Changes in lognormal shape parameter guide design of patient-specific radiochemotherapy cocktails

BAG1, MGMT, FOXO1, and DNAJA1 as potential drug targets for radiosensitizing cancer cell lines

BACKGROUND AND PURPOSE

Activation of some signaling pathways can promote cell survival and have a negative impact on tumor response to radiotherapy. Here, the role of differences in expression levels of genes related to the poly(ADP-ribose) polymerase-1 (PARP-1), heat shock protein 90 (Hsp90), B-cell lymphoma 2 (Bcl-2), and phosphoinositide 3-kinase (PI3K) pathways in the survival or death of cells following X-ray exposure was investigated.

METHODS

Eight human cell cultures (MCF-7 and MDA-MB-231: breast cancers; MCF-12A: apparently normal breast; A549: lung cancer; L132: normal lung; G28, G44 and G112: glial cancers) were irradiated with X-rays. The colony-forming and real-time PCR based on a custom human pathway RT² Profiler PCR Array assays were used to evaluate cell survival and gene expression, respectively.

RESULTS

The surviving fractions at 2 Gy for the cell lines, in order of increasing radioresistance, were found to be as follows: MCF-7 (0.200 ± 0.011), G44 (0.277 ± 0.065), L132 (0.367 ± 0.023), MDA-MB-231 (0.391 ± 0.057), G112 (0.397 ± 0.113), A549 (0.490 ± 0.048), MCF-12A (0.526 ± 0.004), and G28 (0.633 ± 0.094). The rank order of radioresistance at 6 Gy was: MCF-7 < L132 < G44 < MDA-MB-231 < A549 < G28 < G112 < MCF-12A. PCR array data analysis revealed that several genes were differentially expressed between irradiated and unirradiated cell cultures. The following genes, with fold changes: BCL2A1 (21.91), TP53 (8743.75), RAD51 (11.66), FOX1 (65.86), TCP1 (141.32), DNAJB1 (3283.64), RAD51 (51.52), and HSPE1 (12887.29) were highly overexpressed, and BAX (-127.21), FOX1 (-81.79), PDPK1 (-1241.78), BRCA1 (-8.70), MLH1 (-12143.95), BCL2 (-18.69), CCND1 (-46475.98), and GJA1 (-2832.70) were highly underexpressed in the MDA-MB-231, MCF-7, MCF-12A, A549, L132, G28, G44, and G112 cell lines, respectively. The radioresistance in the malignant A549 and G28 cells was linked to upregulation in the apoptotic, DNA repair, PI3K, and Hsp90 pathway genes BAG1, MGMT, FOXO1, and DNAJA1, respectively, and inhibition of these genes resulted in significant radiosensitization.

CONCLUSIONS

Targeting BAG1, MGMT, FOXO1, and DNAJA1 with specific inhibitors might effectively sensitize radioresistant tumors to radiotherapy.

A Review on Tumor Control Probability (TCP) and Preclinical Dosimetry in Targeted Radionuclide Therapy (TRT)

Targeted radionuclide therapy (TRT) uses radiopharmaceuticals to specifically irradiate tumor cells while sparing healthy tissue. Response to this treatment highly depends on the absorbed dose. Tumor control probability (TCP) models aim to predict the tumor response based on the absorbed dose by taking into account the different characteristics of TRT. For instance, TRT employs radiation with a high linear energy transfer (LET), which results in an increased effectiveness. Furthermore, a heterogeneous radiopharmaceutical distribution could result in a heterogeneous dose distribution at a tissue, cellular as well as subcellular level, which will generally reduce the tumor response. Finally, the dose rate in TRT is protracted, relatively low, and variable over time. This allows cells to repair more DNA damage, which may reduce the effectiveness of TRT. Within this review, an overview is given on how these characteristics can be included in TCP models, while some experimental findings are also discussed. Many parameters in TCP models are preclinically determined and TCP models also play a role in the preclinical stage of radiopharmaceutical development; however, this all depends critically on the calculated absorbed dose. Accordingly, an overview of the existing preclinical dosimetry methods is given, together with their limitation and applications. It can be concluded that although the theoretical extension of TCP models from external beam radiotherapy towards TRT has been established quite well, the experimental confirmation is lacking. Thus, requiring additional comprehensive studies at the sub-cellular, cellular, and organ level, which should be provided with accurate preclinical dosimetry.

TOPAS a tool to evaluate the impact of cell geometry and radionuclide on alpha particle therapy

Due to the increasing clinical application of alpha particles, accurate assessment of their dosimetry at the cellular scale should be strongly advocated. Although observations of the impact of cell and nuclear geometry have been previously reported, this effect has not been fully quantified. Additionally, alpha particle dosimetry presents several challenges and most conventional methodologies have poor resolution and are limited to average parameters across populations of cells. Meaningful dosimetry studies with alpha particles require detailed information on the geometry of the target at a subcellular scale.

METHODS

The impact of cellular geometry was evaluated for 3 different scenarios, a spherical cell with a concentric nucleus, a spherical cell with an eccentric nucleus and a model of a cell attached to a flask, consisting of a hemispherical oblate ellipsoid, all exposed to 1,700 211At radionuclide decays. We also evaluated the cross-fire effect of alpha particles as function of distance to a source cell. Finally, a nanodosimetric analysis of absorbed dose to the nucleus of a cell exposed to 1 Gy of different alpha emitting radionuclides was performed.

RESULTS

Simulated data shows the dosimetry of self-absorbed-dose strongly depends on activity localization in the source cell, but that activity localization within the source cell did not significantly affect the cross-fire absorbed dose even when cells are in direct contact with each other. Additionally, nanodosimetric analysis failed to show any significant differences in the energy deposition profile between different alpha particle emitters.

CONCLUSIONS

The collected data allows a better understanding of the dosimetry of alpha particles emitters at the sub-cellular scale. Dosimetric variations between different cellular configurations can generate complications and confounding factors for the translation of dosimetric outcomes into clinical settings, but effects of different radionuclides are generally similar.

Advancements in the use of Auger electrons in science and medicine during the period 2015-2019

Auger electrons can be highly radiotoxic when they are used to irradiate specific molecular sites. This has spurred basic science investigations of their radiobiological effects and clinical investigations of their potential for therapy. Focused symposia on the biophysical aspects of Auger processes have been held quadrennially. This 9th International Symposium on Physical, Molecular, Cellular, and Medical Aspects of Auger Processes at Oxford University brought together scientists from many different fields to review past findings, discuss the latest studies, and plot the future work to be done. This review article examines the research in this field that was published during the years 2015-2019 which corresponds to the period since the last meeting in Japan. In addition, this article points to future work yet to be done. There have been a plethora of advancements in our understanding of Auger processes. These advancements range from basic atomic and molecular physics to new ways to implement Auger electron emitters in radiopharmaceutical therapy. The highly localized doses of radiation that are deposited within a 10 nm of the decay site make them precision tools for discovery across the physical, chemical, biological, and medical sciences.

A preliminary study on treatment of human breast cancer xenografts with a cocktail of paclitaxel, doxorubicin, and 131I-anti-epithelial cell adhesion molecule (9C4)

Triple-negative breast cancer often has devastating outcomes and treatment options remain limited. Therefore, different treatment combinations are worthy of testing. The efficacy of a cocktail of paclitaxel, doxorubicin, and 131I-anti-epithelial cell adhesion molecule (EpCAM) (9C4) to treat breast cancer was tested. Efficacy was tested with an MDA-MB-231 human breast cancer xenograft model. Anti-EpCAM (9C4) was demonstrated to bind to MDA-MB-231 human adenocarcinoma cells in vitro. Subsequently, mice-bearing MDA-MB-231× enografts were treated with either 131I-anti-EpCAM (9C4), unlabeled anti-EpCAM (9C4), paclitaxel, doxorubicin, or a cocktail of all of the agents. Tumor volume was measured for up to 70-day postinjection. Exponential regression was performed on tumor growth curves for each of the therapy groups. Statistical comparison of the growth constants λ of the regression models for each of the treatment groups with that of the cold antibody and control groups was done using extra sum-of-square F-tests. Biexponential clearance of 131I-anti-EpCAM (9C4) was observed with biological clearance half-times of 1.14 and 17.6 days for the first and second components, respectively. The mean growth rate of the tumors in animals treated with a cocktail of all of the agents was slower than in those treated with unlabeled anti-EpCAM (9C4) (P = 0.022). These preliminary data suggest that a cocktail of 131I-anti-EpCAM (9C4), paclitaxel, and doxorubicin may be suitable for treating breast cancers with high expression of EpCAM.

Strong synergism between small molecule inhibitors of HER2, PI3K, mTOR and Bcl-2 in human breast cancer cells

Targeting pro-survival cell signaling components has been promising in cancer therapy, but the benefit of targeting with single agents is limited. For malignancies such as triple-negative breast cancer, there is a paucity of targets that are amenable to existing interventions as they are devoid of the human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), and estrogen receptor (ER). Concurrent targeting of cell signaling entities other than HER2, PR and ER with multiple agents may be more effective. Evaluating modes of interaction between agents can inform efficient selection of agents when used in cocktails. Using clonogenic cell survival, interaction between inhibitors of HER2 (TAK-165), phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) (NVP-BEZ235), and the pro-survival gene (Bcl-2) (ABT-263) in three human breast cell lines (MDA-MB-231, MCF-7 and MCF-12A) ranged from strong to very strong synergism. The strongest synergy was demonstrated in PR and ER negative cells. Inhibition of PI3K, mTOR and Bcl-2 could potentially be effective in the treatment of triple-negative cancers. The very strong synergy observed even at lowest concentrations of inhibitors indicates that these cocktails might be able to be used at a minimised risk of systemic toxicity. Concurrent use of multiple inhibitors can potentiate conventional interventions like radiotherapy and chemotherapy.

The advantage of antibody cocktails for targeted alpha therapy depends on specific activity

Nonuniform dose distributions among disseminated tumor cells can be a significant limiting factor in targeted α therapy. This study examines how cocktails of radiolabeled antibodies can be formulated to overcome this limitation.

METHODS

Cultured MDA-MB-231 human breast cancer cells were treated with different concentrations of a cocktail of 4 fluorochrome-conjugated monoclonal antibodies. The amount of each antibody bound to each cell was quantified using flow cytometry. A spreadsheet was developed to "arm" the antibodies with any desired radionuclide and specific activity, calculate the absorbed dose to each cell, and perform a Monte Carlo simulation of the surviving fraction of cells after exposure to cocktails of different antibody combinations. Simulations were performed for the α-particle emitters (211)At, (213)Bi, and (225)Ac.

RESULTS

Activity delivered to the least labeled cell can be increased by 200%-400% with antibody cocktails, relative to the best-performing single antibody. Specific activity determined whether a cocktail or a single antibody achieved greater cell killing. With certain specific activities, cocktails outperformed single antibodies by a factor of up to 244. There was a profound difference (≤16 logs) in the surviving fraction when a uniform antibody distribution was assumed and compared with the experimentally observed nonuniform distribution.

CONCLUSION

These findings suggest that targeted α therapy can be improved with customized radiolabeled antibody cocktails. Depending on the antibody combination and specific activity of the radiolabeled antibodies, cocktails can provide a substantial advantage in tumor cell killing. The methodology used in this analysis provides a foundation for pretreatment prediction of tumor cell survival in the context of personalized cancer therapy.

Survival of tumor and normal cells upon targeting with electron-emitting radionuclides

PURPOSE

Previous studies have shown that the mean absorbed dose to a tissue element may not be a suitable quantity for correlating with the biological response of cells in that tissue element. Cell survival can depend strongly on the distribution of radioactivity at the cellular and multicellular levels. Furthermore, when cellular absorbed doses are examined, the cross-dose from neighbor cells can be less radiotoxic than the self-dose component. To better understand how the nonuniformity of activity among cells can affect the dose response, a computer model of a 3D tissue culture was previously constructed and showed that activity distribution among cells is significantly more relevant than the mean absorbed dose for low-energy-electron emitters. The present work greatly expands upon those findings.

METHODS

In the present study, we used this same computer model but restricted the number of labeled cells to a fraction of the whole cell population (50%, 10%, and 1%, respectively). The labeled cells were randomly distributed among the whole cell population.

RESULTS

While the activity distribution is an important factor in determining the tissue response for low-energy-electron emitters, the fraction of labeled cells has an even more pronounced effect on survival response. For all electron energies studied, reducing the percentage of cells labeled significantly increases the surviving fraction of the whole population.

CONCLUSIONS

This study provides abundant information on killing tumor and normal cells under some conditions relevant to targeted radionuclide therapy of isolated tumor cells and micrometastases. The percentage of cells labeled, activity distribution among the labeled cells, and electron energy play key roles in determining their response. Most importantly, and not previously demonstrated, lognormal activity distributions can have a profound impact on the response of the tumor cells even when the radionuclide emits high-energy electrons.

Induction of lethal bystander effects in human breast cancer cell cultures by DNA-incorporated Iodine-125 depends on phenotype

PURPOSE

This study uses a three-dimensional cell culture model to investigate lethal bystander effects in human breast cancer cell cultures (MCF-7, MDA-MB-231) treated with (125)I-labeled 5-iodo-2 -deoxyuridine ((125)IdU). These breast cancer cell lines respectively form metastatic xenografts in nude mice in an estrogen-dependent and independent manner.

MATERIALS AND METHODS

In the present study, these cells were cultured in loosely-packed three-dimensional architecture in a Cytomatrix™ carbon scaffold. Cultures were pulse-labeled for 3 h with (125)IdU to selectively irradiate a minor fraction of cells, and simultaneously co-pulse-labeled with 0.04 mM 5-ethynyl-2'-deoxyuridine (EdU) to identify the radiolabeled cells using Click-iT(®) EdU and flow cytometry. The cultures were then washed and incubated for 48 h. The cells were then harvested, serially diluted, and seeded for colony formation. Aliquots of cells were subjected to flow cytometry to determine the percentage of cells labeled with (125)IdU/EdU. Additional aliquots were used to determine the mean (125)I activity per labeled cell. The percentage of labeled cells was about 15% and 10% for MCF-7 and MDA cells, respectively. This created irradiation conditions wherein the cross-dose to unlabeled cells was small relative to the self-dose to labeled cells. The surviving fraction relative to EdU-treated controls was measured.

RESULTS

Survival curves indicated significant lethal bystander effect in MCF-7 cells, however, no significant lethal bystander effect was observed in MDA-MB-231 cells.

CONCLUSIONS

These studies demonstrate the capacity of (125)IdU to induce lethal bystander effects in human breast cancer cells and suggest that the response depends on phenotype.

A method to predict response of cell populations to cocktails of chemotherapeutics and radiopharmaceuticals: validation with daunomycin, doxorubicin, and the alpha particle emitter (210)Po

There is considerable interest in the use of α-emitting radionuclides in radioimmunotherapy. However, the high toxicity of α-emitting radionuclides often does not permit administration of high activities for fear of normal tissue toxicity. Accordingly, targeting procedures need to be optimized for improved tumor control and minimized normal tissue toxicity. To guide design of effective cocktails of α-emitting radiopharmaceuticals and chemotherapy drugs, approaches that can predict biological response of a cell population on a cell-by-cell basis are needed.

METHODS

Cells were concomitantly treated with the α-particle emitting radiochemical (210)Po-citrate and daunomycin, or with (210)Po-citrate and doxorubicin. The responses of the treated cell populations were measured with a colony forming assay. The nonuniform cellular incorporation of the radiochemical and drugs was determined simultaneously on a cell-by-cell basis using flow cytometry. Monte Carlo methods were used to simulate cell survival on the basis of individual cell incorporation of each cytotoxic agent and validated by direct comparison with the experimental clonogenic cell survival.

RESULTS

Both daunomycin and doxorubicin enhanced the toxicity of the α-particles with a magnitude greater than expected based on single-agent toxicities. Cell survival obtained by Monte Carlo simulation was in good agreement with clonogenic cell survival for the combination treatments.

CONCLUSION

Flow cytometry assisted Monte Carlo simulations can be used to predict toxicity of cocktails of α-emitting radiopharmaceuticals and chemotherapy drugs in a manner that takes into account the effects of nonuniform distributions of agents within cell populations.

Monte Carlo simulation of irradiation and killing in three-dimensional cell populations with lognormal cellular uptake of radioactivity

PURPOSE

The biological response of tissue exposed to radiations emitted by internal radioactivity is often correlated with the mean absorbed dose to a tissue element. However, experimental studies show that even when the mean absorbed dose to the tissue element is constant, the response of the cell population within the tissue element can vary significantly depending on the distribution of radioactivity at the cellular and multicellular levels. The present work develops theoretical models to simulate these observations.

MATERIALS AND METHODS

Two theoretical models were created to simulate experimental three-dimensional cell culture models with homogeneous and inhomogeneous tissue environments. The cells were assigned activities according to lognormal distributions of an alpha particle emitter or a monoenergetic electron emitter. Absorbed doses to the cell nuclei were assessed with point-kernel geometric-factor and Electron Gamma Shower version nrc (EGSnrc) Monte Carlo radiation transport simulations, respectively. The self- and cross-dose to individual cell nuclei were calculated and a Monte Carlo method was used to determine their fate. Survival curves were produced after tallying the live and dead cells.

RESULTS

Both percent cells labeled and breadth of lognormal distribution affected the dose distribution at the cellular level, which in turn, influenced the shape of the cell survival curves.

CONCLUSIONS

Multicellular Monte Carlo dosimetry-models offer improved capacity to predict response to radiopharmaceuticals compared to approaches based on mean absorbed dose to the tissue.

Flow cytometry-assisted Monte Carlo simulation predicts clonogenic survival of cell populations with lognormal distributions of radiopharmaceuticals and anticancer drugs

PURPOSE

Although the distribution of therapeutic agents within cell populations may appear uniform at the macroscopic level, the distribution at the multicellular level is nonuniform. As such, the mean agent concentration in tissue may not be a suitable quantity for use in predicting biological effects. Failure in chemotherapy and targeted radionuclide therapy has been attributed, in part, to the ubiquity of lognormal distributions of therapeutic agents. To improve capacity to predict biological response, this work develops approaches that determine the fate of a cell population on a cell-by-cell basis.

METHODS

Incorporation of the α-particle emitting radiochemical ((210)Po-citrate) and two anticancer drugs (daunomycin and doxorubicin) by Chinese hamster V79 cells was determined using flow cytometry. Monte Carlo simulation was used to estimate cell survival on the bases of mean and individual cell incorporation of each cytotoxic agent. The interrelationships between the Monte Carlo simulated cell survival and clonogenic cell survival were evaluated.

RESULTS

Cell survival obtained by Monte Carlo simulation based on individual cell incorporation was in good agreement with clonogenic cell survival for all agents. However, the agreement was poor when the simulation was carried out using the mean cell incorporation of the agents.

CONCLUSION

These data indicate that, with the aid of flow cytometry, Monte Carlo simulations can be used to predict the toxicity of therapeutic agents in a manner that takes into account the effects of lognormal and other nonuniform distributions of agents within cell populations.