**3.6 Patient-derived cells**

Animal models used in laboratories have been greatly avoided due to the fact that they are costly and require a large number of laborers. This approach was replaced by the use of *in vitro* models wherein despite having several advantages; still, the application is constrained due to poor cell-to-cell and cell-to-matrix interactions. *In vitro* culture of cells has been observed to acquire multiple genetic and epigenetic variations that eventually make the cells lose their originality. The above-listed models comprise their own merits and demerits in respect of cellular response, cellular composition, and structural features. The above-mentioned models consist of a few advantages and disadvantages with respect to cellular composition, mimicking the *in vivo* physiology of original tumor architecture, tumor microenvironment (TME) and the response to different exogenous stimuli. Therefore, patient-derived cells have come into the picture which is generally a co-culture-based technology that is grown in a


#### **Table 2.**

*Summary of recent organ-on-a-chip models.*

culture medium supplemented with all sorts of nutrients [89]. Different studies have exemplified the use of patient-derived cells as a preclinical model in drug discovery (screening and responses) in several types of cells. Patient-derived xenograft (PDX) models are made of minute pieces of tumor tissue of the surgical patients, utilized for implantation into an immune-deficient mouse. In a study, Fong et al. used PDX

models from prostate cancer to investigate tumor-stromal interactions via the use of a 3D hydrogel system [90]. Likewise, in another study, Liu et al. demonstrated the establishment of patient-derived cell cultures from colorectal cancer cells of biopsies of cancerous and non-cancerous tissue that could grow in *in vitro* culture indefinitely by recapitulating exactly the same phenotypic and genotypic features of the original tissue [91]. Some of the researchers have also elaborated patient-derived 3D culture using a scaffold-based organoid culture that is prepared to preserve the genomic features of the original tissue [92].
