while oxaliplatin had no effect. Altogether, we found a similar mode of action for cisplatin and carboplatin, while the activity of oxaliplatin appeared to differ. This might be clinically relevant as due to the difference in mode of action oxaliplatin could be active in tumors which show resistance towards cisplatin and carboplatin.

Cisplatin is one of the most commonly used drugs for the treatment of various solid neoplasms, including testicular, lung, ovarian, head and neck, and bladder cancers. Unfortunately, the therapeutic efficacy of cisplatin against colorectal cancer is poor. Various mechanisms appear to contribute to cisplatin resistance in cancer cells, including reduced drug accumulation, enhanced drug detoxification, modulation of DNA repair mechanisms, and finally alterations in cisplatin DNA damage signaling preventing apoptosis in cancer cells. Regarding colorectal cancer, defects in mismatch repair and altered p53-mediated DNA damage signaling are the main factors controlling the resistance phenotype. In particular, p53 inactivation appears to be associated with chemoresistance and poor prognosis. To overcome resistance in cancers, several strategies can be envisaged. Improved cisplatin analogues, which retain activity in resistant cancer, might be applied. Targeting p53-mediated DNA damage signaling provides another therapeutic strategy to circumvent cisplatin resistance. This review provides an overview on the DNA repair pathways involved in the processing of cisplatin damage and will describe signal transduction from cisplatin DNA lesions, with special attention given to colorectal cancer cells. Furthermore, examples for improved platinum compounds and biochemical modulators of cisplatin DNA damage signaling will be presented in the context of colon cancer therapy.

To assess the toxicity of nanomaterials, most in vitro studies have been performed under submerged conditions, which do not reflect physiological conditions upon inhalation. An air−liquid interface (ALI) exposure may provide more reliable data on dosimetry and prevent interactions with cell culture media components. Therefore, an ALI exposure was combined with a high-throughput RT-qPCR approach to evaluate the toxicological potential of CuO and TiO 2 nanoparticles (NP) in A549 cells. While TiO 2 NP did not show any cytotoxicity or other effects compromising genomic stability up to 25.8 μg/cm 2 , CuO NP revealed a dose-dependent cytotoxicity, starting at 4.9 μg/cm 2 . Furthermore, CuO NP altered distinct gene expression patterns indicative for disturbed metal homeostasis, stress response, and DNA damage induction. Thus, induction of metal homeostasis associated genes (MT1X, MT2A) at 0.4 μg/cm 2 and higher suggested uptake and intracellular dissolution of CuO NP, which was verified by a dose-dependent increase in intracellular copper concentration. Starting at 4.9 μg/cm 2 , oxidative stress markers (HMOX1, HSPA1A) were induced dose-dependently, supported by elevated ROS levels. Furthermore, a dose-dependent induction of genes associated with DNA damage response (DDIT3, GADD45A) was observed, in concordance with an increase in DNA strand breaks. Finally, transcriptional data suggested the induction of apoptosis at high doses, while flow cytometric analysis revealed increased numbers of either late apoptotic or necrotic cells and clearly necrotic cells at the highest concentrations. Thus, an ALI cell culture system was successfully combined with a comprehensive high-throughput RT-qPCR system, allowing the quantification of NP deposition and their impact on genomic stability. For CuO NP, in principle the data confirm observations made under submerged conditions with respect to intracellular copper ion release, as well as oxidative and genotoxic stress response. However, the results derived from ALI exposure allow the assessment of dose−response-relationships as well as the comparison of relative toxic potencies of different NP.

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