A Concept of Biopharmaceutical Nanosatellite

Abstract

The article is a short overview of a proposal of a CubeSat type nanosatellite designed to conduct biopharmaceutical tests on the low earth orbit. Motivations behind the emerging demand for such solution nowadays and in the close future are emphasized. The possible objectives and challenges to be addressed in the planned biopharmaceutical CubeSat missions are discussed. In particular, it is hard to imagine progress of the space tourism and colonization of Moon and Mars without a wide-ranging development of pharmaceutics dedicated to be used in space. Finally, an exemplary layout of a 3U type CubeSat is presented. We underline that, thanks to recent development in both nanosatellite technologies and lab-on-a-chip type biofluidic systems, the proposed idea becomes now both feasible and relatively affordable.

Introduction

A huge progress has been made over recent years in the development of various functional tissues and organoids that may play a significant role in the preclinical stage of drug development and personalized medicine. The progress in the discipline benefited significantly from advancement of new technologies such as three-dimensional (3D) bioprinting,¹ microfluidics,² and organ-on-a-chip.³ The technologies became a basis of viable business models that promise further rapid expansion of the commercial applications in various branches of medicine, pharmacy, and biotechnology.

Another unprecedented business activity is currently observed in the domain of space technologies. This is mostly stimulated by development of information accumulating, transmitting, and processing solutions employing fully functional nanosatellites, in particular, those in the CubeSat standard. This includes swarm CubeSats systems devoted to Earth imaging and global Internet access. Furthermore, the cargo delivery to the low Earth orbit (LEO) is taken over by companies such as Space X. Further solutions are in advanced stage of development by companies such as Rocket Lab, Blue Origin, Virgin Galactic, or Stratolaunch Systems. These new possibilities will not only significantly decrease costs of placing nanosatellites on Earth orbit but also contribute to development of human space activity including space tourism.

But there is even more about space going on nowadays. The plans of building settlements on Moon and Mars are becoming more serious, clear, and feasible.⁴ This is mostly because of the effort of European Space Agency (ESA), China National Space Administration, National Aeronautics and Space Administration (NASA), and Space X.

Therefore, in the eve of space colonization,⁵ we have to ask ourselves whether humans are ready for this and if not what kind of difficulties has be to overcome by addressing them early enough to be ready on time. In our opinion, one of such challenges is development of different kinds of drugs that will be used during the manned long-term space activity, including colonization of Moon and Mars as well human activities related to the space mining in the deep space. This is motivated by the following main facts:

During the long-drawn space missions, humans are exposed to elevated cosmic radiation level, which increases possibility of tumor development.

The microgravity conditions affect significantly the metabolic processes that may result in diseases and injuries.

Very limited research has been conducted to determine whether the expected Earth-based pharmacokinetics and pharmacodynamics of a drug are altered in a microgravity environment.

Action of the pharmaceutics is affected by the cosmic stresses such as microgravity and cosmic radiation.

There is no data currently to provide a basis for clinical recommendations.

Therefore, there is a need to develop a set of drugs that are designed to be used in the space environment. Testing platform for drugs in space is to be built. As we discuss hereunder, such objectives seem to be possible to achieve, thanks to the combination of nanosatellite technologies with the 3D cell cultures and lab-on-a-chip systems designed to the drug testing applications.

Objectives and Challenges

The idea of using CubeSats to conduct relatively cheap astrobiological research in space is not new. For instance, missions such as GenSat-1,⁶ PharmaSat 1,⁷ and O/OREOS⁸ were conducted successfully in recent years. Furthermore, CubeSat missions such as EcAMSat⁹ and BioSentinel¹⁰ are in the advanced stage of preparation. The BioSentinel experiment is especially interesting since it is going to be carried beyond LEO and launched by the first flight of Space Launch System rocket,¹¹ which is designed to conduct both lunar and martian missions. The BioSentinel is a 6U type mission that contains a microfluidic card equipped with three-color light emitting diode (LED) detection system, allowing to analyze metabolic properties of the yeast Saccharomyces cerevisiae in deep space. The reference system will be placed at the International Space Station (ISS), where microgravity is similar but the amount of radiation is suppressed with respect to the deep space environment due to the effect of Earth's magnetic field.

Investigation of the effect of cosmic radiation on basic model with yeast might be the first step toward testing drugs alone and in combination. There is no basic data in the literature on the effect of radiation on DNA structure in cells. Radioprotective mechanism of action of drugs on DNA structure has to be elucidated and yeast cells may provide a suitable model.¹² When basic information on genetic alteration under radiation condition is gathered, the next step will be to test effect of drugs in 3D cell culture, which mimics natural development of tumor. Currently, the most broadly studied groups of drugs in oncology are immunologic and antiangiogenic drugs.¹³ To plan to test novel antitumor drugs that exhibit immunomodulatory and antiangiogenic properties, the challenge is to build precise model of tumor environment in cell culture; therefore, cell culture should not consist only of cancer cells but also epithelial cells of vessels and cells of immunologic system. Also, it is extremely interesting to gain insight into cancer stem cell biology in space condition; therefore, the next dimension of cellular model is to incorporate cancer stem cells.

Basic test to perform on cell culture is alamarBlue^®. This is cell assay that allows to quantitatively measure cell viability.¹⁴ Changes in viability are detected by absorbance plate reader. Also genetic expression of cells may be measured with other types of assays. Specifically, taking into account the progress in automation and miniaturization of the so-called omics techniques¹⁵ (such as DNA sequencing), there is emerging possibility to apply them to biotechnology and pharmacology research conducted in space.¹⁶

The novelty we are proposing to implement in the space environment is the cell cultures equipped with (micro-)fluidic system, designed to conduct biopharmaceutical studies. Although prokaryotic cells such bacteria (e.g., Escherichia coli) and fungi (e.g., yeast S. cerevisiae) provide a well-established standard for studying impact of radiation on genetic information (e.g., double-strand breaks), testing of pharmaceutics requires the use of more sophisticated eukaryotic cell cultures.

The problem is, however, that conducting animal cell cultures, even in laboratory environment, requires special conditions and processing. Miniaturization of such laboratory setup to the size of, let say, 2U, and choice of adequate cell cultures are, therefore, a serious challenge.

The type of cell cultures which are both the most stable ones and also one of the most relevant to be studied in the space environment are cancer cells. One of the characteristic features of the tumor cells is their immortality, which means that they divide continuously. Despite this property, culturing cancer cells is demanding, even in laboratory conditions—they require special condition and treatment to grow. Maintaining continuity of cell culture in space is much more demanding, as it needs automation in changing medium and passaging. This is to ensure culturing in specialized fluidic systems. However, recent advances in development of the cancer-on-a-chip^17,18 systems give us the basics to claim that the required miniaturization of the biopharmaceutical device is possible to achieve.

To give an intuition of some relevant orders of magnitude, let us consider a cell culture confined to the volume of 1 cm³ that is going to be conducted for a period of up to 1 month. This period should be long enough to already see some effects of microgravity and radiation. Typically, ∼1,000 cancer cells are plated in let us say 4 mL of medium, and these cells can divide in logarithmic rate at the beginning with plateau growth later occurring depending on refeeding (the process can be modeled by the Gompertz curve). For a period of 1 week, number of cells can increase 10 times. In the first week, growth is faster, whereas in the second week, growth rate can be two times lower. Usually, once a week, the medium should be changed, resulting in slight increase of rate of cell growth. Therefore, if we want to simulate laboratory conditions in a nanosatellite, we should ensure the medium is changed four times in the period of 1 month. Culturing medium in suspension should ensure 90% viability rate in conditions 37°C, 5% CO₂, and 16%–19% O₂. Major importance in the project is development of suitable suspension-culture medium that requires little or no additional task to maintain the culture.

Detailed analysis of dynamics of cancer growth as a function of control parameters has to be performed to optimize the experimental setup. Preliminary steps can be performed with the use of Gompertz model of the tumor growth in a constrained environment. In such a case, the number of cancer cells in time t is given by the following formula^19,20: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} N ( t ) = { N_0 } \exp \left\{ { \ln \left( { { \frac { { N_ \infty } } { { N_0 } } } } \right) \left[ { 1 - \exp ( - \lambda t ) } \right] } \right\} , \tag { 1 } \end{align*} \end{document}

where N₀ is the initial number of cancer cells and \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $${N_ \infty }$$ \end{document} is the upper bound on the number of cells in the culture. In particular, in the considered exemplary setup with the maximal volume constrained to 1 cm³, we can estimate that \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $${N_ \infty } \sim {10^9}$$ \end{document} . Extracting from Equation (1) the initial doubling time \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} { \rm { DT } } : = - \frac { 1 } { \lambda } \ln \left[ { 1 - { \frac { \ln 2 } { \ln \left( { { \frac { { N_ \infty } } { { N_0 } } } } \right) } } } \right] , \tag { 2 } \end{align*} \end{document}

and comparing it with doubling time scales for cells culture under consideration (which may range from hours to hundreds of days), parameter \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$\lambda$$ \end{document} of the model can be determined. Based on this, experimental details can be fixed such that the plateau of the culture size is reached in the period of ∼1 month. Then, impact of the antitumor treatment on dynamics of the tumor growth can be modeled by generalization of Equation (1) (see, Ref.²⁰).

Although the discussion presented here concerns the novel possibility of cultivating mammalian cell cultures with the use of nanosatellites, the subject of conducting cell colonies in space is of (theoretical and experimental) investigations since around three decades now.^21–23 In particular, in July 1995 during the STS-70 Space Shuttle mission, experiments with colon carcinoma cells were performed by employing Bioreactor Demonstration System. The experiment was repeated in August 1997 during the STS-85 mission. In has been shown that the carcinoma cells aggregated to form masses, which were around 30 times the volume of the controlled cultures on the ground.²⁴ This proved that space environment, due to the effect of microgravity, provides favorable conditions to development of tissue-like 3D structures of living organisms (which can be relevant also for Earth applications such as tissue engineering). Afterward, the space experiments with cell colonies were performed on ISS. In particular, the ADvanced Space Experiment Processor²⁵ has been used for this purpose. The system contains Cell Culturing (CellCult) laboratory that comprises one rotating 50-mL bioreactor together with auxiliary systems. Furthermore, the ISS Columbus module is equipped with the Biolab,²⁶ which supports biological experiments on cells and tissue cultures. Another relevant equipment is the Microgravity Science Glovebox (MSG), installed in the ISS Destiny module.²⁷ Employing the MSG, Angiex, Inc.²⁸ has recently initiated experiments on vascular-targeted cancer therapy with endothelial cells, which line the walls of blood vessels. The studies are up to date the most similar to the idea of research direction presented in this article. However, to the best of our knowledge, no lab-on-a-chip systems or 3D cell cultures have been used in the tumor treatment experiments performed on ISS. Furthermore, owing to limited lifetime of the ISS and costs of performing commercial activity on ISS, development of low-budget nanosatellite missions becomes justified, which we discuss in more detail in the next section.

Cubesat Overview

According to our estimates, the 3U size in the CubeSat standard is sufficient to accommodate all key systems of the basic biopharmaceutical nanosatellite. An exemplary CubeSat contains three functional modules, each of the 1U size (10 × 10 × 10 cm³), as presented in Figure 1.

Fig. 1.

Block structure of the 3U biopharmaceutical CubeSat. Each module is of the 1U size. EPS, electrical power system; UHF, ultra high frequency.

Module 1 contains system responsible for control, data processing, communication, orientation, and energy supply. Communication with the satellite can be conducted simultaneously in the ultra high frequency (UHF) (or/and very high frequency) band and the S-band. Although the basic control uses the UHF in downlink and uplink mode, the S-band in the downlink mode is devoted to transmit scientific data. The S-band transmission is provided by the patch antenna working at the conventional 2.4 GHz WiFi frequency. There are a few (∼5) observational 5 min windows a day. The 9,600 bps downlink transfer of information is planned. This means that within a single observational window ∼350 kB of data can be transferred, including control information and error correction. This amount of information is expected to be sufficient to cover partially preprocessed data from the scientific instruments (absorbance red green blue sensors, radiation sensor, visual imaging, and environmental sensors). The transceiver module is responsible for managing transmission at both UHF and S-band frequencies. The data are managed and processed at the Motherboard connected through I²C port with the other subsystems. Among them, the Magnetorquer will allow to fix correct orientation (toward to Earth) of the S-band antenna. Furthermore, Module 1 contains electrical power system and batteries.

Module 2 contains reservoir of cell culture medium, air (O₂ and CO₂ mixture) tank, sink for the fluidic system, and temperature stabilization system. The estimated volume of the cell culture medium reservoir needed to conduct 1 month long studies is 100 mL.

Module 3 contains experimental unit equipped with fluidic system and tumor cell culture, camera for tumor growth imaging, LED absorbance detectors for metabolism monitoring, and dose of the pharmacological active substance. Details of the experimental setup are to be specified in the forthcoming steps of the development of the project.

Both experimental elements contained in Module 1 and Module 2 are enclosed in temperature stabilization system providing incubating conditions for the cell culture, that is, 37°C. The system is crucial since it must provide stable conditions for the whole experimental setup. The temperature stabilization system will also be the most energy consuming. However, owing to other constrains, the system has to be designed such that its power consumption does not exceed around 2W. Achieving such a goal will require application of specialized insulating solutions to prevent against both cooling and excessive heating of the system (the temperature of a satellite at LEO is varying from around −100°C to around 100°C).

All four longer sides of the CubeSat are covered by photovoltaic cells providing in total ∼7W with 3V supply voltage. Furthermore, at least 25Wh in the battery pack will be needed.

The proposed construction is designed to operate at the LEO for a period up to ∼3 months. Depending on the orbit details, there might be a need to complement the nanosatellite with an additional deorbitation system. Furthermore, one has to keep in mind that although the LEO provides higher amount of radiation comparing with the Earth, testing the effects related, for example, with human exploration of Mars requires to go beyond LEO, where the amount or radiation is higher. This will be, in particular, the scope of the 6U type BioSentinel experiment.

Furthermore, it is crucial to emphasize that the process of drug development requires extensive both preclinical and clinical studies that are unavoidably long drawn and expensive. The studies performed with the use of nanosatellite laboratories would contribute to the final phase of preclinical trials, which should be preceded with detailed on ground investigations, including simulated microgravity conditions (utilizing clinostats and random positioning machines) as well as exposition to radiation (e.g., gamma radiation). Such studies would allow to reduce the number of configurations to be tested in space and optimize the overall costs of the drug development. Despite this, even for a single pharmaceutical to be developed, multiple missions will be necessary to be conducted, investigating different aspects of pharmacokinetics and pharmacodynamics (e.g., dose–response relationship). Furthermore, as it has already been mentioned, development of drugs devoted to human exploration beyond LEO would require higher levels of radiation, which can be achieved only at much higher orbits, including interiors of the Van Allen radiation belts. This will unavoidably influence on complexity of CubeSat missions, increasing the number of units to six or more. Specifically, the more powerful communication systems as well as orbit correction systems, such as ion thruster, will be required.

Let us finally discuss the important issue of timing. Numerous human missions beyond LEO (lunar orbit, L₂ Southern Near Rectilinear Halo Orbit [NRHO], Moon landing, etc.) are planned in the second half of 20s of this century. Furthermore, human missions to Mars are expected in early 30s or even yet in late 20s. At the same time, the ISS will operate until late 20s, with no further plans for a new LEO manned station by NASA or ESA. In contrast, the Lunar Orbital Platform-Gateway successor of ISS is expected to be placed at the highly elliptical NRHO around the Moon, where the level of cosmic radiation is comparable with that in deep space. Therefore, there are roughly no >5 years to develop pharmaceutics dedicated to be used in space beyond LEO. Taking into account the typical time scales of let us say a new antitumor treatment, half a decade is not a long period of time. This is just enough to perform 2 years of preclinical trials on ground, 2 years of preclinical test with the use of CubeSats (roughly four missions), and 1 year of clinical trials. Furthermore, although the need to develop new “space drugs” will significantly increase in the late 20s, the ISS will become inaccessible to conduct the tests. In contrast, owing to further reduction in both launch costs and CubeSats themselves, the nanosatellite biopharmaceutical laboratories will become seemingly the only reliable alternative. They will provide low-cost, fast in preparation, flexible in design, modular, low risk, and easy to launch solution. Worth stressing is that due to emerging market of small rockets, such as RocketLab (Electron rocket), Virgin Galactic (LauncherOne system), Stratolaunch Systems (Pegasus rocket), and others, sending CubeSats to LEO will became both cheaper and more flexible.

Summary

The purpose of this article was to emphasize an emerging need to start performing biopharmaceutical tests in space. We have stressed that combination of two recently rapidly expanding technologies, that is, lab/organ-on-a-chip and nanosatellites may make such studies accessible and affordable. The expected cost of a single mission is not >2 million Euro. Such relatively low costs space experiments if well designed can provide scientifically unique and practical data with a potential for successful commercialization. In particular, it is hard to imagine progress in the space tourism and colonization of Moon and Mars without a wide-ranging development of pharmaceutics dedicated to be used in space. Especially, owing to the increased risk of cancer due to the cosmic radiation, antitumor drugs are to be developed.

Footnotes

Acknowledgment

The authors thank Anna Kornakiewicz for her invaluable support at the initial stage of development of the idea presented in this article.

Author Disclosure Statement

No competing financial interests exist.

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