OBJECTIVES:Chemotherapy is one of the major treatments of cancer. However, the emergence of resistance to chemotherapeutic agents is still a major obstacle in the successful management of resistant tumors. Therefore, development of new mechanisms to overcome drug resistance is essential and may be further developed into effective therapies that can flip the switch from drug resistance to susceptibility. The aim of this study was to evaluate a combination consisting of a ketogenic diet and melatonin to determine whether it would inhibit cisplatin- and vincristine-resistant breast cancer.

METHODS:In the in vitro part of the study, drug-resistant cell lines were treated with melatonin and real-time polymerase chain reaction was used to measure levels of gene expression involved in apoptosis and resistance. On the protein level, the activity of caspase-3 and the level of vascular endothelin growth factor protein were determined. In the in vivo part, tumor-bearing mice received one of the following treatments: ketogenic diet, melatonin, combination of melatonin and ketogenic diet, vehicle, or chemotherapy.

RESULTS:Successful inhibition of resistant cell lines was achieved by melatonin. This inhibition was mediated by induction of apoptosis, inhibition of angiogenesis, and downregulation of resistance genes. A synergistic anticancer effect was observed between melatonin and the ketogenic diet against resistant breast tumors inoculated in mice with a cure rate of 70%.

CONCLUSIONS:The combination of melatonin and a ketogenic diet represents a promising option to overcome drug resistance in cancer chemotherapy. However, further testing on the protein level using flow cytometry is important to better understand the mechanisms of action.

Although hyperthermia offers clinical appeal to sensitize cells to chemotherapy, this approach has been limited in terms of long-term outcome as well as economic and technical burden. Thus, a more detailed knowledge about how hyperthermia exerts its effects on chemotherapy may illuminate ways to improve the approach. Here we asked whether hyperthermia alters the response to chemotherapy-induced DNA damage and if this mechanism is involved in its sensitizing effect, in BRCA-competent models of ovarian and colon cancer. Notably, we found that hyperthermia delayed the repair of DNA damage caused by cisplatin or doxorubicin, acting upstream of different repair pathways to block histone polyADP-ribosylation (PARylation), a known effect of chemotherapy. Further, hyperthermia blocked this histone modification as efficiently as pharmacological inhibitors of polyADP-ribosyl polymerase (PARPi), producing comparable delay in DNA repair, induction of double strand breaks (DSB) and cell cytotoxicity after chemotherapy. Mechanistic investigations indicated that inhibiting PARylation by either hyperthermia or PARPi induced lethal DSB upon chemotherapy treatment, not only by reducing DNA repair but also by preventing replication fork slowings. Overall, our work reveals how PARP blockade - either by hyperthermia or small molecule inhibition - can increase chemotherapy-induced damage in BRCA-competent cells.

PURPOSE:Cervical cancer is the second most prevalent cancer in women worldwide. Survival of patients has been improved by cisplatin-based chemotherapy, but its effectiveness is limited due to its adverse effects on many tissues, especially nephrotoxicity. To optimize the efficacy of CDDP, we propose a combination therapy using natural products with minimal side effects. Vitamin C being a natural antioxidant is capable of selectively targeting cancer cells at pharmacological concentrations. Vitamin C synergistically enhances the activity of chemotherapeutic agents without increasing toxicity to normal cells. Therefore, we exploited co-therapy with cisplatin and vitamin C to kill cervical cancer cells.

METHODS:We elucidated the role of CDDP and VC on cervical cancer cell line (SiHa) by using cell growth assays, DNA fragmentation analysis, comet assay, in vitro morphological assessment of apoptosis (AO/EB and DAPI staining), ROS analysis by DCFDA, flow cytometry, biochemical assays (GST, GSH, NO, catalase, TPA) and Western blotting.

RESULTS:Our results clearly demonstrated that CDDP and VC treatment exhibited ameliorative effect on induction of cell death by p53 overexpression and generation of hydrogen peroxide in SiHa cells, thereby reducing the dosage of CDDP required to induce cell death in cancer cells.

CONCLUSIONS:These studies provide novel approaches to combat cisplatin resistance in cervical cancer.

Vitamin C (VC) is an important antioxidant and enzyme co-factor that works by stimulating the immune system and protecting against infections. It is well known that melanoma cells are more susceptible to VC than any other tumor cells. However, the role of VC in the treatment of colon cancer has not been studied. Cisplatin (CDDP) is a DNA damaging agent and is widely used for treating cancer, while the role of p53 in CDDP-induced cell death has been stressed. Using cell growth assays, morphological methods, Western blotting, flow cytometry, and DNA fragmentation analysis, we measured the expression of p53 level involved in the effect of VC on CDDP-induced apoptosis of HCT116, a human colon cancer cell line. CDDP plus VC treatment resulted in significantly increased apoptosis along with upregulation of p53 compared to untreated cells and/or CDDP-treated cells. These results suggest that VC enhanced CDDP sensitivity and apoptosis via upregulation of p53.