Cancer as a programmed death of an organism

Do External or Internal Factors Lead to Tumor Development? It Is Still Unknown

Arguments supporting the "bad luck" hypothesis presented by C. Tomasetti and B. Vogelstein ((2015) Science, 347, 78-81) and A. V. Lichtenstein ((2017) Biochemistry (Moscow), 82, 75-80) are critically discussed. Those arguments are not sufficient for recognition of the "bad luck" hypothesis and the leading role of internal factors in spontaneous tumor development.

What is "phenoptosis" and how to fight it?

Phenoptosis is the death of an organism programmed by its genome. Numerous examples of phenoptosis are described in prokaryotes, unicellular eukaryotes, and all kingdoms of multicellular eukaryotes (animals, plants, and fungi). There are very demonstrative cases of acute phenoptosis when actuation of a specific biochemical or behavioral program results in immediate death. Rapid (taking days) senescence of semelparous plants is described as phenoptosis controlled by already known genes and mediated by toxic phytohormones like abscisic acid. In soya, the death signal is transmitted from beans to leaves via xylem, inducing leaf fall and death of the plant. Mutations in two genes of Arabidopsis thaliana, required for the flowering and subsequent formation of seeds, prevent senescence, strongly prolonging the lifespan of this small semelparous grass that becomes a big bush with woody stem, and initiate substitution of vegetative for sexual reproduction. The death of pacific salmon immediately after spawning is surely programmed. In this case, numerous typical traits of aging, including amyloid plaques in the brain, appear on the time scale of days. There are some indications that slow aging of higher animals and humans is also programmed, being the final step of ontogenesis. It is assumed that stepwise decline of many physiological functions during such aging increases pressure of natural selection on organisms stimulating in this way biological evolution. As a working hypothesis, the biochemical mechanism of slow aging is proposed. It is assumed that mitochondria-generated reactive oxygen species (ROS) is a tool to stimulate apoptosis, an effect decreasing with age the cell number (cellularity) of organs and tissues. A group of SkQ-type substances composed of plastoquinone and a penetrating cation were synthesized to target an antioxidant into mitochondria and to prevent the age-linked rise of the mitochondrial ROS level. Such targeting is due to the fact that mitochondria are the only cellular organelles that are negatively charged compared to the cytosol. SkQs are shown to strongly decrease concentration of ROS in mitochondria, prolong lifespan of fungi, invertebrates, fish, and mammals, and retard appearance of numerous traits of aging. Clinical trials of SkQ1 (plastoquinonyl decyltriphenylphosphonium) have been successfully completed so that the Ministry of Health of the Russian Federation recommends drops of very dilute (0.25 µM) solution of this antioxidant as a medicine to treat the syndrome of dry eye, which was previously considered an incurable disease developing with age. These drops are already available in drugstores. Thus, SkQ1 is the first mitochondria-targeted drug employed in medical practice.

Cancer: evolutionary, genetic and epigenetic aspects

There exist two paradigms about the nature of cancer. According to the generally accepted one, cancer is a by-product of design limitations of a multi-cellular organism (Greaves, Nat Rev Cancer 7:213–221, 2007). The essence of the second resides in the question “Does cancer kill the individual and save the species?” (Sommer, Hum Mutat 3:166–169, 1994). Recent data on genetic and epigenetic mechanisms of cell transformation summarized in this review support the latter point of view, namely that carcinogenesis is an evolutionary conserved phenomenon—a programmed death of an organism. It is assumed that cancer possesses an important function of altruistic nature: as a mediator of negative selection, it serves to preserve integrity of species gene pool and to mediate its evolutionary adjustment. Cancer fulfills its task due apparently to specific killer function, understanding mechanism of which may suggest new therapeutic strategy.

The risk to develop a recurrence of a gastric cancer-is it independent of time?

BACKGROUND AND AIMS

Recurrence is the main reason for early death of cancer patients. Therefore, survival curves are regarded as crucial tools for clinicians to evaluate therapies and to estimate the patients' prognosis. Current models for the development of recurrence are based on the assumption of a residual cancer cell burden after therapy. Accordingly, in assumption of an exponential cell growth of the cancer cells an S-shaped decline of the survival curve is expected with earlier onset in case of advanced cancer and a later manifestation in case of little residual tumour. However, many survival curves do not reflect any S-shaped configuration and thus may question the current concept.

MATERIALS AND METHODS

To test, whether the incidence for developing a recurrence may be considered as remaining constant over time, we analysed survival data of 446 patients with gastric cancer, operated from 1975-2001 in the Surgical Department of the RWTH Aachen.

RESULTS

All survival curves, even after sub-grouping according to UICC stage, show a monotonous decline without any apparent S-shape. The impact of TNM and UICC stage to predict the survival in patients is estimated by Cox regression, for estimation the risk for death a logistic regression is performed. Whereas the presence of metastasis lowers the prognosis significantly with a hazard ratio of 1.57 and an odds ratio of 7.56, respectively, a significant relevance for the UICC stage, the tumour size or the lymph node status cannot be proven. Furthermore, the two assumptions: (1) that 20% of patients who are still alive after 5 years have been cured, and (2) that the remainder develop a recurrence in constantly 7.3% per month, are able to configure the survival curve almost precisely (correlation coefficient between calculated and observed survival rate r > 0.99).

CONCLUSION

The absence of any S-shaped survival curve configuration is not in accordance with the focus on residual tumour clones with its exponential growth as the decisive process for recurrence development. In contrast, the monotonous decline of surviving patients is best reflected by a constant incidence of recurrence. The (time) constancy of the recurrence incidence encourages the view of recurrent cancer as a chronic problem of a carcinogenic environment. Furthermore, it supports new anticancer therapies which rather targets cell regulation and immunology instead of acting cytotoxic.