Junyi Zhang

HSP90 Inhibitor–SN-38 Conjugate Strategy for Targeted Delivery of Topoisomerase I Inhibitor to Tumors

The clinical benefits of chemotherapy are commonly offset by insufficient drug exposures, narrow safety margins, and/or systemic toxicities. Over recent decades, a number of conjugate-based targeting approaches designed to overcome these limitations have been explored. Here, we report on an innovative strategy that utilizes HSP90 inhibitor–drug conjugates (HDC) for directed tumor targeting of chemotherapeutic agents. STA-12-8666 is an HDC that comprises an HSP90 inhibitor fused to SN-38, the active metabolite of irinotecan. Mechanistic analyses in vitro established that high-affinity HSP90 binding conferred by the inhibitor backbone could be exploited for conjugate accumulation within tumor cells. In vivo modeling showed that the HSP90 inhibitor moiety was required for selective retention of STA-12-8666, and this enrichment promoted extended release of active SN-38 within the tumor compartment. Indeed, controlled intratumoral payload release by STA-12-8666 contributed to a broad therapeutic window, sustained biomarker activity, and remarkable degree of efficacy and durability of response in multiple cell line and patient-derived xenograft models. Overall, STA-12-8666 has been developed as a unique HDC agent that employs a distinct mechanism of targeted drug delivery to achieve potent and sustained antitumor effects. These findings identify STA-12-8666 as a promising new candidate for evaluation as novel anticancer therapeutic. Mol Cancer Ther; 14(11); 2422–32. ©2015 AACR.

Abstract 4409: STA-12-8666: a first-in-class HSP90 inhibitor drug conjugate (HDC) designed to selectively deliver chemotherapy to tumors

Chemotherapeutic drugs have been a mainstay of cancer therapy for decades; however, their effectiveness is often hampered by inefficient drug exposures and undesirable toxicity to normal tissues. Here we report on a novel drug delivery system, termed heat shock protein 90 (HSP90) inhibitor-drug conjugates (HDC), based on the property that small molecule inhibitors of HSP90 are preferentially retained in tumors cells in contrast to their rapid clearance from the circulation and normal tissues. By attaching chemotherapeutic drugs to HSP90 inhibitor backbones, HDC technology exploits this inherent retention property to efficiently deliver cytotoxic payloads directly into tumor tissues and provide extended drug exposure. STA-12-8666 is an HDC that comprises an HSP90 inhibitor fused to the topoisomerase inhibitor SN-38 (active metabolite of irinotecan). In vivo modeling showed that the HSP90 inhibitor moiety was required for tumor-selective retention of STA-12-8666. Prolonged exposure of STA-12-8666 provided extended release of active SN-38 within the tumor compartment, generating up to two weeks of biomarker engagement (γ-H2AX) in contrast to 3-4 days with irinotecan. The broad therapeutic window exhibited by STA-12-8666 conferred superior efficacy and durability over irinotecan treatment alone - resulting in complete or near complete responses (CR) across a broad spectrum of solid tumor models, including an irinotecan-insensitive bladder cancer model and an aggressive lung cancer model where biweekly treatment of STA-12-8666 was initiated at a starting tumor volume 5-times greater that of typical studies. CRs were also observed in a human pancreatic PDX model following 3 doses of STA-12-8666, which were maintained for more than a month. Of note, recurrent PDX tumors remained sensitive to subsequent therapeutic challenge with STA-12-8666 suggesting HDC delivery may circumvent common mechanisms of resistance to irinotecan. Preliminary findings from an ongoing Phase 1 dose escalation study in dogs with spontaneous tumors suggest a well-managed safety profile and encouraging tumor responses. Overall, STA-12-8666 is a promising investigational agent prototypical of a platform technology that can be applied to other cytotoxic payloads to improve therapeutic indices as well as generating new pharmaceutical entities for evaluation as novel anticancer drugs. Citation Format: David A. Proia, Donald L. Smith, Junyi Zhang, Dan Zhou, John-Paul Jimenez, Jim Sang, Sarah Rippy, Cheryl London, Luisa S. Ogawa, Jun Jiang, Teresa Przewloka, Manuel Sequeira, Jaime Acquaviva, Suqin He, John Chu, Chaohua Zhang, Yuan Liu, Josephine Ye, Vladimir Khazak, Igor Astsaturov, Takayo Inoue, Noriaki Tatsuta, Richard C. Bates, Andrew Sonderfan, Dinesh Chimmanamada, Weiwen Ying. STA-12-8666: a first-in-class HSP90 inhibitor drug conjugate (HDC) designed to selectively deliver chemotherapy to tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4409. doi:10.1158/1538-7445.AM2015-4409

Abstract 2509: Hsp90-inhibitor drug conjugates (HDC): Novel tumor-selective drug delivery platform with unprecedented anticancer activity

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Various strategies have been used to make chemotherapeutic compounds more tumor selective in order to increase their safety and efficacy, but they were met with only limited success. Antibody Drug Conjugates (ADCs) and folate receptor mediated drug delivery (FRDC) are the emerging concepts in the drug delivery field, but they are limited to high potent toxins and narrow sets of indications. We established a novel tumor-directed drug delivery platform technology based on the unique property of Hsp90 inhibitors. One prominent feature of Hsp90 inhibitors is their ability to be retained selectively in tumor cells for a prolonged period of time. The difference in residency time in tumor against plasma and normal tissues is 10-25 fold. Moreover, the chaperone protein Hsp90 is overexpressed 2-3 fold in tumor compared to normal tissues. Combining the overexpression Hsp90 and longer residency of its inhibitors in tumor, a strategy to link anticancer drugs to an Hsp90 inhibitor, where the attached “payload” is released in the tumor selectively for prolonged periods, was conceived. Results: Though the HDC concept is applicable to most small molecule anticancer drugs, we chose a common topoisomerase-1 inhibitor (SN-38) for proof-of-concept studies. More than 100 Hsp90 inhibitor/SN38 conjugates were synthesized; we chose STA-12-8666 as our lead molecule based on its in vitro and in vivo pharmacokinetic properties. The conjugate binds strongly to Hsp90 as determined by client protein degradation assays and has good stability in plasma of several species (human>rat>mouse). In xenograft tumor tissue distribution studies, we demonstrate that mice dosed once weekly with 50 mg/kg STA-12-8666 clear the parental HDC and its cleavage products, SN-38 and the Hsp90 inhibitor, from plasma and normal tissue within 24 hr. However, we detected 0.6 µM and 0.3 µM SN-38 in tumor at 24h and 48h, respectively. SN-38 was not detected in tumor at 24h or 48h with an equivalent dose of the SN-38 prodrug, irinotecan. Xenograft studies using multiple cell lines demonstrated superior efficacy for STA-12-8666 compared to irinotecan. For example, in MCF-7 breast cancer xenografts, STA-12-8666 produced 70% regression in tumor volume compared to moderate tumor growth inhibition by irinotecan with no regression. Similar results were observed in in colon, SCLC, ovarian, bladder, NSCLC, melanoma models. Preliminary toxicological evaluation of STA-12-8666 resulted in better or comparable toxicities to that of irinotecan. Conclusion: We designed a novel tumor-directed drug delivery platform by conjugating previously validated small molecule chemotherapeutics to HSP90 inhibitors. Our lead candidate STA-12-8666, has great tissue distribution profile, superior in vivo antitumor activity and better safety profile than the active control irinotecan, warranting its clinical evaluation. Citation Format: Dinesh Chimmanamada, David Proia, Takayo Inoue, Luisa Shin Ogawa, Suqin He, Manuel Sequeira, Donald Smith, John-Paul Jimenez, Chaohua Zhang, Jim Sang, Jaime Acquaviva, Masazumi Nagai, Yuan Liu, Josephine Ye, Dan Zhou, Andrew Sonderfan, Ritu Singh, Noriaki Tatsuta, Teresa Przewloka, Jun Jiang, Junyi Zhang, Weiwen Ying. Hsp90-inhibitor drug conjugates (HDC): Novel tumor-selective drug delivery platform with unprecedented anticancer activity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2509. doi:10.1158/1538-7445.AM2014-2509

Abstract 1619: Hsp90 inhibitor drug conjugates (HDCs): Construct design and preliminary evaluation

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Most cytotoxic agents are often broadly active but non-selective, and have the disadvantage of high toxicity due to collateral damage to normal tissues. Drugs that target specific protein drivers of cancer cell growth are more tumor selective, yet often lead to tumor resistance via point mutations in their target or activation of alternative signaling pathways. Targeted delivery strategies, such as Antibody-Drug Conjugates (ADCs), offer a solution to these limitations by delivering potent anti-cancer payloads more directly to tumors. Hsp90 is a chaperone protein required by many cancer cells to maintain the stability and function of numerous proteins that drive cancer cell growth, survival, and metastasis. Small molecule inhibitors of Hsp90 such as ganetespib, PU-H71 and 17-AAG are found to be retained in tumors with half- time up to 65 hours in mouse xenografts. These properties are believed to be due to overexpression of an active form of Hsp90 in cancer cells as compared to normal tissues, and have recently been applied for tumor imaging in patients. Results: We have developed a small molecule drug conjugate platform technology using the unique properties of Hsp90 proteins and Hsp90 inhibitors. We have synthesized HDCs with various Hsp90 inhibitor scaffolds including resorcinol, purine, geldanamycin, etc. A cell-based client protein degradation assay is carried out to confirm the intracellular uptake and the Hsp90 binding of the conjugates. While different Hsp90 inhibitor scaffolds offer different DMPK and toxicology profiles, cellular uptake and Hsp90 binding are not greatly affected by the different chemical classes of Hsp90 inhibitors. Over 30 payloads have been conjugated with Hsp90 inhibitors so far. We have selected the payloads based on the hypothesis that HDC can improve the safety profile of a cytotoxic drug, expand the application of chemotherapeutic agents to different tumor types, combat drug resistance, and enable novel anticancer approach. Examples of payloads include topoisomerase inhibitors (camptothecin), microtubule modulators (taxanes), proteasome inhibitors (carfilzomib), CDK inhibitors (flavopiridol) and others. Unlike most other conjugate technologies, HDC does not require lengthy spacing between the anchor Hsp90 inhibitor and the payload. Linker cleavage mechanism is considered a key feature in the HDC design. We have been able to incorporate several linkers such as disulfide, hydrazone, peptide, carbamate, carboxylate, etc. into our HDC designs. Conclusion: In this HDC platform, we provide a method which can be applied to many well-studied mechanisms for modulating cancer pathways and stopping tumor cell growth. We have created a promising platform technology which can result in many anticancer agents in the near future. Citation Format: Weiwen Ying, Dinesh Chimmanamada, Junyi Zhang, Teresa Przewloka, Jun Jiang, Genliang Lu, Sami Osman, James Loch, Dharma Vutukuri, Shoujun Chen, Robert Stein, John Chu, David Proia, Pat Rao, Takayo Inoue, Luisa Shin Ogawa, Ritu Singh, Noriaki Tatsuta. Hsp90 inhibitor drug conjugates (HDCs): Construct design and preliminary evaluation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1619. doi:10.1158/1538-7445.AM2014-1619