Which of the following statements is TRUE regarding drug development strategies for RXR- heterodimer receptors?Group of answer choicesDevelopment of drugs for specific receptor isoforms must always be designed to interact with amino acids outside the ligand binding domain, since the sequences in that domain are so similar between isoforms.It is possible to develop selective RXR binding drugs that target specific RXR-nuclear receptor heterodimers, despite the fact that RXRs interact with many different nuclear receptors.To develop drugs that target human RXR-heterodimer receptors, researchers only conduct their experiments with human receptors in human cell-based assays, since the structure and function of these receptors varies so widely across species.Since RXR heterodimer receptors are always found in the cytoplasm in the absence of hormone, a drug that inhibits ligand induced nuclear translocation would effectively block its activity.

The statement that is TRUE regarding drug development strategies for RXR- heterodimer receptors is: "It is possible to develop selective RXR binding drugs that target specific RXR-nuclear receptor heterodimers, despite the fact that RXRs interact with many different nuclear receptors."

This is because RXR (Retinoid X Receptor) forms heterodimers with various nuclear receptors, and it is possible to develop drugs that selectively bind to specific RXR-nuclear receptor heterodimers. This selectivity can be achieved by designing drugs that interact with unique regions of the receptor or by exploiting differences in the conformational changes induced by ligand binding.

The other statements are not necessarily true:

1. Development of drugs for specific receptor isoforms does not always have to interact with amino acids outside the ligand binding domain. It is possible to achieve selectivity within the ligand binding domain itself.

2. While it is important to conduct experiments with human receptors in human cell-based assays, it is not the only method. Animal models and in vitro studies are also used in drug development.

3. RXR heterodimer receptors are not always found in the cytoplasm in the absence of hormone. They can also be located in the nucleus, and their location can change depending on the presence of ligands and other factors. Therefore, a drug that inhibits ligand induced nuclear translocation would not necessarily block its activity.