Repopulation characteristics and cell kinetic parameters resulting from multi-fraction irradiation of xenograft tumors in SCID mice

Exploring the Phytochemical Profile and Biological Activities of Clerodendrum infortunatum

Clerodendrum infortunatum (C. infortunatum), the hill glory bower, is reputed as the prodigious treasure for Indian folk medicine. The study has focused on exploring the phytochemistry and antitumor potential of the C. infortunatum root extract in vitro and in vivo. The ethyl acetate root extract has demonstrated the highest cytotoxicity in a series of nine human tumor cell lines. Further fractionation of the same has yielded seven compounds. The structures of these compounds were confirmed with spectroscopic techniques. Considering the toxicity observed with the crude extract, cytotoxicity of these compounds was further assessed in two breast carcinoma cell lines (MCF-7[ER/PR-positive HER2-negative] and MDA-MB-231 [ER/PR/HER2-negative]) and in two cervical cancer [human papilloma virus (HPV)-negative C33A and HPV-positive SiHa] cell lines. Betulinic acid (BA) was found as the active principle contributing the cytotoxic activity, and cervical cancer cell lines documented the minimum IC₅₀ value in 24 h. In order to validate the in vitro experimental data, we have established a xenograft model of HPV-positive cervical cancer in female NOD/SCID mice treated with BA using doxorubicin as the positive control. BA treatment gradually reduced the tumor size, maintaining healthy hematological and biochemical parameters, and improved the survival rate of tumor-bearing mice considerably. Thus, our findings suggest that the C. infortunatum root extract has a promising anticancer property against HPV-positive cervical cancer and supports its usage by traditional healers for treating cervical cancer.

Factors Impacting Differential Outcomes in the Definitive Radiation Treatment of Anal Cancer Between HIV-Positive and HIV-Negative Patients

BACKGROUND

Anal squamous cell carcinoma (ASCC) is uncommon, yet seen more frequently in the setting of the human immunodeficiency virus (HIV). Chemoradiotherapy is the definitive modality of treatment for patients with ASCC; this study examines factors impacting clinical outcomes in a large cohort of HIV-positive and HIV-negative patients.

METHODS

A retrospective review was conducted of patients treated for nonmetastatic ASCC at a single institution between 2005 and 2018. Freedom from local recurrence (FFLR), freedom from distant metastasis, and overall survival (OS) were calculated using the Kaplan-Meier method, and univariate and multivariate analysis were performed using the Cox proportional hazards model.

RESULTS

During the study period, 111 patients initiated definitive treatment for ASCC. Median age of the entire cohort was 56.7 years (interquartile range, 51.5-63.5), with 52 patients (46.8%) being HIV-positive. At median follow-up of 28.0 months, the 2- and 5-year FFLR were 78.2% (95% confidence interval [CI], 70.4-87.0) and 74.6% (95% CI, 65.8-84.5), respectively. Multivariate analysis revealed time from diagnosis to treatment initiation (median, 8 weeks; hazard ratio, 1.06; 95% CI, 1.03-1.10) to be significantly associated with worse FFLR and OS. HIV-positive patients had a trend toward worse FFLR (log-ranked p = .06). For HIV-positive patients with post-treatment CD4 less than 150 cells per mm3 , there was significantly worse OS (log-ranked p = .015).

CONCLUSION

A trend toward worse FFLR was seen in HIV-positive patients, despite similar baseline disease characteristics as HIV-negative patients. Worse FFLR and OS was significantly associated with increased time from diagnosis to treatment initiation. Poorer OS was seen in HIV-positive patients with a post-treatment CD4 count less than 150 cells per mm3 .

IMPLICATIONS FOR PRACTICE

Human immunodeficiency virus (HIV)-positive patients with anal squamous cell carcinoma can represent a difficult clinical scenario. Definitive radiation with concurrent chemotherapy is highly effective but can result in significant toxicity and a decrease in CD4 count that could predispose to HIV-related complications. As HIV-positive patients have largely been excluded from prospective clinical trials, this study seeks to provide greater understanding of their outcomes with radiation therapy, potential predictors of worse local control and overall survival, and those most at risk after completion of treatment.

In silico analysis of cell cycle synchronisation effects in radiotherapy of tumour spheroids

Tumour cells show a varying susceptibility to radiation damage as a function of the current cell cycle phase. While this sensitivity is averaged out in an unperturbed tumour due to unsynchronised cell cycle progression, external stimuli such as radiation or drug doses can induce a resynchronisation of the cell cycle and consequently induce a collective development of radiosensitivity in tumours. Although this effect has been regularly described in experiments it is currently not exploited in clinical practice and thus a large potential for optimisation is missed. We present an agent-based model for three-dimensional tumour spheroid growth which has been combined with an irradiation damage and kinetics model. We predict the dynamic response of the overall tumour radiosensitivity to delivered radiation doses and describe corresponding time windows of increased or decreased radiation sensitivity. The degree of cell cycle resynchronisation in response to radiation delivery was identified as a main determinant of the transient periods of low and high radiosensitivity enhancement. A range of selected clinical fractionation schemes is examined and new triggered schedules are tested which aim to maximise the effect of the radiation-induced sensitivity enhancement. We find that the cell cycle resynchronisation can yield a strong increase in therapy effectiveness, if employed correctly. While the individual timing of sensitive periods will depend on the exact cell and radiation types, enhancement is a universal effect which is present in every tumour and accordingly should be the target of experimental investigation. Experimental observables which can be assessed non-invasively and with high spatio-temporal resolution have to be connected to the radiosensitivity enhancement in order to allow for a possible tumour-specific design of highly efficient treatment schedules based on induced cell cycle synchronisation.

The sensitivity of a cell to a dose of radiation is largely affected by its current position within the cell cycle. While under normal circumstances progression through the cell cycle will be asynchronous in a tumour mass, external influences such as chemo- or radiotherapy can induce a synchronisation. Such a common progression of the inner clock of the cancer cells results in the critical dependence on the effectiveness of any drug or radiation dose on a suitable timing for its administration. We analyse the exact evolution of the radiosensitivity of a sample tumour spheroid in a computer model, which enables us to predict time windows of decreased or increased radiosensitivity. Fractionated radiotherapy schedules can be tailored in order to avoid periods of high resistance and exploit the induced radiosensitivity for an increase in therapy efficiency. We show that the cell cycle effects can drastically alter the outcome of fractionated irradiation schedules in a spheroid cell system. By using the correct observables and continuous monitoring, the cell cycle sensitivity effects have the potential to be integrated into treatment planing of the future and thus to be employed for a better outcome in clinical cancer therapies.

Cytostatic potential of novel agents that inhibit the regulation of intracellular pH

Cells within the acidic extracellular environment of solid tumours maintain their intracellular pH (pHi) through the activity of membrane-based ion exchange mechanisms including the Na(+)/H(+) antiport and the Na(+)-dependent Cl(-)/HCO(3)(-) exchanger. Inhibition of these regulatory mechanisms has been proposed as an approach to tumour therapy. Previously available inhibitors of these exchangers were toxic (e.g. 4,4-diisothiocyanstilbene-2,2-disulphonic acid), and/or non-specific (e.g. 5-N-ethyl-N-isopropyl amiloride). Using two human (MCF7, MDA-MB231) and one murine (EMT6) breast cancer cell lines, we evaluated the influence of two new agents, cariporide (an inhibitor of the Na(+)/H(+) antiport) and S3705 (an inhibitor of the Na(+)-dependent Cl(-)/HCO(3)(-) exchanger) on the regulation of intracellular pH (pHi). The cytotoxicity of the two agents was assessed by using clonogenic assays. Our results suggest that cariporide has similar efficacy and potency to 5-N-ethyl-N-isopropyl amiloride for inhibition of Na(+)/H(+) exchange while S3705 is more potent and efficient than 4,4-diisothiocyanstilbene-2,2-disulphonic acid in inhibiting Na+-dependent Cl(-)/HCO3(-) exchange. The agents inhibited the growth of tumour cells when they were incubated at low pHe (7.0-6.8), but were non-toxic to cells grown at doses that inhibited the regulation of pHi. Our results indicate that cariporide and S3705 are selective cytostatic agents under in vitro conditions that reflect the slightly acidic microenvironment found in solid tumours.

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

Effects of mitomycin C on the oxygenation and radiosensitivity of murine and human tumours in mice

BACKGROUND AND PURPOSE

Mitomycin C was one of the first chemotherapeutic agents to be shown to have preferential cytotoxicity toward hypoxic cells in vitro. Consequently, it has been used clinically with radiotherapy, and has stimulated considerable interest for analogue development. More recent studies also suggested a possible role for the drug in enhancing tumour blood flow; we therefore undertook a comprehensive examination of mitomycin C as a potential radiosensitizer in murine and human tumours growing in mice.

MATERIALS AND METHODS

Two dissimilar human tumour xenograft systems, SiHa and WiDr cells, were used as was the murine SCCVII line. Effects of mitomycin C treatment on the regional and microregional blood flow in these tumours was evaluated, and cell sorting based on dye perfusion techniques was used to study the cytotoxicity of mitomycin C as a single agent or in combination with radiation in the xenograft systems.

RESULTS

Contrary to our expectations, no preferential killing of less-well oxygenated tumour cells in situ was observed, nor were any consistent effects on tumour blood flow found. The inclusion of mitomycin C with radiation did, however, produce a modest increase in cell killing in the hypoxic subpopulations of the xenograft system with the largest hypoxic fraction.

CONCLUSIONS

Our results indicate that combined treatment with mitomycin C and radiation cannot be rationalized on the expectation of either complementary cytotoxicity of the modalities, or of drug-induced improvement in tumour oxygenation.

Cell kinetics and repopulation parameters of irradiated xenograft tumours in SCID mice: comparison of two dose-fractionation regimens

The extent and mechanism(s) of repopulation were assessed in SiHa (human cervical squamous cell carcinoma) xenografts in SCID mice for two fractionated irradiation regimens. Mice in one arm of the study received 50 Gy in 20 fractions over 23 days with a 14 day split between 10 fraction, 5 day courses. The other tumours were treated with 50 Gy in 20 fractions over 10 consecutive days. Cell kinetics and tumour regrowth parameters were monitored during and after treatment by measuring tumour volume and analysing cellular DNA content and proliferation parameters with flow cytometry. Repopulation occurred rapidly, beginning during irradiation and largely attributable to an increased growth fraction and decreased potential doubling time, apparently triggered by increased cell loss. Cell cycle time, in contrast, remained relatively constant throughout. Extrapolation of these results to humans suggests that treatment times should be minimised whenever possible, since regrowth rates exceeded those predicted from pretreatment Tpot measurements.

Increase in the fraction of necrotic, not apoptotic, cells in SiHa xenograft tumours shortly after irradiation

BACKGROUND AND PURPOSE

Approximately 18% of the cells recovered by rapid mechanical dissociation of SiHa xenograft tumours contain large numbers of DNA strand breaks. The number of damaged cells increases to 30-40% 4-6 h after exposure to 5 or 15 Gy, returning to normal levels by 12 h. This observation is reminiscent of the rate of production of apoptotic cells in other murine and human xenograft tumours. The nature of this damage, rate of development and relation to cell proliferation rate were therefore examined in detail.

MATERIALS AND METHODS

SiHa human cervical carcinoma cells were grown as xenograft tumours in SCID mice. Single-cell suspensions were prepared as a function of time after irradiation of the mouse and examined for DNA damage using the alkaline comet assay. Cell cycle progression was measured by flow cytometry evaluation of anti-bromodeoxyuridine-labelled tumour cells.

RESULTS

Significant numbers of apoptotic cells could not be detected in irradiated SiHa tumours using an end-labelling assay, electron microscopy, or histological examination of thin sections. Instead, xenograft cells exhibiting extensive DNA damage in the comet assay were predominantly necrotic cells. The increase in the proportion of heavily damaged cells 4-6 h after irradiation could be the result of an interplay between several factors including loss of viable cells and change in production or loss of necrotic cells. Analysis of the progression of BrdUrd-labelled cells confirmed that while 35% of cells from untreated SiHa tumours had divided and entered G1 phase by 6 h after BrdUrd injection, none of the labelled cells from tumours exposed to 5 or 15 Gy had progressed to G1.

CONCLUSIONS

The increase in the percentage of SiHa tumour cells with extensive DNA damage 4-6 h after irradiation is attributable to necrosis, not apoptosis. Cell cycle progression and cell loss are likely to influence the kinetics of appearance of both apoptotic and necrotic cells in irradiated tumours.