Many types of treatment are available for cancer today. The choice of the most appropriate one, or combination of them, depends on the type of cancer a person has and how the disease is advanced.

Major treatment options include:

- the surgical removal of the tumor mass from the body;

- the local use of high doses of radiation to kill cancer cells and make the tumor mass smaller;

- the systemic use of drugs that may

• kill rapidly proliferating cells (chemotherapy),
• help the immune system to fight cancer cells (immunotherapy),
• target specific molecular traits of cancer cells that help them proliferate and spread (targeted therapy); or
• kill or impair cancer cell that depend on hormones for their growth (hormone therapy for breast and prostate cancer).

Despite the great advancements made in treating cancers during the past decades, however, the tolerance of cancer cells to classical chemotherapeutic treatments and/or last generation therapies still remains a major challenge.

The insensitivity of cancer cells to treatments can be a pre-existing property of a patient’s tumor or it can develop during the course of therapy. In both cases, it represents a major cause of tumor relapses and death of the disease.

Why do cancer cells resist?

To date, different factors have been associated with chemosensitivity and drug resistance of cancer cells.

Pre-existing resistance
Treatments with chemotherapy and targeted drugs can have reduced efficacy because of the presence of insensitive subpopulations of cancer cells, within the tumor mass,  that are defined by pre-existing mutations in genes that are key to cancer cell growth and response to chemicals. Relevant genes are involved in controlling drug accumulation within the cell, the repair of DNA, or programs that control cell death.

Acquired resistance
Importantly, during drug treamtents new mutations or alteration in cancer cell gene expression can arise that cause the altered expression of different signaling pathways or the modification of drug targets. This can convert the originally treatable cancer cells into treatment resistant tumor cells.
Not only mutations but also other types of alterations affecting the so-called “packaging of DNA” into the ordered structures of chromatin, can contribute to the development of therapy resistance.

The tumor microenvironment
Moreover, tumors are made of not only cancer cells, but also the environment surrounding them with various types of cells including  fibroblasts, immune,  and inflammatory cells, as well as the extracellular matrix with collagen fibers, various signaling molecules,  blood vessels and others, that can communicate with cancer cells and contribute in determining  the response to therapy.
The stiffness of tumor microenvironment, for example, is associated with impaired drug distribution within the tumor mass, and with the activation of oncogenic signals that in turn have been shown to be associated with drug resistance.
The immune system has an intrinsic potential to constrain the development of tumor tissues by recognizing emerging cancer cells and operating their clearance. However, cancer cells can hide from the immune system by hijacking the immune checkpoints and favoring the establishment of an immunosuppressive microenvironment, that is known to enhance cancer development and cancer resistance to immunotherapies.

Patient derived 3D cancer cell culture systems such as human tumor organoids and spheroids, are state of the art models in disease modelling and represent a very promising experimental tool to reproduce and study a tumor in the laboratory, in a physiologically relevant and predictive way.
Tumor organoids are exclusively derived from cancer stem cells that in culture undergo different cancer cell specification. This type of systems can be maintained in culture for prolonged periods, even months.
Spheroids are instead cell culture systems in which a mix of cancer cells and diverse type of cells from the tumor microenvironment are cultured together for a relatively short period of time (3-6 weeks).
These systems imitate in vitro the in vivo structural organization of solid tumors, their cellular layered assembling and polarity, cell-cell physical interactions,  gene expression, nutrient and oxygen gradients, and tissue microenvironment (in the case of tumor spheroids).
It has been reported that the response of 3D systems to drugs and pharmacological compounds recapitulates the mechanisms of drug response and resistance found in vivo, in solid tumors.
Cancer cell lines have long been used as model systems.
They allow thorough experimentations and are very useful to study a molecular pathway or  carry out screenings.  However, they do not fully recapitulate the multicellularity of human tumors as well as their heterogeneity, and do not address the tumor microenvironment. Moreover, they provide information on therapy responses that does not cover the large heterogeneity of individual patients' tumors.
Implanting cancer tissue chips into mice (patient derived tumor xenograft) emerged as another advanced model. Tumor chips cover the multicellularity and microenvironmental features of human tumors, and they more closely resemble the physiological features of the tumor of origin and predict tumor clinical responses to therapy. However, xenograft engraftment may occur with low efficiency, the procedure is expensive and time consuming, and requires the intensive use of experimental animals.
Patient derived tumor organoids and spheroids, instead, are one of the most promising alternatives to mimic the original cancer tissue. They can be generated and propagated with high efficiency, as well as frozen in liquid nitrogen and recovered later for further use, and investigations at the single patient level.

P-CARE partners are working together to implement patient derived tumor organoids and spheroids as new tools to tackle key problems of cancer treatment.
We do not start from scratch. A previous endeavour - the Interreg project named PreCanMed that was realized thanks to the Interreg Italia-Austria Regional Development Fund of the EU - introduced the tumor organoids technology in the program area and created the foundation for the p-care effort.

PreCanMed main outcomes included:

- the interregional development of patient-derived tumor organoids as advanced tools for disease modelling;

- the generation of genomics information on them;

- the development of standardized protocols and procedures for organoid generation (SOPs), with technical material freely available to all interested researchers;

- the creation of an interregional biobank for tumor organoids and collected biological material.

Building on this, p-care is now committed to push forward the use of advanced 3D culture systems for studying cancer drug resistance and fighting it.

Bioinformatics analysis of the omics profiles of patient-derived organoids and spheroids will enable the identification of particular biological pathways that mediate immunotherapy or chemotherapy resistance. These pathways will be targeted by defined chemical compounds in a patient specific manner.  On the basis of bioinformatics analysis, we will identify a panel of potential drugs for each patient-derived system. These drugs will be tested in combination with standard treatments for their potential in reducing cancer cell resistance to either immunotherapy or chemotherapy, and limiting the growth of specific patient-derived organoids and spheroids.

In order to find new chemical compounds against cancer drug resistance, p-care is also testing whether existing drugs – originally approved for different medical indications – can restore the sensitivity of resistant cancer cells to standard therapies (immunotherapy or chemotherapy).
In a nutshell, this approach, named drug repositioning or drug repurposing, consists in finding new uses to ‘old’ drugs outside the scope of their original medical indication.
Why should a drug intended, for example, to lower blood cholesterol levels restrain the growth of cancer cells?
For most existing drugs, only a limited number of indirect targets and mechanisms of action within the cells are known, meaning that investigating their activity outside their original disease context may reveal new cues about their potential.
A hallmark example of such concept is represented by statins that, as other mevalonate pathway inhibitors, were reported not only to reduce cholesterol levels, but also to exert an inhibitory effect on key drivers of tumor development and metastasis. Nowadays statins are tested in cancer therapy.
The drug repositioning approach is increasingly becoming attractive because offers many advantages over developing a new drug from scratch. Indeed, it is less risky and more rapid because much work has already been done, from a safety point of view, in preclinical models and humans.
We will test different libraries of approved drugs in combination with either standard chemotherapy or immunotherapy on resistant patient-derived organoids and spheroids.