Despite recent advances in both targeted therapy and immunotherapy, the overall survival (OS) for metastatic prostate cancer (PCa) remains low. This renewal application is to continue our productive efforts to develop a new tubulin inhibitor that can overcome drug resistance associated with FDA approved tubulin inhibitors, and will therefore, increase OS in PCa and other types of cancers where anti-tubulin drugs are used. The support from the previous periods of funding has resulted in a new drug candidate, Veru-111, which is under Phase 2 clinical trials for metastatic PCa. While Veru-111 is on a promising path to gain future FDA approval, there are significant room for improvement. The goals of this renewal are: (1) to develop the next generation of Veru-111 to proactively address its anticipated drug resistance; and (2) to develop targeted Veru- 111 drug conjugates to increase drug accumulation in prostate tumors and to target PCa bone metastasis. Aim 1. Develop a new generation of Veru-111, that can overcome both taxane resistance and the anticipated Veru-111 resistance. Preliminary data: We have discovered a hybrid scaffold based on Veru-111 and Azixa, represented by SHIP-216, that can overcome resistances to both taxanes and Veru-111. Approaches: Guided by high-resolution X-ray crystal structures, we will optimize the SHIP-216 scaffold to further improve its potency and drug-like properties. New analogs will be evaluated against a panel of PCa cell lines, including both taxane- and Veru-111-resistant cell lines to select the best five analogs for in vivo efficacy studies in Aim 3. Aim 2. Conjugate Veru-111 with PSMA targeting moieties to increase drug accumulation in PCa tumors and conjugate Veru-111 with bisphosphonates for more efficacious targeting of bone metastasis. Preliminary data: we have demonstrated Veru-111 itself can significantly reduce bone metastasis in a PDX model. We have also developed linkers for conjugating Veru-111 with PSMA targeting moieties or bisphosphonates. Approaches: we will optimize the length and composition of the linkers to PSMA targeting moieties and use different bisphosphonates in conjugation, to generate focused sets of Veru-111 drug conjugates. These conjugates will be first evaluated in vitro for stability and activation to select the best four conjugates (two in PMSA and two in bisphosphonates conjugates) for further in vivo efficacy studies in Aim 3. Aim 3. We will determine the maximum tolerable dose (MTD), pharmacokinetics (PK), and in vivo efficacy of the selected nine compounds from Aims 1-2 in both PCa cell line models and a PDX model to select the overall best compound to support subsequent clinical trials in the Veru-111 portfolio. Preliminary data: we have already shown that SHIP-216 as a new Veru-111 analog is highly efficacious against multiple xenograft models, including the 22Rv1 PCa and the Veru-111 resistant DU-145/VxR PCa models. Approaches: We will evaluate all selected new compou...