Baeck, Johan

Abstract Purpose: R,R-1,2 cyclohexanediamine-pyrophosphato-platinum(II) (PT-112) is a novel immunogenic cell death–inducing small molecule under phase II development in several cancer types. It inhibits ribosome biogenesis and causes organelle stresses, leading to selective immunogenic cell death in cancer cells. The possibility of PT-112’s pyrophosphate moiety driving high drug concentrations to bone sites of disease has led to an interest in PT-112’s use in multiple myeloma. In this study, we present findings from phase I and in vivo studies for PT-112 in relapsed or refractory multiple myeloma. Experimental Design: PT-112 biodistribution was analyzed in mice via laser ablation inductively coupled plasma mass spectrometry. The activity of PT-112 was assessed in de novo and transplantable Tg(Igkv3-5*-MYC)#Plbe (Vk*MYC) multiple myeloma mouse models as monotherapy or combination therapies. M-spike levels and survival were measured. A phase I dose escalation study of PT-112 monotherapy was conducted using a 3 + 3 design in patients with heavily pretreated relapsed or refractory multiple myeloma with exhausted available therapies. Results: In vivo biodistribution imaging revealed high concentrations in the bone, kidney, lung, skin, and liver. PT-112 was active in Vk*MYC multiple myeloma mouse models, both alone and in combination. Phase I data showed that PT-112 monotherapy was safe and well-tolerated, establishing a recommended phase II dose of 360 mg/m2 on days 1, 8, and 15 of a 28-day cycle. Confirmed responses and other signals of activity were observed. Conclusions: These results suggest a lack of cross-resistance with the standard of care and support the translational value of the Vk*MYC model system. Further clinical investigation of PT-112 is warranted in multiple myeloma.

TPS292 Background: PT-112 is a novel small I-O molecule currently in development for several cancers. Preclinical studies have shown the robust induction of immunogenic cell death by PT-112, leading to an anti-cancer adaptive immune response. Biodistribution experiments in mice showed PT-112’s partial bone affinity. In two prior phase I studies, late-line metastatic castration-resistant prostate cancer patients (mCRPC pts) were treated with evidence of anti-cancer activity, including tumor volume reductions, improvements in PET and bone scans, PSA and alkaline phosphatase (ALP) reductions, and anecdotal cases of improvement in disease-related pain. This, taken together with the immunogenic and osteotropic properties observed in preclinical work, provided a strong rationale to further explore PT-112 in mCRPC, an immunologically “cold” disease with a high prevalence of bone metastases. Moreover, in an analysis of >6,000 mCRPC pts, circulating tumor cell (CTC) declines (CTC0 and CTC conversions) were correlated with improvements in survival to a greater extent than PSA declines (PSA50) (Heller et al., JCO, 36:6 2017), prompting incorporation of CTC changes as a secondary endpoint. Methods: The primary objective of the study is to define the dose regimen of PT-112 for pivotal study. Pts are randomized to one of three arms, receiving IV PT-112 on 28-day cycles via one hour infusions on (1) Days 1 and 15 at 250 mg/m2, (2) Days 1 and 15 at 360 mg/m2, or (3) Days 1 and 15 of cycle 1 at 360 mg/m2 followed by 250 mg/m2 on Day 15 of subsequent cycles. Key eligibility criteria include radiographically progressive disease at study entry; ≥3 life-prolonging therapies for metastatic disease including 1-2 taxanes, ≥1 new generation anti-androgen therapies, and other drugs FDA approved on the basis of survival; and allowing bone-only metastatic disease. Efficacy assessments comprise disease control rate at 4 months (DCR4) using RECIST and PCWG3 criteria, objective response rate, CTC0 and CTC conversion, PSA50 and ALP reductions. Additionally, T cell receptor sequencing is conducted to characterize treatment-induced changes in T cell fraction and clonal expansions, as a means of generating meaningful supportive data on the immune mechanism of PT-112 monotherapy. A Fleming two-stage design will be used to assess each arm, with a 20% DCR4 as the null hypotheses, requiring ≥6 of 25 pts responding in stage one and ≥14 of 45 in total to reject the null. In addition, other efficacy measures, such as CTC responses, as well as exposure/response and exposure/safety analyses will be applied to characterize the risk/benefit ratio and select the optimal dose regimen for PT-112. As of October 11th, 2022, 38 pts have been enrolled out of a planned maximum of 135. Clinical trial information: NCT02266745 .