Table 3.

Strengths and weaknesses of various biological screening models used for natural products.

Screening Models	Strengths	Weaknesses
In-vivo animal models	Physiological similarities to humans; pathophysiological relevance is high; activity on the level of whole organism and transgenic models may be generated.	Require to manage animal facility; need larger amounts of test samples; ethical consideration; low-throughput; may be species related differences.
In-vitro cellular target-based assays	Known molecular target; no need to determine the mechanism of action separately; efficacy of hits at cellular level, high-throughput	Observed efficacy may not be a result of the mechanism originally expected because a drug generally bind at more than one target; may not be able to reflect whole mechanism of the hits; no assurance for in-vivo efficacy; requirement of cell culture facility
In-vitro phenotype cell-based assays	Potential to discover new molecular target; medium to high-throughput; efficacy of hits at cellular level	No assurance for in-vivo efficacy; requirement of cell culture facility; identification of molecular target may need great effort; possibility of poor structure activity relationship of hits in the optimization phase
In-vitro assays with isolated proteins	No animal or cell culture facilities required; high-throughput screening	Hits may be unable to reach the target for interaction into cells or in-vivo (hits with low bioavailability)
In-situ/ex-vivo isolated tissues or organs	Higher-throughput than animal models; good pathophysiological relevance	Lower-throughput than cell-based bioassays; ethical consideration; short life of isolated tissues and organs