Higher anti-tumour efficacy of platinum(IV) complex LA-12 is associated with its ability to bypass M-phase entry block induced in oxaliplatin-treated human colon cancer cells

Inhibition of Chk1 stimulates cytotoxic action of platinum-based drugs and TRAIL combination in human prostate cancer cells

Checkpoint kinase 1 (Chk1) plays an important role in regulation of the cell cycle, DNA damage response and cell death, and represents an attractive target in anticancer therapy. Small-molecule inhibitors of Chk1 have been intensively investigated either as single agents or in combination with various chemotherapeutic drugs and they can enhance the chemosensitivity of numerous tumor types. Here we newly demonstrate that pharmacological inhibition of Chk1 using potent and selective inhibitor SCH900776, currently profiled in phase II clinical trials, significantly enhances cytotoxic effects of the combination of platinum-based drugs (cisplatin or LA-12) and TRAIL (tumor necrosis factor-related apoptosis inducing ligand) in human prostate cancer cells. The specific role of Chk1 in the drug combination-induced cytotoxicity was confirmed by siRNA-mediated silencing of this kinase. Using RNAi-based methods we also showed the importance of Bak-dependent mitochondrial apoptotic pathway in the combined anticancer action of SCH900776, cisplatin and TRAIL. The triple drug combination-induced cytotoxicity was partially enhanced by siRNA-mediated Mcl-1 silencing. Our findings suggest that targeting Chk1 may be used as an efficient strategy for sensitization of prostate cancer cells to killing action of platinum-based chemotherapeutic drugs and TRAIL.

Heat shock protein 90: biological functions, diseases, and therapeutic targets

Heat shock protein 90 (Hsp90) is a predominant member among Heat shock proteins (HSPs), playing a central role in cellular protection and maintenance by aiding in the folding, stabilization, and modification of diverse protein substrates. It collaborates with various co-chaperones to manage ATPase-driven conformational changes in its dimer during client protein processing. Hsp90 is critical in cellular function, supporting the proper operation of numerous proteins, many of which are linked to diseases such as cancer, Alzheimer's, neurodegenerative conditions, and infectious diseases. Recognizing the significance of these client proteins across diverse diseases, there is a growing interest in targeting Hsp90 and its co-chaperones for potential therapeutic strategies. This review described biological background of HSPs and the structural characteristics of HSP90. Additionally, it discusses the regulatory role of heat shock factor-1 (HSF-1) in modulating HSP90 and sheds light on the dynamic chaperone cycle of HSP90. Furthermore, the review discusses the specific contributions of HSP90 in various disease contexts, especially in cancer. It also summarizes HSP90 inhibitors for cancer treatment, offering a thoughtful analysis of their strengths and limitations. These advancements in research expand our understanding of HSP90 and open up new avenues for considering HSP90 as a promising target for therapeutic intervention in a range of diseases.

Cisplatin or LA-12 enhance killing effects of TRAIL in prostate cancer cells through Bid-dependent stimulation of mitochondrial apoptotic pathway but not caspase-10

Searching for new strategies for effective elimination of human prostate cancer cells, we investigated the cooperative cytotoxic action of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and two platinum-based complexes, cisplatin or LA-12, and related molecular mechanisms. We demonstrated a notable ability of cisplatin or LA-12 to enhance the sensitivity of several human prostate cancer cell lines to TRAIL-induced cell death via an engagement of mitochondrial apoptotic pathway. This was accompanied by augmented Bid cleavage, Bak activation, loss of mitochondrial membrane potential, activation of caspase-8, -10, -9, and -3, and XIAP cleavage. RNAi-mediated silencing of Bid or Bak in Bax-deficient DU 145 cells suppressed the drug combination-induced cytotoxicity, further underscoring the involvement of mitochondrial signaling. The caspase-10 was dispensable for enhancement of cisplatin/LA-12 and TRAIL combination-induced cell death and stimulation of Bid cleavage. Importantly, we newly demonstrated LA-12-mediated enhancement of TRAIL-induced cell death in cancer cells derived from human patient prostate tumor specimens. Our results provide convincing evidence that employing TRAIL combined with cisplatin/LA-12 could contribute to more effective killing of prostate cancer cells compared to the individual action of the drugs, and offer new mechanistic insights into their cooperative anticancer action.

Chk1 Inhibitor SCH900776 Effectively Potentiates the Cytotoxic Effects of Platinum-Based Chemotherapeutic Drugs in Human Colon Cancer Cells

Although Chk1 kinase inhibitors are currently under clinical investigation as effective cancer cell sensitizers to the cytotoxic effects of numerous chemotherapeutics, there is still a considerable uncertainty regarding their role in modulation of anticancer potential of platinum-based drugs. Here we newly demonstrate the ability of one of the most specific Chk1 inhibitors, SCH900776 (MK-8776), to enhance human colon cancer cell sensitivity to the cytotoxic effects of platinum(II) cisplatin and platinum(IV)- LA-12 complexes. The combined treatment with SCH900776 and cisplatin or LA-12 results in apparent increase in G1/S phase-related apoptosis, stimulation of mitotic slippage, and senescence of HCT116 cells. We further show that the cancer cell response to the drug combinations is significantly affected by the p21, p53, and PTEN status. In contrast to their wt counterparts, the p53- or p21-deficient cells treated with SCH900776 and cisplatin or LA-12 enter mitosis and become polyploid, and the senescence phenotype is strongly suppressed. While the cell death induced by SCH900776 and cisplatin or LA-12 is significantly delayed in the absence of p53, the anticancer action of the drug combinations is significantly accelerated in p21-deficient cells, which is associated with stimulation of apoptosis beyond G2/M cell cycle phase. We also show that cooperative killing action of the drug combinations in HCT116 cells is facilitated in the absence of PTEN. Our results indicate that SCH900776 may act as an important modulator of cytotoxic response triggered by platinum-based drugs in colon cancer cells.

Loss of PTEN Facilitates Rosiglitazone-Mediated Enhancement of Platinum(IV) Complex LA-12-Induced Apoptosis in Colon Cancer Cells

We demonstrated for the first time an outstanding ability of rosiglitazone to mediate a profound enhancement of LA-12-induced apoptosis associated with activation of mitochondrial pathway in human colon cancer cells. This effect was preferentially observed in the G1 cell cycle phase, independent on p53 and PPARγ proteins, and accompanied with significant changes of selected Bcl-2 family protein levels. Further stimulation of cooperative synergic cytotoxic action of rosiglitazone and LA-12 was demonstrated in the cells deficient for PTEN, where mitochondrial apoptotic pathway was more stimulated and G1-phase-associated dying was reinforced. Our results suggest that combined treatment with rosiglitazone and LA-12 might be promising anticancer strategy in colon-derived tumours regardless of their p53 status, and also favourable in those defective in PTEN function.

Platinum(IV) complex LA-12 exerts higher ability than cisplatin to enhance TRAIL-induced cancer cell apoptosis via stimulation of mitochondrial pathway

In search for novel strategies in colon cancer treatment, we investigated the unique ability of platinum(IV) complex LA-12 to efficiently enhance the killing effects of tumor necrosis factor-related apoptosis inducing ligand (TRAIL), and compared it with the sensitizing action of cisplatin. We provide the first evidence that LA-12 primes human colon cancer cells for TRAIL-induced cytotoxicity by p53-independent activation of the mitochondrial apoptotic pathway. The cooperative action of LA-12 and TRAIL was associated with stimulation of Bax/Bak activation, drop of mitochondrial membrane potential, caspase-9 activation, and a shift of the balance among Bcl-2 family proteins in favor of the pro-apoptotic members. In contrast to cisplatin, LA-12 was a potent inducer of ERK-mediated Noxa and BimL protein upregulation, and more effectively enhanced TRAIL-induced apoptosis in the absence of Bax. The cooperative action of LA-12 and TRAIL was augmented following the siRNA-mediated silencing of Mcl-1 in both Bax proficient/deficient cells. We newly demonstrated that LA-12 induced ERK-mediated c-Myc upregulation, and proved that c-Myc silencing inhibited the mitochondrial activation and apoptosis in colon cancer cells treated with LA-12 and TRAIL. The LA-12-mediated sensitization to TRAIL-induced apoptosis was demonstrated in several colon cancer cell lines, further underscoring the general relevance of our findings. The selective action of LA-12 was documented by preferential priming of cancer but not normal colon cancer cells to TRAIL killing effects. Our work highlights the promising potential of LA-12 over cisplatin to enhance the colon cancer cell sensitivity to TRAIL-induced apoptosis, and provides new mechanistic insights into their cooperative action.