Can targeting apoptosis resolve the cancer saga?

Modulation of effector caspase cleavage determines response of breast and lung tumor cell lines to chemotherapy

In spite of compelling evidence-implicating caspases in drug-induced apoptosis, how tumors modulate caspase expression and activity to overcome the cytotoxicity of anticancer agents is not fully understood. To address this issue, we investigated the role of caspases-3 and caspase-7 in determining the response of breast and lung tumor cell lines to chemotherapy. We found that an early and late apoptotic response correlated with weak and strong cellular caspase-activation, respectively. The results highlight an underappreciated relationship of temporal apoptotic response with caspase-activation and drug resistance. Moreover, the extent of tumor growth restoration after drug withdrawal was dependent on the degree of endogenous blockage of caspase-3 and caspase-7 cleavages. This points to an unrecognized role of caspase modulation in tumor recurrence and suggests that targeting caspase cleavage is a rational approach to increasing potency of cancer drugs.

Monitoring caspase-3 activation with a multimodality imaging sensor in living subjects

PURPOSE

Capsase-3 plays an important role in chemotherapy-induced apoptosis in many cancers. Herein, we applied a multimodality reporter vector to monitor caspase-3 activation indirectly in live cells and tumors of living animals undergoing apoptosis.

EXPERIMENTAL DESIGN

A fusion protein (MTF) was constructed by combining three different reporter proteins, red fluorescent protein (mRFP1), firefly luciferase (FL), and HSV1-sr39 truncated thymidine kinase (TK), linked through a caspase-3 recognizable polypeptide linker. After cleavage by caspase-3, a significant gain in mRFP1, FL, and TK activity are observed by fluorescence-activated cell sorting and enzyme-based assays. A melanoma cell line (B16F10-mtf-hrl) stably expressing mtf (to measure caspase-3 activation) and hrl-IRES-gfp (to determine the decrease in a number of viable cells) vectors was generated to measure two independent molecular events upon treatment.

RESULTS

Upon induction with 8 mumol/L staurosporine, the fusion protein showed a 2.8-fold increase in FL (P = 0.03), a 1.5-fold increase in TK (P = not significant), and a 2-fold increase in mRFP1 (P = 0.05) activity in 293T cells. Bioluminescence and micropositron emission tomography imaging of the apoptotic B16F10-mtf-hrl tumors showed a 2-fold higher FL activity (897 versus 416) and a 2-fold higher TK activity (10.3 versus 3.87) than control tumors when normalized with RL activity. Using a similar normalization approach, the time kinetics of caspase-3 activation by two protein kinase-C inhibitors was noninvasively monitored in living mice.

CONCLUSION

This multimodality caspase sensor vector could effectively and noninvasively monitor caspase-3 activation from single live cells to a multicellular tumor environment and, thus, would be a valuable tool for drug screening in preclinical models and future patient cell based therapy.

Differential activity of caspase-3 regulates susceptibility of lung and breast tumor cell lines to Paclitaxel

Recent development of tumor resistance to paclitaxel presents a major problem to cancer treatment. An unsettled controversy in the cancer chemotherapy field, however, is whether caspases play a prominent role in paclitaxel-induced death in tumors. Previous studies suggest that cleavage of caspase-3 is not instrumental for the execution of death in tumors treated with paclitaxel, while other reports indicate that caspase-dependent pathways may be critical for paclitaxel cytotoxicity. In this study, we investigated the role of caspase-3 in breast and lung tumor cell line sensitivity to paclitaxel. Clonogenic survival and live/dead viability-assays, together with enzymatic activity and cell proliferation assays, reveal that the levels of paclitaxel-induced caspase-3 enzymatic activity in tumor cells correlate directly with tumor sensitivity to the drug.We observed a 2-fold increase in caspase-3 activity in 4T1-Luc breast tumor cells, but a 3-fold and 4-fold decrease in A549 and A427 lung tumor cell lines, respectively. Together, our results suggest that caspase-activation and activity levels are not only key determinants of paclitaxel-induced death in tumors but also serve as good indicators for tumor susceptibility to paclitaxel therapy. Our studies also indicate that within clinically relevant doses of paclitaxel, the ability to rid tumor populations of dormant tumor cells controls the rate of tumor recurrence.

Additive cytotoxic effect of apoptin and chemotherapeutic agents paclitaxel and etoposide on human tumour cells

Gene therapy experiments in animal models have shown that apoptin expression results in tumour regression without any significant side effects. Therefore, apoptin is regarded as a potential anticancer drug for clinical applications. In this study, we analysed whether chemotherapeutic agents combined with apoptin treatment could result in enhanced cytotoxicity in human tumour cell cultures. Combined treatment with recombinant adenovirus AdAptVP3 expressing apoptin and etoposide clearly showed an additive cytotoxic effect on human osteosarcoma U2OS cells. Paclitaxel treatment combined with apoptin expression significantly inhibited the survival of p53-positive human osteosarcoma U2OS and non-small lung carcinoma A549 cells, p53-negative human osteosarcoma Saos-2 cells and p53-mutant human prostate cancer Du145 cells, already at low doses of the chemotherapeutic agent. Our results indicate that the cytotoxicity-enhancing action by the tumour-specific apoptin in combination with chemotherapeutic agents might offer an effective and safe antitumour therapeutics.

Caspase-2 deficiency enhances aging-related traits in mice

Alteration of apoptotic activity has been observed in a number of tissues in aging mammals, but it remains unclear whether and/or how apoptosis may affect aging. Caspase-2 is a member of the cysteine protease family that plays a critical role in apoptosis. To understand the impact of compromised apoptosis function on mammalian aging, we conducted a comparative study on caspase-2 deficient mice and their wild-type littermates with a specific focus on the aging-related traits at advanced ages. We found that caspase-2 deficiency enhanced a number of traits commonly seen in premature aging animals. Loss of caspase-2 was associated with shortened maximum lifespan, impaired hair growth, increased bone loss, and reduced body fat content. In addition, we found that the livers of caspase-2 deficient mice had higher levels of oxidized proteins than those of age-matched wild-type mice, suggesting that caspase-2 deficiency compromised the animal's ability to clear oxidatively damaged cells. Collectively, these results suggest that caspase-2 deficiency affects aging in the mice. This study thus demonstrates for the first time that disruption of a key apoptotic gene has a significant impact on aging.

Dissecting the senescence-like program in tumor cells activated by Ras signaling

Activated Ras signaling can induce a permanent growth arrest in osteosarcoma cells. Here, we report that a senescence-like growth inhibition is also achieved in human carcinoma cells upon the transduction of H-Ras(V12). Ras-induced tumor senescence can be recapitulated by the transduction of activated, but not wild-type, MEK. The ability for H-Ras(V12) to suppress tumor cell growth is drastically compromised in cells that harbor endogenous activating ras mutations. Notably, growth inhibition of tumor cells containing ras mutations can be achieved through the introduction of activated MEK. Tumor senescence induced by Ras signaling can occur in the absence of p16 or Rb and is not interrupted by the inactivation of Rb, p107, or p130 via short hairpin RNA or the transduction with HPV16 E7. In contrast, inactivation of p21 via short hairpin RNA disrupts Ras-induced tumor senescence. In summary, this study uncovers a senescence-like program activated by Ras signaling to inhibit cancer cell growth. This program appears to be intact in cancer cells that do not harbor ras mutations. Moreover, cancer cells that carry ras mutations remain susceptible to tumor senescence induced by activated MEK. These novel findings can potentially lead to the development of innovative cancer intervention.