PROJECT SUMMARY Lethal prostate cancer preferentially spreads to the bone. Standard of care treatment for bone-metastatic prostate cancer includes androgen-deprivation therapy (ADT). While initially effective, ADT is not curative and, moreover, is associated with increased bone comorbidities. As such, new therapeutic strategies that not only target the metastatic tumor, but also treat associated skeletal comorbidities are urgently needed. We previously demonstrated an important cancer cell-intrinsic role for Ca2+/calmodulin-dependent protein kinase kinase 2 (CAMKK2) in prostate cancer progression and improved bone strength following systemic CAMKK2 inhibition. However, whether targeting CAMKK2 can inhibit prostate cancer bone metastasis and counteract disease- or therapy-linked comorbidities are unknown. This knowledge gap needs to be addressed to determine whether CAMKK2 inhibitors, currently under development, can be used to treat this advanced stage of the disease and hence, inform future clinical trials. The goal of this proposal is to define CAMKK2’s role in prostate cancer bone metastasis and associated bone disease. These findings will help drive the development of new CAMKK2- targeted therapies and can inform future clinical trials. Moreover, we anticipate that CAMKK2 inhibition may also improve the safety and efficacy of existing treatments. It is our central hypothesis that CAMKK2 promotes prostate cancer progression by altering the bone-tumor microenvironment as well as through cancer cell autonomous mechanisms. We additionally propose that inhibition of CAMKK2 will both impair prostate cancer bone metastasis and counteract ADT-mediated bone complications. To test our hypothesis, we propose the following two specific aims: Aim 1: Delineate CAMKK2’s cell autonomous and non-autonomous roles in bone- metastatic prostate cancer. Aim 2: Determine the effect of CAMKK2 inhibition on therapy-linked, prostate cancer-bone comorbidities. Under the first aim, we will test how disruption of CAMKK2 in the host (cell non- autonomous) and/or cancer (cell autonomous) impacts different stages of prostate cancer bone metastasis in syngeneic and xenograft mouse models of prostate cancer under hormone-naïve and castration-resistant settings. In the second aim, the effects of CAMKK2 inhibition on tumor-bearing bone microarchitecture will be assessed using micro-CT and bone quality/strength will be assessed ex vivo. This proposal is innovative because it explores new roles for CAMKK2 in bone-metastatic prostate cancer by examining effects on both the tumor itself and surrounding bone. These studies are highly significant because they will not only delineate new roles for CAMKK2, but also establish its potential as an excellent drug target for the treatment of bone- metastatic, castration-resistant prostate cancer, alone or in combination with existing therapies.